2021/05/15 更新

写真a

サイトウ ケンジ
齊藤 健二
SAITO Kenji
所属
教育研究院 自然科学系 生産デザイン工学系列 准教授
自然科学研究科 材料生産システム専攻 准教授
工学部 工学科 准教授
職名
准教授
外部リンク

学位

  • 博士(工学) ( 2007年3月   大阪大学 )

研究キーワード

  • ナノワイヤー

  • 触媒

  • 無機多孔結晶

  • 結晶成長

研究分野

  • ナノテク・材料 / 無機・錯体化学

  • ナノテク・材料 / エネルギー化学

  • ナノテク・材料 / ナノ材料科学

経歴

  • 新潟大学   自然科学研究科 材料生産システム専攻   准教授

    2017年4月 - 現在

  • 新潟大学   工学部 工学科   准教授

    2017年4月 - 現在

  • 新潟大学   研究推進機構   助教

    2016年4月 - 2017年3月

  • 新潟大学   経営戦略本部 若手研究者育成推進室   助教

    2012年6月 - 2016年3月

所属学協会

委員歴

  • 触媒学会   東日本地区代議員  

    2009年4月 - 2012年3月   

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    団体区分:学協会

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論文

  • An efficient catalyst film fabricated by electrophoretic deposition of cobalt hydroxide for electrochemical water oxidation 査読

    Ryouchi Takeuchi, Tetsuya Sato, Takeshi Masaki, Kaoru Aiso, Debraj Chandra, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    Journal of Photochemistry and Photobiology A: Chemistry358   395 - 401   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.  

    The hexagonal-shaped β-Co(OH)2 discs were electrophoretically deposited on an electrode to yield a stably adherent and uniform β-Co(OH)2 layer. The electrocatalytic water oxidation at the β-Co(OH)2 layer-deposited electrode was investigated to seek efficient water oxidation catalyst for artificial photosynthesis as promising energy-providing systems for the future. The β-Co(OH)2 layer did not work as a water oxidation catalyst in a K2SO4 solution at pH 7.0 when applying 1.70 V vs. reversible hydrogen electrode (RHE), although the layer was oxidized to the CoO(OH) layer. In a phosphate buffer solution (pH 7.0), the β-Co(OH)2 layer was dissolved and oxidatively re-deposited as the Co-Pi catalyst (Science, 321 (2008) 1072–1075.) when applying the same potential. While in a Na2B4O7 solution at pH 9.4, the β-Co(OH)2 layer was oxidized to the CoO(OH) layer with the hexagonal-disc-shape remained when applying 1.7 V vs. RHE, and the formed CoO(OH) layer works efficiently for electrocatalytic water oxidation in contrast to no catalytic activity in a K2SO4 solution at pH 9.4. The catalytic performance of the formed CoO(OH) layer was evaluated
    the overpotential (η) of 0.42 V for current generation of 100 μA cm−2 and the Tafel slope of 0.21 ∼ 0.29 V dec−1 were provided for water oxidation at pH 9.4, which are comparable with efficient cobalt-based catalyst films reported so far.

    DOI: 10.1016/j.jphotochem.2017.09.052

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  • Visible Light-Driven Water Oxidation on an In Situ N2-Intercalated WO3 Nanorod Photoanode Synthesized by a Dual-Functional Structure-Directing Agent 査読

    Dong Li, Ryouchi Takeuchi, Debraj Chandra, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    ChemSusChem11 ( 7 ) 1151 - 1156   2018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-VCH Verlag  

    With a view to developing a photoanode for visible light-driven water oxidation in solar water splitting cells, pure-monoclinic WO3 nanorod crystals with N2 intercalated into the lattice were synthesized by using hydrazine with a dual functional role—as an N atom source for the in situ N2 intercalation and as a structure-directing agent for the nanorod architecture—to gain higher incident photon-to-current conversion efficiency at 420 nm than with most previously reported WO3 electrodes.

    DOI: 10.1002/cssc.201702439

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  • Preparation of Stable Silver Nanoparticles Having Wide Red-To-Near-Infrared Extinction 査読

    Kawamura Shiori, Matsubara Kazuki, Sakai Sotaro, Sasaki Kazuhisa, Saito Masataro, Saito Kenji, Yagi Masayuki, Norimatsu Wataru, Sasai Ryo, Kusunoki Michiko, Eguchi Miharu, Yin Shu, Asakura Yusuke, Yui Tatsuto

    GLOBAL CHALLENGES2 ( 3 )   2018年3月

  • Facile Templateless Fabrication of a Cobalt Oxyhydroxide Nanosheet Film with Nanoscale Porosity as an Efficient Electrocatalyst for Water Oxidation 査読

    Chandra Debraj, Tanaka Kou, Takeuchi Ryouchi, Abe Naoto, Togashi Takanari, Kurihara Masato, Saito Kenji, Yui Tatsuto, Yagi Masayuki

    CHEMPHOTOCHEM2 ( 3 ) 332 - 339   2018年3月

  • Superior Inorganic Ion Cofactors of Tetraborate Species Attaining Highly Efficient Heterogeneous Electrocatalysis for Water Oxidation on Cobalt Oxyhydroxide Nanoparticles 査読

    Ryouchi Takeuchi, Tetsuya Sato, Kou Tanaka, Kaoru Aiso, Debraj Chandra, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    ACS APPLIED MATERIALS & INTERFACES9 ( 42 ) 36955 - 36961   2017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  

    A heterogeneous catalyst incorporating an inorganic ion cofactor for electrochemical water oxidation was exploited using a CoO(OH) nanoparticle layer-deposited electrode. The significant catalytic current for water oxidation was generated in a Na2B4O7 solution at pH 9.4 when applying 0.94 V versus Ag/AgC1 in contrast to no catalytic current generation in the K2SO4 solution at the same pH. HB4O7 and B4O72- ions were indicated to act as key cofactors for the induced catalytic activity of the CoO(OH) layer. The Na2B4O7 concentration dependence of the catalytic current was analyzed based on a Michaelis-Menten-type kinetics to provide an affinity constant of cofactors to the active sites, K-m = 28 +/- 3.6 mM, and the maximum catalytic current density, I-max = 2.3 +/- 0.13 mA cm(-2). The I-max value of HB4O7- and B4O72- ions was 1.4 times higher than that (1.3 mA cm(-2)) for the previously reported case of CO32- ions. This could be explained by the shorter-range proton transfer from the active site to the proton-accepting cofactor because of the larger size and more flexible conformation of HB4O7 and B(4)O(7)(2-)ions compared with that of CO32- ions.

    DOI: 10.1021/acsami.7b13817

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  • Mechanistic Insight into Reversible Core Structural Changes of Dinuclear mu-Hydroxoruthenium(II) Complexes with a 2,8-Di-2-pyridyl-1,9,10-anthyridine Backbone Prior to Water Oxidation Catalysis 査読

    Masanari Hirahara, Sho Nagai, Kosuke Takahashi, Shunsuke Watabe, Taisei Sato, Kenji Saito, Tatsuto Yui, Yasushi Umemura, Masayuki Yagi

    INORGANIC CHEMISTRY56 ( 17 ) 10235 - 10246   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:AMER CHEMICAL SOC  

    proximal,proximal-(p,p)-[Ru-2(II)(tpy)(2)LXY](n+) (tpy = 2,2';6',2 ''-terpyridine, L = 5-phenyl-2,8-di-2-pyridyl-1,9,10-anthyridine, and X and Y = other coordination sites) yields the structurally and functionally unusual Ru-II(mu-OH)Ru-II core, which is capable of catalyzing water oxidation with key water insertion to the core (Inorg. Chem. 2015, 54, 7627). Herein, we studied a sequence of bridging-ligand substitution among p,p-[Ru-2(tpy)(2)L(mu-Cl)](3+) (RU2(mu-Cl)), p,p-[Ru-2(tpy)(2)L(mu-OH)](3+) (Ru-2(mu-OH)), p,p-[Ru-2(tpy)(2)L-(OH)(OH2)](3+) (Ru-2(OH)(OH2)), and p,p-[Ru-2(tpy)(2)L-(OH)(2)](2+) (Ru-2(OH)(2)) in aqueous solution. Ru-2(mu-Cl) converted slowly (10(-4) s(-1)) to Ru-2(mu-OH), and further Ru-2(mu-OH) converted very slowly (10(-6) s(-1)) to Ru-2(OH)-(OH2) by the insertion of water to reach equilibrium at pH 8.5-12.3. On the basis of density functional theory (DFT) calculations, Ru-2(OH)(OH2) was predicted to be thermodynamically stable by 13.3 kJ mol(-1) in water compared to Ru-2(mu-OH) because of the specially stabilized core structure by multiple hydrogen-bonding interactions involving aquo, hydroxo, and L backbone ligands. The observed rate from Ru-2(mu-OH) to Ru-2(OH)(2) by the insertion of an OH- ion increased linearly with an increase in the OH- concentration from 10 to 100 mM. The water insertion to the core is very slow (similar to 10(-6) s(-1)) in aqueous solution at pH 8.5-12.3, whereas the insertion of OH- ions is accelerated (10(-5)-10(-4) s(-1)) above pH 13.4 by 2 orders of magnitude. The kinetic data including activation parameters suggest that the associative mechanism for the insertion of water to the Ru-II(mu-OH)Ru-II core of Ru-2(mu-OH) at pH 8.5-12.3 alters the interchange mechanism for the insertion of an OH- ion to the core above pH 13.4 because of relatively stronger nucleophilic attack of OH- ions. The hypothesized p,p-[Ru-2(tpy)(2)L(mu-OH2)](4+) and p,p-[Ru-2(tpy)(2)L(OH2)(2)](4+) formed by protonation from Ru-2(mu-OH) and Ru-2(OH)(OH2) were predicted to be unstable by 71.3 and 112.4 kJ mol(-1) compared to Ru-2(mu-OH) and Ru-2(OH)(OH2), respectively. The reverse reactions of Ru-2(mu-OH), Ru-2(OH)(OH2), and Ru-2(OH)(2) to Ru-2(mu-Cl) below pH 5 could be caused by lowering the core charge by protonation of the mu-OH- or OH- ligand.

