Faculty Profiles - TORIMOTO Tsukasa

Papers - TORIMOTO Tsukasa

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Titanium Dioxide/Adsorbent Hybrid Photocatalysts for Photodestruction of Organic Substances of Dilute Concentrations Invited

Catal Today Vol. 58 page： 133-140 2000

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

Utilities of hybrid photocatalyst consisting of TiO2 and an adsorbent such as activated carbon in photoinduced mineralization of organic substances of very dilute present concentrations are demonstrated for the photodecomposition of propionaldehyde in air atmosphere, and propyzamide and bromoform dissolved inwater. The substrates of target were adsorbed on the adsorbent
support, and then a high concentration environments of the substrate was formed around the loaded TiO2, resulting in an increase in the photodestruction rate. Evidences for the diffusion of propionaldeyde adsorbed on the mordenite support to the loaded TiO2 are presented. Merits of the use of the adsorbents as the support for TiO2 loading is discussed.

Electrochemical Preparation of ZnS/CdS Superlattice and Its Photoelectrochemical Properties

T. Torimoto, A. Obayashi, S. Kuwabata, and H. Yoneyama

Electrochem. Commun. Vol. 2 ( 5 ) page： 359-362 2000

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

Superlattice electrodes composed of three molecular layers of CdS and one to three molecular layers of ZnS were prepared on gold (111) film by using electrochemical atomic layer epitaxy. The prepared electrodes exhibited similar behavior to those of n-type semiconductor
electrodes. The energy gap was not changed at all by changing the number of molecular layers of ZnS and by increasing the number of periods in the superlattice structure up to four. The magnitude of the anodic photocurrent was, however, influenced by these variables. It increased with an increase in the number of periods in the superlattice structure and decreased with increasing number of molecular layers of ZnS.

半導体ナノ粒子アレイの作製と光電気化学特性 Invited

表面 Vol. 38 ( 7 ) page： 353-363 2000

Preparation of Size-quantized ZnS Thin Films Using Electrochemical Atomic Layer Epitaxy and Their Photoelectrochemical Properties Reviewed

T. Torimoto, A. Obayashi, S. Kuwabata, H. Yasuda, H. Mori, and H. Yoneyama

Langmuir Vol. 16 ( 16 ) page： 5820-5824 2000

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

Size-quantized ZnS thin films were prepared by sequential underpotential deposition of S and Zn on Au{111} substrates. Observations of the high-resolution electron microscope and the energy-dispersive X-ray spectrometer revealed that ZnS films were epitaxially deposited on the Au{111} facet with a stoichiometric composition. The scanning tunneling microscope images showed that the surface of the prepared films was flat in an atomic level and no large protrusion was contained, while etch pits with the height of the monatomic step of Au{111}, which were formed in the UPD of the first S layer on the naked Au surface, were seen through ZnS films with independence of the number of ZnS layers deposited. The ZnS film-deposited Au electrodes showed anodic photocurrents in an aqueous solution containing triethanolamine as a sacrificial electron donor. The energy gap determined from the action spectra decreased with an increase of the film thickness up to ca. 15.5 ZnS layers at which the bulk band gap was obtained.

(26) Effects of Surface Charges and Surface States of Chemically Modified Cadmium Sulfide Nanoparticles Immobilized to Gold Electrode Substrate on Photoinduced Charge Transfers Reviewed

M. Miyake, T. Torimoto, M. Nishizawa, T. Sakata, H. Mori, and H. Yoneyama

Langmuir Vol. 15 ( 8 ) page： 2714-2718 1999

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

Cadmium sulfide nanoparticles (Q-CdS) modified with 2-mercaptoethanesulfonate and 2-amiaoethanethiol in a molar ratio of 2:1 were covalently immobilized onto-an Au surface covered with a self-assembled monolayer of 3,3'-dithiobis(succinimidylpropionate), and the resulting electrodes were further immobilized with Q-CdS using glutaraldehyde as a binding agent. The degree:of anodic photocurrents was greatly influenced by charged conditions of hole scavengers used because of the presence of sulfonate groups on the Q-CdS surfaces; triethylamine having positive charges gave large photocurrents, triethanolamine medium photocurrents, and formate small photocurrents. If Q-CdS having a large emission from their surface trap states was used, anodic photocurrents were depressed with increasing anodic polarization from the onset potentials which were ca. -1.1 V vs SCE for the use of any kinds of hole scavengers, and the greatest depression appeared at -0.25 V, beyond which a steep increase in anodic photocurrents was seen. In contrast, no significant depression in photocurrents was observed and anodic photocurrents were monotonically increased, in the case of using Q-CdS having an intense band-gap emission. When the energetic position at the emission maximum is correlated to the potential at which the greatest photocurrent depression appeared, photocurrent-potential characteristics are discussed in terms of involvements of surface states in the photoelectrode reactions.

