Mixed Matrix Membranes Based on ZIF-8 Nanoparticles/Poly(4-styrene sulfonate) Fillers for Enhanced CO2 Separation

The structures and properties of fillers are key factors in determining the gas separation performance of mixed matrix membranes (MMMs). In this study, nanosized podlike fillers were designed by polymer chains (poly(4-styrene sulfonate), PSS) to string and wrap ZIF-8 nanoparticles and were named PSS-ZIF. In podlike PSS-ZIF fillers, PSS chains on the surface of ZIF-8 were the same as the shell, and the internal ZIF-8 nanoparticles were the same as beans in PSS-ZIF. Then, PSS-ZIF was incorporated into Pebax MH 1657 (Pebax) to fabricate MMMs for efficient CO2/CH4 separation. The podlike PSS-ZIF fillers were crucial for enhancing CO2 permeability and CO2/CH4 selectivity in MMMs. On the one hand, the external PSS chains on the shell of PSS-ZIF formed 1D transport pathways, which accelerated CO2 transport. On the other hand, the internal ZIF-8 nanoparticles with 3D porous structure in PSS-ZIF were connected by PSS chains, which constructed 3D transport pathways in MMMs. It was advantageous to increase CO2/CH4 selectivity. Therefore, the constructed 1D and 3D transport pathways expedited CO2 transport, improving CO2 permeability and selectivity simultaneously. The results showed that Pebax/PSS-ZIF MMMs presented excellent CO2/CH4 separation performance. The CO2 separation performance of the membrane containing 7 wt % PSS-ZIF was particularly impressive, with a CO2 permeability of 528 ± 8 Barrer and a CO2/CH4 separation factor of 36 ± 0.7. Compared with those of the pure Pebax membrane, the CO2 permeability and CO2/CH4 separation factor of Pebax/PSS-ZIF increased by 96 and 44%, respectively. The design of MMMs doped with podlike fillers will offer a potential application for CO2 capture.