Nanosized Core-Shell Zeolitic Imidazolate Frameworks-Based Membranes for Gas Separation

The field of mixed matrix membranes (MMMs) for separation technology has advanced by using metal-organic frameworks (MOFs) with significant gas adsorption. Herein, the nanosized zeolitic imidazolate frameworks (ZIFs) core-shell crystals, i.e., ZIF-67@ZIF-8 (ZIF-67 acting as core and ZIF-8 as shell) are synthesized using the seed-mediated growth method. ZIF-67@ZIF-8 nanocrystals present higher surface area, gas uptake, and thermal stability in comparison with the ZIF-8 and ZIF-67 nanoparticles. Nanosized ZIF-67@ZIF-8 fillers are loaded into the synthesized polyimide and Pebax 1657 matrices and the gas separation properties are compared with the pure ZIF-67 and ZIF-8 MMMs. The highest H-2 permeability of 1150 barrer and H-2/CH4 selectivity of 21.5 is observed for 20 wt% of ZIF-67@ZIF-8 MMM, which demonstrates 100% improvement compared to the permeability of the pristine polyimide membrane. H-2 permeability of ZIF-67@ZIF-8 MMMs increases by up to 86% and 50% in comparison to the ZIF-67 and ZIF-8 MMMs, respectively. This indicates that the interaction and dispersibility of the particles with the polymer matrices can be tuned through the careful engineering of the double-layered fillers. At the same time, the internal core would impart higher gas uptake and permeability to the overall system.