PHOTOCHEMISTRY ON SURFACES - PHOTODEGRADATION OF 1,3-DIPHENYLISOBENZOFURAN OVER METAL-OXIDE PARTICLES

Steady-state and diffuse reflectance laser flash photolyses have been carried out to elucidate the mechanism of photodegradation of 1,3-diphenylisobenzofuran (DPBF) on solid surfaces of Al2O3, TiO2, and ZnO. In the absence of oxygen, the semiconductor supports TiO2 and ZnO catalyze the photodegradation by accepting electrons from excited DPBF. The fluorescence of degassed DPBF on TiO2 and ZnO is quenched relative to that on alumina, thereby offering independent confirmation of charge transfer. In oxygenated samples, the primary mechanism of photodegradation involves reaction with singlet oxygen. This is confirmed by the studies on the insulator surface Al2O3, where significant degradation is observed only in the case of air-equilibrated samples. The dependence of the rate of DPBF photodegradation on the surface coverage indicates that only the molecules that are in direct contact with the surface undergo photodegradation. The results that highlight the role of the support material in guiding the course of a photochemical reaction are described here.