Tuning the Gas Separation Performance of CuBTC by Ionic Liquid Incorporation

The efficient separation of gases has industrial, economic, and environmental importance. Here, the gas separation performance of a metal organic framework (MOP) is enhanced by ionic liquid (IL) incorporation. One of the most commonly used ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), was incorporated into a commercially available MOF, CuBTC. Detailed characterization by combining spectroscopy with diffraction, electron microscopy, and thermal analysis confirmed that the structures were intact after incorporation. Adsorption isotherms of CH4, H-2, N-2, and CO2 in IL-incorporated CuBTC were experimentally measured and compared with those of pristine CuBTC. Consequently, ideal selectivities for CO2/ CH4, CO2/N-2, CO2/H-2, CH4/N-2, CH4/H-2, and N-2/H-2 separations were calculated. The results showed that the CH4 selectivity of CuBTC over CO2, H-2, and N-2 gases becomes at least 1.5 times higher than that of pristine CuBTC upon the incorporation of IL. For example, the CH4/H-2 selectivity of CuBTC increased from 26 to 56 at 0.2 bar when the IL loading was 30 wt %. These results show that the incorporation of ILs into MOFs can lead to unprecedented improvements in the gas separation performance of MOFs. The tunable physicochemical properties of ILs combined with a large number of possible MOF structures open up opportunities for the rational design of novel materials for meeting future energy challenges.