Increasing M2(dobdc) Loading in Selective Mixed-Matrix Membranes: A Rubber Toughening Approach

Abstract

Mixed-matrix membranes (MMMs) were formed by incorporating M2(dobdc) (M = Mg, Ni; dobdc4– = 2,5-dioxido-1,4-benzenedicarboxylate) metal–organic framework (MOF) nanoparticles in a series of poly(ether-imide) copolymers. Addition of the MOF nanoparticles improved the permeability of H2, N2, CH4, and CO2 relative to the pure copolymer by increasing gas solubility and, in most cases, diffusivity. More limited improvements in diffusivity were observed for the more strongly adsorbing gases. Because of such transport considerations, improvements in permeability and selectivity were most pronounced for H2/CH4 and H2/N2 separations. Incorporation of a greater ether content within the copolymers led to the formation of defect-free MMMs by physically sealing polymer–MOF interfacial defects, allowing higher MOF loadings to be achieved. For Mg2(dobdc), selective, defect-free films could be formed with loadings of up to 51 wt %. However, at these high loadings, films became weak and brittle. The mechanical properties o...