Photocatalysis on titanium oxide catalysts: Approaches in achieving highly efficient reactions and realizing the use of visible light

Abstract

The photocatalytic reactivities of various Ti-based photocatalysts have been investigated for various different types of reactions in order to achieve as highly efficient photocatalytic reactivities as possible. The reactivity of powdered TiO2 is dramatically enhanced by the addition of small amounts of Pt which initiates an effective charge separation of the photo-formed electrons and holes. The highly dispersed titanium oxide species prepared and encapsulated within the zeolite cavities as well as into the SiO 2 matrices exhibit high photocatalytic reactivities due to the high reactivities of their charge transfer excited states. With regard to the use of visible light, ion implantation of metal ions such as Cr or V into powdered TiO2 catalysts has been found to modify the electronic state of TiO 2 , resulting in the shift of the absorption band to longer wavelength regions, i.e., into the visible light region. The extent of the shift strongly depends on the type and concentration of the implanted metal. The present study focuses on the preparation of the photocatalysts, a detailed characterization of the active sites and their dynamics, the direct detection of the reaction intermediate species, as well as a clarification of the mechanisms behind the observed photocatalytic reactions at the molecular level. This work significantly contributes to advances in the design of photocatalysts which will be able to operate efficiently and effectively not only under UV irradiation but, most ideally, under visible light.