Enhancing acid recovery efficiency by implementing oligomer ionic bridge in the membrane matrix

• A novel AEM method implementing a multi-amine ionic bridge.
• An extraordinarily high separation factor.
• A versatile method in creating AEMs with connective ionic channels.

We report a strategy in improving the diffusion dialysis efficiency of anion exchange membranes (AEMs) by implementing a multi-amine oligomer bridge in the membrane matrix. The multi-amine oligomer, poly-dimethyl aminoethyl methacrylate (PD) was prepared via free radical polymerization, followed by partial quaternization with methyl iodide. The remaining tertiary amine groups were designed to react with benzyl bromide groups in the polymer brominated poly(2,6-dimethyl-1,4-phenylene oxide (BPPO) matrix, thus creating an intermolecular connection. The intermolecular connection serves as crosslinks and also helps to regulate the interconnectivity of the hydrophilic regions. By tuning the molecular weight and the remaining tertiary amine groups within PD, series of AEMs were fabricated. These membranes show potential in recovering waste acid via diffusion dialysis. For example, membrane M-5 shows an extraordinarily high separation factor (SH/Fe) of ∼2074 along with acceptable proton dialysis coefficient (UH=0.0098 m/h). The SH/Fe is much higher than that of the conventional quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO) membrane without oligomer cross-linker (UH=0.0080–0.0132 m/h,SH/Fe=5–60). The improvement in diffusion dialysis efficiency could be attributed to the improved interconnectivity of the hydrophilic regions, which stems from the incorporation of inter-chain ionic bridge.

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