Faculty Profiles - Yamakata Akira

PubMed

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

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

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

Journal of Catalysis 390 81 - 89 2020.8

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 2020.8

Heteroatom Dopants Promote Two‐Electron O 2 Reduction for Photocatalytic Production of H 2 O 2 on Polymeric Carbon Nitride Reviewed

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 2020.6

Activation of a Pt-loaded Pb<inf>2</inf>Ti<inf>2</inf>O<inf>5.4</inf>F<inf>1.2</inf> photocatalyst by alkaline chloride treatment for improved H<inf>2</inf> evolution under visible light Reviewed

Wakayama, H., Kato, K., Kashihara, K., Uchiyama, T., Miyoshi, A., Nakata, H., Lu, D., Oka, K., Yamakata, A., Uchimoto, Y., Maeda, K.

Journal of Materials Chemistry A 8 ( 18 ) 9099 - 9108 2020.4

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

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 2020.4

How g-C3N4 Works and Is Different from TiO2 as an Environmental Photocatalyst: Mechanistic View

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 2020.1

Language：English Publishing type：Research paper (scientific journal) Publisher：NLM (Medline)

Graphitic carbon nitride (CN) as a popular visible light photocatalyst needs to be better understood for environmental applications. The behaviors of CN as an environmental photocatalyst were systematically studied in comparison with a well-known TiO2 photocatalyst. The two photocatalysts exhibit different photocatalytic oxidation (PCO) behaviors and dependences on the experimental conditions (e.g., pH, Pt loading, and the kind of organic substrate and scavenger). The PCO of organic substrates was significantly enhanced by loading Pt on TiO2 under UV light (λ &gt
320 nm), whereas Pt-CN exhibited a lower PCO activity than bare CN under visible light (λ &gt
420 nm). While the presence of Pt enhances the charge separation in both TiO2/UV and CN/visible light systems (confirmed by transient IR absorption spectroscopic analysis), the opposite effects of Pt are ascribed to the different mechanisms of •OH generation in the two photocatalytic systems. The negative effect of Pt on CN is ascribed to the fact that Pt catalytically decomposes in situ-generated H2O2 (a main precursor of OH radical), which hinders •OH production. The production of OH radicals on CN is favored only at acidic pH but 1O2 generation is dominant in alkaline pH. The pH-dependent behaviors of reactive oxygen species generation on CN were confirmed by electron paramagnetic resonance spin trap measurements.

DOI： 10.1021/acs.est.9b05044

PubMed

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

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

ACS Applied Energy Materials 3 ( 1 ) 1207 - 1214 2020.1

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

The fabrication of heterojunctions with different band gap semiconductors is a promising approach to increase photoelectrochemical (PEC) activity. The PEC activity is determined by the charge separation; hence, the behaviors of charge carriers at the junctions should be elucidated. However, it has been quite challenging since the distinction of carriers located in different layers has been extremely hard. In this work, we succeeded in the identification of the individual electron- and hole-transfer kinetics at CoOx/BiVO4/SnO2 double heterojunctions by measuring transient absorption (TA) from the visible to mid-IR region: we found that the absorption peaks of electrons and holes depend on the materials. From the change in spectral shape after the selective photoexcitation of BiVO4, it was confirmed that electrons excited in the BiVO4 rapidly transferred to the SnO2 layer after similar to 3 ps, but the holes remained in the BiVO4 and further transferred to CoOx in a few picoseconds. As a result, recombination of charge carriers was suppressed and 2.4 and 3.6 times a large amount of carriers are surviving at 5 mu s on BiVO4/SnO2 and CoOx/BiVO4/SnO2, respectively, compared to bare BiVO4. For such picosecond-rapid and effective charge separation, the previously well proposed sole intralayer or interlayer charge separation mechanism is not enough. Hence the synergetic effect of these two mechanisms, the band-bending-assisted charge transfer across the heterojunction, is proposed. The enhanced PEC activity of CoOx/BiVO4/SnO2 electrodes was reasonably explained by this synergistic charge separation kinetics. This fundamental knowledge of charge carrier dynamics will be beneficial for the design of superior solar energy conversion systems.

DOI： 10.1021/acsaem.9b02262

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 Reviewed

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 2020.1

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

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

Solar RRL 4 ( 8 ) 1900461 2020.1

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

Copolymerized carbon nitride nanosheets (NS-C3N4) are synthesized by heating a mixture of urea and 2-aminobenzonitrile (ABN) at 823 K for 2 h in air. The visible light-absorption capability of the copolymerized NS-C3N4 can be improved with an increase in the ABN content in the starting material, while maintaining the rather negative conduction band potential of NS-C3N4. With the aid of a ruthenium(II) complex catalyst, the copolymerized NS-C3N4 becomes active for CO2 reduction into formate (>90% selectivity) under visible light (lambda > 400 nm) in the presence of triethanolamine as an electron donor. The activity is enhanced with increasing the starting ABN content to reach a maximum at a certain amount, beyond which it declines. The optimized material, modified with a silver promoter and a phosphonate-functionalized ruthenium(II) catalyst, gives a high turnover number of 6000 (vs Ru catalyst) for formate production. Physicochemical analyses indicate that increasing the starting ABN concentration improves the visible light-absorption capability of the copolymerized NS-C3N4, but increases the number of trap states, which can work as recombination centers of photogenerated electrons and holes. Therefore, an appropriate adjustment of the ABN comonomer amount is essential to obtain copolymerized NS-C3N4, which shows high photocatalytic activity.