単分散半導体ナノ粒子の調製とその応用 Invited

鳥本　司, 桑畑　進，米山　宏

マテリアルインテグレーション Vol. 12 page： 53-59 1999

Photoinduced Destruction of Bromoform Dissolved in Water Using TiO2-loaded Adsorbent Reviewed

H. Yoneyama, H. Kanemoto, N. Takeda, and T. Torimoto

Z. Phys. Chem. Vol. 213 page： 43-48 1999

Influences of Initial Particle Size on Preparation of Monodisperse CdS Nanoparticles with Size-selective Photoetching Reviewed

T. Torimoto, H. Kontani, T. Sakata, H. Mori, and H. Yoneyama

Chem. Lett. ( 5 ) page： 379-380 1999

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

It was found that the size-selective photoetching of CdS particles prepared in Nafion films could be achieved only for particles having the particle sizes smaller than about 12 nm in the diameter. The particles greater than this threshold size were photocorroded until complete dissolution was attained.

Preparation and Photoelectrochemical Properties of Two-Dimensionally Organized CdS Nanoparticle Thin Films Reviewed

T. Torimoto, N. Tsumura, M. Miyake, M. Nishizawa, T. Sakata, H. Mori, and H. Yoneyama

Langmuir Vol. 15 ( 5 ) page： 1853-1858 1999

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

Two-dimensionally organized CdS nanoparticle films were prepared with the use of the Langmuir-Blodgett (LB) technique. 2-Aminoethanethiol-modified CdS nanoparticles were spread on a water subphase which contained glutaraldehyde as a cross-linking agent for binding the surface-modified CdS nanoparticles with each other, and the cross-linking reaction was undertaken under several different compressions of the CdS nanoparticle layer spread on the water subphase. Surface pressure-area isotherms of the CdS monoparticulate layer taken after the cross-linking were largely different depending on the area used for the cross-linking. By transfer of the CdS monoparticulate film prepared at the air-water interface to the 2-aminoethanethiol-modified gold substrate using the LB technique, CdS monoparticulate films containing different surface concentrations were prepared on the gold substrate. It was easily done to cumulate the monoparticulate film on the gold substrate using the same transfer technique. The prepared CdS nanoparticles films showed n-type photosensitivities which were enhanced by increasing the number of cumulation of monoparticulate films.

Effects of Mordenite Support on Photodegradation of Gaseous Organic Compounds over TiO2 Photocatalyst Reviewed

N. Takeda, T. Torimoto, and H. Yoneyama

Bull. Chem. Soc. Jpn. Vol. 72 ( 7 ) page： 1615-1621 1999

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

Effects of mordenite as a support material for TiO2 on photodegradation rates of gaseous propionaldehyde, acetone, and propane were investigated using TiO2 (50 wt%)-loaded mordenite as a photocatalyst in reference to unsupported TiO2. The supported photocatalyst allowed adsorption of all the substrates several times greater than the unsupported photocatalyst, resulting in higher photooxidation rates for them. Detailed analysis suggests that the enhancement of the decomposition rate caused by the use of mordenite support is more remarkable for lower amounts of adsorption of the substrates on the support. The concentration of oxygen was found to have little influence on the photodegradation rates, suggesting that the rate of degradation of the organic substrates was not decided by photogenerated electron transfer processes but by the consumption of photogenerated holes by adsorbed organic substrates.

Fabrication of CdS Nanoparticle Chains along DNA Double Strands Reviewed

T. Torimoto, M. Yamashita, S. Kuwabata, T. Sakata, H. Mori, and H. Yoneyama

J. Phys. Chem. B Vol. 103 ( 42 ) page： 8799-8803 1999

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

Positively charged CdS nanoparticles having diameter of 3.0 +/- 0.2 nm were prepared by the chemical modification of their surfaces with thiocholine. Chains of size-quantized CdS nanoparticles were prepared by using the electrostatic interaction between positively charged nanoparticle surfaces and the phosphate groups of DNA molecules. The observation by transmission electron microscopy revealed that the CdS nanoparticles were arranged in a quasi one dimension with dense packing. The line width of a nanoparticle array was equal to the diameter of CdS nanoparticles that was ca. 3.0 nm. The average distance between the centers of the adjacent nanoparticles was estimated to be 3.5 nm, which was almost equal to the length of 10 base pairs in DNA double strands.