    DOI: 10.1021/acs.inorgchem.7b00978

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  • Polymer surfactant-assisted tunable nanostructures of amorphous IrOx thin films for efficient electrocatalytic water oxidation 査読

    Debraj Chandra, Tsubasa Sato, Ryouchi Takeuchi, Dong Li, Takanari Togashi, Masato Kurihara, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    CATALYSIS TODAY290   51 - 58   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:ELSEVIER SCIENCE BV  

    Transparent IrOx catalyst films for water oxidation were fabricated on fluorine-doped tin oxide electrodes from Ir precursor complex solutions containing Pluronic P123, Brij 58 or Pluronic F127 as surfactant structure directing agents (SDAs). The thin layers composed of highly dispersed and very small nanoparticles of ca. <= 2 nm were formed for IrOx films derived by Pluronic P123 and Brij 58, both of which act as a 'spacer' between the Ir-building-blocks to inhibit further agglomeration of the nanoparticles. Pluronic F127 with relatively longer hydrophilic poly(ethylene oxide) blocks stabilizes Ir-complexes in the precursor solution due to stronger interaction between its longer ED-units and Ir-complexes, affording the organized mesoporous structures of ca. 8 nm pores templated by micelles formed in the IrOx film derived by Pluronic F127. The cyclic voltammetry revealed the catalytic currents for water oxidation for the SDAs-derived IrOx films were 1.3-1.8 times higher than the IrO, film without SDA. The higher water oxidation activity observed is attributed to the higher intrinsic catalytic activity of Ir-sites on very small nanoparticles in the Pluronic P123 and Brij 58-derived IrOx films, whereas it is attributed to the increased number of active Ir-sites due to the organized mesoporous structures of the Pluronic F127-derived IrOx film. (C) 2017 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.cattod.2017.03.009

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  • Morphology Control of Energy-Gap-Engineered Nb2O5 Nanowires and the Regioselective Growth of CdS for Efficient Carrier Transfer Across an Oxide-Sulphide Nanointerface 査読

    Tomoki Shinohara, Miyu Yamada, Yuki Sato, Shohei Okuyama, Tatsuto Yui, Masayuki Yagi, Kenji Saito

    SCIENTIFIC REPORTS7   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:NATURE PUBLISHING GROUP  

    Semiconductor nanowires with both nano- and micrometre dimensions have been used as effective materials for artificial photosynthesis; however, a single synthesis approach to provide rational control over the macroscopic morphology, which can allow for the high-throughput screening of photocatalytic performance, and carrier transfer between oxide and sulphide nanostructures has been poorly known. Our recent findings indicate that a single parameter, Nb foil thickness, in a vapor-phase synthesis method can alter the macroscopic morphology of resulting Nb2O5 nanowires. Thick Nb foil results in a free-standing Nb2O5 film, whereas a thinner foil leads to fragmentation to give a powder. During the synthesis process, a Rh dopant was provided through metal-organic chemical vapor deposition to reduce the Nb2O5 energy gap. Upon irradiation with visible light (lambda > 440 nm), the free-standing nanowire film [Nb2O5: Rh-NW(F)] showed photoanodic current with a Faradaic efficiency of 99% for O-2 evolution. Under identical irradiation conditions, the powdered counterpart [Nb2O5: Rh-NW(P)] showed activity for O-2 evolution in the presence of an electron acceptor. The poor water-reduction ability was greatly enhanced by the Au-catalysed vapor-liquid-solid (VLS) growth of H-2-evolving CdS onto the reduction sites of Nb2O5: Rh-NW(P) [Au/CdS/Nb2O5: Rh-NW(P)].

    DOI: 10.1038/s41598-017-05292-2

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  • Dual-Functional Surfactant-Templated Strategy for Synthesis of an In Situ N-2-Intercalated Mesoporous WO3 Photoanode for Efficient Visible-Light-Driven Water Oxidation 査読

    Dong Li, Debraj Chandra, Ryouchi Takeuchi, Takanari Togashi, Masato Kurihara, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    CHEMISTRY-A EUROPEAN JOURNAL23 ( 27 ) 6596 - 6604   2017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:WILEY-V C H VERLAG GMBH  

    N-2-Intercalated crystalline mesoporous tungsten trioxide (WO3) was synthesized by a thermal decomposition technique with dodecylamine (DDA) as a surfactant template with a dual role as an N-atom source for N-2 intercalation, alongside its conventional structure-directing role (by micelle formation) to induce a mesoporous structure. N-2 physisorption analysis showed that the specific surface area (57.3m(2)g(-1)) of WO3 templated with DDA (WO3-DDA) is 2.3 times higher than that of 24.5m(2)g(-1) for WO3 prepared without DDA (WO3-bulk), due to the mesoporous structure of WO3-DDA. The Raman and X-ray photoelectron spectra of WO3-DDA indicated intercalation of N-2 into the WO3 lattice above 450 degrees C. The UV/Vis diffuse-reflectance spectra exhibited a significant shift of the absorption edge by 28nm, from 459nm (2.70eV) to 487nm (2.54eV), due to N-2 intercalation. This could be explained by the bandgap narrowing of WO3-DDA by formation of a new intermediate N 2p orbital between the conduction and valance bands of WO3. A WO3-DDA-coated indium tin oxide (ITO) electrode calcined at 450 degrees C generated a photoanodic current under visible-light irradiation below 490nm due to photoelectrochemical water oxidation, as opposed to below 470nm for ITO/WO3-bulk. The incident photon-to-current conversion efficiency (IPCE=24.5%) at 420nm and 0.5V versus Ag/AgCl was higher than that of 2.5% for ITO/WO3-bulk by one order of magnitude due to N-2 intercalation and the mesoporous structure of WO3-DDA.

    DOI: 10.1002/chem.201700088

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  • Light Energy Accumulation from Pyrene Derivative to Tris(bipyridine)ruthenium on Clay Surface 査読

    Daiki Morimoto, Haruya Yoshida, Keita Sato, Kenji Saito, Masayuki Yagi, Shinsuke Takagi, Tatsuto Yui

    LANGMUIR33 ( 15 ) 3680 - 3684   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  

    A novel type of energy donor-acceptor system on a clay surface has been prepared. The energy transfer between an energy-donating cationic pyrene derivative (An-Py2+) and an energy-accepting tris(bipyridine)ruthenium complex (Ru2+) on the clay surface was investigated using absorption, emission, and lifetime measurements. An obvious energy transfer was observed, and one Ru2+ molecule quenched the emission from five molecules of An-Py2+ with an emission quenching efficiency of 85% on the clay surface. This suggests that the light energies absorbed by five of the An-Py2+ molecules were accumulated in the one Ru2+ molecule. Near-quantitative emission quenching was observed for stoichiometric amounts of An-Py2+ and Ru2+. The apparent quenching rate constant is approximately 10(17) L mol(-1) s(-1), and thus the quenching rate constant is 10(7)-10(8) times higher than the diffusion rate constant in a homogeneous solution.

    DOI: 10.1021/acs.langmuir.7b00512

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  • Color tuning of cationic pyrene derivatives on a clay nanosheet: Retardation of gradual redshift on clay 査読

    Daiki Morimoto, Keita Sato, Kenji Saito, Masayuki Yagi, Shinsuke Takagi, Tatsuto Yui

    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY337   112 - 117   2017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 SA  

    A novel type of trimethylanilinium-substituted pyrene derivative, 1,6-di(N,N,N-trimethylanilinium-4-y1) pyrene 2I(-)(An-Py2+), was synthesized. An-Py2+ exhibits strong emission with a high-emission quantum yield (approximately 90%) in aqueous solution. An-Py2+ was hybridized on a clay (Sumecton SA (SSA)) surface, and the photochemical behavior of An-Py2+ on the SSA surface was investigated using absorption and emission spectroscopic analyses, emission quantum yield (Phi(f)), and lifetime (tau) measurements. Effective adsorption of An-Py2+ on SSA was observed, and adsorption limit was estimated to be 100% relative to the cation-exchange capacity (CEC) of SSA. The previously reported pyridinium-substituted pyrene derivatives cause a gradual redshift of both absorption and emission on the SSA surface. In contrast, An-Py2+ effectively suppresses such a redshift on SSA due to anilinium substitution of the pyrene unit. (C) 2017 Elsevier B.V. All rights reserved.

    DOI: 10.1016/jjphotochem.2017.01.023

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  • Carbonate Ions Induce Highly Efficient Electrocatalytic Water Oxidation by Cobalt Oxyhydroxide Nanoparticles 査読

    Kaoru Aiso, Ryouchi Takeuchi, Takeshi Masaki, Debraj Chandra, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    CHEMSUSCHEM10 ( 4 ) 687 - 692   2017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:WILEY-V C H VERLAG GMBH  

    Synthetic models of oxygen evolving complex (OEC) are used not only to gain better understanding of the mechanism and the roles of cofactors for water oxidation in photosynthesis, but also as water oxidation catalysts to realize artificial photosynthesis, which is anticipated as a promising solar fuel production system. However, although much attention has been paid to the composition and structure of active sites for development of heterogeneous OEC models, the cofactors, which are essential for water oxidation by the photosynthetic OEC, remain little studied. The high activity of CoO(OH) nanoparticles for electrocatalytic water oxidation is shown to be induced by a CO32- cofactor. The possibility of CO32- ions acting as proton acceptors for O-O bond formation based on the proton-concerted oxygen atom transfer mechanism is proposed. The O-O bond formation is supposed to be accelerated due to effective proton acceptance by adjacent CO32- ions coordinated on the CoIV center in the intermediate, which is consistent with Michaelis-Menten-type kinetics and the significant H/D isotope effect observed in electrocatalysis.

    DOI: 10.1002/cssc.201601494

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  • In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films 査読

    Kazuhisa Sasaki, Kazuki Matsubara, Shiori Kawamura, Kenji Saito, Masayuki Yagi, Tatsuto Yui

    JOVE-JOURNAL OF VISUALIZED EXPERIMENTS ( 119 )   2017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:JOURNAL OF VISUALIZED EXPERIMENTS  

    Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs within the interlayer space of semiconducting layered titania nanosheet (TNS) films was investigated here. Two types of intermediate films (i.e., TNS films containing methyl viologen (TNS/MV2+) and 2-ammoniumethanethiol (TNS/2-AET(+))) were prepared. The two intermediate films were soaked in an aqueous tetrachloroauric(III) acid (HAuCl4) solution, whereby considerable amounts of Au(III) species were accommodated within the interlayer spaces of the TNS films. The two types of obtained films were then soaked in an aqueous sodium tetrahydroborate (NaBH4) solution, whereupon the color of the films immediately changed from colorless to purple, suggesting the formation of AuNPs within the TNS interlayer. When only TNS/MV2+ was used as the intermediate film, the color of the film gradually changed from metallic purple to dusty purple within 30 min, suggesting that aggregation of AuNPs had occurred. In contrast, this color change was suppressed by using the TNS/2-AET(+) intermediate film, and the AuNPs were stabilized for over 4 months, as evidenced by the characteristic extinction (absorption and scattering) band from the AuNPs.

