Synthesis of ZIF-68 Membrane on a ZnO Modified α-Alumina Support by a Modified Reactive Seeding Method

Large-pore ZIF-68 membranes offer adsorption-based selectivity for separation of gas mixtures or molecular sieving characteristics for the separation of large liquid molecules. ZIF-68 membranes can be grown on ZnO modified α-alumina supports by a modified reactive seeding method. The resultant membranes were around 40 Μm in thickness and were determined to have limited nonselective defects given their adherence to Knudsen diffusion during single gas permeation measurements. Further pervaporation experiments showed that the ZIF-68 membranes synthesized via the modified reactive seeding method had a p-xylene pervaporation flux approximately 5.4 times as large as that reported for similar pore-sized MOF-5 membranes; however, pervaporation flux of larger molecule, ditert-butylbenzene, through the same two MOF membranes showed the flux of the ZIF-68 membrane was 3.4 times smaller than that reported for MOF-5. This reversal in pervaporation flux indicates the ZIF-68 structure is more readily accessible to molecules smaller than its pore size, but larger molecules are subjected to a staunch cut off in flux.