Hybrid carbon molecular sieve membranes having ordered Fe3O4@ZIF-8-derived microporous structure for gas separation

Carbon molecular sieve (CMS) membranes have great promise in CO2 capture. However, tortuous transport passageways restrict the enhancement in the permeability due to the presence of disordered porous structure and dead-end pore. Herein, the growth of ZIF-8 layer on the surface of Fe3O4 formed magnetic core-shell Fe3O4@ZIF-8 particles, which were fixed into 6FDA/ODA:DABA polyimides under magnetic field-induction to fabricate a precursor membrane with vertically oriented chain-like particles. It was then pyrolyzed to form hybrid carbon molecular sieve (HCMS) membranes with ordered microporous structure under high temperature conditions. The cross-section scanning electron microscopy images and N2 adsorption for resultant HCMS membranes indicate that Fe3O4@ZIF-8-derived carbons frameworks were vertically oriented to form the ordered microporous structure, which also had good compatibility with carbon matrix stemmed from 6FDA/ODA:DABA polyimides. The as-prepared HCMS membranes embedded with 5 wt% Fe3O4@ZIF-8 manifested a highest gas separation performance (permeability of 5130 Barrer; CO2/N2 selectivity of 29; CO2/CH4 selectivity of 48), outperforming the pristine CMS membranes, which were near and beyond 2019 CO2/N2 and CO2/CH4 upper bounds, separately. These good separation performances resulted from vertical chain-like microporous particles, which provided fast transport channels to accelerate CO2 diffusion rate. In addition, we supposed that Fe3O4 prevent ZIF-8 frameworks from destruction during the pyrolysis and promote the size screening capability. More importantly, this membrane exhibited excellent aging resistance over 30 days aging testing compared to pristine CMS membranes. Therefore, it affords a feasible way for carbon capture from flue gas and natural gas.