Fabrication of Morphology-Tailored ZIF-67/Polyether- <i>b</i> -Amide Mixed Matrix Membranes via CTAB-Assisted Hydrothermal Synthesis for CO ₂ and CO ₂ /N ₂ Separation

The aim of this study was to evaluate the influence of particle morphology on the gas permeability and selectivity of poly-(ether-<i>block</i>-amide) (PEBAX MH-1657)/zeolitic imidazolate framework-67 (ZIF-67) mixed-matrix membranes. ZIF-67 particles were synthesized using cetyltrimethylammonium bromide (CTAB) as a morphology modulator, and membranes were fabricated via solution casting followed by solvent evaporation. Single-gas permeability and ideal selectivity for carbon dioxide/nitrogen and carbon dioxide/methane were measured using a variable volume/constant pressure setup with a capillary flowmeter, at 10 and 15 bar and 35 °C. The mixed-matrix membranes exhibited enhanced permeability and selectivity; at 10 bar, they surpassed the Robeson upper bound for CO₂/N₂ while approaching the bound for CO₂/CH₄. Maximum values obtained in this study were a CO₂ permeability of 236 Barrer (NC 1%, 15 bar), a CO₂/N₂ selectivity of 110 (PL 5%, 10 bar), and a CO₂/CH₄ selectivity of 27 (PL 1%, 15 bar). Gas permeation results indicated that both pressure and ZIF-67 loading strongly influenced performance, with optimal behavior at 10 bar. Differential scanning calorimetry revealed morphology-dependent modifications of PEBAX crystallinity and glass transition temperature, which contributed to the observed permeability-selectivity trade-offs under different pressures.