Ligand-engineered coordination microenvironments in metallized covalent organic frameworks for efficient photocatalytic CO reduction

Abstract

The catalytic conversion of CO2 into value-added chemicals represents a promising strategy for mitigating atmospheric CO2 levels, yet the development of efficient and selective photocatalysts remains a formidable challenge. Metalated covalent organic frameworks (M-COFs) offer a tunable platform for CO2 photoreduction, but precisely controlling the local coordination microenvironment around active sites to modulate electronic structure and charge-carrier dynamics has proven difficult. Herein, a series of imine-linked COFs bearing different substituents (–H, –CH3, –C(CH3)3), denoted as HCOF, DCOF, and TCOF, were first synthesized under ambient conditions, followed by the post-synthetic coordination anchoring of nickel (Ni) metal centers to construct the corresponding catalysts with atomically dispersed Ni sites (Ni@HCOF, Ni@DCOF, Ni@TCOF). Photocatalytic CO2 reduction tests revealed that Ni@TCOF achieved the highest catalytic activity with a CO production rate of 12 004.37 µmol g−1 h−1 and nearly 100% selectivity, substantially outperforming Ni@DCOF (4958.52 µmol g−1 h−1) and Ni@HCOF (2338.6 µmol g−1 h−1). Comprehensive characterization and mechanistic studies demonstrated that the superior performance originates from the strong electron-donating ability of the tert-butyl substituents, which optimize the local coordination microenvironment around the Ni active sites and promote the separation and transport of photogenerated charge carriers. This work provides profound insights into regulating the local coordination environment of M-COFs through ligand engineering for the development of highly active and selective CO2 reduction catalysts.