Role of amino acid ([HIS]−) and [NTf2]− anions in CO2 capture by phosphonium- and ammonium-based dicationic ionic liquids: combined COSMO-RS and DFT analyses

Abstract

In this study, the CO2 capture potential of dicationic ionic liquids (DILs) based on ammonium and phosphonium cations paired with either histidine ([HIS]−) amino acid or [NTf2]− anions was systematically investigated using combined COSMO-RS and DFT analyses. COSMO-RS simulations of physicochemical and thermodynamic properties—including vapor pressure, density, Henry's law constant, gas selectivity, and activity coefficients—demonstrate that [HIS]-based DILs exhibit lower vapor pressures, higher thermal and chemical stability, enhanced CO2 solubility, and superior selectivity over H2, CO, and CH2, particularly in systems containing the [N4444-R-N4444][HIS]2 dication. DFT studies reveal that the anion's chemical structure critically governs CO2 absorption: [HIS]-DILs form strong hydrogen bonds with CO2, resulting in higher interaction energies, shorter intermolecular distances, and improved thermodynamic efficiency compared to [NTf2]-based systems. These observations are corroborated by frontier molecular orbital analyses, quantum descriptors, and QTAIM calculations, confirming the stronger chemical reactivity and hydrogen-bonding interactions of [HIS]-functionalized DILs. The synergistic effect of dicationic structures with amino acid-functionalized anions maximizes CO2 capture while enhancing biocompatibility, stability, and environmental friendliness. These findings provide a molecular-level understanding that can guide the rational design of next-generation ionic liquids as efficient, cost-effective, and environmentally sustainable CO2 capture agents across industrial applications. © 2026 Elsevier B.V.