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 H₂ permeability of 1150 barrer and H₂/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. H₂ 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.