Yoshimoto Abe

Photocatalytic decomposition of water into H2 and O2 by a two-step photoexcitation reaction using a WO3 suspension catalyst and an Fe3+/Fe2+ redox system

H2 and O2 gas evolution in a stoichiometric ratio (H2:O2 = 2:1) has been realized over a RuO2-WO3 photocatalyst suspended in an aqueous solution containing an Fe3+/Fe2+ redox system. O2 gas was evolved and Fe3+ ions were reduced to Fe2+ ions on a WO3 powder catalyst excited by visible light at less than 460 nm and UV light. Fe2+ ions excited by UV light at less than 280 nm were oxidized back to Fe3+ ions with the evolution of H2 gas. The reaction mechanism is similar to the Z-scheme in photosynthesis.

PHOTOSENSITIZATION OF A POROUS TIO2 ELECTRODE WITH MEROCYANINE DYES CONTAINING A CARBOXYL GROUP AND A LONG ALKYL CHAIN

Porous TiO2 electrodes sensitized using merocyanine dyes containing a carboxyl group and a long alkyl chain, in particular 3-carboxymethyl-5-[2-(3-alkyl-2-benzothiazoli- nyldene)ethylidene]-2-thioxo-4-thiazolidinone, showed remarkably high solar–energy efficiency (4.2%, AM-1.5, 100 mW cm−2).

Photoelectrochemical decomposition of water on nanocrystalline BiVO4 film electrodes under visible light

The nanocrystalline BiVO4 film electrode on conducting glass showed an excellent efficiency (IPCE = 29% at 420 nm) for the decomposition of water under visible light.

Preparation and properties of polysilsesquioxanes: Polysilsesquioxanes and flexible thin films by acid‐catalyzed controlled hydrolytic polycondensation of methyl‐ and vinyltrimethoxysilane

Polymethylsilsesquioxane (PMS) and polyvinylsilsesquioxane (PVS) were prepared by acid-catalyzed controlled hydrolytic polycondensation of methyl- and vinyltrimethoxysilane (MTS and VTS), respectively. The spinnabilities and molecular weights of polysilsesquioxanes were easily controlled by the reaction conditions, such as the molar ratios of water, hydrochloric acid, and methanol to MTS or VTS; nitrogen flow rate; temperature; and stirring rate. PMS and PVS showed spinnability of more than 200 cm when their molecular weights were up to 42,000 (PMS) and 19,000 (PVS) Mw. Transparent, colorless, and flexible films of 0.02–0.10 mm thick were prepared by casting a 20 wt % acetone–methanol (V/V = 1) solution of PMS and PVS on a polymethylpentene shale, followed by heating at 80°C for 3 weeks. The tensile strength of the films, approximately 26 (PMS) and 17 (PVS) MPa, was found to be correlated with the structure of the polysilsesquioxanes. The surface contact angle and electroconductivity of films were also measured.

Stoichiometric water splitting into H2 and O2 using a mixture of two different photocatalysts and an IO3−/I− shuttle redox mediator under visible light irradiation

The stoichiometric splitting of water into H2 and O2 (H2/O2 = 2) under visible light irradiation (lambda > 420 nm) took place for the first time using a mixture of Pt-WO3 and Pt-SrTiO3 (Cr-Ta-doped) photocatalysts and an IO3-/I- shuttle redox mediator.

Preparation of continuous zirconia fibres from polyzirconoxane synthesized by the facile one-pot reaction

A one-pot reaction of zirconium oxychloride octahydrate (ZOC) with ethyl acetoacetate (Hetac) in the presence of triethylamine was investigated. The reaction was carried out in molar ratios of Hetac/ZOC=1.0, 1.5, 2.0 to give highly viscous solutions with good spinnability and stability to self-condensation. Polyzirconoxanes (PZOs) were isolated as white powders by reprecipitation of the solutions with tetrahydrofuron (THF)-hexane that were soluble in acetone, methanol and THF. The molecular weight of PZO was Mn=1000–2000, and was dependent on the molar ratio and the reaction time. Dry spinning of the solution (Hetac/ZOC=1.5) containing 3mol% tris(acetylacetonato)yttrium [Y(acac)3] gave continuous precursor fibres (3.0Y–PZO). Yttria stabilized zirconia fibres of 12–18 μm diameter with a tensile strength of 1.4GPa were obtained by heat treatment of the 3.0Y–PZO at 1100 or 1200 °C. The fibre consisted of submicrometre-sized particles of tetragonal crystallites.

