Rationally designed fluorinated aromatic polyamide membrane for stable air dehumidification

Membrane based dehumidification technology has attracted wide attention. The anti-hydrolytic property of the membrane holds a significant role in its long-term operation in a wet environment. Herein, a series of fluorinated aromatic polyamides (FPA) are first proposed for stable air-dehumidification. Amide bond offers superior hydrolytic stability over chemical bond in the present dehumidification membrane. The deliberately introduced bulky fluorinated group (-CF3) increases the water permeability and enhances the anti-hydrolytic property of the FPA membranes. The membrane separation performance and membrane stability are further tuned by adjusting the molar ratio of para- and meta-amide groups to optimize the intermolecular forces and polymer chain arrangement, which is verified by the refractive index data and wide-angle X-ray diffraction results. The obtained co-FPA membranes exhibit tunable gas and water vapor permeation properties. With increasing para-amide group content, the gas and water vapor permeability of copolyamides gradually decreases and the selectivity of H2O/N2 increases. Meanwhile, the hydrolytic stability of the co-FPA membranes increases with the increase of TPC content as verified by 1H NMR, GPC, and mechanical property tests. Among these co-FPA membranes, the co-FPA-70 membrane exhibits the most excellent hydrolytic stability. The membrane shows almost no change in 1H NMR spectra and 97% retention of tensile strength after 5000 h of hydrolysis reaction. In the meanwhile, it shows excellent separation stability with a water vapor permeability retention of 74% during long-term hydrolysis aging operation. This study demonstrates the great potential of polyamide for the fabrication of dehumidification membranes with high hydrolysis resistance.