Engineering the Polymer–MOF Interface in Microporous Composites to Address Complex Mixture Separations

Poor interfacial compatibility remains a pressing challenge in the fabrication of high-performance polymer–MOF composites. In response, introducing compatible chemistries such as a carboxylic acid moiety has emerged as a compelling strategy to increase polymer–MOF interactions. In this work, we leveraged compatible functionalities in UiO-66-NH 2 and a carboxylic acid-functionalized PIM-1 to fabricate mixed-matrix membranes (MMMs) with improved separation performance compared to PIM-1-based MMMs in industrially relevant conditions. Under pure-gas conditions, PIM-COOH-based MMMs retained selectivity with increasing MOF loading and showed increased permeability due to increased diffusion. The composites were further investigated under industrially relevant conditions, including CO 2 /N 2, CO 2 /CH 4, and H 2 S/CO 2 /CH 4 mixtures, to elucidate the effects of competitive sorption and plasticization. Incorporation of UiO-66-NH 2 in PIM-COOH and PIM-1 mitigated the effects of CO 2 - and H 2 S-induced plasticization typically observed in linear polymers. In CO 2 -based binary mixed-gas tests, all samples showed similar performance as that in pure-gas tests, with minimal competitive sorption contributions associated with the amine functional groups of the MOF. In ternary mixed-gas tests, improved plasticization resistance and interfacial compatibility resulted in PIM-COOH-based MMMs having the highest H 2 S/CH 4 and CO 2 /CH 4 selectivity combinations among the films tested in this study. These findings demonstrate that selecting MOFs and polymers with compatible functional groups is a useful strategy in developing high-performing microporous MMMs that require stability under complex and industrially relevant conditions.