Low-Loading Mixed Matrix Materials: Fractal-Like Structure and Peculiarly Enhanced Gas Permeability

Abstract

Mixed matrix materials (MMMs) containing metal−organic framework (MOF) nanoparticles are attractive for membrane carbon capture. Particularly, adding <5 mass % MOFs in polymers dramatically increased gas permeability, far surpassing the Maxwell model's prediction. However, no sound mechanisms have been offered to explain this unusual lowloading phenomenon. Herein, we design an ideal series of MMMs containing polyethers (one of the leading polymers for CO 2 /N 2 separation) and discrete metal−organic polyhedra (MOPs) with cage sizes of 2−5 nm. Adding 3 mass % MOP-3 in a polyether increases the CO 2 permeability by 100% from 510 to 1000 Barrer at 35 °C because of the increased gas diffusivity. No discernible changes in typical physical properties governing gas transport properties are detected, such as glass transition temperature, fractional free volume, d-spacing, etc. We hypothesize that this behavior is attributed to fractal-like networks formed by highly porous MOPs, and for the first time, we validate this hypothesis using small-angle X-ray scattering analysis.

Retarded O2 transport in Co2+-coordinated supramolecular polymer networks for membrane CO2/O2 separations

“…SPN density, ρ SP (g cm −3 ), was determined using an analytical balance equipped with a density kit. 26,27…”