Core–Shell MIL-125(Ti)@In 2 S 3 S-Scheme Heterojunction for Boosting CO 2 Photoreduction

Heterojunctions based on metal–organic framework (MOF) materials have emerged as promising systems for CO 2 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 In 2 S 3 nanosheets on MIL-125(Ti) for efficient CO 2 photoreduction. Comprehensive characterization elucidates strong interfacial interactions and substantial work function mismatches between MIL-125(Ti) and In 2 S 3, 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 CO 2 reduction process. Moreover, density functional theory calculations reveal that the heterojunction construction significantly facilitates CO 2 activation and lowers the energy barrier. The optimized MT-2@IS achieves an exceptional CH 4 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 In 2 S 3 . This work provides valuable insights into the design of MOF-based heterojunctions and establishes a robust framework for advancing CO 2 photoreduction technologies.