Cross-Linked, Monovalent Selective Anion Exchange Membrane: Effect of Prealkylation and Co-ions on Selectivity

• Published in: ACS applied polymer materials 2023-03, Vol.5 (3), p.1977-1988
• Main Authors: Sarkar, Suman, Patnaik, Pratyush, Mondal, Rakhi, Chatterjee, Uma
• Format: Article
• Language: English
• ISSN: 2637-6105; 2637-6105
• DOI: 10.1021/acsapm.2c02045

Tuning of hydrophobicity, water uptake, and size of the ion channel is very crucial for the monovalent anion-selective membrane (MASM) preparation. In this work, we report the preparation of MASM from the cross-linked polyacrylonitrile-co-polyvinylimidazole (PAN-co-PVI) copolymer. The copolymer was in situ quaternized and cross-linked using the polyacrylonitrile-co-polychloromethylstyrene (PAN-co-PCMSt) copolymer as cross-linker. The benzyl chloride moiety (Ar-CH2Cl) of PAN-co-PCMSt reacts with imidazolium nitrogen of PAN-co-PVI and provides a positive charge on the membrane matrix, whereas the PAN moiety provides greater compatibility with the PAN-co-PVI copolymer matrix. The faster cross-linking without external prealkylation forms a strong network structure with a low ionic charge on the membrane surface. Judicious extent of prealkylation followed by cross-linking forms a controlled network structure and small-sized ionic channel with moderate water uptake and good mechanical stability. The representative AEM0Q and AEM17Q membranes with 0 and 17% prealkylation exhibited a permselectivity (P SO4 2– Cl– ) value of 4.39 and 15.40, respectively, during the separation of 0.01 M NaCl + 0.01 M Na2SO4 by electrodialysis. Upon further increase of prealkylation to 27 and 32%, the water uptake of the membrane increased, which in turn allowed the passage of SO4 2– along with Cl– and decreased the P SO4 2– Cl– value to 4.12 and 2.45, respectively. Similar trends were observed during the separation of NaCl + MgSO4, MgCl2 + Na2SO4, and MgCl2 + MgSO4 mixtures of each 0.01 M concentration.