2023/01/13 更新

写真a

ヤマカタ アキラ
山方 啓
Yamakata Akira
所属
自然科学学域 教授
職名
教授

学位

  • 博士 ( 理学 )

研究キーワード

  • surface dynamics

  • surface spectroscopy

  • Photocatalyst

  • 化学反応ダイナミクス

  • 触媒化学

  • 光触媒

  • 表面化学

  • 超高速赤外分光

研究分野

  • ナノテク・材料 / 機能物性化学

  • ナノテク・材料 / 分析化学

  • ナノテク・材料 / 基礎物理化学

学歴

  • 東京工業大学   Interdisciplinary Graduate School of Science and Engineering  

    1996年4月 - 1999年3月

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  • 東京工業大学   Interdisciplinary Graduate School of Science and Engineering  

    1994年4月 - 1996年3月

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    国名: 日本国

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  • 東京理科大学   Faculty of Science, Division 1  

    1990年4月 - 1994年3月

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    国名: 日本国

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経歴

  • 岡山大学   学術研究院自然科学学域(理)   教授

    2022年4月 - 現在

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  • (独)科学技術振興機構・光エネルギーと物質変換・さきがけ研究員(兼任)

    2011年10月 - 2017年3月

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  • 豊田工業大学   大学院工学研究科   准教授

    2010年8月 - 2022年3月

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  • Department of Chemical Physics of Fritz-Haber-Institut der・派遣研究員(兼任)

    2006年6月 - 2006年8月

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  • 北海道大学   触媒化学研究センター   助教

    2003年10月 - 2010年8月

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  • (財)神奈川科学技術アカデミー・極限表面反応プロジェクト・研究員

    1999年4月 - 2003年9月

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  • 日本学術振興会・特別研究員・DC2 研究員(研究場所:東京工業大学)

    1998年4月 - 1999年3月

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所属学協会

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委員歴

  • 日本化学会:資源・エネルギー・地球化学・核化学・放射化学 ディビジョン   主査  

    2022年3月 - 現在   

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  • J. Photochemistry and Photobiolgy C   Associate Editor  

    2021年1月 - 現在   

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    団体区分:学協会

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  • 日本化学会:資源・エネルギー・地球化学・核化学・放射化学 ディビジョン   副査  

    2020年3月 - 2022年2月   

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    団体区分:学協会

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  • International Workshop on Crystalline Materials and Applications (IWCMA-2019)   Advisory Board  

    2019年   

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    団体区分:学協会

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  • International Conference on Photochemistry and Sustainable Energy (ICPSE 2019)   Advisory Board  

    2019年   

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    団体区分:学協会

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  • 2019年光化学討論会   実行委員  

    2019年   

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    団体区分:学協会

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  • The 24th International Conference on Semiconductor Photocatalysis and Solar Energy Conversion (SPASEC-24)   Advisory Board  

    2019年   

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    団体区分:学協会

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  • The 22nd International Conference on Semiconductor Photocatalysis & Solar Energy Conversion (SPASEC-22)   Advisory Board  

    2017年   

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    団体区分:学協会

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  • International Conference on Photochemistry and Its Applications (ICPA 2017)   Advisory Board  

    2017年   

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    団体区分:学協会

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  • 日本表面真空学会 中部支部   幹事  

    2014年4月 - 現在   

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    団体区分:学協会

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  • 触媒学会「光触媒研究会」   世話人  

    2014年4月 - 現在   

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    団体区分:学協会

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  • 日本表面科学会中部支部   庶務幹事  

    2011年4月 - 2014年3月   

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    団体区分:学協会

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  • 触媒学会「界面分子変換の機構と制御研究会」   世話人  

    2009年4月 - 現在   

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    団体区分:学協会

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  • 表面界面スペクトロスコピー2009   実行委員  

    2009年   

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    団体区分:その他

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  • 電気化学会 『ナノ界面・表面研究懇談会』   常任委員  

    2004年4月 - 現在   

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    団体区分:学協会

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  • 電気化学会 北海道支部常任委員   The Electrochemical Society of Japan, Hokkaido Branch  

    2004年4月 - 2010年8月   

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論文

  • Zr-doped BaTaO2N photocatalyst modified with Na–Pt cocatalyst for efficient hydrogen evolution and Z-scheme water splitting 査読

    Huihui Li, Junie Jhon M. Vequizo, Takashi Hisatomi, Mamiko Nakabayashi, Jiadong Xiao, Xiaoping Tao, Zhenhua Pan, Wenpeng Li, Shanshan Chen, Zheng Wang, Naoya Shibata, Akira Yamakata, Tsuyoshi Takata, Kazunari Domen

    EES Catalysis   2023年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry (RSC)  

    Detailed investigation of photocatalysts, cocatalysts and redox mediators provides a Z-scheme overall water splitting system operating under long-wavelength visible light.

    DOI: 10.1039/d2ey00031h

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  • A general interfacial-energetics-tuning strategy for enhanced artificial photosynthesis 査読

    Tian Liu, Zhenhua Pan, Kosaku Kato, Junie Jhon M. Vequizo, Rito Yanagi, Xiaoshan Zheng, Weilai Yu, Akira Yamakata, Baoliang Chen, Shu Hu, Kenji Katayama, Chiheng Chu

    Nature Communications   13 ( 1 )   7783   2022年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Springer Science and Business Media LLC  

    Abstract

    The demands for cost-effective solar fuels have triggered extensive research in artificial photosynthesis, yet the efforts in designing high-performance particulate photocatalysts are largely impeded by inefficient charge separation. Because charge separation in a particulate photocatalyst is driven by asymmetric interfacial energetics between its reduction and oxidation sites, enhancing this process demands nanoscale tuning of interfacial energetics on the prerequisite of not impairing the kinetics and selectivity for surface reactions. In this study, we realize this target with a general strategy involving the application of a core/shell type cocatalyst that is demonstrated on various photocatalytic systems. The promising H2O2 generation efficiency validate our perspective on tuning interfacial energetics for enhanced charge separation and photosynthesis performance. Particularly, this strategy is highlighted on a BiVO4 system for overall H2O2 photosynthesis with a solar-to-H2O2 conversion of 0.73%.

    DOI: 10.1038/s41467-022-35502-z

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    その他リンク: https://www.nature.com/articles/s41467-022-35502-z

  • Harnessing infrared solar energy with plasmonic energy upconversion 査読

    NATURE SUSTAINABILITY   5   1092 - 1099   2022年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1038/s41893-022-01015-2

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  • Effects of Hydroxy Groups in Anthraquinone Dyes on Photocatalytic Activity of Visible-light-sensitized Pt-TiO2 for Hydrogen Evolution 査読

    Fumiaki Amano, Yasukazu Akaki, Akira Yamakata

    Catalysis Surveys from Asia   2022年10月

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    担当区分:最終著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Springer Science and Business Media LLC  

    DOI: 10.1007/s10563-022-09370-y

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    その他リンク: https://link.springer.com/article/10.1007/s10563-022-09370-y/fulltext.html

  • 固体表面の動力学に追る時間分解中赤外分光 招待 査読

    山方啓, 加藤康作

    光学   51   448 - 454   2022年10月

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    担当区分:筆頭著者, 責任著者   記述言語:日本語   掲載種別:研究論文(学術雑誌)  

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  • Effects of a Nanoparticulate TiO2 Modifier on the Visible-Light CO2 Reduction Performance of a Metal-Complex/Semiconductor Hybrid Photocatalyst 査読

    Mitsuhiko Shizuno, Kosaku Kato, Shunta Nishioka, Tomoki Kanazawa, Daiki Saito, Shunsuke Nozawa, Akira Yamakata, Osamu Ishitani, Kazuhiko Maeda

    ACS Applied Energy Materials   5 ( 8 )   9479 - 9486   2022年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    Graphitic carbon nitride nanosheets (NS-C3N4) combined with a binuclear Ru(II)-Re(I) complex (RuRe) consisting of a photosensitizer and catalytic units are capable of selectively reducing CO2 to CO under visible light (lambda > 400 nm) using triethanolamine as an electron donor. In this system, the grafting of the nanoparticulate rutile TiO2 on the NS-C3N4 surface has previously been shown to enhance photocatalytic performance because of improved charge separation between the NS-C3N4 and the TiO2 and the reinforced adsorption of the RuRe. Here, a more detailed investigation of various polymorphic TiO2 species loaded onto the NS-C3N4 and the visible-light CO2 reduction activity of the resultant photocatalysts was conducted. The experimental results showed that the RuRe/anatase-TiO2/NS-C3N4 outperformed analogues with other TiO2 polymorphs in terms of the CO generation rate, with a maximum catalytic turnover number of similar to 100. Transient absorption and emission spectroscopy measurements were carried out to clarify the origin of the different CO evolution activities provided by different TiO2 modifiers. The results revealed that the TiO2 modifiers not only affected the charge separation ability but also controlled the efficiency of back electron transfer from the Ru-photosensitizer unit in the RuRe to the TiO2. The results also showed that, among the investigated TiO2 polymorphs, anatase best facilitated the forward electron transfer from the NS-C3N4 to the TiO2 while suppressing the undesirable back electron transfer reaction.

    DOI: 10.1021/acsaem.2c01052

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  • One-Step Excitation Overall Water Splitting over a Modified Mg-Doped BaTaO2N Photocatalyst 査読

    Huihui Li, Jiadong Xiao, Junie Jhon M. Vequizo, Takashi Hisatomi, Mamiko Nakabayashi, Zhenhua Pan, Naoya Shibata, Akira Yamakata, Tsuyoshi Takata, Kazunari Domen

    ACS Catalysis   12 ( 16 )   10179 - 10185   2022年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    BaTaO2N responds to visible light up to 650 nm and exhibits photocatalytic activity during the hydrogen and oxygen evolution reactions. However, the difficulty in promoting both processes simultaneously hinders the realization of overall water splitting (OWS) over this material. Herein, we demonstrate the activation and stabilization of BaTaO2N-based photocatalysts for visible-light-driven OWS by combining flux-assisted nitridation with Mg doping and co-loading of Cr2O3/(Na)Rh and IrO2 co-catalysts. RbCl-assisted nitridation produced single-crystal BaTaO2N particles doped with Mg and so promoted charge transfer to the co-catalysts. The coloading of Cr2O3/(Na)Rh and IrO2 at moderate temperatures as co-catalysts to promote the hydrogen and oxygen evolution reactions, respectively, allowed the BaTaO2N photocatalyst to evolve hydrogen and oxygen simultaneously from water. This work highlights the importance of carefully tuning semiconducting and catalytic properties to realize effective charge transfer when preparing narrow-bandgap oxynitrides for OWS.

    DOI: 10.1021/acscatal.2c02394

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  • Effect of Surface Plasmon Resonance and the Heterojunction on Photoelectrochemical Activity of Metal-Loaded TiO2 Electrodes under Visible Light Irradiation 査読

    Chia-Yu Chang, Akira Yamakata, Wenjea J. Tseng

    The Journal of Physical Chemistry C   126   12450 - 12459   2022年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    This study examines the influence of surface plasmon resonance (SPR) and the semiconducting heterojunction on the photoelectrochemical (PEC) activity of metal-loaded TiO2 electrodes under visible light irradiation. Different metal nanoparticles (including Au, Ag, Rh, and Cu) have been selected deliberately and deposited on the TiO2 electrode layers via photodeposition and subsequent annealing at 300 degrees C. UV-vis spectra show an increased absorbance in the visible light region with the metal loading. X-ray photon spectroscopy reveals the formation of CuO, Ag2O, and Ru2O3 after annealing, while only Au remains in its metallic state. The PEC activity increases in the ascending order of Cu < Au < Rh < Ag. This is consistent with the electrochemical impedance measurement where the Ag-loaded TiO2 electrode shows the lowest charge transfer resistance together with the highest ion diffusion rate. Our findings suggest that the presence of semiconducting p-n heterojunctions with associated oxygen-vacancy defects facilitates the enhanced PEC activity by reducing the electron-hole recombination in addition to the SPR effect.

    DOI: 10.1021/acs.jpcc.2c02649

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  • Eliciting the contribution of TiN to photoelectrochemical performance enhancement of Imma-LaTiO2N at neutral pH 招待 査読

    Mirabbos Hojamberdiev, Juan Manuel Mora-Hernandez, Ronald Vargas, Eva Maria Heppke, Kunio Yubuta, Akira Yamakata, Zukhra Kadirova, Leticia Torres-Martinez, Katsuya Teshima, Martin Lerch

    MATERIALS TODAY ENERGY   27   2022年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCI LTD  

    The presence of defects, which act as the recombination hubs for photogenerated charge carriers, hinders the improvement of photocatalytic activity for oxygen evolution reaction of LaTiO2N under visible light irradiation via a four-electron-transfer reaction pathway. Here, we involve titanium nitride (TiN) in a varying content (0e17.8%) to improve the efficiency of charge separation and transport, influencing the photoelectrochemical performance of LaTiO2N. The characterization results confirm the formation of a strong contact between orthorhombic-LaTiO2N and cubic-TiN particles. The photoelectrochemical (PEC) measurements reveal the inverse dependence between electron transfer phenomena and charge carrier recombination, which allows to understand the trend when modifying LaTiO2N with TiN. In fact, the incorporation of 17.8% TiN in the LaTiO2N:TiN material results in a higher photocurrent. Open-circuit potential (OCP) decay and transient absorption spectroscopy (TAS) studies confirm longer lifetimes of charge carriers for increasing amounts of TiN in the synthesized materials. Thus, the main role of TiN is to improve the properties of the semiconductor-electrolyte interface, having verified its impact on the separation and transport of photogenerated charge carriers. Furthermore, computational studies predict that the adsorption of water molecules is favored at the LaTiO2N:TiN surface compared to the individual TiN and LaTiO2N surfaces. (C) 2022 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.mtener.2022.101053

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  • Role of Oxygen Vacancy in the Photocarrier Dynamics of WO3 Photocatalysts: The Case of Recombination Centers 査読

    Kosaku Kato, Yohei Uemura, Kiyotaka Asakura, Akira Yamakata

    The Journal of Physical Chemistry C   126 ( 22 )   9257 - 9263   2022年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    Defects in powder photocatalysts determine the photocatalytic activity. The addition of defects sometimes enhances the activity, but sometimes decreases it. However, the factors determining the difference between these cases have not been fully elucidated yet. Herein, we investigated the effects of oxygen vacancies on photocarrier dynamics in WO3 powder using broadband transient absorption spectroscopy. It was found that the decay of deeply trapped electrons was accelerated when the number of oxygen vacancies was increased by H-2 reduction. This result suggests that oxygen vacancies in WO3 mainly act as recombination centers. This is in contrast to many other photocatalysts such as TiO2 and SrTiO3, where the carrier lifetime increases with increasing oxygen vacancy concentration. These differences can be attributed to the difference in the distance between oxygen vacancies. When defects are dispersed, trapped electrons need to travel over long distances by repeatedly hopping and tunneling between defects to combine with holes, resulting in decelerated recombination. In contrast, when the defects are connected or located close together, the trapped electrons can readily migrate among defects, leading to enhanced recombination. Control of the distance between defects is thus important for enhancing photocatalytic activity.

    DOI: 10.1021/acs.jpcc.2c01662

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  • Enhanced Overall Water Splitting by a Zirconium‐Doped TaON‐Based Photocatalyst 査読

    Jiadong Xiao, Shinji Nishimae, Junie Jhon M. Vequizo, Mamiko Nakabayashi, Takashi Hisatomi, Huihui Li, Lihua Lin, Naoya Shibata, Akira Yamakata, Yasunobu Inoue, Kazunari Domen

    Angewandte Chemie International Edition   61 ( 17 )   2022年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY-V C H VERLAG GMBH  

    Solar-powered one-step-excitation overall water splitting (OWS) using semiconducting materials is a simple means of achieving scalable and sustainable hydrogen production. While tantalum oxynitride (TaON) is one of the few photocatalysts capable of promoting OWS via single-step visible-light excitation, the efficiency of this process remains extremely poor. The present work employed 15 nm amorphous Ta2O5.3.3 H2O nanoparticles as a new precursor together with Zr doping and an optimized nitridation duration to synthesize a TaON-based photocatalyst with reduced particle sizes and low defect densities. Upon loading with Ru/Cr2O3/IrO2 cocatalysts, this material exhibited stoichiometric water splitting into hydrogen and oxygen, with an order of magnitude improvement in efficiency. Our findings demonstrate the importance of inventing/selecting the appropriate synthetic precursor and of defect control for fabricating active OWS photocatalysts.

    DOI: 10.1002/anie.202116573

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  • Identification of a Self-Photosensitizing Hydrogen Atom Transfer Organocatalyst System. 査読 国際誌

    Hiromu Fuse, Yu Irie, Masaaki Fuki, Yasuhiro Kobori, Kosaku Kato, Akira Yamakata, Masahiro Higashi, Harunobu Mitsunuma, Motomu Kanai

    Journal of the American Chemical Society   144 ( 14 )   6566 - 6574   2022年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    We developed organocatalyst systems to promote the cleavage of stable C-H bonds, such as formyl, α-hydroxy, and benzylic C-H bonds, through a hydrogen atom transfer (HAT) process without the use of exogenous photosensitizers. An electronically tuned thiophosphoric acid, 7,7'-OMe-TPA, was assembled with substrate or co-catalyst N-heteroaromatics through hydrogen bonding and π-π interactions to form electron donor-acceptor (EDA) complexes. Photoirradiation of the EDA complex induced stepwise, sequential single-electron transfer (SET) processes to generate a HAT-active thiyl radical. The first SET was from the electron-rich naphthyl group of 7,7'-OMe-TPA to the protonated N-heteroaromatics and the second proton-coupled SET (PCET) from the thiophosphoric acid moiety of 7,7'-OMe-TPA to the resulting naphthyl radical cation. Spectroscopic studies and theoretical calculations characterized the stepwise SET process mediated by short-lived intermediates. This organocatalytic HAT system was applied to four different carbon-hydrogen (C-H) functionalization reactions, hydroxyalkylation and alkylation of N-heteroaromatics, acceptorless dehydrogenation of alcohols, and benzylation of imines, with high functional group tolerance.

    DOI: 10.1021/jacs.2c01705

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  • 時間分解分光計測を利用した光触媒反応機構の解明 招待 査読

    山方啓

    分光研究   71   75 - 89   2022年4月

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    担当区分:筆頭著者, 責任著者   記述言語:日本語   掲載種別:研究論文(学術雑誌)  

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  • Donor-π-Acceptor Type Porphyrin-Fullerene Dyad with Acetylene Bridge for p-Type Dye-sensitized Solar Cell

    Qi Guo, Tomohiro Higashino, Kosaku Kato, Akira Yamakata, Hiroshi Imahori

    Chemistry Letters   51 ( 3 )   260 - 263   2022年3月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:The Chemical Society of Japan  

    DOI: 10.1246/cl.210717

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  • Manipulation of charge carrier flow in Bi4NbO8Cl nanoplate photocatalyst with metal loading 査読

    Kanta Ogawa, Ryota Sakamoto, Chengchao Zhong, Hajime Suzuki, Kosaku Kato, Osamu Tomita, Kouichi Nakashima, Akira Yamakata, Takashi Tachikawa, Akinori Saeki, Hiroshi Kageyama, Ryu Abe

    Chemical Science   13 ( 11 )   3118 - 3128   2022年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1039/d1sc06054f

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  • Unfolding the Role of B Site-Selective Doping of Aliovalent Cations on Enhancing Sacrificial Visible Light-Induced Photocatalytic H2 and O2 Evolution over BaTaO2N 査読

    Mirabbos Hojamberdiev, Ronald Vargas, Zukhra C. Kadirova, Kosaku Kato, Hadi Sena, Aleksei G. Krasnov, Akira Yamakata, Katsuya Teshima, Martin Lerch

    ACS Catalysis   12 ( 2 )   1403 - 1414   2022年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acscatal.1c04547

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  • Overall photosynthesis of H2O2 by an inorganic semiconductor 査読

    Pan Zhenhua, Junie Jhon, M. Vequizo, Kosaku Kato, Akira Yamakata, Kenji Katayama, Chiheng Chu, Kazunari Domen

    Nature Communications   13 ( 1 )   2022年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1038/s41467-022-28686-x

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  • Improvement of Visible‐Light H2 Evolution Activity of Pb2Ti2O5.4F1.2 Photocatalyst by Coloading of Rh and Pd Cocatalysts 査読

    Kenta Aihara, Kosaku Kato, Tomoki Uchiyama, Shuhei Yasuda, Toshiyuki Yokoi, Akira Yamakata, Yoshiharu Uchimoto, Kazuhiko Maeda

    Chemistry - A European Journal   28 ( 43 )   2022年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

    Pb2Ti2O5.4F1.2 modified with various metal cocatalysts was studied as a photocatalyst for visible-light H2 evolution. Although unmodified Pb2Ti2O5.4F1.2 showed negligible activity, modification of its surface with Rh led to the best observed promotional effect among the Pb2Ti2O5.4F1.2 samples modified with a single metal cocatalyst. The H2 evolution activity was further enhanced by coloading with Pd; the Rh−Pd/Pb2Ti2O5.4F1.2 photocatalyst showed 3.2 times greater activity than the previously reported Pt/Pb2Ti2O5.4F1.2. X-ray absorption fine-structure spectroscopy, photoelectrochemical, and transient absorption spectroscopy measurements indicated that the coloaded Rh and Pd species, which were partially alloyed on the Pb2Ti2O5.4F1.2 surface, improved the electron-capturing ability, thereby explaining the high activity of the coloaded Rh−Pd/Pb2Ti2O5.4F1.2 catalyst toward H2 evolution.

    DOI: 10.1002/CHEM.202200875

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  • Influences of pulverization and annealing treatment on the photocatalytic activity of BiVO4 for oxygen evolution 査読

    Kazuya Okuno, Hiromu Kumagai, Junie Jhon M. Vequizo, Kosaku Kato, Makoto Kobayashi, Akira Yamakata, Masato Kakihana, Hideki Kato

    Sustainable Energy &amp; Fuels   6 ( 7 )   1698 - 1707   2022年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry (RSC)  

    Pulverization followed by annealing treatment improved the activity of BiVO4 although the annealing treatment had a negative impact on the non-milled sample.

    DOI: 10.1039/d2se00065b

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  • Photoexcited charge manipulation in conjugated polymers bearing a Ru(ii) complex catalyst for visible-light CO2 reduction 招待 査読

    Akinobu Nakada, Ryuichi Miyakawa, Ren Itagaki, Kosaku Kato, Chinami Takashima, Akinori Saeki, Akira Yamakata, Ryu Abe, Hiromi Nakai, Ho-Chol Chang

    Journal of Materials Chemistry A   10 ( 37 )   19821 - 19828   2022年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry ({RSC})  

    Conjugated polymers have emerged as promising candidates for photocatalyst materials. Design principles that maximize the synergy between the conjugated skeleton and catalyst moiety are strongly desired to be established for achieving efficient photocatalysis. Herein, the photoexcited charge manipulation was demonstrated by molecular engineering in conjugated polymers bearing a Ru(II) complex as the CO2 reduction photocatalyst. Combinational studies based on ultrafast spectroscopies and theoretical calculations revealed that the introduction of an electron-donating carbazole (Cz) skeleton in the polymer enables enhanced photoexcited charge trapping on the Ru(II)-complex catalyst moiety. The carbazole-based polymer [Cz-bpyRu](n) facilitates CO2 reduction under visible light even longer than 500 nm and exhibited 7- to 15-fold greater activity than those of phenyl (Ph) and benzothiadiazole (Bt) counterparts. The findings of this study thus provide insights into molecular engineering for photoexcited charge manipulation to achieve efficient photocatalysis.

    DOI: 10.1039/D2TA02183H

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  • Effects of the rigid and sterically bulky structure of non-fused nonfullerene acceptors on transient photon-to-current dynamics 査読

    Seihou Jinnai, Kasumi Murayama, Keisuke Nagai, Megumi Mineshita, Kosaku Kato, Azusa Muraoka, Akira Yamakata, Akinori Saeki, Yasuhiro Kobori, Yutaka Ie

    Journal of Materials Chemistry A   10 ( 37 )   20035 - 20047   2022年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry (RSC)  

    Non-fused electron-accepting π-conjugated compounds have been investigated recently for application to nonfullerene acceptors (NFAs) in organic solar cells (OSCs).

    DOI: 10.1039/D2TA02604J

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  • Effect of Terminal-Group Halogenation of Naphthalene-Based Nonfullerene Acceptors on Their Film Structure and Photophysical and Photovoltaic Properties 査読

    Tomokazu Umeyama, Tatsuho Wada, Kensho Igarashi, Kosaku Kato, Akira Yamakata, Taiki Takeyama, Yuji Sakamoto, Yasunari Tamai, Hideo Ohkita, Keiichi Ishida, Tomoyuki Koganezawa, Shunsuke Ohtani, Kazuo Tanaka, Hiroshi Imahori

    ACS Applied Energy Materials   4 ( 12 )   14022 - 14033   2021年12月

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acsaem.1c02816

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  • Modified SILAR grown ZnO films on p ‐Si(100) with enhanced charge separation for UV light sensing application 査読

    Jose Presiphil B. Ontolan, Junie Jhon M. Vequizo, Akira Yamakata, Reynaldo M. Vequizo

    physica status solidi (a)   218 ( 22 )   2100363 - 2100363   2021年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

    Herein, the growth of pristine ZnO nanostructures thin film on p-Si(100) by modified successive ionic layer adsorption-reduction method, revealing significant improvement in the charge collection for ultraviolet light detection, is reported. The deposited ZnO exhibits spindle-like and hexagonal structure that grows preferentially along the c-axis. Two-probe electrical measurements validate the rectifying nature of the constructed n-ZnO/p-Si(100), revealing a substantial 11.3-fold increase in photocurrent at room temperature under 375 nm irradiation at +3 V working voltage. The drastic increase in photocurrent is linked to efficient charge separation caused by charge transfer and band bending effects, as indicated by microsecond time-resolved absorption measurements, providing useful information for device development.

    DOI: 10.1002/pssa.202100363

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  • Forward and backward electron transfer on Pt loaded TiO2 photocatalysts under visible-light illumination 査読

    Naohiro Inoue, Kyohei Shiraki, Kosaku Kato, Shu Ashimura, Masaaki Yoshida, Akira Yamakata

    Applied Physics Letters   119 ( 13 )   133905 - 133905   2021年9月

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    担当区分:最終著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AIP Publishing  

    The surface plasmon resonance (SPR) effects of metal nanoparticles prove versatile in terms of equipping wideband-gap photocatalysts, such as TiO2, with visible-light responsiveness. In this regard, Au is the most frequently used material for its SPR, but alternative materials are also being actively developed to effectively utilize solar light from the visible to the near-infrared region. In this work, we found that Pt particles loaded on TiO2 were also active in effecting SPR-induced photocatalysis. Time-resolved absorption measurements confirmed that visible-light irradiation induces electron transfer from Pt to TiO2, and the efficiency of this electron injection increases as the wavelength of the incident light decreases from 660 to 450 nm. Observations of the peak shift of the vibrational frequency of adsorbed CO on Pt confirmed that the Fermi level of Pt decreases as the electron transfer from Pt to TiO2 proceeds. These results imply that Pt nanoparticles can act as sensitizers to induce electron transfer from Pt to TiO2, although Pt is a well-known cocatalyst that enhances H-2 evolution by collecting electrons from TiO2. However, as the intensity of the irradiated light increased beyond 50 mW cm(-2), a portion of the Pt particles started to capture the injected electrons from TiO2, suggesting that the electron transfer from one Pt particle to the other Pt particles via the conduction band of TiO2 proceeds under visible light illumination. These opposing roles may be ascribed to the variation in the size of Pt particles as well as density of electrons injected into TiO2.

    DOI: 10.1063/5.0065074

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  • Time-Retrenched Synthesis of BaTaO2N by Localizing an NH3 Delivery System for Visible-Light-Driven Photoelectrochemical Water Oxidation at Neutral pH: Solid-State Reaction or Flux Method? 査読

    Mirabbos Hojamberdiev, J. Manuel Mora-Hernandez, Ronald Vargas, Akira Yamakata, Kunio Yubuta, Eva Maria Heppke, Leticia M. Torres-Martínez, Katsuya Teshima, Martin Lerch

    ACS Applied Energy Materials   4 ( 9 )   9315 - 9327   2021年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    Among 600 nm class transition-metal oxynitrides, BaTaO2N with a cubic Pm (3) over barm perovskite-type structure is promising for solar water oxidation due to its absorption of visible light up to 660 nm, narrower band gap (E-g = 1.9 eV), appropriate valence band edge position for oxygen evolution, good stability in concentrated alkaline solutions, and nontoxicity. However, high defect density stemmed from long high-temperature ammonolysis limits the separation and transfer efficiency of photogenerated charge carriers in BaTaO2N. Here, a NH3 delivery system is specifically localized just above the synthesis mixture to reduce the synthesis time and defect density of BaTaO2N by a fresh supply of more active nitriding species and minimizing the generation of N-2 and H-2. Particularly, the effects of synthesis temperature (700-950 degrees C), synthesis time (1-8 h), and gas composition are systematically investigated to gain insights into the formation of single-phase BaTaO2N by solid-state reaction and flux method. Time-dependent experiments conducted at 950 degrees C show that single-phase BaTaO2N can be synthesized >= 6 and >= 4 h by solid-state reaction and flux method, respectively, revealing the advantage of the flux method over solid-state reaction in a localized NH3 delivery system. Subsequently, the separation and transfer efficiency and kinetics of photogenerated charge carriers are studied in BaTaO2N samples. Photoelectrochemical studies made it possible to resolve trends during visible-light-induced water oxidation, evidencing the inverse relationship between recombination and charge transfer phenomena. Transient absorption spectroscopy reveals that the dynamics of the photogenerated charge carriers in both types of BaTaO2N samples are different: (i) BaTaO2N synthesized by flux method has a greater number of holes despite the similar number of deeply trapped charge carriers and (ii) solid-state reaction led to the formation of a higher number of free electrons in BaTaO2N. The findings demonstrate the advantage of reducing the transfer distance of active nitriding species to the surface of the synthesis mixture for enhancing the photoelectrochemical water oxidation of BaTaO2N at neutral pH.

