Theoretical Kinetic Analysis of Heterogeneous Photocatalysis: The Effects of Surface Trapping and Bulk Recombination through Defects

A theoretical kinetic model is developed to study the functions of defects in photocatalysis, and the kinetic courses that are related to the defects on the surface and in the bulk are systematically analyzed. The analysis gives a description of the functions of the defects on the surface. It is found that increased speed of surface trapping leads to decreased photocatalytic performance. Surface trapping of electrons at defects is not sufficient to increase the photocatalytic activity, which is dependent on the kinetic courses that follow surface trapping, namely, surface recombination and interfacial transfer. The role of bulk defects as recombination centers is considered. The model gives a simple and general physical and mathematical treatment taking bulk recombination into consideration, based on which the effect of the bulk defects is analyzed.