    DOI: 10.3791/55169

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  • Characterization of Interfacial Charge-Transfer Photoexcitation of Polychromium-Oxo-Electrodeposited TiO2 as an Earth-Abundant Photoanode for Water Oxidation Driven by Visible Light 査読

    Debraj Chandra, Ryougen Tsuriya, Tsubasa Sato, Daisuke Takama, Naoto Abe, Masashi Kajita, Dong Li, Takanari Togashi, Masato Kurihara, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    CHEMPLUSCHEM81 ( 10 ) 1116 - 1122   2016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-V C H VERLAG GMBH  

    Polychromium-oxo-deposited TiO2 ((CrxOy)-O-III/TiO2) electrodes were fabricated by a simple electrochemical technique by using different TiO2 basal electrodes (anatase, rutile, and mixed polymorphic phases P25) as earth-abundant photoanodes for visible-light-driven water oxidation. The high-resolution transmission electron microscopy (HR-TEM) observation illustrated that an (CrxOy)-O-III layer with approximately 2-3nm thickness was formed on the surface of the crystalline TiO2 particles. Upon visible-light irradiation of the electrodes, the photoanodic current based on water oxidation was generated at the (CrxOy)-O-III/TiO2 electrodes. However, the wavelength (below 620nm) for photocurrent generation at (CrxOy)-O-III/TiO2-rutile was longer than that (below 560nm) at (CrxOy)-O-III/TiO2-P25 by 60nm, which is in agreement with the difference (0.2eV) in the conduction band (CB) edge energy between rutile and anatase TiO2. This gives a quantitative account for the photocurrent generation based on interfacial charge transfer (IFCT) from Cr3d of the deposited (CrxOy)-O-III layer to the TiO2 CB. The photocurrent generated for (CrxOy)-O-III/TiO2-rutile was higher than that for (CrxOy)-O-III/TiO2-anatase, which is ascribed to 1)more effective (CrxOy)-O-III deposition on the rutile particles, 2)a larger electrolyte/(CrxOy)-O-III interface for water oxidation as a result of smaller rutile particles (ca. 30-40nm) compared with larger P25 particles (ca. 40-80nm), and 3)more effective use of visible light owing to the low energy IFCT transition of rutile.

    DOI: 10.1002/cplu.201600288

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  • Highly Efficient Electrocatalysis and Mechanistic Investigation of Intermediate IrOx(OH)(y) Nanoparticle Films for Water Oxidation 査読

    Debraj Chandra, Daisuke Takama, Takeshi Masaki, Tsubasa Sato, Naoto Abe, Takanari Togashi, Masato Kurihara, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    ACS CATALYSIS6 ( 6 ) 3946 - 3954   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:AMER CHEMICAL SOC  

    A new transparent iridium oxide (IrOx) film on fluorine-doped tin oxide (FTO) electrodes were achieved from a homogeneous precursor complex solution by employing a facile spin-coating technique. The composition of the nanostructure and crystallinity of the IrOx film is tunable by a simple annealing treatment of a compact complex layer, which is responsible for their significantly different electrocatalytic performances for water oxidation. Transmission electron microscopy (TEM) observations showed uniformly dispersed small IrOx nanoparticles of dimensions ca. 2-5 nm for the film annealed at 300 degrees C, and the nanoparticles gradually agglomerated to form relatively large particles at higher temperatures (400 and 500 degrees C). The IrOx films prepared at different annealing temperatures are characterized by Raman spectroscopic data to reveal intermediate IrOx(OH)(y) nanoparticles with two oxygen binding motifs: terminal hydroxo and bridging oxo at 300 and 350 degrees C annealing, via amorphous IrOx at 400 degrees C, transforming ultimately to crystalline IrO2 nanoparticles at 500 degrees C. Cyclic voltammetry suggests that the intrinsic activity of catalytic Ir sites in intermediate IrOx(OH)(y) nanoparticles formed at 300 degrees C annealing is higher in comparison with amorphous and crystalline IrOx nanoparticles. Electrochemical impedance data showed that the charge transfer resistance (R-ct = 232 Omega) for the IrOx(OH)(y) film annealed at 300 degrees C is lower relative to that of films annealed at higher temperatures. This is ascribable to the facilitated electron transfer in grain boundaries between smaller IrOx particles to lead the efficient electron transport in the film. The high intrinsic activity of catalytic Ir sites and efficient electron transport are responsible for the high electrocatalytic performance observed for the intermediate IrOx(OH)(y) film annealed at 300 degrees C; it provides the lowest overpotential (eta) of 0.24 V and Tafel slope of 42 mV dec(-1) for water oxidation at neutral pH, which are comparable with values for amorphous IrOx center dot nH(2)O nanoparticle films (40-50 mV dec(-1)) reported as some of the most efficient electrocatalysts so far.

    DOI: 10.1021/acscatal.6b00621

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  • Synthesis of copper nanoparticles within the interlayer space of titania nanosheet transparent films 査読

    Kazuhisa Sasaki, Kazuki Matsubara, Shiori Kawamura, Kenji Saito, Masayuki Yagi, Wataru Norimatsu, Ryo Sasai, Tatsuto Yui

    JOURNAL OF MATERIALS CHEMISTRY C4 ( 7 ) 1476 - 1481   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  

    We report the first in situ synthesis of copper nanoparticles (CuNPs) within the interlayer space of inorganic layered semiconductors (titania nanosheet films) through the following steps. A sintered titania nanosheet (s-TNS) film was synthesised, forming a transparent, layered semiconductor film (similar to 2 mu m thick). A considerable amount of copper ions (ca. 68% relative to the cation exchange capacity of TNSs) was intercalated in the s-TNSs using the methyl viologen-containing s-TNSs as the intermediate. The resultant copper-containing s-TNS (TNS/Cu2+) film was treated with an aqueous solution of NaBH4, resulting in a colour change. Extinction spectra of NaBH4-treated films exhibited a wide extinction band at lambda(max) (the extinction band maximum) = 683 nm. The spectral shapes and lambda(max) were similar to those for copper nanoparticles on TiO2 surfaces. Transmission electron microscopy analysis demonstrated the wide distribution of electron dense particles on the titania sheet of NaBH4-treated TNS/Cu2+. XRD analysis and absorption/extinction analysis with different amounts of TNSs suggest that CuNPs were formed within the interlayer space rather than the surface of TNSs through NaBH4 treatment. Repeatable oxidation and reduction behaviour, i.e. colouration and decolouration cycles of the copper species within TNS films, was investigated.

    DOI: 10.1039/c5tc03152d

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  • Photocatalytic reduction of nitrate ions to dinitrogen over layered perovskite BaLa4Ti4O15 using water as an electron donor 査読

    Marie Oka, Yugo Miseki, Kenji Saito, Akihiko Kudo

    APPLIED CATALYSIS B-ENVIRONMENTAL179   407 - 411   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 BV  

    Photocatalytic reduction of NO3- to produce NO2-, NH4+, and N-2 proceeded on BaLa4Ti4O15 powder under UV irradiation accompanied with photochemical decomposition of NO3- to NO2- and O-2 without any sacrificial reagents. Loading of Cu and Ni cocatalysts enhanced the photocatalytic reaction to form N-2. Ni was the most effective cocatalyst. The BaLa4Ti4O15 photocatalyst with the Ni cocatalyst loaded by an impregnation method and subsequent H-2 reduction showed high activity for the reduction of NO3- to form NO2-, NH4+, and N-2. O-2 also formed as an oxidation product of water. The ratio of the number of reacted electron to that of hole was almost unity, indicating water was consumed as an electron donor for the reduction of NO3-. A boric acid of a buffer for pH control was effective to obtain a high yield of N-2. The N-2 yield reached 85% in the presence of a boric acid after 10 h using a 400W high-pressure mercury lamp in 10 mmol/L of an aqueous NaNO3 solution, while it was 50% without the boric acid. The N-2 yield was almost 100% When 3 mmol/L of an aqueous NaNO3 solution was used with a boric acid. (C) 2015 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.apcatb.2015.05.037

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  • Influence of chloro substituent on photoisomerization, redox reactions and water oxidation catalysis of mononuclear ruthenium complexes 査読

    Kosuke Takahashi, Xiaohong Zhang, Masanari Hirahara, Taisei Sato, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY313   117 - 125   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  

    distal-[Ru(Cl-tpy)(pynp)Cl](+) (d-2Cl) (Cl-tpy = 4'-chloro-2,2';6',2"-terpyridine, pynp =2-(2-pyridy1)-1,8-naphthyridine), and distal- and proximal-[Ru(Cl-tpy)(pynp)OH2](2+) (d- and p-2H(2)O) complexes are newly synthesized and characterized to compare structures and physicochemical properties with a 2,2';6',2 ''-terpyridine (tpy) ligand derivatives of distal-[Ru(tpy)(pynp)Cl](+) (d-1Cl), distal- and proximal-[Ru(tpy) (PYnP)OH2](2+) (d- and p-1H(2)O). The equilibrium turned out to be involved in the aquation reaction of d-2Cl to d-2H(2)O in contrast to observed irreversible aquation reaction of d-1Cl under the same conditions. The kinetic analysis showed that the aquation reaction of d-2Cl is slightly slower than that of d-1Cl. The stoichiometric photoisomerization of d-2H(2)O to p-2H(2)O occurs by visible light irradiation as it is for d-1H(2)O, and (2.1%) at 520 nm for photoisomerization of d-2H(2)O was higher than that (1.5%) observed for d-1H(2)O. d-2H(2)O undergoes the two-step reaction involving the successive one-proton-coupled oneelectron reactions of the Ru-II-OH2/Ru-III-OH and Ru-III-OH/Ru-IV=O redox couples, whereas p-2H(2)O undergoes the one-step reaction involving the two-proton-coupled two-electron reaction of the RuII-OH2/Ru-IV=O redox couple. These redox potentials of d- and p-2H(2)O are higher than those for d- and p-1H(2)O at pH 7.0 by 10 similar to 50 my due to the electron-withdrawing chloro substitution. The turnover frequency (k(o2) = 6.3 x 10(-3) s(-1)) of d-2H(2)O for water oxidation was higher than that (3.9 x 10(-4) s(-1)) of p-2H(2)O by a factor of 16. k(o2) for d-2H(2)O was also 1.6 times higher than that (3.8 x 10(-3) s(-1)) for d-1H(2)O, whereas k(o2) for p-2H(2)O was 1.2 times lower than that (4.8 x 10(-4) s(-1)) for p-1H(2)O. (C) 2015 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.jphotochem.2015.05.029

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  • Spectroelectrochemical investigation of electrocatalytic water oxidation by a mononuclear ruthenium complex in a homogeneous solution 査読

    Junichiro Honta, Syouhei Tajima, Taisei Sato, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY313   126 - 130   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  

