Thin-film composite electro-nanofiltration membrane for one-step and efficient fractionation of dyes and salts in high-salinity textile wastewater

The key to achieve sustainable treatment of high-salinity dye-containing wastewater is effective fractionation of dyes and salts. In this study, a thin-film composite electro-nanofiltration membrane was successfully fabricated by co-deposition of levodopa and epsilon-polylysine onto a porous ultrafiltration membrane substrate. With the codeposition of the polylevodopa/epsilon-polylysine composite coating on the substrate membrane, the surface properties were significantly regulated, resulting in decreased pore size, reduced surface negative charge density and lower specific electric resistance, thus enhancing their ion transfer and dye/salt fractionation efficacy. Specifically, the fabricated LDP-4 membrane (molecular weight cut-off of 408 Da) with a 4-h co-deposition experienced a 99.12 % reactive orange 16 dye rejection and 10.15 % NaCl rejection, indicating an impressive selectivity between dyes and salts. Additionally, the LDP-4 electro-nanofiltration membrane as anion conducting membrane exhibited a fast and efficient electro-driven transfer of Cl ions. Notably, under an electric field, the fabricated LDP-4 electro-nanofiltration membrane can efficiently fractionate NaCl from the reactive orange 16/NaCl mixed solution, achieving a 98.89 % desalination efficiency and 99.79 % dye recovery. Furthermore, the LDP-4 membrane demonstrated remarkable anti-fouling property and long-term stability over an 8-cycle electronanofiltration operation. Therefore, the electro-nanofiltration membranes fabricated by co-deposition of levodopa and epsilon-polylysine show a promising potential in sustainable resource recovery from high-salinity dye-containing wastewater.