Positively charged nanofiltration (NF) membranes via UV grafting on sulfonated polyphenylenesulfone (sPPSU) for effective removal of textile dyes from wastewater

Novel positively charged nanofiltration (NF) membranes have been fabricated using sulfonated polyphenylenesulfone (sPPSU) support with hydrophilic properties and fully sponge-like morphology via UV-induced grafting. The resultant NF membranes with a mean effective pore diameter of 1.13–1.20 nm, molecular weight cut off (MWCO) of 1627–1674 Da and high pure water permeability (PWP) of 9–14 LMH bar−1 can be successfully developed by utilizing two different types of positively charged grafting monomers. In view of salt rejections of the resultant NF membranes, it follows the order R(MgCl2)>R(NaCl)>R(MgSO4)>R(Na2SO4) with high rejections to MgCl2 of up to 95.20%. Furthermore, the newly developed NF1 and NF2 membranes demonstrate an impressive prospect for the dye removal from wastewater treatment. Due to their positive surface charges, a superior rejection of up to 99.98% to Safranin O dye can be achieved by NF1 and NF2 membranes. Characterizations of the two NF membranes were further done to elucidate the difference in performance and a variety of factors such as pore size, surface roughness, selective layer thickness and zeta potential were established as the controlling factors.