Characterization and application of a thin-film composite nanofiltration hollow fiber membrane for dye desalination and concentration

Abstract

This study focused on the application of a thin-film composite nanofiltration (NF) hollow fiber membrane formed by interfacial polymerization on a polysulfone/polyethersulfone supporting membrane for dye desalination and concentration. The fabricated NF hollow fiber membrane had a hydrophilic skin layer with an isoelectric point at a pH value of approximately 6.6. Permeation tests revealed that the membrane possessed a molecular weight cut-off (MWCO) of approximately 520Da and a pure water flux of 47.5L/m2h at 0.4MPa. Rejections of different salts followed in the order of MgSO4>Na2SO4>MgCl2>NaCl at a pH value of 6.8, with up to 96.20% rejection for MgSO4. Additionally, due to the negative charge on the membrane surface, rejections of the anionic dyes reactive brilliant blue X-BR and acid red B were 99.99% and 99.90%, respectively. The dye rejection and permeate flux were affected by the dye concentration as well as the presence of NaCl in the X-BR aqueous solutions. Both the dye rejection and permeate flux would decline with the increase of feed dye and salt concentration. The fabricated NF hollow fiber membrane was applied to the process of dye desalination and concentration using an X-BR and NaCl mixed aqueous solution as the pollutant. After finishing the process, the volume of retentate was concentrated 6.25 times, and the dye concentration in the retentate reached 2854.8mg/L. Moreover, the recovery rate of dye was up to 91.4%, and over 95.3% NaCl was removed from the dye/salt mixtures, which indicated that the fabricated composite NF hollow fiber membrane could be successfully applied to the dye desalination and concentration process.