Symmetrical polysulfone/poly(acrylic acid) porous membranes with uniform wormlike morphology and pH responsibility: Preparation, characterization and application in water purification

Well defined porous membranes have been fabricated from polystyrene based block copolymers by self-assembly and non-solvent induced phase separation. However, simplifying the time-consuming preparation steps and overcome the limitation in materials remain challenging. Here, symmetrical polysulfone/poly(acrylic acid) (PSf/PAA) membranes with uniform wormlike morphology were fabricated by a two-stage phase inversion strategy combining a vapor-induced phase separation (VIPS) with a liquid-induced phase separation (LIPS) for the first time. The casting solutions were synthesized via in situ cross-linking polymerization of AA in PSf solution and spread into films without any treatment. After exposing in humid air for a certain time, the films were soaked in a water bath. It was confirmed that the wormlike networks covered the membrane surfaces by tuning the exposure time and AA concentration. The membranes exhibited pH-dependent permselectivity. When the solution pH was varied from 1.3 to 12.5, water flux ranged from ~ 334.1 to ~ 55.4 L m⁻² h⁻¹ bar⁻¹, and molecular weight cutoff of the membrane decreased from 2000 to 600 kg/mol. Moreover, the membranes were able to remove copper ions from water with a maximum static adsorption capacity of ~ 235 mg/g at pH 6, and reused as reusable adsorbents. The present work opens a new path for fabricating symmetrical porous membranes with uniform wormlike morphology and pH responsibility in up-scale for application in water purification, especially the removal of heavy metal anions.