    DOI: 10.1021/acsaem.1c01539

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  • Control of the Photocatalytic Activity of Metastable Layered Oxynitride K2LaTa2O6N through Topochemical Transformation of Tuned Oxide Precursors 査読

    Hiroto Mogi, Kosaku Kato, Shuhei Yasuda, Tomoki Kanazawa, Akinobu Miyoshi, Shunta Nishioka, Takayoshi Oshima, Ya Tang, Toshiyuki Yokoi, Shunsuke Nozawa, Akira Yamakata, Kazuhiko Maeda

    Chemistry of Materials   33 ( 16 )   6443 - 6452   2021年8月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    In the development of oxynitride photocatalysts, thermal ammonolysis of a metal oxide precursor has often been conducted by varying the reaction conditions (e.g., temperatures, reaction times, and ammonia gas flow rates) to obtain high-quality oxynitride particles that efficiently function as photocatalysts. However, this approach may suffer from undesirable changes in the physicochemical properties of the resulting oxynitride, leading to the lowering of the photocatalytic activity. Here, we show that it is possible to control the photocatalytic activity of Ruddlesden-Popper metastable layered oxynitride K2LaTa2O6N, obtained from the Dion-Jacobson phase KLaTa2O7 through a topochemical ammonolysis reaction, by controlling the quality of the KLaTa2O7 template. During the ammonolysis of KLaTa2O7, in the presence of K2CO3, to K2LaTa2O6N, the structural properties (e.g., degree of crystallinity and particle size) of the oxide precursor were replicated in the resulting oxynitride. Namely, the use of KLaTa2O7, possessing a higher degree of crystallinity, led to larger K2LaTa2O6N particles being formed. By increasing the crystallinity of KLaTa2O7, the photocatalytic activity of the resulting K2LaTa2O6N for H2 evolution was improved for reaction in aqueous NaI solution under visible light irradiation. This improvement in performance was due to the longer lifetime of the photogenerated mobile electrons in high-crystallinity K2LaTa2O6N compared with that in the low-crystallinity analogue, as confirmed by femtosecond transient absorption spectroscopy. However, the photocatalytic activity of K2LaTa2O6N derived from well-grown larger KLaTa2O7 particles was an order of magnitude lower than that of the best-performing material. Physicochemical measurements revealed that the large K2LaTa2O6N particles contained a relatively high density of anionic defects on the surface, which shortened the lifetime of the photogenerated charge carriers, leading to lower photocatalytic activity.

    DOI: 10.1021/acs.chemmater.1c01726

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  • Surface Modifications of (ZnSe)0.5(CuGa2.5Se4.25)0.5 to Promote Photocatalytic Z-Scheme Overall Water Splitting 査読

    Shanshan Chen, Junie Jhon M. Vequizo, Zhenhua Pan, Takashi Hisatomi, Mamiko Nakabayashi, Lihua Lin, Zheng Wang, Kosaku Kato, Akira Yamakata, Naoya Shibata, Tsuyoshi Takata, Taro Yamada, Kazunari Domen

    Journal of the American Chemical Society   143 ( 28 )   10633 - 10641   2021年7月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/jacs.1c03555

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  • Simultaneously Tuning the Defects and Surface Properties of Ta3N5 Nanoparticles by Mg–Zr Codoping for Significantly Accelerated Photocatalytic H2 Evolution 査読

    Jiadong Xiao, Junie Jhon, M. Vequizo, Takashi Hisatomi, Jabor Rabeah, Mamiko Nakabayashi, Zheng Wang, Qi Xiao, Huihui Li, Zhenhua Pan, Mary Krause, Nick Yin, Gordon Smith, Naoya Shibata, Angelika Brückner, Akira Yamakata, Tsuyoshi Takata, Kazunari Domen

    Journal of the American Chemical Society   143 ( 27 )   10059 - 10064   2021年7月

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/jacs.1c04861

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  • Buckyball as an Electron Donor in a Dyad of C60 and Xanthene Dye 査読

    Haruka Kano, Kyohei Matsuo, Hironobu Hayashi, Kosaku Kato, Akira Yamakata, Hiroko Yamada, Naoki Aratani

    European Journal of Organic Chemistry   2021 ( 23 )   3377 - 3381   2021年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

    We successfully achieved the synthesis of C-60-xanthlium, X60_NTf2, where fullerene is an electron donor and xanthlium is an electron acceptor. When the precursor compound X60-OH was excited at 550 nm, the C-60 emission was observed at 715 nm. On the other hand, the fluorescence of X60_NTf2 was completely quenched under the same conditions, suggesting that photo-induced intramolecular electron transfer (ET) occurred from the singlet excited state of C-60. The electrochemical measurement proved that the X60_NTf2 is exothermically possible of ET reaction from C-1(60)* to xanthylium to form C-60(.+). Density functional theory (DFT) calculations support the acceptor ability of the xanthylium by showing that the coefficients of the lowest unoccupied molecular orbital (LUMO) were on xanthene moiety. This is a well-arranged model compound to investigate the properties of transiently generated fullerene radical cations.

    DOI: 10.1002/ejoc.202100276

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    その他リンク: https://onlinelibrary.wiley.com/doi/full-xml/10.1002/ejoc.202100276

  • Titanium Dioxide/Polyvinyl Alcohol/Cork Nanocomposite: A Floating Photocatalyst for the Degradation of Methylene Blue under Irradiation of a Visible Light Source 査読

    Nurul Hidayah Mohamad Idris, Jayalakshmi Rajakumar, Kuan Yew Cheong, Brendan J. Kennedy, Teruhisa Ohno, Akira Yamakata, Hooi Ling Lee

    ACS Omega   6 ( 22 )   14493 - 14503   2021年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    Photocatalytic degradation by the titanium dioxide (TiO2) photocatalyst attracts tremendous interest due to its promising strategy to eliminate pollutants from wastewater. The floating photocatalysts are explored as potential candidates for practical wastewater treatment applications that could overcome the drawbacks posed by the suspended TiO2 photocatalysis system. The problem occurs when the powdered TiO2 applied directly into the treated solution will form a slurry, making its reuse become a difficult step after treatment. In this study, the immobilization of titanium dioxide nanoparticles (TiO2 NPs) on the floating substrate (cork) employing polyvinyl alcohol (PVA) as a binder to anchor TiO2 NPs on the surface of the cork was carried out. Characterizations such as Fourier transformer infrared, X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis), zeta potential, photoluminescence spectroscopy, femtosecond to millisecond time-resolved visible to mid-IR absorption spectroscopy, ion chromatography, and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) analyses were employed. XRD analysis revealed the formation of anatase-phase TiO2 NPs. The results demonstrated that the crystallite size was 9.36 nm. The band gap energy of TiO2 NPs was determined as 3.0 eV. PL analysis verified that TiO2 NPs possessed a slower recombination rate of electron-hole pairs as compared to anatase TiO2. The result was attributed by the behavior of photogenerated charge carriers on TiO2 NPs, which existed as shallowly trapped electrons that could survive longer than a few milliseconds in this study. Furthermore, SEM-EDX analysis indicated that TiO2 NPs were well distributed on the surface of the cork. At the optimal mole ratio of TiO2/PVA (1:8), the TiO2/PVA/cork floating photocatalyst degraded at 98.43% of methylene blue (MB) under a visible light source which performed better than under sunlight irradiation (77.09% of MB removal) for 120 min. Besides, the mineralization result has measured the presence of sulfate anions after photocatalytic activities, which achieved 86.13% (under a visible light source) and 65.34% (under sunlight). The superior photodegradation performance for MB was mainly controlled by the reactive oxygen species of the superoxide radical (O-center dot(2)-). The degradation kinetics of MB followed the first-order kinetics. Meanwhile, the Langmuir isotherm model was fitted for the adsorption isotherm. The floating photocatalyst presented good reusability, resulting in 78.13% of MB removal efficiency even after five cycles. Our TiO2/PVA/cork floating photocatalyst fabrication and high photocatalytic performance are potentially used in wastewater treatment, especially under visible light irradiation.

    DOI: 10.1021/acsomega.1c01458

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  • Atomically dispersed antimony on carbon nitride for the artificial photosynthesis of hydrogen peroxide 査読

    Zhenyuan Teng, Qitao Zhang, Hongbin Yang, Kosaku Kato, Wenjuan Yang, Ying-Rui Lu, Sixiao Liu, Chengyin Wang, Akira Yamakata, Chenliang Su, Bin Liu, Teruhisa Ohno

    Nature Catalysis   4 ( 5 )   374 - 384   2021年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Springer Science and Business Media LLC  

    Artificial photosynthesis offers a promising strategy to produce hydrogen peroxide (H2O2)-an environmentally friendly oxidant and a clean fuel. However, the low activity and selectivity of the two-electron oxygen reduction reaction (ORR) in the photocatalytic process greatly restricts the H2O2 production efficiency. Here we show a robust antimony single-atom photocatalyst (Sb-SAPC, single Sb atoms dispersed on carbon nitride) for the synthesis of H2O2 in a simple water and oxygen mixture under visible light irradiation. An apparent quantum yield of 17.6% at 420 nm together with a solar-to-chemical conversion efficiency of 0.61% for H2O2 synthesis was achieved. On the basis of time-dependent density function theory calculations, isotopic experiments and advanced spectroscopic characterizations, the photocatalytic performance is ascribed to the notably promoted two-electron ORR by forming mu-peroxide at the Sb sites and highly concentrated holes at the neighbouring N atoms. The in situ generated O-2 via water oxidation is rapidly consumed by ORR, leading to boosted overall reaction kinetics.Hydrogen peroxide is an interesting target for artificial photosynthesis, although its actual production via the two-electron oxygen reduction reaction remains limited. Now, a carbon nitride-supported antimony single atom photocatalyst has been developed with a superior performance for this process.

    DOI: 10.1038/s41929-021-00605-1

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    その他リンク: http://www.nature.com/articles/s41929-021-00605-1

  • A Na-containing Pt cocatalyst for efficient visible-light-induced hydrogen evolution on BaTaO2N 査読

    Huihui Li, Daling Lu, Shanshan Chen, Takashi Hisatomi, Junie Jhon M. Vequizo, Jiadong Xiao, Zheng Wang, Lihua Lin, Qi Xiao, Yuliang Sun, Yugo Miseki, Kazuhiro Sayama, Akira Yamakata, Tsuyoshi Takata, Kazunari Domen

    Journal of Materials Chemistry A   9 ( 24 )   13851 - 13854   2021年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry (RSC)  

    <p>A well-dispersed Pt cocatalyst obtained using Na as a promoter provides enhanced photocatalytic hydrogen evolution over BaTaO2N under visible light.</p>

    DOI: 10.1039/d1ta01162f

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  • Utilization of Perovskite-Type Oxynitride La0.5Sr0.5Ta0.5Ti0.5O2N as an O2-Evolving Photocatalyst in Z-Scheme Water Splitting 査読

    Hiromu Kumagai, Ryosuke Aoyagi, Kosaku Kato, Akira Yamakata, Masato Kakihana, Hideki Kato

    ACS Applied Energy Materials   2021年3月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acsaem.0c03055

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  • Core–Shell Double Doping of Zn and Ca on β-Ga2O3 Photocatalysts for Remarkable Water Splitting 査読

    Akira Yamakata, Junie Jhon M. Vequizo, Takafumi Ogawa, Kosaku Kato, Shoya Tsuboi, Naohiro Furutani, Masahiro Ohtsuka, Shunsuke Muto, Akihide Kuwabara, Yoshihisa Sakata

    ACS Catalysis   11 ( 4 )   1911 - 1919   2021年2月

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    担当区分:筆頭著者   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acscatal.0c05104

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  • Sequential cocatalyst decoration on BaTaO2N towards highly-active Z-scheme water splitting 査読

    Zheng Wang, Ying Luo, Takashi Hisatomi, Junie Jhon M. Vequizo, Sayaka Suzuki, Shanshan Chen, Mamiko Nakabayashi, Lihua Lin, Zhenhua Pan, Nobuko Kariya, Akira Yamakata, Naoya Shibata, Tsuyoshi Takata, Katsuya Teshima, Kazunari Domen

    Nature Communications   12 ( 1 )   1005   2021年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Springer Science and Business Media LLC  

    <title>Abstract</title>Oxynitride photocatalysts hold promise for renewable solar hydrogen production via water splitting owing to their intense visible light absorption. Cocatalyst loading is essential for activation of such oxynitride photocatalysts. However, cocatalyst nanoparticles form aggregates and exhibit weak interaction with photocatalysts, which prevents eliciting their intrinsic photocatalytic performance. Here, we demonstrate efficient utilization of photoexcited electrons in a single-crystalline particulate BaTaO2N photocatalyst prepared with the assistance of RbCl flux for H2 evolution reactions via sequential decoration of Pt cocatalyst by impregnation-reduction followed by site-selective photodeposition. The Pt-loaded BaTaO2N photocatalyst evolves H2 over 100 times more efficiently than before, with an apparent quantum yield of 6.8% at the wavelength of 420 nm, from a methanol aqueous solution, and a solar-to-hydrogen energy conversion efficiency of 0.24% in Z-scheme water splitting. Enabling uniform dispersion and intimate contact of cocatalyst nanoparticles on single-crystalline narrow-bandgap particulate photocatalysts is a key to efficient solar-to-chemical energy conversion.

    DOI: 10.1038/s41467-021-21284-3

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    その他リンク: http://www.nature.com/articles/s41467-021-21284-3

  • 半導体光触媒粒子中の欠陥が及ぼす光励起キャリアの再結合促進と抑制効果 招待

    山方啓, 加藤康作

    会報光触媒   64   27 - 36   2021年1月

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    担当区分:筆頭著者, 責任著者  

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  • Earth-abundant iron(iii) species serves as a cocatalyst boosting the multielectron reduction of IO3−/I− redox shuttle in Z-scheme photocatalytic water splitting 査読

    Katsuya Murofushi, Kanta Ogawa, Hajime Suzuki, Ryota Sakamoto, Osamu Tomita, Kosaku Kato, Akira Yamakata, Akinori Saeki, Ryu Abe

    Journal of Materials Chemistry A   9 ( 19 )   11718 - 11725   2021年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry ({RSC})  

    <p>The FeIII/FeII redox couple in the amorphous FeOx cocatalyst on the Bi4TaO8Cl photocatalyst captures photoexcited electrons and facilitates the multielectron (6-electrons) reduction of IO3, thus boosting O2 evolution under visible light.</p>

    DOI: 10.1039/D1TA01703A

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  • Cocatalyst engineering of a narrow bandgap Ga-La5Ti2Cu0.9Ag0.1O7S5 photocatalyst towards effectively enhanced water splitting 査読

    Qi Xiao, Jiadong Xiao, Junie Jhon M. Vequizo, Takashi Hisatomi, Mamiko Nakabayashi, Shanshan Chen, Zhenhua Pan, Lihua Lin, Naoya Shibata, Akira Yamakata, Tsuyoshi Takata, Kazunari Domen

    Journal of Materials Chemistry A   9 ( 48 )   27485 - 27492   2021年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry (RSC)  

    The hydrogen evolution activity of Ga-doped La5Ti2Cu0.9Ag0.1O7S5 (Ga-LTCA) was boosted by loading a Rh cocatalyst having uniform dispersion and intimate contact.

    DOI: 10.1039/d1ta08770c

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  • Heavy Metal Effects on the Photovoltaic Properties of Metallocorroles in Dye-Sensitized Solar Cells 査読

    Tomohiro Higashino, Yuma Kurumisawa, Abraham B. Alemayehu, Rune F. Einrem, Debashis Sahu, Daniel Packwood, Kosaku Kato, Akira Yamakata, Abhik Ghosh, Hiroshi Imahori

    ACS Applied Energy Materials   3 ( 12 )   12460 - 12467   2020年12月

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    担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    Finding strategies for effective charge separation is a prerequisite for realizing efficient solar energy conversion in photovoltaic and photocatalytic devices. Porphyrinoids, including porphyrins and related macrocycles such as phthalocyanines and corroles, are versatile ligands that can accommodate a single metal atom for most metal ions, and their photophysical and electro-chemical properties can be tuned by the metal atom in the cavity. Herein, we evaluated the photovoltaic properties of the dyesensitized solar cells (DSSCs) based on Au-III-, (ReO)-O-V-, and (OsN)-N-VI-corroles with COOH anchoring groups at the para- and meta-positions of the meso-phenyl groups. The DSSCs based on Au-III-corroles exhibited a power conversion efficiency (PCE) of 4.2%, which is remarkably higher than those for the (ReO)-O-V- and (OsN)-N-VI-corroles. Femtosecond time-resolved transient absorption measurements have shown that the electron injection from the excited singlet state competes with intersystem crossing, and that intersystem crossing for Au-III-corroles is slower than those for ReVO- and (OsN)-N-VI-corroles. Consequently, the high incident photon-to-current efficiencies and resultant short-circuit current densities and PCEs for Au-III-corroles are attributed to the high electron injection efficiencies owing to the slower intersystem crossing than ReVO- and (OsN)-N-VI-corroles. In addition, the higher PCE for a Au-III-corrole with a meta-COOH group (4.2%) as opposed to a para-COOH group (3.4%) is explained by the stronger Au-TiO2 interactions supported by XPS measurements and theoretical calculations. These results imply that both the substituents and the metal ion have a large influence on the photovoltaic performances. Overall, DSSCs based on the Au-III-corroles were found to exhibit the highest photovoltaic performance among corrole-based DSSCs.

    DOI: 10.1021/acsaem.0c02427

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  • Optically Transparent Colloidal Dispersion of Titania Nanoparticles Storable for Longer than One Year Prepared by Sol/Gel Progressive Hydrolysis/Condensation 査読

    Keito Sano, Fazalurahman Kuttassery, Tetsuya Shimada, Tamao Ishida, Shinsuke Takagi, Bunsho Ohtani, Akira Yamakata, Tetsuo Honma, Hiroshi Tachibana, Haruo Inoue

    ACS Applied Materials & Interfaces   12 ( 40 )   44743 - 44753   2020年10月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    Copyright © 2020 American Chemical Society. The molecular catalyst sensitized system (MCSS), where an excited molecular catalyst adsorbed on a semiconductor such as TiO2 injects electrons to the conduction band of the semiconductor leading to hydrogen evolution/CO2 reduction coupled with an oxidation of water on the molecular catalyst, has been one of the most probable candidates in the approach to artificial photosynthesis. For a full utilization of visible light, however, a serious light scattering of the aqueous suspension of TiO2 in the visible region, which is generally experienced, should be avoided. Here, we report a preparation of optically transparent colloidal dispersion of TiO2 by the sol/gel reaction of TiCl4 through progressive hydrolysis/condensation under the basic condition without any calcination processes. The TiO2 nanoparticles (TiO2(NPs)) obtained were characterized as an amorphous particle (∼10-15 nm) having a microcrystal domain of anatase within several nm by XRD, Raman spectroscopies, XRF, XAFS, TG/DTA, and HRTEM, respectively. The energy-resolved distribution of carrier electron traps in TiO2(NPs) as a fingerprint of TiO2 was characterized through reversed double-beam photo-acoustic spectroscopy to have a close similarity to that of TiO2(ST-01) as well as the observation of carrier traps by transient absorption spectroscopy. Though the powder TiO2(NP) itself was not dispersed well in aqueous solution, the wet TiO2(NPs) as prepared before being dried up provided a completely transparent aqueous dispersion under the acidic condition (1 M HCl). Addition of methanol enabled the colloidal dispersion (TiO2(NPs, MeOH/H2O, 0.1 M HCl)) to keep the optical transparency for longer than 1 year (550 days), which is the first example of TiO2 dispersion storable for such a long period. TiO2(NPs, MeOH/H2O) exhibited a moderate photocatalytic reactivity of H2 evolution with a quantum yield of ∼2.6% upon 365 nm light irradiation. An optically transparent thin film of TiO2(NPs, MeOH/H2O) was also successfully prepared on a glass plate to exhibit an enhanced hydrophilicity upon UV light irradiation.

    DOI: 10.1021/acsami.0c12951

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  • Investigation on the highly active SrTiO3 photocatalyst toward overall H2O splitting by doping Na ion 査読

    Junzhe Jiang, Kosaku Kato, Hirotaka Fujimori, Akira Yamakata, Yoshihisa Sakata

    Journal of Catalysis   390   81 - 89   2020年8月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.jcat.2020.07.025

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  • Synthesis of Three-Layer Perovskite Oxynitride K2Ca2Ta3O9N·2H2O and Photocatalytic Activity for H2 Evolution under Visible Light 査読

    Ya Tang, Kosaku Kato, Takayoshi Oshima, Hiroto Mogi, Akinobu Miyoshi, Kotaro Fujii, Kei-ichi Yanagisawa, Koji Kimoto, Akira Yamakata, Masatomo Yashima, Kazuhiko Maeda

    Inorganic Chemistry   59 ( 15 )   11122 - 11128   2020年8月

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acs.inorgchem.0c01607

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  • Heteroatom Dopants Promote Two‐Electron O2 Reduction for Photocatalytic Production of H2O2 on Polymeric Carbon Nitride 査読

    Peng Zhang, Yawen Tong, Yong Liu, Junie Jhon, M. Vequizo, Hongwei Sun, Can Yang, Akira Yamakata, Fengtao Fan, Wei Lin, Xinchen Wang, Wonyong Choi

    Angewandte Chemie International Edition   59   16209 - 16217   2020年6月

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1002/anie.202006747

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    その他リンク: https://onlinelibrary.wiley.com/doi/full-xml/10.1002/anie.202006747

  • Efficient photocatalytic hydrogen evolution on single-crystalline metal selenide particles with suitable cocatalysts 査読

    Shanshan Chen, Junie Jhon, M. Vequizo, Takashi Hisatomi, Mamiko Nakabayashi, Lihua Lin, Zheng Wang, Akira Yamakata, Naoya Shibata, Tsuyoshi Takata, Taro Yamada, Kazunari Domen

    Chemical Science   11 ( 25 )   6436 - 6441   2020年4月

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1039/D0SC01167C

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  • Activation of a Pt-loaded Pb2Ti2O5.4F1.2 photocatalyst by alkaline chloride treatment for improved H2 evolution under visible light 査読

    Haruki Wakayama, Kosaku Kato, Kodai Kashihara, Tomoki Uchiyama, Akinobu Miyoshi, Hiroko Nakata, Daling Lu, Kengo Oka, Akira Yamakata, Yoshiharu Uchimoto, Kazuhiko Maeda

    J. Mater. Chem. A   8 ( 18 )   9099 - 9108   2020年4月

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  • Identification of Individual Electron- and Hole-Transfer Kinetics at CoOx/BiVO4/SnO2 Double Heterojunctions 査読

    Akira Yamakata, Chandana Sampath, Kumara Ranasinghe, Naruki Hayashi, Kosaku Kato, Junie Jhon, M. Vequizo

    ACS Applied Energy Materials   3 ( 1 )   1207 - 1214   2020年1月

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acsaem.9b02262

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  • How g-C3N4 Works and Is Different from TiO2 as Environmental Photocatalyst: Mechanistic View 査読 国際誌

    Jonghun Lim, Hyejin Kim, Jihee Park, Gun-hee Moon, Junie Jhon, M. Vequizo, Akira Yamakata, Jinwoo Lee, Wonyong Choi

    Environmental Science & Technology   54 ( 1 )   497 - 506   2020年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acs.est.9b05044

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  • 時間分解分光測定による粉末欠陥への光励起キャリアー捕捉過程と光触媒活性に及ぼす影響 査読

    山方啓* and Junie Jhon M. Vequizo,

    触媒 【特集号: 触媒設計を拓く欠陥構造のキャラクタリゼーション】   62 ( 1 )   22 - 28   2020年1月

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    担当区分:筆頭著者, 責任著者  

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  • Synthesis of Copolymerized Carbon Nitride Nanosheets from Urea and 2-Aminobenzonitrile for Enhanced Visible-Light CO2 Reduction with a Ruthenium(II) Complex Catalyst 査読

    Kengo Shibata, Kosaku Kato, Constantine Tsounis, Tomoki Kanazawa, Daling Lu, Shunsuke Nozawa, Akira Yamakata, Osamu Ishitani, Kazuhiko Maeda

    Solar RRL   4 ( 8 )   1900461   2020年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1002/solr.201900461

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  • Synthesis of three-component C<inf>3</inf>N<inf>4</inf>/rGO/C-TiO<inf>2</inf> photocatalyst with enhanced visible-light responsive photocatalytic deNO<inf>x</inf> activity 査読

    Noda, C., Asakura, Y., Shiraki, K., Yamakata, A., Yin, S.

    Chemical Engineering Journal   390   124616 - 124616   2020年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier {BV}  

    In order to realize high efficiency photocatalysis deNO(x) effect, a homogeneous three-component photocatalyst, C3N4/rGO/C-TiO2 was successfully synthesized by an in situ synthesis method. First, C3N4/rGO composite was prepared to increase the contact surface between them. Then, C-TiO2 was crystallized on the surface of the C3N4/rGO to obtain relatively dispersed C-TiO2 nanoparticles on the C3N4/rGO. The as-prepared photocatalyst was evaluated by NO removal ratio under weak visible and UV LED light irradiation. C3N4/rGO/C-TiO2 was compared with sample prepared by simple mixing of C3N4, rGO and C-TiO2 within a solution. As a result, sample prepared by in situ synthesis exhibited the highest photocatalytic activity, together with high apparent quantum efficiency. The transient absorption measurement clarified that the composite photocatalyst possessed longer carrier lifetime if compared to that of each component material, resulted to its higher photocatalytic activity. The three-component photocatalyst is thought to have shown enhancement in photocatalytic activity by Z-scheme mechanism with rGO as an electron mediator to improve the performance of Z-scheme.

    DOI: 10.1016/j.cej.2020.124616

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  • Nano vs. bulk rutile TiO2:N,F in Z-scheme overall water splitting under visible light 査読

    Akinobu Miyoshi, Kosaku Kato, Toshiyuki Yokoi, Jan J. Wiesfeld, Kiyotaka Nakajima, Akira Yamakata, Kazuhiko Maeda

    Journal of Materials Chemistry A   8 ( 24 )   11996 - 12002   2020年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry (RSC)  

    <p>Nitrogen/fluorine-codoped rutile TiO2 nanoparticles worked more efficiently as a water oxidation photocatalyst in visible-light Z-scheme water splitting than a bulk analogue.</p>

    DOI: 10.1039/d0ta04450d

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  • Enhancement of photoelectrochemical activity of TiO<inf>2</inf> electrode by particulate/dense double-layer formation 招待 査読

    Hayashi, N., Kato, K., Yamakata, A.

    The Journal of chemical physics   152 ( 24 )   241101 - 241101   2020年

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    担当区分:責任著者   掲載種別:研究論文(学術雑誌)   出版者・発行元:AIP Publishing  

    DOI: 10.1063/5.0010121

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  • Enhancement of UV-responsive photocatalysts aided by visible-light responsive photocatalysts: Role of WO<inf>3</inf> for H<inf>2</inf> evolution on CuCl 査読

    Takagi, M., Kawaguchi, M., Yamakata, A.

    Applied Catalysis B: Environmental   263   118333 - 118333   2020年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier {BV}  

    WO3 is one of the most popular materials for visible-light photocatalysts. However, its conduction band minimum is too low for water reduction. Here, we found that WO3 can assist water reduction by using visible light in a CuCl2 aqueous solution. Photoirradiation of WO3 in CuCl2 reduces Cu2+ to form indissoluble Cud adducts, and as-produced CuCl/WO3 was active for H-2 evolution under UV-light. This composite has very low reactivity under visible light ( > 400 nm), but visible-light assisted H-2 evolution was observed with simultaneous irradiation with UV light: the activity was increased similar to 1.7 fold. Transient absorption measurements revealed that Z-schematic recombination initially takes place between photogenerated electrons in WO3 and holes in CuCl. As a result, the lifetime of electrons in Cud was increased, enhancing H2 evolution. These results demonstrate that inactive narrow-band gap materials can be used to enhance the activity of wide-band gap materials under sunlight illumination.

    DOI: 10.1016/j.apcatb.2019.118333

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  • Defect-Induced Acceleration and Deceleration of Photocarrier Recombination in SrTiO<inf>3</inf>Powders 査読

    Kato, K., Yamakata, A., Yamakata, A.

    Journal of Physical Chemistry C   124 ( 20 )   11057 - 11063   2020年

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    担当区分:責任著者   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acs.jpcc.0c03369

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  • Cobalt Aluminate Spinel as a Cocatalyst for Photocatalytic Oxidation of Water: Significant Hole-Trapping Effect 査読

    Kanazawa, T., Kato, K., Yamaguchi, R., Uchiyama, T., Lu, D., Nozawa, S., Yamakata, A., Uchimoto, Y., Maeda, K.

