Effective CO2 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.