PHOTOCATALYTIC OXIDATION OF ORGANIC-MOLECULES AT TIO2 PARTICLES BY SUNLIGHT IN AERATED WATER

A key issue in the photoassisted oxidation of organic materials, e.g., oil slicks on sea water, on semiconducting particles is the charging of the particles by electrons as a result of the hole transfer (e.g., to adsorbed organics or to water) being fast, and the two-electron transfer to dioxygen being potentially slower. Such charging leads to recombination, i.e., loss of quantum efficiency. Here we show that at an approximately 1 sun irradiance of n-TiO2 particles in water, the rate of depolarization of the particles by molecular oxygen will not be limited by O2 diffusion. For large (> 1-mu-m) TiO2 particles, but less probably for small (< 0.1-mu-m) ones, the quantum efficiency may be limited by the rate of electron transfer to adsorbed O2. The latter rate depends on the density of shallow (0.1-0.3 eV) surface and near surface electron traps. If the density of these traps is too low, group VIII metal O2 reduction catalysts should increase the rate of electron transfer to O2 and thereby raise the quantum yield.