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Photoelectrochemical Properties of Size-Quantized CdS Thin Films Prepared by an Electrochemical Method 査読有り

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

Langmuir 14 巻 ( 25 ) 頁： 7077-7081 1998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）

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.

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

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

J. Phys. Chem. B 101 巻 ( 14 ) 頁： 2644-2649 1997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）

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.

Effect of Activated Carbon Content in TiO2-loaded Activated Carbon on Photodegradation Behavior of Dichloromethane 査読有り

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

J. Photochem. Photobiol. A: Chem. 103 巻頁： 153-157 1997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 effect of the amount of TiO2 loading on activated carbon support on the photodecomposition of dichloromethane was studied. The apparent adsorption constant of the TiO2-loaded activated carbon for dichloromethane was found to decrease with increase of the fraction of the loaded TiO2. It was found that the apparent rate constant of CO2 evolution became small with increase of the activated carbon content, suggesting that the adsorbed substrate on the activated carbon support was not easily involved in the photodecomposition reaction. However, the use of mixed suspensions of TiO2 and activated carbon showed lower activities than the TiO2-loaded activated carbon for photodegradation of dichloromethane. The role of the activated carbon support in the photodecomposition of dichloromethane is discussed.

Effect of Solvents on Photocatalytic Reduction of Carbon Dioxide Using TiO2 Nanocrystal Photocatalyst Embedded in SiO2 matrices 査読有り

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

J. Photochem. Photobiol. A: Chem 108 巻頁： 187-192 1997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）

Photocatalytic reduction of CO2 in various kinds of solvents was studied using TiO2 nanocrystals embedded in SiO2 matrices (Q-TiO2/SiO2) as the photocatalyst. It was found that the major reduction products were formate and carbon monoxide, and their total amount increased on increasing the concentration of CO2 dissolved. The ratio of formate to carbon monoxide was greatly influenced by the kind of solvent, and increased on increasing the dielectric constant of the solvent. If bulk TiO2 was used as the photocatalyst, the rate of CO2 reduction was low compared to that obtained with Q-TiO2/SiO2, but the ratio of formate to carbon monoxide obtained was not greatly different from that obtained with the Q-TiO2/SiO2. The effect of solvent on the reduction behavior of CO2 is discussed in terms of stabilization of reaction intermediates.

Photoelectrochemical Doping of TiO2 Particles and the Effect of Charge Carrier Density on the Photocatalytic Activity of Microporous Semiconductor Electrode Films 査読有り

T. Torimoto, R. J. Fox, III, and M. A. Fox

J. Electrochem. Soc. 143 巻 ( 11 ) 頁： 3712-3717 1996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）

Irradiation with a very high intensity laser pulse (355 nm) induces blue color in TiO2 powders and films. The blue color, which is assigned to the formation of Ti3+ in the particle, persists in air for several months. With an increase of the concentration of Ti3+ in a given particle, photocatalytic activity is decreased because of a decrease in the thickness of the space-charge layer as deep Ti3+ traps are populated.

Effects of Adsorbents Used as Supports for Titanium Dioxide Loading on Photocatalytic Degradation of Propyzamide 査読有り

T. Torimoto, S. Ito, S. Kuwabata, and H. Yoneyama

Environ. Sci. Technol. 30 巻 ( 4 ) 頁： 1275-1281 1996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）

Photodecomposition in aqueous solution of 3,5-dichloro-N-(3-methyl-1-butyn-3-yl)benzamide, whose popular name is propyzamide, was investigated using naked TiO2 and TiO2-loaded adsorbent supports as photocatalysts. The adsorbent supports used were zeolite (mordenite), silica, and activated carbon. The use of adsorbent supports was found to enhance the rate of mineralization of propyzamide and to reduce the concentration of solution-phase intermediates. The experimental results suggest that the adsorbent support concentrates a target substrate of low solution-phase concentration on its surface, providing the substrate-rich environment at the adsorbent/TiO2 interface, This concentration effect results in an enhanced rate of propyzamide mineralization. The intermediates are also retained on the adsorbent support and subsequently decomposed, thereby reducing the concentration of possibly toxic intermediates in the bulk solution.

