Preparation and gas separation performance of mixed-matrix membranes based on triptycene-containing polyimide and zeolite imidazole framework (ZIF-90)

Defect-free mixed-matrix membranes (MMMs) based on triptycene-containing polyimide and zeolite imidazole framework (ZIF-90) were prepared in systematically varied compositions using priming and solution-casting method for gas separation. Microstructure analyses confirm that hierarchical triptycene units effectively assist in the nanoparticle dispersion and prevent aggregation, which, in conjunction with the favorable interactions between the organic ligands in ZIF-90 and imide moieties, construct desired interfacial morphology. MMMs showed significantly improved permeabilities (e.g., about three times of the pure polymer at 50 wt% loading) with negligible selectivity loss, which drives the separation performance laterally approaching and eventually surpassing the permeability-selectivity upper bound. Solubility and diffusivity analyses indicate that ZIF-90 nanoparticles facilitate fast gas diffusion through their microporous structure and increasing fractional free volume. The good agreement between experimental data and the Maxwell model prediction supports the ideal interfacial contact, demonstrating the great potential of iptycene structure in the development of high performance nanocomposite materials.