Papers - IKEDA Shigeru
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An efficient particulate photocatalyst for overall water splitting based on scandium and magnesium co-doped strontium titanate Invited Reviewed
Shigeru Ikeda, Riku Okamoto, Akira Kimura, Yuhi Nakayasu, Akira Yamakata, Ryota Tomizawa, Taizo Masuda, Koichiro Nakatani
Sustainable Energy & Fuels 8 202 - 209 2024.11
Authorship：Lead author, Corresponding author Publisher：Royal Society of Chemistry (RSC)
A high photocatalytic performance for overall water splitting was demonstrated over a photocatalyst based on a magnesium and scandium co-doped strontium titanate particle composed of a cubic shape having a nanosized step structure on the edge of the particle.
DOI： 10.1039/d3se01408h
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Characterization of the electronic structure of sputter-deposited Mo-doped BiVO4 thin-film photoanodes Reviewed
L. Oktariza, Y. Sato, S. Gofurov, K. Ozawa, M. M. Islam, S. Ikeda, T. Sakurai
Jpn. J. Appl. Phys. 63 02SP41 2024.1
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Crystalline-face-dependent photoelectrochemical properties of single crystalline CuGaSe2 photocathodes for hydrogen evolution under sunlight radiation Invited Reviewed
Shigeru Ikeda, Wakaba Fujita, Ryoji Katsube, Yoshitaro Nose, Hajime Suzuki, Ryu Abe, Kenji Yoshino
Electrochimica Acta 454 142384 - 142384 2023.4
Authorship：Lead author, Corresponding author Publisher：Elsevier BV
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Crystalline phase control of BiVO4 thin films using RF sputtering Reviewed
N. Uezono, J. Liu, P. A. Sachin, M. M. Islam, S. Ikeda, T. Sakurai
Jpn. J. Appl. Phys. 62 SK1001 2023.3
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Incorporation on CuIn(S,Se)2 thin films fabricated by aqueous spray deposition and their photovoltaic properties Reviewed International coauthorship
W. Septina, Y. Kawasaki, T. Harada, S. Ikeda
J. Cryst. Growth 602 126975 2023.1
Authorship：Last author
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Effect of heterojunction structures on photoelectrochemical properties of ZnTe-based photocathodes for water reduction Reviewed
Tooru Tanaka, Ryusuke Tsutsumi, Tomohiro Yoshinaga, Takaki Sonoyama, Katsuhiko Saito, Qixin Guo, Shigeru Ikeda
RSC Advances 13 575 - 583 2022.12
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Process accumulated 8% efficient Cu2ZnSnS4-BiVO4 tandem cell for solar hydrogen evolution with the dynamic balance of solar energy storage and conversion Reviewed International coauthorship
H. Cai, G. Xiao, W. Zhao, X. Wu, Y. Hu, H. Ni, S. Ikeda, Y. H. Ng
Adv. Sci. 10 2022.12
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Research on the Influence of the Interfacial Properties Between a Cu3BiS3 Film and an InxCd1-xS Buffer Layer for Photoelectrochemical Water Splitting Reviewed
Xiaomin Wu, Weidong Zhao, Yucheng Hu, Guohong Xiao, Huanyang Ni, Shigeru Ikeda, Yunhau Ng, Feng Jiang
ADVANCED SCIENCE 9 ( 33 ) 2022.11
Publisher：WILEY
The ternary compound photovoltaic semiconductor Cu3BiS3 thin film-based photoelectrode demonstrates a quite promising potential for photoelectrochemical hydrogen evolution. The presented high onset potential of 0.9 V-RHE attracts much attention and shows that the Cu3BiS3 thin films are quite good as an efficient solar water splitting photoelectrode. However, the CdS buffer does not fit the Cu3BiS3 thin film: the conduction band offset between CdS and Cu3BiS3 reaches 0.7 eV, and such a high conduction band offset (CBO) significantly increases the interfacial recombination ratio and is the main reason for the relatively low photocurrent of the Cu3BiS3/CdS photoelectrode. In this study, the InxCd1-xS buffer layer is found to be significantly lowered the CBO of CBS/buffer and that the In incorporation ratio of the buffer influences the CBO value of the CBS/buffer. The Pt-TiO2/In0.6Cd0.4S/Cu3BiS3 photocathode exhibits an appreciable photocurrent density of approximate to 12.20 mA cm(-2) at 0 V-RHE with onset potential of more than 0.9 V-RHE, and the ABPE of the Cu3BiS3-based photocathode reaches the highest value of 3.13%. By application of the In0.6Cd0.4S buffer, the Cu3BiS3-BiVO4 tandem cell presents a stable and excellent unbiased STH of 2.57% for over 100 h.
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Shogo Ishizuka, Riku Okamoto, Shigeru Ikeda
Advanced Materials Interfaces 9 ( 25 ) 2201266 - 2201266 2022.9
Authorship：Last author Publisher：Wiley
Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/admi.202201266
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Self-flux method in sputtered BiVO4 films for enhanced photoelectrochemical performance Reviewed
J. Liu, N. Uezono, K. Tajima, S. Pawar, M. M. Islam, S. Ikeda, T. Sakurai
ACS Appl. Energy Mater. 5 4191 - 4201 2022.4
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Effects of incorporation of Ag into a kesterite Cu2ZnSnS4 thin film on its photoelectrochemical properties for water reduction Reviewed International coauthorship
Shigeru Ikeda, Thi Hiep Nguyen, Riku Okamoto, Mikas Remeika, Imane Abdellaoui, Muhammad M. Islam, Takashi Harada, Ryu Abe, Takeaki Sakurai
Physical Chemistry Chemical Physics 24 ( 1 ) 468 - 476 2021.11
Authorship：Lead author, Corresponding author Publisher：Royal Society of Chemistry (RSC)
Incorporation of Ag into a crystalline lattice of kesterite Cu<sub>2</sub>ZnSnS<sub>4</sub> thin film was found to be effective for improvements of its photoelectrochemical properties for water reduction.
DOI： 10.1039/D1CP04075H
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Shigeru Ikeda, Riku Okamoto, Shogo Ishizuka
Applied Physics Letters 119 ( 8 ) 083902 - 083902 2021.8
Authorship：Lead author, Corresponding author Publisher：AIP Publishing
DOI： 10.1063/5.0060494
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Jiaqi Liu, Kazuya Tajima, Imane Abdellaoui, Muhammad Monirul Islam, Shigeru Ikeda, Takeaki Sakurai
Energies 14 ( 8 ) 2122-1 - 2122-10 2021.4
Joint Work
Publisher：MDPI AG
BiVO4 films were fabricated by radio frequency (RF) sputtering from a single target. The deposited BiVO4 films were found to be rich in Bi, and the reason for the Bi-richness was investigated. It was inferred from the Monte Carlo simulation that, during sputtering, the transfer process of target atoms through argon gas played a major role in this phenomenon. The transfer process resulted in an imbalanced ratio of Bi and V, arising from the difference in atom mass and interaction radius. The high RF power was found to be effective in adjusting the Bi/V ratio, influencing the sputtering yield. This type of preferential sputtering was maintained by the diffusion of target atoms from the bulk to the surface. BiVO4 films with monoclinic scheelite crystal structures were obtained at high RF power values and found to exhibit photocatalytic performances beneficial for photoanodic applications.
DOI： 10.3390/en14082122
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Mechanism of Incorporation of Zirconium into BiVO4 Visible-Light Photocatalyst Reviewed
Imane Abdellaoui, Muhammad M. Islam, Mikas Remeika, Sorai Kanno, Riku Okamoto, Kazuya Tajima, Sachin A. Pawar, Yun Hau Ng, Christian Budich, Tsuyoshi Maeda, Takahiro Wada, Shigeru Ikeda, Takeaki Sakurai
The Journal of Physical Chemistry C 125 ( 6 ) 3320 - 3326 2021.2
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3.17% efficient Cu2ZnSnS4–BiVO4 integrated tandem cell for standalone overall solar water splitting Reviewed
Dingwang Huang, Kang Wang, Lintao Li, Kuang Feng, Na An, Shigeru Ikeda, Yongbo Kuang, Yunhau Ng, Feng Jiang
Energy & Environmental Science 14 ( 3 ) 1480 - 1489 2021.1
Joint Work
Publisher：Royal Society of Chemistry (RSC)
<p>3.17% efficient Cu<sub>2</sub>ZnSnS<sub>4</sub>–BiVO<sub>4</sub> integrated tandem cell and a large scale 5 × 5 cm integrated CZTS–BiVO<sub>4</sub> tandem device for standalone overall solar water splitting was assembled for the first time.</p>
DOI： 10.1039/D0EE03892J
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Preparation of a CuGaSe2 single crystal and its photocathodic properties Invited Reviewed
S. Ikeda, W. Fujita, R. Okamoto, Y. Nose, R. Katsube, K. Yoshino, T. Harada
RSC Advances 10 ( 66 ) 40310 - 40315 2020.11
Joint Work
Authorship：Lead author, Corresponding author Publisher：ROYAL SOC CHEMISTRY
Chalcopyrite CuGaSe2 single crystals were successfully synthesized by the flux method using a home-made Bridgman-type furnace. The grown crystals were nearly stoichiometric with a Se-poor composition. Although a wafer form of the thus-obtained single crystal showed poor p-type electrical properties due to such unfavorable off-stoichiometry, these properties were found to be improved by applying a post-annealing treatment under Se vapor conditions. As a result, an electrode derived from the Se-treated single crystalline wafer showed appreciable p-type photocurrents. After deposition of a CdS ultrathin layer and a nanoparticulate Pt catalyst on the surface of the electrode, appreciable photoelectrochemical H-2 evolution was observed over the modified electrode under photoirradiation by simulated sunlight with application of a bias potential of 0 V-RHE.
DOI： 10.1039/d0ra07904a
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MoSx-CdS/Cu2ZnSnS4-based thin film photocathode for solar hydrogen evolution from water Reviewed
Kuang Feng, Dingwang Huang, Lintao Li, Kang Wang, Jingbo Li, Takashi Harada, Shigeru Ikeda, Feng Jiang
Applied Catalysis B: Environmental 268 118438 - 118438 2020.7
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Tailored Photoluminescence Properties of Ag(In,Ga)Se2 Quantum Dots for Near-Infrared In Vivo Imaging Reviewed
Tatsuya Kameyama, Hiroki Yamauchi, Takahisa Yamamoto, Toshiki Mizumaki, Hiroshi Yukawa, Masahiro Yamamoto, Shigeru Ikeda, Taro Uematsu, Yoshinobu Baba, Susumu Kuwabata, Tsukasa Torimoto
ACS Applied Nano Materials 3 ( 4 ) 3275 - 3287 2020.4
Joint Work
Publisher：American Chemical Society (ACS)
Copyright © 2020 American Chemical Society. Multinary semiconductor quantum dots (QDs) that have less toxicity and show near-infrared light responsivity have attracted much attention for in vivo bioimaging. In this study, we controlled the optical properties of Ag-In-Se QDs by modulating the nonstoichiometry and the degree of Ga3+ doping. Precise tuning of the Ag/In ratio of Ag-In-Se QDs enabled a sharp band-edge emission to emerge without broad defect-site emission. Ga3+ doping into Ag-In-Se (AIGSe) QDs enlarged their energy gap, resulting in a blue shift of the band-edge PL peak from from 890 to 630 nm. The band-edge PL intensity was remarkably enlarged by surface coating with a thin GaSx shell followed by treatment with trioctylphosphine, the highest PL yield being 38% for the PL peak at 800 nm. Thus-obtained QDs were successfully used as near-IR PL probes for three-dimensional in vivo bioimaging in which the wavelengths of excitation and detection lights could be selected in the first biological window, and then the signals were clearly detected from AIGSe@GaSx core-shell QDs injected into biological tissues by ca. 5 mm in depth.
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Takashi Harada, En Yagi, Shigeru Ikeda
RSC Advances 10 ( 26 ) 15360 - 15365 2020.4
Joint Work
Publisher：Royal Society of Chemistry (RSC)
<p>We present a procedure for the synthesis of WO<sub>3</sub> nanoparticles encapsulated in a hollow silica sphere, and their unique photocatalytic properties.</p>
DOI： 10.1039/D0RA01988G
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Photocarrier Recombination Dynamics in BiVO4 for Visible Light-Driven Water Oxidation Reviewed
Imane Abdellaoui, Muhammad M. Islam, Mikas Remeika, Yui Higuchi, Takato Kawaguchi, Takashi Harada, Christian Budich, Tsuyoshi Maeda, Takahiro Wada, Shigeru Ikeda, Takeaki Sakurai
The Journal of Physical Chemistry C 124 ( 7 ) 3962 - 3972 2020.2
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Three‐Dimensional GeSe Microstructured Air Brick Photocathode for Advanced Solar Water Splitting Reviewed
Kang Wang, Dingwang Huang, Lintao Li, Kuang Feng, Takashi Harada, Shigeru Ikeda, Jingbo Li, Feng Jiang
Solar RRL 4 ( 5 ) 1900559-1 - 1900559-8 2020.1
Joint Work
Publisher：Wiley
Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/solr.201900559
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Photoelectrochemical CO2 Reduction to Formate with the Sacrificial Reagent Free System of Semiconductor Photocatalysts and Formate Dehydrogenase Reviewed
Ishibashi Tomoya, Higashi Masanobu, Ikeda Shigeru, Amao Yutaka
CHEMCATCHEM 11 6227 - 6235 2019.11
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Shigeru Ikeda, Shotaro Fujikawa, Takashi Harada, Thi Hiep Nguyen, Shuji Nakanishi, Tomoaki Takayama, Akihide Iwase, Akihiko Kudo
ACS Applied Energy Materials 2 ( 9 ) 6911 - 6918 2019.9
Joint Work
Publisher：American Chemical Society ({ACS})
Other Link： http://orcid.org/0000-0001-7757-4182
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Promising GeSe nanosheet based thin film photocathode for efficient and stable overall solar water splitting Reviewed
K. Wang, D. Huang, L. Yu, K. Feng, L. Li, T. Harada, S. Ikeda, F. Jiang
ACS Catalysis 9 ( 4 ) 3090 - 3097 2019.3
Joint Work
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Environmentally friendly Cu<sub>2</sub>ZnSnS<sub>4</sub>-based photocathode modified with a ZnS protection layer for efficient solar water splitting. Reviewed
Wang K, Huang D, Yu L, Gu H, Ikeda S, Jiang F
Journal of colloid and interface science 536 9 - 16 2019.2
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Growth of CuSbS2 Single Crystal as an Environmentally Friendly Thermoelectric Material Reviewed
Nagaoka Akira, Takeuchi Manato, Yoshino Kenji, Ikeda Shigeru, Yasui Shintaro, Taniyama Tomoyasu, Nishioka Kensuke
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 216 ( 15 ) 1800861 2019.1
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Tomoya Ishibashi, Shusaku Ikeyama, Manami Ito, Shigeru Ikeda, Yutaka Amao
Chemistry Letters 42 ( 12 ) 1505 - 1508 2018.12
Joint Work
© 2018 The Chemical Society of Japan. Effective light-driven conversion of CO2 to formic acid with a hybrid system consisting of photocatalyst TiO2 nanoparticle (P25), methylviologen (MV2+) as an electron mediating molecule and biocatalyst formate dehydrogenase (FDH) in the presence of triethanolamine (TEOA) as an electron donating molecule was investigated. After 120 min irradiation with a Xe lamp (>300 nm), 152 ¯M of formic acid was produced in a CO2 saturated buffer solution containing TEOA (300 mM), TiO2 nanoparticles (6.8 mg¢L11), MV2+ (0.5 mM) and FDH (7.5 ¯M).
DOI： 10.1246/cl.180731
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Photoelectrochemical Reduction of CO2 to CO Using a CuGaS2 Thin-film Photocathode Prepared by a Spray Pyrolysis Method Reviewed
Ikeda Shigeru, Tanaka Yuta, Kawaguchi Takato, Fujikawa Shotaro, Harada Takashi, Takayama Tomoaki, Iwase Akihide, Kudo Akihiko
CHEMISTRY LETTERS 47 ( 11 ) 1424 - 1427 2018.11
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Over 1% Efficient Unbiased Stable Solar Water Splitting Based on a Sprayed Cu2ZnSnS4 Photocathode Protected by a HfO2 Photocorrosion-Resistant Film Reviewed
Huang Dingwang, Wang Kang, Yu Le, Nguyen Thi Hiep, Ikeda Shigeru, Jiang Feng
ACS ENERGY LETTERS 3 ( 8 ) 1875 - 1881 2018.7
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Structural and electric properties of CuSbS2 compound semiconductor bulk crystals Reviewed
Ikeda Shigeru, Kawaguchi Takato, Koda Yuriko, Iiyama Naoki, Harada Takashi, Nakanishi Shuji, Nakatsuka Shigeru, Nose Yoshitaro
JAPANESE JOURNAL OF APPLIED PHYSICS 57 ( 08RC09 ) 08RC09 2018.7
Joint Work
Authorship：Lead author Publisher：Japan Society of Applied Physics
Other Link： https://iopscience.iop.org/article/10.7567/JJAP.57.08RC09/meta
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Effects of Zirconium Doping Into a Monoclinic Scheelite BiVO4 Crystal on Its Structural, Photocatalytic, and Photoelectrochemical Properties Reviewed
Ikeda Shigeru, Kawaguchi Takato, Higuchi Yui, Kawasaki Naoto, Harada Takashi, Remeika Mikas, Islam Muhammad M, Sakurai Takeaki
FRONTIERS IN CHEMISTRY 6 266 2018.7
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Co-Electrodeposited Cu2ZnSnS4 Thin Film Solar Cell and Cu2ZnSnS4 Solar Cell - BiVO4 Tandem Device for Unbiased Solar Water Splitting Reviewed
Jiang Feng, Li Shuti, Ozaki Chigusa, Harada Takashi, Ikeda Shigeru
SOLAR RRL 2 ( 3 ) 1700205 2018.3
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Thi Hiep Nguyen, Takato Kawaguchi, Jakapan Chantana, Takashi Minemoto, Takashi Harada, Shuji Nakanishi, Shigeru Ikeda
ACS Applied Materials and Interfaces 10 ( 6 ) 5455 - 5463 2018.2
Joint Work
Authorship：Lead author Publisher：American Chemical Society
A silver (Ag)-incorporated kesterite Cu2ZnSnS4 (CZTS) thin film was fabricated by a facile spray pyrolysis method. Crystallographic analyses indicated successful incorporation of various amounts of Ag up to a Ag/(Ag + Cu) ratio of ca. 0.1 into the crystal lattice of CZTS in a homogeneous manner without formation of other impurity compounds. From the results of morphological investigations, Ag-incorporated films had larger crystal grains than the CZTS film. The sample with a relatively low Ag content (Ag/(Ag + Cu) of ca. 0.02) had a compact morphology without appreciable voids and pinholes. However, an increase in the Ag content in the CZTS film (Ag/(Ag + Cu) ca. 0.10) induced the formation of a large number of pinholes. As can be expected from these morphological properties, the best sunlight conversion efficiency was obtained by the solar cell based on the film with Ag/(Ag + Cu) of ca. 0.02. Electrostructural analyses of the devices suggested that the Ag-incorporated film in the device achieved reduction in the amounts of unfavorable copper on zinc antisite defects compared to the bare CZTS film. Moreover, the use of a Ag-incorporated film improved band alignment at the CdS(buffer)-CZTS interface. These alterations should also contribute to enhancement of device properties.
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Hasyiya Karimah Adli, Takashi Harada, Shuji Nakanishi, Shigeru Ikeda
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 19 ( 39 ) 26898 - 26905 2017.10
Joint Work
Publisher：ROYAL SOC CHEMISTRY
The effects of surface treatment with TiCl4 on the structural and electrochemical properties of a porous titanium oxide (pTiO(2)) layer deposited on a fluorine-doped tin oxide (FTO)/glass substrate covered with a dense TiO2 layer (pTiO(2)/dTiO(2)/FTO/glass) were systematically investigated in order to obtain an optimum pTiO(2) layer for use in CH3NH3PbI3 perovskite solar cells. As confirmed by thermal desorption spectroscopy (TDS) analyses, the amount of surface hydroxyl groups in pTiO(2) varied when the pTiO(2)/dTiO(2)/FTO/glass sample was treated with solutions with different concentrations of TiCl4 (i.e., 20, 50, 80, and 100 mM). Photoelectrochemical (PEC) analyses of the pTiO(2)/dTiO(2)/FTO/glass samples after TiCl4 treatment showed significant increments of photocurrent densities compared to the pTiO(2)/dTiO(2)/FTO/glass sample without TiCl4 treatment regardless of the concentration of TiCl4 used in the solution. Electrochemical impedance spectroscopy (EIS) analyses of the TiCl4-treated pTiO(2)/dTiO(2)/FTO/glass samples also indicated a lower recombination probability with an increase in TiCl4 concentration. The results suggest that TiCl4 treatment resulted in passivation of defect sites on the surface of the TiO2 nanoparticles as well as improvement of the interconnectivity between the TiO2 nanoparticles in pTiO(2). In contrast, the power conversion efficiencies (PCEs) and short circuit current densities of CH3NH3PbI3 perovskite solar cells based on these pTiO(2)/dTiO(2)/FTO/glass samples exhibited volcano-like patterns depending on the TiCl4 concentration used for the pTiO(2) treatment: the highest PCE was obtained by using pTiO(2)/d TiO2/FTO/glass treated with 50 mM of TiCl4 solution. Structural analysis of the CH3NH3PbI3 perovskite part performed by X-ray diffraction (XRD) indicated that the formation of CH3NH3PbI3 perovskite was inhibited by the presence of surface hydroxyl groups in the pTiO(2) film without TiCl4 treatment. TiCl4 treatment using TiCl4 solutions with concentrations up to 50 mM enhanced the formation of the CH3NH3PbI3 perovskite layer, whereas TiCl4 treatment using TiCl4 solutions with concentrations higher than 50 mM was detrimental due to the formation of nanoparticulate TiO2 aggregates that induce poor porosity and act as recombination sites.