Preparation and Properties of Size-Quantized TiO2 Particles Immobilized in Polyvinylpyrrolidinone Gel Films 査読有り

H. Uchida, S. Hirao, T. Torimoto, S. Kuwabata, T. Sakata, H. Mori, and H. Yoneyama

Langmuir 11 巻 ( 10 ) 頁： 3725-3729 1995年

記述言語：英語掲載種別：研究論文（学術雑誌）

Size-quantized TiO2 particles immobilized in polyvinylpyrrolidinone (Q-TiO2/PVPD) films, were prepared by electrophoretic deposition of Q-TiO2 colloids in 2-propanol in the presence of PVPD as a stabilizing agent. The Q-TiO2 prepared had the average diameter of 3.3 nm with a standard,deviation of 1.1 nm. Illumination of the Q-TiO2/PVPD film in water-free 2-propanol resulted in the production of acetone as a sole oxidation product and Ti3+ species as the reduction product, and when the Ti3+ species was accumulated, hydrogen evolution began to occur. The same was true for bulk TiO2 particles immobilized in the same matrix, which were prepared by soaking the Q-TiO2/PVPD film in water, but the rate of these photoinduced reactions was much slower than that of the Q-TiO2. The photoformation of Ti3+ in the TiO2 particles was suppressed by introduction of NO3- to 2-propanol, suggesting that the formation of the Ti3+ species is controlled by kinetics of electron transfer to accepters in solution.

Nanometric Surface Design of Size-quantized Semiconductor Microcrystals 招待有り

H. Yoneyama and T. Torimoto

Adv. Mater. 7 巻頁： 492-494 1995年

半導体超微粒子の調製と光触媒活性招待有り

米山　宏，鳥本　司

電気化学 63 巻頁： 2-5 1995年

半導体超微粒子の固定化とその光触媒への応用招待有り

米山　宏，鳥本　司

表面科学 16 巻頁： 173-179 1995年

Effect of Inert Supports for Titanium Dioxide Loading on Enhancement of Photodecomposition Rate of Gaseous Propionaldehyde 査読有り

N. Takeda, T. Torimoto, S. Sampath, S. Kuwabata, and H. Yoneyama

J.Phys.Chem. 99 巻 ( 24 ) 頁： 9986-9991 1995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）

Effects of the use of inert supports for TiO2 loading on photocatalyzed decomposition of propionaldehyde in the gas phase was investigated for mordenite support with various amounts of TiO2 loading and for several kinds of supports such as other zeolites, alumina, silica, and activated carbon. The adsorption constant and the amount of adsorption of propionaldehyde were evaluated for TiO2-loaded supports by obtaining Langmuir adsorption isotherms. By correlating these parameters to the photodecomposition rates of propionaldehyde, the involvement of the support in the photodecomposition reaction is clarified. The photocatalytic activity of TiO2 on mordenite having various amounts of TiO2 loading increases with increase in the amount of loaded TiO2 up to an optimum value (ca. 50 wt %), beyond which a decreasing tendency of the activity appeared. In the region of ascending activity, plenty of adsorbed substrate is available and the activity is controlled by the content of TiO2, while in the region of descending activity, the decrease in the amount of adsorbed substrate due to a decrease in the occupancy of the support by the TiO2 loading is responsible for the activity decrease. The photocatalytic activities are greatly influenced by the kind of inert supports used and show a volcano type dependence on the adsorption constant of the TiO2-loaded supports. In cases where the adsorption constant is low, the decomposition rate is determined by the amount of adsorbed substrate, while if the adsorption constant is very high, plenty of adsorbed substrate is available on the support, but it is not mobile to the loaded TiO2. We conclude that the use of an inert support having a medium adsorption constant is necessary to obtain the highest activity, where a high amount of adsorbed substrate that can be supplied to TiO2 particles is available.

Preparation of CdS Microcrystals Covalently Bound with Viologen Groups and Their Photoelectrochemical Properties 査読有り

T. Torimoto, K. Maeda, T. Sakata, H. Mori, and H. Yoneyama

Chem. Lett ( 6 ) 頁： 977-980 1994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）

CdS microcrystals (Q-CdS) covalently bound with 1-decyl-1'-(3-mercapto) propyl-4,4'-bipyridinium were prepared. The surface viologen groups picked up photo-generated electrons in the conduction band of Q-CdS particles, causing a decrease of their emission. Irradiation of these particles resulted in new absorption peaks which are assigned to viologen radical cation monomers and their dimers. The photo-reduced viologen groups can mediate photo-generated electron transfer from Q-CdS to methylene blue in solution.

Photoinduced Electron Transfer from Zinc Sulfide Microcrystals Modified with Various Alkanethiols to Methyl Viologen 査読有り

H. Inoue, N. Ichiroku, T. Torimoto, T. Sakata, H. Mori, and H. Yoneyama

Langmuir 10 巻 ( 12 ) 頁： 4517-4522 1994年

記述言語：英語掲載種別：研究論文（学術雑誌）

Zinc sulfide microcrystals fully modified with ethanethiol, butanethiol, and octanethiol of about 4 nm diameter with a narrow size distribution were prepared. The rate of photoinduced electron transfer from the microcrystals to methyl viologen (MV(2+)) in solution showed a linear dependence on the concentration of MV(2+), while at bulk ZnS particles the Langmuir-Hinshelwood type kinetics prevailed. It is concluded from the observed logarithmic dependence of the rate constant on the inverse of the chain length of the modified alkanethiols that the electron tunneling controls the photoinduced reduction of MV(2+).

