研究者詳細 - 鳥本　司

論文 - 鳥本　司

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Preparation method allowing self-isolation of CdS nanocrystals emitting intense band-gap luminescence 査読有り

S. Kuwabata, K. Ueda-Sarson, and T. Torimoto

Chem. Lett. 33 巻 ( 10 ) 頁： 1344-1345 2004年8月

Light intensity dependence of the action spectra of photocatalytic reactions with anatase titanium(IV) oxide 査読有り

T. Torimoto, Y. Aburakawa, Y. Kawahara, S. Ikeda, and B. Ohtani

Chem. Phys. Lett. 392 巻 ( 1-3 ) 頁： 220-224 2004年7月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

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.

半導体ナノ粒子の形状制御と光化学特性招待有り

鳥本　司

光化学 35 巻頁： 42-44 2004年

Preparation of Novel Silica-Cadmium Sulfide Composite Nanoparticles Having Adjustable Void Space by Size-Selective Photoetching, 査読有り

T. Torimoto, J. P. Reyes, K. Iwasaki, B. Pal, T. Shibayama, K. Sugawara, H. Takahashi, and B. Ohtani

J. Am. Chem. Soc. 125 巻頁： 316-317 2003年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

The size-selective photoetching technique was used to control the size of a CdS nanoparticle inside a silica shell. With monochromatic light irradiation, the diffuse reflectance spectra of silica-coated CdS nanoparticles were blue-shifted, and the size of the resulting CdS nanoparticles incorporated in the silica shells was adjustable by varying the wavelength of irradiated light. TEM observation revealed that the original CdS nanoparticle seemed to be in close contact with the amorphous silica shell to leave almost no clearance, while the monochromatic light irradiation caused the decrease in the size of CdS particles, resulting in the formation of a void space between the photoetched CdS core particle and the silica shell. The average void spaces available in the shells were calculated to be ca. 1.4 and 2.4 nm with the irradiation at 514 and 458 nm, respectively. These results indicated that the size-selective photoetching technique enables the regulation of void space formed in the core-shell structure by choosing the wavelength of irradiation light.

Layer-by-Layer Accumulation of Cadmium Sulfide Core-Silica Shell Nanoparticles and Size-Selective Photoetching to Make Adjustable Void Space Between Core and Shell 査読有り

T. Torimoto, J. P. Reyes, S.-y. Murakami, B. Pal, B. Ohtani

J. Photochem. Photobiol. A Chem. 160 巻頁： 69-76 2003年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Layer-by-layer accumulation of monolayers of silica-coated cadmium sulfide (CdS) was achieved through repeated monolayer deposition–hydrolysis cycles using CdS particles (average diameter: 5 nm) modified with 3-mercaptopropyltrimethoxysilane (MPTS) and glass substrates. Absorption spectroscopic analyses of the resulting yellow films revealed that each layer had almost the same thickness, the estimated density of which corresponded to ca. 66% of that for close hexagonal packing of nanoparticles. Monochromatic light
irradiation at 488, 458, or 436 nm onto the film immersed in oxygen-saturated aqueous methylviologen solution caused a decrease in the size of the CdS core depending on the irradiation wavelength, while atomic force microscopic analyses suggested that the size of the silica
shell of the immobilized nanoparticles was almost unchanged by irradiation, i.e., the immobilized silica-coated CdS nanoparticles had void spaces between the photoetched core and the silica shell, and their sizes could be regulated by choosing the wavelength of irradiation light. This size-selective photoetching was applied to nanoparticulate films that had been heat-treated at 473, 573 or 673K to observe the blue-shift of the absorption edge of CdS to the irradiation wavelength. The amount of CdS remaining in the film after the photoetching process depended on the temperature of heat treatment. The largest amount among as-prepared and heat-treated samples was obtained at 473K and decreased with an increase in temperature. The growth of particles, i.e., the diminution of particle number, and/or the diminution
of number of separated independent shells may account for this dependence.

Development of Photocatalytic Reaction System for Oxidative Decomposition of Volatile Organic Compounds in Water with Enhanced Aeration 査読有り

R. Villacres, S. Ikeda, T. Torimoto, B. Ohtani

J. Photochem. Photobiol. A:Chem. 160 巻頁： 121-126 2003年

記述言語：英語掲載種別：研究論文（学術雑誌）

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 (H2) 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 (O2)-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 O2. From the results of photocatalytic oxidative decomposition of 2-propanol, it was clarified that the surfaces of TiO2 particles could be sufficiently supplied with O2 from the gas space through the membrane to accelerate the oxidation.

