Effect of the anionic counterpart of amino acid based Ionic liquids upon efficient CO2 Capture: A correlation of experimental and DFT study

Ionic liquids (ILs) are a promising generation of sustainable and efficient CO2 sorbents because of their inherent advantages in providing a flexible alternative to standard amine solutions. In this context, ILs based on amino acids can be excellent candidates for enhanced CO2 sorption. Herein, three ILs consisting of distinctively tailored imidazolium cation paired with amino acid anions have been synthesized and characterized by both experimental techniques and DFT studies. The potential and influence of propane-sultone modified imidazolium cation [1MeimPS]+ and amino-acid anions ([Trp]-, [Tyr]-, [His]-), on CO2 capacity were investigated at 298.15 K and pressures up to 4 MPa were evaluated. Among them, [1MeimPS][His], exhibited the notable capability in terms of CO2 sorption (0.6767 mol fraction) at 1 MPa pressure and 298.15 K with the lowest viscosity recorded. Moreover, a direct association between CO2 capacity and pressure rise was observed. CO2 recyclability measurements revealed an exceptional CO2 solubility even after four cycles. The DFT investigation was carried out to compute the interaction energies and investigate the underlying interaction between ILs and CO2, which corresponded very well with the experimental findings. The exploration of various interaction descriptors offered a deeper understanding of the interactions between ILs and CO2. Frontier Molecular Orbitals (FMO) parameters showed that the suggested ILs are robust, viable and chemically reactive. The atoms in molecules theory (QTAIM) and Interaction Region Indicator (IRI) analysis revealed that the CO2 mainly interacted with anions through hydrogen bonding and van der Waal forces. The NBO data implied that stable charge transfers occurred from CO2 towards ILs. This study suggests a practical method for boosting CO2 solubility by changing the physicochemical properties of ILs and makes this research a significant contribution to the recent literature and provide insights for more effective carbon capture systems and industrial applications.