Surface modification of reverse osmosis membrane with tannic acid for improving chlorine resistance

Abstract

In this work, the polyamide reverse osmosis (RO) membrane surface was modified by tannic acid (TA), a cheap and commercial polyphenol, for improving chlorine resistance of membrane. TA was introduced onto the RO membrane surface via an exceptionally simple method, i.e., ethanol/TA solution activation before heat-treatment. Specifically, the membrane obtained after interfacial polymerization was treated with ethanol/TA solution before heat-treatment during the RO membrane preparation process. By surface characterization, the introduction of TA onto the RO membrane surface was confirmed. Besides, a long time (30 h) washing test showed that the modification layer was robust. Furthermore, the introduction process improved the RO membrane flux (by 27.7%) meanwhile retaining a high rejection of 98.82 ± 0.18%. Chlorination experiments were performed under the acidic (pH 4.0), neutral and alkaline (pH 8.0) conditions. The chlorinated RO membranes were characterized systematically by membrane flux and rejection evaluation, attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscope. The results showed that TA as a sacrificial layer improved chlorine resistance. Importantly, the membrane modified with TA exhibited a high chlorine resistance after 8000 ppm·h chlorination exposure. This work provides a simple and effective method to improve chlorine resistance of RO membrane.