Photochemical Hydrogen Evolution from Aqueous Triethanolamine Solutions Sensitized by Binaphthol-Modified Titanium(IV) Oxide under Visible Light Irradiation 査読有り

S. Ikeda, C. Abe, T. Torimoto, B. Ohtani

J. Photochem. Photobiol. A: Chem. 160 巻頁： 61-67 2003年

記述言語：英語掲載種別：研究論文（学術雑誌）

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 (H2) 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 H2, was elucidated.

作用スペクトル解析による懸濁系半導体光触媒の活性評価と制御

24 巻頁： 39-45 2003年

Quantitative Analysis of Defective Sites in Titanium(IV) Oxide Photocatalyst Powders 査読有り

S. Ikeda, N. Sugiyama, S. Murakami, H. Kominami, Y. Kera, H. Noguchi, K. Uosaki, T. Torimoto, and B. Ohtani

Phys. Chem. Chem. Phys. 5 巻頁： 778-783 2003年

記述言語：英語掲載種別：研究論文（学術雑誌）

The molar amounts of defective sites (Md) 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
Md with the rate constant of electron-hole recombination determined by femtosecond pump-probe diffuse reflection spectroscopy revealed that Md could be a quantitative parameter of recombination between a photoexcited electron and a positive hole. The fact that there was no linear relation between Md and the specific surface area suggests that the surface area was not directly reflected on Md . A reciprocal correlation between photocatalytic activity for water oxidation in aqueous silver sulfate solution and Md revealed that the rate of recombination is one of the predominant physical properties governing the activities of TiO2 powders in this reaction system.

サイズ選択光エッチングによる半導体ナノ粒子の単分散化と光電気化学特性制御

化学工業 53 巻 ( 7 ) 頁： 522-527 2002年

芳香族有機化合物を表面に固定した酸化チタン微粒子の調整と光科学特性の評価

池田　茂、　鳥本　司、　大谷文章

光触媒 7 巻頁： 48-51 2002年

作用スペクトル解析による光触媒活性構造の解明にかかわる研究と課題

鳥本　司、　大谷文章

光触媒 7 巻頁： 32-37 2002年

Visible Light-induced Hydrogen Evolution from Aqueous Suspensions of Titanium(IV) Oxide Modified with Binaphthol 査読有り

Electrochemistry 70 巻 ( 6 ) 頁： 442-446 2002年

記述言語：英語掲載種別：研究論文（学術雑誌）

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.

Photoelectrochemical Activities of Ultrathin Lead Sulfide Films Prepared by Electrochemical Atomic Layer Epitaxy

T. Torimoto, S. Takabayashi, H. Mori, and S. Kuwabata

J. Electroanal. Chem. 522 巻頁： 33-39 2002年

記述言語：英語掲載種別：研究論文（学術雑誌）

PbS ultrathin films were prepared by sequential underpotential deposition of S and Pb on Au(111) substrates. Observations of the resulting films with high resolution electron microscopy and energy dispersive X-ray spectrometry revealed the deposition of PbS thin films having the cubic rock salt crystal structure, the (200) planes of which were parallel to the Au surface. The scanning tunneling microscope images showed that the surface of the prepared PbS film was flat on an atomic level and no large protrusions were present, while etch pits with the height of the monatomic step of Au(111) were seen through the deposited films irrespective of the number of PbS monolayers. The PbS film-deposited Au electrodes showed anodic photocurrents in an aqueous solution containing triethanolamine as a sacrificial electron donor. The onset wavelength of their action spectra was largely blue-shifted from that of the bulk PbS due to the size quantization effects. The energy gap of the PbS thin films determined from the action spectra of anodic photocurrents decreased with an increase in the film thickness.

Discrimination of the Active Crystalline Phases in Anatase-Rutile Mixed Titanium(IV) Oxide Photocatalysts through Action Spectrum Analyses 査読有り

T. Torimoto, N. Nakamura, S. Ikeda, and B. Ohtani

Phys. Chem. Chem. Phys. 4 巻 ( 23 ) 頁： 5910-5914 2002年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

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 H2 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 H2 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.

