Fabrication of loose nanofiltration membranes by regulation TA-Fe(III) coordination for efficient dye/divalent salt separation

Traditional textile wastewater treatment methods face significant challenges in achieving effective dye/salt separation with low energy consumption. In this study, a high-performance loose nanofiltration (LNF) membrane based on metal-polyphenol bio-adhesion was fabricated. By exchanging Fe 3+ onto Laponite (Lp) nanosheets, the coordination between tannic acid (TA) and Fe 3+ was controlled, optimizing the structure of the selective layer. Subsequently, PVP was introduced to regulate membrane structure owing to the hydrogen bonding between TA and PVP, thereby enhancing both separation performance and stability of the membrane. The optimized Fe@Lp/TA-PVP membrane exhibited favorable separation performance by modulating preparation conditions including the Fe 3+ exchanging on Lp nanosheets, PVP concentration, and coating time. The LNF membrane possessed high water permeability (167.7 L·m −2 ·h −1 ·bar −1 ) and favorable separating efficiency for dyes from salts. A high rejection of 99.9 % was achieved for Congo Red and Methyl Blue, while the rejection of Na 2 SO 4 and MgCl 2 remained low, at 8.93 % and 2.21 %, respectively. Besides, the membrane demonstrated desirable antifouling capability. Therefore, this work enriches the applications of metal-polyphenol coordination in water treatment, provides new insights into the design of LNF membranes.