In this study, a zeolitic imidazole framework (ZIF-8) was prepared, and physico-chemical characterizations were performed to investigate the influences of triethylamine (TEA) on the crystallinity, particle size, morphology, and defects of ZIF-8 synthesized via an aqueous room temperature approach with a relatively low molar ratio of ligands to metal salts. Increasing the concentration of TEA by raising the TEA/total molar ratio from 0.004 to 0.007 prompted the formation of pure phase ZIF-8, whereas a TEA/total molar ratio below 0.004 did not result in a yield of ZIF-8. The particle size of ZIF-8 decreased from approximately 288 to 133 nm with increasing TEA/total molar ratio, except at a TEA/total molar ratio of 0.007. However, an excessive TEA/total molar ratio alters the 2-MeIM chemistry, and partially forms hydroxylated 2-MeIM. Thus, this study shows that at relatively low molar ratios of ligands to metal salts, up to a maximum TEA/total molar ratio of 0.006, the TEA concentration plays an important role in assisting crystal formation and in controlling the particle size of ZIF-8. The proposed procedure enables pure phase nanoscale ZIF-8 to be synthesized with a high product yield and with minimal chemical usage.

The MMM consisting of ZIF-8 after facile ammonia modification provides excellent separation properties with increases CO₂ permeability up to 43% and ideal CO₂/CH₄ selectivity up to 72% even only 0.5 wt% fillers were embodied.

In this study, zeolitic imidazole framework 8 (ZIF-8) particles of different sizes were synthesized in aqueous media by varying the concentration of the base-type additive, triethylamine (TEA). ZIF-8 with particle sizes of ∼134 nm and ∼288 nm with surface areas of 418.44 m² g⁻¹ and 491.54 m² g⁻¹ were obtained without altering the crystalline structure. Synthesized ZIF-8 was further heat treated at 100 °C for a minimum of 12 hours, which led to an enhancement of its phase crystallinity and a surface area of 981.1 m² g⁻¹. Mixed matrix membranes (MMMs) were prepared via the dry–wet phase inversion method by dispersing as-synthesized ZIF-8s, heat-treated ZIF-8s and commercial ZIF-8 (∼493 nm) into a polysulfone (PSf) matrix. The thermal stability and mechanical strength of the membranes showed significant improvement after the incorporation of ZIF-8s. The MMMs were further subjected to the permeation experiments of CO₂ and CH₄. Although the majority of MMMs showed less selectivity than the neat PSf membrane, the incorporation of heat-treated ZIF-8 of the smallest size, exhibited CO₂/CH₄ selectivity of 28.5, which is significantly higher than the 19.43 obtained for the neat PSf membrane. Therefore, different ZIF-8 treatment protocols and particle sizes affect the MMMs performance significantly.

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.