Rational Design of Novel COF/MOF S-Scheme Heterojunction Photocatalyst for Boosting CO2 Reduction at Gas–Solid Interface

Solar-driven photoreduction of CO₂ into valuable fuels offers a sustainable technology to relieve the energy crisis as well as the greenhouse effect. Yet the exploration of highly efficient, selective, stable, and environmental benign photocatalysts for CO₂ reduction remains a major issue and challenge. The interfacial engineering of heterojunction photocatalysts could be a valid approach to boost the efficiency of the catalytic process. Herein, we propose a novel covalent organic framework/metal organic framework (COF/MOF) heterojunction photocatalyst, using olefin (C═C) linked covalent organic framework (TTCOF) and NH₂-UiO-66 (Zr) (NUZ) as representative building blocks, for enhanced CO₂ reduction to CO. The optimized TTCOF/NUZ exhibited a superior CO yield (6.56 μmol g^-1 h^-1) in gas-solid system when irradiated by visible light and only with H₂O (g) as weak reductant, and it was 4.4 and 5 times higher than pristine TTCOF and NUZ, respectively. The photogenerated electrons transfer route was proposed to follow the typical step-scheme (S-scheme), which was affirmed by XPS, in situ XPS and EPR characterizations. The boosting CO₂ photoreduction activity could be credited to the special charge carrier separation in S-scheme heterojunction, which can accelerate photogenerated electrons transportation and improve the redox ability at the interface. This work paves the way for the design and preparation of novel COF/MOF S-scheme heterostructure photocatalysts for CO₂ reduction.