Highly Stable Lanthanide-Organic Frameworks Based on {Ln6O8} Clusters with Photocatalytic Reduction of CO2 to CO

Abstract

Metal-organic frameworks (MOFs) with adjustable structures, diverse chemical functionalities, and excellent CO₂ capture ability have shown important potential application in the photocatalytic reduction of CO₂ to valuable fuel to curb the energy crisis. In this work, a series of new isostructural lanthanide-organic frameworks based on hexanuclear {Ln₆O₈} clusters, {(DMA)₂ [Ln₆(μ₃-OH)₈(H₂O)₆(SBTC)₃]}_n (Ln-MOFs, Ln = Eu, Dy, Gd, Tb, Yb; H₄SBTC = 5,5'-(ethene-1,2-diyl) di-isophthalic acid; DMA = dimethylamine cation) were synthesized by the solvothermal method. Ln-MOFs were metal-organic frameworks formed by {Ln₆(μ₃-OH)₈} clusters and poly(carboxylic acid) ligands H₄SBTC, which exhibited excellent photocatalytic properties for the reduction of CO₂ to CO. Among these Ln-MOFs, the production rate of photocatalytic reduction of CO₂ to CO by Eu-MOF was 663.00 μmol·h^-1·g^-1 and the selectivity reached 94.2%, utilizing [Ru(bpy)₃]Cl₂·6H₂O as photosensitizers. Experimental characterizations and density functional theory (DFT) calculations unveiled that the effective charge separation, strong CO₂ binding affinity, weak H₂O adsorption energy, as well as low reaction energy barriers for the *COOH intermediates over Eu-MOF play an important role in possessing superior photoactivity. This study provides insights into the field of Ln-MOF materials for efficient photocatalytic CO₂ reduction and conversion applications.