Core-Shell MIL-125(Ti)@In₂S₃ S-Scheme Heterojunction for Boosting CO₂ Photoreduction

Heterojunctions based on metal-organic framework (MOF) materials have emerged as promising systems for CO₂ photoreduction under sacrificial agent-free conditions. However, the rational design and precise construction of these heterostructures remain significant challenges. In this study, we report the development of a core-shell heterojunction via the in situ growth of In₂S₃ nanosheets on MIL-125(Ti) for efficient CO₂ photoreduction. Comprehensive characterization elucidates strong interfacial interactions and substantial work function mismatches between MIL-125(Ti) and In₂S₃, which drive the formation of a robust interfacial electric field (IEF) and facilitate the establishment of an S-scheme heterojunction. The S-scheme heterojunction retains the strong oxidative and reductive potentials of its components, promoting efficient charge separation and transfer. In situ infrared spectroscopy provides evidence that the formation of the S-scheme heterojunction significantly enhances the production of critical intermediates essential for the CO₂ reduction process. Moreover, density functional theory calculations reveal that the heterojunction construction significantly facilitates CO₂ activation and lowers the energy barrier. The optimized MT-2@IS achieves an exceptional CH₄ production rate of 27.65 μmol g^-1 h^-1 without the use of photosensitizers or sacrificial agents, representing 27-fold and 8.9-fold improvements compared to pristine MIL-125(Ti) and In₂S₃. This work provides valuable insights into the design of MOF-based heterojunctions and establishes a robust framework for advancing CO₂ photoreduction technologies.