Water film-mediated photocatalytic oxidation of oxalate on TiO2

Water films on minerals under humid environment can be photocatalytic hotspots when exposed to sunlight or artificial sources of ultraviolet (and visible) radiation. In this study, we resolved the water film -mediated photocatalysis of oxalate adsorbed on TiO 2 using in situ infrared spectroscopy. We found that 0.5 to 4 monolayer(ML) thick water films enhanced the photodecomposition rates of oxalate under 21 kPa O 2 . We explained this through the combined actions of direct hole transfer, ligand-to-metal-charge transfer, as well as the production of hydroxyl radicals and reactive oxygen species. Rates were, however, substantially slower in the absence of O 2 because charge recombination, together with water film -mediated charge localization, disrupted hole transfer and hydroxyl radical production. Our work adds insight into the impact of humidity on controlling important photocatalytic processes in nature (drying soils, atmospheric aerosols), and technology (water and air treatment).