Combining tannic acid-modified support and a green co-solvent for high performance reverse osmosis membranes

Abstract

In this work, a support modified by tannic acid (TA) and a green co-solvent (dimethyl carbonate (DMC)) were used jointly to prepare high performance polyamide (PA) reverse osmosis (RO) membranes. The membrane characterization results showed that (1) the leaf-like structure became more pronounced on the membrane surface owing to the addition of DMC and (2) TA made the PA active layer thinner and denser. Because of these improvements of skin layer structure, the RO membranes prepared using TA and DMC (i.e., polysulfone (PSf)/TA-RO@DMC) had a better performance than the membranes prepared without using TA and DMC (i.e., PSf-RO) and those prepared using only TA (i.e., PSf/TA-RO) or only DMC (i.e., PSf-RO@DMC). By joining hands, TA and DMC endowed the RO membranes with a high flux of 64.2 ± 1.8 L m−1 h−2 and a high salt rejection of 99.03 ± 0.02% (the testing condition: 15.5 bar pressure, 2000 ppm NaCl feed and 25 °C). Besides, chlorination was used to improve the membrane performance further. The chlorination results showed that chlorinated PSf/TA-RO@DMC had a higher performance than chlorinated PSf-RO@DMC. This is because TA increased the compactness of PA active layer, which weakened the effect of chlorine attack on PA. After chlorination, the flux and salt rejection of PSf/TA-RO@DMC can be improved further to 90.5 ± 6.3 L m−1 h−2 and 99.25 ± 0.02%, respectively (the testing condition: 15.5 bar pressure, 2000 ppm NaCl feed and 25 °C).