Preparation and characterization of a novel bipolar membrane by plasma-induced polymerization

A novel monomer, 2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxyl-propyl ester (GMA-IDA), and the porous poly(vinylidene fluoride) (PVDF) membrane were used to prepare a bipolar membrane by plasma-induced polymerization. The method utilized the porous PVDF membrane as a substrate, and GMA-IDA monomer was grafted onto both sides of the PVDF membrane by using plasma-induced polymerization. The GMA-IDA monomer, which is a bipolar unit, covered on both sides of the PVDF membrane surface. Then a bipolar membrane was obtained after both sides of the membrane were treated with an acid and base solution, respectively. Results of contact angle of the PVDF-GMA-IDA bipolar membrane were dramatically decreased after the GMA-IDA monomer was grafted onto the surface of the PVDF membrane. Fourier transform infrared spectroscopy and scanning electron microscopy were also used to identify the grafting polymerization of the GMA-IDA monomer on the PVDF membrane surface. Characterization of the I–V curves revealed that the critical voltage was independent of the concentration and the type of electrolyte. Moreover, the critical voltage of the PVDF-GMA-IDA bipolar membrane was around 0.88 V. However, the limiting current was increased by the concentration of electrolyte and diffusion coefficient. The current efficiency of the bipolar membrane showed that a maximum value was observed depending on operation conditions.