Highly Efficient and Selective Visible‐light Photocatalytic CO2 Reduction to CO Using a 2D Co(II)‐Imidazole MOF as Cocatalyst and Ru(bpy)3Cl2 as Photosensitizer

Abstract

AbstractThe first application of an imidazole MOF, the 2D Co(II)‐ imidazole framework, {[Co(TIB)2(H2O)4]SO4} (TIB stands for 1,3,5‐tris(1‐imidazolyl) benzene) (CoTIB) in photocatalytic CO2 reduction was carried out, and compared with that of ZIF‐67. The CO2/CoTIB (1.0 mg)/Ru(bpy)3Cl2 (bpy=2,2’‐bipyridine) (11.3 mg)/CH3CN (40 mL)/TEOA (10 mL)/H2O (400 μL) system produced 76.9 μmol of CO in 9 h, corresponding to the efficiency of 9.4 mmol g−1 h−1 (TOF: 7.3 h−1) with a >99% selectivity. Its catalytic activity is even higher than that of ZIF‐67 based on TOF values. However, CoTIB is non‐porous and has a very poor CO2 adsorption capacity and poor conductivity. Extensive photocatalytic experiments and energy‐level diagrams suggest that the reduction did not depend on the CO2 adsorption by the cocatalyst, but can occur by the direct electron transfer from conduction‐band maximum (CBM) of the cocatalyst to the zwitterionic alkylcarbonate adduct formed by the reaction of TEOA and CO2. In addition, the process utilizes the short‐lived singlet state (1MLCT), not the long‐lived triplet state (3MLCT) of Ru(bpy)3Cl2 to transfer electrons to the CBM of CoTIB. We found that the high efficiency of a cocatalyst, a photosensitizer, or a photocatalytic system depends on the matching of all related energy levels of the photosensitizer, the cocatalyst, CO2, and the sacrificial agent in the reaction system.