The dynamic behavior and intrinsic mechanism of CO₂absorption by amino acid ionic liquids

Reducing carbon dioxide emissions is one of the possible solutions to prevent global climate change, which is urgently needed for the sustainable development of our society. In this work, easily available, biodegradable amino acid ionic liquids (AAILs) with great potential for CO₂absorption in the manned closed space such as spacecraft, submarines and other manned devices are used as the basic material. Molecular dynamics simulations andab initiocalculations were performed for 12 AAILs ([P4444][X] and [P66614][X], [X] = X = [GLy]⁻, [Im]⁻, [Pro]⁻, [Suc]⁻, [Lys]⁻, [Asp]²⁻), and the dynamic characteristics and the internal mechanism of AAILs to improve CO₂absorption capacity were clarified. Based on structural analysis and the analysis of interaction energy including van der Waals and electrostatic interaction energy, it was revealed that the anion of ionic liquids dominates the interaction between CO₂and AAILs. At the same time, the CO₂absorption capacity of AAILs increases in the order [Asp]²⁻< [Suc]⁻< [Lys]⁻< [Pro]⁻< [Im]⁻< [Gly]⁻. Meanwhile, the synergistic absorption of CO₂by multiple-sites of amino and carboxyl groups in the anion was proved by DFT calculations. These findings show that the anion of AAILs can be an effective factor to regulate the CO₂absorption process, which can also provide guidance for the rational and targeted molecular design of AAILs for CO₂capture, especially in the manned closed space.