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 COF-SO3H 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.