(349b) Engineering the Polymer-MOF Interface in Microporous Composites to Address Complex Mixture Separations

Polymers of intrinsic microporosity (PIMs) have exceptional gas separation performance that surpasses the permeability–selectivity trade-off curve typical of polymer membranes. Despite the attractive property sets, PIMs are still subject to polymer-specific limitations such as plasticization and aging. To address these limitations, polymer–nanofiller composite membranes have become a compelling strategy. However, particle agglomeration and non-selective interfacial voids due to poor interfacial compatibility between the polymer and the fillers remain a major challenge in designing MMMs. Significant efforts in material design have been drawn to improve filler–polymer compatibility, while the effects of filler addition on competitive sorption and binary- and ternary- mixed gas transport remain less explored. In this work, we leveraged the interaction between a UiO-66-NH₂ MOF and a carboxylic acid-functionalized PIM-1 (PIM-COOH) to fabricate defect-free MMMs with improved gas separation performance compared to the UiO-66-NH₂/PIM-1 MMM analog.

Through replicate film-formation and pure-gas permeation tests, lower sample-to-sample variation was found in MMMs with improved interfacial compatibility. Sorption–diffusion analysis revealed that MOF incorporation increases pure-gas diffusion, while the sorption coefficient remains relatively constant, suggesting that the highly porous MOF significantly reduces activation energies of diffusion for molecules that are smaller than the MOF pore aperture. Furthermore, incorporation of MOF in PIM-COOH mitigates CO₂- and H₂S-induced plasticization effects compared to PIM-1 MMMs.

The effects of MOF incorporation on mixed-gas transport in MMMs were probed through CO₂/CH₄, CO₂/N₂, and H₂S/CO₂/CH₄ tests. Increased CO₂-based mixed-gas selectivities were observed for all samples, regardless of MOF addition. In H₂S/CO₂/CH₄ mixtures, all films demonstrated significant competitive sorption effects with H₂S and higher H₂S/CH₄ mixed-gas selectivities and lower CO₂/CH₄ selectivities compared to the pure gas case. Notably, the highest H₂S/CH₄ and CO₂/CH₄ selectivity combinations were found for the PIM-COOH-based MMM due to increased polymer inter-chain rigidity provided by the MOF. This study demonstrated the strategy of tuning MOF and polymer composition to improve interfacial compatibility and highlights the importance of testing new membrane formulations in industrially-relevant mixtures.