Photocatalysts, such as TiO2, can be used to degrade a wide range of organic contaminants found in polluted air. TiO2 photocatalysts are active at ambient temperatures and pressures in the presence of UV irradiation and oxygen and have been shown to oxidize toluene, trichloroethylene (TCE), methanol/ethanol and many other organic compounds. In this proposal, solid state MAS NMR (magic angle spinning nuclear magnetic resonance) techniques will be utilized to identify surface species formed during heterogeneous photocatalytic oxidation reactions on TiO2. These surface species may be reaction intermediates, surface poisons or partial oxidation products. Spectroscopic studies of TCE enhancement of toluene photooxidation will be conducted to determine the origin of the enhancement for deactivation. The proposed research will provide insight into the role of surface species in photocatalytic oxidation reactions on TiO2 that could lead to the development of improved photocatalysts.