Quartz Crystal Microbalance Study on Photoelectrochemical Deposition of Lead(IV) Oxide on Titanium(IV) Oxide Nanoparticulate Films 査読有り

T. Torimoto, S. Si, and B. Ohtani

Electrochemistry 70 巻 ( 6 ) 頁： 438-441 2002年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Photoelectrochemical quartz crystal microbalance measurements were used for in situ monitoring of the photoelectrochemical deposition of PbO2 onto a TiO2 nanoparticulate film electrode. It was found that the photodeposition behavior of PbO2 was influenced by pH of solution. At pH 3.8, the mass of the TiO2 film electrode decreased in the initial stage of irradiation due to the desorption of Pb2+ from the TiO2, surface and then linearly increased due to PbO2 deposition with an increase in the charge flowing as a photocurrent, while the initial decrease of the mass was much smaller at pH 1.8.

サイズ選択光エッチングによる単分散半導体ナノ粒子の作製招待有り

4 巻 ( 2 ) 頁： 27-30 2001年

半導体ナノ粒子の調製・固定化と光電気化学特性招待有り

69 巻 ( 11 ) 頁： 866-871 2001年

Characterization of Ultrasmall CdS Nanoparticles Prepared by the Size-Selective Photoetching Technique 査読有り

T. Torimoto, H. Kontani, Y. Shibutani, S. Kuwabata, T. Sakata, H. Mori, and H. Yoneyama

J. Phys. Chem. B 105 巻 ( 29 ) 頁： 6838-6845 2001年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Ultrasmall CdS nanoparticles were prepared by the size-selective photoetching technique. The smallest size of the CdS nanoparticles was obtained by the irradiation with the monochromatic light having the wavelength of 365 nm, while the absorbance of CdS nanoparticles monotonically decreased, for the whole wavelength, to null if the irradiation was performed using a wavelength less than 365 nm. The surface modification of US nanoparticles with thiophenol caused the red-shift of the absorption spectra due to the electric interaction between the bound thiophenol molecules and the CdS core, the degree being enhanced with a decrease in the particle size. H-1 NMR signals of thiophenol bound on the surface of the smallest US nanoparticles prepared by 365-nm irradiation were shifted upfield compared to those obtained for the larger thiophenol-modified CdS nanoparticles prepared by the longer wavelength irradiation, and the signals appeared in positions similar to those of chemically synthesized CdS cluster molecules. The observation with transmission electron microscopy revealed that the smallest thiophenol-modified CdS nanoparticles had an edged pyramidal shape with a size of about 1.7 nm in contrast to the larger CdS nanoparticles of almost spherical shape. The particle size and chemical compositions of the smallest thiophenol-modified US nanoparticles roughly agreed with those of Cd32S14(SC6H5)(36). 4DMF, which has been reported to be one of the largest chemically synthesized US cluster molecules. The similarity between the emission and excitation properties indicated that the smallest thiophenol-modified CdS nanoparticles had the energy structure almost equal to that of Cd32S14(SC6H5)(36). 4DMF.

Photoelectrochemical Properties of Size-Quantized Semiconductor Photoelectrodes Prepared by Two-Dimensional Cross-Linking of Monodisperse CdS Nanoparticles 査読有り

T. Torimoto, N. Tsumura, H. Nakamura, S. Kuwabata, T. Sakata, H. Mori, and H. Yoneyama

Electrochim. Acta 45 巻 ( 20 ) 頁： 3269-3276 2000年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Two-dimensionally organized CdS nanoparticle films were prepared with the use of Langmuir-Blodgett (LB) technique. Propanethiol-modified CdS nanoparticles were spread on water subphase, which contained 1,6-hexanedithiol as a cross-linking agent for binding the surface-modified CdS nanoparticles with each other. Surface pressure-area isotherms of CdS monoparticle layer taken after the cross-linking were largely different from those obtained without addition of 1,6-hexanedithiol in water subphase. After the cross-linking, the CdS monoparticle layer was transferred from the air-water interface to 1,6-hexanedithiol-modified gold substrate using the LB technique to give CdS monoparticulate film electrodes with dense packing of the nanoparticles on the gold substrate. By repeating the same techniques, the monoparticulate him was cumulated with desired amounts. The prepared CdS nanoparticle films showed n-type photosensitivities in proportion to the cumulation number of the monoparticle layers for less than five layers. Beyond that value, a saturation tendency of the photocurrent appeared.

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