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.