THE ROLE OF OXYGEN IN PHOTOOXIDATION OF ORGANIC-MOLECULES ON SEMICONDUCTOR PARTICLES

The kinetics of O2 reduction accompanying oxidation of organic compounds on photocatalytic semiconductor particles is analyzed. The rate-controlling processes are defined and the electron reactivities are derived for two cases: A, electrons moving freely in the semiconductor particle and reacting with O2 anywhere on its surface and B, electrons trapped at or near the surface of the semiconductor particle and transferred from the traps only to nearby O2 molecules. Of these, case B appears realistic. Taking the properties of TiO2 particles as an example, it is shown that a sufficiently fast O2 reduction rate, of essence for attaining a high quantum efficiency in the photoassisted oxidation of organics, is achieved only when catalytic sites are incorporated in the TiO2 surface.