(383c) Microscopic Gas Diffusion in Mixed Matrix Membranes Containing Uio-66-NH2 Crystals with Modified External Surface

Membrane gas separation technology has experienced rapid advancements recently. Among these advancements is the development of mixed matrix membranes (MMMs) based on UiO-66-NH₂, a type of metal organic framework (MOF), which is dispersed in polymers to form MMMs. Such membranes have shown promising gas separation properties due to the synergy between the ease of processability offered by polymers and promising gas separation capabilities of UiO-66-NH₂. A clear pathway to optimize these membranes is to increase MOF loading. However, such an increase can lead to interfacial defects, which in turn decrease the membrane's selectivity. Post-synthetic modification (PSM) of the surface of UiO-66-NH₂ MOF fillers with a nanoscopic oligomer shell has shown enhancement in the polymer-filler compatibility in MMMs and improved gas separation efficiency. Quantification and understanding of gas diffusion changes on different microscopic length scales as a result of PSM is needed to optimize the MMM performance by PSM.

In this study, quantification of microscopic gas diffusion in MMMs composed of neat UiO-66-NH₂ or UiO-66-NH₂ subjected to PSM with 6FDA-Durene oligomers was performed as a function of increasing MOF loading up to ~66 weight percent. The diffusion measurements were performed using ¹³C pulsed field gradient (PFG) NMR utilizing a high field (14 T) and high magnetic field gradients (up to 17 T/m). PFG NMR diffusion studies were carried out for one-component gases (CO₂ and CH₄) at different temperatures and for a broad range of displacements larger than the average MOF crystal size. As the UiO-66-NH₂ loading in the MMM was increased, a clear increase in the self-diffusivities for both sorbates was observed. Diffusion results for MMMs composed of neat UiO-66-NH₂ will be compared with those for UiO-66-NH₂ after PSM.