Superior chlorine-resistance of hyperbranched polyglycerol (hPG) grafted polyamide reverse osmosis membrane and its chlorine-resistant mechanism

Polyamide reverse osmosis (RO) membranes with high separation performance and excellent chlorine-resistant properties are highly desirable. Many strategies have been developed to fabricate chlorine-resistant RO membranes but often at the expense of a trade-off between separation performance, chemical stability and chlorineresistance. Herein, in this study, we grafted unique three-dimensional hyperbranched polyglycerol (hPG) onto the polyamide RO membrane to simultaneously improve the chlorine-resistance of the polyamide RO membranes without compromising separation performance. The effects of hPG grafting on the surface morphology, surface properties, as well as the perm-selectivity and the chlorine-resistance of the modified RO membrane were systematically investigated. Results show that the hPG grafted polyamide RO membranes reached a high water permeance of 3.27 +/- 0.17 L m- 2 h- 1 bar- 1 while maintaining an excellent NaCl rejection (99.30 +/- 0.15%). Importantly, the hPG grafted PA RO membranes exhibit the impressive chlorine-resistance with the maximum exposure of 20,000 ppm & sdot;h where the NaCl rejection of the membrane was still 98.69 +/- 0.39%, surpassing most of the reported chlorine-resistant polyamide RO membrane with the maximum exposure of 2000-16,000 ppm & sdot;h. Both simulation and XPS results suggest that the chlorine-resistant mechanism of the hPG grafted RO membrane is because of the reactivity inertness and steric hindrance of hPG, repelling chlorine away from the membrane surface and thus preventing the PA from chlorine attacking with the suppressed Orton rearrangement of the PA. Our findings demonstrate that the hPG grafted RO membrane possesses exceptional chlorine-resistance and high separation performance, which has a great potential for the practical applications.