A microporous polymer ultrathin membrane for the highly efficient removal of dyes from acidic saline solutions

Membranes with excellent water permeance and high dye removal efficiency are highly desired for textile industry wastewater treatment. However, the high acidity and salinity in such wastewater impose great challenges in dye removal efficiency for conventional polyamide-based membranes. This study presents a type of acid-tolerant polyarylate (PAR) nanofiltration (NF) membrane that tackles such challenges. The PAR active layer is produced via interfacial polymerization using 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane (TTSBI) and isophthaloyl dichloride (IPC) as monomers, and formed on top of a single-walled carbon nanotube (SWCNT) nanofilm. The supporting SWCNT layer contributes to the ultrathin thickness of the PAR active layer and the extremely high membrane permeating flux of ~210 L m−2 h−1 bar−1, while the inclusion of TTSBI monomer grants the PAR active layer surface negatively charged that makes a high dye rejection of >99% at a wide range of feed solution pH and salinity possible. Furthermore, a high selectivity for dye and NaCl was observed with a stable NaCl retention of ~10%, when the membrane is tested at a pH ranging from 2 to 9 and feed NaCl concentration ranging from 1000 to 5000 ppm. The PAR NF membrane is therefore a promising tool for the highly efficient treatment of acidic and high salinity textile dye wastewaters.