Strategic Dual Cross-Linking of Partially Quaternized Membranes Containing Dangling Alkyl Spacers for Enhanced Anion Selectivity with Antibacterial and Antibiofouling Properties

We investigated the Cl–/SO42−permselectivity and antibacterial properties of polyvinylidene fluoride-g-poly[2-(dimethylamino) ethyl methacrylate] (PVDF-g-PDMAEMA)-based anion-exchange membranes (AEMs) prepared by a nonsolvent induced phase inversion process. In this work, we assessed the contribution of the chain length of the quaternizing agent using two distinct alkyl spacers: methyl (C1) and decyl (C10) groups, followed by dual cross-linking. The dual-step cross-linking process included in situ cross-linking achieved individually with xylene dichloride (XDC) or poly(methyl methacrylate)-co-poly(chloromethylstyrene) (PMMA-co-PCMSt), followed by surface cross-linking using N,N,N′,N′-tetramethyl-1,6-hexanediamine (TMHDA). Thus, the impact of a small molecular cross-linker (XDC) and a polymeric cross-linker (PMMA-co-PCMSt) on the selectivity of the membranes was studied. Among the four dual-cross-linking network-architected robust membranes, the representative PDC membrane, featuring a C10 side chain and dual cross-linking with PMMA-co-PCMSt and TMHDA, achieved a remarkable Cl–/SO42− permselectivity value of 28.25 using a 0.05 M NaCl + 0.05 M Na2SO4 mixture. Additionally, this membrane demonstrated outstanding antibacterial efficacy against E. coli and B. subtilis, with 99.9% bacterial inhibition (BI) in each case. Dynamic biofouling studies showed that the PDC membrane retained better performance, with only a 55% decline in desalination efficiency after five continuous cycles, compared to 67.9% for the commercial Ionsep AEM, highlighting its superior antibiofouling properties.