Secondary interfacial reaction of p-aminodiphenylamine enables polyamide reverse osmosis membrane with enhanced and regenerative chlorine resistance

Developing polyamide (PA) reverse osmosis (RO) membrane with chlorine resistance is of great significance for simplifying pretreatment processes and saving operating costs. Herein, we constructed an active layer capable of highly chlorine stability and regenerative chlorine resistance by introducing p-amino diphenylamine (p-ADA) with redox activity via a facile secondary interfacial reaction (s-IR) on PA membrane surface. The calculation of resistance-in-series model indicated that the introduction of p-ADA facilitated the increase of NaCl transmembrane resistance without sacrificing membrane permeance. Chlorination experiments under acid conditions proved the protection effect of p-ADA grafted layer due to its oxidation resistance, avoiding the direct attack by free chlorine to amide bonds of polyamide membrane. By virtue of the convertible modality of the p-ADA molecule between the quinone and benzene structures during redox process, modified membranes presented the capability of regenerative chlorine resistance. After the "chlorination-reduction" cycle experiments, the normalized flux of modified membranes remained 0.522 while contrasted PA membranes showed a flux of 0.278; and the corresponding normalized NaCl rejection of modified membranes maintained at 0.998 significantly higher than that of PA membranes (0.963). This study presents a straightforward and efficient approach to enhance the chlorine resistance of PA RO membranes.