Sadao Murasawa

An efficient TiO2 thin-film photocatalyst : photocatalytic properties in gas-phase acetaldehyde degradation

Abstract A semitransparent TiO2 film with extraordinarily high photocatalytic activity was prepared on a glass substrate by sintering a TiO2 sol at 450 °C. Crystallographic analysis by X-ray diffraction and Raman spectroscopy showed that the film was purely anatase. The photocatalytic properties of the film were investigated by measuring the photodegradative oxidation of gaseous acetaldehyde at various concentrations under strong and weak UV light irradiation conditions. The photocatalytic activity of the film was higher than that of one of the most active commercial TiO2 powders, Degussa P-25. The kinetics of acetaldehyde degradation as catalyzed by the TiO2 film as well as by P-25 powder were analyzed in terms of the Langmuir-Hinshelwood model. It is shown that the number of adsorption sites per unit true surface area is larger with the TiO2 film, as analyzed in the powder form, than with P-25 powder. Meanwhile, the first-order reaction rate constant is also much larger with the film than with P-25 powder. Moreover, under most experimental conditions, particularly with high concentrations of acetaldehyde and weak UV illumination intensity, the quantum efficiency was found to exceed 100% on an absorbed-photon basis, assuming that only photo-generated holes play a major role in the reaction. This leads to the conclusion that the photodegradative oxidation of acetaldehyde is not mediated solely by hydroxyl radicals, generated via hole capture by surface hydroxyl ions or water molecules, but also by photocatalytically generated superoxide ion, which can be generated by the reduction of adsorbed oxygen with photogenerated electrons.

Laser plate printing system using TiO2 photoreceptor

The halftone dot image formed on a Titanium Dioxide (TiO2) photoreceptor with liquid toner has high resolution and sufficient sharpness. We have applied these materials to the graphic arts industry in two ways: one is the application to a direct digital color proofing (DDCP) system, the other is to a direct digital plate printing (DDPP) system. In the DDPP system, dot image is directly recorded on a TiO2 photoreceptor (TiO2 press plate) without using dot film. The exposure light source is an He-Ne laser which is the same light source as that of the DDCP system. Therefore, a proofing image and color separation press plates are produced using the same apparatus and materials. In offset printing, a TiO2 press plate is capable of producing a high quality print. Dots on the paper have fine shape and uniform density distribution. The quality is little affected by the increase of fountain solution. The TiO2 press plate is also applicable to high quality color printing because of its consistent printing quality and high stability of plate size.

Direct digital color proofing system using titanium dioxide photoreceptor

High quality and high work efficiency direct digital color proofing (DDCP) system is an important demand in pre-press industry. This system requires halftone dot reproducibility, high-speed output, and easy image processing. We have reported that the fine image can be obtained by electrophotography using both titanium dioxide (TiO2) photoreceptor and liquid toner. In these reports, we proposed that this system is applicable to the graphic art industry since the image has high resolution and sufficient sharpness. A large number of attempts have been made to apply the electrophotographic method to the color proofing process. However, color proofer by electrophotography faces some problems. One of the issues related to the electrographic process is the consistency, i.e., color density and dot area. We have solved this problem by controlling the voltage applied to the counter electrode, which compensates for the effective potential difference during development. In order to confirm the possibility of DDCP system with TiO2 photoreceptor, we evaluated the image made by a prototype color proofer. The purpose of this paper is to evaluate the image quality and show the novel DDCP system with TiO2 photoreceptor and liquid toner.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.