High CO₂ Absorption Capacity of Metal-Based Ionic Liquids: A Molecular Dynamics Study

The absorption of CO2 is of importance in carbon capture, utilization, and storage technology for greenhouse gas control. In the present work, we clarified the mechanism of how metal-based ionic liquids (MBILs), Bmim[XCln]m (X is the metal atom), enhance the CO2 absorption capacity of ILs via performing molecular dynamics simulations. The sparse hydrogen bond interaction network constructed by CO2 and MBILs was identified through the radial distribution function and interaction energy of CO2-ion pairs, which increase the absorption capacity of CO2 in MBILs. Then, the dynamical properties including residence time and self-diffusion coefficient confirmed that MBILs could also promote the diffusion process of CO2 in ILs. That's to say, the MBILs can enhance the CO2 absorption capacity and the diffusive ability simultaneously. Based on the analysis of structural, energetic and dynamical properties, the CO2 absorption capacity of MBILs increases in the order Cl− → [ZnCl4]2-→ [CuCl4]2-→ [CrCl4]- → [FeCl4]-, revealing the fact that the short metal–Cl bond length and small anion volume could facilitate the performance of CO2 absorbing process. These findings show that the metal–Cl bond length and effective volume of the anion can be the effective factors to regulate the CO2 absorption process, which can also shed light on the rational molecular design of MBILs for CO2 capture and other key chemical engineering processes, such as IL-based gas sensors, nano-electrical devices and so on.