Interfacial factors that affect the photoefficiency of semiconductor-sensitized oxidations in nonaqueous media

Three types of platinized n-type anatase titanium dioxide powders were synthesized for use as photosensitizers in the oxidation of {alpha}-methylstyrene in acetonitrile suspensions. The oxidized, reduced, and n-octyl surface derivatized powders had mean particle diameters which ranged from 6.2 to 6.8 {mu}m and BET surface areas (N{sub 2} adsorption) which varied from 72 to 75 m{sup 2}/g. Photooxidations that employed the synthesized oxidized powders had an incident monochromatic photon-to-product efficiency of 0.037 {plus minus} 0.002 using 366 nm light. This represents a 7.6-fold increase in the photoefficiency when compared with platinized commercial anatase. This increased efficiency is attributed to surface characteristics that promote interfacial charge transfer versus electron-hole recombination. The powders posses a high roughness factor (approximately 300) and a surface topography that can be described by a fractal dimension (D {approx} 3.0). An additional 2.3-fold increase over the synthesized oxidized powders is realized for the n-octyl-derivatized powders. This additional improvement is attributed to an increase in the surface affinity of the semiconductor particles for the nonpolar hydrocarbon starting material.