Design and Development of Hyper Active Photocatalyst

本研究旨在合理化半导体粉末的光催化活性的最决定性因素是表面积和结晶度的假设。表面积越大，反应底物分子在表面吸附越多，活性越高，而颗粒的结晶度越高，引起电子-空穴复合的晶体缺陷越小。因此，期望具有大表面积和高结晶度的半导体粒子具有较高的光催化活性。我们开发了不用水制备氧化钛的新方法；(1)有机介质的水热结晶（HyCOM），(2)热分解（TD），(3)醇中的转移水解结晶（THyCA）。所制得的氧化钛粉体具有表面积大、锐钛矿结晶度高的特点。正如这些物理性质所预期的那样，这些粉末在曝气和脱氧条件下都表现出光催化活性，这明显高于高活性的市售氧化钛（IV） （Degussa P-25）。从而确定了超高半导体光催化剂的设计原理，并开发了新的合成方法。利用飞秒激光系统，阐明了电子-空穴复合的降低率。

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.