    ACS Catalysis   10 ( 9 )   4960 - 4966   2020年

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    担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    Here we show that nanoparticulate CoAl2O4 spinel serves as an efficient cocatalyst for photocatalytic oxidation of water. The O-2 evolution activity of CoAl2O4/g-C3N4 from an aqueous solution of AgNO3 under visible light irradiation was similar to 10 times that of unmodified g-C3N4 and also exceeded that of an analogue modified with a well-known Co3O4 cocatalyst for each optimal preparation condition. Transient absorption spectroscopy indicated that the CoAl2O4 cocatalyst with Co2+ as the main cobalt species at the A site of the spinel possessed better hole-capturing properties than the Co3O4 cocatalyst, which was the main reason for the improved water-oxidation performance.

    DOI: 10.1021/acscatal.0c00944

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  • Fe/Ru Oxide as Versatile and Effective Cocatalyst for Boosting Z-Scheme Water Splitting: Suppressing Undesirable Backward Electron Transfer 査読

    Akinobu Nakada, Hajime Suzuki, Junie Jhon, M. Vequizo, Kanta Ogawa, Masanobu Higashi, Akinori Saeki, Akira Yamakata, Hiroshi Kageyama, Ryu Abe

    ACS Applied Materials & Interfaces   11 ( 49 )   45606 - 45611   2019年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acsami.9b14802

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  • Achievement of High Photocatalytic Performance to BaTi4O9 toward Overall H2O Splitting 査読

    Yuichi Hiramachi, Hirotaka Fujimori, Akira Yamakata, Yoshihisa Sakata

    ChemCatChem   11 ( 24 )   6213 - 6217   2019年10月

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1002/cctc.201901564

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  • Solar-Driven Photoelectrochemical Water Oxidation over an n-Type Lead-Titanium Oxyfluoride Anode 査読

    Naoki Hirayama, Hiroko Nakata, Haruki Wakayama, Shunta Nishioka, Tomoki Kanazawa, Ryutaro Kamata, Yosuke Ebato, Kosaku Kato, Hiromu Kumagai, Akira Yamakata, Kengo Oka, Kazuhiko Maeda

    J. Am. Chem. Soc.   141 ( 43 )   17158 - 17165   2019年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/jacs.9b06570

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  • Effect of Na-doping on Electron Decay kinetics in SrTiO3 Photocatalyst 査読

    Kosaku Kato, Junzhe Jiang, Yoshihisa Sakata, Akira Yamakata

    ChemCatChem   11 ( 24 )   6349 - 6354   2019年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1002/cctc.201901669

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  • Crucial impact of reduction on the photocarriers dynamics on SrTiO3 powders studied by transient absorption spectroscopy 査読

    Junie Jhon, M. Vequizo, Shunta Nishioka, Junji Hyodo, Yoshihiro Yamazaki, Kazuhiko Maeda, Akira Yamakata

    J. Mater. Chem. A   7 ( 45 )   26139 - 26146   2019年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1039/C9TA08216F

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  • Enhanced water splitting through two-step photoexcitation by sunlight using tantalum/nitrogen-codoped rutile titania as a water oxidation photocatalyst 査読

    Shunta Nishioka, Kei-ichi Yanagisawa, Daling Lu, Junie Jhon, M. Vequizo, Akira Yamakata, Koji Kimoto, Miki Inada, Kazuhiko Maeda

    Sustainable Energy & Fuels   3 ( 9 )   2337 - 2346   2019年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1039/C9SE00289H

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  • Enhanced Visible Light Response of TiO<inf>2</inf> Codoped with Cr and Ta Photocatalysts by Electron Doping 査読

    Fumiaki Amano, Masashi Nakata, Junie Jhon M. Vequizo, Akira Yamakata

    ACS Applied Energy Materials   2 ( 5 )   3274 - 3282   2019年5月

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    掲載種別:研究論文(学術雑誌)  

    © 2019 American Chemical Society. The importance of electron concentration in rutile TiO2 photocatalysts motivated us to apply H2 reduction treatment to visible-light-responsive TiO2 photocatalysts sensitized by chromium ion doping. We found that H2 reduction treatment of rutile TiO2 particles codoped with Ta and Cr (TiO2:Ta/Cr) enhanced photocatalytic activity for O2 evolution by water oxidation under visible irradiation (>2.2 eV). The enhanced visible light activity of H2-treated TiO2:Ta/Cr was attributed to the increase of electron concentration, which was confirmed by UV-vis diffuse reflectance and electron spin resonance (ESR) spectroscopy. The H2-treated TiO2:Ta/Cr photocatalyst was repeatedly used in aqueous media in spite of the presence of doped electrons. Photoluminescence and transient absorption spectroscopies revealed that electron doping with H2 treatment decreased the midgap states working as deep traps of photoexcited electrons and increased the accumulation of the photoexcited electrons in the conduction band. The optimized H2 reduction temperature was decreased with an increase in the amount of higher valence Ta5+ used as a donor-type dopant. This study shows that the precise control of the bulk electronic structure of rutile TiO2 by a combination of codoping and H2 reduction treatment improves the visible-light-driven photocatalytic activity because of the decrease of the trapping sites at deep energy levels and the recombination between deeply trapped electrons and valence band holes.

    DOI: 10.1021/acsaem.9b00126

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  • Effect of CuFe2O4 ferrite on photocatalysis and carrier dynamics of electrospun α-Fe2O3 nanofibers by time-resolved transient absorption spectroscopy 査読

    Pei-Hsuan Hung, Junie Jhon, M. Vequizo, Ren-An Wu, Akira Yamakata, Wenjea J. Tseng

    Ceram. Int.   45 ( 12 )   15676 - 15680   2019年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.ceramint.2019.05.080

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  • Oxygen-Doped Ta3N5 Nanoparticles for Enhanced Z-Scheme Carbon Dioxide Reduction with a Binuclear Ruthenium(II) Complex under Visible Light 査読

    Kanemichi Muraoka, Junie Jhon, M. Vequizo, Ryo Kuriki, Akira Yamakata, Tomoki Uchiyama, Daling Lu, Yoshiharu Uchimoto, Osamu Ishitani, Kazuhiko Maeda

    ChemPhotoChem   3 ( 10 )   1027 - 1033   2019年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1002/cptc.201900120

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  • Construction of Spatial Charge Separation Facets on BaTaO2N Crystals by Flux Growth Approach for Visible-Light-Driven H2 Production 査読

    Ying Luo, Sayaka Suzuki, Zheng Wang, Kunio Yubuta, Junie Jhon, M. Vequizo, Akira Yamakata, Hiromasa Shiiba, Takashi Hisatomi, Kazunari Domen, Katsuya Teshima

    ACS Applied Materials & Interfaces   11 ( 25 )   22264 - 22271   2019年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acsami.9b03747

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  • Improvement of photocatalytic activity under visible-light irradiation by heterojunction of Cu ion loaded WO3 and Cu ion loaded N-TiO2 査読

    Tomoya Iihoshi, Takeshi Ohwaki, Junie Jhon, M. Vequizo, Akira Yamakata

    Applied Catalysis B: Environmental   248   249 - 254   2019年2月

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.apcatb.2019.01.046

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  • Sodium titanium oxide bronze nanoparticles synthesized via concurrent reduction and Na+-doping into TiO2(B) 査読

    Hasegawa, George, Tanaka, Moeko, Vequizo, Junie Jhon M., Yamakata, Akira, Hojo, Hajime, Kobayashi, Makoto, Kakihana, Masato, Inada, Miki, Akamatsu, Hirofumi, Hayashi, Katsuro

    NANOSCALE   11 ( 3 )   1442 - 1450   2019年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    A mixed valence compound, sodium titanium oxide bronze (NaxTiO2-B), combines intriguing properties of high electric conductivity and good chemical stability together with a unique one-dimensional tunnel crystal structure available for cation storage. However, this compound has not been studied for a long period because of the strongly reductive condition at high temperature required for its preparation, which limits the morphological control such as the preparation of nanocrystals. For the first time in this paper, the topotactic synthesis of nano-sized NaxTiO2-B with high specific surface area (>130 m(2) g(-1)) from TiO2(B) nanoparticles has been demonstrated. The reaction of metastable TiO2(B) with NaBH4 allows carrier electrons to be doped simultaneously with incorporation of Na+ ions into the interstitial sites of the host Ti-O lattice at relatively low temperature. An electrochemical investigation of Li+- and Na+-ion storage behaviors suggests that the incorporated Na+ ions are mainly placed in the 6-fold coordination sites of bronze. In addition, optical measurements including time-resolved transient spectroscopy revealed that the doped electrons in the NaxTiO2-B nanoparticles are predominantly in the Ti3+ state and behave as a small polaron. The pelletized NaxTiO2-B nanoparticles shows a good electronic conductivity of 1.4 x 10(-2) S cm(-1) at 30 degrees C with an activation energy of 0.17 eV, which is attributable to the thermal barrier for the polaron hopping.

    DOI: 10.1039/c8nr08372j

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  • Clear and transparent nanocrystals for infrared-responsive carrier transfer 査読

    Sakamoto, M., Kawawaki, T., Kimura, M., Vequizo, J.J.M., Matsunaga, H., Ranasinghe, C.S.K., Yamakata, A., Matsuzaki, H., Furube, A., Teranishi, T.

    Nature communications   10 ( 1 )   406 - 406   2019年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1038/s41467-018-08226-2

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  • Near infrared light induced plasmonic hot hole transfer at a nano-heterointerface 査読

    Zichao Lian, Masanori Sakamoto, Hironori Matsunaga, Junie Jhon M. Vequizo, Akira Yamakata, Mitsutaka Haruta, Hiroki Kurata, Wataru Ota, Tohru Sato, Toshiharu Teranishi

    Nature Communications   9 ( 1 )   2314 - 2314   2018年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Nature Publishing Group  

    Localized surface plasmon resonance (LSPR)-induced hot-carrier transfer is a key mechanism for achieving artificial photosynthesis using the whole solar spectrum, even including the infrared (IR) region. In contrast to the explosive development of photocatalysts based on the plasmon-induced hot electron transfer, the hole transfer system is still quite immature regardless of its importance, because the mechanism of plasmon-induced hole transfer has remained unclear. Herein, we elucidate LSPR-induced hot hole transfer in CdS/CuS heterostructured nanocrystals (HNCs) using time-resolved IR (TR-IR) spectroscopy. TR-IR spectroscopy enables the direct observation of carrier in a LSPR-excited CdS/CuS HNC. The spectroscopic results provide insight into the novel hole transfer mechanism, named plasmon-induced transit carrier transfer (PITCT), with high quantum yields (19%) and long-lived charge separations (9.2 μs). As an ultrafast charge recombination is a major drawback of all plasmonic energy conversion systems, we anticipate that PITCT will break the limit of conventional plasmon-induced energy conversion.

    DOI: 10.1038/s41467-018-04630-w

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  • Curious Behaviors of Photogenerated Electrons and Holes at the Defects on Anatase, Rutile, and Brookite TiO2 Powders: A Review 招待 査読

    Akira Yamakata, Junie Jhon, M. Vequizo

    J. Photochem. Photobiol. C-Photochem.   40   234 - 243   2018年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.jphotochemrev.2018.12.001

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  • Plasmonic p–n Junction for Infrared Light to Chemical Energy Conversion 査読

    Zichao Lian, Masanori Sakamoto, Junie Jhon, M. Vequizo, Chandana Sampath, Kumara Ranasinghe, Akira Yamakata, Takuro Nagai, Koji Kimoto, Yoichi Kobayashi, Naoto Tamai, Toshiharu Teranishi

    J. Am. Chem. Soc.   141 ( 6 )   2446 - 2450   2018年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/jacs.8b11544

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  • Expansion of the photoresponse window of a BiVO4 photocatalyst by doping with chromium(VI) 査読

    Kazuya Okuno, Hideki Kato, Junie Jhon, M. Vequizo, Akira Yamakata, Hisayoshi Kobayashi, Makoto Kobayashi, Masato Kakihana

    RSC Advances   8 ( 67 )   38140 - 38145   2018年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1039/C8RA07830K

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  • A Copolymerization Approach to Improving Ru(II)-Complex/C3N4 Hybrid Photocatalysts for Visible-Light CO2 Reduction 査読

    Constantine Tsounis, Ryo Kuriki, Kengo Shibata, Junie Jhon, M. Vequizo, Daling Lu, Akira Yamakata, Osamu Ishitani, Rose Amal, Kazuhiko Maeda

    ACS Sustainable Chemistry & Engineering   6 ( 11 )   15333 - 15340   2018年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acssuschemeng.8b03782

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  • Effects of Interfacial Electron Transfer in Metal Complex−Semiconductor Hybrid Photocatalysts on Z‑Scheme CO2 Reduction under Visible Light 査読

    Akinobu Nakada, Ryo Kuriki, Keita Sekizawa, Shunta Nishioka, Junie Jhon, M. Vequizo, Tomoki Uchiyama, Nozomi Kawakami, Daling Lu, Akira Yamakata, Yoshiharu Uchimoto, Osamu Ishitani, Kazuhiko Maeda

    ACS Catalysis   8 ( 10 )   9744 - 9754   2018年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acscatal.8b03062

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  • Undoped Layered Perovskite Oxynitride Li2 LaTa2 O6 N for Photocatalytic CO2 Reduction with Visible Light. 査読 国際誌

    Takayoshi Oshima, Tom Ichibha, Ken Sinkou Qin, Kanemichi Muraoka, Junie Jhon M Vequizo, Keisuke Hibino, Ryo Kuriki, Shunsuke Yamashita, Kenta Hongo, Tomoki Uchiyama, Kotaro Fujii, Daling Lu, Ryo Maezono, Akira Yamakata, Hideki Kato, Koji Kimoto, Masatomo Yashima, Yoshiharu Uchimoto, Masato Kakihana, Osamu Ishitani, Hiroshi Kageyama, Kazuhiko Maeda

    Angewandte Chemie (International ed. in English)   57 ( 27 )   8154 - 8158   2018年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Oxynitrides are promising visible-light-responsive photocatalysts, but their structures are almost confined with three-dimensional (3D) structures such as perovskites. A phase-pure Li2 LaTa2 O6 N with a layered perovskite structure was successfully prepared by thermal ammonolysis of a lithium-rich oxide precursor. Li2 LaTa2 O6 N exhibited high crystallinity and visible-light absorption up to 500 nm. As opposed to well-known 3D oxynitride perovskites, Li2 LaTa2 O6 N supported by a binuclear RuII complex was capable of stably and selectively converting CO2 into formate under visible light (λ>400 nm). Transient absorption spectroscopy indicated that, as compared to 3D oxynitrides, Li2 LaTa2 O6 N possesses a lower density of mid-gap states that work as recombination centers of photogenerated electron/hole pairs, but a higher density of reactive electrons, which is responsible for the higher photocatalytic performance of this layered oxynitride.

    DOI: 10.1002/anie.201803931

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  • Binary flux-promoted formation of trigonal ZnIn2S4 layered crystals using ZnS-containing industrial waste and their photocatalytic performance for H2 production 査読

    Mirabbos Hojamberdiev, Yanfei Cai, Junie Jhon, M. Vequizo, Mohammad Mansoob Khan, Ronald Vargas, Kunio Yubuta, Akira Yamakata, Katsuya Teshima, Masashi Hasegawa

    Green Chemistry   20 ( 16 )   3845 - 3856   2018年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1039/C8GC01746H

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  • Enhanced photocatalytic NOx decomposition of visible-light responsive F-TiO2/(N,C)-TiO2 by charge transfer between F-TiO2 and (N,C)-TiO2through their doping levels 査読

    Shio Komatsuda, Yusuke Asakura, Junie Jhon, M. Vequizo, Akira Yamakata, Shu Yin

    Appl. Catal. B-Environ.   238   358 - 364   2018年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.apcatb.2018.07.038

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  • Excited-State Dynamics of Graphitic Carbon Nitride Photocatalyst and Ultrafast Electron Injection to a Ru(II) Mononuclear Complex for Carbon Dioxide Reduction 査読

    Ryo Kuriki, Chandana Sampath, Kumara Ranasinghe, Yasuomi Yamazaki, Akira Yamakata, Osamu Ishitani, Kazuhiko Maeda

    J. Phys. Chem. C.   122 ( 29 )   16795 - 16802   2018年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acs.jpcc.8b03996

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  • Homogeneous Electron Doping into Non-Stoichiometric Strontium Titanate Improves Its Photocatalytic Activity for Hydrogen and Oxygen Evolution 査読

    Shunta Nishioka, Junji Hyodo, Junie Jhon, M. Vequizo, Shunsuke Yamashita, Hiromu Kumagai, Koji Kimoto, Akira Yamakata, Yoshihiro Yamazaki, Kazuhiko Maeda

    ACS Catal.   8 ( 8 )   7190 - 7200   2018年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acscatal.8b01379

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  • Fabrication of robust TiO2 thin films by atomized spray pyrolysis deposition for photoelectrochemical water oxidation 査読

    Chandana Sampath Kumara Ranasinghe, Junie Jhon M. Vequizo, Akira Yamakata

    Journal of Photochemistry and Photobiology A: Chemistry   358   320 - 326   2018年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier B.V.  

    Photoelectrodes are highly essential for the photoelectrochemical water splitting process and development of novel fabrication techniques is vital for further enhancement of activity. In this study, we successfully fabricated highly active TiO2 thin films by using novel atomized spray pyrolysis deposition (ASPD) technique. The ASPD technique utilizes a unique atomization process to produce highly fine aerosols which resulted in a highly crystalline TiO2 nanostructure. The deposition process was optimized by controlling deposition temperatures and precursor amounts. XRD and SEM studies confirmed the formation of anatase TiO2 phase and a highly interconnected nano-flakes on FTO substrate at 550 °C. The photoelectrochemical activity of the optimized thin films showed a photocurrent density of ∼5 mA cm−2 at 1.0 V (vs. Ag/AgCl) in 0.1 M Na2SO4 (aq) under 375 nm (150 mW cm−2) illumination. This photocurrent was much higher than the two other anatases TiO2 thin films fabricated by conventional spray pyrolysis deposition (SPD) using the same precursor and anatase TiO2 powder (particle size ∼21 nm). Transient IR absorption study revealed that the SPD powder based thin films have deeply trapped electrons, whereas ASPD thin films consisted with only free and/or shallowly trapped electrons. Higher crystallinity and enhanced electron conductivity of the TiO2 thin films fabricated by ASPD are responsible for this stable and high photoelectrochemical activity.

    DOI: 10.1016/j.jphotochem.2017.09.006

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  • Role of CoOx cocatalyst on Ta3N5 photocatalysts studied by transient visible to mid-infrared absorption spectroscopy 査読

    Junie Jhon M. Vequizo, Mirabbos Hojamberdiev, Katsuya Teshima, Akira Yamakata

    Journal of Photochemistry and Photobiology A: Chemistry   358   315 - 319   2018年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier B.V.  

    Tantalum nitride (Ta3N5) photocatalysts attract considerable attention owing to their visible light absorption below 600 nm and suitable band structures for reduction and oxidation of water to generate hydrogen and oxygen gas. Herein, we investigated the effects of CoOx on the dynamics of photogenerated charge carriers in Ta3N5 powder photocatalysts by using microsecond to millisecond transient visible to mid-IR absorption spectroscopy. Transient absorption measurements revealed that most of the electrons in Ta3N5 are deeply trapped at the defects, most likely originating from oxygen vacancies and reduced Ta species. Two important roles of CoOx were elucidated: effective capture of holes to prolong electron lifetime and reduction of defects as recombination centers, which further elongates the lifetime of both electrons and holes.

    DOI: 10.1016/j.jphotochem.2017.09.005

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  • Structural changes of water molecules during photoelectrochemical water oxidation on TiO2 thin film electrodes 査読

    Chandana Sampath Kumara Ranasinghe, Akira Yamakata

    Physical Chemistry Chemical Physics   20 ( 5 )   3388 - 3394   2018年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry  

    Behaviors of photogenerated charge carriers and structural changes of water molecules on TiO2 photoelectrodes were investigated by using time-resolved visible to mid-IR absorption spectroscopy. From the spectra measured in the visible to NIR region, it was shown that the lifetime of trapped electrons and holes becomes longer upon applying more positive potentials. This result was reasonably explained by the enhancement of the upward band bending at the water/TiO2 interface. On the other hand, from the spectra measured in the mid-IR region, structural changes of the water molecules were observed. When a TiO2 electrode was photoexcited at the potential where the water oxidation starts, a new absorption peak appeared at 3620 cm-1 with a slight decrease in the intensity of hydrogen-bonded water. This new peak was assigned to the isolated O-H band of water molecules. Usually, TiO2 surfaces exhibit super-hydrophilic properties with strong hydrogen-bonding
    however, the obtained result was opposite. Therefore, the appearance of this isolated O-H band was ascribed to the cleavage of the hydrogen-bonding networks resulting from the production of reaction intermediates such as OH radicals or H2O2. The intensity of the isolated O-H decreases when applying more positive potentials, where the O2 evolution proceeds more efficiently. This could be ascribed to the rapid consumption of the reaction intermediates. At these potentials, the intensity of hydrogen-bonded water was also further decreased.

    DOI: 10.1039/c7cp06646e

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  • Oxygen induced enhancement of NIR emission in brookite TiO2 powders: Comparison with rutile and anatase TiO2 powders 査読

    Junie Jhon M. Vequizo, Sunao Kamimura, Teruhisa Ohno, Akira Yamakata

    Physical Chemistry Chemical Physics   20 ( 5 )   3241 - 3248   2018年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry  

    Brookite TiO2 attracts considerable attention in photocatalysis owing to its superior performance in several photocatalytic reactions. In this work, we investigated the behavior of charge carriers in brookite, rutile, and anatase TiO2 by using photoluminescence (PL) and transient absorption (TA) spectroscopies. PL measurements revealed that brookite TiO2 exhibits a visible and a NIR emission at ∼520 nm and ∼860 nm, respectively. Addition of methanol vapor quenched both the visible and NIR emissions by the hole-consuming reaction of methanol. However, exposure to O2 shows curious behaviors: the visible emission was quenched but the NIR emission was enhanced. These results can be accounted for by the enhancement of upward band bending resulting in the effective separation of electrons and holes into the bulk and the surface, respectively. Furthermore, the shallowly trapped electrons, which are responsible for visible PL, are consumed by O2
    hence, the visible emission is quenched. However, in the case of NIR emission, the deeply trapped electrons are responsible and they are mainly located at the surface defects. The O2 adsorption promotes the hole accumulation at the surface and then assists the recombination of these deeply trapped electrons, resulting in the enhancement of the NIR emission. We also found that the lifetime of NIR emission (τ1 = 43 ± 0 ns and τ2 = 589 ± 1 ns) was much longer than that of visible emission (τ1 = 15 ± 0 ns and τ2 = 23 ± 0 ns), since the mobility of these deeply trapped electrons to encounter with holes is lower than that of the shallowly trapped electrons. However, even for this slow NIR emission, the actual lifetime of the deeply trapped electrons estimated by TA (1.5 ± 0.0 μs and 17 ± 0 μs) was one or two orders of magnitude longer, confirming that non-radiative recombination is dominant and it is much slower than radiative recombination: TAS and PL provide detailed information on the radiative and non-radiative recombination processes. The PL of anatase and rutile TiO2 powders was also measured and the difference from brookite TiO2 was discussed.

    DOI: 10.1039/c7cp06975h

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  • Visible-light CO2 reduction over a ruthenium(ii)-complex/C3N4 hybrid photocatalyst: The promotional effect of silver species 査読

    Kazuhiko Maeda, Daehyeon An, Chandana Sampath Kumara Ranasinghe, Tomoki Uchiyama, Ryo Kuriki, Tomoki Kanazawa, Daling Lu, Shunsuke Nozawa, Akira Yamakata, Yoshiharu Uchimoto, Osamu Ishitani

    Journal of Materials Chemistry A   6 ( 20 )   9708 - 9715   2018年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry  

    Hybrid photocatalysts constructed with a mononuclear Ru(ii)-complex (RuP), silver nanoparticles, and carbon nitride nanosheets (NS-C3N4) photocatalyze CO2 reduction to selectively form formate under visible light. The structure of the nanoparticulate silver species, which worked as promoters for the reaction, was characterized by X-ray diffraction, UV-VIS diffuse reflectance spectroscopy, high-resolution transmission microscopy, and X-ray absorption fine-structure spectroscopy. The silver promoters were loaded on the surface of NS-C3N4 by an impregnation method from an aqueous solution containing AgNO3 or an in situ photodeposition method. Impregnation of NS-C3N4 with 2.0 wt% Ag followed by reduction with H2 at 473 K (further modified with RuP) resulted in the highest photocatalytic activity, giving a turnover number of 5700 (based on RuP), which was the greatest value among the formate-generating hybrid systems with a mononuclear complex. While the optimized photocatalyst contained highly dispersed Ag2O-like nanoclusters as the major silver species, experimental results suggested that highly dispersed Ag0 species are more important for enhancing CO2 reduction activity, that is, the obtained experimental results led us to conclude that there are two major factors affecting activity: one is the feature size of silver species (smaller is better), and the other is the oxidation state of silver (metallic is better).

    DOI: 10.1039/c8ta03245a

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  • Nitrogen/fluorine-codoped rutile titania as a stable oxygen-evolution photocatalyst for solar-driven Z-scheme water splitting 査読

    Akinobu Miyoshi, Junie Jhon M. Vequizo, Shunta Nishioka, Yuma Kato, Muneaki Yamamoto, Shunsuke Yamashita, Toshiyuki Yokoi, Akihide Iwase, Shunsuke Nozawa, Akira Yamakata, Tomoko Yoshida, Koji Kimoto, Akihiko Kudo, Kazuhiko Maeda

    Sustainable Energy & Fuels   2   2025 - 2035   2018年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry ({RSC})  

    DOI: 10.1039/C8SE00191J

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  • Engaging the flux-grown La1-xSrxFe1-yTiyO3 crystals in visible-light-driven photocatalytic hydrogen generation 査読

    Mirabbos Hojamberdiev, Kenta Kawashima, Mahesh Kumar, Akira Yamakata, Kunio Yubuta, Aleksander Gurlo, Masashi Hasegawa, Kazunari Domen, Katsuya Teshima

    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY   42 ( 44 )   27024 - 27033   2017年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Perovskite LaFeO3 is regarded as one of the promising photocatalysts for solar splitting of water to hydrogen and oxygen due to its suitable band edge positions, visible light absorbance, and high chemical stability. To further improve its photocatalytic performance of LaFeO3, the effects of solute concentration in the KCl-flux growth and partial A- and B-site substitution are investigated in this work. Controlling the solute concentration in the range of 1-20 mol% is crucial to grow phase-pure LaFeO3 crystals with idiomorphic shape. With increasing the solute concentration, the flux-based growth route gradually changes to a solid state-based growth route because of a decrease in solubility and an increase in the crystallization core number. The La1-xSrxFe1-yTiyO3 (x,y = 0,0; 0,0.15; 0.15,0; 0.1125,0.0375; 0.0375,0.1125; and 0.075,0.075) crystals were also synthesized by a KCl-flux method to explore the effect of partial Sr2+-to-La3+ and/or Ti4+-to-Fe2-4+ substitution on photocatalytic performance of LaFeO3. The Sr2+ Ti4+ co-substitution is found to enhance the photocatalytic performance of LaFeO3 as compared with the corresponding individual substitution (Sr2+ or Ti4+). The highest photocatalytic hydrogen generation rate (83.2 mu mol h(-1)) was observed for Pt-photodeposited La0.925SF0.075Fe0.925Ti0.075O3 crystals in 5-h reaction due to the improvement of both bulk properties and photoactivity and the reduction in both grain boundaries and lattice defects stemmed from the Sr2+-Ti4+ co-substitution and KCl flux growth. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ijhydene.2017.09.036

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  • Cation-dependent restructure of the electric double layer on CO-covered Pt electrodes: Difference between hydrophilic and hydrophobic cations 査読

    Akira Yamakata, Masatoshi Osawa

    JOURNAL OF ELECTROANALYTICAL CHEMISTRY   800   19 - 24   2017年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE SA  

    Structural changes in water layers on a CO-covered Pt electrode triggered by rapid pulsed laser heating of the interface are studied using potential transient measurements. When the laser energy density is below 20 mJ cm(-2), the water layers undergo a change in orientation, which causes a negative shift in the rest potential that recovers within 20 ps with the cooling of the interface. In contrast, when the laser intensity exceeds 20 mJ cm(-2), the CO is desorbed and the rest potential first experiences a positive shift, which is followed by a negative shift. This positive shift is caused by replacement of the CO by water and subsequent restructuring of the water layer. The restructuring rate depends strongly on the electrolyte cation: the rest potential reaches a maximum value within 100 ps for hydrophilic cations such as H+ and Li+, whereas it takes &gt;10 ms for hydrophobic cations such as Et4N+ and Bu4N+. Surface-enhanced IR absorption measurements suggest that the water molecules around the hydrophobic cations are more strongly hydrogen-bonded than those around the hydrophilic cations. Because the restructuring involves a reforming of the hydrogen-bonding network at the electric double layer, Et4N+ and Bu4N+, which have more strongly hydrogen-bonded hydration shells, require more time than H+ and Li+. (C) 2016 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.jelechem.2016.12.034

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  • Elucidating the impact of A-site cation change on photocatalytic H-2 and O-2 evolution activities of perovskite-type LnTaON(2) (Ln = La and Pr) 査読

    Mirabbos Hojamberdiev, Maged F. Bekheet, Judy N. Hart, Junie Jhon M. Vequizo, Akira Yamakata, Kunio Yubuta, Aleksander Gurlo, Masashi Hasegawa, Kazunari Domen, Katsuya Teshima

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS   19 ( 33 )   22210 - 22220   2017年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    Transition metal (oxy) nitrides with perovskite-type structures have been regarded as one of the promising classes of inorganic semiconductor materials that can be used in solar water splitting systems for the production of hydrogen as a renewable and storable energy carrier. The performance of transition metal (oxy) nitrides in solar water splitting is strongly influenced by the crystal structure-related dynamics of photogenerated charge carriers. Here, we have systematically assessed the influence of A-site cation exchange on the visible-light-induced photocatalytic H-2 and O-2 evolution activities, photoanodic response, and dynamics of photogenerated charge carriers of perovskite-type LnTaON(2) (Ln = La and Pr). The structural refinement results reveal the orthorhombic Imma and Pnma structures for LaTaON2 and PrTaON2, respectively; the latter has a more distorted crystal structure from the ideal cubic perovskite due to the smaller size of Pr3+ cations. Compared with LaTaON2, PrTaON2 exhibits lower photocatalytic H-2 and O-2 gas evolution activities and photoanodic response owing to an excessive amount of intrinsic defects associated with anionic vacancies and reduced tantalum species stemming from a long high-temperature nitridation process under reductive NH3 atmosphere. Transient absorption signals evidence the faster decay of photogenerated electrons (holes) in Pt (CoOx)-loaded LaTaON2 than that in Pt (CoOx)-loaded PrTaON2, consistent with the photocatalytic and photoelectrochemical performance of the two photocatalysts. This study suggests that in addition to selecting a suitable A-site cation, it is prerequisite to synthesize LnTaON(2) (Ln = La and Pr) crystals with a low defect density to improve their photo-conversion efficiency for solar water splitting.

