Effective CO 2 Photoreduction Synergistically Boosted by Built-In Electronic Field and Coplanar Covalent Triazine Frameworks

The catalytic efficiency in photocatalytic CO2 reduction is affected by insufficient charge separation drive and limited carrier transport, and constructing covalent metal–organic frameworks (CMOFs) with high planarity and a large built-in electric field (IEF) is an effective method to address these issues. Nevertheless, achieving such structures remains a great challenge. Herein, Cu-based covalent triazine frameworks (CTF-Z) with outstanding coplanarity were synthesized by introducing inherently coplanar triazine rings as linkers and triangular aldehyde-functionalized pyrazole copper clusters (Cu3) as monomers. The pyrazole-triazine-benzene rings in CTF-Z frameworks form a donor–acceptor–donor (D-A-D) configuration, constructing a nearly planar geometry with a dihedral angle of 0.001° and the local IEF, indicating a strong driving force for intramolecular charge separation. Therefore, CTF-Z can effectively photocatalyze CO2 reduction into CO with a production rate of 73.65 μmol g–1 h–1 without sacrificial agents and photosensitizers. The photocatalytic activity of CTF-Z is 4.5 times higher than that of FDM-71 with a larger dihedral angle. Experimental and theoretical investigations revealed that the triazine ring exhibits higher electronegativity and electron-accepting capability in the D-A-D structure, which promotes more electrons to participate in the redox reaction on the surface and effectively reduces the energy barrier of the rate-determining step. It is beneficial to form *COOH intermediates and effectively improve the photocatalytic performance. This work presents a facile and efficient molecular-level strategy for constructing CMOFs with enhanced separation and migration efficiency of photogenerated charge carriers.