Construction of S-deficient In2S3/Vs-CuIn5S8 heterojunctions for photocatalytic reduction of CO2 to multi‑carbon products.

The conversion of carbon dioxide into hydrocarbon fuels aids in reducing humanity's reliance on fossil fuels. This study utilized indium nitrate hydrate and terephthalic acid as precursors to construct an indium-based organic framework MIL-68. Through solvothermal sulfidation, three-dimensional hierarchical In2S3 (IS) nanoflower tubes were synthesized, which were further combined with CuIn5S8 (CIS) to form In2S3/CuIn5S8(IS/CIS) composites. Subsequent high-temperature calcination yielded sulfur vacancy-rich IS/Vs-CIS composites. Comprehensive characterization via SEM, XPS, and photoelectrochemical analysis revealed that sulfur vacancies and heterojunction synergistically optimized band structure and charge transfer efficiency. Under visible-light-driven CO2 reduction, IS/Vs-CIS demonstrated exceptional activity with ethane production rates reaching 16.49 μmol∙g-1∙h-1, respectively, alongside excellent cycling stability. In situ FTIR and DFT calculations confirmed that sulfur vacancies reduced the energy barrier for *HCOO intermediate formation and promoted CC coupling for ethane generation. A proposed Z-scheme heterojunction mechanism elucidated the charge separation and CO2 reduction pathway, where sulfur vacancies served as active sites to enhance catalytic performance. This work provides a novel strategy for designing sulfide-based photocatalysts toward efficient CO₂-to-hydrocarbon conversion systems.