Development of Hyper Active Semiconductor Photocatalyst

本研究旨在验证半导体粉末光催化活性最主要的决定因素是比表面积和结晶度的假设。比表面积越大，表面吸附的反应底物分子越多，活性越高，而颗粒结晶度越高，引起电子-空穴复合的晶体缺陷越小。因此，人们期望具有大比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)醇中转移水解结晶(ThyCa)。所制备的钛(IV)氧化物粉末具有较大的比表面积和较高的锐钛矿相结晶度。从这些物理性能来看，这些粉末在充气和除氧条件下都表现出明显高于高活性商用氧化钛(Degussa P-25)的光催化活性。从而确定了超高纯度半导体光催化剂的设计原则，开发了新的合成方法。利用飞秒激光系统，阐明了电子-空穴复合的减慢速率。

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.