DOI： 10.1039/c7cp04132b
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Photoelectrochemical water reduction over wide gap (Ag,Cu)(In,Ga)S-2 thin film photocathodes Reviewed
Wilman Septina, Minori Sugimoto, Ding Chao, Qing Shen, Shigeru Nakatsuka, Yoshitaro Nose, Takashi Harada, Shigeru Ikeda
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 19 ( 19 ) 12502 - 12508 2017.5
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
The effects of partial replacement of Cu with Ag in a Cu(In,Ga) S-2 (CIGS) thin film on its structural, optical, electrostructural, and photoelectrochemical (PEC) properties were investigated, in order to improve its performance for PEC water reduction under sunlight illumination. Results from X-ray diffraction (XRD) analyses revealed the successful partial replacement of Cu with Ag to form solid-solutions with different Ag/(Ag + Cu) ratios (A(x)CIGS, x = Ag/(Ag + Cu) = 0.1, 0.2, 0.3 and 0.4), as confirmed by a gradual change in the (112) reflections to smaller 2 theta angles with increasing Ag/(Ag + Cu) ratio. Analyses of the photoabsorption properties of the materials using photoacoustic spectroscopy indicated changes in the band gap energies associated with increasing the Ag/(Ag + Cu) ratio. In addition, valence band maximum potentials of A(x) CIGS were deepened gradually with increasing Ag/(Ag + Cu) ratio. After modifying these A(x) CIGS films with a CdS ultrathin (ca. 70 nm) layer and a Pt catalyst, the PEC water reduction properties were evaluated in an electrolyte solution with the pH adjusted to 6.5, under simulated sunlight (AM 1.5G) radiation. Compared to the CdS- and Pt-modified Ag-free A(x) CIGS (A(0) CIGS) films, appreciable enhancements in the PEC properties were observed for electrodes based on A(x) CIGS (x 4 0) films, and the best PEC performance was obtained for the electrode based on the A(0.2) CIGS film. However, the electrode derived from the A(x) CIGS film with Ag/(Ag + Cu) ratios higher than 0.3 showed diminished PEC properties due to the partial conversion of its semiconducting properties from p-type to n-type.
DOI： 10.1039/c7cp01348e
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Investigation on Stability of Electroplated-Sulfurized CuInS2-based Photocathode Modified with an In2S3 Layer for H-2 Evolution under Various pH Conditions Reviewed
Gunawan, Haris Abdul, Widiyandari Hendri, Septina Wilman, Ikeda Shigeru
ORIENTAL JOURNAL OF CHEMISTRY 33 ( 2 ) 556 - 561 2017.4
Joint Work
Publisher：Oriental Scientific Publishing Company
We investigated photoelectrochemical water splitting properties of Pt-In2S3/CuInS2 photocathodes from near neutral toward basic condition (pH 6, 9, and 13). Half-cell solar-to-hydrogen (HC-STH) of Pt-In2S3/CuInS2 measured under 0.2 M NaH2PO4 was the highest when the pH of the solution was 13 (4.7% at 0.42 V vs. RHE) with a maximum photocurrent density of 16.3 mA cm-2 (at 0 V vs. RHE) and onset potential of 0.9 V vs. RHE (defined as cathodic photocurrent of 0.1 mA cm-2). However, it suffers from rapid degradation of the photocurrent over the time course when kept at 0 V vs. RHE under constant illumination. On the other hand, the photocathode showed relatively stable photocurrent when measured under near neutral condition (pH 6): HC-STH of 2.85% (at 0.28 V vs. RHE) with a maximum photocurrent density of 16.3 mA cm-2 (at 0 V vs. RHE) and onset potential of 0.72 V vs. RHE were obtained from the photocathode. Passivation using In2S3 oxygen-free can stabilize the photocathode at alkaline pH (pH 13).
DOI： 10.13005/ojc/330202
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Effects of Indium Incorporation on Structural and Photovoltaic Properties of Cu2ZnSnS4 Thin Films Reviewed
Thi Hiep Nguyen; Harada, Takashi; Fujikawa, Shotaro; Nakanishi, Shuji; Ikeda, Shigeru
ECS TRANSACTIONS 75 ( 50 ) 15 - 22 2017.1
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Cu2ZnSnS4-based Thin Film Solar Cells with More Than 8% Conversion Efficiency Obtained by Using A Spray Pyrolysis Technique
Thi Hiep Nguyen; Harada, Takashi; Nakanishi, Shuji; Ikeda, Shigeru
PVSC, 2016 IEEE 43rd ( 7749637 ) 470 - 472 2016.11
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Impact of Precursor Compositions on the Structural and Photovoltaic Properties of Spray-Deposited Cu2ZnSnS4 Thin Films Reviewed
Thi Hiep Nguyen, Shotaro Fujikawa, Takashi Harada, Jakapan Chantana, Takashi Minemoto, Shuji Nakanishi, Shigeru Ikeda
CHEMSUSCHEM 9 ( 17 ) 2414 - 2420 2016.9
Joint Work
Authorship：Lead author Publisher：WILEY-V C H VERLAG GMBH
Pure sulfide Cu2ZnSnS4 thin films were fabricated on Mo-coated glass substrates by facile spray deposition of aqueous precursor solutions containing Cu(NO3)(2), Zn(NO3)(2), Sn(CH3SO3)(2), and thiourea followed by annealing at 600 degrees C. When a precursor solution containing a stoichiometric composition of Cu, Zn, and Sn was used, the resulting Cu2ZnSnS4 thin film contained a Cu2-xS impurity phase owing to the evaporation of Sn components during the annealing process. The Cu2-xS impurity in the Cu2ZnSnS4 thin film was removed by reducing the concentration of Cu in the precursor solution. This resulted in an improvement of the structural features (i.e., grain sizes and compactness) as well as the electric properties such as acceptor densities, the nature of the acceptor defects, and carrier lifetimes. A solar cell based on the Cu2ZnSnS4 film with an empirically optimal composition showed conversion efficiency of 8.1%. The value achieved was one of the best efficiencies of Cu2ZnSnS4-based cells derived from a non-vacuum process.
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Effect of Indium Doping on Surface Optoelectrical Properties of Cu2ZnSnS4 Photoabsorber and Interfacial/Photovoltaic Performance of Cadmium Free In2S3/Cu2ZnSnS4 Heterojunction Thin Film Solar Cell Reviewed
Feng Jiang, Chigusa Ozaki, Gunawan, Takashi Harada, Zeguo Tang, Takashi Minemoto, Yoshitaro Nose, Shigeru Ikeda
CHEMISTRY OF MATERIALS 28 ( 10 ) 3283 - 3291 2016.5
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
Maximum conversion efficiency of 6.9% was 20 obtained over an electrodeposited Cu(2)ZnSnS(4-)based thin film solar cell with a Cd-free In2S3 buffer layer by applying a rapid post-heat treatment to the In2S3/Cu2ZnSnS4 stacked layer. It was found that post-heating of the In2S3/Cu2ZnSnS4 stack promoted an increment of the acceptor density of the Cu2ZnSnS4 layer close to the In2S3-Cu2ZnSnS4 heterointerface of the In2S3/Cu2ZnSnS4 stack. Moreover, the diffusion of In also resulted in a red-shift of the band gap energy of Cu2ZnSnS4 from 1.47 to 1.40 eV. Due to extension of external quantum efficiency response of the solar cell to the long wavelength region, the solar cell based on the post-heated In2S3/Cu2ZnSnS4 stack reached appreciably large short circuit current density of more than 20 mA cm(-2). The energy difference between the conduction band minimum of In2S3 and that of Cu2ZnSnS4 at the In2S3/Cu2ZnSnS4 heterointerface was determined to be a slightly positive value of 0.11 eV, indicating formation of a "notch-type" conduction band offset for efficient suppression of the interface recombination.
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Effects of TiO2 Properties on Performance of CH3NH3PbI3 Perovskite Photovoltaic Cells Reviewed
Hasyiya K. Adli, Takashi Harada, Seigo Ito, Shuji Nakanishi, Shigeru Ikeda
MRS Advances 1 ( 47 ) 3185 - 3189 2016.4
Joint Work
Authorship：Lead author Publisher：Materials Research Society
The effects of TiCl4 post-treatment on the physicochemical properties of porous TiO2 (pTiO2) layers fabricated at 300 °C and 400 °C (denoted as pTiO2(300) and pTiO2(400), respectively) in CH3NH3PbI3 perovskite photovoltaic cells were investigated. Water contents (physisorbed water and water derived from surface hydroxyl groups) of pTiO2(300) and pTiO2(400) before and after TiCl4 post-treatment were measured by using temperature desorption spectroscopy (TDS). Moreover, structural analysis of the CH3NH3PbI3 perovskite part was performed by X-ray diffraction (XRD). In the case of pTiO2(300), the content of water was increased by the TiCl4 post-treatment due to the removal of residual organic compounds that existed before the treatment. It then caused a change in the surface activity of pTiO2(300) and enhancement of solar cell performance and photocurrent density, though suppression of CH3NH3PbI3 perovskite formation occurred. In comparison, contents of water were decreased for pTiO2(400), leading to enhancement of the conversion of PbI2 to CH3NH3PbI3 perovskite. As a result, there were significant increases in short circuit current density (Jscs) and PCEs. The results showed that TiCl4 post-treatment is an effective approach to prepare high-performance CH3NH3PbI3 perovskite solar cells without heat treatment at a very high temperature.
DOI： 10.1557/adv.2016.272
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Investigating relation of photovoltaic factors with properties of perovskite films based on various solvents Reviewed
Zeguo Tang, Soichiro Tanaka, Seigo Ito, Shigeru Ikeda, Kozo Taguchi, Takashi Minemoto
NANO ENERGY 21 51 - 61 2016.3
Joint Work
Publisher：ELSEVIER SCIENCE BV
Methylammonium lead iodide (MAPbl(3)) perovskite solar cells are fabricated by two-step sequential deposition processes. The influence of the properties of Pbl(2) precursor film on the cell performance is investigated based on different solvents. The X-ray diffraction (XRD) patterns, Urbach energy value and scan electron microscope (SEM) images reveal that solvents have considerable influence on the crystal structure, band tail and morphology of Pbl(2) precursor films. The addition of a small amount of dimethyl sulfoxide (DMSO) in N,N-dimethylformamide (DMF) solvent promotes the compactness and uniformity of Pbl(2) precursor films, but also causes defect in band tail. The relation of the properties of perovskite film with photovoltaic parameters is explored. A high conversion efficiency of 16.6% for solar cells based on mixed solvents with 10 vol% DMSO is achieved. Meanwhile, light beam-induced current (LBIC) images directly evidence the improvement of uniformity for perovskite solar cells caused by DMSO addition. (C) 2016 Elsevier Ltd. All rights reserved.
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Impact of alloying duration of an electrodeposited Cu/Sn/Zn metallic stack on properties of Cu2ZnSnS4 absorbers for thin-film solar cells Reviewed
Feng Jiang, Shigeru Ikeda, Zeguo Tang, Takashi Minemoto, Wilman Septina, Takashi Harada, Michio Matsumura
PROGRESS IN PHOTOVOLTAICS 23 ( 12 ) 1884 - 1895 2015.12
Joint Work
Authorship：Lead author Publisher：WILEY-BLACKWELL
The impacts of preheating of an electrodeposited Cu/Sn/Zn (CTZ) stack precursor on structural changes of the CTZ precursor and the impact on structural and electric properties of the finally obtained Cu2ZnSnS4 (CZTS) films are discussed in detail. We found that preheating for relatively long durations improved the qualities of CZTS films: these films were composed of large grains and had compact and flat surface morphologies. The best solar cell with efficiency of 8.1% was obtained on the basis of a CZTS film derived from the CTZ precursor preheated for 200 min. The external quantum efficiency response of the cell indicated efficient utilization of photons with relatively long wavelength regions because of its good structural and electronic properties. On the other hand, a short circuit current density-temperature property of one of the best cells in this study suggested that the CZTS film had deep acceptor levels and/or an appreciable energy barrier to the Mo back contact. Moreover, an open circuit voltage-temperature property of the corresponding device showed activation energy of 1.18 eV, indicating preferential occurrence of CdS-CZTS interface recombination. Copyright (C) 2015 John Wiley & Sons, Ltd. Copyright (C) 2015 John Wiley & Sons, Ltd.
DOI： 10.1002/pip.2638
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Pt/In2S3/CdS/Cu2ZnSnS4 Thin Film as an Efficient and Stable Photocathode for Water Reduction under Sunlight Radiation Reviewed
Feng Jiang, Gunawan, Takashi Harada, Yongbo Kuang, Tsutomu Minegishi, Kazunari Domen, Shigeru Ikeda
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 137 ( 42 ) 13691 - 13697 2015.10
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
An electrodeposited Cu2ZnSnS4 (CZTS) compact thin film modified with an In2S3/CdS double layer and Pt deposits (Pt/In2S3/CdS/CZTS) was used as a photocathode for water splitting of hydrogen production under simulated sunlight (AM 1.5G) radiation. Compared to platinized electrodes based on a bare CZTS film (Pt/CZTS) and a CZTS film modified with a CdS single layer (Pt/CdS/CZTS), the Pt/In2S3/CdS/CZTS electrode exhibited a significantly high cathodic photocurrent. Moreover, the coverage of the In2S3 layer was found to be effective for stabilization against degradation induced by photocorrosion of the CdS layer. Bias-free water splitting with a power conversion efficiency of 0.28% was achieved by using a simple two-electrode cell consisting of the Pt/In2S3/CdS/CZTS photocathode and a BiVO4 photoanode.
DOI： 10.1021/jacs.5b09015
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Effects of Porosity and Amount of Surface Hydroxyl Groups of a Porous TiO2 Layer on the Performance of a CH3NH3PbI3 Perovskite Photovoltaic Cell Reviewed
Hasyiya Karimah Adli, Takashi Harada, Wilman Septina, Shuji Hozan, Seigo Ito, Shigeru Ikeda
JOURNAL OF PHYSICAL CHEMISTRY C 119 ( 39 ) 22304 - 22309 2015.10
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
The structural and physicochemcal properties of a porous titanium oxide layer (pTiO(2)) in CH3NH3PbI3 perovskite photovoltaic cells were systematically investigated by Raman spectroscopy, nitrogen sorption, and temperature desorption spectroscopy analyses. When the heat treatment temperature (T-pTO) during the fabrication of pTiO(2) was changed from 400 to 700 degrees C, its porosity and amount of surface hydroxyl groups were varied without alteration of the crystalline structure (anatase). Power conversion efficiencies (PCEs) of solar cells based on pTiO(2) prepared at different temperatures showed a volcanic-like pattern depending on T-pTO of pTiO(2); the highest PCE was obtained by using pTiO(2) prepared at T-pTO of 550 degrees C. Structural analyses of the CH3NH3PbI3 perovskite part performed by X-ray diffraction indicated that formation of CH3NH3PbI3 perovskite was inhibited by the presence of a large amount of surface hydroxyl groups on pTiO(2) prepared at relatively low T-pTO (<550 degrees C). On the other hand, significant reduction of porosity of pTiO(2) occurred when pTiO(2) was prepared at relatively high T-pTO (>550 degrees C) because of extinction of micropores and sintering between the TiO2 particles; such a structural alteration hindered the penetration of CH3NH3I into the pore channel of TiO2 filled by PbI2, resulting in a large amount of PbI2 remaining in the finally obtained photovoltaic cell. Hence, the optimum T-pTO (550 degrees C) for fabrication of pTiO(2) should be determined by its porous nature and sufficient removal of surface hydroxyl groups.
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Masaaki Kurihara, Wilman Septina, Toshiyuki Hirano, Yasuhiro Nakajima, Takashi Harada, Shigeru Ikeda
JAPANESE JOURNAL OF APPLIED PHYSICS 54 ( 9 ) 91203-1 - 91203-5 2015.9
Joint Work
Authorship：Lead author, Corresponding author Publisher：IOP PUBLISHING LTD
A detailed process of fabricating Cu(In,Ga)(S,Se)(2) via the spray pyrolysis of a thiourea-based precursor solution followed by selenization is reported. The optimization of the selenization condition for the fabrication of the Cu(In,Ga)(S,Se)(2) film led to a conversion efficiency of 7.8% for the Cu(In,Ga)(S,Se)(2)-based device. We also showed that 1-methylthiourea was a more suitable sulfur source for the spray pyrolysis technique, resulting in a conversion efficiency of 8.7% (V-OC = 0.52 V, J(SC) = 31 mA cm(-2), and FF = 0.54) without any antireflection coating. (C) 2015 The Japan Society of Applied Physics
Other Link： http://stacks.iop.org/1347-4065/54/i=9/a=091203?key=crossref.563a6f847dbeac0424714232c3b88eae
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Cu2ZnSnS4 thin film solar cells with 5.8% conversion efficiency obtained by a facile spray pyrolysis technique Reviewed
Thi Hiep Nguyen, Wilman Septina, Shotaro Fujikawa, Feng Jiang, Takashi Harada, Shigeru Ikeda
RSC ADVANCES 5 ( 95 ) 77565 - 77571 2015.9
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
An attempt was made to fabricate Cu2ZnSnS4 (CZTS) thin film absorber on a Mo-coated glass substrate by using facile spray pyrolysis deposition of a precursor film from an aqueous solution containing Cu(NO3)(2), Zn(NO3)(2), Sn(CH3SO3)(2) and thiourea. In order to obtain a stable solution for the spray pyrolysis deposition without formation of an SnO2 precipitate, the mixing order of source materials was found to be important. Annealing of the thus-obtained precursor film in sulfur vapor at temperatures ranging from 580 degrees C to 600 degrees C resulted in successful formation of homogeneous films composed of CZTS crystallites. Based on structural analyses of CZTS films having different Sn contents, an Sn-rich composition compared to its stoichiometric amount was found to be essential for efficient grain growth of the resulting CZTS films. A solar cell based on the Sn-rich CZTS film obtained by an optimum annealing condition exhibited maximum conversion efficiency of 5.8%.
DOI： 10.1039/c5ra13000j
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Investigation of the Electric Structures of Heterointerfaces in Pt- and In2S3-Modified CuInS2 Photocathodes Used for Sunlight-Induced Hydrogen Evolution Reviewed
Gunawan, Wilman Septina, Takashi Harada, Yoshitaro Nose, Shigeru Ikeda
ACS APPLIED MATERIALS & INTERFACES 7 ( 29 ) 16086 - 16092 2015.6
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
Copper indium disulfide (CuInS2) modified with art In2S3 layer and a Pt catalyst showed a more efficient photoelectrochemical (PEC) property for hydrogen evolution from a nearly neutral (pH 6) 0.2 M NaH2PO4 solution under simulated sunlight illumination (AM 1.5G) than that of a CuInS2 electrode modified with a CdS layer and a Pt catalyst. Analysis of the PEC properties of In2S3 modified CuInS2 (In2S3/CuInS2) and CdS-modified CuInS2 (CdS/CuInS2) in solutions containing an electron scavenger (Eu3+) showed identical enhancement of the PEC properties of In2S3/CuInS2 when compared to those of CdS/CuInS2, indicating the formation of a favorable heterointerface in In2S3/CuInS2 for efficient charge separation. Spectroscopic evaluation of conduction band offsets revealed that In2S3/CuInS2 had a notch-type conduction band offset, whereas a cliff-type offset was formed in CdS/CuInS2: these results also revealed a,better interface electric structure of In2S3/CuInS2 than that of CdS/CuInS2.
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T. Hamada, A. Fukuyama, F. Jiang, S. Ikeda, T. Ikari
PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 12, NO 6 12 ( 6 ) 725 - 728 2015.5
Joint Work
Publisher：WILEY-V C H VERLAG GMBH
Cu2ZnSnS4 (CZTS) is paid attention to the low-cost and nontoxic solar cell material. In this study, CZTS thin film was deposited by using an electrodeposition technique followed by a sulfurization after preheating the deposited metallic precursor layer. We investigated the film properties of CZTS thin films for understanding the effect of preheating time on the photovoltaic properties such as carrier lifetime and recombination mechanism by using a microwave photoconductivity decay (mu-PCD) and a photoluminescence (PL) measurement. The results of the mu-PCD measurements showed that carrier lifetime increased with increasing the preheating time and longer carrier lifetime was observed in a part of deposited thin film. The PL measurements showed the peak energy shift to lower energy region by a surface position of the sample preheated for 150 min. We found the CZTS crystal quality improved but the homogeneity worsened with increasing the preheating time. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Photosplitting of Water from Wide-Gap Cu(In,Ga)S-2 Thin Films Modified with a CdS Layer and Pt Nanoparticles for a High-Onset-Potential Photocathode Reviewed
Wilnan Septina, Gunawan, Shigeru Ikeda, Takashi Harada, Masanobu Higashi, Ryu Abe, Michio Matsumura
JOURNAL OF PHYSICAL CHEMISTRY C 119 ( 16 ) 8576 - 8583 2015.4
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
Photoelectrochemical water splitting from photocathodes based on wide-gap Cu(In,Ga)S-2 (CIGS) thin films modified with a CdS layer and Pt nanoparticles was investigated. CIGS films with various amounts of Ga were fabricated using spray pyrolysis followed by sulfurization. As analyzed using 0.1 M Na2SO4 (pH 9) as an electrolyte under illumination of simulated sunlight (AM 1.5G), both photocurrent densities and onset potentials of the photocathodes were gradually improved by an increase in the amount of Ga in the CIGS films up to a Ga/(In + Ga) ratio of 0.25 (Pt-CdS/CIGS(25)). Further inclusion of Ga in the CIGS film was detrimental for both photocurrent density and onset potential. The maximum photocurrent density of 6.8 mA cm(-2) (at 0 V vs RHE) and the highest photocurrent onset potential of 0.89 V vs RHE were obtained by using the Pt-CdS/CIGS(25) photocathode. Achievements of a relatively wide interface band gap of the CIGS/CdS heterointerface and formation of relatively large grains in the Pt-CdS/CIGS(25) sample were likely to be responsible for such superior water reduction properties
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Cu(In,Ga)(S,Se)(2) Thin Film Solar Cell with 10.7% Conversion Efficiency Obtained by Selenization of the Na-Doped Spray-Pyrolyzed Sulfide Precursor Film Reviewed
Wilman Septina, Masaaki Kurihara, Shigeru Ikeda, Yasuhiro Nakajima, Toshiyuki Hirano, Yoshihito Kawasaki, Takashi Harada, Michio Matsumura
ACS APPLIED MATERIALS & INTERFACES 7 ( 12 ) 6472 - 6479 2015.4
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
Selenium-rich Cu(In,Ga)(S,Se)(2) (CIGSSe) thin films on an Mo-coated soda-lime glass substrate were fabricated by spray pyrolysis of an aqueous precursor solution containing Cu(NO3)(2), In(NO3)(3), Ga(NO3)(3), and thiourea followed by selenization at 560 degrees C for 10 min. We studied the effects of intentional sodium addition on the structural and morphological properties of the fabricated CIGSSe films by dissolving NaNO3 in the aqueous precursor solution. The addition of sodium was found to affect the morphology of the final CIGSSe film: the film had denser morphology than that of the CIGSSe film obtained without addition of NaNO3. Photoelectrochemical measurements also revealed that the acceptor density of the nondoped CIGSSe film was relatively high (N-a = 7.2 x 10(17) cm(-3)) and the addition of sodium led to a more favorable value for solar cell application (N-a = 1.8 x 10(17) cm(-3)). As a result, a solar cell based on the sodium-modified CIGSSe film exhibited maximum conversion efficiency of 8.8%, which was significantly higher than that of the cell based on nondoped CIGSSe (4.4%). In addition, by applying MgF2 antireflection coating to the device, the maximum efficiency was further improved to 10.7%.
