SIMPLE PHOTOCATALYSIS MODEL FOR PHOTOEFFICIENCY ENHANCEMENT VIA CONTROLLED, PERIODIC ILLUMINATION

Under steady illumination, aqueous phase photocatalytic oxidation reac tions using titanium dioxide characteristically exhibit low quantum yi elds, i.e., the incident light is used inefficiently in the process. S czechowski, Koval, and Noble(1) reported substantially higher photoeff iciencies (defined as reaction rate divided by incident photon rate) f or TiO2 while using controlled, periodic illumination instead of conti nuous illumination in a flow system. We propose a transient kinetic mo del which suggests that rapid consumption of preadsorbed reactant inve ntory by photoproduced holes (or by their oxidation product, OH radica l, etc.) accounts for such high photoefficiencies with periodic illumi nation and that the characteristically slow adsorption of additional o xygen and/or electron transfer to oxygen is responsible for low quantu m yields observed under steady illumination. A model simulation provid es 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 cons tant measurements on the same photocatalysts.