Photochemistry of ketones adsorbed on porous silica

The Phetochemical reactions of several families of ketones adsorbed on various forms of silica have been investigated. The influence of surface coverage, silica average pore diameter, temperature, applied magnetic fields, and additives on the product distributions have been determined. The results are consistent with a model in which the silica surface consists of two major regions, one consisting of stronger binding sites (active silanol groups) and the other consisting of weaker binding sites (free silanol groups). The relative proportions of these two types of sites are related to the pore size of the silica, smaller pores correlating with a larger fraction of the stronger binding sites and larger pores correlating with a smaller fraction of the stronger binding sites. At low coverage, the initial location of a ketone in one of the two binding sites is an important factor in determining the product distributions. Some preliminary results are reported on the time resolved spectroscopy of ketones adsorbed on silica investigated by diffuse reflectance absorption spectrescopy.