DOI： 10.1021/am507684x
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Enhancement of Solar Hydrogen Evolution from Water by Surface Modification with CdS and TiO2 on Porous CuInS2 Photocathodes Prepared by an Electrodeposition-Sulfurization Method Reviewed
Jiao Zhao, Tsutomu Minegishi, Li Zhang, Miao Zhong, Gunawan, Mamiko Nakabayashi, Guijun Ma, Takashi Hisatomi, Masao Katayama, Shigeru Ikeda, Naoya Shibata, Taro Yamada, Kazunari Domen
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 53 ( 44 ) 11808 - 11812 2014.10
Joint Work
Authorship：Lead author Publisher：WILEY-V C H VERLAG GMBH
Porous films of p-type CuInS2, prepared by sulfurization of electrodeposited metals, are surface-modified with thin layers of CdS and TiO2. This specific porous electrode evolved H-2 from photoelectrochemical water reduction under simulated sunlight. Modification with thin n-type CdS and TiO2 layers significantly increased the cathodic photocurrent and onset potential through the formation of a p-n junction on the surface. The modified photocathodes showed a relatively high efficiency and stable H-2 production under the present reaction conditions.
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Gunawan, Septina Wilman, Ikeda Shigeru, Harada Takashi, Minegishi Tsutomu, Domen Kazunari, Matsumura Michio
CHEMICAL COMMUNICATIONS 50 ( 64 ) 8941 - 8943 2014.8
Joint Work
Publisher：ROYAL SOC CHEMISTRY
A highly efficient CuInS2-based photocathode for water reduction with a maximum applied bias photon-to-current efficiency of ca. 2% was prepared by using a novel In2S3 surface modifier.
DOI： 10.1039/C4CC03634D
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Selective production of CuSbS2, Cu3SbS3, and Cu3SbS4 nanoparticles using a hot injection protocol Reviewed
Shigeru Ikeda, Shinji Sogawa, Yuji Tokai, Wilman Septina, Takashi Harada, Michio Matsumura
RSC ADVANCES 4 ( 77 ) 40969 - 40972 2014.8
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
Homogeneous Cu-Sb-S nanocrystals with several compositions can be synthesized in a solution through the hot-injection method. Photoelectrochemical analyses of films of these nanoparticles revealed that these nanoparticles have p-type semiconductive characters.
DOI： 10.1039/c4ra07648f
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Efficiency evaluation in solar cell by chemically processed hierarchically stacked debundled pristine carbon nanotubes Reviewed
M. Alam Khan, Shigeru Ikeda, Michio Matsumura
ELECTROCHIMICA ACTA 130 406 - 411 2014.7
Joint Work
Publisher：PERGAMON-ELSEVIER SCIENCE LTD
Pristine SWCNT and MWCNT were individualized and debundled in an N-N dimethyl tetraformamide solvent by a combination of ultrasonication and centrifugation. The wt% (mg) of the pristine CNTs loading were optimized with respect to quantity of solvent (ml). Choice of solvent, ultracentrifugation speed and ultrasonication time were essential parameters for obtaining good individualization of pristine CNTs. By using such CNTs, a thin nanotubes layer (similar to 15 nm) were inserted at the different hierarchical positions into bulk heterojunction solar cell devices made of poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester with weight ratio of 1:1. By inserting such a pristine SWCNTs between PEDOT:PSS and P3HT:PCBM layers, an increase in the solar cell efficiency from 1.51% ((J(sc) of 6.68 mA/cm(2),V-oc of 0.60, FF of 37) to 2.65% (J(sc) of 11 mA/cm(2),V-oc of 0.58, FF of 42) were observed. However, functionalized CNTs shows a degrading efficiency of 0.25% which can be attributed to degradation of corrugated tubular surface side walls leading to potential loss of their optoelectronic properties. The enhanced efficiency of devices with pristine SWCNTs can be conjectured to better opto-electrical properties, enhanced transition, improved local structure and the undamaged tubes. The microstructures of the heterojunction active layer were examined by using AFM, TEM, UV-Vis spectra, IV curve and EQE techniques. (C) 2014 Elsevier Ltd. All rights reserved.
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Hydrolysis of crystalline cellulose to glucose in an autoclave containing both gaseous and liquid water Reviewed
Takashi Harada, Yuji Tokai, Akira Kimura, Shigeru Ikeda, Michio Matsumura
RSC ADVANCES 4 ( 51 ) 26838 - 26842 2014.6
Joint Work
Publisher：ROYAL SOC CHEMISTRY
Hydrolysis of cellulose was investigated in an autoclave. The yield of glucose produced from crystalline cellulose was dependent on the amount of water added to the autoclave. The highest glucose yield of 17% was obtained after 5 h reaction at 190 degrees C in the presence of a small amount of liquid water in the autoclave. When hydrolysis was carried out in saturated vapor pressure in the autoclave in which cellulose was separated from liquid water, nearly the same yield of 15% was obtained. However, when cellulose was soaked in water, the yield was decreased to about 5%. The results suggested that water vapor plays an important role in hydrolysis of the beta-1,4-glycosidic bonds of cellulose. In addition, hydrolysis of the beta-1,4-glycosidic bonds and degradation of produced glucose under hydrothermal conditions were investigated by using cellobiose (a dimer of glucose) and authentic glucose, respectively.
DOI： 10.1039/c4ra02396j
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Pure Sulfide Cu2ZnSnS4 Thin Film Solar Cells Fabricated by Preheating an Electrodeposited Metallic Stack Reviewed
Feng Jiang, Shigeru Ikeda, Takashi Harada, Michio Matsumura
ADVANCED ENERGY MATERIALS 4 ( 7 ) 1301381-1 - 1301381-4 2014.5
Joint Work
Authorship：Lead author Publisher：WILEY-V C H VERLAG GMBH
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Fabrication of an efficient electrodeposited Cu2ZnSnS4-based solar cells with more than 6% conversion efficiency using a sprayed Ga-doped ZnO window layer Reviewed
Feng Jiang, Shigeru Ikeda, Takashi Harada, Akiko Ide, Akiko Mochihara, Kenji Yoshino, Michio Matsumura
RSC ADVANCES 4 ( 46 ) 24351 - 24355 2014.5
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
By the combination of electrochemical deposition of a high-quality Cu2ZnSnS4 (CZTS) thin film photoabsorber and low-temperature spray deposition of Ga-doped ZnO (GZO) transparent conductive oxide, we fabricated a non-vacuum-processed CZTS solar cell. Despite various unoptimized parameters for the TCO layer, such as deposition temperatures and control of film thicknesses, we could obtain the best conversion efficiency of 6.43% with a short circuit current density, an open circuit voltage and a fill factor of 16.6 mA cm(-2), 678 mV and 0.571, respectively.
DOI： 10.1039/c4ra03857f
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Photoelectrochemical Characterizations of CuInS2 and Cu(In,Ga)S2 Thin Films Fabricated by A Spray Pyrolysis Method Reviewed
Ikeda, Shigeru; Iga, Yuta; Septina, Wilman; Harada, Takashi; Matsumura, Michio
ADVANCED MATERILS RESEARCH 894 427 - 431 2014.3
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CuSbS2-based thin film solar cells prepared from electrodeposited metallic stacks composed of Cu and Sb layers
Shigeru Ikeda, Yuta Iga, Wilman Septina, Takashi Harada, Michio Matsumura
Conference Record of the IEEE Photovoltaic Specialists Conference ( 6745005 ) 2598 - 2561 2014.2
Joint Work
Authorship：Lead author Publisher：Institute of Electrical and Electronics Engineers Inc.
Polycrystalline copper antimony sulfide (CuSbS2) films were fabricated by sulfurization of electrodeposited metallic stacks of Cu and Sb layers with various Cu/Sb atomic ratios at 450°C in H2S (5% in Ar). Structural analyses using X-ray diffraction revealed that CuSbS2 films obtained from Cu-poor and Cu-rich metallic stacks (Cu/Sb = 0.7 and 1.3) contained impurity phases, whereas single-phase CuSbS2 film was formed from the stoichiometric stack (Cu/Sb = 1). Morphological studies using SEM indicated that adherence of thus-formed CuSbS2 films to the Mo substrate was dependent on the precursor composition: a CuSbS2 film with poor adherence having many crevices was formed when the Cu-rich metallic stack was used, while CuSbS2 films with good adherences were obtained when Cu-poor and stoichiometric metallic stacks were used. Performance of solar cells with an Al:ZnO/CdS/CuSbS2/Mo structure also depended on structural characteristics of these CuSbS2 films, i.e., a preliminary conversion efficiency of ca. 3% was obtained for device based on the CuSbS 2 film obtained from the stoichiometric metallic stack, whereas the devices derived from Cu-poor and Cu-rich metallic stacks showed the conversion efficiency less than 1%. © 2013 IEEE.
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Thin film solar cell based on CuSbS2 absorber fabricated from an electrochemically deposited metal stack Reviewed
Wilman Septina, Shigeru Ikeda, Yuta Iga, Takashi Harada, Michio Matsumura
THIN SOLID FILMS 550 700 - 704 2014.1
Joint Work
Authorship：Lead author Publisher：ELSEVIER SCIENCE SA
Copper antimony sulfide (CuSbS2) thin films were fabricated by sulfurization of an electrodeposited metallic stack composed of Cu and Sb on a Mo-coated glass (Mo/glass) substrate. A CuSbS2 film containing appreciable impurity components was obtained when the precursor metallic stack was heated monotonically from room temperature to 450 degrees C in Ar followed by sulfurization. The film also showed poor adherence due to a large number of crevices; there were many appreciable pinholes over the entire surface of the film. On the other hand, a CuSbS2 film without any impurity phases was obtained when the metallic precursor film was pretreated at 510 degrees C in Ar for 60 min just before sulfurization at 450 degrees C. It was also observed that the thus-obtained CuSbS2 film showed good adhesion to the Mo/glass substrate and almost no notable pinholes. As expected from structural analyses, the 510 degrees C-pretreated film worked as a relatively efficient absorber for the thin film solar cell with an Al:ZnO/CdS/CuSbS2/Mo/glass structure: it gave preliminary conversion efficiency of 3.1%. (C) 2013 Elsevier B.V. All rights reserved.
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Mechanistic aspects of preheating effects of electrodeposited metallic precursors on structural and photovoltaic properties of Cu(2)Zn(5)nS(4) thin films Reviewed
Yixin Lin, Shigeru Ikeda, Wilman Septina, Yoshihito Kawasaki, Takashi Harada, Michio Matsumura
SOLAR ENERGY MATERIALS AND SOLAR CELLS 120 218 - 225 2014.1
Joint Work
Authorship：Lead author Publisher：ELSEVIER SCIENCE BV
Effects of 350 degrees C preheating of electrochemically stacked Cu-Sn-Zn layers in an inert atmosphere on structural and morphological properties of quaternary kesterite Cu2ZnSnS4 (CZTS) films obtained by sulfurization of the metallic layers were investigated. When the CZTS film was fabricated without the 350 degrees C preheating, the film contained a secondary Cu2SnS3 phase and other impurities. The CZTS film also showed poor adhesion to the bottom molybdenum (Mo) substrate with many crevices and voids in the film; a very thick MoS2 layer was formed at the top part of the Mo layer. These structural failures of the CZTS film were significantly reduced when the metallic precursor was preheated at 350 degrees C before sulfurization for 20 min: the CZTS film thus-obtained exhibited no secondary phases, good adhesion to the bottom Mo layer, flat and densely packed surface morphology, no appreciable crevices or voids, and formation of a relatively thin MoS2 layer. Based on results of studies on structural transformations during 350 degrees C preheating and successive sulfurization, such differences in properties of resulting CZTS films are attributed to differences in formation pathways. Moreover, since 350 degrees C preheating for a longer duration was found to be detrimental for the properties of resulting CZTS films, there should be an optimum duration of preheating to achieve a good CZTS film for solar cell application. As expected from these properties, the solar cell with an Al:ZnO/CdS/CZTS/Mo structure derived from the metallic precursor preheated at 350 degrees C for 20 min showed the best conversion efficiency of 5.6%. (C) 2013 Elsevier B.V. All rights reserved.
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Fabrication of Cu2ZnSnSe4 thin films from an electrodeposited Cu-Zn-Sn-Se/Cu-Sn-Se bilayer Reviewed
Wilman Septina, Shigeru Ikeda, Takashi Harada, Michio Matsumura
PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 10, NO 7-8 10 ( 7-8 ) 1062 - 1066 2013.8
Joint Work
Authorship：Lead author Publisher：WILEY-V C H VERLAG GMBH
In this study, a novel sequential electrodeposition of Cu-Zn-Sn-Se and Cu-Sn-Se layers was applied for fabrication of a Cu2ZnSnSe4 (CZTSe) thin film. The desired Cu-Zn-Sn-Se/Cu-Sn-Se bilayer was obtained at a selected applied potential from electrolytes containing corresponding metal and selenium ions. Annealing of the bilayer film under argon (Ar) flow induced significant losses of Sn and Se components due probably to evaporation of the SnSe compound. Suppression of these losses could be realized by introduction of Se vapor during the annealing: as a result, a CZTSe thin film with an ideal Cu-poor/Zn-rich composition for solar cell application was obtained. The solar cell with a device with the structure of glass/Mo/CZTSe/CdS/ZnO/AZO derived from thus-obtained CZTSe film exhibited a conversion efficiency of 1.1%, while the device still possessed a significant leakage current and a high series resistance. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Synthesis of Nickel Nanoparticles Encapsulated in a Hollow Silica Shell Reviewed
Takashi Harada, Takuji Misaka, Takao Sakata, Shigeru Ikeda, Michio Matsumura
ADVANCED MATERIALS DESIGN AND MECHANICS II 372 132 - 135 2013.8
Joint Work
Authorship：Lead author Publisher：TRANS TECH PUBLICATIONS LTD
A core-hollow shell composite composed of a nickel (Ni) nanoparticle core encapsulated in a hollow silica shell (Ni@SiO2) was prepared by using a nanocrystalline salt of nickel tris-hydrazine complex, which acted as not only a nickel source but also a solid template to produce the core-hollow shell structure. Structural characterizations using TEM and N-2 adsorption-desorption measurements of the thus-obtained Ni@SiO2 powder revealed that it was composed of a Ni nanoparticle core of ca. 4.0 nm in diameter and a rectangular-shaped hollow silica shell with a micropore (ca. 0.5 nm in diameter) system.
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The Effect of Annealing Temperature and KCN Etching on the Photovoltaic Properties of Cu(In,Ga)(S,Se)(2) Solar Cells Using Nanoparticles Reviewed
Duy-Cuong Nguyen, Ken Fukatsu, Keiji Tanimoto, Shigeru Ikeda, Michio Matsumura, Seigo Ito
INTERNATIONAL JOURNAL OF PHOTOENERGY 2013 416245-1 - 416245-7 2013.5
Joint Work
Publisher：HINDAWI PUBLISHING CORPORATION
Cu(In,Ga)S-2 nanoparticles were synthesized by a hot-injection method under a low-vacuum ambience, which were printed and annealed with Se vapor for Cu(In,Ga)(S,Se)(2) solar cells. The Cu(In,Ga)S-2 nanoparticles were around 14 nm, and the stable ink was obtained by dispersing the nanoparticles in hexanethiol. The crystallinity of the Cu(In,Ga)(S,Se)(2) films increased with the increase in annealing temperature. Cu(In,Ga)(S,Se)(2) solar cells with KCN etching after annealing showed better photovoltaic properties than KCN etching before annealing and without etching. The best cell was observed at an annealing temperature of 540 degrees C and KCN etching after annealing; the parameters of this cell were a short-circuit photocurrent density of 27.12 mA/cm(2), open-circuit voltage of 0.42V, fill factor of 0.38, and conversion efficiency of 4.3%.
DOI： 10.1155/2013/416245
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Fabrication of Pores in a Silicon Carbide Wafer by Electrochemical Etching with a Glassy-Carbon Needle Electrode Reviewed
Tomohiko Sugita, Kazuki Hiramatsu, Shigeru Ikeda, Michio Matsumura
ACS APPLIED MATERIALS & INTERFACES 5 ( 7 ) 2580 - 2584 2013.4
Joint Work
Publisher：AMER CHEMICAL SOC
An electrochemical method for making pores in a silicon carbide (SiC) wafer, in which a glassy-carbon (GC) needle electrode was used for processing, is described. By bringing the GC electrode into contact with SiC at its tip end in 20 mol dm(-3) HF solution and applying an anodic potential of or higher than 4 V vs Ag/AgCl to it, SiC was etched at the SiC/GC contact area, leading to pore formation in SiC. The diameter of the pore was almost the same as the diameter of the tip of the GC electrode (about 130 mu m). By addition of sulfuric acid to the HF solution, the rate of pore formation was increased. As a result, the depth of pores formed after processing for 5 h at 10 V vs Ag/AgCl was increased from 15.3 mu m to about 33 mu m by addition of sulfuric acid at a concentration of 3.0 mol dm(-3).
DOI： 10.1021/am303167c
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Pore Formation in a p-Type Silicon Wafer Using a Platinum Needle Electrode with Application of Square-Wave Potential Pulses in HF Solution Reviewed
Tomohiko Sugita, Kazuki Hiramatsu, Shigeru Ikeda, Michio Matsumura
ACS APPLIED MATERIALS & INTERFACES 5 ( 4 ) 1262 - 1268 2013.2
Joint Work
Publisher：AMER CHEMICAL SOC
By bringing an anodically biased needle electrode into contact with n-type Si at its tip in a solution containing hydrofluoric acid, Si is etched at the interface with the needle electrode and a pore is formed. However, in the case of p-type Si, although pores can be formed, Si is likely to be corroded and covered with a microporous Si layer. This is due to injection of holes from the needle electrode into the bulk of p-type Si, which shifts its potential to a level more positive than the potential needed for corrosion and formation of a microporous Si layer. However, by applying square-wave potential pulses to a Pt needle electrode, these undesirable changes are prevented because holes injected into the bulk of Si during the period of anodic potential are annihilated with electrons injected into Si during the period of cathodic potential. Even under such conditions, holes supplied to the place near the Si/metal interface are used for etching p-type Si, leading to formation of a pore at the place where the Pt needle electrode was in contact.
DOI： 10.1021/am302314y
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Single-step electrodeposition of a microcrystalline Cu2ZnSnSe4 thin film with a kesterite structure Reviewed
Wilman Septina, Shigeru Ikeda, Akio Kyoraiseki, Takashi Harada, Michio Matsumura
ELECTROCHIMICA ACTA 88 436 - 442 2013.1
Joint Work
Authorship：Lead author Publisher：PERGAMON-ELSEVIER SCIENCE LTD
Single-step electrodeposition synthesis of a Cu2ZnSnSe4 (CZTSe) film on a Mo-coated glass substrate from an acidic electrolyte containing Cu(II), Zn(II), Sn(IV), and Se(IV) species was investigated. The desired CZTSe film as the main phase was obtained at some selected applied potential ranges through reaction among binary selenides, Cu2Se, ZnSe and SnSe2, which were continuously formed in the present electrolyte containing all of the elements. Sulfurization of the as-deposited film at several temperatures under H2S gas flow resulted in the formation of corresponding mixed compounds of CZTSe and Cu2ZnSnS4 (CZTS), i.e., Cu2ZnSn(S,Se)(4) (CZTSSe): specifically, sulfurization at temperatures higher than 500 degrees C resulted in the formation of single-phase CZTSSe with S-rich compositions. By analyzing linear sweep voltammograms (LSVs) of sulfurized films under chopped irradiation, the films were confirmed to have p-type photoresponses; the film obtained by 500 degrees C sulfurization showed the largest photoresponse because of its sufficiently large grain size and less voids, whereas the presence of an anodic spike in the LSV curve as well as the observation of a broad external quantum efficiency (EQE) spectrum suggested the requirement of further improvement in film quality for photovoltaic application. (c) 2012 Elsevier Ltd. All rights reserved.
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Fabrication of CuInS2 and Cu(In, Ga) S-2 thin films by a facile spray pyrolysis and their photovoltaic and photoelectrochemical properties Reviewed
Shigeru Ikeda, Midori Nonogaki, Wilman Septina, Gunawan Gunawan, Takashi Harada, Michio Matsumura
CATALYSIS SCIENCE & TECHNOLOGY 3 ( 7 ) 1849 - 1854 2013.1
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
Polycrystalline CuInS2 chalcopyrite thin films were formed on a Mo-coated glass substrate by annealing of spray deposited precursor films in a sulfur atmosphere. Structural and photoelectrochemical analyses of CuInS2 films obtained by annealing at 500 degrees C and 600 degrees C revealed that a well-defined crystalline film was obtained by the 600 degrees C annealing. Owing to these favorable properties, the solar cell with an Al: ZnO/CdS/CIS/Mo/glass structure based on the 600 degrees C annealed CuInS2 film showed higher conversion efficiency than that obtained on the cell derived from the 500 degrees C annealed CuInS2. Partial incorporation of Ga in the CuInS2 film with a Ga/In ratio of ca. 0.2 to form a Cu(In, Ga) S-2 mixed crystal without any reduction of photoelectrochemical properties can be achieved by introduction of a Ga source in the sprayed solution. As a result, the solar cell based on the 600 degrees C annealed Cu(In, Ga) S-2 film showed the best conversion efficiency (5.8%) of the present sprayed chalcopyrite films. By introduction of a CdS thin layer followed by loading Pt deposits, moreover, the 600 degrees C annealed Cu(In, Ga) S-2 film worked as a photocathode for photoelectrochemical water splitting with applied bias potential of 40.65 V.