    Electrochemical water oxidation by [Ru(EtOtpy)(bpy)OH2](2+) (1) (EtOtpy =4'-ethoxy-2,2':6'2 ''-terpyridine, bpy = 2,2'-bipydidine) was investigated in a homogeneous solution under weakly acidic conditions (pH 5.3). The cyclic voltammogram of a 1 aqueous solution showed that successive proton-coupled electron transfer reactions of Ru-II-OH2 Ru-III-OH and Ru-III-OH/Ru-IV=O redox pairs and high anodic current above 1.1 V vs SCE. Electrocatalytic water oxidation was corroborated by the bulk electrolysis at 1.5 V; the significant amount of O-2 was evolved compared with the blank during the electrolysis. Potential-step chronocoulospectrometry (PSCCS) from 0.0 V to 1.52 V vs SCE was conducted to observe the change of 1 in solution during the electrocatalysis. The in situ UV visible spectral change showed oxidation of I (Ru-II-OH2) to Ru-III-OH and to further oxidation of Ru-III-OH to Ru-IV=O, and that the Ru-IV=O species mainly exists in a steady state after 200 s in the electrocatalysis. The in situ UV-vis spectral change in a reverse potential step from 1.52V to 0.22V vs SCE exhibited that Ru-II-OH2 completely recovers by two electron re-reduction process from the steady state in the electrocatalysis. The observation of Ru-IV=O in a steady state suggests that a rate determining step in the catalytic cycle is oxidation of Ru-IV=O to Ru-V=O rather than the O-O bonding formation by nucleophilic attack of water to Ru-V=O in the electrocatalysis in a homogeneous solution. (C) 2015 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.jphotochem.2015.06.010

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  • Emission amplification of Ru(bpy)(3)(2+) via energy transfer from pyrene derivatives on synthesized clay 査読

    Keita Sato, Satomi Hagiwara, Daiki Morimoto, Kenji Saito, Masayuki Yagi, Shinsuke Takagi, Tatsuto Yui

    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY313   9 - 14   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  

    Tetracationic pyrene derivatives (Py4+) and dicationic tris(bipyridine)ruthenium(II) (Ru2+) were hybridized on a synthetic clay (SSA) surface; the hybrid is denoted as Py4+/Ru2+/SSA. The photochemical properties of the Py4+/Ru2+/SSA system, especially the energy transfers from Py4+ to Ru2+, were investigated. Absorption analysis revealed fading of Ru2+; this hypochromic effect suggests that the Ru2+ and Py4+ weakly interacted on the SSA surface. The remarkable quenching of the emission from Py4+ by the coadsorbed Ru2+ was probably stimulated by energy transfer from Py4+ to Ru2+. Emission of Ru2+ was amplified 4-5 times within the Py4+/Ru2+/SSA system; the maximum emission quantum yield of Ru2+ was 30.4 +/- 3.8%. Very interestingly, the three independent photochemical behaviors of By(4+)/Ru2+/SSA, namely fading of Ru2+, stimulation of emission quenching of Py4+, and emission amplification of Ru2+, occurred at almost identical critical amounts of adsorbed Ru2+ (11-13% cation exchange capacity (CEC)). Molecular distribution modeling of the SSA surface suggests that Py4+ and Ru2+ adjoined on the SSA surface when the amount of adsorbed Ru2+ exceeded ca. 11% CEC. On the other hand, the unique photochemical and photophysical properties might arise from the adjoined geometrical arrangement of Py4+ and Ru2+ coadsorbed on the SSA surface. (C) 2015 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.jphotochem.2015.05.015

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  • Intercrystal Self-Assembly for the Design of High-Quality Nickel Molybdate Nanocrystals 査読

    Kenji Saito, Shotaro Kazama, Yuki Sato, Tatsuto Yui, Masayuki Yagi

    INORGANIC CHEMISTRY54 ( 18 ) 8869 - 8871   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  

    Nanowire of nickel molybdate hydrate, being recognized as an emerging supercapacitor material, was synthesized from the intercrystal self-assembly process (commonly referred to as oriented aggregation or attachment). The detailed lattice image of a NiMoO4 center dot 0.75H(2)O nanowire and the intermediate nanostructure before reaching the interplanar binding were successfully captured by means of high-resolution transmission and scanning electron microscopies. NiMoO4 center dot 0.75H(2)O possessed highly crystalline surface and internal nanostructures.

    DOI: 10.1021/acs.inorgchem.5b00625

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  • Mechanisms and Factors Controlling Photoisomerization Equilibria, Ligand Exchange, and Water Oxidation Catalysis Capabilities of Mononuclear Ruthenium(II) Complexes 査読

    Masanari Hirahara, Tomoya Hakamata, Aaron B. League, Mehmed Z. Ertem, Kosuke Takahashi, Sho Nagai, Keisuke Inaba, Hirosato Yamazaki, Kenji Saito, Tatsuto Yui, Christopher J. Cramer, Masayuki Yagi

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY ( 23 ) 3892 - 3903   2015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:WILEY-V C H VERLAG GMBH  

    The photoisomerization equilibrium between distal- and proximal-[Ru(tpy)(pyqu)OH2](2+) [d- and p-RuH2O, tpy = 2,2;6,2-terpyridine, pyqu = 2-(2-pyridyl)quinoline] is characterized. The kinetic analysis of the pD-dependent photoisomerization reactions (monitored by H-1 NMR) of d-RuH2O and p-RuH2O shows (1) that both hydroxo isomers, distal- and proximal-[Ru(tpy)(pyqu)OH](+), are inert to photoisomerization, and (2) that the back reaction (distal to proximal) is 3.0 times faster than the forward reaction (proximal to distal). Isolation of distal- and proximal-[Ru(tpy)(pyqu)Cl](+) (d- and p-RuCl) as well as d- and p-RuH2O isomers enabled comprehensive studies on geometric structures, ligand exchange and redox reactions, and water oxidation catalysis for these isomers. The observed aquation rate constant (9.2x10(-2)s(-1) at 40 M) of p-RuCl to form p-RuH2O is 1700 times higher than that (5.4x10(-5)s(-1) at 63 M) of d-RuCl at 298 K owing to the steric repulsion between a chloro ligand and the 8-proton of the quinoline moiety. The turnover frequency (TOF = 1.7x10(-3)s(-1)) of p-RuH2O for catalytic water oxidation is 1.7 times greater than that (1.0x10(-3)s(-1)) for d-RuH2O, in contrast to the [Ru(tpy)(pynp)OH2](2+) isomer system, in which the TOF of the distal isomer is higher than that of the proximal one by one order of magnitude. The mechanisms and factors controlling the photoisomerization equilibria and water oxidation catalysis of the d- and p-RuH2O isomers are discussed on the basis of experimental and theoretical investigations.

    DOI: 10.1002/ejic.201500642

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  • New Series of Dinuclear Ruthenium(II) Complexes Synthesized Using Photoisomerization for Efficient Water Oxidation Catalysis 査読

    Masanari Hirahara, Sho Nagai, Kosuke Takahashi, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    INORGANIC CHEMISTRY54 ( 15 ) 7627 - 7635   2015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  

    A new series of proximal proximal-[Ru-2(tpy)(2)(L)XY](n+) (p,p-Ru2XY, tpy = 2,2':6',2 ''-terpyridine, L = 5-phenyl-2,8-di(2-pyridyl)-1,9,10-anthyridine, X and Y = other coordination sites) were synthesized using, photoisomerization of a mononuclear complex. The p,p-Ru2XY complexes undergo unusual reversible bridge-exchange reactions to generate p,p-Ru-2(mu-Cl), p,p-Ru-2(mu-OH), and p,p-Ru-2(OH)(OH2) with mu-Cl, mu-OH, as well as hydroxo and aquo ligands at X and Y sites of p,p-Ru2XY, respectively. The geometric and electronic structures of these complexes were characterized based on UV vis and H-1 NMR spectra, X-ray crystallography, and density functional theory (DFT) calculations. H-1 NMR data showed C-2 symmetry of p,p-Ru-2(OH)(OH2) with the distorted L chelate and nonequivalence of two tpy ligands, in contrast to the C-2 symmetry of p,p-Ru-2(mu-Cl) and p,p-Ru-2(mu-OH). However, irrespective of the lower symmetry, p,p-Ru-2(OH)(OH2) is predominantly formed in neutral and weakly basic conditions due to the specially stabilized core structure by multiple hydrogen-bond interactions among aquo, hydroxo, and backbone L ligands. The electrochemical data suggested that p,p-Ru-2(OH)(OH2) (Ru-II-OH:Ru-II-OH2) is oxidized to the Ru-III-OH:Ru-III-OH state at 0.64 V vs saturated calomel electrode (SCE) and further to Ru-IV=O:Ru-IV-OH at 0.79 V by successive 1-proton-coupled 2-electron processes at pH 7.0. The cyclic voltammogram data exhibited that the p,p-Ru-2(OH)(OH2) complex works more efficiently for electrocatalytic water oxidation, compared with a similar mononuclear complex distal-[Ru(tpy)(L)OH2](2+) (d-RuOH2) and p,p-Ru-2(mu-Cl) and p,p-Ru-2(mu-OH), showing that the p,p-Ru-2 core structure with aquo and hydroxo ligands is important for efficient electrocatalytic water oxidation. Bulk electrolysis of the p,p-Ru-2(OH)(OH2) solution corroborated the electrocatalytic cycle involving the Ru-III-OH:Ru-III-OH state species as a resting state. The mechanistic insight into O-O bond formation for O-2 production was provided by the isotope effect on electrocatalytic water oxidation by p,p-Ru-2(OH)(OH2) and d-RuOH2 in H2O and D2O media.

    DOI: 10.1021/acs.inorgchem.5b01264

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  • Open Pore Architecture of an Ordered Mesoporous IrO2 Thin Film for Highly Efficient Electrocatalytic Water Oxidation 査読

    Debraj Chandra, Naoto Abe, Daisuke Takama, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    CHEMSUSCHEM8 ( 5 ) 795 - 799   2015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:WILEY-V C H VERLAG GMBH  

    We report the first accessible channel-like open pore architecture of ordered 2D hexagonal mesoporous IrO2 films and its utilization as an efficient anode for electrocatalytic water oxidation. A well-ordered mesostructure of circa 7nm pores were obtained by a facile one-pot soft-templating strategy, employing a [Ir(OH)(6)](2-) precursor stabilized by a triblock copolymer PluronicF127 as a pore-directing template. A mesoporous IrO2 film calcined at 400 degrees C (approximate to 70nm thick) affords a high surface area of 512m(2)cm(-3) and 2times higher O-2 evolution during the electrocatalytic water oxidation relative to an untemplated IrO2 coating film.

    DOI: 10.1002/cssc.201402911

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  • Sustainable Synthesis of Niobia Thin Films with Open Mesopore Channels 査読

    Kenji Saito, Yuki Sato, Shohei Okuyama, Kazuki Matsubara, Tatsuto Yui, Masayuki Yagi

    INORGANIC CHEMISTRY54 ( 5 ) 2171 - 2175   2015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 current approaches to electrochemically synthesizing valve metal derived nanochannel films with longitudinal nanospaces aligned at a right angle to planar substrates rely on highly toxic fluoride compounds and require severe reaction conditions. Herein, we report on a fluoride-free, room-temperature, electrochemical synthesis Of a genuine mesoporous niobia thin filth from the parent metal. The electrochemical reaction is driven by only a 1 V bias with respect to a Pt counter electrode in at aqueous solution. The solution contained an inexpensive, less toxic potassium hydroxide, and the reaction produced favorable byproducts, namely, recyclable K8Nb6O19 and H-2.

