Energy and electron transfer reactions on silica gel and titania-silica mixed oxide surfaces

The energy and electron transfer reactions of anthracene co-adsorbed with an electron donor on silica gel and titania-silica mixed oxides have been studied by a combination of steady state reflectance, emission spectroscopy, and nanosecond diffuse reflectance laser flash photolysis. Bimolecular rate constants for energy and electron transfer between anthracene and azulene have been measured; kinetic analysis of the decay of the anthracene triplet state and radical cation show that the kinetic parameters depend on the titania content of the sample and the azulene loading. The rate of energy and electron transfer reactions increases as a function of azulene loading and decreases with increasing titania content in titania-silica mixed oxides. These findings indicate that the observed rate of reaction is determined by the rate of diffusion of anthracene on the titania-silica surfaces whereas, in contrast, the observed rate of reaction on silica gel is predominantly governed by the rate of diffusion of azulene.