DOI： 10.1039/c3cy00020f
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An inorganic/organic hybrid solar cell consisting of Cu2O and a fullerene derivative Reviewed
M. Alam Khan, Wilman Septina, Shigeru Ikeda, Michio Matsumura
THIN SOLID FILMS 526 191 - 194 2012.12
Joint Work
Publisher：ELSEVIER SCIENCE SA
We fabricated inorganic/organic hybrid solar cells consisting of a p-type Cu2O layer and a fullerene derivative (PCBM) layer, which were prepared by wet processes. The Cu2O layer was grown by electrochemical deposition from an alkaline solution (pH 12.5) containing copper (II) sulfate and lactic acid. A PCBM layer was deposited on it by spin-casting a solution of PCBM. The optimized solar cell showed short circuit current density of 1.5 mA/cm(2), open circuit voltage of 0.4 V, and overall power conversion efficiency of 0.095% under the condition of AM 1.5 G (100 mW/cm(2)). Improvement in mobility and lifetime of electrons in the Cu2O layer is considered to be the key to increase efficiency further. (c) 2012 Elsevier B.V. All rights reserved.
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A perspective on fabricating carbon-based nanomaterials by photocatalysis and their applications Reviewed
Yun Hau Ng, Shigeru Ikeda, Michio Matsumura, Rose Amal
ENERGY & ENVIRONMENTAL SCIENCE 5 ( 11 ) 9307 - 9318 2012.11
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
Combining semiconductor photocatalysts with carbon nanostructures has been extensively investigated due to their enhanced photochemical conversion activity. While many nanocomposite synthesis methods have been reported, the emerging use of photocatalytic reactions in synthesizing these carbon-based semiconductor composites and even pure carbon nanomaterials is increasingly capturing the attention of the research community. Being categorized under photocatalysis, these carbon-based nanomaterials are designed by either utilizing the conduction band electron or valence band hole of a photocatalyst. This perspective surveys the literature, discusses the principle of the method and highlights the recent progress in the development of this synthetic method. Ongoing challenges and new possible solutions encountered in this research area are outlined.
DOI： 10.1039/c2ee22128d
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Cu2ZnSn(S,Se)(4) Thin Film Prepared from a Single-step Electrodeposited Cu-Zn-Sn-Se Precursor
Wilman Septina, Shigeru Ikeda, Akio Kyoraiseki, Takashi Harada, Michio Matsumura
2012 38TH IEEE PHOTOVOLTAIC SPECIALISTS CONFERENCE (PVSC) 2702 - 2706 2012.10
Joint Work
Authorship：Lead author Publisher：IEEE
Cu2ZnSn(S,Se)(4) thin film has been fabricated by sulfurization of a novel single-step electrodeposited Cu-Zn-Sn-Se precursor. Based on EDX analysis of the precursor film, the atomic percentages of Cu, Zn, Sn and Se measured to be 38.48%, 11.53%, 13.62% and 36.37%, respectively. The A1 Raman mode of Cu2ZnSnSe4 was detected from the film which suggests the formation of the quaternary compound during the deposition. Annealing of the precursor film at 550 degrees C under H2S-gas flow resulted in the formation of crystalline Cu2ZnSn(S,Se)(4) compound. Photoelectrochemical measurement of the film revealed that the Cu2ZnSn(S,Se)(4) thus-obtained had a p-type semiconductor photoresponse with the band gap energy of 1.48 eV.
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Homogeneous electrochemical deposition of in on a Cu-covered Mo substrate for fabrication of efficient solar cells with a CuInS2 photoabsorber Reviewed
Sun Min Lee, Shigeru Ikeda, Yasunari Otsuka, Wilman Septina, Takashi Harada, Michio Matsumura
ELECTROCHIMICA ACTA 79 189 - 196 2012.9
Joint Work
Authorship：Lead author Publisher：PERGAMON-ELSEVIER SCIENCE LTD
Electrochemical deposition of indium (In) on a copper-covered molybdenum-coated glass substrate from several acidic InCl3 solutions was studied for fabrication of CuInS2-based solar cells. When In was deposited using a simple acidic InCl3 solution at -0.80 V (vs. Ag/AgCl), island-shaped growth was observed, whereas a homogeneous In film was obtained from InCl3 solution containing citric acid and sodium citrate at -0.98 V (vs. Ag/AgCl). Electrochemical and structural analyses revealed that the citric acid additive had a function for smoothing the surface of the In deposit. The mixing with sodium citrate induced appreciable inhibition of H-2 evolution during the In deposition, leading to high current efficiency of >90%. The CuInS2 film derived from the homogeneous In had a uniform thickness with a smooth surface, while the CuInS2 film obtained from the island-shaped In deposit showed a large variation in thickness with recessed areas. The CuInS2 film derived from the homogeneous In was showed better photoelectrochemical response than that of the film fabricated from the island-shaped In. As expected from these differences, the solar cell with an Al:ZnO/CdS/CuInS2/Mo structure derived from the homogeneous In film showed the best conversion efficiency of 7.8% with relatively high reproducibility. (C) 2012 Elsevier Ltd. All rights reserved.
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Isotope tracing study on oxidation of water on photoirradiated TiO2 particles Reviewed
Thuan Duc Bui, En Yagi, Takashi Harada, Shigeru Ikeda, Michio Matsurnura
APPLIED CATALYSIS B-ENVIRONMENTAL 126 86 - 89 2012.9
Joint Work
Publisher：ELSEVIER SCIENCE BV
Water is oxidized to molecular oxygen on a TiO2 photocatalyst using electron acceptors such as Ag+ and Fe3+ ions. However, there has been no information about whether this reaction occurs or not using molecular oxygen as the electron acceptor. We found by analysis of oxygen in the gas phase using O-18-enriched water that this reaction does in fact occur. The quantum efficiency was higher with rutile-form particles than with anatase-form particles. O-2 was photocatalytically produced using O atoms supplied solely from water even in the presence of O-2 in the system. These results are important for deepening the understanding of TiO2 photocatalysts because molecular oxygen is used most frequently as the electron acceptor and the intermediates of oxidation of water are involved in various kinds of photocatalytic reactions. (c) 2012 Elsevier B.V. All rights reserved.
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Structural regulation of electrochemically deposited copper layers for fabrication of thin film solar cells with a CuInS2 photoabsorber Reviewed
Sun Min Lee, Shigeru Ikeda, Yasunari Otsuka, Takashi Harada, Michio Matsumura
JOURNAL OF NON-CRYSTALLINE SOLIDS 358 ( 17 ) 2424 - 2427 2012.9
Joint Work
Authorship：Lead author Publisher：ELSEVIER SCIENCE BV
Electrodeposition of Cu layers on a Mo-coated glass (Mo/glass) substrate from CuSO4 solutions containing citric acid and sodium citrate was studied for fabrication of CuInS2-based solar cells. When the deposition was performed using the CuSO4 solution containing citric acid, a Cu layer consisting of less-compact roundish grains with a rugged surface morphology was obtained. On the other hand, a compact Cu layer composed of large angular grains was formed from the CuSO4 solution containing sodium citrate. Electrochemical studies revealed that both organic additives worked as complexing agents to reduce the concentration of free Cu2+ ions. but complexation abilities of these additives were different, leading to the structural difference in the resulting Cu layers. The CuInS2 film derived from the former less-compact Cu layer had good adhesion between the CuInS2 film and Mo/glass, whereas the CuInS2 film obtained from the latter compact Cu layer was partially exfoliated because of large volume expansion stresses during the transformation of Cu and In stacked layers into the CuInS2 film. As expected from these differences, the solar cell with an Al:ZnO/CdS/CuInS2/Mo/glass structure derived from the former less-compact Cu layer showed better properties than those of the solar cell derived from the latter compact Cu layer. (C) 2011 Elsevier B.V. All rights reserved.
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Two routes for mineralizing benzene by TiO2-photocatalyzed reaction Reviewed
Thuan Duc Bui, Akira Kimura, Suguru Higashida, Shigeru Ikeda, Michio Mafsurnura
APPLIED CATALYSIS B-ENVIRONMENTAL 107 ( 43102 ) 119 - 127 2011.8
Joint Work
Publisher：ELSEVIER SCIENCE BV
When benzene was oxidized on TiO2-photocatalysts, muconaldehyde as well as phenol was identified as a product. Muconaldehyde was not produced from phenol, indicating that muconaldehyde and phenol are produced as initial stable intermediates by independent pathways. The amount of muconaldehyde produced in the reaction solution was low because it was rapidly oxidized on the photocatalyst. The contributions of the two pathways to the mineralization of benzene were analyzed by isotopic tracing methods using labeled benzene ((C6H6)-C-13) and labeled phenol ((C6H5OH)-C-13). The results showed that a larger part (60-70%) of benzene is initially converted to muconaldehyde. The percentage was dependent on the properties of TiO2 powders. It was also found that anatase-form powders show higher activity for oxidation of benzene than rutile powders do, whereas rutile-form powders show higher activity for oxidation of phenol than anatase powders do. (C) 2011 Elsevier B.V. All rights reserved.
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Plasmon-Enhanced Photocatalytic Activity of Cadmium Sulfide Nanoparticle Immobilized on Silica-Coated Gold Particles Reviewed
Tsukasa Torimoto, Hiroki Horibe, Tatsuya Kameyama, Ken-ichi Okazaki, Shigeru Ikeda, Michio Matsumura, Akira Ishikawa, Hajime Ishihara
JOURNAL OF PHYSICAL CHEMISTRY LETTERS 2 ( 16 ) 2057 - 2062 2011.8
Joint Work
Publisher：AMER CHEMICAL SOC
Nanocomposite photocatalysts of CdS nanoparticles immobilized on Au core-SiO2 shell particles, in which the SiO2 layer acts as an insulator layer to prevent direct electron transfer from photoexcited CdS to Au particles, were prepared. The photocatalytic activity of CdS particles for H-2 evolution was greatly dependent on the distance between CdS and Au particles, due to the locally enhanced electric field produced by photoexcitation of the localized surface plasmon resonance (LSPR) peak of Au particles. Increase in Au core size enlarged the optimal distance between Au and CdS for the enhancement of photocatalysis. This behavior was theoretically reproduced by solving a self-consistent equation system, in which the range of energy dissipation became wider for larger diameter of the Au sphere, and then the balance with the enhancement of photoexcitation of CdS particles by the LSPR-induced electric field was changed.
DOI： 10.1021/jz2009049
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Formation of Through-Holes in Si Wafers by Using Anodically Polarized Needle Electrodes in HF Solution Reviewed
Tomohiko Sugita, Chia-Lung Lee, Shigeru Ikeda, Michio Matsumura
ACS APPLIED MATERIALS & INTERFACES 3 ( 7 ) 2417 - 2424 2011.7
Joint Work
Publisher：AMER CHEMICAL SOC
Electrochemical pore formation in Si using an anodized needle electrode was studied. In the electrochemical process, a Pt, Ir or Pd needle with a diameter of 50-200 mu m was brought into contact at its tip with a Si wafer, which was not connected to an external circuit, in HF solution. By applying an anodic potential to the needle electrode against a Pt counter electrode, a pore with a diameter slightly larger than the diameter of the needle electrode was formed in both p-type and n-type Si, of which current efficiency was higher for n-type Si. Through-holes were electrochemically formed in p-type and n-type Si wafers at speeds higher than 30 mu m min(-1) using a sharpened Ir needle electrode. A model was proposed to explain the results, in which the pore formation was attributed to successive dissolution of Si atoms near the 3-phase (Si/metal/HF solution) boundary by positive holes injected from the needle electrode to the surface of Si.
DOI： 10.1021/am2003284
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A superstrate solar cell based on In-2(Se,S)(3) and CuIn(Se,S)(2) thin films fabricated by electrodeposition combined with annealing Reviewed
Shigeru Ikeda, Ryo Kamai, Sun Min Lee, Tetsuro Yagi, Takashi Harada, Michio Matsumura
SOLAR ENERGY MATERIALS AND SOLAR CELLS 95 ( 6 ) 1446 - 1451 2011.6
Joint Work
Authorship：Lead author Publisher：ELSEVIER SCIENCE BV
Stacked thin films composed of In-2(Se,S)(3) and CuIn(Se,S)(2) layers were grown on a fluorine-doped tin oxide (FTO)-coated glass substrate using electrodeposition of the corresponding selenide (In2Se3 and CuInSe2) precursors followed by annealing in H2S flow (5% in Ar). Structural characterizations of both layers revealed that the resulting film quality strongly depended on annealing conditions of both CuIn(Se,S)(2) and In-2(Se,S)(3) layers: a compact and uniform film was obtained by annealing both layers at 400 degrees C. Performance of Au/CuIn(Se,S)(2)/In-2(Se,S)(3)/FTO superstrate-type solar cells also followed these structural characteristics, i.e., a preliminary conversion efficiency of 2.9% was obtained on the device based on 400 degrees C-annealed In-2(Se,S)(3) and CuIn(Se,S)(2) layers. (C) 2010 Elsevier B.V. All rights reserved.
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Potentiostatic electrodeposition of cuprous oxide thin films for photovoltaic applications Reviewed
Wilman Septina, Shigeru Ikeda, M. Alam Khan, Takeshi Hirai, Takashi Harada, Michio Matsumura, Laurence M. Peter
ELECTROCHIMICA ACTA 56 ( 13 ) 4882 - 4888 2011.5
Joint Work
Authorship：Lead author Publisher：PERGAMON-ELSEVIER SCIENCE LTD
Potentiostatic deposition of Cu(2)O thin films on glass substrates coated with F-doped SnO(2) from an alkaline electrolyte solution (pH 12.5) containing copper (II) sulfate and lactic acid was studied for fabrication of a Cu(2)O/Al-doped ZnO (AZO) heterojunction solar cell. The band gap of the electrodeposited Cu(2)O films was determined by photoelectrochemical measurements to be around 1.9 eV irrespective of the applied potentials. The solar cells with a glass/FTO/Cu(2)O/AZO structure were fabricated by sputtering an AZO film onto the Cu(2)O film followed by deposition of an Al contact by vacuum evaporation. The highest efficiency of 0.603% was obtained with a Cu(2)O film deposited at -0.6V (vs. Ag/AgCl). This was attributed to better compactness and purity of the Cu(2)O film than those of the Cu(2)O films deposited at other potentials. (C) 2011 Elsevier Ltd. All rights reserved.
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Fabrication of CuInS2 films from electrodeposited Cu/In bilayers: effects of preheat treatment on their structural, photoelectrochemical and solar cell properties Reviewed
Sun Min Lee, Shigeru Ikeda, Tetsuro Yagi, Takashi Harada, Ahmed Ennaoui, Michio Matsumura
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 13 ( 14 ) 6662 - 6669 2011.4
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
Polycrystalline CuInS2 films were fabricated by sulfurization of electrodeposited Cu and In metallic precursor films in a Cu-rich composition at 520 degrees C in H2S (5% in Ar). Structural analyses revealed that the adherence of the thus-formed CuInS2 film to the Mo substrate was strongly dependent on heating profiles of the Cu/In bilayer film: a CuInS2 film with poor adherence having many crevices was formed when the Cu/In bilayer film was heated monotonously from room temperature to 520 degrees C in Ar within 25 min followed by sulfurization, whereas CuInS2 films with good adherence were obtained when the Cu/In films were pretreated at 110 degrees C in Ar for 10-60 min just before increasing the temperature up to 520 degrees C for sulfurization. It was also clarified that the CuInS2 film obtained without 110 degrees C pretreatment had pinholes inside the film, whereas the CuInS2 films formed after 110 degrees C pretreatment showed no notable pinholes. Photoelectrochemical responses of these CuInS2 films in an electrolyte solution containing Eu(III) indicated that the CuInS2 films obtained after 110 degrees C pretreatment had higher external quantum efficiency (EQE) values than those of films obtained without 110 degrees C pretreatment, mainly due to better adherence of 110 degrees C pretreated CuInS2 films to the Mo substrate than the CuInS2 film obtained without 110 degrees C pretreatment. The performance of solar cells with an Al:ZnO/Zn(S,O)/CdS/CuInS2/Mo structure also depended on the structural characteristics of the CuInS2 films, i.e., preliminary conversion efficiencies of ca. 5% were obtained for devices based on the CuInS2 films obtained after 110 degrees C pretreatment, whereas the device prepared by the CuInS2 film without 110 degrees C pretreatment showed the conversion efficiency less than 1.5%.
DOI： 10.1039/c0cp02204g
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Emission spectroscopy of divalent-cation-doped GaN photocatalysts Reviewed
Takeshi Hirai, Takashi Harada, Shigeru Ikeda, Michio Matsumura, Nobuo Saito, Hiroshi Nishiyama, Yasunobu Inoue, Yoshiyuki Harada, Nobuhito Ohno, Kazuhiko Maeda, Jun Kubota, Kazunari Domen
JOURNAL OF APPLIED PHYSICS 110 ( 11 ) 113526-1 - 113526-7 2011.2
Joint Work
Publisher：AMER INST PHYSICS
Photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectra of GaN particles doped with divalent cations (Mg(2+), Zn(2+), and Be(2+)), which promote photocatalytic overall water splitting, were investigated. The PL and TRPL spectra were mainly attributed to donor-acceptor pair recombination between the divalent cation dopants and divalent anion impurities (O(2)- and S(2-)) unintentionally introduced from raw materials, which form acceptor and donor levels, respectively. These levels are likely to provide holes and electrons required for photocatalytic reactions, contributing to the photocatalytic activity of the GaN-based photocatalysts for overall water splitting. (C) 2011 American Institute of Physics. [doi:10.1063/1.3665225]
DOI： 10.1063/1.3665225
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Photoreduction of Water by using Modified CuInS2 Electrodes Reviewed
Shigeru Ikeda, Takayuki Nakamura, Sun Min Lee, Tetsuro Yagi, Takashi Harada, Tsutomu Minegishi, Michio Matsumura
CHEMSUSCHEM 4 ( 2 ) 262 - 268 2011.2
Joint Work
Authorship：Lead author Publisher：WILEY-BLACKWELL
Polycrystalline CuInS2 films were fabricated by sulfurization of electrodeposited Cu and In metallic precursor films. Structural analyses revealed that the CuInS2 film formed compact agglomerates of crystallites with grain sizes of ca. 0.5-1.5 mu m. Photoelectrochemical characterization revealed that the film was p-type with a flat band potential of 0.3-0.4 V (vs Ag/AgCl at pH 4), which is suitable for water reduction but cannot be for water oxidation. Upon loading Pt deposits, the film worked as a hydrogen (H-2) liberation electrode under cathodic polarization. Moreover, by introduction of n-type thin layers such as CdS and ZnS on the CuInS2 surface before the Pt loading, appreciable improvements of H-2 liberation efficiency were achieved: for the CdS modified sample, spectral response data showed incident photon to current efficiency as high as 20% at wavelengths ranging from ca. 500 to 750 nm. Appreciable H-2 evolution on this sample under potentials of power-producing regions was also confirmed.
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Electrochemical method for slicing Si blocks into wafers using platinum wire electrodes Reviewed
Chia-Lung Lee, Yuji Kanda, Shigeru Ikeda, Michio Matsumura
SOLAR ENERGY MATERIALS AND SOLAR CELLS 95 ( 2 ) 716 - 720 2011.2
Joint Work
Publisher：ELSEVIER SCIENCE BV
Straight grooves were formed in single crystalline Si wafers and poly-crystalline Si blocks in an aqueous solution containing HF by an electrochemical method using Pt wires (phi=50 mu m) and a Pt foil as catalytic electrodes and a counter electrode, respectively. The grooves were formed by applying anodic potential of about 2.25 V vs. Ag/AgCl to the Pt wires, which were in contact with Si. The grooving rate and morphologies were dependent on HF concentrations. The grooving rate was also dependent on the pressure applied to the Si/Pt interface. Grooves with a width of about 55 mu m were formed at the edge of a 250-mu m-thick single crystalline wafer at a rate of 3.2 mm/h by processing in 15 mol dm(-3) HF under a pressure of about 54 x 10(4) g/cm(2). This pressure was necessary to increase the grooving rate. Possibly, an insulating porous silicon layer formed between Si and Pt was destroyed under this pressure. On applying this process to a poly-crystalline Si block, a Si wafer with a size of 1 x 1 cm(2) was obtained by the electrochemical method. However, the slicing speed was lowered as the depth of grooves increased and it took 120 h to obtain the wafer. The slow exchange of HF solution in the groove was thought to be the main reason for the slow speed of slicing the Si block. (C) 2010 Elsevier B.V. All rights reserved.
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Development of New Methods for Fine-Wiring in Si Using a Wet Catalytic Reaction Reviewed
Chia-Lung Lee, Tomohiko Sugita, Koji Tatsumi, Shigeru Ikeda, Michio Matsumura
TECHNOLOGY EVOLUTION FOR SILICON NANO-ELECTRONICS 470 129 - 134 2011.2
Joint Work
Publisher：TRANS TECH PUBLICATIONS LTD
Using a new wet process based on a catalytic reaction, pores and grooves were formed in Si using Au, Pt, or Ag as the catalyst. The diameter of the pore can be as small as 50 nm. However, to produce wiring in Si wafers, we primarily formed pores with a diameter of about 5 mu m. These pores were filled with Cu by electrochemical plating, forming Cu wires developed to the wafer surface. In the process, the catalyst particles remaining at the bottom of the pore acted as seeds for the deposition of Cu and helped fill the pores without the formation of voids. In order to control the position of pores and grooves formed in Si, methods using catalytic electrodes were also developed.
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Catalytic Activity and Regeneration Property of a Pd Nanoparticle Encapsulated in a Hollow Porous Carbon Sphere for Aerobic Alcohol Oxidation Reviewed
Takashi Harada, Shigeru Ikeda, Fumihiro Hashimoto, Takao Sakata, Keita Ikeue, Tsukasa Torimoto, Michio Matsumura
LANGMUIR 26 ( 22 ) 17720 - 17725 2010.11
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
A core-shell composite consisting of a palladium (Pd) nanoparticle and a hollow carbon shell (Pd@hmC) was employed as a catalyst for aerobic oxidation of various alcohols. The core-shell structure was synthesized by consecutive coatings of Pd nanoparticles with siliceous and carbon layers followed by removal of the intermediate siliceous layer. Structural characterizations using TEM and N-2 adsorption-desorption measurements revealed that Pd@hmC thus-obtained was composed of a Pd nanoparticle core of 3-6 nm in diameter and a hollow carbon shell with well-developed mesopore (ca. 2.5 nm in diameter) and micropore (ca. 0.4-0.5 nm in diameter) systems. When compared to some Pd-supported carbons. Pd@hmC showed a high level of catalytic activity for oxidation of benzyl alcohol into benzaldehyde using atmospheric pressure of O-2 as an oxidant. The Pd@hmC composite also exhibited a high level of catalytic activity for aerobic oxidations of other primary benzylic and allylic alcohols into corresponding aldehydes. The presence of a well-developed pore system in the lateral carbon shell enabled efficient diffusion of both substrates and products to reach the central Pd nanoparticles. leading to such high catalytic activities. This core-shell structure also provided high thermal stability of Pd nanoparticles toward coalescence and/or aggregation due to the physical isolation of each Pd nanoparticle from neighboring particles by the carbon shell: this specific property of Pd@hmC resulted in possible regeneration of catalytic activity for these aerobic oxidations by a high-temperature heat treatment of the sample recovered after catalytic reactions.
