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. (c) 2008 Elsevier B.V. All rights reserved.