Vesicles-shaped MOF-based mixed matrix membranes with intensified interfacial affinity and CO2 transport freeway

The trade-off between gas permeability and selectivity represents a huge challenge for membrane separation. In this work, we design unique polystyrene-acrylate (PSA) modified hollow ZIF-8 (PHZ) nanospheres via a facile hard template-incomplete etching strategy as fillers for mixed matrix membranes (MMMs). In the vesicles shaped PHZ, the hollow core builds a low-resistance CO2 transport freeway, leading to improved CO2 permeability. Meanwhile, the outside PSA layer intensifies the interface affinity between ZIF-8 and Pebax through molecular chains entanglements and hydrogen bonding, enhancing membrane selectivity. Through controlling the PSA etching process, both the hollow core with tunable size and the outside PSA layer with adjustable thickness are achieved. The 10 wt% PHZ-2/Pebax MMMs present the best performance with a CO2 permeability of 172.4 Barrer and CO2/N2 selectivity of 87.9. The higher CO2/N2 selectivity proves that the PSA layer on the PHZ has better compatibility with Pebax. The higher CO2 permeability is attributed to the low-resistance hollow core. The gas separation performance of PHZ-based MMMs not only well exceeded the 2008 Robeson upper-bond line but also was superior to those of other published MOF-based MMMs. The concept of vesicle-shaped PHZ paves a way to concurrently enhance both the gas permeability and selectivity of MMMs.