Photoelectrochemical Characterization of Nearly Monodisperse CdS Nanoparticles-Immobilized Gold Electrodes Reviewed

M. Miyake, T. Torimoto, T. Sakata, H. Mori, and H. Yoneyama

Langmuir Vol. 15 ( 4 ) page： 1503-1507 1999

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

Several kinds of nearly monodisperse size-quantized CdS particles (Q-CdS) capped with 2-aminoethanethiol were prepared by means of size selective photoetching and were covalently immobilized onto a gold electrode substrate coated previously with a self-assembled monolayer of 2-aminoethanethiol. The potential of the conduction band edge of Q-CdS estimated from the onset potential of photocurrents was negatively shifted with a decrease in the diameter of CdS nanoparticles, the results being in good accord with the theoretical prediction.

Influence of Carbon Black as an Adsorbent used in TiO2 Photocatalyst Films on Photodegradation Behaviors of Propyzamide Reviewed

N. Takeda, N. Iwata, T. Torimoto, and H. Yoneyama

J. Catal. Vol. 177 page： 240-246 1998

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

The photodecomposition of propyzamide in the aqueous solution was investigated using TiO2-carbon black composite films. It was found that the photodecomposition rate was largely influenced by the content of carbon black in the photocatalyst film. The decomposition rate increased with increasing the carbon black content up to an optimal value, beyond which the photocatalytic activity showed a decreasing tendency. The increase of the photodecomposition rate seems to result from increase of adsorbability for propyzamide in the TiO2-carbon black composite films. With further increase of carbon black from the optimum value, however, relative occupation of TiO2 to carbon black decreases, and the time needed for adsorbed propyzamide on carbon black to diffuse to TiO2 particles becomes great, resulting in the decrease of the apparent photocatalytic activity of the film. Experiments employing a circulating photoreactor system also showed that the TiO2-carbon black composite films had higher photocatalytic activities than the naked TiO2 film.

半導体ナノ粒子表面上での光誘起電子移動 Invited

米山　宏，鳥本　司

触媒 Vol. 40 page： 544-551 1998

Photoelectrochemical Properties of Size-Quantized CdS Thin Films Prepared by an Electrochemical Method Reviewed

T. Torimoto, S. Nagakubo, M. Nishizawa, and H. Yoneyama

Langmuir Vol. 14 ( 25 ) page： 7077-7081 1998

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

Size-quantized CdS thin films were prepared by sequential underpotential deposition of S and Cd on Au(lll). The prepared films in an aqueous solution containing triethanolamine as a sacrificial electron donor showed n-type photoelectrode behaviors. Action spectra of anodic photocurrents were red-shifted with an increase of the film thickness toward characteristic values of those of bulk materials. The energy gap of the film determined from the action spectra showed a remarkable tendency of decrease with an increase of the film thickness up to 3.5 nm. Beyond 3.5 nm the rate of decrease with increase in the film thickness declined. An energy gap value characteristic of bulk materials was obtained with CdS films greater than 6.8 nm.

Effect of Structural Variation on Photocurrent Efficiency in Alkyl-Substituted Porphyrin Solid-State Thin Layer Photocells

M. A. Fox, J. V. Grant, D. Melamed, T. Torimoto, C.-y. Liu, and A. J. Bard

Chem. Mater. Vol. 10 ( 7 ) page： 1771-1776 1998

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

Three structurally variant alkyl-substituted porphyrins [zinc(II) 2,3,7,8,12,13,17,18-octa-n-decylporphyrin 2, metal(II) meso-5,10,15,20-tetra-n-undecylporphyrin 3 (metal = cobalt, copper, palladium, and zinc), and zinc(II) meso-5,10,15,20-tetrakis(phenoxy-n-nonyl)porphyrin 4] exist as photoconductive insulators and produce significant short circuit photocurrent and open circuit photopotential when irradiated as solid thin films in an indium-tin oxide sandwich cell. Liquid crystalline phase stability, the identity of the inserted metal, and the nature of its supramolecular packing all influence the observed photoelectrochemical response. Porphyrin 2, which has a stable liquid crystalline phase, produces higher steady-state photocurrents than do the corresponding meso-substituted porphyrins 3 and 4, although liquid crystallinity is not an absolute requirement for observation of a photoresponse. Among porphyrins 3, the zinc complex gave the highest steady-state photocurrent. When a phenyl ring orthogonal to the porphyrinic plane was present (as in 4), the observed photovoltaic response was significantly diminished, probably because of difficulties in achieving effective close packing.

