Graphene oxide modified polyamide reverse osmosis membranes with enhanced chlorine resistance

Improving chlorine resistance of polyamide (PA) reverse osmosis membranes is one of the major challenges in reverse osmosis membrane technology. In this study, few-layered graphene oxide (GO) was assembled onto polyamide thin film composite membrane surfaces through a spin-coating method to address this challenge. The coating solutions were used at different pH values and with different dispersion solvents. It was found that the pH values have great effects on membrane performance including maximizing water flux at a pH value of 6-7. XPS results indicate that the GO layer can protect the PA functional layer by absorbing chlorine radicals to form O-Cl bond. All modified membranes demonstrate a good suppression of membrane degradation in salt rejection upon chlorine exposure, and the degree of resistance to chlorine was enhanced with the increase of the number of GO layers. The GO(1)-coated membrane with GO nanosheets dispersed in ethanol showed increased water flux and good chlorine resistance. For instance, salt rejection varied from 95.3% to 91.6% for the first two hours, while unmodified membrane dropped to 80%. After 16 h of chlorine exposure, measured salt rejection of GO(1)-coated membrane was 75% but unmodified membrane was a less effective 63%.