Abstract
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, CO(2), CH(4), and N(2) adsorption capacities decreased from 112.0, 46.4, and 19.6 cc (STP) g(MIL-53(Al)) (-1) to 42.2, 13.0, and 4.3 cc (STP) g(MIL-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 CO(2) over CH(4) and N(2) separations, respectively, as compared with pristine MIL-53(Al). The isosteric heat of adsorption (Qst) values show that IL incorporation increases CO(2) affinity and decreases CH(4) and N(2) affinities. Cycling adsorption-desorption measurements show that the composite could be regenerated with almost no decrease in the CO(2) 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 CO(2) separation.