Amphiphilic Zeolitic Imidazolate Framework for Improved CO₂ Separation in PIM-1 Mixed Matrix Membranes

This study aims to enhance the compatibility between filler and polymer in mixed matrix membranes (MMMs), addressing an important challenge in membrane development. ZIF-94, known for its affinity to CO₂, was partially modified with 2-undecylimidazolate (umIm) through the solvent-assisted ligand exchange (SALE) method to improve its compatibility with the prototypical polymer of intrinsic microporosity PIM-1. The modified ZIF-94 (ZIF-94-umIm) can be considered as an amphiphilic MOF with both hydrophilic and hydrophobic moieties, while maintaining a considerably high CO₂ adsorption capacity (2.34 mmol g^-1 at 90 kPa and 0 °C). Gas separation experiments were performed using mixed gas compositions of 15/85 CO₂/N₂ at 3 bar and 35 °C. The resulting MMM with a 5 wt.% loading exhibited an enhanced CO₂ separation performance, with ca. 70% and 10% increases in CO₂ permeability (8900 Barrer) and CO₂/N₂ selectivity (20.2), respectively, compared to pristine PIM-1 membranes. In addition, thin film nanocomposite membranes were prepared showing a 23.5 CO₂/N₂ selectivity at 2350 GPU of CO₂. This modification strategy shows a great potential for improving the CO₂ capture technologies, highlighting the potential of tailoring MOF fillers for advanced membrane materials in gas separation applications.