Utilizing low ZIF-8 loading for an asymmetric PSf/ZIF-8 mixed matrix membrane for CO₂/CH₄ separation

Asymmetric mixed-matrix membranes (MMMs) were synthesized by incorporating zeolitic imidazole framework 8 (ZIF-8) into polysulfone (PSf) polymer matrix for CO₂/CH₄ separation. ZIF-8 was synthesized in aqueous media at room temperature with a base-type additive, triethylamine (TEA). The prepared ZIF-8 shows high crystallinity with a surface area of 1032 m² g⁻¹ and a particle size of ∼133 nm. MMMs were then prepared by incorporating the synthesized ZIF-8 up to 10 wt% (total solids) into PSf via a dry/wet phase inversion. The prepared MMMs exhibit significant improvement in thermal and mechanical stability even at a filler loading as low as 0.25 wt%. Uniform dispersion of ZIF-8 throughout the PSf matrix was evident via SEM, up to 1 wt% filler loading. The permeation behavior of MMMs varies with the ZIF-8 loading; i.e. insignificant change was observed at the low filler loading (0.25 wt%), while severe performance deterioration occurred at high filler loading (10 wt%). At an optimal ZIF-8 loading of 0.5 wt%, CO₂ permeance was enhanced by 37% and CO₂/CH₄ selectivity was also enhanced by 19% as compared to that of neat PSf membrane.