Creating Chemisorption Sites for Enhanced CO₂ Photoreduction Activity through Alkylamine Modification of MIL-101-Cr

The lower CO2 utilization and poor charge conductivities have limited the application of metal–organic frameworks (MOFs) in photocatalysis. In this work, different alkylamines [ethylenediamine (EN), diethylenetriamine (DETA), and triethylenetetramine (TETA)] were successfully introduced into MIL-101-Cr by postmodification and created abundant CO2 chemisorption sites in structures. Photocatalysis reaction showed that the alkylamine modification promoted the charge separation and migration rate and enhanced the reduction potential of the electron generated by the MOF photocatalyst. Among them, the EN-modified material exhibits the highest CO generation rate of 47.2 μmol·h–1·g–1 with a high selectivity of 96.5%, much superior than the pristine MOFs MIL-101-Cr and MIL-101-SO3H, as well as the DETA- and TETA-modified products, which can be ascribed to the abundant chemisorption sites for CO2 reactants and the optimized pore size in structures. The strategy of introduction of alkylamine groups as CO2 chemisorption sites has been demonstrated to be a new pathway for the design of efficient MOF catalysts for CO2 photoreduction.