Photocatalytic Reduction of Carbon Dioxide in the Presence of Nitrate Using TiO2 Nanocrystal Photocatalyst Embedded in SiO2 Matrices Reviewed

B.-J. Liu, T. Torimoto, and H. Yoneyama

J. Photochem. Photobiol. A : Chem. Vol. 115 ( 2-3 ) page： 227-230 1998

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

Photocatalytic reduction of CO2 in the presence of nitrate ions in various solvents was studied using TiO2 nanocrystals embedded in SiO2 matrices as photocatalysts. Both formate and carbon monoxide were produced as the reduction products of CO2, ammonia as the reduction product of nitrate, and in addition to these products, urea was formed as a major reduction product of both CO2 and NO3-. The selectivity of these reactions was greatly influenced by the kind of solvents used, and with increasing the dielectric constant of solvents, the amount of formate and carbon monoxide produced decreased, while those of urea and ammonia increased. These results suggest that the reduction reaction of nitrate ions was the rate-determining step of the formation of urea.

Characteristic Features of Size-selective Photoetching of CdS Nanoparticles as a Means of Preparation of Monodisperse Particles Reviewed

T. Torimoto, H. Nishiyama, T. Sakata, H. Mori, and H. Yoneyama

J. Electrochem. Soc. Vol. 145 ( 6 ) page： 1964-1968 1998

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

The photocorrosion behavior of CdS nanoparticle colloid containing particles ranging from 4 to 10 nm was investigated using two kinds of monochromatic light, one of which was prepared by passing light from a Xe lamp through interference filters, and the other was obtained by an Ar ion laser. CdS particles were photocorroded to smaller particles until irradiated photons were not absorbed anymore; and the CdS particles obtained after the complete photocorrosion by laser light were much smaller than those resulting from the use of monochromatic light of comparable wavelength. The size selective photocorrosion with the Ar ion laser allowed the preparation of much smaller particles than those in the original colloid. It was found that the rate of photocorrosion decreased when the pH of the colloid was raised, while the fluorescence intensity due to bandgap transition increased. The importance of hole trap sites in the photodissolution of CdS is discussed based on these findings.

Photocatalytic Reduction of CO2 Using Surface-modified CdS Photocatalysts in Organic Solvents

B.-J. Liu, T. Torimoto, and H. Yoneyama

J. Photochem. Photobiol. A : Chem. Vol. 113 page： 93-97 1998

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

The photocatalytic reduction of carbon dioxide on CdS particles with and without surface modification by several kinds of thiol compounds was investigated in various kinds of solvents. Formate and carbon monoxide were obtained as the major reduction products, and the ratio of the former to the latter was largely influenced by the kind of solvents when naked cadmium sulfide was used as the photocatalyst, and with increase of the dielectric constant of the solvent, the ratio increased. Even if CdS particles were modified by thiol compounds, the effect of the solvent was not eventually altered, but the ratio of formate to carbon monoxide became greater with increase of the surface modification of CdS. The observed effect of the surface modification of CdS is discussed in terms of involvement of Cd2+ sites adjacent to surface vacancies of CdS photocatalysts in adsorption of anion radicals of CO2.

Evaluation of Diffusibility of Adsorbed Propionaldehyde on Titanium Dioxide-Loaded Adsorbent Photocatalyst Films from Its Photodecomposition Rate Reviewed

N. Takeda, M. Ohtani, T. Torimoto, S. Kuwabata, and H. Yoneyama

J. Phys. Chem. B Vol. 101 ( 14 ) page： 2644-2649 1997

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

Photocatalytic degradation of gaseous propionaldehyde over TiO2-loaded adsorbent films was investigated after adsorption equilibrium was obtained using silica, alumina, activated carbon, and several kinds of zeolites as adsorbents. Irradiation of one-tenth of the TiO2-loaded adsorbent film caused complete mineralization of the adsorbed substrate in the entire film, although the rates obtained in that case were much lower than one-tenth of the rates obtained with the total area irradiation, indicating a considerable contribution of supply of the adsorbed substrate from the nonirradiated part of the film to the irradiated part. The apparent diffusion coefficient D-app of adsorbed substrate was evaluated by applying the time course of CO2 evolution obtained in the area-selective photodecomposition reaction to a one-dimensional diffusion model. The D-app values estimated for various kinds of TiO2-loaded adsorbent supports explain well the differences in the photodecomposition rates obtained at these photocatalysts. On the basis of experimental results, the effect of diffusion of the adsorbed substrate on the photodecomposition kinetics is quantitatively discussed.

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Papers - TORIMOTO Tsukasa