Highly efficient metal/solvent-free chemical fixation of CO2 at atmospheric pressure conditions using functionalized porous covalent organic frameworks

Abstract

The development of metal-free heterogeneous catalysts for selective carbon capture and utilization (CCU) as a C1-feedstock under mild conditions has significant potential towards sustainable fixation of atmospheric CO2 into value-added products. Herein, we report utilization of polar functionalized covalent-organic framework (COF-SO3H) as metal-free heterogeneous catalyst for efficient fixation of CO2 into cyclic carbonates. The COFSO3H possesses large 1D channels functionalized with polar (–NH, and –SO3H) groups rendering selective adsorption property for CO2 with a high heat of interaction (Qst) energy of 42.2 kJ/mol. Interestingly, the value of Qst for COF-SO3H was found to be about 10.8 kJ/mol higher than that of analogous COF (COF-H) which lacks the polar sulfonic acid group. The presence of basic –NH sites combined with Brønsted acid (–SO3H) sites make COF-SO3H a suitable material for metal/solvent-free chemical fixation of CO2 with epoxides. Indeed, COF-SO3H catalyzes cycloaddition of CO2 with epoxides to generate cyclic carbonates under metal/solvent-free atmospheric pressure conditions. Moreover, COF-SO3H is highly recyclable for several cycles with retaining the catalytic activity and structural rigidity. This work represents a rare demonstration of metal/solvent-free chemical fixation of CO2 under atmospheric pressure conditions using polar-functionalized COF.