Ag2CrO4/g-C3N4/graphene oxide ternary nanocomposite Z-scheme photocatalyst with enhanced CO2 reduction activity

Graphitic carbon nitride (g-C3N4)-based photocatalysts holds great promise on photocatalytic CO2 conversion into solar fules; however, the efficiency of pristine g-C3N4 is currently limited by its poor visible light absorption and rapid charge recombination. Employing silver chromate (Ag2CrO4) nanoparticles as photosensitizer and graphene oxide (GO) as cocatalyst, a novel ternary Ag2CrO4/g-C3N4/GO composite photocatalyst was fabricated for photocatalytic CO2 reduction into methanol (CH3OH) and methane (CH4). The ternary composites exhibited an enhanced CO2 conversion activity with a turnover frequency of 0.30 h–1, which was 2.3 times that of pristine g-C3N4 under simulated sunlight irradiation. The enhanced photocatalytic activity was due to broadened light absorption, higher CO2 adsorption and more efficient charge separation. Specifically, due to the matched band structure and appropriate loading ratio of Ag2CrO4, a direct Z-scheme Ag2CrO4/g-C3N4 heterojunction is formed, driven by the internal electric field across the Ag2CrO4/g-C3N4 interface. The formation of the direct Z-scheme heterojunction is substantiated by radical scavenging experiments and density functional theory calculations, and it benefits the photocatalytic reaction by accelerating the charge separation and improving the redox ability. Furthermore, GO cocatalyst not only promotes the charge transfer but also provides plentiful CO2 adsorption and catalytic sites. This work exemplifies the facile development of ternary g-C3N4-based photocatalysts with high CO2-conversion activity by coupling a small amount of Ag-based photosensitizer and metal-free cocatalyst.