    DOI: 10.1039/c7cp03714g

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  • Interfacial Manipulation by Rutile TiO2 Nanoparticles to Boost CO2 Reduction into CO on a Metal-Complex/Semiconductor Hybrid Photocatalyst 査読

    Keisuke Wada, Chandana Sampath Kumara Ranasinghe, Ryo Kuriki, Akira Yamakata, Osamu Ishitani, Kazuhiko Maeda

    ACS APPLIED MATERIALS & INTERFACES   9 ( 28 )   23869 - 23877   2017年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Metal-complex/semiconductor hybrids have attracted attention as photocatalysts for visible-light CO2 reduction, and electron transfer from the metal complex to the semiconductor is critically important to improve the performance. Here rutile TiO2 nanoparticles having 5-10 nm in size were employed as modifiers to improve interfacial charge transfer between semiconducting carbon nitride nanosheets (NS-C3N4) and a supramolecular Ru(II)-Re(I) binuclear complex (RuRe). The RuRe/TiO2/NS-C3N4 hybrid was capable of photocatalyzing CO2 reduction into CO with high selectivity under visible light (lambda &gt; 400 nm), outperforming an analogue without TiO2 by a factor of 4, in terms of both CO formation rate and turnover number (TON). The enhanced photocatalytic activity was attributed primarily to prolonged lifetime of free and/or shallowly trapped electrons generated in TiO2/NS-C3N4 under visible-light irradiation, as revealed by transient absorption spectroscopy. Experimental results also indicated that the TiO2 modifier served as a good adsorption site for RuRe, which resulted in the suppression of undesirable desorption of the complex, thereby contributing to the improved photocatalytic performance. This study presents the first successful example of interfacial manipulation in a metal-complex/semiconductor hybrid photocatalyst for improved visible-light CO2 reduction to produce CO.

    DOI: 10.1021/acsami.7b07484

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  • Solar-driven Z-scheme water splitting using tantalum/nitrogen co-doped rutile titania nanorod as an oxygen evolution photocatalyst 査読

    Akinobu Nakada, Shunta Nishioka, Junie Jhon M. Vequizo, Kanemichi Muraoka, Tomoki Kanazawa, Akira Yamakata, Shunsuke Nozawa, Hiromu Kumagai, Shin-ichi Adachi, Osamu Ishitani, Kazuhiko Maeda

    JOURNAL OF MATERIALS CHEMISTRY A   5 ( 23 )   11710 - 11719   2017年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    A visible-light-driven water-splitting system that involves two-step photoexcitation (Z-scheme) was constructed using rutile TiO2 nanorod doped with Ta and N (TiO2:Ta/N) as an O-2 evolution photocatalyst. The Ta-doped TiO2 nanorods, prepared by a solvothermal synthesis, underwent nitridation to possess visible-light absorption under mild conditions, even at 623 K under an ammonia flow. The TiO2: Ta/N powders modified with a RuO2 cocatalyst were active under visible light up to 540 nm for water oxidation for producing O-2 in the presence of reversible electron acceptors (IO3- or Fe3+), while TiO2: N exhibited negligible activity. The results of time-resolved infrared absorption spectroscopy indicated that co-doping Ta with N into TiO2 prolonged the lifetime of photogenerated free electrons, leading to high photocatalytic activity. Simultaneous H-2 and O-2 evolution via water splitting was achieved using a combination of RuO2-modified TiO2: Ta/N, Ru-loaded SrTiO3:Rh and an Fe3+/Fe2+ redox couple under visible-light irradiation (lambda &gt; 420 nm) and under AM 1.5G simulated sunlight.

    DOI: 10.1039/c6ta10541f

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  • Trapping-Induced Enhancement of Photocatalytic Activity on Brookite TiO2 Powders: Comparison with Anatase and Rutile TiO2 Powders 査読

    Junie Jhon M. Vequizo, Hironori Matsunaga, Tatsuya Ishiku, Sunao Karnimura, Teruhisa Ohno, Akira Yamakata

    ACS CATALYSIS   7 ( 4 )   2644 - 2651   2017年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Brookite TiO2 is a promising material for active photocatalysts. However, the principal mechanism that determines the distinctive photocatalytic activity between anatase, rutile, and brookite TiO2 has not yet been hilly elucidated. Therefore, in this work, we studied the behavior of photogenerated electrons and holes in these TiO2 powders by using femtosecond to millisecond time-resolved visible to mid-IR absorption spectroscopy. We found that most of the photogenerated electrons in brookite TiO2 are trapped at powder defects within a few ps. This electron trapping decreases the number of surviving free electrons, but it extends the lifetime of holes as well as the trapped electrons because the probability of electrons to encounter holes is decreased by this electron-trapping. As a result, the number of surviving holes increases, which is beneficial for photocatalytic oxidation. In contrast, the reactivity of electrons is decreased to some extent by trapping, but they still remain active for photocatalytic reductions. Electron trapping also takes place on anatase and rutile TiO2 powders, but the trap-depth in anatase is too shallow to extend the lifetime of holes and that of rutile is too deep than the thermal energy (kT) at room temperature for the electron consuming reactions. As a result of the moderate depth of the electron trap in brookite, both electrons and holes are reactive for photocatalytic,reductions and oxidations. These results have clearly demonstrated that the presence of an appropriate depth of the electron trap can effectively contribute to enhance the overall photocatalytic activity.

    DOI: 10.1021/acscatal.7b00131

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  • The contrasting effect of the Ta/Nb ratio in (111)-layered B-site deficient hexagonal perovskite Ba5Nb4−xTaxO15 crystals on visible-light-induced photocatalytic water oxidation activity of their oxynitride derivatives 査読

    Mirabbos Hojamberdiev, Maged F. Bekheet, Ehsan Zahedi, Hajime Wagata, Junie Jhon, M. Vequizo, Akira Yamakata, Kunio Yubuta, Aleksander Gurlo, Kazunari Domen, Katsuya Teshima

    Dalton Trans.   45 ( 31 )   12559 - 12568   2016年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1039/c6dt02095j

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  • Photocatalytic property of metal ion added SrTiO3 to Overall H2O splitting 査読

    Yoshihisa Sakata, Yoshiko Miyoshi, Tatsuya Maeda, Kohki Ishikiriyama, Yuki Yamazaki, Hayao Imamura, Yeilin Ham, Takashi Hisatomi, Jun Kubota, Akira Yamakata, Kazunari Domen

    APPLIED CATALYSIS A-GENERAL   521   227 - 232   2016年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    The effects of the metal ion addition to SrTiO3 to the overall H2O splitting were investigated to improve the photocatalytic activity. The addition of metal ions was carried out by impregnation method. The preparation condition of metal ion added SrTiO3 was examined with applying Na+ ion as additive and SrTiO3 prepared by polymerizable complex method. The photocatalytic activity was markedly improved by the addition of Na+ ion and calcined above 1173 K. The preferable state of the photocatalyst was Na ion (2 atm%) added SrTiO3 obtained by calcination at 1273 K and the photocatalytic activity with a Rh0.3Cr1.7O3 (Rh:0.3 wt%) co-catalyst was 16 mmol/h for H-2 and 8 mmol/h for O-2 production. The apparent quantum yield (AQY) was 16% under the irradiation of 360 nm. The photocatalytic performance of Na+ ion added various SrTiO3 and the effects of various metal ion addition to SrTiO3 to the photocatalytic activity of the overall H2O splitting were investigated to discuss the influence of the added metal ions to the photocatalytic activity. (C) 2015 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.apcata.2015.12.013

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  • Enhancement of photoelectrochemical activity of SnS thin-film photoelectrodes using TiO2, Nb2O5, and Ta2O5 metal oxide layers 査読

    Junie Jhon M. Vequizo, Masanori Yokoyama, Masaya Ichimura, Akira Yamakata

    APPLIED PHYSICS EXPRESS   9 ( 6 )   067101   2016年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

    Tin sulfide (SnS) fine photoelectrodes fabricated by three-step pulsed electrodeposition were active for H-2 evolution. The incident-photon-conversion-efficiency increases from 900 nm and offers a good fit with the absorption spectrum. The activity was enhanced by 3.4, 3.0, and 1.8 times compared to bare SnS by loading Nb2O5, TiO2, and Ta2O5, respectively. Nb2O5 was most efficient because its conduction band is low enough to facilitate effective electron transfer from SnS; it also has sufficiently high potential for H-2 evolution. The overall activity is determined by the competitive interfacial electron transfer between SnS/metal-oxide and metal-oxide/water. Therefore, constructing appropriate heterojunctions is necessary for further improving photoelectrochemical systems. (C) 2016 The Japan Society of Applied Physics

    DOI: 10.7567/APEX.9.067101

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  • 酸化チタン光触媒のキャリアーダイナミクス-粉末におけるアナターゼとルチルの特異的な挙動- 査読

    山方啓

    光化学   47 ( 1 )   25 - 32   2016年4月

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    記述言語:日本語   出版者・発行元:光化学協会  

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  • Dynamics of Photogenerated Charge Carriers on Ni- and Ta-Doped SrTiO3 Photocatalysts Studied by Time-Resolved Absorption and Emission Spectroscopy 査読

    Akira Yamakata, Masayuki Kawaguchi, Ryosuke Murachi, Masahiro Okawa, Itaru Kamiya

    JOURNAL OF PHYSICAL CHEMISTRY C   120 ( 15 )   7997 - 8004   2016年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The behavior of photogenerated charge carriers on SrTiO3 photocatalysts doped with transition metals (such as Ni and Ta) was examined by time-resolved visible to mid-IR absorption and emission spectroscopy. When SrTiO3 was co-doped with Ni and Ta, the catalyst absorbed visible light and exhibited photocatalytic activity undervisible light irradiation. However, activity under UV light was decreased significantly compared to that before doping. The results of time-resolved measurements showed that monodoping of Ni or Ta accelerated the recombination but co-doping Ni with Ta increased the lifetime of charge carriers compared to those without doping. Furthermore, electrons excited by a visible laser pulse had longer lifetimes compared to those excited by a UV laser pulse. Time-resolved photoluminescence measurements suggested that doped Ni cations act as recombination centers, giving a luminescence peak at similar to 8000 cm(-1) due to the downward d-d transition at Ni2+. However, the lifetime of the emission was much shorter than that of free or shallowly trapped electrons. These results suggest that recombination at the Ni cations is not the dominant process. In addition, the reactivity of photogenerated electrons was decreased dramatically by doping; electrons did not react with exposed O-2, although holes maintained reactivity with MeOH. These results confirm that the decrease in the steady-state activity of doped SrTiO3 under UV light irradiation is responsible for the decrease in reactivity of photogenerated electrons.

    DOI: 10.1021/acs.jpcc.6b01494

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  • Nature-Inspired, Highly Durable CO2 Reduction System Consisting of a Binuclear Ruthenium(II) Complex and an Organic Semiconductor Using Visible Light 査読

    Ryo Kuriki, Hironori Matsunaga, Takuya Nakashima, Keisuke Wada, Akira Yamakata, Osamu Ishitani, Kazuhiko Maeda

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   138 ( 15 )   5159 - 5170   2016年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    A metal-free organic semiconductor of mesoporous graphitic carbon nitride (C3N4) coupled with a Ru(II) binuclear complex (RuRu') containing photosensitizer and catalytic units selectively reduced CO2 into HCOOH under visible light (lambda &gt; 400 nm) in the presence of a suitable electron donor with high durability, even in aqueous solution. Modification of C3N4 with Ag nano particles resulted in a RuRu'/Ag/C3N4 photocatalyst that exhibited a very high turnover number (&gt;33000 with respect to the amount of RuRu'), while maintaining high selectivity for HCOOH production (87-99%). This turnover number was 30 times greater than that reported previously using C3N4 modified with a mononuclear Ru(II) complex, and by far the highest among the metal-complex/semiconductor hybrid systems reported to date. The results of photocatalytic reactions, emission decay measurements, and time-resolved infrared spectroscopy indicated that Ag nanoparticles on C3N4 milliseconds from the conduction band of C3N4, which were transferred to photocatalytic CO2 reduction driven by two-step photoexcitation of C3N4 and Ag/C3N4 hybrid photocatalyst worked efficiently in water containing a proper nature of C3N4 and low solubility of CO2 in an aqueous environment. collected electrons having lifetimes of several the excited state of RuRu', thereby promoting RuRu'. This study also revealed that the RuRu'/electron donor, despite the intrinsic hydrophobic nature of C3N4 and low solubility of CO2 in an aqueous environment.

    DOI: 10.1021/jacs.6b01997

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  • KCl flux-induced growth of isometric crystals of cadmium-containing early transition-metal (Ti4+, Nb5+, and Ta5+) oxides and nitridability to form their (oxy)nitride derivatives under an NH3 atmosphere for water splitting application 査読

    Mirabbos Hojamberdiev, Hajime Wagata, Kunio Yubuta, Kenta Kawashima, Junie Jhon M. Vequizo, Akira Yamakata, Shuji Oishi, Kazunari Domen, Katsuya Teshima

    APPLIED CATALYSIS B-ENVIRONMENTAL   182   626 - 635   2016年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    In this study, we have attempted to experimentally validate the results of previous theoretical calculations predicting the possible formation of the CdTiO3-xNy, CdNbO2N, and CdTaO2N phases by applying conventional one- and two-step fabrication methods under an NH3 flow. For the two-step method, CdTiO3, Cd2Nb2O2, and Cd2Ta2O7 crystals were first grown by a KCl flux method, and the effects of solute concentration and cooling rate on the crystal growth were studied. The formability of their (oxy)nitride derivatives was investigated by changing the nitridation temperature (750-950 degrees C) and time (1-10 h) of oxide precursors. It was found that the CdTiO3-xNy, CdNbO2N, and CdTaO2N phases cannot be formed by the applied conventional methods due to the low volatilization temperature of cadmium and the susceptibility of titanium and niobium to reduction under an NH3 atmosphere. Under high-temperature NH3 atmosphere, only Cd2Ta2O2 was fully converted to single-phase Ta3N5. The results from the photocatalytic O-2 evolution test of bare and CoOx-loaded Ta3N5 crystalline structures, converted from Cd2Ta2O2 (Cd-Ta3N5) and Na2CO3-treated Ta2O3 (Na-Ta3N5) and Cd2Ta2O2 (Na-Cd-Ta3N5) crystals by nitridation at 850 degrees C for 20h under an NH3 flow, revealed that the CoOx-loaded Ta3N5 showed more than two times higher O-2 evolution rate (655 mu mol), whereas the CoOx-loaded Cd-Ta3N5 and Na-Cd-Ta3N5 exhibited nearly four (501 mu mol) and three (422 mu mol) times higher O-2 evolution rates at 5 h compared with their bare counterparts. An improved photocatalytic activity for O-2 evolution is related to the higher density of nucleation centers of CoOx nanoparticles in the form of dangling bonds in porous Ta3N5 structures and long-lived photogenerated holes, as attested by time-resolved absorption spectroscopy. (C) 2015 Elsevier B.V. All rights reserved.

    DOI: 10.1016/bj.apcatb.2015.10.002

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  • Transient Absorption and FT-IR Analysis of the Carrier Dynamics of TiO2 Photocatalysts

    Vequizo Junie Jhon, Matsunaga Hironori, Okamura Shou, Ohno Teruhisa, Yamakata Akira

    表面科学学術講演会要旨集   36 ( 0 )   217 - 217   2016年1月

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    記述言語:英語   出版者・発行元:公益社団法人 日本表面科学会  

    The behavior of photocarriers in anatase, rutile, and brookite TiO&lt;sub&gt;2&lt;/sub&gt; was studied by using transient absorption and FT-IR spectroscopy. In anatase, free electrons survive &gt; 1 ms. In contrast, most of the electrons in rutile are deeply trapped at the defects. In brookite, some of the electrons are deeply trapped, but some also survive in the conduction band. FT-IR results revealed that the rate of charge accumulation is faster in anatase but slower in rutile and brookite.

    DOI: 10.14886/sssj2008.36.0_217

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  • Flux-mediated doping of SrTiO3 photocatalysts for efficient overall water splitting 査読

    Yeilin Ham, Takashi Hisatomi, Yosuke Goto, Yosuke Moriya, Yoshihisa Sakata, Akira Yamakata, Jun Kubota, Kazunari Domen

    JOURNAL OF MATERIALS CHEMISTRY A   4 ( 8 )   3027 - 3033   2016年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    SrTiO3 is a photocatalyst that is well known for its activity for the overall water splitting reaction under UV light irradiation. In this study, the effects of SrCl2 flux treatments and Al doping on the photocatalytic properties of SrTiO3 were investigated. The SrTiO3, which showed an apparent quantum efficiency of 30% at 360 nm in the overall water splitting reaction, the highest value reported so far, was prepared by SrCl2 flux treatments in alumina crucibles. Scanning electron microscopy and X-ray diffractometry revealed that the flux-treated SrTiO3 consisted of well-crystalline particles with a cubic shape reflecting the perovskite-type structure. Inductively coupled plasma optical emission spectroscopy revealed that Al ions from the alumina crucibles were incorporated into the SrTiO3 samples. The SrTiO3 that was treated with SrCl2 flux in Al-free conditions showed a marginal improvement in photocatalytic activity despite the high crystallinity and the clear crystal habit. Doping SrTiO3 with Al improved the photocatalytic activity even without SrCl2 treatment. These results suggested that Al doping was a principal factor in the dramatic improvement in the water splitting activity of the flux-treated SrTiO3. The effects of flux treatments and Al doping on the morphology and water splitting activity of SrTiO3 were discussed separately.

    DOI: 10.1039/c5ta04843e

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  • フェムト秒時間分解分光測定を用いた光触媒のキャリアダイナミクス

    松永 大典, Vequizo Junie Jhon, 山方 啓

    表面科学学術講演会要旨集   36   218 - 218   2016年

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    記述言語:日本語   出版者・発行元:公益社団法人 日本表面科学会  

    時間分解分光装置を用いて、酸化チタンのアナターゼとルチルの粉末と単結晶における光励起キャリアーの挙動を調べた。アナターゼの場合、粉末の自由電子は単結晶の自由電子より長い寿命を有していた。一方、ルチルの場合、粉末の自由電子は単結晶の自由電子より寿命が短いことがわかった。ルチル粉末では、数ピコ秒以内に自由電子が深くトラップされるため、自由電子の寿命が極端に短いことがわかった。

    DOI: 10.14886/sssj2008.36.0_218

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  • 時間分解分光測定を利用した金属微粒子を担持した光触媒のキャリアーダイナミクス

    山方 啓

    表面科学学術講演会要旨集   36   216 - 216   2016年

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    記述言語:日本語   出版者・発行元:公益社団法人 日本表面科学会  

    光触媒の活性を向上させるためには,光励起キャリアーの動きやエネルギー状態を理解することが必要である.我々は可視から中赤外域の過渡吸収測定をフェムト秒から秒の時間領域で行うことで電子や正孔の動きとエネルギー状態を独立に調べる手法を確立した.講演では、この手法を用いて,PtやCoOx微粒子を担持したTiO2やSrTiO3,LaTiO2N光触媒粒子の中における電子と正孔の挙動を明らかにした.

    DOI: 10.14886/sssj2008.36.0_216

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  • Morphology-sensitive trapping states of photogenerated charge carriers on SrTiO3 particles studied by time-resolved visible to Mid-IR absorption spectroscopy: The effects of molten salt flux treatments 査読

    Akira Yamakata, Ham Yeilin, Masayuki Kawaguchi, Takashi Hisatomi, Jun Kubota, Yoshihisa Sakata, Kazunari Domen

    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY   313   168 - 175   2015年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE SA  

    The effects of the morphology-change of SrTiO3 particles on the behavior of photogenerated charge carriers are studied by time-resolved absorption (TA) spectroscopy from the visible to mid-IR region. In the case of as-purchased defect-rich commercial SrTiO3 particles, most of the charge carriers are deeply trapped, showing a transient absorption peak at 11,000 cm(-1). Scanning electron microscopy reveals that the irregular-shaped primary particles are heavily aggregated and that the photocatalytic activity for the water splitting reaction is negligibly small. However, when this powder is flux-treated by SrCl2, fine cubic SrTiO3 crystals exposing well-defined surfaces are formed and the photocatalytic activity is greatly improved. TA measurements show that the spectral shape is changed dramatically: the number of deeply trapped electrons is reduced, and that of shallowly trapped electrons producing the absorption band at 2500 cm(-1) is increased. The change in electron trap depth, observed upon flux treatment, is due to the decrease in the number of defects. We also found that further flux treatment in an Al2O3 crucible (i) induces Al doping into SrTiO3, (ii) enhances the photocatalytic activity, (iii) changes the spectral shape, and (iv) prolongs the lifetime of shallowly trapped electrons. The increase in photocatalytic activity is presumably due to the change in lifetime. (C) 2015 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.jphotochem.2015.05.016

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  • Distinctive Behavior of Photogenerated Electrons and Holes in Anatase and Rutile TiO2 Powders 査読

    Akira Yamakata, Junie Jhon M. Vequizo, Hironori Matsunaga

    JOURNAL OF PHYSICAL CHEMISTRY C   119 ( 43 )   24538 - 24545   2015年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    TiO2 powders have been widely used for photocatalysts; however, why anatase shows higher activity than ruffle has been a long-standing question. Here, we have elucidated the difference in the behavior of photogenerated electrons and holes by time-resolved visible to mid-IR absorption spectroscopy. In anatase TiO2, a considerable number of free electrons survive longer than 1 ms, but they are deeply trapped within a few picoseconds in the case of ruffle TiO2. The longer lifetime of free electrons is responsible for the higher activity for reduction processes on anatase TiO2. However, deep electron trapping in ruffle TiO2 elongates lifetime of holes and promotes multihole processes such as water oxidation. However, the low reactivity of deeply trapped electrons fails to increase the overall activity. These peculiar behaviors of electrons and holes are induced by defects on the powder particles and less sensitive to the physical properties such as particle size and specific surface area.

    DOI: 10.1021/acs.jpcc.5b09236

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  • NH3-Assisted Flux Growth of Cube-like BaTaO2N Submicron Crystals in a Completely Ionized Nonaqueous High-Temperature Solution and Their Water Splitting Activity 査読

    Mirabbos Hojamberdiev, Kunio Yubuta, Junie Jhon M. Vequizo, Akira Yamakata, Shuji Oishi, Kazunari Domen, Katsuya Teshima

    CRYSTAL GROWTH & DESIGN   15 ( 9 )   4663 - 4671   2015年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    As the 600 nm-class photocatalyst, BaTaO2N is one of the promising candidates of the perovskite-type oxynitride family for photocatalytic water splitting under visible light. The oxynitrides are routinely synthesized by nitriding corresponding oxide precursors under a high-temperature NH3 atmosphere, causing an increase in the defect density and a decrease in photocatalytic activity. To improve the photo catalytic activity by reducing the defect density and improving the crystallinity, we here demonstrate an NH3-assisted KCl flux growth approach for the direct synthesis of BaTaO2N crystals. The effects of various fluxes, solute concentration, and reaction time and temperature on the phase evolution and morphology transformation of the BaTaO2N crystals were systematically investigated. By changing the solute concentration from 10 to 50 mol %, it was found that phase-pure BaTaO2N crystals could only be grown with the solute concentrations of &gt;= 10 mol % using the KCl flux, and the solute concentration of 10 mol % was solely favorable to directly grow cube-like BaTaO2N crystals with an average size of about 125 nm and exposed {100} and {110} faces at 950 degrees C for 10 h. The time- and temperature-dependent experiments were also performed to postulate the direct growth mechanisms of cube-like BaTaO2N submicron crystals. The BaTaO2N crystals modified with Pt and CoOx nanopartides showed a reasonable H-2 and O-2 evolution, respectively, due to a lower defect density and higher crystallinity achieved by an NH3-assisted KCl flux method.

    DOI: 10.1021/acs.cgd.5b00927

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  • NH3-Assisted Flux-Mediated Direct Growth of LaTiO2N Crystallites for Visible-Light-Induced Water Splitting 査読

    Kenta Kawashirna, Mirabbos Hojamberdiev, Hajirne Wagata, Kunio Yubuta, Junie Jhon M. Vequizo, Akira Yamakata, Shuji Oishi, Kazunari Domen, Katsuya Teshima

    JOURNAL OF PHYSICAL CHEMISTRY C   119 ( 28 )   15896 - 15904   2015年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Photocatalytic overall water splitting on (oxy)nitrides under visible light is one of the interesting approaches to fulfill the growing demand for clean and renewable energy. The improvement of the fabrication method is however important for reducing the defect density of (oxy)nitride crystals. The present study aims to investigate the direct growth of the LaTiO2N (LTON) crystallites with less defect density by an NH3-assisted flux method and to demonstrate the visible-light-induced photocatalytic water oxidation activity in relation to their crystallite morphology. Single-phase LaTiO2N crystallites (average size of 120 +/- 39 nm) in round shape with smooth surface and high crystallinity were grown by an NH3-assisted flux method using the KCl flux with the solute concentration of 5 mol % at 950 degrees C for 10 h. The photocatalytic water oxidation activity of bare and CoOx-loaded LaTiO2N crystallites grown directly by an NH3-assisted flux method (1-step-LTON) was evaluated under visible light by comparing with the LaTiO2N crystallites fabricated by a two-step method (2-step-LTON), converting La2Ti2O7 to LaTiO2N by high-temperature nitridation. Within the first 2 h of the photocatalytic water oxidation half-reaction, the O-2 evolution rates of bare and CoOx-loaded 1-step-LTON crystallites were 82 mu mol.h-(1) and 204 mu mol.h(-1), respectively, which are much higher than that of bare and CoOx-loaded 2-step-LTON crystallites (37 mu mol.h(-1) and 177 mu mol.h(-1)) due to less defect density of the LaTiO2N crystallites achieved by a direct fabrication route using KCl flux. An NH3-assisted flux growth is a promising route for the direct fabrication of the LaTiO2N crystallites with less defect density that is beneficial for the enhancement of photocatalytic water oxidation half-reaction.

    DOI: 10.1021/acs.jpcc.5b03718

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  • 時間分解可視中赤外分光法を用いた光励起キャリアーの反応活性評価

    山方啓, 久保田純, 堂免一成

    触媒   115   52 - 54   2015年3月

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    記述言語:日本語  

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  • Behavior and Energy State of Photogenerated Charge Carriers in Single-Crystalline and Polycrystalline Powder SrTiO3 Studied by Time-Resolved Absorption Spectroscopy in the Visible to Mid-Infrared Region 査読

    Akira Yamakata, Junie Jhon M. Vequizo, Masayuki Kawaguchi

    JOURNAL OF PHYSICAL CHEMISTRY C   119 ( 4 )   1880 - 1885   2015年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The effects of defects on the behavior of photogenerated charge carriers in SrTiO3 (STO) are studied by time-resolved absorption spectroscopy from the visible to mid-IR region. In the case of defect-free single-crystalline STO, free and shallowly trapped electrons are dominant, but they recombine within 50 ns. By contrast, in the case of defect-rich powder STO, the electron lifetime is much longer than 1 ms. The transient absorption spectra show that most of the charge carriers in powder STO are trapped in the defects, which elongates their lifetime. We found that these trapped carriers are nevertheless reactive toward O-2 or CH3OH that depends on the trap depth. The steady-state photocatalytic activity is strongly correlated with the lifetime and the reactivity of the trapped charge carriers: the energy state of electrons can be deduced from the spectral shape, especially in the mid-IR region.

