Effects of the crystalline structure of Ga2O3 on the photocatalytic activity for CO production from CO2

Ga2O3 samples with different crystalline structures were prepared by calcination of a gallium nitrate powder around 800 K. Ga2O3 samples with mixed phases of gamma and beta showed high photocatalytic activity for CO production from CO2 reduction with water, and the activity was even higher than that for an Ag-loaded beta-Ga2O3. The photocatalytic activity increased with time. The increase was attributed to the appearance of GaOOH resulting from the interaction of Ga2O3 with water during the reaction as revealed by XRD and XPS analyses. In situ FT-IR measurements revealed that bicarbonates and bidentate carbonate species were adsorbed on GaOOH. Therefore, the increase of the photocatalytic activity with time would be derived from the formation of GaOOH phase on the gamma-Ga2O3 and beta-Ga2O3 sample.