Preparation of Ga2O3 photocatalyst highly active for CO2 reduction with water without cocatalyst

Ga2O3 samples were synthesized by calcination of gallium nitrate powder at a given temperature ranging from 673 K to 1173 K (denoted as T-Ga2O3 with T, calcination temperature). XRD and XAFS structural analyses revealed that samples calcined at temperatures below 673 K were consisted of defective ε phase, whereas those calcined above 773 K of β and γ phases, and β phase dominated above 923 K. All calcined Ga2O3 samples promoted photocatalytic CO2 reduction with water to produce CO, H2 and O2. As for the H2 production by water splitting, the H2 production rates were well correlated with the surface areas of calcined Ga2O3 samples. It was also found that the water splitting and the CO2 reduction proceeded fully independently. 823-Ga2O3 showed the highest activity for the CO2 reduction, suggesting that the coexistence of β and γ phases plays a key role on the photocatalytic CO2 reduction.