Novel benzenesulfonamide-based ionic liquids for energy-efficient CO2 capture and conversion

Abstract

The capture and utilization of carbon dioxide (CO₂) from the post-combustion of fossil fuels has been identified as a highly effective strategy for reducing carbon emissions. Herein, a series of novel substituted benzenesulfonamide ionic liquids (BSA-ILs) were designed and synthesized via facile acid–base neutralization reactions for the purpose of achieving reversible CO₂ capture and catalyzing CO₂ chemical fixation. Addressing the inherently high viscosity of neat BSA-ILs (551.2–7785.7 mPa s), propylene carbonate (PC), a green product derived from CO₂ chemical fixation, was selected as a diluent to form BSA-IL mixed absorbents (BSA-IL-MAs). The optimized system exhibited a high CO₂ uptake capacity of 1.38 mol of CO₂ per mol BSA-IL, an excellent CO₂/N₂ selectivity of 18.36, and a remarkable 99.0% conversion of epichlorohydrin under mild, solvent-free, metal-free, halogen-free, co-catalyst-free and atmospheric pressure conditions. Meanwhile, the findings demonstrated a certain positive correlation between the CO₂ uptake capacity/conversion and the pK_a of the substituted BSA. Notably, the BSA-IL system retained nearly intact CO₂ capture performance and catalytic activity after five consecutive absorption–desorption and catalytic cycles, with an extremely low E-factor of 0.11. Spectroscopic characterization confirmed the formation of a new carbonyl moiety peak in CO₂-saturated BSA-ILs, indicating that chemisorption dominated the CO₂ uptake process. NMR investigations and DFT calculations further elucidated the interactions between BSA-ILs, CO₂ and epoxide substrates, validating the feasibility of the proposed reaction pathways. This work provides a sustainable, efficient and industrially feasible integrated platform for CO₂ capture and utilization, offering a paradigm for low-carbon catalytic conversion systems.