Layer-by-layer self-assembly TiO2 and graphene oxide on polyamide reverse osmosis membranes with improved membrane durability

Improving membrane durability associated with resistance to chlorine and biofouling is critical important for polyamide (PA) reverse osmosis (RO) membrane technology. Here, few-layered TiO2 nanoparticles and graphene oxide (GO) were layer-by-layer self-assembled onto flat PA reverse osmosis membrane surfaces by hydrogen bonding and physical absorption to address this challenge. Contact angle testing proved that the membrane surface hydrophilicity was improved with the increase of bilayers. The modified PA membrane with bilayer number ≤ 6 showed increased water flux. Moreover, XPS results indicated that TiO2 and GO were attached to the membrane surface with good stability in our experimental conditions, and that GO nanoparticles played a part in improving chlorine resistance due to absorbing chlorine radicals. All modified PA membranes showed an anti-fouling effect and had an inhibitory effect on rejection reduction exposed to chlorine solution. For instance, the water flux of pristine membranes varied from 20.3 l/m2 h to 7.5 l/m2 h while the bilayer6-coated membrane dropped from 23.6 to 17.9 l/m2 h after UV light exposure and incubating with microbial cells for 3 d. Meanwhile, for the chlorine resistance, compared with 60% salt rejection of unmodified membrane, the bilayer6-coated membrane was a more effective 75% after 20 h of chlorine exposure.