(384c) Correlating Variance in MOF Synthesis with Transport in MOF/Polymer Composites

Polymer membranes have proven to be interesting alternatives for industrial separations due to reduced energy consumption, low capital investment, compact module size, and operational simplicity. While several classes of materials have reached commercial-scale production, development of new polymers with improved performance is often limited by a trade-off between permeability and selectivity, exemplified by the Robeson upper bound plots. As a result, various strategies have been developed in order to surpass these upper bounds in an attempt to advance the commercial viability of membrane-based separations for new mixtures. Among these new developments, loading polymers with organic or inorganic fillers affording mixed-matrix membranes (MMMs) has attracted significant attention. Metal–organic frameworks (MOFs) have emerged as promising filler particles due to their high surface area, selectivity, and degree of synthetic tunability. However, these materials frequently suffer from poor synthetic reproducibility. Of the literature reports preparing a well-studied MOF, UiO-66, according to the same procedure, it was found that the range of measured Brunauer–Emmett–Teller (BET) surface areas span ~600-1800 m²/g. This work focuses on one question: what, if any, impact does this variation in physical properties of the MOF have on gas transport in mixed-matrix membranes? Leveraging a UiO-66-NH₂/6FDA-Durene system that has been previously studied in our lab, we aimed to prepare two versions of UiO-66-NH₂ with maximally different porosity by adapting well-studied defect engineering protocols. The chemistry of defect engineering in UiO-66-NH₂ nanoparticles was investigated as it pertains to crystal size and quality, aiming to prepare two samples that vary minimally in size and morphology such that a similar MOF/polymer interface is produced. MOF particles were interrogated via ¹H NMR spectroscopy, powder X-ray diffraction, transmission electron microscopy, and nitrogen sorption experiments in order to ascertain crystal size, quality, and porosity. These data revealed that two samples of UiO-66-NH₂, measuring ~100 and ~130 nm, can be prepared with BET surface areas of ~1150 and 1750 m²/g, respectively. Interestingly, the permeability of light gases increases more for the low-porosity MMM than the high-porosity sample, potentially due to polymer infiltration into the large (~22 Ã…) pore generated from defect engineering. These results suggest that when comparing mixed-matrix membrane performance, careful consideration must be taken with regard to the physical properties of the MOF, even if they are labelled at “chemically” identical.