Deciphering the role of non-covalent interactions in CO2 Capture: A DFT and COSMO-RS study of amino acid-based ionic liquids.

A computational investigation into the interactions between amino acid based ionic liquids (AAILs) and carbon dioxide has provided valued discernments into the molecular mechanisms leading to CO2 capture. Using DFT and COSMO-RS simulations, the adsorption affinity of three AAILs based on lysinate, Arginate and Glycinate based amino acids anions tehthered with with counter cation 1-Methyl-3-(3-sulfopropyl)-imidazolium [1MeimPS]+ with CO2 is explored. The interaction of nCO2 (n = 1) with lysine based AAIL-1CO2 showed superior adsorption energy of -2.820 kcal/mol, whereas arginine based AAIL-1CO2 showed least adsorption energy of -1.966 kcal/mol. Similarly, for nCO2 (n = 2), the lysine based AAIL 2CO2 showed nearly double the adsorption energy of -4.6831 kcal/mol compared to lysine based AAIL 1CO2. On contrary, arginine based AAIL-2CO2 has even less adsorption energy of -1.901 kcal/mol compared to [1MeimPS][Arg]-1CO2. However, the introduction of second CO2 molecule reduces the bond distances for AAILs--1CO2, further strengthened and fine-tuned the CO2 adsorption. Also, CO2 solubility of AAILs is investigated ranging from 288.15 to 353.15 K at 5.0-45 bar revealed that temperature has inverse relationship with solubility, illustrating that the combination of [Gly]- and [Lys]- anions with cation [1MeimPS]+ is effective for efficient CO2 capture and separation. Furthermore, Natural Bond Orbital (NBO) analyis showed the significant charge trasfer in lysine based AAIL nCO2 compared to other ILs. Also, anions have the appreciable chances of strong dispersion interactions with CO2 as revealed by Quantum Atoms in Molecules (QTAIM), and Interaction Region Indicator (IRI) plots. Among, ILs bearing multiple amine groups, lysine based AAIL displayed favorable activity coefficient (γ∞) values suggesting efficient and stable interactions with CO2 as evidenced by Adsorption Energy Eads, QTAIM topologies and IRI isosurfaces. Understanding multiple interactions between ILs and nCO2 paved the ways to design ILs for CO2 adsorption and separation for environmental challenges.