Positively Charged Nanofiltration (NF) Membranes Based On UV Grafting for Effective Removal of Textile Dyes From Wastewater

Novel positively charged nanofiltration (NF) membranes have been fabricated using a support made from proprietary polysulfone 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 LMHbar^-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 of R(MgCl₂) > R(NaCl) > R(MgSO₄) > R(Na₂SO₄) with high rejections to MgCl₂ of more than 95%. 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 99.9% 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.