Tuning of nanofiltration membrane by multifunctionalized nanovesicles to enable an ultrahigh dye/salt separation at high salinity

Abstract

A nanofiltration (NF) membrane capable of efficiently separating dye and salt at high-salinity is of great interest for the effective treatment of the textile wastewater. However, existing NF membranes exhibit either an excessively high salt rejection or a compromised dye rejection at high salinity. To overcome these challenges, herein the highly uniform nanovesicles functionalized with positively-charged molecules and nonreactive polymers were employed to tune the surface charge density and pore size of the thin-film composite (TFC) NF membrane via interfacial polymerization. The tuning proved efficient to simultaneously reduce surface charge density and enlarge pore size to the desired extent, which enabled a very low retention of salts (∼7% for NaCl) while maintaining a rather high dye rejection (∼99.8% for Direct red 23) with a high salt/dye separation factor of 464. Additionally, the separation stability of the finely-tuned membrane was superior to most of other reported NF membranes when treating a high-salinity dye/salt mixture. Meanwhile, the water permeability of the modified TFC membrane was enhanced by a factor of 2.6, reaching up to 205.8 L m−2 h−1 MPa. This study paves a new route to the high-performance NF membrane for an effective treatment of the high-salinity textile wastewater.