Antifouling and Chemical-Resistant Nanofiltration Membrane Modulated by a Functionalized MWCNT Interlayer for Efficient Dye/Salt Separation at High Salinity

Dye/salt separation in textile wastewater is of great importance. Membrane filtration technology is an environmentally friendly and effective approach to solve this issue. In this study, a thin-film composite membrane with a tannic acid (TA)-modified carboxylic multiwalled carbon nanotube (MWCNT) interlayer (M-TA) was prepared by interfacial polymerization with amino-functionalized graphene quantum dots (NGQDs) acting as aqueous monomers. The addition of the M-TA interlayer favored the formation of a thinner, more hydrophilic, and smoother selective skin layer for the composite membrane. The pure water permeability of the M-TA-NGQDs membrane was ∼9.32 L m –2 h –1 bar –1, which was higher than that of the NGQDs membrane without the interlayer. Meanwhile, the M-TA-NGQDs membrane presented better methyl orange (MO) rejection (97.79%) than the NGQDs membrane (87.51%). The optimal M-TA-NGQDs membrane exhibited excellent dye rejection (Congo red (CR): 99.61%; brilliant green (BG): 96.04%) and low salt rejection (NaCl < 15%). Noticeably, the M-TA-NGQDs membrane displayed effective selective separation performance (CR and BG > 99%) for dye/NaCl mixed solutions even at a high NaCl concentration of 50,000 mg/L. Furthermore, the M-TA-NGQDs membrane presented high water permeability recovery ratio values (91.02–98.20%). Importantly, the M-TA-NGQDs membrane showed excellent chemical stability (acid/alkali resistance). Generally, the fabricated M-TA-NGQDs membrane exhibited a great prospect for applications in dye wastewater treatment and water recycling, especially for the effective selective separation of dye/salt mixtures for high-salinity textile dyeing wastewater.