Improved Photocatalytic CO2 Reduction via Engineering Zinc Vacancies in S-Scheme ZnO/ZnIn2S4 Heterostructures

Defect engineering in semiconductor heterojunctions offers a promising avenue for enhancing the photocatalytic activity. This study demonstrates the rational design of an S-scheme ZnO/ZnIn2S4 (ZIS) heterojunction with enriched zinc vacancies (VZn) for efficient photocatalytic CO2 reduction. Two distinct morphologies of ZnO/ZIS composites were synthesized by modulating the sulfur source during ZIS nucleation, resulting in different VZn concentrations. The composite with a higher VZn concentration (B-ZnO/ZIS) exhibited significantly enhanced photocatalytic performance, achieving a CO yield of 233 μmol g–1 under visible light irradiation, which is 27 times higher than that of pristine ZnIn2S4. This remarkable enhancement is attributed to the synergistic effect of abundant VZn and the S-scheme heterojunction, promoting efficient charge separation and transfer, as evidenced by a series of photoelectrochemical and physicochemical characterizations. The S-scheme charge transfer mechanism was further corroborated by X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. In situ Fourier-transform infrared (FTIR) spectroscopy revealed the surface intermediates involved in the CO2 reduction process over B-ZnO/ZIS. This work provides a new strategy for designing high-performance photocatalysts by combining defect engineering and heterojunction construction for efficient CO2 conversion.