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.