Faculty Profiles - Yamakata Akira

Papers - Yamakata Akira

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

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 2019.10

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

Mixed-anion compounds (e.g., oxynitrides and oxysulfides) are potential candidates as photoanodes for visible-light water oxidation, but most of them suffer from oxidative degradation by photogenerated holes, leading to low stability. Here we show an exceptional example of a stable, mixed-anion water-oxidation photoanode that consists of an oxyfluoride, Pb2Ti2O5.4F1.2, having a band gap of ca. 2.4 eV. Pb2Ti2O5.4F1.2 particles, which were coated on a transparent conductive glass (FTO) support and were subject to postdeposition of a TiO2 overlayer, generated an anodic photocurrent upon band gap photoexcitation of Pb2Ti2O5.4F1.2 (lambda <520 nm) with a rather negative photocurrent onset potential of ca. -0.6 V vs NHE, which was independent of the pH of the electrolyte solution. Stable photoanodic current was observed even without loading a water oxidation promoter such as CoOx,. Nevertheless, loading CoOx onto the TiO2/Pb2Ti2O5.4F1.2/FTO electrode further improved the anodic photoresponse by a factor of 2-3. Under AM1.5G simulated sunlight (100 mW cm(-2)), stable water oxidation to form O-2 was achieved using the optimized Pb2Ti2O5.4R1.2 photoanode in the presence of an applied potential smaller than 1.23 V, giving a Faradaic efficiency of 93% and almost no sign of deactivation during 4 h of operation. This study presents the first example of photoelectrochemical water splitting driven by visible-light excitation of an oxyfluoride that stably works, even without a water oxidation promoter, which is distinct from ordinary mixed-anion photoanodes that usually require a water oxidation promoter.

DOI： 10.1021/jacs.9b06570

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

Kosaku Kato, Junzhe Jiang, Yoshihisa Sakata, Akira Yamakata

ChemCatChem 11 ( 24 ) 6349 - 6354 2019.10

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

Photocatalytic water splitting by solar light is an environment-friendly means for generating hydrogen as energy resources. For practical use, photocatalysts with higher activity are desired. Recently it was found that the photocatalytic activity of SrTiO3 is remarkably improved by Na-doping. However, why Na-doping enhances the activity has not been well understood. In this work, we found that Na-doping in SrTiO3 introduces new mid-gap states. Transient absorption measurements revealed that photoexcited electrons were trapped into these states within similar to 20 ps after excitation. These trapped electrons have longer lifetime than those in undoped SrTiO3, and number of surviving electrons in microseconds increased similar to 15 times. These electrons are trapped at the mid-gap states, but still keep reactivity with reactant molecules. Furthermore, they were effectively captured by H-2-evolution cocatalyst, indicating that they can participate in steady-state reactions. This work emphasizes the important role of electron-trapping states introduced by doping on photocatalytic activity.

DOI： 10.1002/cctc.201901669

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

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

J. Mater. Chem. A 7 ( 45 ) 26139 - 26146 2019.10

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

Inducing oxygen vacancy defects in SrTiO3 powders via high temperature treatment in the presence of a mixture of Ar, O-2, dry air, and H-2 ambient gases is a promising strategy to produce homogeneously defective SrTiO3 photocatalysts with a remarkable 40-fold enhancement of H-2 evolution activity. Electron doping of SrTiO3 due to oxygen vacancies triggers the development of a highly active SrTiO3 photocatalyst; however, the photodynamic processes involved in these modifications of SrTiO3 have not been fully elucidated yet. In this work, we investigated the impact of high temperature treatment based on the dynamics of photocarriers by transient absorption spectroscopy (TAS). TAS results revealed that upon band gap excitation of SrTiO3, most of the photoexcited electrons in non-reduced SrTiO3 are deeply trapped in the intrinsic defects as evident from the strong broad absorption signals peaking at 11000 cm(-1) (909 nm, 1.36 eV) and 20000 cm(-1) (500 nm, 2.48 eV), whereas the absorption intensities in this wavenumber region largely decreased in highly reduced SrTiO3, suggesting a possible electron filling of deeply trapped states via reduction treatment (or electron doping). Interestingly, the photoexcited electrons in oxygen-deficient SrTiO3 preferably occupy the shallower electron traps. The lowest energy limit of the electron trap filled by photoexcited electrons is estimated to be at the absorption edge located at 1000 cm(-1) (similar to 0.12 eV below the conduction band), which is much shallower than that of non-reduced SrTiO3 (>0.7 eV). Furthermore, it was found that the electron population in the shallow traps in highly reduced SrTiO3 is nearly 2 orders of magnitude higher compared to that in non-reduced SrTiO3, indicating a large improvement in the electron lifetime. The findings herein offer significant insights into the crucial impact of the reduction of SrTiO(3)via induced oxygen vacancy defects to provide available photoexcited electrons that can be readily utilized for the H-2 generation reaction.