    DOI: 10.1021/ic502580e

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  • Remarkable Stimulation of Emission Quenching on a Clay Surface 査読

    Keita Sato, Kazuki Matsubara, Satomi Hagiwara, Kenji Saito, Masayuki Yagi, Shinsuke Takagi, Tatsuto Yui

    LANGMUIR31 ( 1 ) 27 - 31   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  

    Tetra-cationic pyrene derivative (Py4+) and tris(bipyridine)ruthenium(II) (Ru2+) were hybridized onto the surface of a synthesized clay. We observed the remarkable stimulation of excited Py4+ emission quenching on the clay surface, with a very large apparent quenching rate constant (k(q) = 7.4 +/- 0.7 x10 (15) L mol(-1) s(-1)).

    DOI: 10.1021/la504597t

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  • Facile and simple fabrication of an efficient nanoporous WO3 photoanode for visible-light-driven water splitting 査読

    Xiaohong Zhang, Debraj Chandra, Masashi Kajita, Hidehito Takahashi, Li Dong, Akinori Shoji, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY39 ( 35 ) 20736 - 20743   2014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:PERGAMON-ELSEVIER SCIENCE LTD  

    Tungsten trioxide (WO3) films with nanoporous morphology were prepared by a facile and simple method utilizing commercially available WO3 nanopowder with polyethylene glycol to guide porosity of a nanostructure, and the resulted photoanode was working efficiently for visible-light-driven water oxidation. The SEM observation and XRD measurement revealed formation of interparticulate nanopores between the well-connected WO3 crystaline particles of dimension ca. 100-200 nm. The nanoporous WO3 electrode generated a significant photoanodic current density of 1.8 mA cm(-2) due to water oxidation at 1.0 V versus Ag/AgCl on visible light irradiation (lambda>390 nm, 100 mW cm(-2)). The onset potential of the WO3 electrode was 0.67 V versus a reversible hydrogen electrode (RHE), being lower by 0.56 V than the theoretical potential for water oxidation (1.23 V versus RHE). The incident photon to current conversion efficiency (IPCE) reached 45% at 400 nm of light wavelength and 1.04 V versus Ag/AgCl of an applied potential. The photoanodic current and photostability of the WO3 electrode were improved by addition of Co2+ ions in the electrolyte solution during photoelectrocatalysis. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ijhydene.2014.06.062

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  • Unique and facile solvothermal synthesis of mesoporous WO3 using a solid precursor and a surfactant template as a photoanode for visible-light-driven water oxidation 査読

    Dong Li, Debraj Chandra, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    NANOSCALE RESEARCH LETTERS9   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:SPRINGER  

    Mesoporous tungsten trioxide (WO3) was prepared from tungstic acid (H2WO4) as a tungsten precursor with dodecylamine (DDA) as a template to guide porosity of the nanostructure by a solvothermal technique. The WO3 sample (denoted as WO3-DDA) prepared with DDA was moulded on an electrode to yield efficient performance for visible-light-driven photoelectrochemical (PEC) water oxidation. Powder X-ray diffraction (XRD) data of the WO3-DDA sample calcined at 400 degrees C indicate a crystalline framework of the mesoporous structure with disordered arrangement of pores. N-2 physisorption studies show a Brunauer-Emmett-Teller (BET) surface area up to 57 m(2) g(-1) together with type IV isotherms and uniform distribution of a nanoscale pore size in the mesopore region. Scanning electron microscopy (SEM) images exhibit well-connected tiny spherical WO3 particles with a diameter of ca. 5 to 20 nm composing the mesoporous network. The WO3-DDA electrode generated photoanodic current density of 1.1 mA cm(-2) at 1.0 V versus Ag/AgCl under visible light irradiation, which is about three times higher than that of the untemplated WO3. O-2 (1.49 mu mol; Faraday efficiency, 65.2%) was evolved during the 1-h photoelectrolysis for the WO3-DDA electrode under the conditions employed. The mesoporous electrode turned out to work more efficiently for visible-light-driven water oxidation relative to the untemplated WO3 electrode.

    DOI: 10.1186/1556-276X-9-542

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  • Visible-light-driven water oxidation at a polychromium-oxo-electrodeposited TiO2 electrode as a new type of earth-abundant photoanode 査読

    Masashi Kajita, Kenji Saito, Naoto Abe, Akinori Shoji, Kazuki Matsubara, Tatsuto Yui, Masayuki Yagi

    CHEMICAL COMMUNICATIONS50 ( 10 ) 1241 - 1243   2014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  

    A polychromium-oxo-deposited TiO2 electrode was fabricated as an earth-abundant photoanode for visible-light-driven water oxidation by a simple electrochemical technique. The photoelectrocatalytic water oxidation could occur based on a specific interfacial charge transfer (IFCT) from a Cr-III to the TiO2 conduction band.

    DOI: 10.1039/c3cc47764a

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  • A visible light responsive rhodium and antimony-codoped SrTiO3 powdered photocatalyst loaded with an IrO2 cocatalyst for solar water splitting 査読

    Rikako Asai, Hiroaki Nemoto, Qingxin Jia, Kenji Saito, Akihide Iwase, Akihiko Kudo

    CHEMICAL COMMUNICATIONS50 ( 19 ) 2543 - 2546   2014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  

    IrO2-loaded SrTiO3 doped with rhodium and antimony synthesized by a conventional solid-state reaction splits water under visible light and simulated sunlight irradiation giving 0.1% of the apparent quantum yield at 420 nm. The response wavelength up to 500 nm is the longest among achieved photocatalytic water splitting with one-step photoexcitation.

    DOI: 10.1039/c3cc49279f

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  • The KCaSrTa5O15 photocatalyst with tungsten bronze structure for water splitting and CO2 reduction 査読

    Tomoaki Takayama, Kentaro Tanabe, Kenji Saito, Akihide Iwase, Akihiko Kudo

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS16 ( 44 ) 24417 - 24422   2014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  

    KCaSrTa5O15 with tungsten bronze structure and a band gap of 4.1 eV showed activity for water splitting without cocatalysts. The activity was improved by loading the NiO cocatalyst. The apparent quantum yield of optimized NiO-loaded KCaSrTa5O15 was 2.3% at 254 nm for water splitting. When CO2 gas was bubbled into the reactant aqueous solution, Ag cocatalyst-loaded KCaSrTa5O15 produced CO and H-2 as reduction products of CO2 and H2O, respectively, and O2 as an oxidation product of H2O. The carbon source of CO was confirmed to be CO2 molecules by using (CO2)-C-13. The ratio of the number of electrons to that of holes calculated from the amounts of products (CO, H-2 and O-2) was almost unity. Additionally, the ratio of the turnover number of electrons consumed for CO production to the total number of an Ag atom of the cocatalyst that was the active site for CO2 reduction was 8.6 at 20 h. These results indicate that water was consumed as an electron donor for this photocatalytic CO2 reduction in an aqueous medium. Thus, KCaSrTa5O15 with tungsten bronze structure has arisen as a new photocatalyst that is active for water splitting and CO2 reduction utilizing water as an electron donor.

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  • Crystallization of Tungsten Trioxide Having Small Mesopores: Highly Efficient Photoanode for Visible-Light-Driven Water Oxidation 査読

    Debraj Chandra, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION52 ( 48 ) 12606 - 12609   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:WILEY-V C H VERLAG GMBH  

    DOI: 10.1002/anie.201306004

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  • Monoclinic Ag2Mo2O7 Nanowire: A New Ag-Mo-O Nanophotocatalyst Material 査読

    Kenji Saito, Shotaro Kazama, Kazuki Matsubara, Tatsuto Yui, Masayuki Yagi

    INORGANIC CHEMISTRY52 ( 15 ) 8297 - 8299   2013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  

    We report a template-free facile technique that allows for the first ever synthesis of a monoclinic Ag2Mo2O7 nanowire (m-Ag2Mo2O7-NW), using a commercially available MoO3 particle. The nanowire possessed high crystallinity and structural homogeneity and strongly suggested that the nanowire was grown through an oriented aggregation mechanism in contrast to the case of a typical solution-phase method. The corresponding bulky counterpart showed no photoresponse; however, a complete structural transformation toward a nanowire triggered activity for O-2 evolution in the presence of Ag+ as an electron acceptor under visible-light irradiation.

    DOI: 10.1021/ic401236b

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  • Arrangement effect of the di-μ-oxo dimanganese catalyst and Ru(bpy) 32+ photoexcitation centers adsorbed on mica for visible-light-derived water oxidation 査読

    Masanari Hirahara, Hirosato Yamazaki, Satoshi Yamada, Kazuki Matsubara, Kenji Saito, Tatsuto Yui, Masayuki Yagi

    Catalysis Science and Technology3 ( 7 ) 1776 - 1781   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)  

    A photosynthetic photosystem II (PS II) model was developed by adsorbing [(OH2)(terpy)MnIII(μ-O)2Mn IV(terpy)(OH2)]3+ (1, terpy = 2,2′:6′,2″-terpyridine) as an oxygen evolving center and Ru(bpy)32+ (bpy = 2,2′-bipyridine) as a photoexcitation center onto mica. The mica adsorbates were prepared by three different methods
    Adsorbate A was prepared by adsorption of 1 followed by Ru(bpy)32+ on mica, and Adsorbates B and C were prepared by the opposite adsorption order and co-adsorption of 1 and Ru(bpy) 32+, respectively. The UV-visible diffuse reflectance (DR) spectroscopic data and emission decay measurements of the photoexcited Ru(bpy)32+ suggested the different arrangements of 1 and Ru(bpy)32+ among the three adsorbates in a mica interlayer. For Adsorbate A, Ru(bpy)32+ could be adsorbed near the mica surface, being shallowly intercalated relative to 1. For Adsorbate B, 1 is adsorbed near the mica surface, Ru(bpy)32+ being deeply intercalated relative to 1. For Adsorbate C, either 1 or Ru(bpy) 32+ could be randomly intercalated relative to the other adsorbates. In photochemical water oxidation experiments, a significant amount of O2 was evolved when visible light was used to irradiate an aqueous suspension of Adsorbate A containing a S2O82- electron acceptor in a liquid phase, whereas O2 was not evolved under the same conditions when using Adsorbates B and C. 1 is considered to work for photochemical water oxidation in Adsorbate A due to an efficient electron transport from deeply intercalated 1 to S2O82- ions in a liquid phase via Ru(bpy)32+ photoexcitation near the mica adsorbate surface. © 2013 The Royal Society of Chemistry.

    DOI: 10.1039/c3cy00010a

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  • Fabrication of highly crystalline SnNb2O6 shell with a visible-light response on a NaNbO3 nanowire core 査読

    Kenji Saito, Akihiko Kudo

    Inorganic Chemistry52 ( 10 ) 5621 - 5623   2013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)  

    A visible-light-absorbing SnNb2O6 shell with high crystallinity was successfully fabricated on a NaNbO3 nanowire through a molten salt treatment of the NaNbO3 nanowire of the starting material with SnCl2, whereas the fabrication was not successful on the TT phase of a niobia nanowire. The difference will come from the formation processes of SnNb2O6 crystals (ion-exchange reaction vs thermally induced crystallization reaction). The core/shell nanowire obtained from NaNbO3 showed photocatalytic activity comparable to that of H2 evolution in the presence of an electron donor under visible-light irradiation (λ &gt
    420 nm), compared with the corresponding bulky counterpart. © 2013 American Chemical Society.

