Design and Development of Hyper Active Photocatalyst

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This study aimed at rationalization of the hypothesis that the most decisive factors controlling the photocatalytic activity of semiconductor powders is surface area and crystallinity. The larger the surface area becomes, the more the reaction substrate molecules are adsorbed on the surface, to result in the higher activity, while the higher the crystallinity of particles, the smaller the crystal defect inducing electron-hole recombination. Therefore it is expected that semiconductor particles having large surface area and being high crystallinity should exhibit high photocatalytic activity. We have developed the novel method of titanium(IV) oxide preparation without the use of water; (1) Hydrothermal Crystallization of Organic Media (HyCOM), (2) Thermal Decomposition (TD), and (3) Transfer Hydrolytic Crystallization in Alcohols (THyCA). The titanium(IV) oxide powders thus prepared had large surface area and high crystallinity of anatase crystallites. As expected from these physical properties, these powders showed the photocatalytic activity, under both aerated and deaerated conditions, which is marked higher than that of highly active commercially available titanium(IV) oxide (Degussa P-25). Thus, we have confirmed the principle for the design of ultra-highly semiconductor photocatalyst and developed the novel synthetic methods. By using femtosecond laser systems, the reduced rate of electron-hole recombination was clarified.