MIL-53(Al) as a Versatile Platform for Ionic-Liquid/MOF Composites to Enhance CO2 Selectivity over CH4 and N2

Five different imidazolium-based ionic liquids (ILs) were incorporated into a metal-organic framework (MOF), MIL-53(Al), to investigate the effect of IL incorporation on the CO2 separation performance of MIL-53(Al). CO2, CH4, and N-2 adsorption isotherms of the IL/MIL-53(Al) composites and pristine MIL-53(Al) were measured to evaluate the effect of the ILs on the CO2/CH4 and CO2/N-2 selectivities of the MOF. Of the composite materials that were tested, [BMIM][PF6]/MIL-53(Al) exhibited the largest increase in CO2/CH4 selectivity, 2.8-times higher than that of pristine MIL-53(Al), whilst [BMIM][MeSO4]/MIL-53(Al) exhibited the largest increase in CO2/N-2 selectivity, 3.3-times higher than that of pristine MIL-53(Al). A comparison of the CO2 separation potentials of the IL/MOF composites showed that the [BMIM][BF4]- and [BMIM][PF6]-incorporated MIL-53(Al) composites both showed enhanced CO2/N-2 and CO2/CH4 selectivities at pressures of 1-5 bar compared to composites of CuBTC and ZIF-8 with the same ILs. These results demonstrate that MIL-53(Al) is a versatile platform for IL/MOF composites and could help to guide the rational design of new composites for target gas-separation applications.