Aprotic Heterocyclic Anion-Based Dual-Functionalized Ionic Liquid Solutions for Efficient CO2 Uptake: Quantum Chemistry Calculation and Experimental Research

A series of novel dual-functionalized ionic liquids (FILs) with the combinations of diethylenetriamine cation ([DETAH](+)) and aprotic heterocyclic anion (AHA) are explored for efficient and reversible CO2 capture, which was distinguished from the traditional strategy by increasing the amino group number of ionic liquids. The structural features and the interactions between ions and CO2 were performed under the DFT method, at the B3LYP/6-311+ +G** level. The CO2 absorption loadings of [DETAH][Im], [DETAH][Py], and [DETAH] [Tz] were 11.91, 11.36, and 10.10 mol CO2/kg IL, respectively. After the fifth cycle, their regeneration efficiencies still kept above 90%. Based on the calculation and C-13 NMR results, the reaction mechanisms of CO2 capture into [DETAH][AHA] solutions were clarified. The amino groups of [DETAH](+) reacted with CO2 to produce [DETAH](+)-carbamates, which guaranteed the high absorption rate. Meanwhile, [AHA](-) could also equimolecularly react with CO2 to form carbamate, which subsequently hydrolyzes into HCO3-/CO32-. Notably, the [AHA](-) was protonated during the CO2 absorption process, and [AHA]-H could react with [DETAH](+)-carbamates to produce [DETAH](+), which helped to recycle the active components of the absorbent and further increased the CO2 capacity and regenerability of the absorbent. The novel dual FILs present as an efficient candidate for CO2 capture.