Cation−Anion−CO2 Interactions in Imidazolium‐Based Ionic Liquid Sorbents

A series of functionalized N‐alkylimidazolium based ionic liquids (ImILs) were designed, through anion (carboxylates and halogenated) and cation (N‐alkyl side chains) structural modifications, and studied as potential sorbents for CO2. The sorption capacities of as prepared bare ImILs could be enhanced from 0.20 to 0.60 molar fraction by variation of cation‐anion‐CO2 and IL‐CO2‐water interaction. By combining NMR spectroscopy with molecular dynamics simulations, a good description of interactions between ImIL and CO2 can be obtained. Three types of CO2 sorption modes have been evidenced depending on the structure of the ImIL ion pair: Physisorption, formation of bicarbonate, and covalent interaction through the nucleophilic addition of CO2 to the cation or anion. The highest CO2 sorption capacity was observed with the ImIL containing the 1‐n‐butyl‐3‐methylimidazolium cation associated with the carboxylate anions (succinate and malonate). This study provides helpful clues for better understanding the structure‐activity relationship of this class of materials and the ion pair influence on CO2 capture. Caught in a trap: Three types of CO2 sorption in ionic liquids have been observed: Physi‐sorption, formation of bicarbonate, and covalent interaction between the CO2 and the cation or the anion. Combining NMR spectroscopy and molecular dynamics simulations indicated that the ability to capture is related to the nature and the interaction of the cation and anion.