    DOI: 10.1021/jp510647b

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  • Surface-enhanced IR absorption spectroscopy of the KcsA potassium channel upon application of an electric field 査読

    Akira Yamakata, Hirofumi Shimizu, Shigetoshi Oiki

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS   17 ( 33 )   21104 - 21111   2015年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    Surface-enhanced IR absorption spectroscopy (SEIRAS) is a powerful tool for studying the structure of molecules adsorbed on an electrode surface (ATR-SEIRA). Coupled with an electrochemical system, structural changes induced by changes in the electric field can be detected. All the membrane proteins are subjected to the effect of membrane electric field, but conformational changes at different membrane potentials and their functional relevance have not been studied extensively except for channel proteins. In this contribution, background information of potential-dependent functional and structural changes of a prototypical channel, the KcsA channel, is summarized, and SEIRAS applied to the KcsA channel under the application of the potential is shown. The potassium channels allow K+ to permeate selectively through the structural part called the selectivity filter, in which dehydrated K+ ions interact with backbone carbonyls. In the absence of K+, the selectivity filter undergoes conformational changes to the non-conductive collapsed conformation. To apply the electric field, the KcsA channels were fixed on the gold surface in either upside or reverse orientation. The SEIRA spectrum in K+ or Na+ solution revealed both backbone structural changes and local changes in the OCO-carboxylate groups. Upon application of the negative electric field, the spectrum of OCO was enhanced only in the K+ solution. These results indicate that the negative electric field accumulates local K+ concentration, which turned the collapsed filter to the conductive conformation. ATR-SEIRA serves as an unprecedented experimental system for examining membrane proteins under an electric field.

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  • Behavior and Energy States of Photogenerated Charge Carriers on Pt- or CoOx-Loaded LaTiO2N Photocatalysts: Time-Resolved Visible to Mid-Infrared Absorption Study 査読

    Akira Yamakata, Masayuki Kawaguchi, Naoyuki Nishimura, Tsutomu Minegishi, Jun Kubota, Kazunari Domen

    JOURNAL OF PHYSICAL CHEMISTRY C   118 ( 41 )   23897 - 23906   2014年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Femtosecond to second time-resolved visible to mid-infrared absorption spectroscopy was applied to investigate the behavior of photogenerated electrons and holes on a Pt- or CoOx-loaded LaTiO2N photocatalyst. CoOx-loaded catalyst exhibits the highest activity for water oxidation under visible light (&lt;600 nm) excitation, and the quantum efficiency reaches up to 30%. Transient absorption spectra suggest that most of the photoexcited electrons in LaTiO2N lose activity by deep trapping in the mid-gap states created at 0.74 eV (6000 cm1) below the conduction band. In this case, Pt loading was not so effective for H-2 evolution because the loaded Pt could not effectively capture the trapped electrons from LaTiO2N. The electron transfer was slow, proceeding in 0100 mu s, and was thus ineffective. However, in the case of CoOx loading, we have clearly observed, for the first time, that the holes are captured rapidly by CoOx in a few picoseconds, and the lifetimes of electrons are dramatically prolonged to the second region. This implies that the photogenerated holes and electrons are separated effectively in CoOx and LaTiO2N, respectively. Furthermore, the electron trap becomes shallower, its depth decreasing from 0.74 eV (6000 cm1) to 0.49 eV (4000 cm1) upon CoOx loading, suggesting that the reactivity of the trapped electrons increases. These perturbations of electrons and holes are what cause the dramatic increase in photocatalytic activity. We expected that coloading of Pt and CoOx would further increase the activity, but it was significantly reduced. It was demonstrated that the undesirable process of recombination is accelerated under high loading and coloading.

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  • 電極界面におけるイオンの水和殻崩壊過程の時間分解赤外分光観察 査読

    山方啓, 大澤雅俊, 森田明弘

    Electrochemistry 電気化学および工業物理化学   82 ( 9 )   771 - 776   2014年9月

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  • 光触媒反応機構に関する最新の研究動向 時間分解赤外分光測定で調べた光励起キャリアーの挙動と種々の光触媒の定常反応活性 査読

    天野史章, 山方啓

    触媒   56 ( 2 )   88 - 94   2014年4月

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    記述言語:日本語   出版者・発行元:触媒学会  

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  • Properties of N-H Local Vibration Modes in GaAsN Grown by Chemical Beam Epitaxy

    Kazuma Ikeda, Akira Yamakata, Koushiro Demizu, Nobuaki Kojima, Oshio Ohshita, Masafumi Yamaguchi

    2014 IEEE 40TH PHOTOVOLTAIC SPECIALIST CONFERENCE (PVSC)   1821 - 1824   2014年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

    The structural and electrical properties of N-H complexes in GaAsN grown by chemical beam epitaxy are summarized. Using local vibration mode spectroscopy, some of the vibration frequencies are shown to be the same as those in the material grown by liquid encapsulated Czochralski and metal organic chemical vapor deposition, while no vibration modes are common to those in the material grown by molecular beam epitaxy. The dependencies of the vibration frequencies on measurement temperatures and annealing temperatures, and polarization of the vibration directions are studied to understand the structural properties of N-H complexes. The As source flow rate affects ratios of the defect densities, which indicate that those defects have different formation processes. The charge excitations by irradiation light indicate that the charge relaxation processes caused by those defects are in the orders of micro seconds.

    DOI: 10.1109/PVSC.2014.6925276

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  • Effect of Particle Size on the Photocatalytic Activity of WO3 Particles for Water Oxidation 査読

    Fumiaki Amano, Eri Ishinaga, Akira Yamakata

    JOURNAL OF PHYSICAL CHEMISTRY C   117 ( 44 )   22584 - 22590   2013年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The particle size of a photocatalyst is one of the factors that determine the photon utilization efficiency. Here, we report the effects of the particle size on the photocatalytic activity of tungsten trioxide (WO3) for water oxidation to evolve molecular oxygen in the presence of sacrificial silver nitrate. For the water oxidation, the photocatalytic activity of large aggregates consisting of particles with a small specific surface area (3 m(2) g(-1)) was greater than that of fine particles with a larger specific surface area (11 m(2) g(-1)). Transient infrared absorption spectra revealed that the recombination of photoexcited electrons in the large particles was slower than that in the fine particles. It was found that the fast recombination in the fine particles mostly occurred on the surface. The photocatalytic activity for water oxidation increased with increasing particle size for spherical diameters smaller than 200 nm. These results showed that large particles with a low surface area-to-volume ratio were suitable for photocatalytic oxygen evolution, which requires long-lived holes, because the surface recombination of photogenerated electrons and holes occurred less frequently.

    DOI: 10.1021/jp408446u

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  • Real-Time Observation of the Destruction of Hydration Shells 査読

    Akira Yamakata, Eiji Soeta, Tatsuya Ishiyama, Masatoshi Osawa, Akihiro Morita

    J. Am. Chem. Soc.   135 ( 40 )   977 - 988   2013年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/jp4078882

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  • Real-Time Observation of the Destruction of Hydration Shells under Electrochemical Force 査読

    Akira Yamakata, Eiji Soeta, Tatsuya Ishiyama, Masatoshi Osawa, Akihiro Morita

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   135 ( 40 )   15033 - 15039   2013年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Major alteration or even destruction of the hydration shell around interacting molecules and ions in solution is an important process that determines how hydrated substances interact. Therefore, the direct observation of structural changes in hydration shells around solutes in close contact with other solutes or surfaces is important for understanding chemical processes that take place in solution. In the work described in this paper, time-resolved IR absorption measurements were performed to study the interaction of hydrated Na+ or tetrapropylammonium cation (Pr4N+) with a hydrophobic CO-covered Pt surface; the adsorption force between cations and the surface was controlled by using an electrochemical system. We found that the hydrophobic hydration shell of Pr4N+ is initially stabilized on the hydrophobic surface, but application of a strong force to the cation approaching CO destroys the water layers between them. This process is rather slow, taking a few hundred milliseconds. Hydrophilic Na+ behaves quite differently from Pr4N+ due to the different structure of its hydration shell. These experimental results are supported by molecular dynamics simulations.

    DOI: 10.1021/ja408326d

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  • Photocatalytic activity of titania particles calcined at high temperature: Investigating deactivation 査読

    Fumiaki Amano, Masashi Nakata, Kenji Asami, Akira Yamakata

    Chemical Physics Letters   579   111 - 113   2013年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    We examined the effect of high temperature calcination on the photocatalytic activity and photoexcited electron behavior of rutile TiO 2 with a small specific surface area. Photocatalytic activity for H2 evolution was significantly decreased by calcination at temperatures higher than 500 C, although the specific surface area showed little change. This deactivation was attributed to fast charge carrier recombination. Samples deactivated by high temperature calcination were reduced by hydrogen at 500 or 700 C, increasing both the density of long-lived charge carriers and photocatalytic activity. These results suggest that density of oxygen vacancies is an important factor for photocatalytic reactivity. © 2013 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.cplett.2013.06.038

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  • Structural changes of the KcsA potassium channel upon application of the electrode potential studied by surface-enhanced IR absorption spectroscopy 査読

    Akira Yamakata, Hirofumi Shimizu, Masatoshi Osawa, Shigetoshi Oiki

    CHEMICAL PHYSICS   419   224 - 228   2013年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    Structural changes of the KcsA potassium channel fixed on gold electrode surface in the upright orientation were studied by surface-enhanced IR absorption spectroscopy (SEIRAS). Measurements were performed at neutral pH, where the activation gate is kept closed. Band intensities were enhanced for the asymmetric (1565 cm(-1)) and symmetric (1405 cm(-1)) OCO-carboxylate groups at negative electrode potentials in the K+ solution, but not in the Na+ solution. Even for the reverse-oriented channel, the enhanced OCO-carboxylate band was evident at negative potential. When TBA was loaded in the central cavity, the K+-specific OCO band was not elicited. These results indicate that the negative electrode potential renders the local K+ concentration accumulated at the vicinity of the electrode surface, and the KcsA channel bathed in high K+ changes conformation of the selectivity filter from the collapsed to the open, and OCO-carboxylate groups (D80 and E71) in the back of the filter were rearranged. Crown Copyright (C) 2013 Published by Elsevier B. V. All rights reserved.

    DOI: 10.1016/j.chemphys.2013.02.035

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  • Electronically cross-linked PbS quantum dot networks using polymers as surface ligands 査読

    Wei Lü, Yue Yang, Akira Yamakata, Itaru Kamiya

    Nano   8 ( 2 )   1350013.1-1350013.7   2013年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Bilayer structures of colloidal PbS quantum dots (QDs) with different sizes are fabricated by two methods: chemical bond anchoring and electrostatic adsorption. Unlike the sample prepared by chemical bond anchoring, we find that the electronic connection between different layers is suppressed in the samples prepared by electrostatic adsorption with charged polyelectrolytes. To clarify the electronic coupling between the QDs and the polyelectrolytes, QDs directly stabilized by charged polyelectrolytes were synthesized. Transmission electron microscopy investigation shows that cross-linked QD networks are formed. Time-resolved photoluminescence measurements indicate that the carrier lifetimes of QDs in networks were greatly reduced. The photoluminescence peak energy increases with a third root of the excitation power. All these observations can be consistently explained considering spatially separated photoexcited carriers in a type-II band alignment. The abnormal behaviors of electrostatic adsorption sample are discussed based on these results. © 2013 World Scientific Publishing Company.

    DOI: 10.1142/S1793292013500136

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  • Cobalt-Modified Porous Single-Crystalline LaTiO2N for Highly Efficient Water Oxidation under Visible Light 査読

    Fuxiang Zhang, Akira Yamakata, Kazuhiko Maeda, Yosuke Moriya, Tsuyoshi Takata, Jun Kubota, Katsuya Teshima, Shuji Oishi, Kazunari Domen

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   134 ( 20 )   8348 - 8351   2012年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Highly efficient water oxidation utilizing visible photons of up to 600 nm is a crucial step in artifical photosynthesis. Here we present a highly active photocatalyst for visible-light-driven water oxidation, consisting of single-crystalline meso- and macroporous LaTiO2N (LTON) with a band gap of 2.1 eV, and earth-abundasnt cobalt oxide (CoOx) as a cocatalyst. The optimized CoOx/LTON had a high quantum efficiency of 27.1 +/- 2.6% at 440 nm, which substantially exceeds the values reported for previous particulate photocatalysts with a 600-nm absorption edge.

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  • Infrared Spectroscopic Study of the Potential Change at Cocatalyst Particles on Oxynitride Photocatalysts for Water Splitting by Visible Light Irradiation 査読

    Xuwang Lu, Athula Bandara, Masao Katayama, Akira Yamakata, Jun Kubota, Kazunari Domen

    JOURNAL OF PHYSICAL CHEMISTRY C   115 ( 48 )   23902 - 23907   2011年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Visible light-induced changes in Pt/(Ga1-xZnx)(Ni1-xOx), Pt/TaON, and Pt/LaTiO2N powder photocatalysts were investigated using infrared spectroscopy with adsorbed CO probe molecules on Pt cocatalysts. Among these photocatalyst materials, only the (Ga1-xZnx)(N1-xOx) photocatalyst has achieved overall water splitting with visible-light irradiation, although all of these materials have suitable band gaps for the reaction. For Pt/(Ga1-xZnx)(N1-xOx) and Pt/TaON, the C-O stretching vibrations of adsorbed CO on Pt shifted to a lower frequency under visible light irradiation. However, no frequency shift was observed for Pt/LaTiO2N. This lower-frequency shift indicates a negative electronic potential shift of the Pt cocatalysts, which results in hydrogen evolution. Differences in the light intensity dependence of the potential shifts of these photocatalysts were observed, and the involvement of a different recombination mechanism of photoexcited carriers in these photocatalysts will be discussed. These results clarify some of the reasons for the activities of various photocatalytic materials for overall water splitting.

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  • Effect of Photoexcited Electron Dynamics on Photocatalytic Efficiency of Bismuth Tungstate 査読

    Fumiaki Amano, Akira Yamakata, Kohei Nogami, Masatoshi Osawa, Bunsho Ohtani

    JOURNAL OF PHYSICAL CHEMISTRY C   115 ( 33 )   16598 - 16605   2011年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Photoexcited carrier dynamics of bismuth tungstate (Bi(2)WO(6)) photocatalysts was investigated by time-resolved infrared (IR) absorption spectroscopy. Monotonic absorption at the mid-IR region, which is attributable to absorption by photoexcited electrons, was monitored as a function of time delay from the microsecond to millisecond range after photoexcitation. Bi(2)WO(6) particles with different crystalline content were prepared by hydrothermal reaction at several temperatures and used to elucidate the relation between density of photoexcited carriers and steady-state photocatalytic efficiency. Photocatalytic efficiency was tested using two reactions: oxidative decomposition of acetic acid in an aqueous solution (reaction 1) and oxidative decomposition of acetaldehyde in air (reaction 2). Crystallization of Bi(2)WO(6) particles suppressed the fast recombination of photoexcited electrons and holes within 1 its. In the case of crystallized particles, the density of the photoexcited electron increased with an increase in the crystalline content, and the photocatalytic efficiency for reaction 1 strongly depended on the crystalline content, indicating that photoexcited electrons remaining in the submillisecond time range significantly affect the reaction rate. On the other hand, photocatalytic efficiency for reaction 2 showed a proportional relation with specific surface area rather than crystalline content. The difference in a decisive factor depending on reaction condition is considered to be the slower rate of reaction of photoexcited electrons with molecular oxygen, which might occur within a time range between 200 mu s and 3 ms over Bi(2)WO(6).

    DOI: 10.1021/jp2051257

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  • Potential-Dependent Recombination Kinetics of Photogenerated Electrons in n- and p-Type GaN Photoelectrodes Studied by Time-Resolved IR Absorption Spectroscopy 査読

    Akira Yamakata, Masaaki Yoshida, Jun Kubota, Masatoshi Osawa, Kazunari Domen

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   133 ( 29 )   11351 - 11357   2011年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Recombination kinetics of photogenerated electrons in n-type and p-type GaN photoelectrodes active for H-2 and O-2 evolution, respectively, from water was examined by time-resolved IR absorption (TR-IR) spectroscopy. Illumination of a GaN film with UV pulse (355 nm and 6 ns in duration) gives transient interference spectra in both transmittance and reflection modes. Simulation shows that the interference spectra are caused by photogenerated electrons. We observed that recombination in the microsecond region is greatly affected by the applied potentials, the lifetime becoming longer at negative and positive potentials for n- and p-type GaN electrodes, respectively. There is a good correlation between potential dependence of the steady-state reaction efficiency and that of the number of surviving electrons in the millisecond region. We also performed potential jump measurement to examine the shift in Fermi level by photogenerated charge carriers. In the case of n-type GaN, the electrode potential jumps to the negative side by accumulation of electrons in the bulk. However, in the case of p-type GaN, the electrode potential first jumps to the negative side within 20,us and gradually shifts to the positive side in a few milliseconds, while the number of charge carriers is constant at &gt;0.2 ms. This two-step process is ascribed to electron transport from the bulk to the surface of GaN, because the electrode potential is sensitive to the number of electrons in the bulk. The results confirm that TR-IR combined with potential jump measurement provides useful information for understanding the behavior of charge carriers in photo electrochemical systems.

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  • 半導体量子構造と光エネルギー変換の最前線

    山方 啓

    触媒   53 ( 3 )   201 - 201   2011年4月

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  • 表面増強赤外分光でみた電極-電解液界面の水の構造と挙動 査読

    大澤 雅俊, 山方 啓

    分析化学 = Japan analyst   60 ( 1 )   1 - 9   2011年1月

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    記述言語:日本語   掲載種別:研究論文(学術雑誌)   出版者・発行元:The Japan Society for Analytical Chemistry  

    水は電極-電解液界面でどう振る舞うであろうか? これは電気化学で最も基本的でかつ重要な研究課題の一つである.Helmholtzによる1853年の電気二重層の提案から始まった電極界面構造の研究は,1960年代になって,水は界面の電場に沿って配列し,電位(表面電荷)によってその配向を変化させる,という現在一般的に受け入れられているモデルに到達した.しかし,これを直接確認する手段がなく,詳細は永年不明のままであった.最近の計算化学と電極界面のその場測定方法の進展により,電極界面を分子レベルでより詳細に検討することが可能になり,新しい知見が得られるようになってきている.本稿では,表面増強赤外分光(SEIRAS)による解析を中心として,最近の進展の一端を紹介する.

    DOI: 10.2116/bunsekikagaku.60.1

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  • Destruction of the Water Layer on a Hydrophobic Surface Induced by the Forced Approach of Hydrophilic and Hydrophobic Cations 査読

    Akira Yamakata, Masatoshi Osawa

    JOURNAL OF PHYSICAL CHEMISTRY LETTERS   1 ( 9 )   1487 - 1491   2010年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Structural change of the water layers is the primary step for the direct interactions among the hydrated substances in aqueous solutions. We have studied how the water layers on a solid surface is destroyed by the approach of several hydrophilic and hydrophobic cations, which are used as model substances. The combined use of electrochemical system and IR spectroscopy enables the study of the destruction process of water layers during the close contact among them. We have observed for the first time that hydrophilic cations cause greater destruction of the interfacial water structure than hydrophobic cations. This result is ascribed to the different orientations of water molecules around the cations; H-bonds around hydrophilic cations expand toward the outer hydration shells, while they are closed inside the primary shell in the case of hydrophobic cations. These different orientations of water molecules cause different effects on the interfacial water structures.

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  • タングステン酸ビスマス粒子の光触媒活性と励起電子寿命の相関 査読

    天野 史章, 山方 啓, 野上 皓平, 大澤 雅俊, 大谷 文章

    触媒   52 ( 2 )   128 - 130   2010年3月

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    記述言語:日本語   出版者・発行元:触媒学会  

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  • 水分解光触媒の光励起キャリアーダイナミクス : キャリアダイナミクスと定常反応活性との比較 査読

    山方 啓

    分光研究 = Journal of the spectroscopical research of Japan   59 ( 1 )   12 - 19   2010年2月

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    記述言語:日本語   出版者・発行元:日本分光学会  

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  • ATR-SEIRAS Investigation of the Fermi Level of Pt Cocatalyst on a GaN Photocatalyst for Hydrogen Evolution under Irradiation 査読

    Masaaki Yoshida, Akira Yamakata, Kazuhiro Takanabe, Jun Kubota, Masatoshi Osawa, Kazunari Domen

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   131 ( 37 )   13218 - 13219   2009年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The interaction of photogenerated carries in GaN photocatalyst with Pt cocatalyst for hydrogen evolution under irradiation was investigated from in situ ATR-SEIRAS measurement by following the CO vibrational frequency. After irradiation, the CO frequency shifted higher, indicating that the Fermi Level of Pt particles was positively shifted by the photogenerated holes. Thereafter, a Lower frequency peak appeared, indicating that the Fermi level of some Pt particles was negatively shifted to the hydrogen evolution potential by photogenerated electrons, which is the essential function of cocatalysis for hydrogen evolution.

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  • 金属表面の光照射プロセス : 固気界面から固液界面へ 査読

    山方 啓, 大澤 雅俊

    光化学 = Photochemistry   40 ( 2 )   78 - 84   2009年8月

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    記述言語:日本語   出版者・発行元:光化学協会  

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  • Destruction of the hydration shell around tetraaolkylammonium ions at the electrochemical interface 査読

    Akira Yamakata, Masatoshi Osawa

    Journal of the American Chemical Society   131 ( 20 )   6892 - 6893   2009年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    The structure and behavior of the hydration shells around tetraethyl-, -propyl-, and -butylammonium ions (Et4N+, Pr4N+, and Bu4N+, respectively) at a CO-covered Pt electrode was studied by surface-enhanced IR absorption spectroscopy. Selective concentration of cations at the electrochemical interface by controlling the applied potential facilitates the observation of the hydration shells without interference from hydrated anions. We report for the first time that the hydration shells around Pr4N+ and Bu4N+ are decomposed at sufficiently negative potentials because of the strong electrostatic attraction with the surface. On the other hand, the hydration shell around Et4N+, the smallest ion, is more stable and does not decompose in the potential range examined. The difference in the stability can be ascribed to the difference in the size of the central cation. On the other hand, the hydration shells are easily deconstructed on a bare Pt surface because of the stronger interaction with the surface. Copyright © 2009 American Chemical Society.

    DOI: 10.1021/ja8100374

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  • ビピリジン分子による電解水素発生の促進 : 有機分子による反応活性サイトの創成 査読

    内田 太郎, 山方 啓, 佐々木 陽一, 大澤 雅俊

    觸媒 = Catalyst   51 ( 2 )   129 - 131   2009年3月

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    記述言語:日本語   出版者・発行元:触媒学会  

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  • 時間分解表面増強赤外分光による電極触媒反応解析 査読

    Samjeske Gabor, 山方 啓, 内田 太郎, 大澤 雅俊

    表面科学 : hyomen kagaku = Journal of the Surface Science Society of Japan   30 ( 2 )   68 - 74   2009年2月

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    記述言語:日本語   出版者・発行元:日本表面科学会  

    DOI: 10.1380/jsssj.30.68

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  • Visible Light Responsive Pristine Metal Oxide Photocatalyst: Enhancement of Activity by Crystallization under Hydrothermal Treatment 査読

    Fumiaki Amano, Akira Yamakata, Kohei Nogami, Masatoshi Osawa, Bunsho Ohtani

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   130 ( 52 )   17650 - +   2008年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Photocatalytic activities of amorphous and crystal bismuth tungstate (Bi(2)WO(6))were investigated using oxidative decomposition of gaseous acetaldehyde under visible light irradiation (&gt;400 nm). Here, for the first time, negligible photocatalytic activity of amorphous Bi(2)WO(6) owing to the fast recombination of electron-hole pairs and the high quantum efficiency of Bi(2)WO(6) crystallites under visible light were demonstrated by action spectrum analysis and time-resolved infrared absorption measurements. Crystallization of the amorphous phase provided a red shift of the photoabsorption edge and marked increase in the lifetime of photoexcited electrons, resulting in an increase of photocatalytic activity.

    DOI: 10.1021/ja807438z

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  • CO/Pt電極界面における電気二重層の構造ダイナミクス 査読

    山方 啓, 大澤 雅俊

    表面科学 : hyomen kagaku = Journal of the Surface Science Society of Japan   29 ( 9 )   526 - 531   2008年9月

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    記述言語:日本語   出版者・発行元:The Surface Science Society of Japan  

    The dynamics of the water molecules on a CO-covered Pt electrode has been studied by laser-induced potential transient measurements. This is a model system to elucidate the behavior of water molecules in the electric double layer during electrochemical reactions. At the potentials where CO is stably adsorbed, the Pt surface is negatively charged and water molecules are oriented pointing the hydrogen atoms toward the surface. The laser irradiation heats the interface and disturbs the orientation of water, which induces a potential jump toward the negative direction. We found that the amplitude of the potential jump on the CO-covered surface is much larger than on the CO-free surface. The finding suggests that the water molecules are more flexible on the CO-covered surface due to the weaker water-CO interaction than water-Pt interaction. Stronger laser pulse irradiation additionally induces the desorption of CO, which result in the adsorption of water with the hydrogen atom pointing toward the surface and induces a positive potential shift. The potential shift takes ∼70 microseconds to reach the maximum, which becomes slower as the electric field becomes intense. The intense field and hydrogen-bonded cations affect water structure in a long range and the collective motion of the water layers.

    DOI: 10.1380/jsssj.29.526

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  • Hydrogen Evolution Reaction Catalyzed by Proton-Coupled Redox Cycle of 4,4′-Bipyridine Monolayer Adsorbed on Silver Electrodes 査読

    UCHIDA Taro, MOGAMI Hirokazu, YAMAKATA Akira, SASAKI Yoichi, OSAWA Masatoshi

    J Am Chem Soc   130 ( 33 )   10862 - +   2008年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/ja803446s

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  • Dynamics of double-layer restructuring on a platinum electrode covered by CO: Laser-induced potential transient measurement 査読

    Akira Yamakata, Masatoshi Osawa

    JOURNAL OF PHYSICAL CHEMISTRY C   112 ( 30 )   11427 - 11432   2008年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The dynamic behavior of water molecules on CO-covered Pt electrode has been studied by laser induced temperature jump method. A 532-nm laser pulse quickly heats up the interface (Delta T approximate to 90 K) and perturbs the orientation of water, which results in a negative jump of the rest potential. The potential is relaxed with cooling the substrate (similar to 20 mu s). This behavior is identical to that on the CO-free surface, but the amplitude of the negative jump is more than 30 times larger on the CO-covered surface. This large difference can be ascribed to the differences in the electric field at the interface and also in the interactions of water-Pt and water-CO; water is more flexible on CO. At high laser power densities exceed a threshold, the negative potential jump is followed by a slightly slower (similar to 70 mu s) irreversible potential shift toward the positive direction. Infrared reflection absorption spectroscopy and picosecond two-pulse correlation experiments reveal that the subsequent positive shift arises from thermally activated desorption of CO. Adsorption of water and restructuring of the electric double layer after CO desorption is responsible to the positive shift. The rate of restructuring becomes slower as the initial potential becomes lower due to the increase in the electric field and the number of hydrated cations. The intense field and the hydrogen-bonding affect water structure in a long-range and enhance the collective motion of the water layers.

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  • Surface-enhanced infrared absorption spectroscopic studies of adsorbed nitrate, nitric oxide, and related compounds 1: Reduction of adsorbed NO on a platinum electrode 査読

    Kou Nakata, Akinori Okubo, Katsuaki Shimazu, Akira Yamakata, Shen Ye, Masatoshl Osawa

    LANGMUIR   24 ( 8 )   4352 - 4357   2008年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Surface-enhanced infrared absorption spectroscopy (SEIRA) was used to examine the adsorption state of nitrogen monoxide (nitric oxide, NO) and the reduction of the adsorbed species. The SEIRA spectra gave two distinct bands at 1723-1733 and 1575-1607 cm(-1) with an additional weak band at 1656-1676 cm(-1) at 0.20 V, the frequencies of which are slightly dependent on the surface coverage. The former two bands are attributed to the on-top and bridged NO, respectively. While the on-top NO stably remained on the surface in the potential range of 0.05-0.60 V, the bridged NO decreased in its intensity with increasing electrode potential. The reduction of the adsorbed NO obeys first-order kinetics with respect to the adsorbed NO. The rate constants are 2.24 +/- 0.03 and 0.24 +/- 0.09 s(-1) at -0.10 V for the on-top and bridged NO, respectively. Tafel slopes obtained from the potential dependence of the rate constant indicate that the rate-determining step is the first electron-transfer process.

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  • Surface-enhanced infrared absorption spectroscopic studies of adsorbed nitrate, nitric oxide, and related compounds 2: Nitrate ion adsorption at a platinum electrode 査読

    Kou Nakata, Yota Kayama, Katsuaki Shimazu, Akira Yamakata, Shen Ye, Masatoshi Osawa

    LANGMUIR   24 ( 8 )   4358 - 4363   2008年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The adsorbed species formed from the nitrate ion were examined using surface-enhanced infrared absorption spectroscopy (SEIRAS). The main band was observed at 1547-1568cm(-1) at 0.2 V in 0.01 M NaNO3 + 0.1 MHClO4. Although this band is close to that assigned to the adsorbed NO in the literature, it is assigned to the N=O stretching vibration of the chelating bidentate form of nitrate for the following reasons. (i) Nitrate gives a single band, while NO has three bands independent of the coverage. (ii) The band intensity remained constant in the potential range from 0.1 to 0.6 V. while that of the bridged NO at around 1600 cm(-1) decreased in this range. (iii) The rate constants for the reduction and/or desorption at negative potentials are about 3 times higher than those of the bridged NO. (iv) The adsorbed species from nitrate is replaced with CO more easily than the bridged NO.

