Highly Reversible and Efficient Absorption of Low-Concentration NO by Amino-Acid-Based Ionic Liquids

A series of environmentally benign functional ionic liquids (ILs) based on l-proline as the anion to efficiently absorb low-concentration NO have been investigated in this work. The results indicate that the ILs with an l-proline anion have high absorption capacities for 0.16 vol % NO, reaching a maximum absorption capacity of 0.51 mol of NO per mol of IL at 30 °C and ambient pressure for l-proline choline IL ([Ch][l-Pro]). The absorbed NO could be recovered from [Ch][l-Pro], and the regenerated IL had no significant loss of NO absorption capacity for at least 7 recycles. We verified the mechanism through both experimental and theoretical methods. The results indicate that the absorption of NO in [Ch][l-Pro] mainly resulted from a chemical process—NO and the secondary amine group in the anion form a NONOate with a chemical formula [l-Pro]−–(NO)–NO. We believe that this efficient and reversible absorption of low-concentration NO by the ILs has potential as a new NO capture technique.