Building well-defined magnetic channels in PIM-1 mixed matrix membranes with ZIF-8 wrapped Fe3O4 nanoparticle for effective O2/ N2 separation

Magnetic mixed matrix membranes (MMMs) show great potential for enhancing O2/N2 separation efficiency by leveraging the inherent magnetic property differences between O2 (paramagnetic) and N2 (diamagnetic). However, one of the major challenges is the establishment and precise control of magnetic channels between magnetic fillers and polymer matrix. To address this issue, herein, ZIF-8 wrapped Fe3O4 nanoparticles (Fe3O4@ZIF-8) were synthesized using a step-by-step assembly method, and then integrated into polymer of intrinsic microporosity (PIM-1) matrix to develop MMMs with well-defined magnetic channels for O2/N2 separation. In comparison with Fe3O4, Fe3O4@ZIF-8 nanoparticles exhibited significantly enhanced compatibility with the polymer matrix, thereby facilitating uniform dispersion and improving interfacial adhesion. Gas permeation experiments revealed that the magnetic PIM-1/Fe3O4@ZIF-8 MMMs demonstrated enhanced O2/N2 separation performance due to the combined effects of magnetic responsiveness and the presence of ZIF-8 magnetic channels. Under a magnetic field strength of 56mT, the magnetic MMM with a 4 wt% loading of Fe3O4@ZIF-8 exhibited optimal O2/N2 separation performance with O2 permeability of 710 Barrer and O2/N2 selectivity of 3.64. These values represented a significant improvement of 42% and 24%, respectively, compared to pure PIM-1 membrane. Moreover, the simultaneous improvement of permeability and selectivity enabled the achievement of Robeson's 2008 upper bound for O2/N2 separation, underscoring the great potential of Fe3O4@ZIF-8 nanoparticles for designing magnetic MMMs with favorable structural attributes and exceptional separation efficiency.