Tetsuro Kawahara

Photocatalytic activity of rutile-anatase coupled TiO2 particles prepared by a dissolution-reprecipitation method.

Rutile TiO(2) particles were partly dissolved into aqueous solutions of H(2)SO(4), and the Ti(4+) ions were reprecipitated by adding NH(3) aq. Rutile-anatase coupled TiO(2) particles were prepared by heating the solid recovered after centrifugation of the suspension. The content of anatase (c(A), wt%) could be controlled arbitrarily by changing the dissolved amount of rutile. The photocatalytic activity for the gas-phase oxidation of acetaldehyde was evaluated. The first-order rate constant, k, strongly depended on both c(A) and heating temperature (T(c)), increasing with an increase in T(c) at T(c)</=800 degrees C. The sample with c(A)=0.5 wt% prepared at T(c)=800 degrees C exhibited a much higher level of activity (k=0.94 h(-1)m(-2)) than those of pure rutile (k=0.08 h(-1)m(-2)) and anatase (k=0.34 h(-1)m(-2)). This remarkable enhancing effect was explained mainly in terms of photoinduced interfacial electron transfer from anatase to rutile.

Evaluation of Photocatalytic Activity by Dye Decomposition

A novel rapid evaluation method for the photocatalytic activity of TiO2 thin films was developed. An organic dye with a polyvinyl alcohol (PVA) binder was spin coated on the TiO2 thin film, and the decrease in the absorbance of the dyes absorption peak during UV light irradiation was measured. Acid Blue 9 (Brilliant Blue FCF; CI-42090) could be used as the probe, while Methylene Blue (CI-52015) was not applicable to this method because of the reversible color change after the UV irradiation was stopped. PVA has virtually no interaction with oxidizing radicals, therefore, it is regarded as a simple binder holding dye molecules in the coated dye-PVA film. It was found that the ambient humidity during the UV irradiation strongly accelerates the discoloration rate of the dye, probably due to the increase in the photogenerated oxidizing radicals on the TiO2 surface. This dye discoloration could be explainedby the one-dimensional diffusion model with a first order reaction.

A Large-Area Patterned TiO2/SnO2 Bilayer Type Photocatalyst Prepared by Gravure Printing

Anatase TiO2 films (thickness = 50 nm) were formed in shape of stripes (width = 1.6 mm, interval = 0.4 mm) by gravure printing on commercially available SnO2 coated soda-lime glass substrates (dimension = 300 × 300 mm). Its photocatalytic activity was examined for the gas-phase oxidation of CH3CHO in comparison with a simple TiO2 photocatalyst formed on a silica glass. The patterned TiO2/SnO2 bilayer type photocatalyst showed a high photocatalytic activity in an H2O bearing atmosphere. On the other hand, neither the patterning nor stacking effect was observed for the same reaction under dry conditions. These results could be explained in terms of the reducing potential of the electrons in the conduction band of the SnO2 layer.

Ag(core)–AgCl(shell) standard microelectrode-loaded TiO2

Micrometer-sized Ag(core)-AgCl(shell) composite crystals have been formed on TiO2 thin films by a two-st epelectrochemical method to provide information on the thermodynamic condition for efficient photoinduced interfacial electron transfer.

Low-Temperature Photocleaning of Sulfur-Poisoned Au Nanoparticles on Titanium Dioxide Film

Anatase-type TiO 2 films were formed on SiO 2 film-coated glass substrates by a sol-gel method. Nanometer-sized gold particles were highly dispersed on the surfaces of the TiO 2 film (Au/TiO 2 -TF) and TiO 2 particles (Au/TiO 2 -P) using a deposition-precipitation method. X-ray photoelectron spectra of Au/TiO 2 -TF adsorbed with sulfur from Sg molecules indicated that the sulfurs are selectively adsorbed on the Au surfaces with the two kinds of chemisorption modes, atomic and molecular adsorption (S-Au/TiO 2 -TF). Light-irradiation (λ ex > 300 nm) to S-Au/TiO 2 -TF and S-Au/TiO 2 -P in water at 298 K gave rise to desorption of the sulfur with the Au particle size almost maintained. Kinetic analysis showed that the rate constant for the sulfur desorption from S-Au/TiO 2 -TF in an opened reaction system is larger than that from S-Au/TiO 2 P in a closed reaction system by a factor of ca. 3.6.