DOI： 10.1039/C9TA08216F

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

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 2019.7

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

Rutile TiO2 codoped with tantalum and nitrogen (TiO2:Ta,N) was assessed as a water oxidation photocatalyst for Z-scheme water splitting driven by visible light. This material was prepared by thermal ammonolysis of TiO2:Ta with dry NH3 at 773 K, while samples of the oxide precursor were synthesized using a microwave-assisted solvothermal technique, applying various conditions. The photocatalytic activity of the TiO2:Ta,N during water oxidation to O-2 from an aqueous FeCl3 solution was found to be greatly affected by the synthesis parameters. The rate of O-2 evolution was increased upon increasing the level of Ta doping in conjunction with a highly-crystalized TiO2:Ta precursor resulting from applying a higher temperature during synthesis of the oxide. IrO2 loading of the TiO2:Ta,N photocatalyst also improved the O-2 evolution activity. The optimized IrO2/TiO2:Ta,N photocatalyst was applied to a Z-scheme water splitting system in combination with Ru/SrTiO3:Rh and in the presence of redox mediators (Fe3+/2+ or [Co(bpy)(3)](3+/2+)). Under AM1.5G simulated sunlight, this system exhibited a maximum solar-to-hydrogen energy conversion efficiency of 0.039%, which was nearly twice as high as the previously reported system with the use of RuO2/TiO2:Ta,N (0.021%).

DOI： 10.1039/C9SE00289H

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

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

ACS Applied Energy Materials 2 ( 5 ) 3274 - 3282 2019.5

Publishing type：Research paper (scientific journal)

© 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

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

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 2019.5

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

Low charge separation efficiencies are regarded as obstacles that limit the improvement in the photocatalytic performance of BaTaO2N. In this study, we demonstrated that the anisotropic facets ({100} and {110} facets) of BaTaO2N for efficient spatial charge separation were successfully constructed using the one-pot flux-assisted nitridation approach. As a result, the photocatalytic activity for H-2 production on BaTaO2N with coexposed {100} and {110} facets was nearly 10-fold over that of BaTaO2N with only {100} facets and that of the conventional irregularly shaped sample. This finding provides an innovative approach to the development of efficient (oxy)nitride photocatalysts for solar energy conversion.

DOI： 10.1021/acsami.9b03747

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

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

Ceram. Int. 45 ( 12 ) 15676 - 15680 2019.5

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

Pristine and Cu-doped alpha-Fe2O3 nanofibrous photocatalysts were prepared facilely by electrospinning followed by thermal calcination for removal of the polymeric template. The addition of Cu resulted in formation of copper ferrite (CuFe2O4) in the alpha-Fe2O3 matrix. Photogenerated electrons and holes in the photocatalysts were found trapped in semiconducting midgaps by the time-resolved transient absorption spectroscopy under pulsed light irradiations (355 nm wavelength). The Cu-doped alpha-Fe2O3 showed an increased carriers population when compared to the pristine counterpart. The finding was in good agreement with the methylene-blue (MB) dye degradation under ultraviolet-light irradiations, in which an enhanced MB removal was found for the Cu-doped alpha-Fe2O3 photocatalyst. The MB dye removal was directly correlated with the presence of CuFe2O4 ferrite in the alpha-Fe(2)O(3)matrix; from which, the semiconducting heterojunction at the interface led to a prolonged lifetime of the carriers and a resultant increase on the carriers population and MB photodegradation.

DOI： 10.1016/j.ceramint.2019.05.080

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

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 2019.5

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

Metal-complex/semiconductor hybrids are promising photocatalysts for visible-light CO2 reduction with high selectivity for the formation of a desired product. Herein we applied nanoparticulate Ta3N5/SiO2 as the semiconductor component of a hybrid system with the aid of a binuclear ruthenium(II) complex. The Ta3N5/SiO2 material was prepared by the nitridation of nanoparticulate Ta2O5/SiO2 (which had been previously synthesized by a sol-gel method) under a flow of NH3 gas at 973-1223 K. The synthesized hybrid reduced CO2 into formate with very high selectivity (>99 %) under irradiation with visible light (lambda>480 nm). The activity increased with nitridation temperature up to 1023 K, beyond which it began to drop. The optimized photocatalyst, which consisted of oxygen-doped Ta3N5 as revealed by UV-visible diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy, exhibited 6 times higher activity than that for an analogous hybrid constructed with bulk Ta3N5. Physicochemical analyses indicated that reducing the defect density by high-temperature nitridation contributed to the suppression of charge recombination, which resulted in higher activity of Ta3N5/SiO2, while a nitridation temperature that was too high was undesirable because of a decrease in the reactivity of photogenerated holes due to a loss of the doped oxygen content in Ta3N5.

