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.

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Photocatalytic reduction of carbon dioxide to hydrocarbon fuel provides a sustainable strategy for addressing the increasing energy crisis as well as alleviating the greenhouse effect. Yet, seeking effective, affordable, and metal-free photocatalysts is still a challenging issue. Herein, a novel nitrogen selfdoped covalent triazine-based framework (NCTF-1) was prepared via a simple hydrothermal process for photocatalytic CO 2 reduction to CH 4 using visible light. NCTF-1 exhibited a CH 4 evolution rate of 11.48 μmol g −1 h −1 , corresponding to ninefold enhancement, compared with bare covalent triazine-based frameworks (CTF-1). The photocatalytic enhancement mechanism was probed by a variety of instrumental measurements. Results showed that the modification of nitrogen atoms in NCTF-1 could extend the responsive range of the visible-light spectrum, promote CO 2 capture, and thus greatly elevate the photocatalytic CO 2 reduction activity. Notably, NCTF-1 displayed a satisfactory selectivity for CO 2 conversion with CH 4 accounting for over 85% of the reduction products. This study offers a promising avenue for achieving robust CO 2 -to-CH 4 conversion and provides insight into the impact of nitrogen self-doping on covalent triazine-based frameworks.

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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