DOI： 10.1002/solr.201900461

How g-C3N4 Works and Is Different from TiO2 as Environmental Photocatalyst: Mechanistic View Reviewed International journal

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 2020.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Graphitic carbon nitride (CN) as a popular visible light photocatalyst needs to be better understood for environmental applications. The behaviors of CN as an environmental photocatalyst were systematically studied in comparison with a well-known TiO2 photocatalyst. The two photocatalysts exhibit different photocatalytic oxidation (PCO) behaviors and dependences on the experimental conditions (e.g., pH, Pt loading, and the kind of organic substrate and scavenger). The PCO of organic substrates was significantly enhanced by loading Pt on TiO2 under UV light (lambda > 320 nm), whereas Pt-CN exhibited a lower PCO activity than bare CN under visible light (lambda > 420 nm). While the presence of Pt enhances the charge separation in both TiO2/UV and CN/visible light systems (confirmed by transient IR absorption spectroscopic analysis), the opposite effects of Pt are ascribed to the different mechanisms of center dot OH generation in the two photocatalytic systems. The negative effect of Pt on CN is ascribed to the fact that Pt catalytically decomposes in situ-generated H2O2 (a main precursor of OH radical), which hinders center dot OH production. The production of OH radicals on CN is favored only at acidic pH but O-1(2) generation is dominant in alkaline pH. The pH-dependent behaviors of reactive oxygen species generation on CN were confirmed by electron paramagnetic resonance spin trap measurements.

DOI： 10.1021/acs.est.9b05044

PubMed

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

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

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：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

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

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

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

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 Reviewed

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

Chemical Engineering Journal 390 124616 - 124616 2020

Language：English Publishing type：Research paper (scientific journal) Publisher：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

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

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

Enhancement of photoelectrochemical activity of TiO<inf>2</inf> electrode by particulate/dense double-layer formation Invited Reviewed

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

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

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 Reviewed

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

Applied Catalysis B: Environmental 263 118333 - 118333 2020

Language：English Publishing type：Research paper (scientific journal) Publisher：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

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

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 2019.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

The atificial Z-scheme is a promising and rational strategy for solar-to-chemical energy conversion such as water-splitting. In the Z-scheme, backward redox processes are an essential drawback that should be overcome to increase its efficiency. Here, we demonstrate that the simple co-loading of Fe/Ru oxide, (Fe,Ru)O-x, onto various photocatalysts effectively improves the efficiency of water oxidation by suppressing the undesirable backward oxidation of the redox reagent Fe2+. The (Fe,Ru)O-x co-loading on Bi4TaO8Cl afforded the highest water-splitting activity (apparent quantum efficiency of 1.6% at 420 nm) among the Z-scheme systems employing mixed-anion compounds as O-2-evolving photocatalysts. The results of photoelectrochemical and electrochemical measurements along with time-resolved spectroscopy clarified the key roles of Fe/Ru oxide; the Ru oxide component functions as a "collector" of photogenerated carriers and active sites for surface redox reactions, while the Fe oxide component acts as a "blocker" against unfavorable Fe2+ oxidation. The versatile availability of Fe/Ru oxide has been demonstrated for other visible-light-responsive photocatalysts.

DOI： 10.1021/acsami.9b14802

Achievement of High Photocatalytic Performance to BaTi4O9 toward Overall H2O Splitting Reviewed

Yuichi Hiramachi, Hirotaka Fujimori, Akira Yamakata, Yoshihisa Sakata

ChemCatChem 11 ( 24 ) 6213 - 6217 2019.10

Publishing type：Research paper (scientific journal)

The improvement of photocatalytic activity of BaTi O to overall H O splitting was investigated. From the evaluation of co-catalysts, Rh Cr O was preferable. However, this co-catalyst was degrading with the progress of the photocatalytic reaction. When CoO was co-loaded as the co-catalyst for O evolution reaction over the surface, the steady progress of the photocatalytic reaction can be confirmed. Here, effective way and condition for loading CoO co-catalyst as well as effective preparation method of BaTi O were demonstrated in order to improve the photocatalytic activity of BaTi O with Rh Cr O and CoO co-catalysts to the overall H O splitting. As the results, the photocatalyst prepared by preferable method and condition showed high photocatalytic activity to the overall H O splitting, where the apparent quantum yield (AQY) at 313 nm reached to 41 %. 4 9 2 0.7 1.3 3 x 2 x 4 9 4 9 0.7 1.3 3 x 2 2

DOI： 10.1002/cctc.201901564