Photoredox Coupling of CO2 Reduction with Benzyl Alcohol Oxidation over Ternary Metal Chalcogenides (ZnmIn2S3+m, m = 1–5) with Regulable Products Selectivity

Integrating photocatalytic CO2 reduction with selective benzyl alcohol (BA) oxidation in one photoredox reaction system is a promising way for the simultaneous utilization of photogenerated electrons and holes. Herein, ZnmIn2S3+m (m = 1–5) semiconductors (ZnIn2S4, Zn2In2S5, Zn3In2S6, Zn4In2S7, and Zn5In2S8) with various composition faults were synthesized via a simple hydrothermal method and used for effective selective dehydrocoupling of benzyl alcohol into high-value C–C coupling products and reduction of CO2 into syngas under visible light. The absorption edge of ZnmIn2S3+m samples shifted to shorter wavelengths as the atomic ratio of Zn/In was increased. The conduction band and valence band position can be adjusted by changing the Zn/In ratio, resulting in controllable photoredox ability for selective BA oxidation and CO2 reduction. For example, the selectivity of benzaldehyde (BAD) product was reduced from 76% (ZnIn2S4, ZIS1) to 27% (Zn4In2S7, ZIS4), while the selectivity of hydrobenzoin (HB) was increased from 22% to 56%. Additionally, the H2 formation rate on ZIS1 (1.6 mmol/g/h) was 1.6 times higher than that of ZIS4 (1.0 mmol/g/h), and the CO formation rate on ZIS4 (0.32 mmol/g/h) was three times higher than that of ZIS1 (0.13 mmol/g/h), demonstrating that syngas with different H2/CO ratios can be obtained by controlling the Zn/In ratio in ZnmIn2S3+m. This study provides new insights into unveiling the relationship of structure–property of ZnmIn2S3+m layered crystals, which are valuable for implementation in a wide range of environment and energy applications.