DOI： 10.1021/la102824s
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Multicomponent sulfides as narrow gap hydrogen evolution photocatalysts Reviewed
Shigeru Ikeda, Takayuki Nakamura, Takashi Harada, Michio Matsumura
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 12 ( 42 ) 13943 - 13949 2010.11
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
A series of mixed crystals composed of Cu2ZnSnS4, Ag2ZnSnS4 and ZnS was prepared by co-precipitation of the corresponding metal ions in aqueous sodium sulfide followed by annealing in a sulfur atmosphere. Ideal solid solutions of Cu2ZnSnS4 and Ag2ZnSnS4 with a kesterite structure ((CuxAg1-x)(2)ZnSnS4 (0 <= x <= 1)) were successfully obtained by this procedure, as confirmed by their X-ray diffraction (XRD) patterns and energy-diffuse X-ray (EDX) analyses. On the other hand, the solubility of ZnS in these kesterite compounds was found to be limited: the upper limit of the ratio of ZnS to (CuxAg1-x)(2)ZnSnS4 was less than 0.1, regardless of the Cu-Ag ratio in (CuxAg1-x)(2)ZnSnS4. Based on the results for dependence of their photoabsorption properties on atomic compositions, a plausible band structure is discussed. Evaluation of the photocatalytic activity for H-2 evolution of these mixed crystals from an aqueous solution containing S2- and SO32- ions upon loading Ru catalysts under simulated solar radiation (AM 1.5) revealed that active compounds for this reaction should contain both dissolved ZnS and Ag components. The dissolved ZnS in (CuxAg1-x)(2)ZnSnS4 gave upward shifts of their conduction band edges. Moreover, the presence of Ag in the solid solution provided n-type conductivity, leading to efficient migration of photogenerated electrons to the surface to induce water reduction into H-2.
DOI： 10.1039/c0cp00267d
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Determination of Oxygen Sources for Oxidation of Benzene on TiO2 Photocatalysts in Aqueous Solutions Containing Molecular Oxygen Reviewed
Thuan Duc Bui, Akira Kimura, Shigeru Ikeda, Michio Matsumura
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 132 ( 24 ) 8453 - 8458 2010.6
Joint Work
Publisher：AMER CHEMICAL SOC
Photocatalytic oxidation of benzene to CO2 was studied in aqueous solutions using different kinds of TiO2 powders, and isotopic oxygen tracers ((H2O)-O-18 and O-18(2)) were used to investigate the oxidation process. Phenol was produced as a main intermediate in solution. When anatase powders, which showed high activity for oxidation of benzene, were used, 70-90% of oxygen introduced into phenol was from water. On the other hand, when rutile powders were used, only 20-40% of the oxygen was from water. The rest was from molecular oxygen in both cases. The rate of phenol production by using molecular oxygen was nearly the same between anatase and rutile powders. Hence, the high activity of anatase powders for oxidation of benzene to CO2 is attributed to their high activity for oxidation of benzene to phenol, which is considered to be the rate-determining step, using water as the oxygen source. The processes using water and molecular oxygen as the oxygen sources are ascribed, respectively, to oxygen transfer and hole transfer processes in the initial step of benzene oxidation.
DOI： 10.1021/ja102305e
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Thuan Duc Bui, Akira Kimura, Shigeru Ikeda, Michio Matsumura
APPLIED CATALYSIS B-ENVIRONMENTAL 94 ( 43102 ) 186 - 191 2010.2
Joint Work
Publisher：ELSEVIER SCIENCE BV
TiO2-photocatalyzed reaction was conducted in pure benzene in which TiO2 particles were suspended. Benzene was oxidatively decomposed into CO2, as most of organic compounds. However, the rate of CO2 evolution from benzene was gradually lowered as the reaction continued, which was in contrast to the cases of other non-aromatic organic compounds, such as alcohols or acids. To clarify the reason for the decrease in activity of TiO2, intermediates produced in the solution phase and on the surface of TiO2 were analyzed using chemical and physical techniques. Several kinds of intermediates were identified: phenolic compounds, aldehydes, carboxylic acids, and polymeric substance. Of these products, catechol and polymeric substance, which were observed only on the surface of TiO2 powder, were found to be responsible for the lowering of the photocatalytic activity of TiO2. (C) 2009 Elsevier B.V. All rights reserved.
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Shigeru Ikeda, Ryo Kamai, Tetsuro Yagi, Michio Matsumura
JOURNAL OF THE ELECTROCHEMICAL SOCIETY 157 ( 1 ) B99 - B103 2010.1
Joint Work
Authorship：Lead author Publisher：ELECTROCHEMICAL SOC INC
Copper indium diselenide (CuInSe2) thin films were grown on a fluorine-doped tin oxide (FTO) glass substrate covered with a thin layer of cadmium sulfide (CdS) by an electrodeposition method. The annealing of the films in a sulfur atmosphere resulted in a partial replacement of selenium with sulfur to form CuIn(Se,S)(2) solid solutions. Structural characterizations of the annealed samples by using X-ray diffraction, energy-diffused X-ray analysis, and UV/visible/near-infrared absorption spectra revealed that the sulfur contents and the photoabsorption onsets strongly depended on the annealing temperature. The performance of FTO/CdS/CuIn(Se,S)(2)/Au superstrate-type solar cells was highest when the CuIn(Se,S)(2) layer was annealed at 350 degrees C in a sulfur atmosphere. A capacitance-voltage analysis of the CuIn(Se,S)(2)/CdS junctions showed that the hole density in CuIn(Se,S)(2) was increased by annealing at a high temperature, contributing to the improvement in the photocurrent. However, annealing at a high temperature led to the interdiffusion of CdS into the CuIn(Se,S)(2) layer, resulting in the lowering of the solar cell performance. As a result of the trade-off between these factors, annealing at 350 degrees C gave the best result for CuInSe2 films made by the electrodeposition method. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3254167] All rights reserved.
DOI： 10.1149/1.3254167
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Acceleration of groove formation in silicon using catalytic wire electrodes for development of a slicing technique Reviewed
Mohamed Shaker Salem, Chia-Lung Lee, Shigeru Ikeda, Michio Matsumura
JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 210 ( 2 ) 330 - 334 2010.1
Joint Work
Publisher：ELSEVIER SCIENCE SA
A novel electrochemical technique for silicon slicing in which anodic potential is applied to a platinum wire, keeping it in contact with silicon, is proposed. Since silicon was dissolved in a solution containing hydrogen fluoride at the site of contact with the platinum wire electrode, a goove was formed in the silicon. The grooving speed depended on the concentration of hydrogen fluoride and additives in the solution. A grooving speed of 0.85 mm/h was obtained at room temperature using an electrolyte composed of 30 wt% hydrofluoric acid, 1 mM iodine, and 0.03 vol% glycerol. Iodine acted as a catalyst for the oxidaton of silicon, and glycerol prevented the filling of grooves with gases. Further increase in grooving speed to 1.0 mm/h was achieved by applying pulsed potentials oscillating between 1 and 2 V vs. Ag/AgCl in the same electrolyte. (C) 2009 Elsevier B.V. All rights reserved.
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Shigeru Ikeda, Hideyuki Kobayashi, Yoshimitsu Ikoma, Takashi Harada, Suzuko Yamazaki, Michio Matsumura
APPLIED CATALYSIS A-GENERAL 369 ( 43102 ) 113 - 118 2009.11
Joint Work
Authorship：Lead author Publisher：ELSEVIER SCIENCE BV
TiO(2) particles encapsulated in hollow silica shells with controlled shell thicknesses were fabricated. Compared to naked TiO(2) without coverage by a hollow silica shell, all of these composites showed low levels of photocatalytic activity for gas-phase decomposition of acetone into CO(2). The activities over these composites tended to decrease with increase in thickness of the lateral silica shell. These results can be explained by a decrease in the diffusion of acetone with increase in thickness of the silica shell, leading to hampering of supply of the substrate to the surfaces of core TiO(2) particles. In contrast, for the overall photodecomposition of gaseous 2-propanol into CO(2), the presence of the lateral silica shell was found to be beneficial, i.e., the composite induced a high level of activity compared to the activity of naked TiO(2). The enhancement of activity for this reaction was likely to be due to condensation of the intermediate product of acetone in the void spaces, leading to an increase in the collision probability between acetone and the surface of the TiO(2) core. (C) 2009 Elsevier B.V. All rights reserved.
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Formation of 100 mu m Deep Vertical Pores in Si Wafers by Wet Etching and Cu Electrodeposition Reviewed
Chia-Lung Lee, Shinsuke Tsuru, Yuji Kanda, Shigeru Ikeda, Michio Matsumura
JOURNAL OF THE ELECTROCHEMICAL SOCIETY 156 ( 12 ) D543 - D547 2009.10
Joint Work
Publisher：ELECTROCHEMICAL SOC INC
Pores with diameters of about 5 mu m were formed in n-type Si(100) wafers by wet etching using aggregated Au particles, each about 1 mu m, as catalysts. The pores were as deep as 100 mu m after etching for 5 h. In the pores of the Si wafers, which were almost perpendicular to the Si surface, Cu was electrochemically deposited from an aqueous solution of CuSO(4) using Au particles remaining at the bottom of the pores as seeds for deposition. When a potential of about - 0.275 V vs Ag/AgCl was applied to the Si wafer, Cu deposition started from the bottom of each pore and continued to fill the whole pore with a depth of about 70 mu m in 16 h. The selective Cu deposition in the pores is due to an electrocatalytic effect of Au/Cu for Cu plating. In these processes, therefore, Au particles acted as catalysts for pore formation and also as seeds for Cu electrodeposition, making it possible to fabricate connections through wafers by a simple method. However, it was difficult to increase the deposition rate by applying potentials more cathodic than - 0.40 V vs Ag/AgCl because Cu was deposited on the Si surface at these potentials. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3237139] All rights reserved.
DOI： 10.1149/1.3237139
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Yun Hau Ng, Shigeru Ikeda, Yoshihiro Morita, Takashi Harada, Keita Ikeue, Michio Matsumura
JOURNAL OF PHYSICAL CHEMISTRY C 113 ( 29 ) 12799 - 12805 2009.7
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
In an attempt to clarify the origin of the high activity and durability for aerobic oxidation of alcohols over a platinum (Pt)-carbon composite, i.e., Pt nanoparticles embedded in microporous carbon (nPt@hC), the catalytic reaction mechanism and microstructure of Pt nanoparticles were investigated in detail. By means of kinetic analyses, catalytic oxidation on nPt@hC was found to proceed through the formation of Pt-alcoholates, the beta-hydride elimination to form Pt-hydride species (Pt-H), and oxidation of Pt-H with molecular oxygen. It was also revealed that the P-hydride elimination step was a rate-determining step in this reaction. These findings and results of structural studies indicate that the achievement of high catalytic activity on nPt@hC is due to stabilization of its transition state of a positively charged carbocationic component by the electron-rich carbon matrix surrounding Pt nanoparticles, leading to lowering activation energy. Moreover, detailed investigation of the surface characteristics of Pt nanoparticles in nPt@hC after catalytic reactions by using various analytical methods revealed that the durability of nPt@hC for aerobic oxidation of alcohols is due to the suppression of aggregation of Pt nanoparticles and prevention of chemical poisoning of Pt surfaces.
DOI： 10.1021/jp903561q
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Shigeru Ikeda, Hideyuki Kobayashi, Tomohiko Sugita, Yoshimitsu Ikoma, Takashi Harada, Michio Matsumura
APPLIED CATALYSIS A-GENERAL 363 ( 43102 ) 216 - 220 2009.7
Joint Work
Authorship：Lead author Publisher：ELSEVIER SCIENCE BV
A composite of titanium(IV) oxide (TiO(2)) particles (core) and nanoporous silica (shell) was prepared by successive coating of a carbon layer and an octadecyl-functionalized silica layer on TiO(2), followed by heat treatment to remove the organic components. Transmission electron microscope (TEM) observation and nitrogen (N(2)) sorption analyses showed that the composite has a unique rattle-type structure, i.e., TiO(2) particles were encapsulated in the hollow silica shell having well-developed porosity. When the photocatalytic activity for gas phase decomposition of acetone over the composite was compared with that over naked TiO(2) without the lateral silica shell, the activity over the composite tended to become higher than that over naked TiO(2) as the initial amount of acetone in the system was reduced. The enhancement of decomposition rate under a diluted condition was due to condensation of acetone on the lateral silica shell, which resulted in enhancement of the collision rate between the substrate and the surface of the TiO(2) core. (C) 2009 Elsevier B.V. All rights reserved.
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Yun Hau Ng, Shigeru Ikeda, Sang-in Park, Yoshihiro Morita, Takashi Harada, Michio Matsumura
TOPICS IN CATALYSIS 52 ( 43258 ) 627 - 633 2009.4
Joint Work
Authorship：Lead author Publisher：SPRINGER/PLENUM PUBLISHERS
Photodeposition of Pt nanoparticle and phenolic polymer on TiO2 in a deaerated aqueous system containing hexachloroplatinic acid and phenol were investigated. We observed that reductive deposition of Pt nanoparticles with electrons proceeded rapidly, while the oxidative deposition of a phenolic polymer with positive holes was relatively slow. The difference ensured the encapsulation of Pt nanoparticles between the polymer layer and TiO2. Carbonization of the polymer components followed by removing TiO2 resulted in the formation of two types of Pt-carbon nanocomposites with different morphologies of carbons, depending on photoirradiation duration. These composites exhibited high levels of catalytic activity and reusability for aqueous oxidation of 1-phenylethanol with molecular oxygen.
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Electrochemical Grooving of Si Wafers Using Catalytic Wire Electrodes in HF Solution Reviewed
Chia-Lung Lee, Yuji Kanda, Takeshi Hirai, Shigeru Ikeda, Michio Matsumura
JOURNAL OF THE ELECTROCHEMICAL SOCIETY 156 ( 2 ) H134 - H137 2009.1
Joint Work
Publisher：ELECTROCHEMICAL SOC INC
Si wafers were electrochemically grooved in HF solution using metal wires (Pt and Au wires) as catalytic wire electrodes and a Pt plate as a counter electrode. By applying anodic potentials of about 2.0 V vs Ag/AgCl to the Pt or Au wire electrodes, which were in contact with Si, Si was etched at the place where the wires were in contact. As a result, grooves were formed in Si. The widths of the grooves formed using Pt wires with diameters of 30 and 50 mu m were about 35 and 55 mu m, respectively. The grooving rate was typically in the range of 400-600 mu m/h at room temperature. The grooving rate was faster for the thinner wire electrodes because the diffusion of chemical species to and from the Si/Pt interface became easier for the thinner electrodes. The grooving rate was increased by increasing the anodic potential or temperature, although the Si surface was roughened to some extent under such conditions.
DOI： 10.1149/1.3033735
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Efficient Reductive Alkylation of Aniline with Acetone over Pt Nanoparticles Encapsulated in Hollow Porous Carbon Reviewed
Takashi Harada, Shigeru Ikeda, Natsumi Okamoto, Yun Han Ng, Suguru Higashida, Tsukasa Torimoto, Michio Matsumura
CHEMISTRY LETTERS 37 ( 9 ) 948 - 949 2008.9
Joint Work
Authorship：Lead author Publisher：CHEMICAL SOC JAPAN
Reductive alkylation of aniline with acetone over various Pt catalysts was Studied Under atmospheric pressure of hydrogen at room temperature. It was found that our newly designed Pt catalyst, i.e., Pt nanoparticles encapsulated in hollow porous carbon. showed excellent catalytic activity in comparison with activities of other Pt catalysts. Moreover, one-pot reductive alkylation of nitrobenzene with acetone proceeded smoothly over the catalyst.
DOI： 10.1246/cl.2008.948
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Rhodium nanoparticle encapsulated in a porous carbon shell as an active heterogeneous catalyst for aromatic hydrogenation Reviewed
Takashi Harada, Shigeru Ikeda, Yun Hau Ng, Takao Sakata, Hirotaro Mori, Tsukasa Torimoto, Michio Matsumura
ADVANCED FUNCTIONAL MATERIALS 18 ( 15 ) 2190 - 2196 2008.8
Joint Work
Authorship：Lead author Publisher：WILEY-V C H VERLAG GMBH
Rhodium (Rh) nanoparticle (core)-carbon (shell) powder was prepared by double-layer coating of a silica layer and a mesoporous silica/carbon layer on an Rh nanoparticle followed by chemical etching with aqueous hydrofluoric acid to remove siliceous components. The use of various techniques for characterization of the structure showed that the powder thus-obtained had a rattle-like structure: Rh nanoparticles were encapsulated in the hollow carbon-shell having well-developed porosity. The porous wall structure of the lateral carbon shell provides channels and hydrophobic void spaces that allow efficient penetration and absorption of organic species present in aqueous media. This offers a microenvironment with a high concentration of organic substrates inside the shell. Moreover, the surfaces of medial Rh nanoparticles were free from any ligands, i.e., the active surface site(s) was exposed to induce organic transformations. These unique properties, which cannot be achieved by conventional Rh nanoparticles stabilized with organic agents, led to excellent catalytic activity for hydrogenation of various aromatic and heterocyclic rings in water.
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An efficient and reusable carbon-supported platinum catalyst for aerobic oxidation of alcohols in water Reviewed
Yun Hau Ng, Shigeru Ikeda, Takashi Harada, Yoshihiro Morita, Michio Matsumura
CHEMICAL COMMUNICATIONS 3181-3183 ( 27 ) 3181 - 3183 2008.7
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
Platinum nanoparticles embedded in a hollow porous carbon shell prepared by a photocatalytic reaction acted as a reusable catalyst for the aerobic oxidation of alcohols under atmospheric pressure of oxygen in water.
DOI： 10.1039/b803912g
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High sintering resistance of platinum nanoparticles embedded in a microporous hollow carbon shell fabricated through a photocatalytic reaction Reviewed
Yun Hau Ng, Shigeru Ikeda, Takashi Harada, Takao Sakata, Hirotaro Mori, Akio Takaoka, Michio Matsumura
LANGMUIR 24 ( 12 ) 6307 - 6312 2008.6
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
Platinum (Pt) nanoparticles encapsulated in microporous carbon with a hollow structure (nPt@hC) were fabricated on the basis of a titanium(IV) oxide (TiO2) photocatalytic reaction. From the tomogram of a sample studied by using a transmission electron microscope (TEM), the Pt nanoparticles were found to be embedded in the carbon shell and were physically separated from each other by the carbon matrix. Owing to this unique structure, the Pt particles showed high resistance to sintering when subjected to thermal treatment at temperatures up to 800 degrees C. As a result, hydrogenation reactions using various heat-treated nPt@hCs as catalysts indicated that loss of catalytic activity was minimized. Thus, the present system will be a promising system for optimizing catalyst nanostructures utilized in processes requiring rigorous conditions.
DOI： 10.1021/la800045u
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Precise determination of the first hyperpolarizability of a fluorescent triindole derivative with dicyanovinyl groups by the deconvolution method Reviewed
Ikeda Shigeru, Kumagai Hironobu, Ooi Hideo, Konishi Koji, Hiyoshi Hidetaka, Wada Tatsuo
CHEMICAL PHYSICS LETTERS 458 ( 4-6 ) 337 - 340 2008.6
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Pore formation in silicon by wet etching using micrometre-sized metal particles as catalysts Reviewed
Chia-Lung Lee, Kazuya Tsujino, Yuji Kanda, Shigeru Ikeda, Michio Matsumura
JOURNAL OF MATERIALS CHEMISTRY 18 ( 9 ) 1015 - 1020 2008.3
Joint Work
Publisher：ROYAL SOC CHEMISTRY
Au, Pt, or Ag particles with particle sizes of ca. 1 mm were used as catalysts for boring pores in p-type Si( 100) wafers by wet etching in aqueous solutions containing hydrofluoric acid and hydrogen peroxide. Boring speed was fastest when Pt particles were used as the catalyst. However, the sidewalls of the pores and the surface of the wafer were covered with a nanoporous silicon layer of ca. 500 nm in thickness, and the pore showed a tapered structure. When micrometre-sized Ag particles were used, no deep pores were formed because the particles were unstable in the solution. In contrast to Pt and Ag particles, Au particles bored straight pores under some conditions. However, the morphology of pores depended on the shape of the Au particles. Spherical Au particles formed straight pores, whereas non-spherical Au particles formed pores with spiral sidewalls. When Au particles formed aggregates consisting of a small number of particles (< 10 particles), crooked pores tended to be formed. In contrast, when the aggregates were composed of a larger number of particles, straight pores were formed and the boring speed was faster than the pores formed with isolated Au particles.
DOI： 10.1039/b715639a
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Photocatalytic route for synthesis of hollow porous carbon/Pt nanocomposites with controllable density and porosity Reviewed
Yuri Hau Ng, Shigeru Ikeda, Takashi Harada, Sangin Park, Takao Sakata, Hirotaro Mori, Michio Matsumura
CHEMISTRY OF MATERIALS 20 ( 3 ) 1154 - 1160 2008.2
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
Simultaneous photoreduction of Pt(IV) ions and photooxidative polymerization of phenol on the surface of titanium(IV) oxide (TiO2) under ultraviolet light irradiation induced the formation of a composite, Pt-loaded TiO2 covered with a layer of phenolic polymer. Subsequent carbonization of the polymer layer and removal of TiO2 core particles yielded hollow carbon incorporated with platinum nanoparticles (nPt@hC). By varying the photoirradiation time, appreciable changes in density and porosity of the polymer layer and the carbon shell in nPt@hC were observed: prolonged irradiation induced a densification of the carbon matrix, resulting in a decrease in pore volume. Mainly due to the modulation of active surface of Pt nanoparticles, the densification of carbon was found to influence catalytic activity for hydrogenation of normal olefins.
