Surface initiated polydopamine grafted poly([2-(methacryoyloxy)ethyl]trimethylammonium chloride) coatings to produce reverse osmosis desalination membranes with anti-biofouling properties

Commercial polyamide (PA) reverse osmosis (RO) membranes were surface modified in a sequential two-step polymerization process to impart anti-biofouling properties to the membrane surface. In the first step, a 2-bromoisobutyryl bromide initiator-polydopamine (BiBBr-initiator-PDA) layer was deposited onto the membrane surface from a Tris(hydroxymethyl)aminomethane buffered solution of dopamine hydrochloride and 2-bromoisobutyryl bromide at ambient conditions. In the second step, polymer chains of [2-(methacryloyloxy)ethyl]trimethylammonium chloride (MTAC) were grafted-from the BiBBr-initiator-PDA surface using activators regeneration by electron transfer-atom transfer radical polymerization for between 1 and 24 h. The modified surfaces were characterized using attenuated reflectance-Fourier transform infrared spectroscopy and water contact angle and their pure water flux, saline water flux and ability to reject salt were determined. Results showed that the water flux and salt rejection properties of the PDA-g-PMTAC modified membranes were similar to the unmodified PA RO membranes. Chlorine resistance tests showed the coating had enhanced stability in regards to salt rejection properties. Significantly, after six days of incubation in nutrient solution there was 93.2% less bacteria on the PDA-g-MTAC modified PA RO membranes, compared to the unmodified membranes.