The effect of surficial function groups on the anti-fouling and anti-scaling performance of thin-film composite reverse osmosis membranes

Membrane fouling, including organic fouling and inorganic scaling, is one of the most prevalent problems in reverse osmosis (RO) membranes, which usually increases operating costs and reduces efficiency. In this study, various surface modified thin-film composite (TFC) RO membranes were developed to systematically investigate the effect of type of ionic groups (-COOH, –NH2, and zwitterions) on the membrane anti-fouling and anti-scaling performances. Compared with the pristine polyamide-based membrane, all the modified membranes maintained their surface topography with a "ridge-and-valley" structure, but their surface hydrophilicity were significantly improved and zeta potential values were changed. The results of fouling tests show that TFC-g-PEI membrane with positive zeta potential is beneficial to the anti-fouling performance against cationic foulants, but is very unfavorable against anionic foulants, although the surface hydrophilicity is very good. The zwitterion-modified membranes with different anions (carboxylate, sulfonate, and phosphate groups) have little difference in anti-fouling performance against organic foulants, but have obvious influence on anti-scaling performance. All the zwitterion-modified membranes exhibited good anti-fouling performances against charged and electroneutral foulant, owing to their remarkable hydrophilicity and neutrality. Interestingly, TFC-g-PEI-SO3H membrane exhibited the best anti-scaling performance because of the low pKsp value of calcium sulfate. In conclusion, the research of this study may provide the development direction for the preparation of anti-fouling and anti-scaling membranes.