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.

Converting CO 2 into carbonaceous fuels via photocatalysis represents an appealing strategy to simultaneously alleviate the energy crisis and associated environmental problems, yet designing with high photoreduction activity catalysts remains a compelling challenge. Here, combining the merits of highly porous structure and maximum atomic efficiency, we rationally constructed covalent triazine-based frameworks (CTFs) anchoring copper single atoms (Cu-SA/CTF) photocatalysts for efficient CO 2 conversion. The Cu single atoms were visualized by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images and coordination structure of Cu-N-C 2 sites was revealed by extended X-ray absorption fine structure (EXAFS) analyses. The as-prepared Cu-SA/CTF photocatalysts exhibited superior photocatalytic CO 2 conversion to CH 4 performance associated with a high selectivity of 98.31%. Significantly, the introduction of Cu single atoms endowed the Cu-SA/CTF catalysts with increased CO 2 adsorption capacity, strengthened visible light responsive ability, and improved the photogenerated carriers separation efficiency, thus enhancing the photocatalytic activity. This work provides useful guidelines for designing robust visible light responsive photoreduction CO 2 catalysts on the atomic scale. covalent triazine-based frameworks, Cu single atoms, photocatalytic CO 2 reduction, visible light, selectivity

It is of pivotal significance to explore robust photocatalysts to promote the photoreduction of CO2 into solar fuels. Herein, an intelligent metal‐insulator‐semiconductor (MIS) nano‐architectural photosystem was constructed by electrostatic self‐assembly between cetyltrimethylammonium bromide (CTAB) insulator‐capped metal Ni nanoparticles (NPs) and covalent triazine‐based frameworks (CTF‐1). The metal‐insulator‐CTF composites unveiled a substantially higher CO evolution rate (1254.15 μmol g−1 h−1) compared with primitive CTF‐1 (1.08 μmol g−1 h−1) and reached considerable selectivity (98.9 %) under visible‐light irradiation. The superior photocatalytic CO2 conversion activity over Ni‐CTAB‐CTF nanoarchitecture could be attributed to the larger surface area, reinforced visible‐light response, and CO2 capture capacity. More importantly, the Ni‐CTAB‐CTF nanoarchitecture endowed the photoexcited electrons on CTF‐1 with the ability to tunnel across the thin CTAB insulating layer, directionally migrating to Ni NPs and thereby leading to the efficient separation of photogenerated electrons and holes in the photosystem. In addition, isotope‐labeled (13CO2) tracer results verified that the reduction products come from CO2 rather than the decomposition of the photocatalysts. This study opens a new avenue for establishing a highly efficient and selective artificial photosystem for CO2 conversion.