Incorporation of a Binuclear Cobalt Complex into MOFs for Photocatalytic CO₂ Reduction with H₂O as an Electron Donor

The development of molecular composite photocatalysts for cost-effective, sacrificial-reagent-free CO₂ reduction is desirable but challenging. Herein, we employed an <i>in situ</i> encapsulation strategy to encapsulate the binuclear cobalt complex (Co₂L) within NH₂-MIL-125 and synthesized a range of MOF-based composites with varying cobalt content for photocatalytic CO₂ reduction. The photocatalytic results showed that the catalytic performance increased with the increase in Co₂L content, reaching a rapid CO generation rate of 27.95 μmol·g^-1·h^-1, over 5 times that of bare NH₂-MIL-125, with water as the electron donor instead of any organic sacrificial agent. This composite catalyst effectively harnesses the advantages of both molecular catalysts and MOFs, leveraging the superior catalytic activity of molecular catalysts while also capitalizing on the light absorption and water oxidation capabilities of MOFs, resulting in a remarkable ability for photocatalytic CO₂ reduction. The photocatalytic mechanism involving electron transfer and CO₂ activation has been revealed by photoluminescence spectroscopy, <i>in situ</i> X-ray photoelectron spectroscopy, <i>in situ</i> diffuse reflectance infrared Fourier transform spectroscopy, and other control experiments.