Synergistic effect of molecular sieving and adsorption inhibition in MOF-based mixed matrix membranes for efficient O2/N2 separation

Oxygen/nitrogen (O2/N2) separation is of great importance but faces huge challenges owing to their similar molecular size and close polarity. In this work, we construct a polymer of intrinsic microporosity (PIM-1) based mixed matrix membrane (MMM) for efficient O2/N2 separation by using ZIF-8 as the sieving filler along with surface modification of o-carborane (o-CB) to strengthen selective N2 adsorption fixation as well as polymer-filler interfaces. Markedly, the o-CB on the outer surface of ZIF-8 not only affords the requisite interfacial compatibility in molecular sieving MMMs, but also increases the diffusion difference between O2 and N2 by the preferential adsorption with N2 molecules. This synergistic effect of molecular sieving and adsorption inhibition achieves efficient O2/N2 diffusion differential separation. As expected, the optimal membrane with o-CB-ZIF-8 loading of 35 wt% exhibits an O2 permeability of 796.5 Barrer and a mixed O2/N2 selectivity of 8.9 with O2/N2 (20:80, vol.) mixtures, exceeding the latest 2015 upper bound limits. Moreover, the according membrane module with o-CB-ZIF-8 loading of 20 wt% also displays moderate O2 permeability of 391.7 Barrer and O2/N2 selectivity of 5.5 under pressure of 1 bar. This work may provide a feasible platform for designing high-performance MOF-based membranes in air separations.