Synthesis of an aminated poly(vinylidene fluride-g-4-vinyl benzyl chloride) anion exchange membrane for membrane capacitive deionization(MCDI)

•A synthesis of an aminated PVDF-g-VBC copolymer was quaternized with trimethylamine.•A partially fluorinated AEMs was prepared by the casting method.•The MCDI efficiency of AEMs was measured and compared with CDI process.

In this study, PVDF was dehydrofluorinated using an alkaline treatment and modified using 4-vinyl benzyl chloride to prepare a PVDF-g-VBC copolymer. A solution of the PVDF-g-VBC copolymer was anion exchanged to introduce a quaternary ammonium group using a quaternary ammonium reaction. In addition, an ion exchange membrane was prepared using a casting method, and a PVDF-g-VBC ion exchange membrane was made by heat treatment. Raman and Fourier-transform infrared (FT-IR) spectroscopy were performed to elucidate the molecular structure. The water uptake (W.U), ion exchange capacity (IEC) and electrical resistance (E.R) of the membrane were measured using a weight method, titration, and LCR meter, respectively. The water uptake of the PVDF-g-VBC ion exchange membrane ranged from 12.5% to 56.2%, and the results were lower than that of AMX (Tokuyama) (30%). The ion exchange capacity and electrical resistance range were 0.39–1.31 meq/g and from 15.50 to 2.00 Ω cm2, respectively. The electrical resistance was observed to decrease as the ion exchange capacity increased. The lowest electrical resistance measured, 2.00 Ω cm2, is lower than that of an AMX membrane (2.40 Ω cm2). When the anion exchange membrane was applied to the membrane capacitive deionization (MCDI) process, an excellent salt removal rate of 79.4% was achieved, which was 51.6% higher than when the membrane was applied in the capacitive deionization (CDI) process, 27.8%.

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