Simple Photocatalysis Model for Photoefficiency Enhancement via Controlled, Periodic Illumination

Abstract

Under steady illumination, aqueous phase photocatalytic oxidation reactions using titanium dioxide characteristically exhibit low quantum yields, i.e., the incident light is used inefficiently in the process. Sczechowski, Koval, and Noble1 reported substantially higher photoefficiencies (defined as reaction rate divided by incident photon rate) for TiO2 while using controlled, periodic illumination instead of continuous illumination in a flow system. We propose a transient kinetic model which suggests that rapid consumption of preadsorbed reactant inventory by photoproduced holes (or by their oxidation product, OH radical, etc.) accounts for such high photoefficiencies with periodic illumination and that the characteristically slow adsorption of additional oxygen and/or electron transfer to oxygen is responsible for low quantum yields observed under steady illumination. A model simulation provides trends of photoefficiency with variation of the length of light and dark periods which resemble the observed photoefficiency trends, but fundamental comparisons await photoefficiency and individual rate constant measurements on the same photocatalysts.