Fabrication of Zn vacancies-tunable ultrathin-g-C3N4@ZnIn2S4/SWNTs composites for enhancing photocatalytic CO2 reduction

Zinc vacancy (VZn) concentrations were successfully regulated on the hierarchical flower spherical ZnIn2S4 (ZIS) by controlling the hydrothermal temperature. The photo-electrochemical experiments indicated that the carrier separation efficiency of ultrathin-g-C3N4@ZIS/SWNTs (UCN@ZIS/SWNTs) composite with different VZn concentrations (poor-VZn ZIS (pZIS) and rich-VZn ZIS (rZIS)) had an efficient improvement because of the construction of UCN@ZIS heterojunction and the multiple channels for charge transfer provided by SWNTs. In-situ FTIR results indicate that the presence of VZn and the enriched surface-active site on UCN contributes to CO2 activation and H2O dissociation. Additionally, the yield of CO and CH4 over UCN@rZIS/SWNTs composite reached 33.7 µmol g−1 and 39.8 µmol g−1, respectively, and the selectivity of CH4 reached 54.1 % under the synergistic effect of VZn, the surface-active site of UCN and charge-transfer channels. This work established an ideal defect model for enhancing CO2 photocatalytic reduction performance and product selectivity, which may provide a new way to improve photocatalytic efficiency and a better understanding of the photocatalytic reaction mechanisms.