Cooperative CO(2) absorption by amino acid-based ionic liquids with balanced dual sites

In this study, a variety of functionalized ILs with dual sites including amino acid group (AA) and basic anion (R) were synthesized to investigate the suppression and cooperation between the sites in CO(2) absorption. The basic anions selected in this study with different basicity include sulfonate (Su), carboxylate (Ac), imidazolium (Im), and indolium (Ind). These ILs ([P(66614)](2)[AA–R]) were applied to CO(2) absorption. The results present that CO(2) capacity increases first and then decreases later with the continuous increase in the activity of the anion site. Combined with CO(2) absorption experiments, IR and NMR spectroscopic analyses and DFT calculation demonstrate that the ability of one site to capture CO(2) would be suppressed when the activity of another site is much stronger. Thus, the cooperation of dual site-functionalized ILs and high CO(2) capacity might be achieved through balancing the two sites to be equivalent. Based on this point, [P(66614)](2)[5Am–iPA] was further synthesized by taking the advantage of the conjugated benzene ring. As expected, [P(66614)](2)[5Am–iPA] showed capacity as high as 2.38 mol CO(2) per mol IL at 30 °C and 1 bar without capacity decrease even after 10 times recycling performance of CO(2) absorption and desorption.