Polyvinyl alcohol-based monovalent anion selective membranes with excellent permselectivity in selectrodialysis

Recently, monovalent anion selective membranes (MASMs) with excellent permselectivity for selectrodialysis applications have become both very desirable and competitive. In this study, a series of polyvinyl alcohol-based MASMs were fabricated by depositing a thin electronegative layer with a loose structure on the surface of base membranes through interfacial polymerization. The base membranes were prepared by blending quaternized polyethyleneimine (QPEI) and polyvinyl alcohol (PVA) or modified PVA with hydrophobic alkyl chains of different lengths. Due to the hydration energy effect, the base membrane QPEI/PVA-C10, which had the longest hydrophobic alkyl chain, showed the highest permselectivity, 2.47, for a Cl − /SO 4 2− system. The thin loose porous electronegative layer for as-prepared MASMs inhibited the transfer flux of large SO 4 2− from 4.91 × 10 −8 (QPEI/PVA) to 1.96 × 10 −8  mol/cm 2 s (QPEI/PVA-5), but scarcely diminished that of Cl − (4.84–4.56 × 10 −8  mol/cm 2 s for QPEI/PVA series membranes). Because of the hydration energy and Donnan exclusion effects, the membrane QPEI/PVA-C10-5, which used the longest hydrophobic alkyl chain and largest 4D2SA concentration, showed the highest permselectivity, specifically 6.31, higher than that of commercial Neosepta ACS (5.27) as well as an acceptable membrane area resistance of 5.11 ± 0.07 Ω cm 2. Moreover, QPEI/PVA-C10-5 and QPEI/PVA-5 both illustrated a reasonable long-term operational stability for commercial selectrodialysis applications. This work suggests an effective approach to guide the fabrication of MASMs in selectrodialysis applications.