DOI： 10.1021/cm702034w
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Origin of visible light absorption in GaN-Rich (Ga1-xZnx)(N1-xOx) photocatalysts Reviewed
Takeshi Hirai, Kazuhiko Maeda, Masaaki Yoshida, Jun Kubota, Shigeru Ikeda, Michio Matsumura, Kazunari Domen
JOURNAL OF PHYSICAL CHEMISTRY C 111 ( 51 ) 18853 - 18855 2007.12
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
Photoluminescence (PL) and photoluminescence excitation (PLE) spectra of (Ga1-xZnx)(N1-xOx) with compositions of x = 0.05-0.20 (i.e., GaN-rich) were measured at 10 K in an attempt to clarify the origin of the visible light activity of this material as a photocatalyst. It was found that the PL spectra of GaN-rich (Ga1-xZnx)(N1-xOx) can be interpreted to correspond to impurity levels, specifically acceptor levels formed by the substitution of Zn for Ga in GaN. The PL and PLE spectra suggest that the visible light absorption of this material occurs via the Zn-related acceptor levels.
DOI： 10.1021/jp709811k
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Size-selective photocatalytic reactions by titanium(IV) oxide coated with a hollow silica shell in aqueous solutions Reviewed
Shigeru Ikeda, Hideyuki Kobayashi, Yoshimitsu Ikoma, Takashi Harada, Tsukasa Torimoto, Bunsho Ohtani, Michio Matsumura
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 9 ( 48 ) 6319 - 6326 2007.12
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
A novel core-shell composite photocatalyst, commercially available titanium(IV) oxide (TiO2) particles directly incorporated into a hollow amorphous silica shell, was fabricated by successive coating of TiO2 with a carbon layer and a silica layer followed by heat treatment to remove the carbon layer. The composite induced efficient photocatalytic reactions when relatively small substrates were used, such as methanol dehydration and decomposition of acetic acid, without any reduction in the intrinsic activity of original TiO2, but did not exhibit efficient photocatalytic activity for decomposition of large substrates, methylene blue and polyvinyl alcohol. The uniquesize-selective properties of the composites are due to their structural characteristics, i.e., the presence of a pore system and a void space in the silica shell and between the shell and medial TiO2 particles, respectively. The loading of alkylsilyl groups on the surface of the composite led to highly photostable. oatability: the floated sample also induced efficient photocatalytic reaction for decomposition of acetic acid while retaining floatation at the gas/water interface.
DOI： 10.1039/b709891j
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Encapsulation of titanium(IV) oxide particles in hollow silica for size-selective photocatalytic reactions Reviewed
Shigeru Ikeda, Yoshimitsu Ikoma, Hideyuki Kobayashi, Takashi Harada, Tsukasa Torimoto, Bunsho Ohtani, Michio Matsumura
CHEMICAL COMMUNICATIONS 3753-3755 ( 36 ) 3753 - 3755 2007.9
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
A core-shell composite of TiO2 particles encapsulated in a hollow silica was fabricated, and the core-shell composite showed size-selective photocatalytic activity for decomposition of organics without reducing the intrinsic activity of the naked TiO2 core.
DOI： 10.1039/b704468b
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Selective adsorption of glucose - Derived carbon precursor on amino-functionalized porous silica for fabrication of hollow carbon spheres with porous walls Reviewed
Shigeru Ikeda, Koji Tachi, Yun Hau Ng, Yoshimitsu Ikoma, Takao Sakata, Hirotaro Mori, Takashi Harada, Michio Matsumura
CHEMISTRY OF MATERIALS 19 ( 17 ) 4335 - 4340 2007.8
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
Coating of polysuccharide (PS) generated by hydrothermal treatment of glucose on Stober's silica particles was examined. Uniform surface coverage of PS was achieved when the silica particles, the surfaces of which had been modified with amino groups, were mixed during the hydrothermal reaction of glucose. On the other hand, bare silica could not be coated with PS upon addition to the hydrothermal reaction solution; instead, this produced spherical PS particles with diameters of a few tens of nanometers beside silica particles. The significant effect of surface amino-functionalization of silica particles on the coverage of PS is attributable to induction of an electrostatic attraction between the positively charged amino-functionalized silica surface and negatively charged PS. When silica (core)-porous silica (shell) spheres were used instead of Stober's silica, efficient filling of the pores of the silica shell with PS could also be achieved by amino-functionalization of the surface of the porous silica shell. The silica (core)- PS (shell) materials as-obtained were converted into isolated hollow carbon spheres with well-developed porous shell structures by heat treatment under a vacuum followed by treatment with aqueous hydrofluoric acid.
DOI： 10.1021/cm0702969
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A simple method for preparing highly active palladium catalysts loaded on various carbon supports for liquid-phase oxidation and hydrogenation reactions Reviewed
Takashi Harada, Shigeru Ikeda, Mayu Miyazaki, Takao Sakata, Hirotaro Mori, Michio Matsumura
JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL 268 ( 43102 ) 59 - 64 2007.5
Joint Work
Authorship：Lead author Publisher：ELSEVIER SCIENCE BV
Preparation of nanosized palladium (Pd) catalysts supported on various carbon supports using a simple liquid-phase reduction of aqueous Pd complexes with potassium borohydride (KBH4) was investigated. We found that addition of appropriate amounts of sodium hydroxide (NaOH) into aqueous solutions of sodium tetrachloropalladate (Na2PdCl4) followed by reduction with KBH4 produced highly dispersed Pd nanoparticles less than 5 nm in diameter on any carbon supports. Ultraviolet-visible light (UV-vis) absorption spectra of aqueous Na2PdCl4 solutions in the presence of various amounts of NaOH clarified the occurrence of partial or complete ligand exchange of the Pd complex from chloride ions (C1(-)) to hydroxide ions (OH-). Hence, the production of small Pd nanoparticles on carbon supports is likely to be induced by structural change in the precursor complex prior to the reduction with KBH4. Moreover, evaluation of catalytic activities for liquid-phase oxidation of benzyl alcohol into benzaldehyde using oxygen and hydrogenation of the C=C bond in cinnamaldehyde with hydrogen revealed that catalytic functions were significantly dependent on the size and the dispersion of Pd particles; i.e., both reactions proceeded efficiently on small Pd catalysts highly dispersed on carbon supports but did not occur efficiently on Pd particles of relatively large sizes or with poor dispersion on those supports. (c) 2006 Elsevier B.V. All rights reserved.
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Evaluation of electron-hole recombination properties of titanium(IV) oxide particles with high photocatalytic activity Reviewed
Shin-Ya Murakami, Hiroshi Kominami, Yoshiya Kera, Shigeru Ikeda, Hidenori Noguchi, Kohei Uosaki, Bunsho Ohtani
RESEARCH ON CHEMICAL INTERMEDIATES 33 ( 43164 ) 285 - 296 2007.3
Joint Work
Publisher：VSP BV
Electron-hole recombination in nano-sized titanium(IV) oxide (TiO2) particles with various physical properties, which have been shown to be highly active photocatalysts, was evaluated by quantitative analysis of reduced titanium species (Ti3+), which might be formed at crystalline defective sites in TiO2 particles through photo-irradiation in the presence of a hole scavenger under deaerated conditions. These highly active photocatalyst samples were synthesized by hydrothermal crystallization in organic media (HyCOM method) and post-calcination. The Ti3+ density decreased with increasing calcination temperature (T-c), and a linear correlation was observed between the Ti3+ density and rate constant for electron-hole recombination evaluated by femtosecond pump-probe diffuse reflection spectroscopy. Reaction rate (R-Ag) and the amount of silver ions (Ag+) adsorbed on TiO2 particles ([Ag+]ads) were measured for photocatalytic silver metal deposition along with oxygen formation from an aqueous Ag+ solution under deaerated conditions, and the slope of the R-Ag versus [Ag+](ads) plot was determined. Kinetic investigation of this reaction showed that the reciprocal of the slope was approximately related to the ratio of the rates for electron-hole recombination and electron trapping (k(r)/k(e) ratio). The k(r)/k(e) ratio decreased as T-c increased, and the logarithm of the k(r)/k(e) ratio was linearly related with Ti3+ density. These two parameters were used as a measure for the recombination properties of TiO2 photocatalysts with various physical properties.
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Fabrication of hollow carbon nanospheres encapsulating platinum nanoparticles using a photocatalytic reaction Reviewed
Yun Hau Ng, Shigeru Ikeda, Takashi Harada, Suguru Higashida, Takao Sakata, Hirotaro Mori, Michio Matsumura
ADVANCED MATERIALS 19 ( 4 ) 597 - 602 2007.2
Joint Work
Authorship：Lead author Publisher：WILEY-V C H VERLAG GMBH
The fabrication of Pt nanoparticles encapsulated in hollow carbon nanospheres using TiO2 nanoparticles as both the photocatalyst and the inorganic mold is demonstrated (see figure). These spheres are found to have high surface area and ultrathin shells with well-developed microporosity, and thus can be used as catalysts. This new imprinting method can be used to synthesize any desired nanostructures using predesigned TiO2 photocatalysts.
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Ligand-free platinum nanoparticles encapsulated in a hollow porous carbon shell as a highly active heterogeneous hydrogenation catalyst Reviewed
Shigeru Ikeda, Satoru Ishino, Takashi Harada, Natsumi Okamoto, Takao Sakata, Hirotaro Mori, Susumu Kuwabata, Tsukasa Torimoto, Michio Matsumura
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 45 ( 42 ) 7063 - 7066 2006.10
Joint Work
Authorship：Lead author Publisher：WILEY-V C H VERLAG GMBH
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Preparation of platinized strontium titanate covered with hollow silica and its activity for overall water splitting in a novel phase-boundary photocatalytic system Reviewed
Shigeru Ikeda, Ko Hirao, Satoru Ishino, Michio Matsumura, Bunsho Ohtani
CATALYSIS TODAY 117 ( 43103 ) 343 - 349 2006.9
Joint Work
Authorship：Lead author Publisher：ELSEVIER SCIENCE BV
Platinum-loaded strontium titanate (Pt-SrTiO3) (core) -silica (shell) powder was prepared by double-layer winding of a carbon and a silica layer on Pt-SrTiO3 followed by heat treatment to remove the carbon layer. Scanning electron microscope (SEM) observation and analyses of the BET surface area suggested that the powder has a void space between Pt-SrTiO3 (core) and silica (shell). When the surface of the powder was partially modified with a fluoroalkylsilylation agent, thus-obtained material assembled at a gas-water interface and acted as a photocatalyst for overall water splitting to produce hydrogen (H-2) and oxygen (O-2). Probably due to the suppression of a backward reaction, production of water from H-2 and O-2, on the platinum, the overall efficiency of this system was higher than that of the conventional suspension system. Moreover, while the Pt-SrTiO3 powders directly covered with fluoroalkylethylsilyl groups showed low photostability, i.e., prolonged irradiation precipitated some of the surface-modified particles in water owing to photocatalytic decomposition of surface fluoroalkylethylsilyl groups, this material could retain its location at the phase boundary. (C) 2006 Elsevier B.V. All rights reserved.
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Photocatalytic activity of hydrothermally synthesized tantalate pyrochlores for overall water splitting Reviewed
S Ikeda, M Fubuki, YK Takahara, M Matsumura
APPLIED CATALYSIS A-GENERAL 300 ( 2 ) 186 - 190 2006.1
Joint Work
Authorship：Lead author Publisher：ELSEVIER SCIENCE BV
Tantalate and mobate pyrochlores, Ca2M2O7 (M = Nb, Ta) and A(2)Ta(2)O(6) (A = Na, K), were prepared by a hydrothermal method. These oxides were crystallized directly from tantalum or niobium alkoxide in the presence of sodium, potassium or calcium cation in basic solutions at temperatures between 373 and 448 K, and their crystallinity was improved by calcination in air. Stoichiometric liberations Of H-2 and O-2 were achieved over tantalate pyrochlores loaded with a small amount of nickel oxide (NiO) as a catalyst for H2 production, while the NiO-loaded mobate pyrochlore showed no photocatalytic, activity. The photocatalytic functions of the tantalate pyrochlores were attributed to their energy levels of the bottom of conduction bands being much more negative than those of the niobate pyrochlores. (c) 2005 Elsevier B.V. All rights reserved.
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Direct observation of amphiphilic silica particles assembled at an oil-water interface Reviewed
S Ikeda, YK Takahara, S Ishino, M Matsumura, B Ohtani
CHEMISTRY LETTERS 34 ( 10 ) 1386 - 1387 2005.10
Joint Work
Authorship：Lead author Publisher：CHEMICAL SOC JAPAN
The location of amphiphilic silica particles, on which have both hydrophobic and hydrophilic surfaces, at a n-decane-water interface was investigated. By scanning electron microscopy observation of the particles fixed at the interface with a curable poly(dimethylsiloxane), we found that each hemisphere of a amphiphilic particle are immersed in the oil or aqueous phase.
DOI： 10.1246/cl.2005.1386
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Porous polystyrene microspheres having dimpled surface structures prepared within micellar assemblies of amphiphilic silica particles in water Reviewed
YK Takahara, S Ikeda, K Tachi, T Sakata, T Hasegawa, H Mori, M Matsumura, B Ohtani
CHEMICAL COMMUNICATIONS 4205-4207 ( 33 ) 4205 - 4207 2005.9
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
Production of porous polystyrene microspheres having dimpled surface structures was demonstrated using amphiphilic and hydrophobic silica particles as structure-directing agents.
DOI： 10.1039/b507123b
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Photocatalytic preparation of encapsulated gold nanoparticles by jingle-bell-shaped cadmium sulfide-silica nanoparticles Reviewed
Pal, B; Torimoto, T; Ikeda, S; Shibayama, T; Sugawara, K; Takahashi, H; Ohtani, B
TOPICS IN CATALYSIS 35 ( 43163 ) 321 - 325 2005.7
Joint Work
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YK Takahara, Y Hanada, T Ohno, S Ushiroda, S Ikeda, M Matsumura
JOURNAL OF APPLIED ELECTROCHEMISTRY 35 ( 43289 ) 793 - 797 2005.7
Joint Work
Authorship：Lead author Publisher：SPRINGER
Cyclohexane was oxidized under visible light in a titanium dioxide suspension containing hydrogen peroxide. Cyclohexanol and cyclohexanone were detected as products. Under similar experimental conditions, nonyl aldehyde was oxidized to nonylic acid. The reaction rate for the oxidation on rutile particles was faster than that on anatase particles. When hydrogen peroxide was added to suspensions of these particles, both rutile and anatase particles became yellow-colored due to the formation of peroxide complexes on their surfaces. The difference between the reaction rates for rutile and anatase particles suggests that the properties of the peroxide complexes formed on these particles are different. The properties of these complexes were studied by UV-vis spectroscopy.
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Asymmetrically modified silica particles: A simple particulate surfactant for stabilization of oil droplets in water Reviewed
YK Takahara, S Ikeda, S Ishino, K Tachi, K Ikeue, T Sakata, T Hasegawa, H Mori, M Matsumura, B Ohtani
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 127 ( 17 ) 6271 - 6275 2005.5
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
Spherical silica particles that are able to assemble at a phase boundary of a dual-phase mixture of water and an immiscible organic solvent were prepared by a partial modification of their surface hydroxyl groups with an alkylsilylation agent. Scanning electron microscopic observation of these particles in which their remaining surface hydroxyl groups had been selectively modified with colloidal gold particles revealed that each particle has an asymmetric surface structure: one side of the surface is hydrophilic and the other is hydrophobic. We found that these particles could form a micellar structure in water in the presence of an organic solution of a toluene/polystyrene mixture. The micellar structure was evidenced by formation of golf-ball-like polystyrene particles with dimples imprinting morphologies of the hydrophobic part of modified silica particles.
DOI： 10.1021/ja043581r
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SI Mostafa, S Ikeda, B Ohtani
JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL 225 ( 2 ) 181 - 188 2005.1
Joint Work
Publisher：ELSEVIER SCIENCE BV
Synthesis procedures are described for the complexes [M(L-H)(AcO)(H(2)O)(2)] (M(II) = Mn, Ni), [M(L-H)Cl(n)(H(2)O)(m)] (M = Fe(III), n = 2, m = 2; M = Pd(II), n = 1, m = 1; m = Ag(I), n = 0, m = 2) and [M(L-H)(2)(H(2)O)(n)] (M = Co(II), n = 2; M = Cu(II), [WO(2)](2+), n=0) where L is the Schiff-base derived from salicylaldehyde and 3-aminopropyltriethoxysaline (APTSsal) that is chemically anchored on Y-zeolite. Characterization of these complexes was accomplished by elemental analyses, infrared and diffuse-reflectance spectra and magnetic moment. The anchored Schiff-bases imposed stable planar coordination sphere on the metal ions, allowing epoxidation of 1-octene in the axial position in the presence of molecular oxygen. The epoxidation of 1-octene was also achieved by employing the partly modified Y-zeolite with n-octadecyltrichlorosilane (OTS) Schiff-base complexes in the presence of 30% H(2)O(2) under a phase-boundary system. (C) 2004 Elsevier B.V. All rights reserved.
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Oxidation of hydrophobic alcohols using aqueous hydrogen peroxide over amphiphilic silica particles loaded with titanium(IV) oxide as a liquid-liquid phase-boundary catalyst Reviewed
KM Choi, S Ikeda, S Ishino, K Ikeue, M Matsumura, B Ohtani
APPLIED CATALYSIS A-GENERAL 278 ( 2 ) 269 - 274 2005.1
Joint Work
Authorship：Lead author Publisher：ELSEVIER SCIENCE BV
Phase-boundary catalysis (PBC), a new concept of a heterogeneous catalytic system for oxidation of various hydrophobic alcohols with aqueous hydrogen peroxide (H2O2), has been investigated. A part the external surface of silica (SiO2) particles loaded with titanium(IV) oxides was modified with hydrophobic alkyl groups to obtain amphiphilic particles, having both hydrophobic and hydrophilic surfaces on each particle. The amphiphilic particles were spontaneously assembled at interfaces between dual phase mixtures of aqueous solutions and water-immiscible organic compounds. Upon addition to a dual phase mixture of aqueous H2O2 and toluene-containing hydrophobic alcohols, these particles acted as an efficient catalyst for the reaction, to produce corresponding aldehydes and ketones selectively. Notable features of the PBC system are that the oxidation proceeds even without agitation and that only a few percent of titanium species was detected as dissolved species. Productions of aldehydes and ketones were also observed when titanium loaded SiO2 without modification with alkyl groups was employed for the reaction. However, a large amount of titanium loaded on the material was leached during the reaction. These results indicate that surface-covered alkyl groups not only bring about effective contact with hydrophobic alcohols in the organic phase but also give stability against leaching, leading to heterogeneous catalytic functions. (C) 2004 Elsevier B.V. All rights reserved.
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Photocatalytic preparation of encapsulated gold nanoparticles by jingle-bell-shaped cadmium sulfide-silica nanoparticles Reviewed
B. Pal, T. Torimoto, S. Ikeda, T. Shibayama, K. Sugawara, H. Takahashi, B. Ohtani
Top. Cat. 35 ( 3-4 ) 321-325 2005
Gold (Au) nanoparticles were deposited inside silica: (SiO2) shells containing cadmium sulfide (CdS) nanoparticles through photocatalytic reduction of potassium dicyanogold(I) by CdS. Photocatalytic Au deposition occurred only when core-shell nanoparticles having a void space between the core and shell, i.e., a jingle-bell-shaped structure, were used. These core-shell nanoparticles were prepared by size-selective photoetching of SiO2 -covered CdS nanoparticles. The size of Au nanoparticles could be controlled by adjustment of the void space in SiO2-covered CdS. Dissolution of CdS by acid treatment from the Au-deposited jingle-bell nanoparticles did not have any effect on the surface-plasmon absorption by Au. These facts indicate that Au nanoparticles of adjustable size can be prepared in an SiO2 shell that prevents mutual coalescence of Au nanoparticles but allows permeation of molecules and ions.
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Overall water splitting on tungsten-based photocatalysts with defect pyrochlore structure Reviewed
S Ikeda, T Itani, K Nango, M Matsumura
CATALYSIS LETTERS 98 ( 4 ) 229 - 233 2004.12
Joint Work
Authorship：Lead author Publisher：KLUWER ACADEMIC/PLENUM PUBL
Defect pyrochlore-type oxides, AMWO(6) (A = Rb, Cs; M = Nb, Ta), loaded with nickel oxide showed photocatalytic activity for overall water splitting under ultraviolet-light irradiation. The conduction bands of the materials are thought to be composed of the W5d orbital hybridized with the Nb5d or Ta4d orbital.
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Hadi Nur, Shigeru Ikeda, Bunsho Ohtani
Journal of the Brazilian Chemical Society 15 ( 5 ) 719 - 724 2004.9
Joint Work
Publisher：Sociedade Brasileira de Quimica
The catalytic potential of phase-boundary catalyst for acid-catalyzed reactions has been demonstrated by NaY zeolite loaded with alkylsilane-covered niobic acid in the liquid phase hydration of 1,2-epoxyoctane with water. The catalyst was prepared by impregnation of niobic acid on the external surface of NaY and followed by a partial modification of the external surface of NaY with alkylsilyl groups. When the particles were added to a mixture of water and 1,2-epoxyoctane, they were feasibly located just at the liquid-liquid phase boundary and efficiently catalyzed hydration of the epoxide even without stirring. In order to investigate the effect of the location of the active sites, alkylsilylated HZSM-5 and sulfonic acid functionalized NaY in which the active sites are located dominantly on the internal surface of zeolites were prepared. In that case, mechanical stirring was needed to increase the reaction rate. It was suggested that alkylsilylation on the external surface of zeolite, when the active site is mainly inside the pore, could not change the mode of the catalytic action
it is still necessary to stir the reaction mixture to drive the mass transfer of substrates and reagents. -
Light intensity dependence of the action spectra of photocatalytic reactions with anatase titanium(IV) oxide Reviewed
T Torimoto, Y Aburakawa, Y Kawahara, S Ikeda, B Ohtani
CHEMICAL PHYSICS LETTERS 392 ( 43103 ) 220 - 224 2004.7
Joint Work
Publisher：ELSEVIER SCIENCE BV
Light intensity dependence of action spectra of photocatalytic reactions was investigated using anatase single-phase titanium(IV) oxide powders as photocatalysts. The action spectra normalized at 350 nm were not changed in methanol dehydrogenation with the range of intensities of ca. 0.1-10 mW cm(-2), while those for acetic acid decomposition were red-shifted with increase in light intensity. The apparent quantum yield of the former was almost independent of the irradiation intensity, but that of the latter was declined with increase in light intensity, the degree being considerably enhanced with the irradiation at shorter wavelength when the light intensity was higher than 2 mW cm-2. These can be explained by the difference in the utilization efficiency of photogenerated charge carriers. (C) 2004 Elsevier B.V. All rights reserved.
