Interphase-engineered Pebax®1657/Fe3O4@ZIF-8 membranes for CO2/N2 separation: role of magnetic alignment and humidity

This study reports the effects of magnetic alignment of the hybrid Fe 3 O 4 @ZIF-8 filler and operating parameters (humidity, membrane swelling, feed pressure, and long-term stability) on CO 2 /N 2 separation in Pebax® 1657 thin-film nanocomposite membranes. The combined effects of filler loading, magnetic alignment, and humidity were systematically analysed to elucidate their influence on the structure and gas transport behaviour of Pebax® 1657. Structural characterization using scanning electron microscopy, differential scanning calorimetry, Fourier-transform infrared spectroscopy, and positron annihilation lifetime spectroscopy revealed that magnetic alignment modifies the microstructure of the Pebax® 1657 matrix, improving the selectivity. Compared with the pristine Pebax® 1657 membrane (CO 2 permeance 7.3 GPU, CO 2 /N 2 selectivity 56.9), the incorporation of Fe 3 O 4 @ZIF-8 and magnetic alignment improves the separation performance under both dry and humid conditions, however with significantly reduced permeance. The optimized membrane containing 4 wt% Fe 3 O 4 @ZIF-8, fabricated under an external magnetic field, exhibited a CO 2 /N 2 selectivity of 117.9 with a CO 2 permeance of 5.7 GPU under humid conditions. The enhanced separation performance is attributed to the reduced aggregation (effect of magnetic orientation) and rigidified polymer regions that preferentially suppress N 2 transport while maintaining CO 2 sorption affinity (effect of filler). Additionally, humidity-assisted transport further enhances CO 2 permeance through plasticization and increased CO 2 solubility in rigidified Pebax® 1657/Fe 3 O 4 @ZIF-8 matrix. • Fe 3 O 4 @ZIF-8 is incorporated in Pebax®1657 for improved CO 2 /N 2 separation. • Magnetic alignment limits filler aggregation, improving selectivity. • Humidity-assisted transport significantly increases CO 2 permeability and separation. • Membranes exhibit excellent long-term operational stability. • Humid operation enables surpassing the Robeson 2008 upper bound.