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  • Structure of water at the electrified platinum-water interface: A study by surface-enhanced infrared absorption spectroscopy 査読

    Masatoshi Osawa, Minoru Tsushima, Hirokazu Mogami, Gabor Samjeske, Akira Yamakata

    JOURNAL OF PHYSICAL CHEMISTRY C   112 ( 11 )   4248 - 4256   2008年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode is used to examine the structure of water on a polycrystalline Pt electrode in H2SO4 and HClO4 as a function of applied potential. The electrode surface covered with CO is used as the reference in recording spectra, which enables us to obtain the absolute infrared spectrum of the interfacial water layer (monolayer or bilayer) in contact with the surface with negligible interference from the bulk water. The spectrum of the interfacial water is largely different from that of bulk water and changes around the potential of zero charge of the electrode. The spectral changes are ascribed to the potential-dependent reorientation of water molecules from a weakly hydrogen-bonded oxygen-up orientation at the negatively charged surface to a strongly hydrogen-bonded nearly flat orientation at the positively charged surface in agreement with theoretical simulations reported in the literature. Clear experimental evidence of the formation of a stable ice-like structured water on the positively charged surface is reported.

    DOI: 10.1021/jp710386g

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  • 表面増強赤外吸収分光法による電極界面の超高速ダイナミクスの追跡 査読

    山方 啓, 大澤 雅俊

    Electrochemistry 電気化学および工業物理化学 : denki kagaku   76 ( 3 )   208 - 213   2008年3月

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    記述言語:日本語   出版者・発行元:The Electrochemical Society of Japan  

    DOI: 10.5796/electrochemistry.76.208

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  • 固液界面の水分子の構造とエネルギー移動ダイナミクス 査読

    山方 啓

    分光研究   57 ( 1 )   23 - 24   2008年

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    記述言語:日本語   出版者・発行元:The Spectroscopical Society of Japan  

    DOI: 10.5111/bunkou.57.23

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  • Time-resolved infrared absorption study of nine TiO2 photocatalysts 査読

    Akira Yamakata, Taka-aki Ishibashi, Hiroshi Onishi

    CHEMICAL PHYSICS   339 ( 1-3 )   133 - 137   2007年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    Electron kinetics of nine TiO2 catalysts were compared in a microsecond time domain. Each catalyst was band-gap excited with an UV light pulse, and electron-induced absorption of mid infrared light was observed as a function of time delay. The probability of electron-hole recombination in the bulk, electron attachment to adsorbed oxygen, and hole attachment to adsorbed methoxy species was estimated. (C) 2007 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.chemphys.2007.05.010

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  • 分子はどうやって活性点にたどり着くのか? 査読

    山方 啓

    触媒 = Catalysts & Catalysis   48 ( 8 )   611 - 611   2006年12月

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  • Laser-induced potential jump at the electrochemical interface probed by picosecond time-resolved surface-enhanced infrared absorption spectroscopy 査読

    A Yamakata, T Uchida, J Kubota, M Osawa

    JOURNAL OF PHYSICAL CHEMISTRY B   110 ( 13 )   6423 - 6427   2006年4月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Picosecond time-resolved surface-enhanced infrared absorption spectroscopy (SEIRAS) has been used for the first time to examine the potential jump at the electrochemical interface induced by a visible pulse irradiation. The potential dependent shift of the C-O stretching vibration of CO adsorbed on a Pt electrode was utilized to monitor the potential jump. A 6-cm(-1) red-shift was observed with a time delay of similar to 200 ps with respect to a visible pump-pulse irradiation (532 nm, 35 ps duration, 3 mJ cm(-2)). The observed red-shift is ascribed to the heating of the in-plane frustrated translational mode of CO and the negative shift of potential. These two contributions can be separated with the aid of the transient of the background reflectivity of the electrode surface. The heating of water layers near the surface is mainly responsible for the potential jump through the orientation change of water molecules. This method is promising as a tool to examine ultrafast electrode dynamics.

    DOI: 10.1021/jp060387d

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  • Adsorbed structures of 4,4 '-bipyridine on Cu(111) in acid studied by STM and IR 査読

    YX Diao, MJ Han, LJ Wan, K Itaya, T Uchida, H Miyake, A Yamakata, M Osawa

    LANGMUIR   22 ( 8 )   3640 - 3646   2006年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The adsorption of 4,4'-bipyridine (BiPy) on Cu(111) has been investigated in 0.1 M HClO4 by cyclic voltammetry, electrochemical scanning tunneling microscopy (STM), and surface-enhanced infrared adsorption spectroscopy (SEIRAS). Cyclic voltammetry showed the double layer region extending from -0.2 to 0.26 V and a pair of redox waves superposing on hydrogen evolution wave at more negative potentials. Diprotonated BiPy, BiPyH22+, is adsorbed flat on the Cu(111) (1 x 1) surface and forms a well-ordered monolayer with a (3 x 4) symmetry in the double-layer potential region. At more negative potential, BiPyH22+ is reduced to its monocation radical, BiPyH2 center dot+, and forms another well-ordered structure in which the radicals are stacked in molecular rows with a face-to-face self-dimer as the building unit. The SEIRA spectra of both BiPyH22+ and BiPyH2 center dot+ are dominated by gerade modes which should be IR-inactive for the centrosymmetric species. The breakdown of the selection rule of IR absorption is ascribed to the vibronic coupling associated with charge transfer between BiPyH22+ and the surface and between the radicals.

    DOI: 10.1021/la052765w

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  • Study on photogenerated charge carriers dynamics in sulfur-doped titanium dioxide by transient IR absorption 査読

    Kan Takeshita, Akira Yamakata, Taka-aki Ishibashi, Hiroshi Onishi, Kazumoto Nishijima, Teruhisa Ohno

    J. photochem. Photobiol. B. Chemistry   117   269 - 275   2006年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

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  • Transient IR absorption study of charge carriers photogenerated in sulfur-doped TiO2 査読

    K Takeshita, A Yamakata, T Ishibashi, H Onishi, K Nishijima, T Ohno

    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY   177 ( 2-3 )   269 - 275   2006年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE SA  

    Sulfur-doped TiO2 was prepared by two methods; one was simple oxidation annealing of TiS2, the other was mixing of titanium isopropoxide and thiourea. These two sulfur-doped TiO2, preparations showed fairly different photocatalytic activity under visible light. The dynamics of photogenerated charge carriers were studied by the transient absorption measurement in the region of mid-IR. In both samples, excitation by 532 nm pulse led to photocarrier generation to the same extent. Nevertheless, the reactivity of the photocarriers was totally different. Photogenerated electrons and holes transferred to reactant gas in the latter sample, whereas they did not in the former sample. We attributed the different carrier behavior to the difference in the distribution of S atoms or particle size. These observations can explain the difference in capability of photocatalysis under visible light. (c) 2005 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.jphotochem.2005.06.006

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  • Potential oscillations in galvanostatic electrooxidation of formic acid on platinum: A time-resolved surface-enhanced infrared study 査読

    G Samjeske, A Miki, S Ye, A Yamakata, Y Mukouyama, H Okamoto, M Osawa

    JOURNAL OF PHYSICAL CHEMISTRY B   109 ( 49 )   23509 - 23516   2005年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The mechanism of temporal potential oscillations that occur during galvanostatic formic acid oxidation on a Pt electrode has been investigated by time-resolved surface-enhanced infrared absorption spectroscopy (SEIRAS). Carbon monoxide (CO) and formate were found to adsorb on the surface and change their coverages synchronously with the temporal potential oscillations. Isotopic solution exchange (from (HCOOH)-C-13 to (HCOOH)-C-12) and potential step experiments revealed that the oxidation of formic acid proceeds dominantly through adsorbed formate and the decomposition of formate to CO2 is the rate-determining step of the reaction. Adsorbed CO blocks the adsorption of formate and also suppresses the decomposition of formate to CO2, which raises the potential to maintain the applied current. The oxidative removal of CO at a high limiting potential increases the coverage of formate and accelerates the decomposition of formate, resulting in a potential drop and leading to the formation of CO. This cycle repeats itself to give the sustained temporal potential oscillations. The oscillatory dynamics can be explained by using a nonlinear rate equation originally proposed to explain the decomposition of formate and acetate on transition metal surfaces in UHV.

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  • 時間分解赤外分光法でみた表面反応ダイナミクス 査読

    山方 啓, 大澤 雅俊

    触媒 = Catalysts & Catalysis   47 ( 5 )   334 - 340   2005年8月

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    記述言語:日本語   出版者・発行元:触媒学会  

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  • Time-resolved infrared absorption study of photochemical reactions over metal oxides 査読

    A Yamakata, T Ishibashi, K Takeshita, H Onishi

    TOPICS IN CATALYSIS   35 ( 3-4 )   211 - 216   2005年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:SPRINGER/PLENUM PUBLISHERS  

    The present account describes how photochemical reactions over metal oxides are traced by time-resolved infrared (IR) absorption spectroscopy. The ac-coupled amplification of the IR signal allows detection of transient absorbance changes as small as 10(-6) with a time resolution of 50 ns. Band-gap excited electrons in TiO2 and NaTaO3 present a structureless absorption of IR light from 3000 to 1000 cm(-1). Reaction-perturbed decay of this absorption evidences the assignment to photoexcited electrons, not to holes. The efficiency of the water splitting reaction on NaTaO3-based catalysts correlates with the quantity of electrons detected by the IR absorption. A short-lived intermediate state of 2-propanol oxidation on TiO2 is identified by its vibrational band at 1640 cm(-1) superposed on the structureless absorption of electrons. Ru dye (N3) on a TiO2 film is irradiated with a 532-nm light pulse to simulate dye-sensitized solar cells. The neutralization rate of dye cations and the decay rate of electrons injected in the film are quantified, leading to a three-state model which describes the relaxation of injected electrons. These results demonstrate the ability of this method in tracing photochemical kinetics over metal oxides.

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  • Carrier dynamics in TiO2 and Pt/TiO2 powders observed by femtosecond time-resolved near-infrared spectroscopy at spectral region of 0.9 to 1.5 μm with direct absorption method 査読

    IWATA, K, TAKAYA, T, HAMAGUCHI, H, YAMAKATA, A, ISHIBASHII, T, ONISHI, H, KURODA, H

    J Phys Chem B   108 ( 52 )   20233 - 20239   2004年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Iwata, K., Takaya, T., Hamaguchi, H., Yamakata, A., Ishibashi, T., Onishi, H., Kuroda, H.:“Carrier dynamics in TiO2 and Pt/TiO2 powders observed by femtosecond time-resolved near-infrared spectroscopy at spectral region of 0.9 to 1.5 μm with direct absorption method”, J. Phys. Chem. B 108, 20233-20239, (2004).*

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  • In situ surface-enhanced infrared study of hydrogen bond pairing of complementary nucleic acid bases at the electrochemical interface 査読

    Y Sato, H Noda, F Mizutani, A Yamakata, M Osawa

    ANALYTICAL CHEMISTRY   76 ( 18 )   5564 - 5569   2004年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Surface-enhanced infrared absorption spectroscopy with a Kretschmann-type attenuated total reflection configuration has been used to study hydrogen-bonded pairing between 6-amino-8-purinethiol, a thiol-derivatized adenine, immobilized on a gold electrode surface, and thymidine, a complimentary base derivative of adenine, in 0. 1 M NaClO4 aqueous solution as a function of applied potential. 6-Amino-8-purinethiol is adsorbed on a gold surface via a sulfur atom to form a S-Au bond. Nearly half of the adsorbed molecules are protonated, and the long axis of the adenine moiety is tilted from the surface normal at open circuit potential. As the potential increases, the acid-base equilibrium is shifted toward the unprotonated form and the adenine moiety is reoriented toward a nearly perpendicular configuration. The hydrogen bond interaction between the adsorbed 6-amino-8purinethiol with thymidine in solution is greatly affected by the protonation and orientation of the adenine moiety and is controllable by the applied potential. Due to steric hindrance, an adenine-thymine-type hydrogen bond pair is formed only at potentials more positive than 0. 1 V (vs SCE) where the unprotonated adenine moiety is perpendicularly oriented.

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  • Effect of annealing temperature on back electron transfer and distribution of deep trap sites in dye-sensitized TiO2, studied by time-resolved infrared spectroscopy 査読

    K Takeshita, Y Sasaki, M Kobashi, Y Tanaka, S Maeda, A Yamakata, TA Ishibashi, H Onishi

    JOURNAL OF PHYSICAL CHEMISTRY B   108 ( 9 )   2963 - 2969   2004年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The effect of annealing temperature on electron dynamics in Ru complex-sensitized TiO2 films was studied by highly sensitive measurement of transient IR absorption. The amount of electron injection and the back electron transfer rate were not influenced to a large extent by annealing temperature, but the distribution of deep trap sites was considerably influenced. The difference in solar cell efficiency due to annealing temperature was mainly attributed to the difference in the nature of deep trap sites. By extending the probe light window from the mid-IR (1000-4000 cm(-1)) to the near-IR (-10000 cm(-1)) region, we investigated deep trap sites directly and found that electrons in deep trap sites have absorption in the near-IR region whose peak locates around 7500 cm(-1). As a whole, the electron dynamics in the films annealed at higher than 400 degreesC were considerably different compared with those in the films annealed at lower than 400 degreesC.

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  • Photodynamics of NaTaO3 catalysts for efficient water splitting 査読

    A Yamakata, T Ishibashi, H Kato, A Kudo, H Onishi

    JOURNAL OF PHYSICAL CHEMISTRY B   107 ( 51 )   14383 - 14387   2003年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Electrons photoexcited in catalysts based on NaTaO3 were observed by time-resolved infrared (IR) absorption spectroscopy. The electrons excited by 266-nm pump pulse exhibited a monotonic absorption of mid-IR light. The recombination kinetics of the excited electrons with holes was monitored in a vacuum as a function of time delay ranging from 100 ns to 1 s. When the Na content and La dopant were optimized to achieve high activity in the steady-state reaction of water splitting, the recombinative decay was hindered to increase the amount of electrons. The electrons were transferred to NiO ultrafine particles, loaded as a cocatalyst, within 1 mus following the pulse excitation. Exposing the catalysts to water vapor affected the electron decay and efficient electron transfer to water via the cocatalyst was evidenced.

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  • Effects of water addition on the methanol oxidation on Pt/TiO2 photocatalyst studied by time-resolved infrared absorption spectroscopy 査読

    A Yamakata, TA Ishibashi, J Onishi

    JOURNAL OF PHYSICAL CHEMISTRY B   107 ( 36 )   9820 - 9823   2003年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The reaction kinetics of electrons photoexcited in a Pt/TiO2 catalyst were observed by time-resolved infrared absorption in the presence of methanol-water vapor mixtures. The recombinative decay of the electrons was completed in microseconds on the catalyst exposed to a vacuum. The decay was suspended in the catalyst exposed to pure methanol vapor due to an effective hole-consuming reaction by adsorbed methoxy species. The suspension was released as partial water pressure was increased, indicating that the holes reacted with the methoxy species without the aid of adsorbed water or hydroxyl species. The excess electrons remaining in the catalyst were consumed by adsorbed water in a time domain of 0.1 s. The water-induced promotion of the methanol oxidation reaction described in the literature was interpreted with these results.

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  • 時間分解赤外分光法を用いた二酸化チタン光触媒反応中間体の観察 査読

    山方 啓, 石橋 孝章, 大西 洋

    表面科学   24 ( 9 )   563 - 567   2003年9月

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    記述言語:日本語   出版者・発行元:The Surface Science Society of Japan  

    Oxidation of 2-propanol to acetone on a Pt/TiO&lt;Sub&gt;2&lt;/Sub&gt; photocatalyst by UV pulse irradiation was observed by time-resolved IR spectroscopy (TR-IR). The hole transfer to the 2-propanol, which triggers the oxidation, was completed within 0.5 μs. Transient vibrational spectra showed a new band at 1640 cm&lt;Sup&gt;−1&lt;/Sup&gt;, which appeared immediately after the irradiation. This band gradually transformed to a band at 1700 cm&lt;Sup&gt;−1&lt;/Sup&gt;, which was assigned to the C=O stretching mode of acetone, the product of 2-propanol oxidation. Thus, the band at 1640 cm&lt;Sup&gt;−1&lt;/Sup&gt; was suggested to be the reaction intermediate that transforms to acetone. We discussed the origin of this band using density functional calculation, and an acceptable agreement was obtained with the anion radical of acetone adsorbed on the catalyst.

    DOI: 10.1380/jsssj.24.563

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  • Effects of accumulated electrons on the decay kinetics of photogenerated electrons in Pt/TiO2 photocatalyst studied by time-resolved infrared absorption spectroscopy 査読

    A Yamakata, TA Ishibashi, H Onishi

    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY   160 ( 1-2 )   33 - 36   2003年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE SA  

    The effects of accumulated electrons on the decay kinetics of photogenerated electrons in Pt/TiO2 photocatalyst were examined using time-resolved infrared (TR-IR) absorption spectroscopy. When the catalyst was irradiated by a UV pulse in the presence of methanol gas, the lifetime of the electrons was drastically elongated through the effective hole-consuming reaction by the adsorbed methoxy groups. When the catalyst was further irradiated by a second UV pulse in the presence of these long-lived electrons, the number of electrons generated by the second pulse was smaller than that generated by the first pulse though these pulse energies were the same. By increasing the interval between these two pulses, the number of electrons generated by the second pulse was gradually restored to equal that generated by the first pulse. These changes were ascribed to the enhancement of the rate of electron-hole recombination due to the long-lived electrons. (C) 2003 Elsevier Science B.V. All rights reserved.

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  • Microsecond kinetics of photocatalytic oxidation on Pt/TiO2 traced by vibrational spectroscopy 査読

    A Yamakata, T Ishibashi, H Onishi

    CHEMICAL PHYSICS LETTERS   376 ( 5-6 )   576 - 580   2003年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    2-Propanol oxidation to acetone was examined by time-resolved infrared spectroscopy on a Pt/TiO2 photocatalyst in an aqueous solution. Holes generated by the band-gap excitation were found to attach to the adsorbed reactant within the first 0.5 mus. Subsequent rearrangement of atoms in the hole-attached reactant was observed on a series of time-resolved vibrational spectra. The C=O stretching band of a reaction intermediate to be converted to acetone appeared at time delays of 0-20 mus. The observed wavenumber of the intermediate, 1640 cm(-1), was compared with theoretically predicted C=O stretching frequencies of possible species. An acceptable agreement was obtained with the anion radical of acetone adsorbed on the catalyst. (C) 2003 Elsevier B.V. All rights reserved.

    DOI: 10.1016/S0009-2614(03)01034-0

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  • Photophysics and electron dynamics in dye-sensitized semiconductor film studied by time-resolved mid-IR spectroscopy 査読

    Kan Takeshita, Yutaka Sasaki, Masahiro Kobashi, Yuki Tanaka, Shuichi Maeda, Akira Yamakata, Taka-Aki Ishibashi, Hiroshi Onishi

    Journal of Physical Chemistry B   107 ( 17 )   4156 - 4161   2003年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Photophysics and electron dynamics in dye-sensitized semiconductor film were studied by transient mid-IR spectroscopy, in particular on the nano- to millisecond time scale. As sensitizers, a Ru complex and 9-phynol xanthane derivatives were used. We simultaneously observed electrons injected into the conduction band of a semiconductor and the change of vibration bands due to formation of a cation of a dye molecule. The transient absorption components derived from these two species decayed differently. From this observation, we found that injected electrons decay through two paths
    one was back electron transfer, and the other was decay to deep trap sites that cannot be detected by mid-IR light. We could also estimate the amount of electron injection for different dye-sensitized TiO2. Our transient mid-IR spectroscopy in long time scale introduces a semi-new approach to the slow dynamics in dye-sensitized semiconductors including back electron transfer.

    DOI: 10.1021/jp0275645

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  • Kinetics of the photocatalytic water-splitting reaction on TiO2 and Pt/TiO2 studied by time-resolved infrared absorption spectroscopy 査読

    A Yamakata, T Ishibashi, H Onishi

    JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL   199 ( 1-2 )   85 - 94   2003年5月

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    記述言語:英語   出版者・発行元:ELSEVIER SCIENCE BV  

    The present account describes how the water-splitting reaction on TiO2 (P-25) and Pt/TiO2 catalysts is traced by time-resolved infrared (IR) absorption spectroscopy. The ac-coupled amplification of the IR signal allows detection of transient absorbance-change as small as 10(-6) with a time-resolution of 50 ns. The TiO2 or Pt/TiO2 catalyst irradiated by a 355 run UV-pulse at time = 0 presents a transient IR absorption which monotonically increases in intensity with decreasing wavenumber from 3000 to 1000 cm(-1). Photogenerated electrons trapped in shallow mid-gap states are proposed to cause the absorption. The decay kinetics of the electrons traced by monitoring the IR absorbance at 2000 cm(-1) is sensitive to vapor atmospheres. The electrons recombine with the complementary holes along a multi-exponential rate law in the catalysts placed in a vacuum. Dioxygen arriving from the gas-phase captures the electrons at delay time of 10-100 mus following the UV irradiation. In the presence of water vapor, holes in the TiO2 catalyst are captured by an adsorbed reactant (probably hydroxyl species) within 2 mus and the recombination is obstructed thereafter. The excess electrons cannot transfer to another adsorbate to be reduced (probably proton) and hence reduce the catalyst itself. On the Pt/TiO2 catalyst exposed to water, the electron transfer takes place at 10 mus or later, following the hole transfer completed within 2 mus. The hole transfer on Pt/TiO2 is insensitive to the pressure of water vapor whereas the rate of the electron transfer is enhanced with the increasing pressure at 1-10Torr. Transient response of an adsorbate vibration is also observed. The O-H stretching band of an adsorbed hydroxyl species at 3677 cm-1 thermally shifted to the low-wavenumber side, when the TiO2 catalyst is irradiated by the UV-pulse. (C) 2003 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S1381-1169(03)00021-9

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  • Photophysics and electron dynamics in dye-sensitized semiconductor film studied by time-resolved mid-IR spectroscopy 査読

    K Takeshita, Y Sasaki, M Kobashi, Y Tanaka, S Maeda, A Yamakata, T Ishibashi, H Onishi

    JOURNAL OF PHYSICAL CHEMISTRY B   107 ( 17 )   4156 - 4161   2003年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Photophysics and electron dynamics in dye-sensitized semiconductor film were studied by transient mid-IR spectroscopy, in particular on the nano- to millisecond time scale. As sensitizers, a Ru complex and 9-phynol xanthane derivatives were used. We simultaneously observed electrons injected into the conduction band of a semiconductor and the change of vibration bands due to formation of a cation of a dye molecule. The transient absorption components derived from these two species decayed differently. From this observation, we found that injected electrons decay through two paths; one was back electron transfer, and the other was decay to deep trap sites that cannot be detected by mid-IR light. We could also estimate the amount of electron injection for different dye-sensitized TiO(2). Our transient mid-IR spectroscopy in long time scale introduces a semi-new approach to the slow dynamics in dye-sensitized semiconductors including back electron transfer.

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  • 時間分解赤外分光法による酸化チタン/吸着色素間の電子移動の追跡

    竹下 寛, 佐々木 豊, 小橋 昌浩, 田中 由紀, 前田 修一, 山方 啓, 石橋 孝章, 大西 洋

    触媒   45 ( 2 )   181 - 183   2003年3月

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    記述言語:日本語   出版者・発行元:触媒学会  

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  • 時間分解赤外分光でみた二酸化チタン微粒子から吸着分子への電荷移動 査読

    山方 啓, 石橋 孝章, 大西 洋

    表面科学 : hyomen kagaku = Journal of the Surface Science Society of Japan   24 ( 1 )   46 - 52   2003年1月

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    記述言語:日本語   出版者・発行元:The Surface Science Society of Japan  

    Behavior of the electrons and holes photogenerated in TiO&lt;Sub&gt;2&lt;/Sub&gt; particles was observed by time-resolved infrared absorption spectroscopy in the presence of oxygen, water, and methanol vapor. The electrons photogenerated by a band-gap excitation displayed a structureless, broad absorption of IR light from 3000 to 900 cm&lt;Sup&gt;−1&lt;/Sup&gt;, which was assigned to the intra-conduction-band transition and/or excitation from mid-gap traps to the conduction band. This electron-induced absorption was probed as a function of time delay after the photoexcitation. Electron decay caused by the recombination with holes and by the charge-transfer reactions with adsorbates were kinetically analyzed. The electron decay was accelerated in the presence of oxygen gas due to an electron-capture reaction at the interface, whereas was decelerated in methanol vapor due to an effective hole-capture by methoxy groups. On platinized TiO&lt;Sub&gt;2&lt;/Sub&gt; particles exposed to water vapor, a hole-capture reaction completed within 2 μs after band-gap excitation, whereas the electron-capture reaction occurred in 10 μs or later. These results demonstrate the effectiveness of this method to identify individual steps of photo-induced reactions at interfaces.

    DOI: 10.1380/jsssj.24.46

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  • Pressure dependence of electron- and hole-consuming reactions in photocatalytic water splitting on Pt/TiO2 studied by time-resolved IR absorption spectroscopy 査読

    A Yamakata, T Ishibashi, H Onishi

    INTERNATIONAL JOURNAL OF PHOTOENERGY   5 ( 1 )   7 - 9   2003年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PHOTOENERGY CENTER AIN SHAMS UNIV,  

    The decay kinetics of photogenerated electrons in the water splitting reaction on a Pt/TiO2 photocatalyst was studied by time-resolved IR absorption spectroscopy. The decay of the photogenerated electrons within 2 mus was decelerated when the catalyst was exposed to water vapor. The holes were consumed by the reaction with water instead of by the recombination with the electrons. On the other hand, the decay at 10-900 mus was accelerated by the exposure. The electrons were consumed by the reaction with water. The rate of the hole-consuming reaction was independent of the pressure of water vapor, whereas that of the electron-consuming reaction increased with the pressure from 1 to 10 Torr. The different pressure dependences indicate different reactants involved in the oxidative and reductive reactants.

    DOI: 10.1155/s1110662x03000047

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  • Time-resolved infrared absorption study of electron- and hole-capture reactions on photoexcited Pt/TiO2 in the presence of methanol-water vapor mixture 査読

    A Yamakata, TA Ishibashi, H Onishi

    SCIENCE AND TECHNOLOGY IN CATALYSIS 2002   145   157 - 160   2003年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:KODANSHA LTD  

    The decay kinetics of electrons and holes photogenerated in Pt/TiO2 was studied by time-resolved infrared absorption spectroscopy in methanol vapor, water vapor, and a mixture of the two. The holes were exhausted within 50 ns in the presence of methanol and it was concluded that they attached directly to methanol-derived adsorbates without the aid of water-derived hydroxyl radicals.

    DOI: 10.1016/s0167-2991(03)80184-2

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  • Microscopic identification of a bimolecular reaction intermediate 査読

    Hiroshi Uetsuka, Akira Sasahara, Akira Yamakata, Hiroshi Onishi

    Journal of Physical Chemistry B   106 ( 44 )   11549 - 11552   2002年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    How a molecule impinging from an ambient phase attaches to and reacts with a preadsorbed reactant was studied by scanning tunneling microscopy (STM). A carboxylate (RCOO-) chemisorbed on a TiO2(110) surface was exchanged by another carboxylate (R′COO-) via an SN2-like mechanism when the RCOO--covered TiO2 surface was exposed to R′COOH vapor at room temperature or below. An R′COOH impinging from the gas phase was temporarily bound to a preadsorbed RCOO- yielding a bimolecular intermediate. The trapped R′COOH was inserted into the monolayer and dissociated to produce an adsorbed R′COO-. One of the carboxylates (RCOO- or R′COO-) was then pushed out of the monolayer to restore the intermediate and released to the vapor phase. The individual reaction steps were resolved using time-lapse imaging.

    DOI: 10.1021/jp026253r

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  • Microscopic identification of a bimolecular reaction intermediate 査読

    H Uetsuka, A Sasahara, A Yamakata, H Onishi

    JOURNAL OF PHYSICAL CHEMISTRY B   106 ( 44 )   11549 - 11552   2002年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    How a molecule impinging from an ambient phase attaches to and reacts with a preadsorbed reactant was studied by scanning tunneling microscopy (STM). A carboxylate (RCOO-) chemisorbed on a TiO2(110) surface was exchanged by another carboxylate (R'COO-) via an S(N)2-like mechanism when the RCOO--covered TiO2 surface was exposed to R'COOH vapor at room temperature or below. An R'COOH impinging from the gas phase was temporarily bound to a preadsorbed RCOO- yielding a bimolecular intermediate. The trapped R'COOH was inserted into the monolayer and dissociated to produce an adsorbed R'COO-. One of the carboxylates (RCOO- or R'COO-) was then pushed out of the monolayer to restore the intermediate and released to the vapor phase. The individual reaction steps were resolved using time-lapse imaging.