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Amphiphilic NaY zeolite particles loaded with niobic acid: Materials with applications for catalysis in immiscible liquid-liquid system Reviewed
H Nur, S Ikeda, B Ohtani
REACTION KINETICS AND CATALYSIS LETTERS 82 ( 2 ) 255 - 261 2004.7
Joint Work
Publisher：AKADEMIAI KIADO
The catalytic potential of catalysts for acid-catalyzed reactions has been demonstrated by NaY zeolite loaded with alkylsilane-covered niobic acid in the liquid phase hydration of 1,2-epoxyoctane with water. The catalytic activity of the catalysts was correlated to the amphiphilic character of the solid catalyst particles.
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Asymmetrically modified titanium(IV) oxide particles having both hydrophobic and hydrophilic parts of their surfaces for liquid-liquid dual-phase photocatalytic reactions Reviewed
S Ikeda, Y Kowata, K Ikeue, M Matsumura, B Ohtani
APPLIED CATALYSIS A-GENERAL 265 ( 1 ) 69 - 74 2004.6
Joint Work
Authorship：Lead author Publisher：ELSEVIER SCIENCE BV
Titanium(IV) oxide (TiO2)-based photocatalyst particles assembled at the phase boundary of a liquid-liquid dual-phase mixture were prepared by partial modification of the external surface of each particle with alkylsilyl groups. The average surface coverage of alkylsilyl groups was estimated by elemental analyses of carbon and ash components of the samples and floatability on aqueous ethanol solutions. Results revealed that the hydrophobicity-hydrophilicity of asymmetrically modified samples was comparable to that of samples fully covered with alkylsilyl groups. TiO2 particles asymmetrically or fully modified with alkylsilyl groups showed photocatalytic activity for benzene oxidation to produce phenol from an aerated benzene-water dual-phase mixture even without agitation, while bare TiO2 required mechanical agitation to induce the photocatalytic reaction. However, prolonged irradiation precipitated some of the surface-modified particles in the aqueous layer due to photocatalytic decomposition of surface alkylsilyl groups. The photostability was improved by employment of TiO2 particles coated with porous silica (SiO2) as a starting material. Compared with the SiO2-coated TiO2 particles fully modified with alkylsilyl groups (o-Si/Ti), the asymmetrically modified SiO2-TiO2 particles (w/o-Si/Ti) showed slightly higher photocatalytic activity for benzene oxidation. On the other hand, a notable difference between the two types of particles was observed in photocatalytic hydrogen evolution in the presence of sacrificial donors from a benzene-water mixture and from an aqueous solution under deaerated conditions; w/o-Si/Ti showed the activity more than two-fold greater than that of o-Ti/Si, presumably because of efficient contact of w/o-Si/Ti with both aqueous and organic phases compared with o-Si/Ti, which was rather difficult to contact with the aqueous phase. (C) 2004 Elsevier B.V. All rights reserved.
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Elucidation of the local structure of active titanium(IV) sites on silica-based phase-boundary catalysts for alkene epoxidation with aqueous hydrogen peroxide Reviewed
K Ikeue, S Ikeda, A Watanabe, B Ohtani
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 6 ( 9 ) 2523 - 2528 2004.5
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
Structural and functional aspects of active titanium sites for phase boundary catalytic (PBC) epoxidation of 1-octene with hydrogen peroxide (H2O2) were investigated in detail using X-ray absorption fine structure (XAFS) analysis and ultraviolet and visible-light diffuse reflectance (UV-Vis-DR) spectroscopy. By analysis of the Ti K-edge X-ray absorption near edge fine structure (XANES) spectra of several titanium-loaded silica catalysts, the ratio of the amount of 4-coordinated titanium oxide (T-tet) to that of a 6-coordinated one (T-oct) was determined. Monotonic increments of catalytic activity for epoxide production and efficiency of H2O2 utilization with the ratio T-tet/(T-tet + T-oct) revealed that the highly active catalysts mainly include T-tet but not T-oct. UV-Vis-DR spectra of samples with external surfaces partially covered with alkylsilyl groups indicated that there are at least two kinds of T, sites with different ligands. One site anchors an acidic hydroxyl (T-tet(OH)), giving absorption centered at the wavelength of ca. 230 nm and the other, exhibiting an absorption peak at the wavelength of ca. 210 nm, is directly attached to an alkylsilyl group (T-tet(OSiR)) formed via reaction of an acidic hydroxy of T-tet(OH) with an alkylsilane reagent. Since the catalysts have both an alkylsilyl-grafted hydrophobic surface and a hydroxy-terminated hydrophilic surface, it is postulated that the former is located on both hydrophilic (T-tet(OH,w)) and hydrophobic (T-tet(OH(9)o)) surfaces and the latter, T-tet(OSiR), exists only on the hydrophobic surface. From analyses of catalytic activities of several catalysts with different distributions of these T-tet sites, both T-tet(OH,o) and T-tet(OSiR) sites on the hydrophobic surface were proved to be active, while T-tet(OH,w) on the hydrophilic surface did not work for the present PBC system. Among the sites on the hydrophobic surface, moreover, it was found that a T-tet(OSiR) site acted as a more effective site for selective epoxidation when compared with T-tet(OH,o), which induced ring-opening of epoxide to give a by-product, 1,2-octanediol.
DOI： 10.1039/b316818b
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Photocatalytic organic syntheses: selective cyclization of amino acids in aqueous suspensions Invited Reviewed
Ohtani, B; Pal, B; Ikeda, S
CATALYSIS SURVEYS FROM ASIA 7 ( 43134 ) 165 - 176 2003.9
Joint Work
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Development of a novel photocatalytic reaction system for oxidative decomposition of volatile organic compounds in water with enhanced aeration Reviewed
R Villacres, S Ikeda, T Torimoto, B Ohtani
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 160 ( 43102 ) 121 - 126 2003.8
Joint Work
Authorship：Lead author Publisher：ELSEVIER SCIENCE SA
A novel photocatalytic reaction system, composed of solution and gas spaces that are divided by a thin Teflon film and titanium(IV) oxide (TiO2)-coated mesh or cloth, for the treatment of contaminated aqueous solutions was developed to be operated with enhanced aeration without bubbling of air in the solution. First, the photocatalytic activities of TiO2 particles immobilized on two kinds of support material, stainless steel mesh (SSM) and fiberglass cloth (FGC), were investigated for photocatalytic oxidation of 2-propanol, as a model volatile organic compound, dissolved in aerated aqueous solution. The TiO2 particles immobilized on both support materials exhibited photocatalytic activity to oxidize 2-propanol into acetone and carbon dioxide (CO2), and the activity levels of the TiO2 particles immobilized on the two kinds of support materials were comparable. Presumably due to the presence of a small amount of metal species originating in SSM that might work as reduction catalysts, molecular hydrogen (H-2) was also liberated on the TiO2-immobilized SSM. Results of analysis of weight loss after photoirradiation suggested that the stability of the TiO2-immobilized FGC was better than that of the TiO2-immobilized SSM. On the basis of these results, FGC was employed in construction of a photocatalytic reactor equipped with an oxygen (O-2)-permeable Teflon membrane in order to make oxygen pass from a gas space to a solution space and to keep the surface of the immobilized TiO2 photocatalyst, facing an aqueous solution containing volatile organic compounds, saturated with dissolved O-2. From the results of photocatalytic oxidative decomposition of 2-propanol, it was clarified that the surfaces of TiO2 particles could be sufficiently supplied with O-2 from the gas space through the membrane to accelerate the oxidation. (C) 2003 Elsevier Science B.V. All rights reserved.
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Photochemical hydrogen evolution from aqueous triethanolamine solutions sensitized by binaphthol-modified titanium(IV) oxide under visible-light irradiation Reviewed
S Ikeda, C Abe, T Torimoto, B Ohtani
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 160 ( 43102 ) 61 - 67 2003.8
Joint Work
Authorship：Lead author Publisher：ELSEVIER SCIENCE SA
Surface modification of titanium(IV) oxide (TiO2) powders with 1, 1-binaphthalene-2,2'-diol (bn(OH)(2)), having two phenolic hydroxyls and atropisomeric chirality, in refluxed ethanol led to the formation of a deep yellow-colored surface complex, giving visible-light absorption at a wavelength below ca. 550-600 nm. Quantitative analyses of the surface complex revealed that absorption intensity at 450 nm in diffuse reflection (DR) measurement was almost proportional to its amount and that its amount depended strongly on the amount of surface hydroxyl groups of TiO2 but not on the crystal structure of TiO2, anatase, and rutile. The bn(OH)(2) complexation was also applied to platinized TiO2 to drive photocatalytic molecular hydrogen (H-2) evolution from deaerated triethanolamine solutions under visible-light irradiation at a wavelength even longer than 540 nm. The photonic efficiency of the photocatalytic reaction at 450 nm was estimated to be 0.02% for bn(OH)(2)-modified TiO2 (JRC-TIO-3) loaded with 0.1 wt.% of platinum. On the basis of these experimental results, the reaction mechanism, which involves visible-light excitation of the surface complex, injection of electrons from the complex to TiO2, and migration of the electrons to platinum deposits, where reduction of H+ takes place to give H-2, was elucidated. (C) 2003 Elsevier Science B.V. All rights reserved.
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Photocatalytic redox-combined synthesis of L-pipecolinic acid from L-lysine by suspended titania particles: effect of noble metal loading on the selectivity and optical purity of the product Reviewed
B Pal, S Ikeda, H Kominami, Y Kera, B Ohtani
JOURNAL OF CATALYSIS 217 ( 1 ) 152 - 159 2003.7
Joint Work
Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE
Photocatalytic (> 300 nm) conversion of L-(S)-lysine (L-Lys), in its neutralized aqueous solution, into L-pipecolinic acid (L-PCA) under deaerated conditions at 298 K was investigated in detail using suspended TiO2 powders (Degussa P-25, Ishihara ST-01, and HyCOM TiO2) loaded with platinum (Pt), rhodium (Rh), or palladium (Pd). A common feature of the results of experiments using a wide variety of metalloaded TiO2 photocatalysts is that the rate of PCA formation (r(PCA)) was greatly reduced when higher optical purity of PCA (OPPCA), i.e., enantio excess of the L-isomer of PCA, was obtained; higher rPCA was achieved by the use of Pt-loaded TiO2 powders, while these powders gave relatively low OPPCA. Selectivity of PCA yield (S-PCA), i.e., amount of PCA production based on L-Lys consumption, also tended to increase with decrease in OPPCA, giving a master curve in the plots of OPPCA versus S-PCA. Among the TiO2 powders used in this study, HyCOM TiO2 showed relatively high OPPCA and S-PCA but not optimum S-PCA and OPPCA simultaneously. In order to interpret such relations, the mechanism of stereoselective synthesis of the L-isomer of PCA (L-PCA) was investigated using isotope-labeled alpha-N-15-L-lysine with quantitative analysis of incorporation of N-15 in PCA and ammonia (NH3), a by-product. It was observed for several photocatalysts that the N-15 proportion (P-15) in PCA was almost equal to OPPCA, suggesting that oxidative cleavage by photogenerated positive holes of the epsilon-amino moiety of L-Lys gave optically pure L-PCA through retention of chirality at the alpha-carbon in the presumed intermediate, a cyclic Schiff base (alpha-CSB), which undergoes reduction by photoexcited electrons into PCA. From P-15 in NH3 and PCA, the selectivity of oxidation between alpha and epsilon-amino groups in L-Lys by photoexcited positive holes (h(+)) and the efficiency of reduction of alpha-CSB (produced via epsilon-amino group oxidation to give optically pure PCA) and epsilon-CSB (produced via alpha-amino group oxidation to give racemic PCA) by photoexcited electrons (e(-)) were calculated. The former was found to be independent of the kind of photocatalyst, especially the loaded metal, while the latter was influenced markedly only by the loaded metal. It was clarified that OPPCA and S-PCA obtained for various TiO2 powders used in the present study were strongly governed by the reduction stage, i.e., the efficiency of reduction of two types of CSB. When S-PCA was relatively low, photocatalysts, favoring the reduction of alpha-CSB rather than epsilon-CSB, gave higher OPPCA but lower S-PCA, since some epsilon-CSB remained unreduced to give racemic PCA. In contrast, at higher S-PCA, both CSBs were reduced nonselectively and OPPCA was found to be determined mainly by the selectivity in the oxidation stage. The relatively low yield of molecular hydrogen (H-2) when higher S-PCA was achieved is consistent with the mechanism in which H-2 liberation occurs instead of the reduction of CSBs by e(-). Thus, the general tendency of plots between OPPCA and S-PCA could be explained by the above-described redox-combined mechanism of photocatalysis.
(C) 2003 Elsevier Science (USA). All rights reserved -
Photoinduced chemical reactions on natural single crystals and synthesized crystallites of mercury(II) sulfide in aqueous solution containing naturally occurring amino acids Reviewed
B Pal, S Ikeda, B Ohtani
INORGANIC CHEMISTRY 42 ( 5 ) 1518 - 1524 2003.3
Joint Work
Publisher：AMER CHEMICAL SOC
Photoirradiation at >300 nm of aqueous suspensions of several natural crystal specimens and synthesized crystallites of mercury(II) sulfide (HgS) induced deaminocyclization of optically active or racemic lysine into pipecolinic acid (PCA) under deaerated conditions. This is the first example, to the best of our knowledge, of photoinduced chemical reactions of natural biological compounds over natural minerals. It was found that the natural HgS crystals had activity higher than those of synthesized ones but lower than those of other sulfides of transition metals, e.g., CdS and ZnS, belonging to the same II-IV chalcogenides. In almost all of the photoreactions, decompostion of HgS occurred to liberate hydrogen sulfide (H2S) and Hg2+, and the latter seemed to have undergone in-situ reductive deposition on HgS as Hg-0 after a certain induction period (24-70 h) during the photoirradiation, as indicated by the darkened color of the suspensions. The formation of PCA, presumably through combination of oxidation of lysine and reduction of an intermediate, cyclic Schiff base, could also be seen after a certain induction time of the Hg-0 formation. This was supported by the fact that the addition of small amount of Hg2+ (0.5 wt % of HgS) increased the PCA yield by almost 2-fold. We also tried to elucidate certain aspects of the plausible stereochemical reactions in relation to the chiral crystal structure of HgS. Although, in some experiments, slight enantiomeric excess of the product PCA was observed, the excess was below or equal to the experimental error and no other supporting analytical data could not be obtained; we cannot conclude the enantiomeric photoproduction of PCA by the natural chiral HgS specimen.
DOI： 10.1021/ic025916g
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Quantitative analysis of defective sites in titanium(IV) oxide photocatalyst powders Reviewed
S Ikeda, N Sugiyama, S Murakami, H Kominami, Y Kera, H Noguchi, K Uosaki, T Torimoto, B Ohtani
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 5 ( 4 ) 778 - 783 2003.2
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
The molar amounts of defective sites (M-d) in several titanium(IV) oxide (TiO2) powders were determined using photoinduced reactions of electron accumulation in deaerated aqueous solutions containing sacrificial hole scavengers and subsequent reduction of methylviologen to its cation radical. Measurements of pH dependence of typical anatase and rutile TiO2 powders showed that these defective sites were of electronic energy just below the conduction band edge of TiO2 in ranges of 0-0.35 V for anatase and 0-0.25 V for rutile, A linear relation of M-d with the rate constant of electron-hole recombination determined by femtosecond pump-probe diffuse reflection spectroscopy revealed that M-d could be a quantitative parameter of recombination between a photoexcited electron and a positive hole. The fact that there was no linear relation between M-d and the specific surface area suggests that the surface area was not directly reflected on M-d. A reciprocal correlation between photocatalytic activity for water oxidation in aqueous silver sulfate solution and M-d revealed that the rate of recombination is one of the predominant physical properties governing the activities of TiO2 powders in this reaction system.
DOI： 10.1039/b206594k
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Discrimination of the active crystalline phases in anatase-rutile mixed titanium(IV) oxide photocatalysts through action spectrum analyses Reviewed
T Torimoto, N Nakamura, S Ikeda, B Ohtani
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 4 ( 23 ) 5910 - 5914 2002.12
Joint Work
Publisher：ROYAL SOC CHEMISTRY
The active crystalline phases in powdered titanium(IV) oxide (TiO2) photocatalysts of anatase-rutile mixtures were investigated by measuring the action spectra of the photocatalytic reactions of H-2 evolution, Ag deposition and acetic acid decomposition. All of the pure anatase powders used in this study gave action spectra for the three kinds of reaction that were blue-shifted by about 30 nm from those of the pure rutile powders, being consistent with their photoabsorption behavior observed in the diffuse reflectance spectra. On the other hand, the action spectra of the mixed TiO2 powders varied, depending both on the kind of photocatalytic reaction and the content of the crystalline phases. In the case of H-2 evolution, the action spectra were intermediate between those of the pure anatase and rutile phases and were shifted toward that of the rutile phase with a decrease in the content of the anatase phase; i.e., the action spectra are governed mainly by the photoabsorption of each powder. The Ag deposition and acetic acid decomposition reactions gave action spectra of the mixed TiO2 powders that were similar to those of pure rutile and anatase phases, respectively, regardless of the content of the crystalline phases; the active phase in the former was rutile while that in the latter was anatase, even when these active phases were only minor parts of the mixed powder. The results indicate that the active crystalline phase differs with the kind of photocatalytic reaction even if the same mixed TiO2 powders were used as photocatalysts.
DOI： 10.1039/b207448f
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A Di Paola, E Garcia-Lopez, S Ikeda, G Marci, B Ohtani, L Palmisano
CATALYSIS TODAY 75 ( 43104 ) 87 - 93 2002.7
Joint Work
Publisher：ELSEVIER SCIENCE BV
Some probe catalytic photooxidation reactions with aliphatic and aromatic organic compounds having different acid strengths, i.e. methanoic acid, ethanoic acid, benzoic acid and 4-nitrophenol, were carried out in aqueous systems by using polycrystalline TiO(2) powders doped with various transition metal ions (Co, Cr, Cu, Fe, Mo, V and W). The Co-doped powder showed to be more photoactive than the bare TiO(2) for methanoic acid degradation while the behaviour of TiO(2)/Cu and TiO(2)/Fe was similar to that of the support. TiO(2)/W was the most efficient sample for the photodegradation of benzoic acid and 4-nitrophenol, TiO(2) the most active powder for ethanoic acid. A tentative explanation is provided by taking into account: (i) the dissociation constants (K(a)) of the different acids used as substrates; (ii) their aliphatic or aromatic nature; (iii) the points of zero charge (PZC) of the photocatalysts; (iv) their relative rate constants for photoelectron-hole recombination (k(r)) determined by femtosecond pump-probe diffuse reflectance spectroscopy. (C) 2002 Elsevier Science B.V. All rights reserved.
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Visible light-induced hydrogen evolution from aqueous suspensions of titanium(IV) oxide modified with binaphthol Reviewed
S Ikeda, C Abe, T Torimoto, B Ohtani
ELECTROCHEMISTRY 70 ( 6 ) 442 - 445 2002.6
Joint Work
Authorship：Lead author Publisher：ELECTROCHEMICAL SOC JAPAN
The reaction between titanium(IV) oxide (TiO2) powders and 1,1'-binaphthalene-2,2'-diol (bn(OH)(2)), both of which are originally colorless, led to the formation of surface TiO2-bn(OH)(2) complexes giving a broad absorption in the visible-light region below ca. 550 nm. When the surface complex was made on TiO2 loaded with platinum deposits, the powder exhibited photocatalytic activity for H-2 evolution from deaerated triethanolamine solution under visible-light irradiation (>430 nm). On the basis of the experimental results, the reaction mechanism seems to involve visible-light excitation of the surface complexes, electron injection to TiO2, and its migration to platinum deposits, where reduction of H+ takes place.
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Preparation of polycrystalline TiO(2) photocatalysts impregnated with various transition metal ions: Characterization and photocatalytic activity for the degradation of 4-nitrophenol Reviewed
A Di Paola, G Marci, L Palmisano, M Schiavello, K Uosaki, S Ikeda, B Ohtani
JOURNAL OF PHYSICAL CHEMISTRY B 106 ( 3 ) 637 - 645 2002.1
Joint Work
Publisher：AMER CHEMICAL SOC
A set of polycrystalline TiO(2) photocatalysts loaded with various ions of transition metals (Co, Cr, Cu, Fe, Mo, V, and W) were prepared by using the wet impregnation method. The samples were characterized by using some bulk and surface techniques, namely X-ray diffraction, BET specific surface area determination, scanning, electron microscopy, point of zero charge determination, and femtosecond pump-probe diffuse reflectance spectroscopy (PP-DRS). The samples were employed as catalysts for 4-nitrophenol photodegradation in aqueous suspension, used as a probe reaction. The characterization results have confirmed the difficulty to find a straightforward correlation between photoactivity and single specific properties of the powders. Diffuse reflectance measurements showed a slight shift in the band gap transition to longer wavelengths and an extension of the absorption in the visible region for almost all the doped samples. SEM observation and EDX measurements indicated a similar morphology for all the particles, and a not homogeneous distribution of the metal species onto the surface of catalyst particles. The impregnated samples revealed recombination rates always higher than that of bare TiO(2). The photoactivity of TiO(2) was reduced by the presence of transition metal ions with the exception of W, which instead played a beneficial role. The results of femtosecond pump-probe diffuse reflectance spectroscopy appear quite in accord with the observed photocatalytic activity only for the lowest values of electron-hole recombination rate of the samples.
DOI： 10.1021/jp013074l
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Direct observation of bimodal amphiphilic surface structures of zeolite particles for a novel liquid-liquid phase boundary catalysis Reviewed
S Ikeda, H Nur, T Sawadaishi, K Ijiro, M Shimomura, B Ohtani
LANGMUIR 17 ( 26 ) 7976 - 7979 2001.12
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
Amphiphilic NaY zeolite particles were prepared by a partial modification of the external surface of NaY with alkylsilyl groups. When the particles were added to a mixture of aqueous hydrogen peroxide and normal alkene, they were feasibly located just at the liquid-liquid phase boundary and efficiently catalyzed epoxidation of the alkenes even without stirring. Fluorescence microscopic observation of these particles selectively modified with fluorescent dye revealed that each particle has a bimodal amphiphilic surface structure; one side of the external surface is hydrophilic and the other is hydrophobic.
