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

The first application of an imidazole MOF, the 2D Co(II)-imidazole framework, {[Co(TIB) 2 (H 2 O) 4 ]SO 4 } (TIB stands for 1,3,5-tris(1-imidazolyl) benzene) (CoTIB) in photocatalytic CO 2 reduction was carried out, and compared with that of ZIF-67. The CO 2 /CoTIB (1.0 mg)/Ru(bpy) 3 Cl 2 (bpy = 2,2'-bipyridine) (11.3 mg)/CH 3 CN (40 mL)/TEOA (10 mL)/H 2 O (400 μL) system produced 76.9 μmol of CO in 9 h, corresponding to the efficiency of 9.4 mmol g À 1 h À 1 (TOF: 7.3 h À 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 CO 2 adsorption capacity and poor conductivity. Extensive photocatalytic experiments and energy-level diagrams suggest that the reduction did not depend on the CO 2 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 CO 2 . In addition, the process utilizes the short-lived singlet state ( 1 MLCT), not the long-lived triplet state ( 3 MLCT) of Ru(bpy) 3 Cl 2 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, CO 2 , and the sacrificial agent in the reaction system.

Donor–acceptor type triphenylamine-based porous aromatic frameworks (TPA-PAFs) for photosynthesis of benzimidazoles

“…2 Recently, various classes of photocatalysts have been developed, including semiconductor materials (g-C 3 N 4 , 3 TiO 2 , 4,5 etc . ), organometallic complexes (Ru(bpy) 3 Cl 2 , bpy = bipyridine, 6 Ir(ppy) 3 , ppy = 2-phenylpyridine, 7 etc . ), molecular organic dyes (fluorescein, 8 etc ) and polymetallic oxides.…”