Improvement in monovalent cation selectivity and stability of multilayers polyelectrolyte modified SPPSU membrane by doping PVA in substrate

Electrodialysis utilizing monovalent selective cation exchange membranes have wide application prospects in waste acid recycling and lithium-ion extraction. While the multilayered modification of substrate membranes with polyelectrolytes is one of the effective ways to improve the monovalent selectivity of standard cation exchange membrane, the stability of such modified membranes is often poor owing to the detachment of the polyelectrolyte layers. This study proposes a novel strategy utilizing covalent bonding between the modification layers and the substrate. The approach involves doping poly (vinyl alcohol) (PVA) into a sulfonated polyphenyl sulfone (SPPSU) substrate, followed by the alternate deposition of polyethyleneimine (PEI) and poly (sodium 4-styrenesulfonate) (PSS) via the layer-by-layer (LBL) assembly method. Subsequently, glutaraldehyde (GA) was employed as a dual-functional crosslinker to achieve simultaneous crosslinking within the substrate and at the interface of substrate and modification layer. The optimized membrane, SPPSU@4PVA(PEI/PSS) 2.5 , exhibited a low surface resistance of 6.77 Ω·cm 2 , a high Na + /Mg 2+ selectivity over 13, and a Na + flux of 4.5 × 10 −8  mol·cm −2 ·s −1 . Most notably, the performance remained after 60 h of continuous electrodialysis operation. This dual-crosslinking strategy enhances both the selectivity and stability of polyelectrolyte-modified monovalent selective cation exchange membranes.