High-flux PSF/PES-COOH hollow fiber loose nanofiltration membrane for high-efficiency dye-salt separation

Loose nanofiltration membranes show great potential to realize the effective separation of dyes and salts but still show low capacity for treating textile wastewater due to low membrane flux. In this work, a high-flux hollow fiber nanofiltration membrane (HFNFM) for the separation of dyes and salts was fabricated through a simple one-step non-solvent induced phase separation (NIPS) method. A carboxylated polyethersulfone (PES-COOH) was synthesized by the polycondensation based on Williamson reaction using diallyl bisphenol sulfur as a commoner followed by the thio-ene reaction with thioglycolic acid. Then PES-COOH was blended with polysulfone (PSF) for hollow fiber spinning based on the NIPS method. The effects of the ratio of PSF to PES-COOH on the membrane structure and performance were studied with scanning electron microscope (SEM), differential scanning calorimetry (DSC), X-ray photoelectron spectrometer (XPS), water contact angle and zeta potential measurements. Upon optimization, the PSF/PES-COOH HFNFM displayed a water flux of 159.6 L m−2 h−1 bar−1, and a rejection of 99.2 % for Congo red at a dye concentration of 100 mg/L and operating pressure of 0.1 MPa. With the effective dye-salt fractionation which was comparative to literature reports, the membrane showed unprecedentedly high flux, which can be attributed to the double layer finger-like structure and hydrophilic PES-COOH as additives. The membrane also presented excellent stability and antifouling property during the treatment of simulated textile wastewater.