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1‐n‐Butyl‐3‐methylimidazolium methyl sulfate is incorporated into MIL‐53(Al). Detailed characterization is done by X‐ray fluorescence, Brunauer–Emmett–Teller surface area, scanning electron microscopy, X‐ray diffraction, Fourier‐transform infrared spectroscopy, and thermogravimetric analysis. Results show that ionic liquid (IL) interacts directly with the framework, significantly modifying the electronic environment of MIL‐53(Al). Based on the volumetric gas adsorption measurements, CO2, CH4, and N2 adsorption capacities decreased from 112.0, 46.4, and 19.6 cc (STP) gMIL‐53(Al) −1 to 42.2, 13.0, and 4.3 cc (STP) gMIL‐53(Al) −1 at 5 bar, respectively, upon IL incorporation. Data show that this postsynthesis modification leads to more than two and threefold increase in the ideal selectivity for CO2 over CH4 and N2 separations, respectively, as compared with pristine MIL‐53(Al). The isosteric heat of adsorption (Qst) values show that IL incorporation increases CO2 affinity and decreases CH4 and N2 affinities. Cycling adsorption–desorption measurements show that the composite could be regenerated with almost no decrease in the CO2 adsorption capacity for six cycles and confirm the lack of any significant IL leaching. The results offer MIL‐53(Al) as an excellent platform for the development of a new class of IL/MOF composites with exceptional performance for CO2 separation.

Five different imidazolium-based ionic liquids (ILs) were incorporated into am etal-organic framework (MOF), MIL-53(Al),t oi nvestigate the effect of IL incorporation on the CO 2 separation performance of MIL-53(Al). CO 2 ,C H 4 ,a nd N 2 adsorption isothermso ft he IL/MIL-53(Al) composites and pristine MIL-53(Al)w ere measured to evaluatet he effect of the ILs on the CO 2 /CH 4 and CO 2 /N 2 selectivities of the MOF. Of the composite materials that were tested,[ BMIM][PF 6 ]/ MIL-53(Al) exhibited the largesti ncreasei nC O 2 /CH 4 selectivity,2 .8-times higher than that of pristine MIL-53(Al), whilst [BMIM][MeSO 4 ]/MIL-53(Al) exhibited the largest increase in CO 2 /N 2 selectivity,3 .3-times highert han that of pristine . Ac omparison of the CO 2 separation potentials of the IL/MOF composites showed that the [BMIM][BF 4 ]-and [BMIM][PF 6 ]-incorporated MIL-53(Al) composites both showed enhanced CO 2 /N 2 and CO 2 /CH 4 selectivities at pressures of 1-5 bar compared to composites of CuBTC and ZIF-8w ith the same ILs. These results demonstrate that MIL-53(Al) is av ersatile platform for IL/MOF composites and could help to guide the rational design of new composites for target gas-separation applications.

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