Experiments were combined with atomically detailed simulations and density functional theory (DFT) calculations to understand the effect of incorporation of an ionic liquid (IL), 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), into a metal organic framework (MOF with a zeolitic imidazolate framework), ZIF-8, on the CO2 separation performance. The interactions between [BMIM][PF6] and ZIF-8 were examined in deep detail, and their consequences on CO2/CH4, CO2/N2, and CH4/N2 separation have been elucidated by using experimental measurements complemented by DFT calculations and atomically detailed simulations. Results suggest that IL-MOF interactions strongly affect the gas affinity of materials at low pressure, whereas available pore volume plays a key role for gas adsorption at high pressures. Direct interactions between IL and MOF lead to at least a doubling of CO2/CH4 and CO2/N2 selectivities of ZIF-8. These results provide opportunities for rational design and development of IL-incorporated MOFs with exceptional selectivity for target gas separation applications.
Keywords: CO2 separation; Grand canonical Monte Carlo (GCMC); density functional theory (DFT); ionic liquid (IL); metal organic framework (MOF).