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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