Enhanced diffusion dialysis performance of cross-linked poly(aryl piperidine) anion exchange membranes by thiol-ene click chemistry for acid recovery

Abstract

A series of cross-linked QPBP-HT/OT-X% anion exchange membranes (AEMs) were prepared by introducing unsaturated olefins during the quaternization of poly(biphenyl piperidine) polymers (QPBP), followed by a thiol-ene “Click” reaction with a dithiol cross-linker for diffusion dialysis. In particular, the ethoxy (EO) group in 3,6-dioxa-1,8-octanedithiol (OT) can enhance the hydrophilicity of AEM and the ion-dipole interactions existing with cationic groups can effectively tune the nanostructure within AEM, which is jointly verified by AFM and SAXS. Compared with the original QPBP AEM, the ion exchange capacity of cross-linked QPBP-HT/OT-X% AEMs did not change significantly, but the water uptake and swelling rate showed a decreasing trend, which led to an obvious improvement in dimensional stability. Diffusion dialysis tests showed that QPBP-OT-5% AEM containing EO groups achieved a better dialysis coefficient (UH+) of 41.72 × 10−3 m h−1 and an excellent separation factor (S) of 103.56, which was significantly superior than QPBP-HT-X% AEMs containing hydrophobic crosslinkers and commercial DF-120 AEM (UH+ = 9 × 10−3 m h−1, S = 18.5). These results show that the “trade-off” effect between acid flux and ion selectivity can be effectively balanced by introducing hydrophilic EO groups into the cross-linked network of the polymer, which is a perspective design strategy.