Self-cleaning pH-responsive polyvinyl alcohol/chitosan hydrogel membrane for reusable and efficient dye removal

A pH-responsive membrane represents a promising avenue for sustainable water treatment, yet its broader application remains limited by stability and reusability concerns. In this study, a polyvinyl alcohol/chitosan (PVA/CS) hydrogel membrane was fabricated and systematically evaluated for its pH-dependent transport behavior and dye removal performance. The hydrogel membrane exhibited distinct pH responsiveness, achieving the highest water flux (22.45 ± 0.66 L m −2  h −1  bar −1 ) at neutral pH (6.5) when tested using pure water. Flux declined under acidic conditions (3.43 ± 0.26 L m −2  h −1  bar −1 ) due to CS swelling and under alkaline conditions due to polymer chain densification. At pH 2, the membrane removed both cationic and anionic dyes with efficiencies exceeding 99.9 % removal. Under neutral conditions, cationic dyes (crystal violet, methylene blue) were consistently removed (>97 %). In contrast, anionic dyes, including Congo red and methyl orange, showed significantly lower rejection (66.04 % and 24.57 %, respectively), attributable to electrostatic repulsion and size-dependent transport. Importantly, the PVA/CS hydrogel membrane demonstrated regeneration capability, enabling up to three reuse cycles with >99 % dye rejection and limited flux decline for cationic dyes at pH 6.5. CS's reversible swelling-contraction behavior facilitated the recovery of membrane performance. Overall, these findings demonstrate that PVA/CS hydrogel membranes functions as pH-responsive separation platforms capable of chemical-free regeneration and limited reuse across a range of pH conditions. In particular, this study experimentally clarifies how intrinsic pH responsiveness can be leveraged to enable regeneration without chemical treatment, while also highlighting the need for further optimization to address performance limitations toward anionic contaminants.