Strategic Design of Mg-Centered Porphyrin Metal-Organic Framework for Efficient Visible Light-Promoted Fixation of CO under Ambient Conditions: Combined Experimental and Theoretical Investigation.

The sunlight-driven fixation of CO into valuable chemicals constitutes a promising approach toward environmental remediation and energy sustainability over traditional thermal-driven fixation. Consequently, in this article, we report a strategic design and utilization of Mg-centered porphyrin-based metal-organic framework (MOFs) having relevance to chlorophyll in green plants as a visible light-promoted highly recyclable catalyst for the effective fixation of CO into value-added cyclic carbonates under ambient conditions. Indeed, the Mg-centered porphyrin MOF showed good CO capture ability with a high heat of adsorption (44.5 kJ/mol) and superior catalytic activity under visible light irradiation in comparison to thermal-driven conditions. The excellent light-promoted catalytic activity of Mg-porphyrin MOF has been attributed to facile ligand-to-metal charge transfer transition from the photoexcited Mg-porphyrin unit (SBU) to the Zr cluster which in turn activates CO, thereby lowering the activation barrier for its cycloaddition with epoxides. The in-depth theoretical studies further unveiled the detailed mechanistic path of the light-promoted conversion of CO into high-value cyclic carbonates. This study represents a rare demonstration of sunlight-promoted sustainable fixation of CO, a greenhouse gas into value-added chemicals.