Decoration of Active Sites in Covalent–Organic Framework: An Effective Strategy of Building Efficient Photocatalysis for CO2 Reduction

The decoration of metal active sites to realize the regulation of catalytic activity of photocatalysts is greatly meaningful. Here, we rationally tune the coordination environment of metal centers in covalent–organic framework (COF) for efficient photocatalytic CO2 reduction. 3,3′,5,5′-Tetraformyl-4,4′-biphenyldiol-COF (TFBD-COF) was synthesized and then used for immobilizing Co2+, followed by the coordination of salicylideneaniline (SA) ligand to construct TFBD-COF-Co-SA that shows excellent photocatalytic CO2 reduction activity and stability. As a result, TFBD-COF-Co-SA shows a CO2-to-CO reduction activity of 7400 μmol·g–1 in 5 h and a 90% selectivity. Different from simply coordinating metal ions to COFs, the CO evolution rate of TFBD-COF-Co-SA is 4.1 times higher than that of TFBD-COF-Co without the coordination of SA ligand. It is confirmed that this heterocatalytic activity of TFBD-COF-Co-SA is comparable to the homocatalytic activity of the Co­(SA)2 complex molecular catalyst calculated on the basis of the number of metal centers.