Mixed matrix membranes consisting of ZIF-8 in rubbery amphiphilic copolymer: Simultaneous improvement in permeability and selectivity

We report the development and assessment of mixed-matrix membranes (MMMs) that showed simultaneous improvement in CO₂ permeability and CO₂/N₂ selectivity based on precise interface and interaction control. Specifically, MMMs were prepared using solution-synthesized ZIF-8 nanoparticles dispersed in a rubbery amphiphilic copolymer matrix, namely, poly(styrene-b-butadiene-b-styrene)-g-poly(oxyethylene methacrylate) (SBS-g-POEM) synthesized by free-radical polymerization. Excellent interface contact and compatibility between the ZIF-8 nanoparticles and SBS-g-POEM matrix were confirmed. The results showed that the polymer matrix did not damage the nanostructure of the ZIF-8, and the POEM chains grafted from the SBS backbones enhanced the compatibility with the ZIF-8. While the MMM based on a neat SBS matrix showed a continuous decrease in selectivity, the MMM based on SBS-g-POEM achieved a simultaneous improvement in permeability (from 261.7 to 522.3 Barrer) and CO₂/N₂ selectivity (from 18.6 to 20.8), indicating the importance of the matrix in tuning the interface and interaction of MMMs. The obtained CO₂/N₂ separation performance is close to the upper bound and one of the highest values for ZIF-8-based MMMs. Furthermore, the MMMs exhibited good mechanical strength (8.5 MPa tensile stress and 940% strain) and excellent thermal stability at least up to 300 °C.