Visible Light Responsive Pristine Metal Oxide Photocatalyst: Enhancement Of Activity By Crystallization Under Hydrothermal Treatment

摘要

Photocatalysts for purification of indoor air should induce complete oxidative decomposition of organic pollutants into carbon dioxide (CO_2), i.e., mineralization, preferably under irradiation of visible light (vis) emitted from lighting devices such as fluorescent light tubes. Recently, development of vis-responsive photocatalysts has been accelerated due to findings of activity of surface-modified tungsten(VI) oxide (WO_3) particles for molecular oxygen reduction. Abe et al. reported that platinum-loaded WO_3 particles exhibited vis-induced photocatalytic activity as high as that of titanium(IV) oxide (TiO_2) particles under ultraviolet-light (UV) irradiation.rnThe activity of semiconductor photocatalysts depends on physical and chemical properties. Since recombination of photoexcited electrons and holes seems to occur at crystal lattice defects, crystallinity (i.e., the extent of crystallization) should be one of the main factors for photocatalytic reaction efficiency. However, there have been few studies indicating a correlation between crystallinity, recombination rate, and photocatalytic activity. It is difficult to evaluate the effect of only one property on photocatalytic activity excluding effects of other properties. For example, crystallization of amorphous metal oxides by heat treatment resulted in simultaneous changes in other properties such as specific surface area, which is another main factor for reaction efficiency.