Abstract
Working mechanisms as photocatalyst of semiconductor particles suspended in solution are reviewed with emphasis on photoelectrochemical aspects. Several techniques useful for determination of electronic energy levels of the photocatalysts and for enhancing apparent photocatalytic activities are described, and their utilities are shown in photodecomposition of water on various kinds of semiconductor particles. Studies on detoxification of inorganic and organic wastes are collected as a promising application field of suspended semiconductor photocatalysts. Finally, significance of the use of quantized semiconductor particles as photocatalysts is discussed.