Abstract
Reverse osmosis (RO) membranes are widely used in the field of water treatment. However, there are inevitably various fouling problems during long-term use. Surface engineering of RO membranes, such as hydrophilic modification, has attracted broad attention for improving the anti-fouling performance. In this work, we constructed a green biomimetic composite modification layer on the surface of polyamide membranes using a dopamine (DA)/tannic acid (TA) co-deposited layer to bridge the polyamide surface and hydrophilic phytic acids (PhA). The DA/TA interlayer could firmly adhere to the RO membranes, reducing the aggregation of DA and providing abundant phenolic hydroxyl sites to graft PhA. Meanwhile, the anchored PhA molecule bearing six phosphate groups could effectively improve the superficial hydrophilicity. The membranes were characterized by the SEM, AFM, XPS, water contact angle test, and zeta potential test. After surface modification, the hydrophilicity, smoothness, and surface electronegativity were enhanced obviously. The flux and rejection of the virgin membrane were 76.05 L·m−2·h−1 and 97.32%, respectively. While the modified D2/T4-PhA membrane showed decent permeability with a water flux of 57.37 L·m−2·h−1 and a salt rejection of 98.29%. In the dynamic fouling test, the modified RO membranes demonstrated enhanced anti-fouling performance toward serum albumins (BSA), sodium alginates (SA), and dodecyl trimethyl ammonium bromides (DTAB). In addition, the modified membrane showed excellent stability in the 40 h long-term test.
Highlights
Membrane-based separation technologies, such as ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO), have become more and more popular in the industries of seawater desalination and wastewater treatment in recent years [1,2,3]
The permselectivity was evaluated by a cross-flow filtration device
The membrane permselectivity was evaluated by the water flux and salt rejection, which were measured using 2000 mg·L−1 NaCl aqueous solution under the pressure of 1.55 ± 0.1 MPa at 25 ◦C
Summary
Membrane-based separation technologies, such as ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO), have become more and more popular in the industries of seawater desalination and wastewater treatment in recent years [1,2,3]. The polyphenols could provide abundant phenolic hydroxyl groups, the hydrophily of DA/TA layers on the membrane surface is still limited. As one of the non-toxic and natural phosphonic acids, phytic acids (PhA) have attracted extensive attention for enhancing the anti-fouling properties of membranes [30,31]. Xiong [30] and Qi [33] constructed PhA-metal complexes through a layer-bylayer self-assembly method to obtain a modified osmosis membrane with fine anti-fouling properties. The co-deposited DA/TA layer could and firmly adhere to the RO membrane, while providing abundant hydroxyl chelating sites to bind PhA. The chemicals, sodium chloride (NaCl), isopropanol, sodium bisulfite (NaHSO3), phytic acid (PhA, ~50% aqueous solution), and hydrochloric acid (HCl) were obtained from Chemart Chemical Technology Co., Ltd. in Tianjin, China. The zeta potential was measured by an electro-kinetic analyzer (SurPASS, Anton Paar GmbH, Graz, Austria)
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