Titanium dioxide (TiO2) has three different crystalline phases: brookite, anatase, and rutile. One of these phases, anatase, was found to be able to decompose water molecules to hydrogen and oxygen under ultraviolet (UV) rays [1]. This discovery was extended to the development of photocatalysts for the decomposition of organics. The photochemical decomposition (degradation, mineralization, etc.) of polluting and hazardous materials by using photocatalysts is considered to be one of the promising processes to solve environmental problems [2-10]. Numerous studies on photocatalysts have been performed from various viewpoints, and their various applications have been proposed for air and water puriƒcation, hazardous waste remediation, water disinfection, and so forth [8]. Strong and urgent demand on the conservation of global environment and its protection from pollution has been instrumental in promoting strongly the research activities in photocatalysis.