    DOI: 10.1021/ic4002175

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  • Diameter-dependent photocatalytic performance of niobium pentoxide nanowires 査読

    Kenji Saito, Akihiko Kudo

    DALTON TRANSACTIONS42 ( 19 ) 6867 - 6872   2013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  

    Thermal reactions of a niobium oxo-oxalate complex, (NH4)(3)[NbO(Ox)(3)]center dot H2O, with ternary amines having more than two methylene chain units as structure directing solvents led to self-assemblies suitable for one dimensional growth to afford amorphous niobium oxide nanowires whose diameters depended on methylene chain lengths in the amines. These nanowires were crystallized at 773 K to obtain the TT phase of Nb2O5 whilst maintaining the same structure as before calcination. There was almost no difference in crystallinities, BET surface areas, and growth directions among the Nb2O5 nanowires. PtCl62- was reduced by photogenerated electrons in the conduction band of the Nb2O5 nanowires following UV light irradiation (lambda > 300 nm) in the presence of an electron donor. Metallic Pt nanoparticles were selectively deposited on a short axis plane of the nanowires prepared with tridodecylamine, whereas the others had the Pt nanoparticles throughout the surfaces. This indicated that photogenerated electrons moved along the nanowire growth direction associated with transfer of holes to the nanowire sidewall. The anisotropic carrier transport afforded the highest activity for photocatalytic H-2 evolution reactions under UV light irradiation (lambda > 300 nm).

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  • Adsorptive and Kinetic Properties on Photocatalytic Hydrogenation of Aromatic Ketones upon UV Irradiated Polycrystalline Titanium Dioxide: Differences between Acetophenone and Its Trifluoromethylated Derivative 査読

    Shigeru Kohtani, Eito Yoshioka, Kenji Saito, Akihiko Kudo, Hideto Miyabe

    JOURNAL OF PHYSICAL CHEMISTRY C116 ( 33 ) 17705 - 17713   2012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  

    Adsorptive and kinetic properties on photocatalytic hydrogenation of acetophenone (AP) and 2,2,2-trifluoroacetophenone (TFAP) have been investigated upon UV irradiated P25 TiO2 in deaerated ethanol. Kinetic, data of An were analyzed by the Langmuir-Hinschelwood kinetic expression, -dCs/dt = k(max)K(irr)Cs/(1 + AK(irr)Cs), where k(max) is the maximum rate and K-irr is the apparent adsorption constant under the irradiation. The hydrogenation of AP proceeded in the light limited controlled manner, in which k(max) increased with increasing light intensity. The hydrogenation of TFAP exhibited first-order kinetics due to the predominant formation of ketal in ethanol. Electron transfer efficiency from conduction band and/or electron trap sites on TiO2 to AP or TFAP was also evaluated. In the case of AP, ca. 75% electrons trapped at relative shallow sites were able to transfer into AP, whereas ca. 25% ones trapped at deep sites remained on the TiO2 surface. For TFAP, all of the trapped electrons transferred into TFAP. Reaction models to account for these experimental results are proposed and discussed in detail.

    DOI: 10.1021/jp3056174

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  • Photocatalytic Reduction of Carbon Dioxide over Ag Cocatalyst-Loaded ALa(4)Ti(4)O(15) (A = Ca, Sr, and Ba) Using Water as a Reducing Reagent 査読

    Kosuke Iizuka, Tomoaki Wato, Yugo Miseki, Kenji Saito, Aldhiko Kudo

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY133 ( 51 ) 20863 - 20868   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  

    Ag cocatalyst-loaded ALa(4)Ti(4)O(15) (A = Ca, Sr, and Ba) photocatalysts with 3.79-3.85 eV of band gaps and layered perovskite structures showed activities for CO2 reduction to form CO and HCOOH by bubbling CO2 gas into the aqueous suspension of the photocatalyst powder without any sacrificial reagents. Ag cocatalyst-loaded BaLa4Ti4O15 was the most active photocatalyst. A liquid-phase chemical reduction method was better than impregnation and in situ photodeposition methods for the loading of the Ag cocatalyst. The Ag cocatalyst prepared by the liquid-phase chemical reduction method was loaded as fine particles with the size smaller than 10 nm on the edge of the BaLa4Ti4O15 photocatalyst powder with a plate shape during the CO2 reduction. CO was the main reduction product rather than H-2 even in an aqueous medium on the optimized Ag/BaLa4Ti4O15 photocatalyst. Evolution of O-2 in a stoichiometric ratio (H-2+CO: O-2 = 2:1 in a molar ratio) indicated that water was consumed as a reducing reagent (an electron donor) for the CO2 reduction. Thus, an uphill reaction of CO2 reduction accompanied with water oxidation was achieved using the Ag/BaLa4Ti4O15 photocatalyst.

    DOI: 10.1021/ja207586e

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  • Multiple photosynthetic reaction centers composed of supramolecular assemblies of a zinc porphyrin dendrimer with pyridylnaphthalenediimide 査読

    Shunichi Fukuzumi, Kei Ohkubo, Kenji Saito, Yukiyasu Kashiwagi, Tony Khoury, Maxwell J. Crossley

    JOURNAL OF PORPHYRINS AND PHTHALOCYANINES15 ( 11-12 ) 1292 - 1298   2011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:WORLD SCI PUBL CO INC  

    Multiple photosynthetic reaction centers have successfully been constructed using a supramolecular complex of zinc porphyrin dendrimer [D(ZnP)(16)] with pyridylnaphthalenediimide (PyNIm) in benzonitrile. The apparent formation constant determined from the fluorescence quenching of the singlet excited state of porphyrin moieties by PyNIm is significantly larger than that determined from the UV-vis spectral change. This indicates that efficient energy migration occurs between the porphyrin units of the dendrimer prior to the electron transfer from the singlet excited state of zinc porphyrin to PyNIm. The charge-separated (CS) state has been successfully detected as the transient absorption spectrum in the laser flash photolysis. The CS lifetime of in the supramolecular complex of D(ZnP)(16) with PyNIm was determined to be 0.83 ms at 298 K.

    DOI: 10.1142/S1088424611004178

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  • Molten Salt Treatment of Sodium Niobate Nanowires Affording Valence Band-Controlled (AgNbO3)-(NaNbO3) Nanowires 招待 査読

    Kenji Saito, Kazunori Koga, Akihiko Kudo

    NANOSCIENCE AND NANOTECHNOLOGY LETTERS3 ( 5 ) 686 - 689   2011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 SCIENTIFIC PUBLISHERS  

    Valence band controlled silver niobate-sodium niobate nanowires [(AgNbO3)-(NaNbO3)NW] were synthesized by molten salt treatment of sodium niobate nanowires (NaNbO3-NW). Characterization of the nanowires using diffuse reflection, X-ray photoelectron spectroscopies, and transmission electron microscopy suggested composite structures consisting of a sodium niobate core and a silver niobate shell. (AgNbO3)-(NaNbO3)NW showed photocatalytic activities for H-2 and O-2 evolution from an aqueous solution containing sacrificial reagents under incident light having wavelength longer than 400 nm.

    DOI: 10.1166/nnl.2011.1226

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  • Multiple photosynthetic reaction centres using zinc porphyrinic oligopeptide-fulleropyrrolidine supramolecular complexes 査読

    Shunichi Fukuzumi, Kenji Saito, Kei Ohkubo, Vincent Troiani, Hongjin Qiu, Suresh Gadde, Francis D'Souza, Nathalie Solladie

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS13 ( 38 ) 17019 - 17022   2011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  

    Multiple charge-separation sites have successfully been constructed using supramolecular complexes of multiporphyrinic oligopeptides [P(ZnP)(n), n = 2, 4, 8] with fulleropyrrolidine bearing a pyridine or imidazole coordinating ligand, which are organized by utilizing pi-pi interaction in addition to the coordination bond.

    DOI: 10.1039/c1cp22364j

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  • Multiple photosynthetic reaction centres composed of supramolecular assemblies of zinc porphyrin dendrimers with a fullerene acceptor 査読

    Shunichi Fukuzumi, Kenji Saito, Kei Ohkubo, Tony Khoury, Yukiyasu Kashiwagi, Mark A. Absalom, Suresh Gadde, Francis D'Souza, Yasuyuki Araki, Osamu Ito, Maxwell J. Crossley

    CHEMICAL COMMUNICATIONS47 ( 28 ) 7980 - 7982   2011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  

    Multiple photosynthetic reaction centres have successfully been constructed using supramolecular complexes of zinc porphyrin dendrimers [D(ZnP)(n): n = 4, 8, 16] with fulleropyrrolidine bearing a pyridine ligand (C(60)py). Efficient energy migration occurs completely between the ZnP units of dendrimers prior to the electron transfer with increasing the generation of dendrimers to attain an extremely long charge-separation lifetime.

    DOI: 10.1039/c1cc11725d

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  • Lithium niobate nanowires for photocatalytic water splitting 査読

    Kenji Saito, Kazunori Koga, Akihiko Kudo

    DALTON TRANSACTIONS40 ( 15 ) 3909 - 3913   2011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  

    Molecule-based preparation of lithium niobate nanowires was achieved by proper combination of a niobium oxooxalate complex, a structure-directing reagent, and a lithium source. Structural and photophysical properties of the nanowires obtained were characterized by several microscopic and spectroscopic techniques. The nanowire was employed as a photocatalyst for overall water splitting, and H-2 or O-2 evolution reaction from an aqueous solution containing a sacrificial reagent under UV light irradiation to show enhanced photocatalytic properties as compared with a bulky counterpart prepared by a solid state reaction. The factors contributing to the enhancement of the photocatalytic performance were suggested to be an increase in active sites for the photocatalytic reaction in conjunction with a large surface area and a small particle size.

    DOI: 10.1039/c0dt01844a

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  • InBO3 Photocatalyst with Calcite Structure for Overall Water Splitting 査読

    Qingxin Jia, Yugo Miseki, Kenji Saito, Hisayoshi Kobayashi, Akihiko Kudo

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN83 ( 10 ) 1275 - 1281   2010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:CHEMICAL SOC JAPAN  

    Indium borate (InBO3) with a calcite structure that was prepared by a solid-state reaction and a two-step precipitation method was employed as a photocatalyst for water splitting under UV light irradiation. The InBO3 photocatalyst prepared by the precipitation method showed higher activity than that prepared by the solid-state reaction when a NiO cocatalyst was loaded on the photocatalyst. In the case of the precipitation method, the photocatalytic activity over NiO/InBO3 strongly depended on the calcination temperature and an excess amount of boric acid in the preparation. The correlation among preparation conditions, physical properties, and photocatalytic activities for water splitting has revealed that crystallinity and particle size mainly contributed to the increase in the photocatalytic activity.

