Properties and interactions of magnetic ionic Liquids: Focus on greenhouse gas capture from MD simulations

Due to their distinctive combination of ionic liquid (IL) characteristics and magnetic susceptibility, magnetic ionic liquids (MILs) have emerged as promising materials for gas capture and separation. In this study, molecular dynamics (MD) simulations were employed to investigate the thermodynamic, transport, and structural properties of selected MILs and their interactions with environmentally relevant gases, including methane (CH 4 ), ammonia (NH 3 ), carbon dioxide (CO 2 ) and sulfur dioxide (SO 2 ). The study focused on both imidazolium-based ([C 4 C 1 im] + ) and phosphonium-based ([P 66614 ] + ) cations paired with various anions, including [FeCl 4 ] − , [FeBr 4 ] − , [MnCl 4 ] 2− and [GdCl 6 ] 3− . Fixed-charge force field parameters were established and validated for phosphonium-based MILs for the first time in the area. Free energy calculations demonstrated that phosphonium-based MILs with multivalent anions exhibit favorable solvation energies for CO 2 and SO 2 gases, indicating a high potential for selective gas capture. A reduction in gas mobility is observed in these multivalent-based MILs/gas systems. The molecular-level insights provided by radial distribution functions (RDFs) elucidate the critical role of anions in determining solvation behavior. This observation underscores the importance of these paramagnetic elements in the interactions between the gases and MILs. This study advances the understanding of gas-MIL interactions and offers a foundation for the rational design of advanced materials for industrial gas capture and environmental remediation processes.