Photoreaction of a ZnO gel film chemically modified with β-diketones

Chelate formation is confirmed by a red shift of the n → π* absorption peak of benzoylacetone (BzAcH) from 309 to 336 nm with its addition to a sol containing Zn2+ ions. The chelate bonds between Zn2+ and BzAc− are mostly maintained in the gel film prepared from the sol. Irradiation of the gel film by a Xe lamp with a cut filter (λex > 300 nm) in the presence of H2O leads to decomposition of the chelate ring. As a result of the photolysis, ZnO–H groups, CH3CHO and other carbonyl compounds are generated with the lost of CH3 groups of the BzAc− ligand and H2O involved in the film. INDO/S calculations on a model complex (Zn(BzAc)(OEt)) assign the n → π* absorption to the electronic transition from a non-bonding molecular orbital (MO) distributed mainly at the phenyl group to an anti-bonding MO localized at the CO bonds. On the basis of these results, a photo-induced hydrolysis mechanism was presented to explain the formation of positive-type patterned ZnO films.

Positive-type patterned ZnO films prepared by a chemically modified sol-gel method

Sol-gel methods have been conveniently used for preparing various metal-oxide thin films at relatively low temperatures. Particularly, chemical modification with β-diketones allows us to carry out most of the sol-gel procedures in the atmosphere owing to the suppression of hydrolysis and condensation of the reactive metal alkoxides [1–5]. Further, the chemically modified gel films exhibit photosensitivity, e.g., their solubility in various solutions changes significantly with light irradiation [6, 7]. Taking advantage of this phenomenon, Tohge and co-workers have produced patterned oxide films such as Al2O3 [8], TiO2 and ZrO2 [6]. These patterned films are attracting considerable interests as onboard (photo)catalysts [9–11] in addition to optical and electrical applications [6–8]. On the other hand, ZnO is an n-type semiconductor with a band gap of ca. 3.3 eV, being utilized as transparent electrodes in solar cells and liquid crystal displays. All the patterned films prepared so far by the chemically modified sol-gel method were negative-type, i.e., the irradiated areas are left as films. This letter reports that a positive-type ZnO patterned film is formed as a result of irradiation on a gel film chemically modified with benzoylacetone. The procedure for preparing ZnO patterned films using the chemically modified sol-gel method is shown in Fig. 1. After zinc acetate, dehydrate (3.76 g) had been dissolved into a mixed solution of ethanol (40 mL) and monoethanolamine (MEA, 0.73 mL), 1benzoylacetone (BzAcH, 2.78 g) was added. To the solution, ethanol (10 mL) and water (6.17 mL) were added, and then the mixture was refluxed at 80 ◦C for 3 h with stirring. The resulting sol was coated on quartz

Synthesis of a Net-Worked Strontium-O-Phenylene-S-Tellurium Hybrid Co-polymer Having a Two-Step Electron Transfer Nature

A strontium-O-phenylene-S-tellurium hybrid co-polymer was prepared by initially reacting 4-hydroxythiophenol with tellurium ethoxide, followed by a subsequent reaction with strontium isopropoxide, and the electronic behavior of the co-polymer was examined. From the results of ESR spectral examinations and ab initio calculations regarding the co-polymer models, the co-polymer was deduced to have a function of two-step electron transfer from the phenylene group to the strontium atom via the tellurium atom.

Syntheses and Electronic Behaviors of Novel Networked Alternating Organic Moiety‐Ruthenium Hybrid Copolymers

The reaction of ruthenium chloride with organic dithiols gave ruthenium‐organic moiety hybrid copolymers. ESR and XPS spectral examinations showed that an electron transfer from the organic moiety to the ruthenium atom took place.

Syntheses and Electronic Behaviors of Osmium‐Organic Moiety Hybrid Materials

Several alternating osmium‐organic moiety hybrid materials were prepared by reacting osmium chloride with organic diols and dithiols. Osmium‐organic moiety units over 60% were thought to be involved in the materials. ESR and XPS spectral analyses indicated that an electron transfer from an organic phenylene moiety to the osmium atom with a partial reduction of the osmium atom took place.