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  • Photocatalytic hydrogenation of acetophenone derivatives and diaryl ketones on polycrystalline titanium dioxide 査読

    Shigeru Kohtani, Eito Yoshioka, Kenji Saito, Akihiko Kudo, Hideto Miyabe

    CATALYSIS COMMUNICATIONS11 ( 13 ) 1049 - 1053   2010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  

    In the absence of molecular oxygen, various aromatic ketones such as acetophenone derivatives and diaryl ketones were photocatalytically hydrogenated on polycrystalline titanium dioxide (Degussa P25) under UV light irradiation (>340 nm). The desired secondary alcohols were obtained with excellent chemical efficiency (almost 100% yields for 10 examples) by choosing ethanol as a sacrificial hole scavenger, which was oxidized into acetaldehyde. (C) 2010 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.catcom.2010.04.022

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  • Niobium-Complex-Based Syntheses of Sodium Niobate Nanowires Possessing Superior Photocatalytic Properties 査読

    Kenji Saito, Akihiko Kudo

    INORGANIC CHEMISTRY49 ( 5 ) 2017 - 2019   2010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  

    Sodium niobates with nanowire morphology (NaNbO(3)-NW) were synthesized in a large scale by use of a niobium oxooxalate complex as the starting material. This NaNbO(3)-NW showed definitely enhanced photocatalytic activity for H(2) or O(2) evolution in the presence of sacrificial reagents and an overall water splitting under UV-light irradiation, as compared with a bulky counterpart (NaNbO(3)-B), This is the first example that an overall water splitting into H(2) and O(2) proceeded on the semiconductor nanowire photocatalyst.

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  • Solar hydrogen production over novel metal sulfide photocatalysts of AGa(2)In(3)S(8) (A = Cu or Ag) with layered structures 査読

    Hiroshi Kaga, Kenji Saito, Akihiko Kudo

    CHEMICAL COMMUNICATIONS46 ( 21 ) 3779 - 3781   2010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  

    Layered metal sulfides of CuGa2In3S8 with a 1.91-eV band gap and AgGa2In3S8 with a 2.27-eV band gap gave 15% apparent quantum yields at 560 nm and 460 nm for H-2 evolution from aqueous solutions containing K2SO3 and Na2S as electron donors with assistance of Rh cocatalysts, respectively, and Rh/CuGa2In3S8 responded to 680 nm for the photocatalytic H-2 evolution.

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  • Solar Water Splitting Using Powdered Photocatalysts Driven by Z-Schematic Interparticle Electron Transfer without an Electron Mediator 査読

    Yasuyoshi Sasaki, Hiroaki Nemoto, Kenji Saito, Akihiko Kudo

    JOURNAL OF PHYSICAL CHEMISTRY C113 ( 40 ) 17536 - 17542   2009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  

    Ru/SrTiO(3):Rh photocatalyst powder for H(2) evolution and varied photocatalyst powders for O(2) evolution Such as BiVO(4) and WO(3) were suspended in acidified aqueous solutions. resulting in showing activities for water splitting into H(2) and O(2) in a stoichiometric ratio without an electron mediator under visible light irradiation. The photocatalytic activities were dependent oil pH. The highest activity was obtained at pH 3.5. An optical microscope observation of the aqueous Suspension containing Ru/SrTiO(3):Rh and BiVO(4) powders at pH 3.5 revealed that these powders aggregated with suitable contact. The condition of Rh doped in SrTiO(3) also affected strongly the photocatalytic activity and quenching of the photoluminescence of BiVO(4). The high photocatalytic activity was obtained and the luminescence was remarkably quenched, when SrTiO(3):Rh containing, Rh species with reversible redox properties was used and mixed. These results indicated that the photocatalytic water splitting and quenching of the photoluminescence Occurred through interparticle electron transfer from the conduction band of BiVO(4) to impurity level consisting of the reversible Rh species doped in SrTiO(3). Thus, We Succeeded in constructing unique and simple Z-scheme photocatalysis systems driven by interparticle electron transfer under visible light irradiation. In addition, the (Ru/SrTiO(3):Rh)-(BiVO(4)) system split water under simulated Sunlight (AM-1.5).

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  • Controlled Synthesis of TT Phase Niobium Pentoxide Nanowires Showing Enhanced Photocatalytic Properties 査読

    Kenji Saito, Akihiko Kudo

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN82 ( 8 ) 1030 - 1034   2009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:CHEMICAL SOC JAPAN  

    The controlled synthesis of niobia nanowires with TT (tief-tief) phase (TT-Nb2O5-NW) that is the stable phase at low temperature was accomplished through calcination of niobium-based amorphous nanowires (Nb2O5-NW) composed of closely packed primary particles, obtained by the reaction of water-soluble niobium oxo-oxalate complex (NH4)(3)[NbO(Ox)(3)]center dot H2O (Ox = oxalate) with trioctylamine (TOA) employed as a structure-directing agent. TT-Nb2O5-NW gave a sharp absorption edge, which agreed well with that of the same crystalline phase of bulk niobia (TT-Nb2O5-B), suggesting no influence on the band gap energies by the shape transformation. An aqueous suspension containing TT-Nb2O5-NW and a sacrificial reagent was irradiated with white light (lambda > 300 nm) from a Xe lamp to afford the enhanced photocatalytic activities for H-2 or O-2 evolution compared with that of conventional TT-Nb2O5-B.

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  • Sensitization of NaMO3 (M: Nb and Ta) Photocatalysts with Wide Band Gaps to Visible Light by Ir Doping 査読

    Akihide Iwase, Kenji Saito, Akihiko Kudo

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN82 ( 4 ) 514 - 518   2009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:CHEMICAL SOC JAPAN  

    NiO/NaNbO3 (BG: 3.5 eV) showed photocatalytic activity for water splitting into H-2 and O-2 under UV irradiation. When NaMO3 (M: Nb and Ta) was codoped with iridium ions and alkaline earth metal ions or lanthanum ions, a new visible-light absorption band was observed in addition to the band gap absorption band of the host material. The codopants of alkaline earth metal and lanthanum ions contributed to maintaining the charge balance and forming of fine crystals of the NaMO3 powder. These NaNbO3 and NaTaO3 codoped with iridium ions and alkaline earth metal ions or lanthanum ions showed photocatalytic activities for H-2 or O-2 evolution from an aqueous solution containing a sacrificial reagent under visible light irradiation.

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  • Nanocrystalline CaZrTi2O7 Photocatalyst Prepared by a Polymerizable Complex Method in the Presence of Cs2CO3 Flux for Water Splitting 査読

    Yugo Miseki, Kenji Saito, Akihiko Kudo

    CHEMISTRY LETTERS38 ( 2 ) 180 - 181   2009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:CHEMICAL SOC JAPAN  

    Photocatalytic and photophysical properties of CaZrTi2O7 were investigated. When the CaZrTi2O7 powder was prepared by a polymerizable complex method in the presence of Cs2CO3 flux, powder with high crystallinity and 100-300 nm of a primary particle size was obtained. The band gap of the CaZrTi2O7 powder was 3.6 eV. It showed a broad photoluminescence band around 580 nm at 77 K. Activated NiO/CaZrTi2O7 showed photocatalytic activity for water splitting into H-2 and O-2 under UV irradiation.

    DOI: 10.1246/cl.2009.180

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  • Synthesis, Characterization, Redox Properties, and Photodynamics of Donor-Acceptor Nanohybrids Composed of Size-Controlled Cup-Shaped Nanocarbons and Porphyrins 査読

    Masataka Ohtani, Kenji Saito, Shunichi Fukuzumi

    CHEMISTRY-A EUROPEAN JOURNAL15 ( 36 ) 9160 - 9168   2009年

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    記述言語:英語   出版者・発行元:WILEY-V C H VERLAG GMBH  

    Cup-shaped nanocarbons (CNC) generated by the electron-transfer reduction of cup-stacked carbon nanotubes have been functionalized with porphyrins (H2P) as light-capturing chromophores. The resulting donor-acceptor nanohybrid has been characterized by thermogravimetric analysis (TGA), Raman and IR spectroscopy, transmission electron microscopy., elemental analysis, and UV/Vis spectroscopy. ne weight of the porphyrins attached to the cup-shaped nanocarbons was determined as 20% by TGA and elemental analysis. ne UV/Vis absorption spectrum of CNC-(H2P2)(n) in DNIF agrees well with that obtained by the superposition of reference porphyrin (ref-H2P) and cup-shaped nanocarbons. The photoexcitation of the CNC-(H2P)(n) nanohybrid results in formation of the charge-separated (CS) state to attain the longest CS lifetime (0.64 +/- 0.01 ms) ever reported for donor-acceptor nanohybrids, which may arise from efficient electron migration following the charge separation. The formation of a radical ion pair was detected directly by electron spin resonance (ESR) measurements under photoirradiation of CNC-(H2P)(n) with a high-pressure mercury lamp in frozen DNIF at 153 K. The observed ESR signal at g=2.0044 agrees with that of ref-H2P center dot+ produced by one-electron oxidation with [Ru(bpy)(3)](+) in deaerated CHCl3, indicating the formation of H2P center dot+ The electron-acceptor ability of the reference CNC compound (ref-CNC) was also examined by the electron-transfer reduction of ref-CNC by a series of semiquinone radical anions.

    DOI: 10.1002/chem.200900427

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  • Bis-ortho-diynyl-arene C(60) adducts on SnO(2) films for photoelectrochemical cells 査読

    Kenji Saito, Arno S. Rettenbacher, Dennis W. Smith, Shunichi Fukuzumi

    JOURNAL OF MATERIALS CHEMISTRY18 ( 27 ) 3237 - 3241   2008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  

    Bis-ortho-diynyl-arene C(60) adducts (BODA-co-C(60)), a novel pre-network polymer of aromatic enediynes possessing a fullerene core that is prepared by the Bergman cyclopolymerization of bis-ortho-diynyl-arene monomer with C(60), have been organized uniformly onto a nanostructured SnO(2) electrode by utilizing the simple drop cast method to maximize the intrinsic high solubility of BODA-co-C(60), over 2 mg/100 mu L in chloroform. The resulting robust and homogeneous film exhibits a continuous smooth absorption with no shoulder, which agrees well with that of a chloroform solution containing BODA-co-C(60), suggesting that no aggregation occurs during the solvent evaporation process. White light was irradiated to a BODA-co-C(60) thin film employed as the working electrode to generate a relatively high anodic photocurrent in the presence of the I(-)/I(3)(-) redox couple. This is characteristic for the photogalvanic type of photocurrent generation and indicates the successful electron injection from the C(60) anions to the SnO(2) nanocrystallites, following the photoinduced charge separation. The result with regard to a photocurrent action spectrum allows us to conclude that polyarylene networks covering a C(60) core act as solubilizer and are not responsible for the photocurrent generation under white light illumination. Thus, this strategy for fullerene solubilization using polyarylene units is critical to a uniform organizing of C(60) onto nanocrystalline SnO(2) as a building block, leading to the construction of an efficient light-to-energy conversion system in combination with the light harvester.

