Dislocated Bilayer MOF Enables High-Selectivity Photocatalytic Reduction of CO2 to CO

The highly selective photoreduction of CO2 into valuable small-molecule chemical feedstocks such as CO is an effective strategy for addressing the energy crisis and environmental problems. However, it remains a challenge because the complex CO2 photoreduction process usually generates multiple possible products and requires a subsequent separation step. In this paper, 2D monolayer and bilayer porphyrin-based metal-organic frameworks (MOFs) are successfully constructed by adjusting the reaction temperature and solvent polarity with 5,10,15,20-tetrakis(4-pyridyl)porphyrin as the light-harvesting ligand. The bilayer MOF is a low-dimensional MOF with a special structure in which the upper and lower layers are arranged in dislocation and are bridged by halogen ions. This bilayer MOF exhibits 100% ultra-high selectivity for the reduction of CO2 to CO under simulated sunlight without any cocatalyst or photosensitizer and can be recycled at least three times. The intrinsic mechanism of this photocatalytic CO2 reduction process is explored through experimental characterization and density functional theory (DFT) calculations. This work shows that the rational design of the number of layers in 2D MOF structures can tune the stability of these structures and opens a new avenue for the design of highly selective MOF photocatalysts.