Improved PhotocatalyticCO₂ Reduction viaEngineering Zinc Vacancies in S‑Scheme ZnO/ZnIn₂S₄ Heterostructures

Abstract

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 (V_Zn) 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 V_Zn concentrations. The composite with a higher V_Zn 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 V_Zn 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.