Quaternized poly(2,6-dimethyl-1,4-phenylene oxide)s with zwitterion groups as diffusion dialysis membranes for acid recovery

For the purpose of simultaneously improving H⁺ dialysis coefficient and selectivity between proton and metal ions in acid diffusion dialysis (DD), a series of quaternized poly(2,6-dimethyl-1,4-phenylene oxide)s (PPO) anion exchange membranes (AEMs) containing zwitterion groups were designed and synthesized via Cu(I)-catalyzed “click chemistry”. The ion exchange capacity (IEC) and degree of functional zwitterion groups were controlled readily by adjusting the amount of the reagent due to the quantitative click reaction. The electrostatic effects of zwitterionic groups provided AEMs with proper water uptake (<65 wt%), dimensional stabilities (<19%) even under elevated temperatures (60 °C) as well as robust mechanical properties. Taking the simulated iron polishing waste solution (HCl, 1.0 mol/L; FeCl₂, 0.2 mol/L) for research, the diffusion dialysis performance of membranes was investigated. As expected, the zwitterionic functionalization of the membrane enhanced the H⁺ dialysis coefficient and selectivity simultaneously. The zwitterion groups-based membranes with a thickness of 30–40 μm showed high acid dialysis coefficient up to 0.037 m/h and selectivity up to 32.7 at 30 °C. Therefore, the introduction of zwitterionic groups into anion exchange membrane is an effective approach for the simultaneous H⁺ dialysis coefficient and selectivity improvement of the membrane in DD for acid recovery.