High flux and high selectivity thin-film composite membranes based on ultrathin polyethylene porous substrates for continuous removal of anionic dyes

Thin-film composite (TFC) nanofiltration (NF) membranes efficiently remove dyes from wastewater. However, most of the membranes often sacrifice water flux for high rejection because of the trade-off between them. The demand for TFC membranes with high rejection and high water flux is increasing. Here, polyethylene (PE) membrane with a thickness of 7 µm was covered by polydopamine and polyethyleneimine (PDA/PEI), and then directly initiated interfacial polymerization (IP) with trimesoyl chloride (TMC), forming the dense and negatively charged polyamide-polyester selective layer. As the amount of PDA/PEI increases, the selective layer becomes denser, leading to the efficient removal of anionic dyes at high water flux. The water flux of the optimal membrane is 61.0 ± 18.3 L m−2 h−1 bar−1, and the removal efficiency is 91.4 ± 0.8% for an anionic dye eosin Y (EY, Mw = 691.9 Da), but poor decolorization for natural VB12 (Mw = 1355.4 Da). Moreover, the TFC membrane shows excellent selectivity for filtrating dye/NaCl mixture solution. The synergistic effect of adsorption-filtration control the removal of anionic dyes from wastewater in large flux. This work utilizes commercial PE porous substrate to fabricate TFC membrane having outstanding separation performance and a low thickness of about 7 µm.