An excellent 3D Cu-MOF with exposed Lewis acidic Cu sites for CO2 adsorption and catalytic fixation via Cyclic Carbonate synthesis

Abstract

A novel 3D porous Cu(II)-metal-organic framework (MOF) with exposed Lewis acidic Cu sites has been synthesized under solvothermal conditions utilizing the new tetratopic linker, 4'-((3,5-dicarboxyphenoxy)methyl)-[1,1'-biphenyl]-3,5-dicarboxylic acid. The synthesized Cu(II)-MOF is thoroughly characterized by various physicochemical methods: powder XRD, TGA, FTIR, and gas adsorption studies. The microporous Cu(II)-MOF material featuring open channels which after activation affords unsaturated Lewis acidic Cu(II) metal sites, proved to be a good capturing agent for CO₂. The gas adsorption isotherms indicate that the activated Cu(II)-MOF′ is efficient in CO₂ uptake and in the presence of epoxides and TBAB as co-catalysts, it leads the CO₂ chemical fixation into five-membered cyclic carbonates under mild and solvent-free reaction conditions. The implication of unsaturated Cu(II) metal sites and their synergism with TBAB for the chemical fixation of CO₂ were probed using various epoxides by observing the appreciable conversion. Moreover, the catalyst Cu(II)-MOF′ upholds its adequate stability as well as recyclability for five consecutive cycles without apparent loss in its catalytic activity. Under nearly similar reaction conditions, the results signify a comparable CO₂ conversion with various reported MOF-based catalysts. Finally, a plausible mechanism for CO₂ fixation with epoxide under the catalytic influence of Cu(II)-MOF′ has been proposed.