Amino-modified bimetallic ZIF (Zn/Co-NH2)/Polyimides-based mixed matrix membranes for enhanced hydrogen separation

Mixed matrix membranes (MMMs) have emerged as promising materials for hydrogen separation, combining the processability of polymers with enhanced permeability and selectivity offered by inorganic fillers. However, challenges such as filler aggregation and poor polymer-filler interfacial compatibility limit their performance. In this study, amino-modified bimetallic ZIF (Zn/Co-ZIF-NH₂) was synthesized and employed as a novel nanofiller to fabricate 6FDA-DAM-based polyimide MMMs, aiming to improve interfacial compatibility between the filler and the polymer matrix. The incorporation of Co²⁺ ions into ZIF-8-NH₂ introduced a synergistic effect, optimizing the balance between the rigidity and flexibility of metal-to-ligand bond linkage, while amino groups promoted robust interfacial interactions with the polymer matrix. Compared to the pure polymeric membrane, the MMM incorporating 40 wt% MOF exhibited a significant enhancement in gas permeability, with H₂ permeability rising from 750 to 3273 Barrer and CO₂ permeability increasing from 840 to 2733 Barrer, corresponding to improvements of 336.4 % and 225 %, respectively. Simultaneously, H₂/CH₄ and CO₂/CH₄ selectivities increased to 33.7 and 28.1, representing improvements of 88.3 % and 41 % over the pristine polymer. These performance metrics exceed the 2008 Robeson upper bounds, demonstrating the effectiveness of Zn/Co-ZIF-NH₂ nanofillers in overcoming the permeability–selectivity trade-off. This study underscores the effectiveness of amino-modified bimetallic MOFs as advanced fillers for high-performance MMMs, particularly suited for hydrogen purification and CO₂ separation applications.