Design and Synthesis\nof Novel Dual-Functional Protic\nIonic Liquids with a Superior High CO<sub>2</sub> Absorption Efficiency

As\na predictive tool, quantum chemical calculations can\nbe used\nto design protic ionic liquids (PILs) and predict the result. By adding\nanionic negative potential sites, two dual-functional PILs diethylenetriamine-barbituric\nacid [C<sub>4</sub>H<sub>14</sub>N<sub>3</sub>]<sub>2</sub>[C<sub>4</sub>H<sub>2</sub>N<sub>2</sub>O<sub>3</sub>] and diethylenetriamine-ethylenolactonium\n[C<sub>4</sub>H<sub>14</sub>N<sub>3</sub>]<sub>2</sub>[C<sub>3</sub>H<sub>2</sub>N<sub>2</sub>O<sub>2</sub>] were designed. The simulation\nresults indicated that multisite absorption of anions and cations\nresulted in an expected absorption ratio exceeding 3:1 (mol CO<sub>2</sub>:mol ILs). Furthermore, the Gibbs free energy and enthalpy\nbarrier were calculated. Based on this, the two PILs were synthesized\nin a controlled manner, and the experimental results demonstrated\nthat 0.25 mol/L [C<sub>4</sub>H<sub>14</sub>N<sub>3</sub>]<sub>2</sub>[C<sub>4</sub>H<sub>2</sub>N<sub>2</sub>O<sub>3</sub>] and [C<sub>4</sub>H<sub>14</sub>N<sub>3</sub>]<sub>2</sub>[C<sub>3</sub>H<sub>2</sub>N<sub>2</sub>O<sub>2</sub>] exhibited a superior CO<sub>2</sub> absorption capacity of 3.152 and 3.466 mol CO<sub>2</sub>/mol ILs,\nrespectively. After five adsorption–desorption experiments,\nthe regeneration rates of [C<sub>4</sub>H<sub>14</sub>N<sub>3</sub>]<sub>2</sub>[C<sub>3</sub>H<sub>2</sub>N<sub>2</sub>O<sub>2</sub>] were all higher than 90%. Finally, the reaction mechanism for CO<sub>2</sub> capture in these PILs was revealed that the significant increase\nin capacity could be attributed to the combined absorption of double\nnegative potential N atoms on anions and primary and secondary amines\non cations by using <sup>13</sup>C NMR.