Synergistic interfacial interaction in polyetherimide/ZIF-7 mixed matrix membranes for enhanced H₂/CO₂ separation

Mixed matrix membranes (MMMs), consisting of a continuous polymer phase and a discontinuous molecular sieve phase, present a promising alternative to polymeric membranes for gas separations due to their advantages of high processability with outstanding separation efficiency. The suppression of sieve-in-a-cage and filler agglomerations, major challenges in existing MMMs, is systematically validated through a combination of polyimide and zeolitic imidazolate framework-7 (ZIF-7) nanofillers to enhance the H₂/CO₂ separation performance. The polyetherimide (Ultem) exhibits excellent interfacial interaction with ZIF-7 nanofillers within the MMMs, enabling the accommodation of high ZIF-7 concentrations, up to 40 wt%, due to its hydrophobic nature. The Ultem/ZIF-7 (60/40 wt/wt) MMMs represent significant enhancements in both H₂ permeability and H₂/CO₂ selectivity, showing increases of 35 % and 65 %, respectively, compared to the pristine Ultem membrane. Furthermore, the enhancement in the intrinsic H₂/CO₂ separation performance of ZIF-7, estimated by the Maxwell equation, is likely attributed to the substantial rigidification of polymer chains in the vicinity of ZIF-7. Additionally, the difference in the activation energy of permeation for H₂ and CO₂ distinctly increases with ZIF-7 contents, highlighting the importance of the interfacial interaction in the separation performance of MMMs.