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Abstract

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