DOI： 10.1002/cptc.201900120

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

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

Applied Catalysis B: Environmental 248 249 - 254 2019.2

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

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 2019.1

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

Clear and transparent nanocrystals for infrared-responsive carrier transfer Reviewed

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

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

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 2018.12

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

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

Akira Yamakata, Junie Jhon, M. Vequizo

J. Photochem. Photobiol. C-Photochem. Rev. 40 234 - 243 2018.12

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

Photocatalytic reactions are governed by photogenerated charge carriers upon band gap excitation. Therefore, for better understanding of the mechanism, the dynamics of photocarriers should be studied. One of the attractive materials is TiO2, which has been extensively investigated in the field of photocatalysis. This review article summarizes our recent works of time-resolved visible to mid-IR absorption measurements to elucidate the difference of anatase, rutile, and brookite TiO2 powders. The distinctive photocatalytic activities of these polymorphs are determined by the electron-trapping processes at the defects on powders. Powders are rich in defects and these defects capture photogenerated electrons. The depth of the trap is crystal phase dependent, and they are estimated to be < 0.1 eV, similar to 0.4 eV and similar to 0.9 eV for anatase, brookite, and rutile, respectively. Electron trapping reduces probability to meet with holes and then elongate the lifetime of holes. Therefore, it works negatively for the reaction of electrons but positively works for the reaction of holes. In the steady-state reactions, both electrons and holes should be consumed. Hence, the balance between the positive and negative effects of defects determines the distinctive photocatalytic activities of anatase, rutile, and brookite TiO2 powders. (C) 2018 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochemrev.2018.12.001

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

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 2018.12

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

Infrared (IR) light represents an untapped energy source accounting for almost half of all solar energy. Thus, there is a need to develop systems to convert IR light to fuel and make full use of this plentiful resource. Herein, we report photocatalytic H-2 evolution driven by near- to shortwave-IR light (up to 2500 nm) irradiation, based on novel CdS/Cu7S4 heterostructured nanocrystals. The apparent quantum yield reached 3.8% at 1100 nm, which exceeds the highest efficiencies achieved by IR light energy conversion systems reported to date. Spectroscopic results revealed that plasmon-induced hot electron injection at p-n heterojunctions realizes exceptionally long-lived charge separation (>273 mu s), which results in efficient IR light to hydrogen conversion. These results pave the way for the exploration of undeveloped low-energy light for solar fuel generation.

DOI： 10.1021/jacs.8b11544

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

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

RSC Advances 8 ( 67 ) 38140 - 38145 2018.11

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

Doping of Cr6+ into BiVO4 was examined in this study. A new absorption band with a 1.84 eV energy threshold appeared with Cr-doping. The theoretical band calculation has revealed that the new absorption is ascribed to the electron transition from the valence band to acceptor levels formed by empty Cr 3d orbitals. It was confirmed that photocatalytic water oxidation in the presence of Ag+ or Fe3+ of an oxidizing reagent was induced by excitation of the new absorption although activity under band gap excitation decreased with Cr-doping. Characteristics of carrier dynamics were also investigated by transient absorption spectroscopy.

DOI： 10.1039/C8RA07830K

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

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 2018.10

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

Copolymerized carbon nitride nanosheets (NS-C3N4) were used as a light absorbing unit while paired with a Ru(II) complex that served as a catalyst for CO2 reduction, forming a hybrid photocatalytic system. Copolymerization with urea and phenylurea in air at 823 K resulted in a carbon nitride material that had wide visible light absorption extending to 650 nm, significantly red-shifted compared to the absorption edge of pristine NS-C3N4, an analogue prepared with only urea (ca. 435 nm). While a hybrid system consisting of pristine NS-C3N4 was found to be inactive under longer wavelength visible light (lambda > 500 nm) due to its large band gap, the copolymerized material was able to catalytically convert CO2 to HCOOH under lambda > 500 nm irradiation. Furthermore, its activity toward HCOOH production is doubled under lambda > 400 nm irradiation after 5 h compared to pristine NS-C3N4. Transient absorption spectroscopy clearly showed improved lifetime of photogenerated free (and/or shallowly trapped) electrons, which should be the key to enhancing the photocatalytic activity of this hybrid system even under shorter wavelength visible light.

