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Model systems are developed and investigated to better understand the effect of polyether-metal ion interactions on gas separation characteristics. These systems help answer current questions raised by the substantial body of research on metal-organic frameworks (MOFs) dispersed in polyethers to improve gas separation performance, where favorable interactions between the metal centers and polyethers are preferred to improve interfacial compatibility. Specifically, we investigate CO2/gas transport properties of supramolecular networks comprising cross-linked poly(ethylene oxide) (XLPEO) and dissociable salts, including LiClO4, Ni(BF4)2, and Cu(BF4)2. Increasing the salt content increases the glass transition temperature (Tg) and generally decreases gas diffusivity and permeability, which can be successfully described using a Tg-integrated free volume model with an expression similar to the Vogel-Tammann-Fulcher (VTF) equation. Surprisingly, low loadings of LiClO4 and Cu(BF4)2 (2 mass% or less) can increase gas permeability by 30%–70% without affecting the CO2/gas selectivity. This increase correlates with polyether-metal ion dynamics as measured by dielectric spectroscopy. Understanding how interaction-mediated dynamics affect gas transport will be instrumental to designing MOF-based mixed matrix materials for gas separations.

Mixed matrix materials (MMMs) comprising porous fillers in polymers can exhibit superior gas separation properties, yet their practical use has been limited by poor interfacial compatibility between the two components. Herein we report a bottom-up approach to synthesize the MMMs by dispersing a metal-organic polyhedron (MOP-3) in monomer solutions before rapid photopolymerization to form interpenetrating networks (IPNs), where the porous MOP-3 nanoparticles serve as molecular dopants. Specifically, MOP-3 with particle sizes of ≈5 nm was dispersed in and infiltrated by either a macromonomer of poly(ethylene glycol) diacrylate (PEGDA) or poly(1,3 dioxolane) acrylate (PDXLA). The introduction of the MOP-3 in the polyethers decreases their glass transition temperatures and even induces the crystallization of polyPDXLA at high loadings. Increasing the MOP loading increases CO2 permeability with a slight decrease in CO2/gas selectivity. For example, as the MOP content increases from 0 to 30 mass% in polyPDXLA, CO2 permeability increases from 190 Barrer to 580 Barrer, and CO2/N2 selectivity decreases from 70 to 62 at 35 °C. These IPNs-based MMMs exhibit separation properties above the Robeson's upper bounds for CO2/N2 and CO2/H2 separation. As the MOPs are soluble in solvents, this approach can be easily integrated into industrial membrane fabrication processes to produce MMMs-based composite membranes in large-scale.

To reduce the diffusion resistance of CO2 and enhance its permeability in mixed matrix membranes (MMMs), lantern Zn/Co-ZIF nanoparticles were loaded in-situ into semi-interpenetrating cross-linked poly(ethylene oxide) (XLPEO) membranes to provide efficient channels for CO2 permeability. TEM and SEM results showed that the Zn/Co-ZIF nanoparticles (diameter 490–550 nm) treated at 145 °C possessed a lantern structure with hollow cores (diameter 380–450 nm) and thin shells (thickness 20–85 nm). XRD and BET results indicated that the nanocrystal structure and porosity of the Zn/Co-ZIF remained intact after etching at 145 °C. Peaks shifts in the infrared spectra confirmed that the Zn/Co-ZIF nanoparticles were well integrated with the XLPEO membrane through hydrogen bonds. Therefore, doping 15 wt% lantern Zn/Co-ZIF nanoparticles into the membrane dramatically increased CO2 permeability by 72% to 761.9 ± 3.0 barrers, while the CO2/N2 selectivity was above the upper bound established by Robeson in 2008.