Preparation and properties of silicon-containing polymer hybrids from 3-methacryloxypropyltrimethoxysilane

The preparation of organic‐inorganic polymer hybrids consisting of carbon‐carbon and siloxane chains was investigated by radical polymerization of 3-methacryloxypropyltrimethoxysilane (MAS) followed by acid-catalyzed hydrolytic polycondensation. The condensation of poly(3-methacryloxypropyltrimethoxysilane) (S-PMA) of various molecular weights Mn = 830‐12000 prepared by polyaddition provided transparent and flexible free-standing hybrid gel films. The mechanical properties of these films were highly dependent on the carbon‐carbon chain length: with an increase in the carbon‐ carbon chain length, the elasticity of gel films increased, while the tensile strength and Young’s modulus decreased. Hydrolyzability of S-PMA decreased with an increase in the carbon‐carbon chain length, resulting in the formation of rubber-like films with flexibility. # 1998 John Wiley & Sons, Ltd.

Preparation of monolithic SiO2TiO2 gels by condensation polymerization of silicic acid and titanium chelates

Abstract The preparation of monolithic gels as a precursor for SiO 2 TiO 2 glasses via polytitanosiloxanes was investigated. The gels were obtained from polytitanosiloxanes formed by condensation polymerization of titanium chelates and silicic acid. Silicic acid was extracted with tetrahydrofuran from an aqueous sodium metasilicate solution neutralized with hydrochloric acid. Titanium chelates used were bis(acetylacetonato)titanium diisopropoxide (ATP) and bis(ethyl acetoacetato)titanium diisopropoxide (ETP). Monolithic gels with a TiO 2 content of less than 20 mol% were formed by the reaction of silicic acid with ATP, whereas the reaction with ETP provided transparent monolithic SiO 2 TiO 2 gels of 5.7–94 mol% TiO 2 . Heat treatment of the gels gave monolithic SiO 2 TiO 2 glasses.

Preparation and properties of polysilsesquioxanes. Function and characterization of coating agents and films

Abstract Coating characteristics of polysilsesquioxanes with various molecular weights prepared by acid-catalyzed hydrolytic polycondensation of trimethoxysilane RSi(OMe) 3 (R=Me, Vinyl) were investigated in relation to the structure. Homogeneous, smooth and crack-free coating films of thickness from 0.25 to 0.95 μm were prepared by 1–10 times dip-coating of an acetone–methanol solution of polysilsesquioxanes on polymer, metal and ceramic substrates. Their mechanical, optical and electrical properties were investigated. The adhesion and hardness of coating films showed the maximum values based on the evaluation of JIS (Japanese Industrial Standard) K5400. They also increased with increasing molecular weight, T 3 unit of polysilsesquioxanes, heating time and sintering temperature. The coating films were revealed to be thermally stable on heating to 800°C. The refractive index of coating films decreased gradually with increasing temperatures up to about 800°C. The transmittance of coating films was higher than 98% at 500 nm. The surface resistivity of the coating films increased with the increase of sintering temperature.

Preparation of SiO2TiO2 fibers from polytitanosiloxanes

Abstract Continuous oxide fibers SiO 2 TiO 2 were obtained by drying spinning of precursor fibers from polytitanosiloxanes (PTS) prepared by the reaction of silicic acid (SA) with titanium chelate (PTP) in the molar ratio of SA/PTP = 0.5 (PTS-0.5) and 1.0 (PTS-1). The precursor fibers, being golden-yellow, turned black and then white on pyrolysis. The fibers underwent decomposition with removal of organic groups to form black fibers at 200–500°C and white fibers at about 1000°C. Crystallization of TiO 2 took place at 850°C (PTS-0.5) and 950°C (PTS-1). Rearrangement of SiOTi linkage of the polymer back-bone into SiOTi m ay lead to the formation of TiO 2 clusters and subsequent crystallization of TiO 2 .