    DOI: 10.1039/b717906e

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  • Nondestructive formation of supramolecular nanohybrids of single-walled carbon nanotubes with flexible porphyrinic polypeptides 査読

    Kenji Saito, Vincent Troiani, Hongjin Qiu, Nathalie Solladie, Takao Sakata, Hirotaro Mori, Mitsuo Ohama, Shunichi Fukuzumi

    JOURNAL OF PHYSICAL CHEMISTRY C111 ( 3 ) 1194 - 1199   2007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  

    Strategies for single-waited carbon nanotube (SWNT) separation are critical to developing nanotubes as useful nanoscale building blocks. Herein, diameter-selective dispersion of HiPco single-walled carbon nanotubes has been accomplished through noncovalent complexation of the nondestructive nanotubes with a flexible porphyrinic polypeptide bearing 16 porphyrin units [P(H2P)(16)] in DMF at 298 K. Supramolecular formation occurs through wrapping of peptidie backbone in P(H-2)P)(16) and pi-pi interaction between porphyrins and nanotubes to extract the large-diameter nanotubes (ca. 1.3 nm) as revealed by ultraviolet-visible-near-infrared and Raman spectroscopy as well as high-resolution transmission electron micropscopy. The photoexcitation of the supramolecular complex affords the long-lived charge-separated state.

    DOI: 10.1021/jp065615i

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  • Nanostructural control of cup-stacked carbon nanotubes with 1-benzyl-1,4-dihydronicotinamide dimer via photoinduced electron transfer 査読

    Kenji Saito, Masataka Ohtani, Shunichi Fukuzumi

    CHEMICAL COMMUNICATIONS ( 1 ) 55 - 57   2007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  

    The photoinduced electron-transfer reduction of cup-stacked carbon nanotubes (CSCNTs) with 1-benzyl-1,4-dihydronicotinamide dimer [(BNA)(2)] results in the electrostatic destacking of CSCNTs to afford CSCNTs with uniform size.

    DOI: 10.1039/b614181a

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  • Organic solar cells. Supramolecular composites of porphyrins and fullerenes organized by polypeptide structures as light harvesters 査読

    Taku Hasobe, Kenji Saito, Prashant V. Kamat, Vincent Troiani, Hongjin Qiu, Nathalie Solladie, Kil Suk Kim, Jong Kang Park, Dongho Kim, Francis D'Souza, Shunichi Fukuzumi

    JOURNAL OF MATERIALS CHEMISTRY17 ( 39 ) 4160 - 4170   2007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  

    We have constructed supramolecular solar cells composed of a series of porphyrin-peptide oligomers [porphyrin functionalized alpha-polypeptides, P(H2P)(n) or P(ZnP)(n) (n = 1, 2, 4, 8, 16)], and fullerenes assembled on a nanostructured SnO2 electrode using an electrophoretic deposition method. Remarkable enhancement in the photoelectrochemical performance as well as the broader photoresponse in the visible and near-infrared regions is seen with increasing the number of porphyrin units in alpha-polypeptide structures. Formation of supramolecular clusters of porphyrins and fullerenes prepared in acetonitrile-toluene = 3 : 1 has been confirmed by transmission electron micrographs (TEM) and the absorption spectra. The highly colored composite clusters of porphyrin-peptide oligomers and fullerenes have been assembled as three-dimensional arrays onto nanostructured SnO2 films using an electrophoretic deposition method. A high power conversion efficiency (g) of similar to 1.6% and the maximum incident photon-tophotocurrent efficiency (IPCE = 56%) were attained using composite clusters of free base and zinc porphyrin-peptide hexadecamers [P(H2P)(16) and P(ZnP)(16)] with fullerenes, respectively. Femtosecond transient absorption and fluorescence measurements of porphyrin-fullerene composite films confirm improved electron-transfer properties with increasing number of porphyrins in a polypeptide unit. The formation of molecular assemblies between porphyrins and fullerenes with a polypeptide structure controls the electron-transfer efficiency in the supramolecular complexes, meeting the criteria required for efficient light energy conversion.

    DOI: 10.1039/b706678c

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  • Electron-transfer reduction of cup-stacked carbon nanotubes affording cup-shaped carbons with controlled diameter and size 査読

    Kenji Saito, Masataka Ohtani, Shunichi Fukuzumi

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY128 ( 44 ) 14216 - 14217   2006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  

    DOI: 10.1021/ja064300d

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  • Stereoselective preparation, structures, and reactivities of phosphine-bridged mixed-metal trinuclear and pentanuclear complexes with tris[2-(diphenylphosphino)ethyl]phosphine 査読

    S Aizawa, K Saito, T Kawamoto, E Matsumoto

    INORGANIC CHEMISTRY45 ( 12 ) 4859 - 4866   2006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 phosphine-bridged linear trinuclear and pentanuclear complexes with Pd(II) - Pt(II) - Pd( II), Ni(II) - Pt( II) - Ni( II), and Rh(III) - Pd( II) - Pt( II) - Pd( II) - Rh( III) metal-ion sequences were almost quantitatively formed by the stepwise phosphine-bridging reaction of the terminal phosphino groups of tris[ 2-(diphenylphosphino) ethyl] phosphine (pp(3)), which is the tetradentate bound ligand of the starting Pd( II) and Ni( II) complexes. The solid-state structures of the trinuclear complexes were determined by X-ray structural analyses, and the structures of the polynuclear complexes in solution were characterized by NMR spectroscopy. The trans and cis isomers of the trinuclear and pentanuclear complexes, which arise from the geometry around the Pt( II) center, were selectively obtained simply by changing the counteranion of the starting complexes: the tetrafluoroborate salts, [MX(pp(3))](BF4) [M = Pd(II) or Ni(II), X = Cl- or 4-chlorothiophenolate (4-Cltp(-))], gave only the trans isomers, and the chloride salt, [PdCl(pp(3))] Cl, gave only the cis isomers. The formation of the trinuclear complex with the 4-Cltp(-) and chloro ligands, trans- [Pt(4-Cltp)(2){ PdCl(pp(3))}(2)](BF4)(2), proceeded with exchange between the thiolato ligand in the starting Pd(II) complex, [Pd(4Cltp)( pp(3))](BF4), and the chloro ligands in the starting Pt(II) complex, trans- [PtCl2(NCC6H5)(2)], retaining the trans geometry around the Pt( II) center. In contrast, the formation reaction between [PdCl(pp(3))] Cl and trans- [ PtCl2(NCC6H5)(2)] was accompanied by the trans-to-cis geometrical change on the Pt(II) center to give the trinuclear complex, cis[ PtCl2 {PdCl(pp(3))}(2)] Cl-2. The mechanisms of these structural conversions during the formation reactions were elucidated by the P-31 NMR and absorption spectral changes. The differences in the catalytic activity for the Heck reaction were discussed in connection with the bridging structures of the polynuclear complexes in the catalytic cycle.

    DOI: 10.1021/ic060277l

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  • An extremely long-lived charge-separated state of zinc tetraphenylporphyrin coordinated with pyridylnaphthalene-diimide 査読

    Kenji Saito, Yukiyasu Kashiwagi, Kei Ohkubo, Shunichi Fukuzumi

    JOURNAL OF PORPHYRINS AND PHTHALOCYANINES10 ( 12 ) 1371 - 1379   2006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:SOC PORPHYRINS & PHTHALOCYANINES  

    The nitrogen of pyridylnaphthalenediimide (PyNIm) coordinates to the metal center of zinc tetraphenylporphyrin (ZnTPP) to form a donor-acceptor complex: ZnTPP-PyNIm. Formation of the ZnTPP-PyNIm complex was probed by UV-vis, fluorescence and NMR spectra. The fluorescence of ZnTPP is strongly quenched and the fluorescence lifetime is shortened significantly in the complex. The transient absorption spectrum of the charge-separated state (ZnTPP center dot+-PyNIm(center dot-)) is successfully detected by laser flash photolysis measurements of the ZnTPP-PyNIm system in benzonitrile. The charge-separated state of the complex produced by the photoinduced electron transfer has the longest lifetime, (450 mu s) at 288 K, ever reported for donor-acceptor systems linked covalently or non-covalently in solution. However, when benzonitrile is replaced by benzene, the triplet excited state ((ZnTPP)-Zn-3*), rather than the charge-separated state, is formed upon laser excitation of the ZnTPP-PyNIm complex, due to the lower energy of (3)ZiiTPP* compared to the charge-separated state in benzene. Copyright (c) 2006 Society of Porphyrins & Phthalocyanines.

    DOI: 10.1142/S1088424606000740

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  • Preparation of mixed-metal polynuclear complexes by stepwise phosphine-bridging reaction 査読

    S Aizawa, T Kawamoto, K Saito

    CHEMISTRY LETTERS33 ( 10 ) 1286 - 1287   2004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:CHEMICAL SOC JAPAN  

    The phosphine-bridged Pd(II)-Pt(II)-Pd(II) trinuclear and Rh(III)-Pd(II)-Pt(II)-Pd(II)-Rh(III) pentanuclear complexes with tris[2-(diphenylphosphino)ethyl]phosphine (PP3) ligands were successfully prepared by stepwise phosphine-bridging reaction of the terminal phosphino groups of the PP3 ligands on the Pd(II) cores.

    DOI: 10.1246/cl.2004.1286

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  • Stepwise selective oxidation of tris(2-(diphenylphosphino)ethyl)phosphine on thiolato palladium(II) complexes 査読

    S Aizawa, T Kawamoto, K Saito

    INORGANICA CHIMICA ACTA357 ( 7 ) 2191 - 2194   2004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 SA  

    One of the equatorially coordinated terminal phosphorus atoms of tris(2-(diphenylphosphino)ethyl)phosphine (pp(3)) ligand on the five-coordinate trigonal-bipyramidal palladium(II) complex, [Pd(4-Cltp)(pp(3))](BF4) (4-Cltp = 4-chlorothiophenolate), was selectively oxidized by photolysis to form the four-coordinate square-planar complex. Further selective oxidation of another coordinated terminal phosphorus atom proceeded quantitatively by the substitution reaction with 4-chlorothiophenolate. The solid state structures of these stepwise-oxidized square-planar complexes were determined by X-ray crystal structure analyses, and the structures of the starting trigonal-bipyramidal and the oxidized complexes in solution have been characterized by P-31 NMR spectroscopy. (C) 2003 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.ica.2003.11.041

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▶ 全件表示

受賞

  • Excellent Presentation Award

    2008年  

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  • 優秀講演賞(学術)

    2008年   日本化学会  

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    受賞国:日本国

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