DOI： 10.1021/acssuschemeng.8b03782

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

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 2018.9

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

The Z-scheme CO2 reduction activity of metal complex-semiconductor hybrid photocatalysts was investigated in detail with a focus on the interfacial electron transfer process. Semiconductors of GaN:ZnO solid solutions, TaON, and Ta/N-codoped TiO2 were examined as components of the hybrid photocatalyst in combination with a binuclear Ru(II) complex. The (photo)physical properties of the semiconductor part were found to strongly affect the efficiency of interfacial electron transfer from/to the Ru complex photosensitizer unit, which was attached to the semiconductor surface. The photocatalytic activity of the hybrids showed a reasonable relationship with the efficiencies of forward and backward electron transfer. Among the three semiconductors, the highest activity was obtained with GaN:ZnO, which had the most negative conduction band potential among the semiconductors examined. The experimental results clearly demonstrated that analyses of the emission quenching process of the excited photosensitizer moiety of the binuclear Ru(II) complex allowed visualization of the interfacial electron transfer between the semiconductor and the Ru complex, giving us a rational guideline to improve the efficiency of the hybrid photocatalyst for Z-scheme CO2 reduction.

DOI： 10.1021/acscatal.8b03062

Undoped Layered Perovskite Oxynitride Li2 LaTa2 O6 N for Photocatalytic CO2 Reduction with Visible Light. Reviewed International journal

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 2018.7

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

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

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

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 2018.7

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

The accumulation of solid waste due to rapid industrialization has a negative impact on the environment. In this study, ZnS-containing waste from the mining-metallurgy industry was utilized for the synthesis of trigonal ZnIn2S4 layered crystals by a flux method using various binary fluxes: CaCl2:InCl3, SrCl2:InCl3, BaCl2:InCl3, NaCl:InCl3, KCl:InCl3, and CsCl:InCl3. Among the binary fluxes used, KCl:InCl3 was found to be the most favorable for the synthesis of phase-pure trigonal ZnIn2S4 layered crystals. The XRD and SEM results revealed that the flux-grown ZnIn2S4 crystals have a trigonal structure and a morphology composed of large stacked layers. Unexpectedly, the UV-vis diffuse reflectance spectrum exhibited the onset of the absorption edge at approximately 700 nm for trigonal ZnIn2S4 crystals. The photocatalytic activities for H-2 production of the Pt-photodeposited ZnIn2S4 samples grown using CaCl2:InCl3, NaCl:InCl3, and KCl:InCl3 fluxes were evaluated. Trigonal ZnIn2S4 crystals grown using the KCl:InCl3 flux in this study exhibited higher photocatalytic activity for H-2 evolution (132 mu mol h(-1)) than previously reported hexagonal ZnIn2S4 synthesized by a hydrothermal method due to the decreased defect density and higher crystallinity achieved by the binary flux method. The presence of secondary crystalline phases (ZnS and In2S3) in ZnIn2S4 crystals grown using NaCl:InCl3 and CaCl2:InCl3 fluxes positively impacted the photocatalytic activity and exhibited photocatalytic H-2 evolution rates of 188 and 232 mu mol h(-1), respectively, because of the efficient separation and transfer of photogenerated charge carriers. The decay of the transient absorption of electrons in three samples at 2000 cm(-1) was monitored by transient absorption spectroscopy, confirming that the lifetime of free electrons becomes longer depending on the binary flux used: KCl:InCl3 < NaCl:InCl3 < CaCl2:InCl3. The binary flux method applied in this study demonstrates that accumulated solid industrial wastes can be turned into beneficial photocatalytic materials.

DOI： 10.1039/C8GC01746H

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 Reviewed

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

Appl. Catal. B-Environ. 238 358 - 364 2018.7

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

Composite type photocatalyst F-TiO2/(N,C)-TiO2 consisted of anatase-type TiO2 with fluorine-doping (F-TiO2) and TiO2 with nitrogen and carbon-doping ((N,C)-TiO2) was prepared by simple physical mixing to exhibit higher visible-light responsive photocatalytic nitrogen oxide (NO) decomposition activity than those of F-TiO2 and (N,C)-TiO2. Transient absorption measurement clarified that the composite possessed longer carrier lifetime compared to that of each material (F-TiO2 or (N,C)-TiO2), resulting in higher photocatalytic activity. In the composite, photoexcited holes and electrons, which are not in impurity level but in valence and conduction band, respectively, should photocatalytically decompose NO, judging from the redox potential of O-2/O-2(center dot-) and the band positions of F-TiO2 and (N,C)-TiO2. The mechanism for higher visible-light photocatalytic activity, or longer carrier lifetime can be explained by charge transfer between F-TiO2 and (N,C)-TiO2 through their impurity levels. The charge transfer should make photoexcited carries spatially separated to enhance the photo catalytic activity.

DOI： 10.1016/j.apcatb.2018.07.038

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