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  • Electron- and hole-capture reactions on Pt/TiO2 photocatalyst exposed to methanol vapor studied with time-resolved infrared absorption spectroscopy 査読

    Akira Yamakata, Taka-Aki Ishibashi, Hiroshi Onishi

    Journal of Physical Chemistry B   106 ( 35 )   9122 - 9125   2002年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    The decay kinetics of photogenerated electrons in a Pt/TiO2 catalyst has been studied by time-resolved infrared absorption (TR-IR) spectroscopy. The electron decay was drastically affected by exposure to methanol vapor, and the electron-hole pair recombination was prevented. A certain fraction of the electrons remained beyond 1 s and slowly decayed from ∼1-9 s. The prevented recombination was interpreted with the effective capture of the holes. The extent of the hole capture was insensitive to the pressure of methanol vapor. An irreversibly adsorbed methoxy groups was proposed to capture the holes on the basis of the steady-state FT-IR spectra of the catalyst exposed to methanol vapor of different pressures. However, the slow decay of the electrons exhibited a positive-order response to the methanol pressure. Undissociated methanol physisorbed and equilibrated with the gas phase, which was identified in the steady-state spectra, should play a key role in the electron capture process. Possible mechanisms of the process are discussed.

    DOI: 10.1021/jp025993x

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  • Electron- and hole-capture reactions on Pt/TiO2 photocatalyst exposed to methanol vapor studied with time-resolved infrared absorption spectroscopy 査読

    A Yamakata, T Ishibashi, H Onishi

    JOURNAL OF PHYSICAL CHEMISTRY B   106 ( 35 )   9122 - 9125   2002年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The decay kinetics of photogenerated electrons in a Pt/TiO2 catalyst has been studied by time-resolved infrared absorption TR-IR) spectroscopy. The electron decay was drastically affected by exposure to methanol vapor, and the electron-hole pair recombination was prevented. A certain fraction of the electrons remained beyond 1 s and slowly decayed from similar to 1-9 s. The prevented recombination was interpreted with the effective capture of the holes. The extent of the hole capture was insensitive to the pressure of methanol vapor. An irreversibly adsorbed methoxy groups was proposed to capture the holes on the basis of the steady-state FT-IR spectra of the catalyst exposed to methanol vapor of different pressures. However, the slow decay of the electrons exhibited a positive-order response to the methanol pressure. Undissociated methanol physisorbed and equilibrated with the gas phase, which was identified in the steady-state spectra, should play a key role in the electron capture process. Possible mechanisms of the process are discussed.

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  • Time-resolved infrared absorption studies of surface OH groups on TiO2 particles irradiated by UV pulses 査読

    A Yamakata, T Ishibashi, H Onishi

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   75 ( 5 )   1019 - 1022   2002年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:CHEMICAL SOC JAPAN  

    The shift of vibrational frequency of surface OH groups on TiO2 particles induced by UV pulse irradiation has been studied by time-resolved IR absorption spectroscopy. By the UV irradiation of the TiO2 particles, the absorption intensity at 3696 cm(-1) was decreased and that at 3654 cm(-1) was increased. These changes were gradually recovered on a millisecond time scale. The transient changes were interpreted by a small (&lt;0.1 cm(-1)) shift of a v(O-H) band at 3677 cm(-1). The temperature jump triggered by the UV pulse caused the shift.

    DOI: 10.1246/bcsj.75.1019

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  • 時間分解赤外分光法を用いた二酸化チタン上の光励起電子と吸着分子への電荷移動反応の観察 査読

    山方 啓, 石橋 孝章, 大西 洋

    触媒   43 ( 6 )   396 - 398   2001年9月

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    記述言語:日本語   出版者・発行元:触媒学会  

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  • Water- and oxygen-induced decay kinetics of photogenerated electrons in TiO2 and Pt/TiO2: A time-resolved infrared absorption study 査読

    A Yamakata, T Ishibashi, H Onishi

    JOURNAL OF PHYSICAL CHEMISTRY B   105 ( 30 )   7258 - 7262   2001年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Electrons photogenerated in TiO2 and Pt/TiO2 catalysts were observed by time-resolved IR absorption spectroscopy. Transient IR absorption of an identical spectrum appeared on TiO2 and Pt/TiO2 irradiated by a 355 nm pump pulse. The absorption was attributed to optical transition of photogenerated electrons trapped in shallow midgap states. Electron- and hole-consuming reactions of adsorbates controlled the decay kinetics of the electrons competing with the electron-hole recombination. On TiO2, O-2 from the gas-phase captured the electrons and accelerated the decay rate at a delay time of 10-100 mus. In water vapor, holes reacted with surface hydroxyls within 2 mus, and the recombination decay of the electrons was obstructed. When Pt/TiO2 was exposed to water, the oxidation and reduction steps of the water splitting reaction affected the decay kinetics in different time domains. Photogenerated holes oxidized water within 2 mus, whereas electrons reduced water at 10-900 mus.

    DOI: 10.1021/jp010802w

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  • Time-resolved infrared absorption spectroscopy of photogenerated electrons in platinized TiO2 particles 査読

    A Yamakata, T Ishibashi, H Onishi

    CHEMICAL PHYSICS LETTERS   333 ( 3-4 )   271 - 277   2001年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    Kinetics of photogenerated electrons in platinized TiO2 (P-25) particles were observed by time-resolved infrared (IR) absorption spectroscopy with AC-coupled detection of cw probe light. The sample irradiated by UV pulse (355 nm and 10 ns) gave transient absorption which monotonously increased in intensity with decreasing wavenumber from 3000 to 900 cm(-1). Photogenerated electrons trapped in shallow mid-gap states were proposed to originate the transient absorption. The decay kinetics of the trapped electrons were fitted to a multi-exponential formula with six lifetimes ranging from 1 x 10(-7) to 3 x 10(-1) s. (C) 2001 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0009-2614(00)01374-9

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  • Exchange reaction of formate with gas-phase acetic acid on Ni(110) 査読

    A Yamakata, J Kubota, JN Kondo, C Hirose, K Domen, F Wakabayashi, K Tamaru

    SURFACE SCIENCE   433   210 - 214   1999年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    The exchange reaction of formate with gas-phase acetic acid on Ni(110) was studied by time resolved infrared reflection absorption spectroscopy. It was found that the preadsorbed for mate was replaced ill the acetate by the introduction of acetic acid on formate-full covered Ni(110), originated from the post-exposed acetic acid. Acetate was also replaced in formate by the introduction of formic acid on acetate-full covered Ni(110). These exchange reactions took place from 240 to 300 K, where decomposition of neither formate nor acetate was observed. Thus, it was confirmed that the preadsorbed formate or acetate was desorbed as formic or acetic acid accompanied by the transfer of hydrogen atoms from post-introduced acetic or formic acid. The activation energy of the exchange reaction of formate with post-introduced acetic acid was estimated to be 17 +/- 2 kJ mol(-1). The small activation energy of the exchange reaction is discussed on the basis of adsorption assisted desorption. (C) 1999 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0039-6028(99)00468-9

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  • In situ observation of the exchange reaction of formate with molecular formic acid on Ni(110) 査読

    A Yamakata, J Kubota, JN Kondo, C Hirose, K Domen, F Wakabayashi, K Tamaru

    JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL   141 ( 1-3 )   73 - 82   1999年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    The exchange reaction of adsorbed formate on Ni(110) with formic acid in gas phase was studied by the time-resolved infrared reflection absorption spectroscopy (TR-IRAS). It was found that the pre-adsorbed deuterated formate (DCOO(a)) was changed to HCOO(a) in the presence of HCOOD(g) at the temperature region from 240 to 300 K. In such a temperature region, the formate was stable on the surface in vacuum and the decomposition of formate was not observed. It was suggested that the pre-adsorbed DCOO(a) was desorbed as DCOOD accepting deuterium atom from HCOOD. The activation energy of the exchange reaction was estimated to be 23 +/- 2 kJ mol(-1). The reaction order with respect to formic acid pressure was 0.3 +/- 0.1, while that as to the coverage of DCOO(a), was unity. Taking into account all the experimental results, the exchange of pre-adsorbed formate with post-exposed formic acid is suggested to proceed via forming a hydrogen-bonded intermediate complex on the formate's site, because all the sites were already occupied by formate. The small activation energy of the exchange reaction is discussed on the basis of 'adsorption-assisted desorption'. We propose that when desorption and adsorption are coupled, the activation energy of the exchange reaction should be described as a sum of the potential energy profiles of a desorbing and an adsorbing molecule. (C) 1999 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S1381-1169(98)00251-9

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  • Exchange reaction of adsorbed formate with gaseous formic acid on Ni(110) studied by time-resolved Fourier transform infrared reflection absorption spectroscopy 査読

    A Yamakata, J Kubota, JN Kondo, C Hirose, K Domen, F Wakabayashi, K Tamaru

    JOURNAL OF PHYSICAL CHEMISTRY B   102 ( 22 )   4401 - 4403   1998年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The dynamic behavior of adsorbed formate on Ni(110) in the presence of gaseous formic acid was studied by time-resolved infrared reflection absorption spectroscopy. The preadsorbed formate (DCOO(a)) was replaced by the postexposed formic acid (HCOOD) to form HCOO(a) on Ni(110) in the temperature region between 230 and 300 K, where the formate was stable under vacuum and no decomposition of formate was observed. It was confirmed that the preadsorbed DCOO(a) desorbed as DCOOD accompanied by formation of HCOO(a) via the deuterium atom transfer from HCOOD.

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  • 時間分解赤外反射吸収分光法によるNi(110)表面に吸着したフォルメートと気相に導入したギ酸の交換反応 査読

    山方 啓, 久保田 純, 野村 淳子, 廣瀬 千秋, 堂免 一成, 若林 文高

    表面科学   19 ( 7 )   441 - 445   1998年

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    出版者・発行元:The Surface Science Society of Japan  

    The exchange reaction of formate (DCOO(a)) with gaseous formic acid (HCOOD) on Ni(110) was investigated below the decomposition temperature of formate (340 K) by means of time-resolved infrared reflection absorption spectroscopy (TR-IRAS). When HCOOD gas was admitted on DCOO(a)-covered Ni(110) at 300 K, the pre-adsorbed DCOO(a) was replaced by HCOO(a). Similar replacement was also observed by introducing H&lt;SUP&gt;12&lt;/SUP&gt; COOH gas onto H-&lt;SUP&gt;13&lt;/SUP&gt;COO(a)-covered Ni(110). In such a temperature region from 240 to 300 K, no decomposition of formate was observed. Thus it was confirmed that those pre-adsorbed formate desorbed as formic acid accompanied by the transfer of hydrogen (deuterium) atom from post-introduced formic acid. The kinetics of the exchange reaction is investigated and the mechanism of that is also discussed.

    DOI: 10.1380/jsssj.19.441

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  • 赤外反射吸収分光法によるNi(110)上に吸着した ギ酸の分解過程の観察 査読

    山方 啓, 久保田 純, 野村 淳子, 廣瀬 千秋, 堂免 一成, 若林 文高

    表面科学   18 ( 7 )   417 - 423   1997年7月

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    記述言語:日本語   出版者・発行元:日本表面科学会  

    The decomposition of the surface formate on Ni(110) was studied by temperature programmed desorption (TPD) and timeresolved infrared reflection absorption spectroscopy (TR-IRAS). It was observed that dehydration proceeded simultaneously with dehydrogenation. The rate-determining step of dehydration was found to be the C-H bond cleavage of formate as is the case of dehydrogenation by analysis of the kinetic isotope effect using HCOO(a) and DCOO(a). These results suggest that the rate-determining steps of dehydration and dehydrogenation are common. We propose a mechanism in which the CO2(a) species formed via the C-H bond cleavage of formate acts as the intermediate not only for dehydrogenation but also for dehydration; dehydration takes place by dissociation of the C-O bond of CO2(a).

    DOI: 10.1380/jsssj.18.417

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  • In situ observation of the dehydration of formate on Ni(110) 査読

    A Yamakata, J Kubota, JN Kondo, C Hirose, K Domen, F Wakabayashi

    JOURNAL OF PHYSICAL CHEMISTRY B   101 ( 26 )   5177 - 5181   1997年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The dehydration of formate adsorbed on Ni(110) has been studied by the direct observation of the CO(a) produced on the surface by means of time-resolved infrared reflection absorption spectroscopy (TR-IRAS). By the quantitative analysis of the temperature-programmed desorption and TR-IRAS results, it was found that the dehydration proceeds simultaneously with the dehydrogenation. The primary kinetic isotope effect (k(H)/k(D)) using HCOO(a) and DCOO(a) was observed not only in the dehydrogenation but also in the dehydration (k(H)/k(D) = 3.3 at 300 K). This result suggests that the rate-determining step (RDS) is the C-H bond dissociation in both processes. These suggestions let us propose a possible mechanism of the dehydration of formate on Ni(110); the RDS of the dehydration is the C-H bond dissociation which is the same as that of the dehydrogenation, and the produced CO2(a) is the precursor of the production of CO(a) and O(a).

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  • Isotope exchange reaction of formate with molecular hydrogen on Ni(110) by IRAS 査読

    A Yamakata, J Kubota, JN Kondo, K Domen, C Hirose

    JOURNAL OF PHYSICAL CHEMISTRY   100 ( 46 )   18177 - 18182   1996年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Kinetics of the CH/CD isotope exchange reaction of formate (HCOO(a)/DCOO(a)) on Ni(110) with gaseous D-2/H-2 was investigated below the decomposition temperature (360 K) by infrared reflection absorption spectroscopy (IRAS). The apparent activation energies of HCOO(a) --&gt; DCOO (a) and DCOO(a) --&gt; HCOO(a) reactions were derived as 52 +/- 5 and 58 +/- 5 kJ . mol(-1), respectively. A half-order dependence of the reaction rate on hydrogen pressure was observed, suggesting that the rate-determining step was the reaction of the adsorbed formate with reversibly adsorbed hydrogen atom. The reaction of HCOO(a) with D-2 was 2.1 +/- 0.3 times faster than that of DCOO(a) with H-2 at 300 K, and the origin of the isotope effect is discussed.

    DOI: 10.1021/jp9611986

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  • SFG Study of Formic Acid on a Pt(110)-(1x2) Surface 査読

    WATANABE N, IWATSU K, YAMAKATA Akira, OHTANI T, KUBOTA Jun, KONDO J. N, WADA A, DOMEN Kazunari, HIROSE Chiaki

    Surf Sci   357 ( 1-3 )   651 - 655   1996年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/0039-6028(96)00239-7

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▼全件表示

書籍等出版物

  • 固体表面キャラクタリゼーション 機能性材料・ナノマテリアルのためのスペクトロスコピー (KS化学専門書)

    山下 弘巳, 吉田 寿雄, 田中 庸裕( 担当: 分担執筆)

    講談社  2022年3月  ( ISBN:4065261260

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    総ページ数:304   記述言語:日本語

    CiNii Books

    ASIN

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  • エネルギー変換型光触媒

    久富隆史, 久保田純, 堂免一成, 山方 啓( 担当: 分担執筆 ,  範囲: コラム9 「時間分解過渡吸収分光法によるキャリアダイナミクスの解明」)

    共立出版㈱  2017年6月 

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    担当ページ:P106-107  

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  • 光触媒/光半導体を利用した人工光合成-最先端科学から実装技術への発展を目指して-

    山方 啓( 担当: 共著 ,  範囲: 第3編第5章 光半導体による水分解の反応機構 時間分解分光測定を用いた光触媒のキャリアーダイナミクス)

    ㈱NTS  2017年1月 

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    担当ページ:p158-167  

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  • 触媒の設計・反応制御 事例集-高活性、長寿命、低コスト化の実現-

    山方 啓( 担当: 共著 ,  範囲: 第8節 赤外分光法を用いた光触媒・光電極反応の解析)

    ㈱技術情報協会  2013年4月 

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    担当ページ:P761-769  

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  • 人工光合成 実用化に向けた最新技術~水素利用・有機物合成・エネルギー・CO2還元~

    山方 啓( 担当: 共著 ,  範囲: 第6章第3節 光励起キャリアーの動きから見る水分解光触媒と水素貯蔵)

    ㈱情報機構  2013年3月 

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    担当ページ:p235-247  

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  • 触媒技術の動向と展望2010

    山方 啓( 担当: 共著 ,  範囲: 第3-8章 時間分解赤外分光法を用いた触媒反応ダイナミクス -光触媒の光励起ダイナミクス-)

    触媒学会  2010年4月 

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    担当ページ:p78-88  

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  • 太陽電池と部材の開発・製造技術~構造・プロセスから見る、耐久性向上・高効率化を目指した各種事例~

    山方 啓( 担当: 共著 ,  範囲: 第4-3項 太陽電池用TiO2透明導電膜の製造技術)

    ㈱情報機構  2010年3月 

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    担当ページ:p227-236  

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  • 色材・顔料・色素の設計と開発ー発色・着色メカニズムから各種応用製品まで

    山方 啓( 担当: 共著 ,  範囲: 第2-4章 酸化チタン)

    ㈱情報機構  2008年2月 

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    担当ページ:p267-280  

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MISC

  • Inorganic assembly catalysts for artificial photosynthesis: general discussion 査読

    Hiromu Kumagai, Leif Hammarstrom, Dong Ryeol Whang, Yuki Shinohara, Jose Martinez, Joshua Karlsson, Peter Summers, Christopher D. Windle, Masanori Kodera, Richard Cogdell, Kristine Rodulfo Tolod, Dogukan Hazar Apaydin, Etsuko Fujita, Alexander Kibler, Fengtao Fan, Elizabeth A. Gibson, Hisanao Usami, Akihide Iwase, Haruo Inoue, Akihiko Kudo, Devens Gust, Kazunari Domen, Flavia Cassiola, Katsuhiko Takagi, Sang Ook Kang, Akira Yamakata, Can Li, Licheng Sun, Hyunwoong Park, Young Soo Kang, Rengui Li, Fabio Di Fonzo, Tohru Setoyama, Osamu Ishitani

    FARADAY DISCUSSIONS   198   481 - 507   2017年6月

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    記述言語:英語   出版者・発行元:ROYAL SOC CHEMISTRY  

    DOI: 10.1039/c7fd90018j

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  • 「研究現場発」【光触媒を使って水素を製造する】山方 啓

    中部経済新聞   2014年9月

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    掲載種別:記事・総説・解説・論説等(商業誌、新聞、ウェブメディア)  

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  • 「拓く研究人」【光触媒で水素安く合成】 山方 啓

    日刊工業新聞   2014年5月

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    掲載種別:記事・総説・解説・論説等(商業誌、新聞、ウェブメディア)  

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  • Research Highlights 国際誌

    Nature Chemistry   13 ( 8 )   1453 - 1456   2013年

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    記述言語:英語  

    2010年5月7日号で “疎水界面に親水性・疎水性イオンが接近する際の水分子の構造変化を調べた研究成果(J. Phys. Chem. Lett. 1, 1487-1491, 2010)” が Research Highlights として紹介された。

    DOI: 10.1039/c3lc90018e

    Scopus

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  • 光励起キャリアーの動きとエネルギー制御

    山方啓

    化学経済   58 ( 14 )   75   2011年12月

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  • Hydrogen Evolution Reaction Catalyzed by 4,4'-Bipyridine Adsorbed on Metal Electrodes: A Combined Infrared and DFT Study 査読

    Taro Uchida, Akira Yamakata, Yoichi Sasaki, Masatoshi Osawa

    ECS Meeting Abstracts   2011年5月

  • News Letter 国際誌

    社団法人日本臓器移植ネットワーク

    Photonics Spectra Magazine   2010年7月

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    2006年7月号で “電極界面をパルスレーザーで高速加熱して誘起される界面水分子の配向変化をピコ秒時間分解観察した研究成果(J. Phys. Chem. B.(Letter) 110, 6423-6427, 2006)” が News Letter として紹介された。

    CiNii Article

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  • 電極表面に吸着した4,4’ビピリジンが触媒する水素発生促進反応機構

    内田太郎, 山方啓, 佐々木陽一, 大澤雅俊

    電気化学秋季大会講演要旨集   2009   2009年

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  • Ag電極に吸着した4,4’-ビピリジンの酸化還元サイクルが触媒する水素発生反応

    内田太郎, 山方啓, 佐々木陽一, 大澤雅俊

    日本化学会講演予稿集   89th ( 1 )   2009年

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  • Enhanced Hydrogen Evolution Reaction on an Ag Electrode Catalyzed by Proton-coupled Redox of 4,4'-Bipyridine Adsorbed on the Surface 査読

    Uchida, T, Mogami, H, Yamakata, A, Sasaki, Y, Osawa, M

    ECS Meeting Abstracts   2008年

  • 電極表面への4,4′-ビピリジンの吸着に伴なう水素発生の促進:表面増強赤外吸収分光による検討

    内田太郎, 山方啓, 大澤雅俊

    電気化学会大会講演要旨集   74th   2007年

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  • ビピリジン電極修飾による電解水素発生の促進効果

    内田太郎, 山方啓, 大澤雅俊

    触媒討論会討論会A予稿集   100th   2007年

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  • 表面増強赤外吸収分光による吸着水素が関与した4,4′-ビピリジンの酸化還元反応の追跡

    内田太郎, 山方啓, 大澤雅俊

    日本化学会北海道支部研究発表会講演要旨集   2007   2007年

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講演・口頭発表等

  • 高速赤外分光を用いる光励起キャリアの挙動および光触媒反応機構の解明 招待

    山方 啓

    日本化学会第103春季年会  2023年3月22日 

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    開催年月日: 2023年3月25日

    会議種別:口頭発表(招待・特別)  

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  • The role of oxygen vacancies for the enhancement of photocatalytic activity 招待

    Akira Yamakata, Kosaku Kato

    International Congress on Pure & Applied Chemistry Kota Kinabalu (ICPAC Kota Kinabalu 2022) 

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    開催年月日: 2022年11月22日 - 2022年11月27日

    会議種別:口頭発表(招待・特別)  

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  • 時間分解分光計測による光触媒の高活性化因子の解明 招待

    山方 啓

    2022年電気化学秋季大会 

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    開催年月日: 2022年9月8日 - 2022年9月9日

    会議種別:口頭発表(招待・特別)  

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  • Defects for the Enhancement of Photocatalytic Activity 招待

    Akira Yamakata

    The 28th North American Catalysis Society Meeting  2023年6月 

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    会議種別:口頭発表(招待・特別)  

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  • Observation of Free Carriers in Non-Fullerene Acceptors with Broadband Mid-Infrared Transient Absorption Spectroscopy 招待

    Akira Yamakata, Kosaku Kato, T. Urakami, M. Higashi, H. Sato, T. Umeyama, H. Imahori

    243rd Meeting of the Electrochemical Society  2023年5月 

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    会議種別:口頭発表(招待・特別)  

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  • 時間分解分光計測を利用した高性能光触媒の開発 招待

    山方 啓

    界面科学コロキウム「光物質変換をささえる分光計測」  2022年12月14日 

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    会議種別:口頭発表(招待・特別)  

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  • Properties of Defects That Determine the Charge Carrier Dynamics in Photocatalysts 招待

    Akira Yamakata, Kosaku Kato, U. Uemura, K. Asakura

    241st Meeting of the Electrochemical Society  2022年5月 

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    会議種別:口頭発表(招待・特別)  

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  • 高性能光触媒の実現を目指した反応機構の解明 招待

    山方啓

    光化学協会応用講座2021-社会実装が進む光触媒:基礎から人工光合成、新型コロナ対応まで-  2022年1月24日 

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    会議種別:口頭発表(招待・特別)  

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  • 太陽光を使って水から水素を製造できる光触媒の研究 招待

    山方啓

    2021年度南山大学・豊田工業大学連携講演会  2021年11月28日 

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    会議種別:口頭発表(招待・特別)  

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  • 時間分解分光計測を利用した光触媒の高活性化因子の解明 招待

    山方啓

    2021年度日本表面真空学会中部支部研究会「金属酸化物表面の成長・反応・計測」  2021年11月13日 

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    会議種別:口頭発表(招待・特別)  

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  • Behavior of Photocarriers for the Remarkable Water Splitting Photocatalysts 招待

    Akira Yamakata, Kosaku Kato

    The 11th Asian Photochemistry Conference (APC 2021)  2021年11月3日 

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    会議種別:口頭発表(招待・特別)  

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  • Charge Carrier Dynamics at the Heterojunctions Studied by Transient Absorption Spectroscopy 招待

    Akira Yamakata, Kosaku Kato

    The 11th International Conference on Flexible and Printed Electronics (ICFPE) 2021  2021年10月1日 

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    会議種別:口頭発表(招待・特別)  

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  • (2020年度光化学協会賞 受賞講演) Development of novel transient absorption spectroscopy and reaction dynamics for highly efficient photocatalysis 招待

    山方啓

    2021年光化学討論会  2021年9月16日 

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    会議種別:口頭発表(招待・特別)  

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  • Core-shell Double Doping for the Remarkable Photocatalytic Water Splitting on Ga2O3 招待

    Akira Yamakata, Junie Jhon M. Vequizo, Kosaku Kato, Yoshihisa Sakata

    Light Energy Conversion with Metal Halide Perovskites, Semiconductor Nanostructures, and Inorganic/Organic Hybrid Materials symposium at 239th Meeting of the Electrochemical Society  2021年6月4日 

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  • 半導体光触媒粒子中の欠陥が及ぼす光励起キャリアの再結合促進と抑制効果 招待

    山方啓

    光機能材料研究会 第81回講演会 「光触媒材料の設計開発と光触媒反応解析の最新動向」  2021年3月1日 

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    会議種別:口頭発表(招待・特別)  

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  • 広帯域時間分解分光による動的エキシトン時間発展の追跡 招待

    山方啓

    科研費・学術変⾰領域研究(A) 「動的エキシトン」 公募説明会・Kick‐off領域会議  2021年1月12日 

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    会議種別:口頭発表(招待・特別)  

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  • Behavior of Photogenerated Charge Carriers on Powder Photocatalysts 招待

    山方 啓

    Materials Research Meeting 2019  2019年12月11日 

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    記述言語:英語  

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  • Defects-induced enhancement of photocatalytic activity of Ga2O3 studied by time-resolved visible to mid-IR absorption spectroscopy 招待

    山方 啓

    The 36th International Japan-Korea Seminar on Ceramics (JK-Ceramics 36)  2019年11月22日 

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    記述言語:英語  

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  • レーザー分光を用いた光触媒反応機構の解明 招待

    山方 啓

    第29回キャラクタリゼーション講習会「触媒および表面の解析に役立つキャラクタリゼーションの基礎と実際」  2019年11月21日 

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    記述言語:日本語  

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  • Enhancement of photocatalytic activity of Ga2O3 by impurity doping 招待

    Akira Yamakata, Junie Jhon, M. Vequizo, Shouta Ishiyama, Taishi Hiramine, Yoshihisa Sakata

    The 13th Pacific Rim Conference of Ceramic Societies (PACRIM13)  2019年10月29日 

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    記述言語:英語  

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  • Charge Carrier Dynamics on Powder Photocatalysts Studied by Time-resolved Visible to Mid-IR absorption 招待

    Akira Yamakata, Junie Jhon, M. Vequizo

    International Conference on Photochemistry and Sustainable Energy (ICPSE 2019)  2019年10月19日 

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    記述言語:英語  

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  • Enhancement of photocatalytic activity of Ga2O3 based photocatalysts studied by time-resolved absorption spectroscopy 招待

    山方 啓

    The 24th International Conference on Semiconductor Photocatalysis and Solar Energy Conversion (SPASEC-24)  2019年10月14日 

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    記述言語:英語  

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  • Impurity Induced Enhancement of Photocatalytic Activity on Ga2O3 招待

    山方 啓

    International Congress on Pure & Applied Chemistry (ICPAC) Yangon 2019  2019年8月7日 

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  • Behaviour of Photogenerated Charge Carriers at the Defects on Photocatalysts 招待

    山方 啓

    The First Symposium on Photo (electro) catalysis (SOP-1)  2019年6月23日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Defects for the Enhancement of Photocatalytic Activity 招待

    Akira Yamakata, Junie Jhon, M. Vequizo, Shouta Ishiyama, Taishi Hiramine, Yoshihisa Sakata

    International Conference on Photocatalysis and Photoenergy 2019 (ICoPP2019)  2019年5月24日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 高性能光触媒の設計を目指した反応機構の解明 招待

    山方 啓

    中央大学理工学部・研究セミナー  2019年1月22日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Curious Behaviors of Photogenerated Charge Carriers at the Defects on Powder Photocatalysts 招待

    山方 啓

    (Keynote) International Workshop on Crystalline Materials and Applications (IWCMA-2019)  2019年1月3日 

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    記述言語:英語   会議種別:口頭発表(基調)  

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  • 時間分解分光測定による高活性光触媒反応のメカニズム解明 招待

    山方 啓

    熊本大学工学部研究セミナー  2018年12月5日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Time-Resolved Visible to mid-IR Absorption Study of Photodynamics on Powder Photocatalysts 招待

    山方 啓

    Research Seminar at National Chiao Tung University  2018年11月20日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Curious Behavior of Photogenerated Electrons and Holes in Single-crystalline and Powder Photocatalysts 招待

    山方 啓

    Research Seminar at National Chung Hsing University  2018年11月19日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Time-resolved Absorption Study on the Behavior of Photogenerated Electrons and Holes in Highly Active Photocatalysts 招待