DOI： 10.1021/la011088c
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Phase-boundary catalysis of alkene epoxidation with aqueous hydrogen peroxide using amphiphilic zeolite particles loaded with titanium oxide Reviewed
H Nur, S Ikeda, B Ohtani
JOURNAL OF CATALYSIS 204 ( 2 ) 402 - 408 2001.12
Joint Work
Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE
A new heterogeneous catalytic system, phase-boundary catalysis, for epoxidation of alkene with aqueous H2O2 is proposed. Amphiphilic titanium-loaded zeolite particles, a part of the external surface of which was covered with hydrophobic alkyl groups and the rest being left hydrophilic, were prepared by deposition of titanium species from titanium(IV) tetra-2-propoxide and attachment of octadecylsilyl groups from n-octadecyltrichlorosilane (ODS) onto an NaY zeolite powder. Due to their amphiphilicity, the catalyst particles lay at the liquid-liquid phase boundary between upper alkene and lower aqueous phases, and they showed catalytic activity for epoxidation of 1-alkenes (e.g., 1-octene) with aqueous hydrogen peroxide. The phase-boundary catalytic system required neither stirring to make an emulsion nor addition of a cosolvent to make a homogeneous solution to drive the epoxidation. The yield of 1,2-epoxyoctane, a sole oxidation product from 1-octene, strongly depended on the apparent interphase area of the aqueous-organic phase boundary. The amphiphilic catalyst exhibited much higher catalytic activity than that of hydrophilic titanium-loaded NaY, without modification by ODS, or of a hydrophobic catalyst with almost full coverage by the alkyl groups. A similar trend in the activities of these catalysts was also observed when the reaction was carried out with vigorous stirring, in the presence of a cosolvent, or in a water-carbontetrachloride (CCl4) Mixture, where the aqueous hydrogen peroxide phase lies above the CCl4 phase. The phase-boundary catalytic system could also be applied to epoxidation of other normal alkenes. Compared with nonporous silica particles, the use of microporous NaY with a relatively large surface area had a beneficial effect, probably due to an increase both in the surface contact between the aqueous and organic layer and in the number of effective active sites of titanium species on its external surface. On the basis of these experimental results, a reaction model is proposed. (C) 2001 Elsevier Science.
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Transition metal doped TiO2: physical properties and photocatalytic behaviour Reviewed
Di Paola, A.; Ikeda, S.; Marci, G.; Ohtani, B.; Palmisano, L.
INTERNATIONAL JOURNAL OF PHOTOENERGY 3 ( 4 ) 171 - 176 2001.12
Joint Work
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Photocatalytic activity of transition-metal-loaded titanium(IV) oxide powders suspended in aqueous solutions: Correlation with electron-hole recombination kinetics Reviewed
S Ikeda, N Sugiyama, B Pal, G Marci, L Palmisano, H Noguchi, K Uosaki, B Ohtani
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 3 ( 2 ) 267 - 273 2001.1
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
Photocatalytic reactions by transition-metal (V, Cr, Fe, Co, Cu, Mo, or W) loaded TiO2 (M-TiO2) powders suspended in aqueous solutions of methanol, (S)-lysine (Lys), or acetic acid were investigated. The photoactivities of various samples were compared with the rate constant (k(r)) of recombination of photoexcited electrons and positive holes determined by femtosecond pump-probe diffuse reflection spectroscopy (PP-DRS). As a general trend, increased loading decreased the rate of formation of the main products (H-2, pipecolinic acid (PCA), and CO2) under UV (> 300 nm) irradiation, and the effect became more intense on increasing the loading. In PP-DRS, these M-TiO2 gave similar decays of absorption at 620 nm arising from excitation by a 310 nm pulse (< 100 fs). The second-order rate constant (k(r)) markedly increased with loading, even at a low level (0.3%) and further increased with an increase in loading up to 5%. The photocatalytic activity of platinized M-TiO2 for H-2 and PCA production under deaerated conditions depended strongly on k(r), but the relation between k(r) and the rate of CO2 production by unplatinized M-TiO2 under aerated conditions was ambiguous; other factor(s) might control the rate of the latter. These different k(r) dependences of photoactivity on the reaction kinetics governed by e(-)-h(+) recombination were attributed to the presence of O-2 and Pt deposits. A simple kinetic model to explain the overall rate of these photocatalytic reactions is proposed, and the effect of recombination kinetics on photoactivity is discussed.
DOI： 10.1039/b008028o
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Transition metal doped TiO2: physical properties and photocatalytic behaviour
A. Di Paola, S. Ikeda, G. Marci, B. Ohtani, L. Palmisano
INTERNATIONAL JOURNAL OF PHOTOENERGY 3 171 - 176 2001
Publisher：HINDAWI PUBLISHING CORPORATION
Two probe photocatalytic reactions, i.e. ethanoic acid and 4-nitrophenol photooxidation, were carried out in different experimental conditions by using suspensions of transition metal (Co, Cr, Cu, Fe, Mo, V and W) doped polycrystalline TiO2 powders in aqueous systems. A beneficial influence of the presence of metal species was observed only with the samples containing copper and tungsten. In particular, the TiO2/Cu powders showed to be more photoactive of bare TiO2 for the ethanoic acid oxidation while the TiO2/W samples were more efficient for 4-nitrophenol degradation. A tentative interpretation is provided on the basis of the values of the points of zero charge of the powders and of the rate constants of recombination of photogenerated electrons and holes, determined by femtosecond pump-probe diffuse reflectance spectroscopy (PP-DRS).
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Mechano-catalytic overall water splitting on some mixed oxides Reviewed
G Hitoki, T Takata, S Ikeda, M Hara, JN Kondo, M Kakihana, K Domen
CATALYSIS TODAY 63 ( 43135 ) 175 - 181 2000.12
Joint Work
Publisher：ELSEVIER SCIENCE BV
Simple transition metal oxides such as NiO, Co3O4, Fe3O4 and Cu2O were found to catalytically decompose water into H-2 and O-2 by mechanical energy, The reaction is regarded as "mechano-catalytic'' overall water splitting" and is a quite novel catalytic reaction. In this paper, some,general aspects on the mechano-catalytic overall water splitting are reviewed on simple oxides. In addition, recent results on the mechano-catalytic activity of a groups of mixed oxides, wolramite-type oxides with a formula of ABO(4) (A = Fe, Co, Ni and Cu, etc., B = W, Mo), are shown. AWO(4) (A = Fe, Co, Ni and Cu) decomposed water into H-2 and O-2 under the supply of mechanical energy, indicating that mechano-catalytic overall water splitting proceeded on wolframite-type compounds containing 3d-transition metals. AMoO(4) (A = Fe, Co, Ni) also decomposed water into H-2 and O-2 under supply of mechanical energy. The reaction properties on wolframite-type oxides are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.
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Shape- and size-selective photocatalytic reactions by layered titanic acid powder suspended in deaerated aqueous alcohol solutions Reviewed
B Ohtani, S Ikeda, H Nakayama, S Nishimoto
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 2 ( 22 ) 5308 - 5313 2000.11
Joint Work
Publisher：ROYAL SOC CHEMISTRY
Protonic titanate of H(x)Ti(2-x/4)Z(x/4)O(4).H2O (HLe; x similar or equal to0.7, Z=vacancy) powder of a layered crystal structure was prepared, suspended in aqueous alcoholic solutions and photoirradiated by light of wavelength > 300 nm at room temperature under a deaerated atmosphere. HLe showed photocatalytic activity of H-2 production, similar to ordinary titanium(IV) oxide powders. The rate and time course of H-2 evolution by HLe depended strongly on the kind of alcohol. Detailed investigation revealed that the photocatalytic activity was regulated by the shape and size of the alcohol, due to the selection of adsorption at the interlayer of HLe.
DOI： 10.1039/b006497l
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Phase-boundary catalysis: a new approach in alkene epoxidation with hydrogen peroxide by zeolite loaded with alkylsilane-covered titanium oxide Reviewed
H Nur, S Ikeda, B Ohtani
CHEMICAL COMMUNICATIONS pp2235-2236 ( 22 ) 2235 - 2236 2000.11
Joint Work
Publisher：ROYAL SOC CHEMISTRY
An NaY zeolite, modified with partly alkylsilane-covered titanium oxide and located at the boundary between aqueous and organic phases (a phase-boundary catalyst), acts as a catalyst for alkene epoxidation without stirring or the addition of a co-solvent to drive liquid-liquid phase transfer.
DOI： 10.1039/b006207n
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Synthesis of (H3O)TiNbO5 center dot 0.26H(2)O via hydronium (H3O+) ion-exchange reaction and its photocatalytic activity for H-2 evolution from aqueous methanol solution Reviewed
H Takahashi, M Kakihana, Y Yamashita, K Yoshida, S Ikeda, M Hara, K Domen
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 2 ( 19 ) 4461 - 4464 2000.10
Joint Work
Publisher：ROYAL SOC CHEMISTRY
(H3O)TiNbO5. 0.26H(2)O powder was prepared from layered titanoniobate, KTiNbO5, using an ion-exchange reaction in acidic aqueous solution. X-ray diffraction, thermogravimetry-differential thermal analysis, energy-dispersive X-ray analysis and infrared spectral data gave the first experimental evidence that the so-called proton-exchanged form HTiNbO5 involves hydrated water or hydrated hydronium ion. The intercalation of water or hydronium ion in KTiNbO5 was not achieved by the conventional high-temperature solid-state reaction method but by the low-temperature polymerizable complex (PC) method. While KTiNbO5 via the PC route, combined with Pt, showed only little improvement of the photocatalytic activity with respect to H-2 evolution from aqueous methanol solution, the water or hydronium ion intercalated species, (H3O)TiNbO5. 0.26H(2)O, with Pt loading, showed much higher activities than the others species studied by an order of magnitude.
DOI： 10.1039/b003808n
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Mechano-catalytic overall water-splitting into hydrogen and oxygen on some metal oxides Invited Reviewed
K Domen, S Ikeda, T Takata, A Tanaka, M Hara, JN Kondo
APPLIED ENERGY 67 ( 43102 ) 159 - 179 2000.9
Joint Work
Publisher：ELSEVIER SCI LTD
This is a novel way to generate hydrogen from pure water by converting mechanical energy to chemical energy. The phenomenological aspects of the mechano-catalytic overall water-splitting are reviewed, and the basic feature of the catalytic process is clearly established. The estimation of the conversion from mechanical to chemical energy is also shown. Experimental results. carried out to reveal the mechanism of the mechano-catalytic reaction are described. (C) 2000 Elsevier Science Ltd. All rights reserved.
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Mechano-catalytic overall water splitting on some mixed oxides Reviewed
G Hitoki, T Takata, S Ikeda, M Hara, JN Kondo, M Kakihana, K Domen
CATALYSIS TODAY 200 ( 43102 ) 255 - 262 2000.8
Joint Work
Publisher：ELSEVIER SCIENCE BV
Simple transition metal oxides such as NiO, Co3O4, Fe3O4 and Cu2O were found to catalytically decompose water into H-2 and O-2 by mechanical energy, The reaction is regarded as "mechano-catalytic'' overall water splitting" and is a quite novel catalytic reaction. In this paper, some,general aspects on the mechano-catalytic overall water splitting are reviewed on simple oxides. In addition, recent results on the mechano-catalytic activity of a groups of mixed oxides, wolramite-type oxides with a formula of ABO(4) (A = Fe, Co, Ni and Cu, etc., B = W, Mo), are shown. AWO(4) (A = Fe, Co, Ni and Cu) decomposed water into H-2 and O-2 under the supply of mechanical energy, indicating that mechano-catalytic overall water splitting proceeded on wolframite-type compounds containing 3d-transition metals. AMoO(4) (A = Fe, Co, Ni) also decomposed water into H-2 and O-2 under supply of mechanical energy. The reaction properties on wolframite-type oxides are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.
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A study of mechano-catalysts for overall water splitting Reviewed
M Hara, M Komoda, H Hasei, M Yashima, S Ikeda, T Takata, JN Kondo, K Domen
JOURNAL OF PHYSICAL CHEMISTRY B 104 ( 4 ) 780 - 785 2000.2
Joint Work
Publisher：AMER CHEMICAL SOC
Mechano-catalytic overall water splitting on Cu2O, NiO, and CO3O4 was investigated in order to reveal the reaction mechanism. The experimental results indicated that metallic elements of these oxides were generated during the reaction. Also, elemental metals Cu, Ni, and Co were oxidized into Cu2O, NiO, and Co3O4, respectively, when water was reduced into Hz by the metal powders under the same reaction condition. The metallic particles covered with the metal oxides evolved both O-2 and H-2 These results suggest that a redox reaction between the metal and metal oxide may be responsible for H-2 and O-2 formation of the mechano-catalytic overall water splitting.
DOI： 10.1021/jp993441h
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Mechano-catalytic overall water splitting (II) nafion-deposited Cu2O Reviewed
M Hara, H Hasei, M Yashima, S Ikeda, T Takata, JN Kondo, K Domen
APPLIED CATALYSIS A-GENERAL 190 ( 43102 ) 35 - 42 2000.1
Joint Work
Publisher：ELSEVIER SCIENCE BV
Some modifications of a mechano-catalyst, Cu2O, and optimization of the reaction conditions were attempted to improve its activity for mechano-catalytic overall water splitting. The rates of evolution of H-2 and O-2 were improved by deposition of nafion onto Cu2O and the choice of an appropriate stirring rod. The irradiation of visible light (lambda > 550 nm) was found to maintain the activity in the time course, which gradually decreased without irradiation. (C) 2000 Elsevier Science B.V. All rights reserved.
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Mechano-catalytic overall water splitting for hydrogen production Reviewed
K Domen, S Ikeda, T Takata, A Tanaka, A Hara, JN Kondo
HYDROGEN ENERGY PROGRESS XIII, VOLS 1 AND 2, PROCEEDINGS 253 - 257 2000
Publisher：INT ASSOC HYDROGEN ENERGY
Mechano-catalytic overall water splitting is a novel way to generate hydrogen from pure water by converting mechanical energy to chemical energy with the aid of some metal oxides. The phenomenological aspects of the mechano-catalytic overall water splitting are reviewed, and the basic feature of the catalytic process is clearly established. Some experimental results for revealing the reaction mechanism are also described.
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Mechano-catalysis - a novel method for overall water splitting Reviewed
S Ikeda, T Takata, M Komoda, M Hara, JN Kondo, K Domen, A Tanaka, H Hosono, H Kawazoe
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 1 ( 18 ) 4485 - 4491 1999.9
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
A novel finding of mechano-catalytic overall water splitting by metal oxides, a way to produce hydrogen by water decomposition, is reported. It was clearly revealed that some simple and mixed oxide powders such as NiO, Co3O4, Cu2O, Fe3O4, and CuMO2 (M=Al, Fe, Ga), when suspended in distilled water by magnetic stirring, decompose water into H-2 and O-2 catalytically. The observed mechano-catalytic overall water splitting was cycled by the conversion of mechanical energy supplied by rubbing these oxide powders against the bottom wall of the reaction vessel with the stirring rod. Typical efficiency of the mechanical-to-chemical energy conversion was estimated to be 4.3% (for NiO).
DOI： 10.1039/a903543e
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Novel methods for preparation of ion-exchangeable thin films Reviewed
R Abe, S Ikeda, JN Kondo, M Hara, K Domen
THIN SOLID FILMS 343 156 - 159 1999.4
Joint Work
Publisher：ELSEVIER SCIENCE SA
Ion-exchangeable thin films of inorganic compounds were prepared by the soft-chemical method. A thin him composed of a layered titanate was prepared by exfoliation of the layered compound H(+)/Cs(x)Ti((2-x/4))square(x/4),O(4) in an aqueous ethyl amine solution. The exfoliated titanate sheets were easily oriented on a substrate by means of spin-coating. A layered potassium niobate, K(4)Nb(6)O(17), was made into a thin film from suspension of fine particles prepared by wet-grinding of the original K(4)Nb(6)O(17) powder. After calcination at 1073 K, the K(4)Nb(6)O(17) thin him had a well-ordered layered structure with the b-axis perpendicular to the substrate surface. The ion-exchange property of those films enabled the intercalation of other cations without destroying the layered structures. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.
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Synthesis of NiO-loaded KTiNbO5 photocatalysts by a novel polymerizable complex method Reviewed
H Takahashi, M Kakihana, Y Yamashita, K Yoshida, S Ikeda, M Hara, K Domen
JOURNAL OF ALLOYS AND COMPOUNDS 285 ( 43102 ) 77 - 81 1999.3
Joint Work
Publisher：ELSEVIER SCIENCE SA
A polymerizable complex (PC) technique was utilized to prepare high-purity stoickiometric KTiNbO5 at reduced temperatures. Heating of a mixed solution of citric acid (CA), ethylene glycol (EG), and K, Ti and Nb ions with a molar ratio of CA:EG:K:Ti:Nb=15:60:1:1:1 at 130 degrees C produced a yellowish transparent polymeric gel without any precipitation, which after pyrolysis at 350-400 degrees C was converted to a powder precursor for KTiNbO5. The complete formation of KTiNbO5 occurred when the powder precursor was heat-treated at 700 degrees C for 2 h in static air. KTiNbO5 via the PC route, combined with NiO, showed more than ten times larger photocatalytic activities for the decomposition of water compared with those for a sample prepared at 1100 degrees C by the conventional solid-state reaction method. The difference in the photocatalytic activities between the two samples was basically understood in terms of the difference in the surface areas. A partial loss of potassium was likely in the host KTiNbO5 material prepared by the high-temperature solid-state reaction method, which was supposed to be a factor altering the surface structure, thus influencing the overall photocatalytic activity of potassium titanoniobates. (C) 1999 Elsevier Science S.A. All rights reserved.
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Mechano-catalytic overall water splitting Reviewed
S Ikeda, T Takata, T Kondo, G Hitoki, M Hara, JN Kondo, K Domen, H Hosono, H Kawazoe, A Tanaka
CHEMICAL COMMUNICATIONS pp.2185-2186 ( 20 ) 2185 - 2186 1998.10
Joint Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
Mechano-catalysis, a novel and simple method to decompose water into H-2 and O-2 in which mechanical energy is directly converted into chemical energy, is demonstrated.
DOI： 10.1039/a804549f
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Preparation of a high active photocatalyst, K2La2Ti3O10, by polymerized complex method and its photocatalytic activity of water splitting Reviewed
S Ikeda, M Hara, JN Kondo, K Domen, H Takahashi, T Okubo, M Kakihana
JOURNAL OF MATERIALS RESEARCH 13 ( 4 ) 852 - 855 1998.4
Joint Work
Authorship：Lead author Publisher：MATERIALS RESEARCH SOCIETY
A layered perovskite type oxide, K2La2Ti3O10, was prepared by a gel technique using the polymerized complex (PC) method. A single phase K3La2Ti3O10 was Obtained by adding twice the potassium required for stoichiometry. The Ni-K2La2Ti3O10 catalyst prepared by the PC method exhibited a higher photocatalytic activity for decomposition of H2O into H-2 and O-2 than that prepared by a conventional solid state reaction.
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Cu2O as a photocatalyst for overall water splitting under visible light irradiation Reviewed
Hara, M; Kondo, T; Komoda, M; Ikeda, S; Shinohara, K; Tanaka, A; Kondo, JN; Domen, K
CHEMICAL COMMUNICATIONS ( 3 ) 357 - 358 1998.2
Joint Work
DOI： 10.1039/a707440i
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Preparation of K2La2Ti3O10 by polymerized complex method and photocatalytic decomposition of water Reviewed
S Ikeda, M Hara, JN Kondo, K Domen, H Takahashi, T Okubo, M Kakihana
CHEMISTRY OF MATERIALS 10 ( 1 ) 72 - 77 1998.1
Joint Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
A polymerized complex (PC) technique was applied to the preparation of a highly active photocatalyst, K2La2Ti3O10, with a layered perovskite type structure to decompose H2O into H-2 and O-2. The catalyst prepared by the PC technique had a higher photocatalytic activity than that prepared by conventional solid-state reaction method.
DOI： 10.1021/cm970221c
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Effect of the particle size for photocatalytic decomposition of water on Ni-loaded K4Nb6O17 Reviewed
S Ikeda, A Tanaka, K Shinohara, M Hara, JN Kondo, KI Maruya, K Domen
MICROPOROUS MATERIALS 9 ( 43226 ) 253 - 258 1997.5
Joint Work
Authorship：Lead author Publisher：ELSEVIER SCIENCE BV
The photocatalytic activities of water splitting by small particles (0.1-2 mu m) of K4Nb6O17 were studied. The milled catalysts were prepared by two kinds of ball-milling methods from the powder whose particles were several tens of micrometers in diameter. The surface area of the milled catalyst measured by N-2 adsorption at 77 K increased by an order of magnitude. The crystal structure was almost retained as K4Nb6O17, as evidenced by the results of X-ray diffraction and scanning electron micrography. The photocatalytic activity for an overall decomposition of water of the Ni-loaded K4Nb6O17 was twice as high as that for the original catalyst. (C) 1997 Elsevier Science B.V.
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Layered niobium oxides - Pillaring and exfoliation Reviewed
K. Domen, Y. Ebina, S. Ikeda, A. Tanaka, J. N. Kondo, K. Maruya
Catalysis Today 28 ( 43102 ) 167 - 174 1996.4
Joint Work
Publisher：Elsevier
Several ion-exchangeable layered niobates were applied to prepare modified layered photocatalysts. K1-xLaxCa2-xNb3O10 (x = 0, 0.25, 0.50, 0.75), a layered perovskite series, with variable interlayer cation density, were used for the modification of the interlayer space by pillaring of silica and titania. The silica-pillaring process was monitored by NMR and the thermal stability was also examined. Silica-pillar was successfully introduced to all the series of perovskites which showed good photocatalytic activity. The preparation of titania-pillared layered niobates was more difficult. In the case of KCa2Nb3O10 (x = 0), we could not introduce a titania pillar, but in the case of K0.5La0.5Ca1.5Nb3O10 (x = 0.5) carrying less interlayer cation density, titania-pillar was introduced although the thermal stability was very poor. K4Nb6O17, another type of layered niobate, was used for the exfoliation and restacking of the niobate sheets. The structure and photocatalytic activity of the product was examined.