Facile synthesis of photocatalysts with highly dispersed metal centers is a high-priority target yet still a significant challenge. In this work, a series of Co-C 3 N 4 photocatalysts with different Co contents atomically dispersed on g-C 3 N 4 have been prepared via one-step thermal treatment of cobalt-based metal-organic frameworks (MOFs) and urea in the air. Thanks to the highly dispersed and rich exposed Co sites, as well as good charge separation efficiency and abundant mesopores, the optimal 25-Co-C 3 N 4 , in the absence of noble metal catalysts/sensitizers, exhibits excellent performance for photocatalytic CO 2 reduction to CO under visible light irradiation, with a high CO evolution rate of 394.4 μmol•g -1 •h -1 , over 80 times higher than that of pure g-C 3 N 4 (4.9 μmol•g -1 •h -1 ). In addition, by this facile synthesis strategy, the atomically dispersed Fe and Mn anchoring on g-C 3 N 4 (Fe-C 3 N 4 and Mn-C 3 N 4 ) have been also obtained, indicating the reliability and universality of this strategy in synthesizing photocatalysts with highly dispersed metal centers. This work paves a new way to develop cost-effective photocatalysts for photocatalytic CO 2 reduction.

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Significance The photosensitizer is one of the important components in the photocatalytic system. Molecular photosensitizers have well-defined structures, which is beneficial in revealing the catalysis mechanism and helpful for further structural design and performance optimization. However, separation and recycling of the molecular photosensitizers is a great problem. Loading them into/on two/three-dimensional supports through covalent bonds, electrostatic interactions, and supramolecular interactions is a method that enhances their separation and recycling capability. Nonetheless, the structures of the resulting composites are unclear. Thus, the development of highly crystalline heterogeneity methods for molecular photosensitizers, albeit greatly challenging, is meaningful and desirable in photocatalysis, through which heterogeneous photosensitizers with well-defined structures, definite catalysis mechanisms, and good catalytic performance would be expected.

The exploitation of highly stable and active catalysts for the conversion of CO2 into valuable fuels is desirable but is a great challenge. Herein, we report that the incorporation of chromophores into metal–organic frameworks (MOFs) could afford robust catalysts for efficient CO2 conversion. Specifically, a porous Nd­(III) MOF (Nd-TTCA; TTCA3– = triphenylene-2,6,10-tricarboxylate) was constructed by incorporating one-dimensional Nd­(CO2) n chains and TTCA3– ligands, which exhibits a very high stability, retaining its framework not only in the air at 300 °C for 2 h but also in boiling aqueous solutions at pH 1–12 for 7 days. More importantly, Nd-TTCA has achieved a 5-fold improvement in photocatalytic activity for reducing CO2 to HCOOH and a 10-fold improvement in catalytic activity for the cycloaddition of CO2 into cyclic carbonate in comparison to those of H3TTCA itself. This work gives a new strategy to design efficient artificial crystalline catalysts for CO2 conversion.