    Akira Yamakata, Junie Jhon, M. Vequizo

    Functional Ceramics forum for the upcoming Annual Materials Science Conference  2018年11月17日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 高活性光触媒の実現を目指した新しい分光測定技術の開発 招待

    山方 啓

    第11回ワークショップ 固体材料合成および評価技術の新展開  2018年11月12日 

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    記述言語:日本語   会議種別:口頭発表(基調)  

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  • ポンププローブ法による界面ダイナミクス 招待

    山方 啓

    2018年電気化学会関東支部セミナー 先端計測技術による電極界面分析の新展開  2018年11月9日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 過渡吸収分光測定を用いた光触媒粒子の光励起ダイナミクス 招待

    山方 啓

    第49回中部化学関係学協会支部連合秋季大会  2018年11月4日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 時間分解分光測定を利用した高活性光触媒の反応機構解明 招待

    山方 啓

    第31回 日本セラミックス協会 秋季シンポジウム 特定セッション「先進的な構造科学と分析技術」  2018年9月5日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Behavior of Photogenerated Charge Carriers on Highly Efficient Photocatalysts 招待

    Akira Yamakata, Junie Jhon, M. Vequizo

    The 8th Advanced Functional Materials and Devices (AFMD 2018)  2018年8月18日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Effects of Surface Defects on Powder Photocatalysts Studied by Time-resolved Visible to Mid-IR Absorption Spectroscopy 招待

    Akira Yamakata, Junie Jhon, M. Vequizo

    International Workshop on Water Splitting: Challenges and Opportunity  2018年8月4日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • The Role of Powder Defects for Efficient Photocatalytic Reactions 招待

    山方 啓

    (Keynote) The 22nd International Conference on Photochemical Conversion and Storage of Solar Energy (IPS-22)  2018年8月1日 

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    記述言語:英語   会議種別:口頭発表(基調)  

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  • Defects Induced Enhancement of Ga2O3 Based Photocatalysts Studied by Time-Resolved Absorption Spectroscopy 招待

    Akira Yamakata, Junie Jhon, M. Vequizo, Yoshihisa Sakata

    2018 International Symposium on Advancement and Prospect of Catalysis Science & Technology  2018年7月26日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • How the Defects Affects the Photocatalytic Activity on Powder and Single crystalline TiO2 招待

    山方 啓

    International Conference on Ceramic Materials and Components for Energy and Environmental Applications (CMCEE-12)  2018年7月23日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Trapping-Induced Enhancement of Photocatalytic Activity on TiO2 Powders 招待

    Akira Yamakata, Junie Jhon, M. Vequizo

    International Congress on Pure & Applied Chemistry (ICPAC) 2018  2018年3月7日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Behaviors of Photogenerated Electrons and Holes on TiO2 Powder Photocatalysts 招待

    山方 啓

    The 22nd International Conference on Semiconductor Photocatalysis & Solar Energy Conversion (SPASEC-22)  2017年11月14日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Behaviors of Electrons and Holes in Photocatalysts Studied by Time-resolved Visible to Mid-IR Absorption Spectroscopy 招待

    山方 啓

    International Conference on Photochemistry and Its Applications (ICPA 2017)  2017年11月11日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Mechanism of Photocatalytic Reactions on TiO2 Powders 招待

    山方 啓

    (Plenary) 19th SPVM National Physics Conference, 2017 ASEAN Conference on Advanced Functional Materials and Nanotechnology (ASEAN-AFMN), and 5th International Meeting on Complex Systems (IMCS)  2017年10月21日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Impact of Metal Ion Doping on Ga2O3 Photocatalysts Studied by Transient Absorption Spectroscopy 招待

    Junie Jhon, M. Vequizo, Akira Yamakata

    2017 ASEAN Conference on Advanced Functional Materials and Nanotechnology (ASEAN-AFMN)  2017年10月19日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 金属酸窒化物複合アニオン型光触媒のキャリアーダイナミクス 招待

    山方 啓

    新学術領域研究 (平成28〜32年度) 複合アニオン化合物の創製と新機能 第2回トピカル会議 (機能)  2017年8月7日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Reaction dynamics at the liquid/solid soft-interfaces 招待

    山方 啓

    科研費新学術領域研究・柔らかな分子系国際シンポジウム  2017年6月27日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Behaviors of Photogenerated Electrons and Holes in Photoelectrochemical Interfaces 招待

    山方 啓

    International Symposium on Pure & Applied Chemistry (ISPAC) 2017  2017年6月8日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Dynamics of Photocarriers of Brookite TiO2 Studied by Spectroscopic Techniques: A Comparison with Anatase and Rutile TiO2 Photocatalysts 招待

    Junie Jhon, M. Vequizo, Hironori Matsunaga, Teruhisa Ohno, ○Akira Yamakata

    第26回日本MRS年次大会  2016年12月20日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 新しい分光技術を利用した光触媒反応の機構解明 招待

    山方 啓

    山口大学 光・エネルギー研究センターシンポジウム 光科学が生み出す新しい世界-光制御と分光技術の最前線-  2016年12月14日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 時間分解分光測定を利用した金属微粒子を担持した光触媒のキャリアーダイナミクス 招待

    山方 啓

    第36回表面科学学術講演会  2016年11月30日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Dynamics of Photocarriers of Metal Nitrides/Oxynitrides Studied by Transient Absorption Spectroscopy: Controlling the Effects of Defects 招待

    Junie Jhon, M. Vequizo, Akira Yamakata, Mirabbos Hojamberdiev, Kenta Kawashima, Hajime Wagata, Kunio Yubuta, Shuji Oishi, Kazunari Domen, Katsuya Teshima

    2016 International Conference on Materials Science and Nanotechnology (ICMSN)  2016年10月21日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 半導体光触媒の光励起ダイナミクス 招待

    山方 啓

    第2回 半導体による太陽光-水素エネルギー変換技術研究会  2016年10月13日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Curious Behaviors of Photogenerated e- and h+ in Anatase and Rutile TiO2 Powders 招待

    山方 啓

    IKM International Symposium on Pure & Applied Chemistry (ISPAC) 2016  2016年8月17日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Behavior of Photogenerated Electrons and Holes on Anatase and Rutile TiO2 Powders 招待

    山方 啓

    Collaborative Conference on 3D and Materials Research (CC3DMR) 2016  2016年6月22日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Behaviors of Photogenerated Charge Carriers in Single-Crystalline and Polycrystalline Powder SrTiO3 招待

    山方 啓

    2015 EMN Meeting on Photocatalysis (Energy Materials Nanotechnology)  2015年11月23日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Control of behavior and energy state of photogenerated charge carriers on photocatalysts 招待

    山方 啓

    JSTさきがけ「光エネルギーと物質変換」領域研究成果報告会  2015年3月26日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 時間分解分光測定を利用した光触媒の開発 招待

    山方 啓

    第32回無機材料に関する最近の研究成果発表会  2015年1月26日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 時間分解赤外分光法を用いた光触媒反応ダイナミクス 招待

    山方 啓

    平成26年度日本分光学会中部支部講演会 (愛知地区)  2014年12月24日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Behavior of Photogenerated Charge Carriers on Transition Metal Doped Visible-light Responsive SrTiO3 Photocatalysts 招待

    山方 啓

    Vietnam Malaysia International Chemical Congress (VMICC)  2014年11月7日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 光励起キャリアーの動きを制御した光触媒の開発 招待

    山方 啓

    日本表面科学会中部支部研究会  2014年10月31日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Charge Carrier Dynamics on Visible-Light Responsive Water-Splitting Photocatalysts 招待

    山方 啓

    (Plenary) 16th Samahang Pisika ng Visayas at Mindanao (SPVM) National Physics Conference, 2014 International Conference on Applied Physics and Materials Science (ICAMS2014)  2014年10月24日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Behavior of Photogenerated Charge Carriers in the Visible Light Responsive Water Splitting LaTiO2N Photocatalysts Studied by Time-Resolved Visible to mid-IR Absorption Spectroscopy 招待

    山方 啓

    UK-Japan Solar Driven Fuel Synthesis Workshop: Materials, Understanding and Reactor Design  2014年9月18日 

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    記述言語:英語   会議種別:ポスター発表  

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  • Electron and Hole Transfer from Photocatalyst to Cocatalysts Studied by Time-resolved Absorption Spectroscopy 招待

    Akira Yamakata, Masayuki Kawaguchi, Jun Kubota, Kazunari Domen

    International Peradeniya University Research Sessions (iPURSE)  2014年7月4日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Behavior of Photogeneraged Charge Carriers in Water Splitting Photocatalysts Studied by Timeresolved Absorption Spectroscopy 招待

    Akira Yamakata, Masayuki Kawaguchi, Jun Kubota, Kazunari Domen

    EMN Spring Meeting (Energy Materials Nanotechnology) 2014  2014年3月1日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 可視から赤外域の過渡吸収測定による光触媒反応の機構解明 招待

    山方 啓

    学術講演会 (神戸大学)  2014年1月30日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Real-time observation of destruction of hydration shells around several cations at electrochemical interface 招待

    山方 啓

    Seventh International Conference on Advanced Vibrational Spectroscopy (ICAVS-7)  2013年8月29日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Real-time observation of destruction processes of hydrophobic hydration shells at the electrified hydrophobic interface 招待

    山方 啓

    The 15th Asian Chemical Congress (15ACC)  2013年8月22日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 光触媒を利用した化学反応 招待

    山方 啓

    名工大オープンキャンパス4大学合同アフタヌーンセミナー  2013年6月15日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 光触媒反応の時間分解赤外分光観察 招待

    山方 啓

    第43回中部化学関係学協会支部連合秋季大会  2012年11月10日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Time-resolved IR absorption study on water-splitting photoelectrodes 招待

    Akira Yamakata, Masaaki Yoshida, Jun Kubota, Masatoshi Osawa, Kazunari Domen

    Cambodian Malaysian Chemical Conference (CMCC) 2012  2012年10月19日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Dynamics of photogenerated electrons in GaN photoelectrochemical systems 招待

    Akira Yamakata, Masaaki Yoshida, Jun Kubota, Masatoshi Osawa, Kazunari Domen

    17th Malaysian Chemical Congress (17MCC)  2012年10月15日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 赤外分光法を用いた光触媒反応の解析 招待

    山方 啓

    第22回キャラクタリゼーション講習会 -触媒および表面のキャラクタリゼーションの原理と実例ー  2012年10月12日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • FD講習を受けた二年目の常微分方程式 招待

    山方 啓

    FD推進ワークショップ  2012年8月8日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 時間分解赤外分光法でみた光触媒のキャリアーダイナミクス 招待

    山方 啓

    ISSP ワークショップ 「表面・界面における輸送と変換」  2012年7月13日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Development and Mechanism of Water Splitting Photocatalysts 招待

    山方 啓

    Seminar at Department of Electrical Engineering, National Chung Hsing University  2012年6月25日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Real-time Observation of Destruction of Hydration Shells at Electrified Interfaces 招待

    山方 啓

    Workshop on Exploring the Structures and Dynamics of Water at Interfaces  2012年6月22日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 電極表面に固定したKcsAの構造変化 招待

    山方 啓, 清水 啓史, 大澤 雅俊, 老木 成稔

    第15回 ミニ公開シンポジウム イオンチャネル研究の現状とこれからについて考える  2012年1月24日 

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    記述言語:日本語  

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  • Surface-enhanced IR study on the dynamics of hydration shells around several cations at the electrochemical interface 招待

    Akira Yamakata, Masatoshi Osawa

    The 14th Asian Chemical Congress 2011  2011年9月7日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Time-resolved IR absorption study on the destruction processes of hydration shells at electrode surfaces 招待

    Akira Yamakata, Masatoshi Osawa

    The 14th Asian Chemical Congress 2011 –Cambodia Satellite Meeting  2011年9月4日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Time-resolved surface-enhanced infrared absorption study on destruction of hydration shells at the electrochemical interface 招待

    山方 啓

    Symposium on Advanced Spectroscopy  2010年10月8日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 固液界面における溶質の水和殻崩壊過程の赤外分光観察 招待

    山方 啓, 大澤 雅俊

    第106回触媒討論会  2010年9月17日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 時間分解赤外分光法を用いた触媒反応機構の解明 招待

    山方 啓

    第50回オーロラセミナー  2010年8月1日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 赤外分光法を用いた表面反応機構の解明 招待

    山方 啓

    2010年日本化学会北海道支部冬季研究発表会(北海道支部奨励賞受賞講演)  2010年1月27日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Structural changes of water layers between ions and a hydrophobic solid surface by their close contact 招待

    Akira Yamakata, Masatoshi Osawa

    The second Asian Spectroscopy Conference  2009年11月30日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Reaction dynamics on catalysis studied by time-resolved IR absorption spectroscopy 招待

    山方 啓, 大澤 雅俊

    日本分光学会年次講演会 (日本分光学会奨励賞受賞講演)  2009年11月16日 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 固液界面における準束縛溶媒分子の配向緩和ダイナミクス 招待

    山方 啓

    特定領域研究高次系分子科学公開シンポジウム  2009年11月 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Orientation Dynamics of Solvent Molecules on Liquid/Solid Interfaces 招待

    山方 啓

    特定領域研究高次系分子科学公開シンポジウム  2009年6月 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 赤外分光・和周波発生分光法を用いた電極界面分子のダイナミクス 招待

    山方 啓

    科研費特定領域研究 高次系分子科学 第6回ミニ公開シンポジウム 表面・界面を観る非線形分光の新しい展開  2009年3月24日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 電極界面における水分子の反応とダイナミクス 招待

    山方 啓

    触媒学会北海道地区札幌講演会 「触媒研究の近未来を語る」  2008年12月10日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 時間分解赤外分光法を用いた電極表面に固定したタンパク質の構造とダイナミクス 招待

    山方 啓

    ミニ公開シンポジウム イオンチャネルの構造ダイナミクス  2008年7月8日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 時間分解赤外分光法を用いた電極・触媒表面ダイナミクスの追跡 招待

    山方 啓

    神戸大学セミナー  2007年11月 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Probing Ultrafast Electrode Dynamics by Picosecond Time-Resolved Surface-Enhanced Infrared Spectroscopy 招待

    Akira Yamakata, Jun Kubota, Masatoshi Osawa

    Workshop on Electrocatalysis: Surface science approaches  2006年10月 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • Picosecond Time-resolved Surface Enhanced IR Absorption Study on Electrochemical Interface 招待

    Akira Yamakata, Jun Kubota, Masatoshi Osawa

    Seminar at Department of Chemical Physics of Fritz-Haber-Institut der Max-Planck-Gesellschaft  2006年7月 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 時間分解赤外分光法を用いた二酸化チタン光触媒反応の観察 招待

    山方 啓

    第4回東京工業大学資源化学研究所フォーラム  2005年3月 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 時間分解赤外分光法でみた光触媒反応ダイナミクス 招待

    山方 啓

    上智大学物理学科談話会  2005年3月 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 時間分解赤外分光法を用いた二酸化チタン光触媒反応中間体の観察 招待

    山方 啓

    第24回表面科学講演大会  2004年11月 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 赤外分光法を用いた酸化チタン参照触媒の光励起ダイナミクス 招待

    山方 啓, 石橋 孝章, 大西 洋

    第25回参照触媒討論会  2004年9月26日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 時間分解赤外分光法を用いた二酸化チタン光触媒反応中間体の観察 招待

    山方 啓

    第21回ライラックセミナー・第10回若手研究者交流会  2004年6月 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • 二酸化チタン新規参照触媒の時間分解赤外分光測定 招待

    山方 啓, 石橋 孝章, 大西 洋

    第24回参照触媒討論会  2003年9月17日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • Time-resolved Infrared Study of Photocatalytic Reactions on TiO2 Particles 招待

    Akira Yamakata, Taka-aki Ishibashi, Hiroshi Onishi

    Seminar at Department of Physical Chemistry of Fritz-Haber-Institut der Max-Planck-Gesellschaft  2003年6月 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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  • 酸化チタン参照触媒の時間分解赤外分光測定 招待

    山方 啓, 石橋 孝章, 大西 洋

    第23回参照触媒討論会  2002年9月17日 

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    記述言語:日本語   会議種別:口頭発表(招待・特別)  

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  • The Reactions of Photogenerated Carriers on Photocatalysts Studied by Time-resolved IR Spectroscopy 招待

    Akira Yamakata, Taka-aki Ishibashi, Hiroshi Onishi

    CRC International Symposium on photochemistry @interfaces  2002年8月 

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    記述言語:英語   会議種別:口頭発表(招待・特別)  

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▼全件表示

産業財産権

  • 構造物及びその製造方法

    山方啓, Junie Jhon, M. Vequizo, Chandana Sampath, Kumara Ranasinghe

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    出願番号:PCT国際特許 K04002US  出願日:2018年1月26日

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  • 構造物及びその製造方法

    山方啓, Junie Jhon, M. Vequizo, Chandana Sampath, Kumara Ranasinghe

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    出願番号:特願2017-013478  出願日:2017年1月27日

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  • 拡散反射配置による時間分解分光装置

    大西 洋, 山方 啓, 石橋 孝章

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    出願人:財団法人神奈川科学技術アカデミー, 独立行政法人科学技術振興機構

    出願番号:特願2003-392026  出願日:2003年11月21日

    公開番号:特開2005-156229  公開日:2005年6月16日

    J-GLOBAL

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  • 時間分解赤外分光法による光触媒の迅速評価法

    大西 洋, 山方 啓, 石橋 孝章

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    出願人:財団法人神奈川科学技術アカデミー

    出願番号:特願2002-371956  出願日:2002年12月24日

    公開番号:特開2004-205256  公開日:2004年7月22日

    J-GLOBAL

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受賞

  • 光化学協会賞

    2020年9月   光化学協会   新しい時間分解分光分析技術の開発と光触媒反応ダイナミクスの新展開

    山方 啓

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  • 豊田奨学基金研究進歩賞

    2020年3月   豊田工業大学   時間分解分光測定を利用した光触媒反応機構の解明

    山方 啓

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  • 2018年度前期教育優秀賞 (受講者30人以上の部)

    2018年11月   豊田工業大学  

    山方 啓

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  • Symposium Award

    2018年3月   International Congress on Pure & Applied Chemistry (ICPAC) 2018   "Trapping-Induced Enhancement of Photocatalytic Activity on TiO2 Powders"

    山方 啓

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  • 2017年度前期教育優秀賞 (受講者30人以上の部)

    2017年10月   豊田工業大学  

    山方 啓

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  • H26年度永井科学技術財団学術賞

    2015年3月   永井科学技術財団  

    山方 啓

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  • 豊田奨学基金研究奨励賞

    2014年3月   豊田工業大学   時間分解赤外分光法を用いた触媒表面反応の解析

    山方 啓

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  • 2013年度前期教育優秀賞 (受講者30人以上の部)

    2013年10月   豊田工業大学  

    山方 啓

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  • 2012年度前期教育優秀賞 (受講者30人以上の部)

    2012年10月   豊田工業大学  

    山方 啓

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  • 日本化学会北海道支部奨励賞

    2010年1月   日本化学会北海道支部   “赤外分光法を用いた表面反応機構の解明”

    山方 啓

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    受賞国:日本国

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  • 日本分光学会奨励賞

    2009年11月   “時間分解赤外分光法を用いた触媒表面反応ダイナミクス”

    山方 啓

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    受賞国:日本国

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  • 日本表面科学会奨励賞

    2004年11月   “時間分解赤外分光法を用いた二酸化チタン光触媒反応中間体の観察”

    山方 啓

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    受賞国:日本国

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▼全件表示

共同研究・競争的資金等の研究

  • 粉末系光触媒材料における欠陥の理解と制御

    2022年10月 - 2024年09月

    泉科学技術振興財団  研究助成 

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    担当区分:研究代表者 

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  • 反応機構に立脚した高活性可視光応答型光触媒の開発

    2022年06月 - 2023年03月

    八雲環境科学振興財団  環境研究助成 

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    担当区分:研究代表者 

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  • 広帯域時間分解分光による動的エキシトン時間発展の追跡

    研究課題/領域番号:20H05838  2020年11月 - 2025年03月

    日本学術振興会  科学研究費助成事業 学術変革領域研究(A)  学術変革領域研究(A)

    山方 啓

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    配分額:72930000円 ( 直接経費:56100000円 、 間接経費:16830000円 )

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  • 表面欠陥準位を制御した新しい光触媒の開発

    2020年11月 - 2021年10月

    ENEOS水素基金 

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  • 人工光合成を実現する異種接合界面の光励起ダイナミクス

    研究課題/領域番号:20H05117  2020年04月 - 2022年03月

    日本学術振興会  科学研究費助成事業 新学術領域研究(研究領域提案型)  新学術領域研究(研究領域提案型)

    山方 啓

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    配分額:6500000円 ( 直接経費:5000000円 、 間接経費:1500000円 )

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  • 異種接合光触媒界面の光励起ダイナミクス

    2020年01月 - 2020年12月

    豊田工業大学・学内競争的資金 研究促進費 

      詳細を見る

  • 欠陥準位を制御した高活性光触媒の開発

    2019年04月 - 2022年03月

    文科省  科研費・基盤研究B 

    山方 啓

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    担当区分:研究代表者  資金種別:競争的資金

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  • 複合アニオン化合物の光励起ダイナミクス

    2019年04月 - 2021年03月

    文科省  科研費・新学術領域研究 

    山方 啓

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    担当区分:研究代表者  資金種別:競争的資金

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  • 金属酸窒化物光触媒の光励起ダイナミクス

    2017年04月 - 2019年03月

    文科省  科研費・新学術領域研究 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 光触媒粒子のキャリアダイナミクス

    2017年04月 - 2018年03月

    北海道大学触媒科学研究所  共同利用・共同研究公募(戦略型) 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 原子層堆積装置を用いた光触媒の活性向上

    2016年10月 - 2017年09月

    豊田工業大学・学内競争的資金  研究促進費 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 表面欠陥の構造とエネルギーを制御した可視光応答型光触媒の高性能化

    2016年04月 - 2019年03月

    文科省  科研費・基盤研究B 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 柔らかな固液界面における化学反応ダイナミクス

    2016年04月 - 2018年03月

    文科省  科研費・新学術領域研究 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 粉末系光触媒の光励起ダイナミクス

    2016年04月 - 2017年03月

    北海道大学触媒科学研究所  共同利用・共同研究公募(課題設定型) 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 赤外分光を用いた酸化物光触媒の表面欠陥サイトの同定

    2015年04月 - 2016年03月

    東京工業大学資源化学研究所  物質・デバイス領域共同研究拠点共同研究 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 可視光応答型光触媒の開発

    2011年10月 - 2013年03月

    豊田工業大学・学内競争的資金  研究促進費 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 光励起キャリアーの動きとエネルギー制御

    2011年04月 - 2017年03月

    科学技術振興機構  さきがけ研究 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 固液界面での光励起キャリアダイナミクスに基づいた革新的水分解光触媒の開発

    2011年04月 - 2016年03月

    文科省  科研費・特別推進研究 

    堂免 一成

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    資金種別:競争的資金

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  • 可視光応答型光触媒のキャリア制御

    2011年04月 - 2015年03月

    文科省  科研費・基盤研究B 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 次代を担う超高効率集光型太陽光発電の日欧共同研究開発 (NGCPV)

    2011年04月 - 2014年10月

    NEDO  革新的太陽光発電技術研究開発プロジェクト 

    山口 真史

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    資金種別:競争的資金

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  • ピコ秒時間分解赤外分光法を用いた可視光型光触媒の光励起キャリアーダイナミクス

    2011年04月 - 2012年03月

    豊田理研スカラー  研究助成 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 酸化物半導体のバンドギャップ制御と光励起キャリアーの長寿命化

    2011年04月 - 2012年03月

    日本板硝子材料工学助成会  研究助成 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 電極界面におけるイオンの水和構造ダイナミクス

    2010年04月 - 2012年03月

    文科省  科研費・特定領域研究 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 固液界面における準束縛溶媒分子の配向緩和ダイナミクス

    2008年04月 - 2010年03月

    文科省  科研費・特定領域研究 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 高活性水素発生電極触媒の開発と機構解明

    2007年10月 - 2008年03月

    北海道大学GCOEプログラム  若手教員イノベーション事業 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 超高速電位ジャンプ法を用いた電子移動・電極反応ダイナミクスの赤外分光解析

    2007年04月 - 2010年03月

    文科省  科研費・若手研究A 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 会議名【210th Electrochemical Society (ECS) Meeting】・メキシコ

    2006年10月

    電気化学会  海外渡航費用 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 固液界面反応の赤外分光イメージング

    2006年04月 - 2008年03月

    文科省  科研費・基盤研究B 

    大澤 雅俊

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    資金種別:競争的資金

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  • ピコ秒時間分解表面増強振動分光法を用いた電極表面キャリアーダイナミクス

    2006年04月 - 2008年03月

    文科省  科研費・特定領域研究 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 赤外表面増強場を用いた振動誘起表面反応の制御

    2005年04月 - 2007年03月

    文科省  科研費・若手研究B 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 触媒学会参照触媒酸化チタンを利用する光触媒の標準化

    2004年04月 - 2005年03月

    文科省  科研費・基盤研究C 

    岡本康昭

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    資金種別:競争的資金

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  • 会議名【11th International conference on Time-resolved Vibrational Spectroscopy】・ イタリア

    2003年06月

    吉田科学振興財団  海外渡航費用 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 光励起キャリアーの動的過程を観測した光触媒活性評価法の確立と触媒探索への応用

    2003年04月 - 2005年03月

    文科省  科研費・萌芽研究 

    山方 啓

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    担当区分:研究代表者  資金種別:競争的資金

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  • 微小電極界面における高速反応ダイナミクスの振動分光解析

    2002年04月 - 2005年03月

    文科省  科研費・基盤研究A 

    大澤 雅俊

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    資金種別:競争的資金

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  • 和周波分光法と赤外吸収分光法を用いたイオン液体(常温溶融塩)の界面分子構造の研究

    2002年04月 - 2004年03月

    文科省  科研費・基盤研究B 

    大西 洋

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    資金種別:競争的資金

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  • アナターゼ型およびルチル型二酸化チタン単結晶薄膜の合成と原子スケール評価

    2002年04月 - 2003年03月

    文科省  科研費・特定領域研究 公募 

    大西 洋

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    資金種別:競争的資金

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  • 会議名【International Conference of Vibrations at Surfaces 10】・フランス

    2001年06月

    新世代研究所  海外渡航費用 

    山方 啓

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

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  • 時間分解マルチプレックス表面和周波分光装置の開発

    2001年04月 - 2004年03月

    文科省  科研費・基盤研究B 

    石橋 孝章

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    資金種別:競争的資金

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  • 時間分解赤外分光法による光触媒上の励起キャリアーによる吸着分子の反応過程観察

    2000年04月 - 2002年03月

    文科省  科研費・奨励研究A 

    山方 啓

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    担当区分:研究代表者  資金種別:競争的資金

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  • 赤外反射吸収分光法による反応条件下の表面反応の研究

    1998年04月 - 1999年03月

    文科省  科研費・特別研究員奨励費 

    山方 啓

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    担当区分:研究代表者  資金種別:競争的資金

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担当授業科目

  • イノベーション特論 (2022年度) 夏季集中

  • 一般化学1 (2022年度) 第3学期  - 金1~2

  • 一般化学1 (2022年度) 第3学期  - 金1~2

  • 先端表面物理化学 (2022年度) 後期  - その他

  • 化学実験法3 (2022年度) 第3学期

  • 教養化学実験 (2022年度) 第4学期  - 木5〜8

  • 教養現代化学A1 (2022年度) 第1学期  - 火1~2

  • 表面物理化学演習 (2022年度) 通年  - その他

  • 表面物理化学特論 (2022年度) 後期  - 火3~4

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メディア報道

  • プラズモンを用いたエネルギーアップコンバージョン -未使用エネルギー赤外光の活用方法に道- インターネットメディア

    京都大学化学研究所広報  2022年10月18日

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    執筆者:本人 

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  • 再生可能エネルギー実現の社会に向けて研究 新聞・雑誌

    タウンニュースてんぱくNo.823  2021年7月29日

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    執筆者:本人 

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  • 水・酸素から過酸化水素生成 九州工大と豊田工大、光触媒を開発 新聞・雑誌

    日刊工業新聞  日刊工業新聞  ニュースリリース  2021年6月11日

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    執筆者:本人以外 

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  • 水と酸素から過酸化水素を生成する高性能光触媒の開発に成功 ― 次世代燃料の製造プロセス開発に向けて ― インターネットメディア

    九州工業大学・豊田工業大学  2021年5月25日

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    執筆者:本人 

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  • 赤外光を電気エネルギーや信号に変換する無色透明な材料の開発 ―見えない電子デバイスの開発へ道― インターネットメディア

    京都大学化学研究所広報  2019年1月24日

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    執筆者:本人 

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  • 新しい赤外光誘起キャリア移動機構の発見 -赤外光のエネルギー利用に期待- インターネットメディア

    京都大学化学研究所広報  2018年6月13日

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    執筆者:本人 

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  • 拓く研究人【光触媒で水素安く合成】 新聞・雑誌

    日刊工業新聞  2014年5月28日

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    執筆者:本人 

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  • 「研究現場発」【光触媒を使って水素を製造する】 新聞・雑誌

    中部経済新聞朝刊  2014年5月28日

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    執筆者:本人 

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  • “光励起キャリアーの動きとエネルギー制御” 新聞・雑誌

    化学経済  2011年12月

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    執筆者:本人 

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