Tuning the selectivity toward CO evolution in the photocatalytic conversion of CO2 with H2O through the modification of Ag-loaded Ga2O3 with a ZnGa2O4 layer

Abstract

Stoichiometric evolutions of CO, H₂, and O₂ were achieved for the photocatalytic conversion of CO₂ with H₂O as an electron donor using Ag-loaded Zn-modified Ga₂O₃. The selectivity toward the evolution of CO over H₂ can be controlled by varying the amount of Zn species added in the Ag-loaded Zn-modified Ga₂O₃ photocatalyst. The production of H₂ gradually decreased with increasing amounts of Zn species from 0.1 to 10.0 mol%, whereas the evolution of CO was almost unchanged. The XRD, XAFS, and XPS measurements revealed that a ZnGa₂O₄ layer was generated on the surface of Ga₂O₃ by modification with Zn species. The formation of the ZnGa₂O₄ layer eliminated the proton reduction sites on Ga₂O₃, although the crystallinity, surface area, and morphology of Ga₂O₃ as well as the particle size and chemical state of Ag did not change. In conclusion, we designed a highly selective photocatalyst for the conversion of CO₂ with H₂O as an electron donor using Ag (the cocatalyst for the CO evolution), ZnGa₂O₄ (the inhibitor of the H₂ production), and Ga₂O₃ (the photocatalyst).