Coupling Ruthenium Bipyridyl and Cobalt Imidazolate Units in a Metal–Organic Framework for an Efficient Photosynthetic Overall Reaction in Diluted CO₂

Abstract

Artificial photocatalytic CO₂ reduction, using water as the reductant, is challenging mainly because it is difficult for multiple functional units to cooperate efficiently. Here, we show that the classic photosensitive and H₂O-oxidizing ruthenium bipyridyl units and CO₂-reducing cobalt imidazolate units can be incorporated into a metal-organic framework using a classic organic ligand, imidazo[4,5-<i>f</i>][1,10]phenanthroline. Under visible light without additional sacrificial agents and photosensitizers, the overall conversion of CO₂ and H₂O to CO and O₂ was achieved by the multifunctional photocatalyst in the CH₃CN/H₂O mixed solvent with a high CO production rate of 11.2 μmol g^-1 h^-1 and CO selectivity of ca. 100%. Thanks to its ultramicroporous structure with moderately strong CO₂ adsorption ability, the photocatalyst also exhibited high performances with CO/CH₄ production rates of 5.15/0.62 and 4.26/0.20 μmol g^-1 h^-1 in the gas phase with pure and even diluted CO₂, respectively. Photoluminescence emission spectroscopy and photoelectrochemical tests confirmed that the photosensitive and catalytic units cooperated well to give suitable photocatalytic redox potentials and fast electron-hole separation.