In-situ UV-Vis DR and XAFS Measurements of Silver Loaded Gallium Oxide Photocatalyst

Abstract

Ag loaded Ga₂O₃ photocatalysts are well known to be highly active for the CO₂ reduction with water to CO. However, Ag changes its chemical state during the reaction, resulting in the decrease of its photocatalytic activity. We have attempted a real time observation of the change in the chemical and physical states of Ag co-catalyst loaded on Ga₂O₃ by monitoring UV-Vis diffuse reflectance spectra and Ag L₃-edge XANES spectra under the atmosphere simulating the photocatalytic CO₂ reduction. It was revealed that Ag initially loaded on Ga₂O₃ in the oxidized state was dissolved as Ag⁺ in water and precipitated as Ag-NPs. Then, some of Ag-NPs aggregated to be larger Ag particles or in the metallic state. Such dynamic process of Ag cocatalyst depends on gas species of the system, i.e. water promoted the formation of Ag-NPs while the adsorption of CO₂ on Ga₂O₃ and/or the oxidized Ag cocatalyst suppressed the formation of Ag-NPs.