Photoelectrochemical Properties of Size-Quantized CdS Microcrystals Modified with Various Amounts of Viologen-Functionalized Thiol 査読有り

T. Torimoto, K. Maeda, J. Maenaka, and H. Yoneyama

J. Phys. Chem. 98 巻 ( 51 ) 頁： 13658-13664 1994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）

Size-quantized CdS microcrystals (Q-CdS) modified with various amounts of electroactive 1-decyl-1'-(3-mercaptopropyl)-4,4'-bipyridinium dibromide (VSH) and electroinactive decanethiol were prepared. The surface-modified VSH was photoreduced by irradiation of Q-CdS to give both dimeric and monomeric radical cations of the viologen, and the formation of the former was enhanced by increasing the amount of the surface-bound VSH. Kinetic analyses revealed that the rate constants for the reduction of the surface-modified VSH and for the reoxidation of the produced radical cations were independent of the amount of the VSH, Q-CdS having the higher amount of VSH showed the higher activity for electron transfer to methylene blue in solution, evidencing that the surface-bound viologen mediated electron transfers from Q-CdS to the electron acceptor in solution.

Effect of Surface Charge of 4-Aminothiophenol-Modified PbS Microcrystal Photocatalysts on Photoinduced Charge Transfer 査読有り

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

J.Phys.Chem. 98 巻 ( 11 ) 頁： 3036-3043 1994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 kinds of quantized PbS microcrystals modified with 4-aminothiophenol (4-ATP/Q-PbS) having different surface coverage were prepared by using two different concentration ratios of [Pb2+]/[S2-] in the synthesis of the 4-ATP/Q-PbS particles. The rates of photoinduced reduction of methylviologen on the two kinds of 4-ATP/Q-PbS particles were influenced by the kind of hole scavengers (sodium tartrate or triethanolamine) and the pH of solutions, and the higher reduction rates were obtained under conditions where the higher amount of adsorption of the hole scavenger occurred. High reduction rates of methylviologen were obtained at the photocatalyst having a high coverage of the surface modifier, because high electrostatic attractive interactions between the hole scavenger and the surface are operative when tartrate was used as a hole scavenger and a high amount of adsorption sites due to a high coverage of the surface modifier are available when triethanolamine was used. The validity of such interpretation was supported by kinetic analysis based on rate equations. Furthermore, it was found that inert electrolyte anions such as ClO4- had a retarding action for the photoreduction of methylviologen when tartrate was used as the hole scavenger, as a result that the adsorbed tartrate anions were replaced by the inert electrolyte anions depending on their concentrations. The adsorbability of inert electrolyte anions (Cl-, Br-, and ClO4-) as well as tartrate anions was found to be influenced by the degree of surface modification of the Q-PbS particles with 4-aminothiophenol. As for the case of using electronically neutral triethanolamine as the hole scavenger, the inert electrolyte anions did not influence the photoreduction rate of methylviologen.

Surface Structures of PbS Microcrystals Modified with 4-Hydroxythiophenol and Their Influences on Photoinduced Charge Transfer 査読有り

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

J. Am. Chem. Soc., 115 巻 ( 5 ) 頁： 1874-1880 1993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）

Quantized PbS microcrystals capped with 4-hydroxythiophenol (ArSH) were prepared using two different concentration ratios of [Pb2+]/[S2-] = 1.2 and 3.0 with fixed concentration ratio of [ArSH]/[Pb2+] = 4.0. The size distributions of the prepared PbS particles were determined. Two different surface structure models of fully occupied and partially occupied surface sites of PbS microcrystals with the capped ArSH are assumed, and chemical compositions of these particles are evaluated by taking the experimentally determined particle size distributions into account. By examining the fitness of the chemical analyses data of the PbS particles to the evaluated compositions, it is proposed that the PbS particles prepared [Pb2+]/[S2-] = 3.0 had the capped ArSH in all the surface sites, while PbS particles prepared with [Pb2+]/[S2-] = 1.2 had some surface sites free from the modifier. The proposed surface structures of the two kinds of PbS microcrystals were rationalized by experimentally found differences both in agglomeration tendencies of the particles and in the effect of the addition of Pb2+ ions on the rate of photoinduced reduction of methyl viologen on the particles.

Effects of Size Quantization of Zinc Sulfide Microcrystallites on Photocatalytic Reduction of Carbon Dioxide 査読有り

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

Chem. Lett. ( 9 ) 頁： 1483-1486 1990年

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