Design and Synthesis of Novel Dual-Functional Protic Ionic Liquids with a Superior High CO2 Absorption Efficiency.

As a predictive tool, quantum chemical calculations can be used to design protic ionic liquids (PILs) and predict the result. By adding anionic negative potential sites, two dual-functional PILs diethylenetriamine-barbituric acid [C4H14N3]2[C4H2N2O3] and diethylenetriamine-ethylenolactonium [C4H14N3]2[C3H2N2O2] were designed. The simulation results indicated that multisite absorption of anions and cations resulted in an expected absorption ratio exceeding 3:1 (mol CO2:mol ILs). Furthermore, the Gibbs free energy and enthalpy barrier were calculated. Based on this, the two PILs were synthesized in a controlled manner, and the experimental results demonstrated that 0.25 mol/L [C4H14N3]2[C4H2N2O3] and [C4H14N3]2[C3H2N2O2] exhibited a superior CO2 absorption capacity of 3.152 and 3.466 mol CO2/mol ILs, respectively. After five adsorption-desorption experiments, the regeneration rates of [C4H14N3]2[C3H2N2O2] were all higher than 90%. Finally, the reaction mechanism for CO2 capture in these PILs was revealed that the significant increase in capacity could be attributed to the combined absorption of double negative potential N atoms on anions and primary and secondary amines on cations by using 13C NMR.