LAUSR

Abstract Confinement of crystals of metal–organic frameworks (MOFs) in polymers to form MOF/polymer mixed-matrix membranes (MMMs) can lead to changes in intra-MOF diffusion. Such changes in intra-MOF diffusion were previously demonstrated for light gases, and attributed to a reduction in MOF framework flexibility. However, to our knowledge, no direct measurements of intra-MOF diffusion in MMMs and of the related MOF confinement effect on diffusion have been reported for organic liquids. In this work, 13C pulsed field gradient (PFG) NMR was used to quantify self-diffusion of methanol, ethanol, p-xylene, and o-xylene inside MOF crystals of the type ZIF-71, which were dispersed in a Torlon polymer to form MMMs. The intra-ZIF self-diffusivities in the MMMs were compared with the corresponding self-diffusivities measured in beds of ZIF-71 crystals. The observed self-diffusivity dependencies on diffusion time were explained by crystal boundary effects. The corresponding values of intra-ZIF self-diffusivities not perturbed by such effects were found to be the same, within uncertainty, in the MMMs and ZIF-71 beds. The observed lack of an influence of the ZIF-71 confinement in Torlon on diffusion is explained, and an option to increase diffusion selectivity is discussed.