Effect of Ag co-catalyst on CO2 adsorption states over Ga2O3 photocatalyst

Ag species in the Ag loaded Ga2O3 (Ag/Ga2O3) photocatalysts were investigated with regard to changes in their structures and the chemical states before and after the photocatalytic CO2 reduction with water. Ag clusters with the size of around one nanometer in as prepared 0.1 wt% Ag/Ga2O3 sample became larger metallic Ag nano-particles with the size of several nanometers after the reaction. In the 1.0 wt% Ag/Ga2O3 sample, Ag nanoparticles having the AgGaO2 interface structure decomposed to aggregated Ag metal particles after the reaction. Such transition in the morphology and chemical states of Ag species could explain the variations in photocatalytic activities of these samples during the reaction, and suggested that at least metallic Ag particles would function as effective co-catalysts. In-situ FT-IR measurements of the Ag/Ga2O3 samples before and after the reaction, we could not detect CO2 molecules adsorbing on metallic Ag nanoparticles in dark. Under light irradiation, however, the absorption bands originated from the photo-adsorbed CO2 species on Ag metal nanoparticles appeared. Thus, we detected the interaction of CO2 molecules and metallic Ag nanoparticles as the effective co-catalysts for CO2 reduction.