Novel negatively charged nanofiltration membrane based on 4,4′-diaminodiphenylmethane for dye removal

Membrane separation processes constitute an economical and efficient technology for the effective treatment of dye wastewater. In this study, 4,4′-diaminodiphenylmethane and 1,3,5-benzenetricarbonyl trichloride were used as monomers to prepare polyamide-based nanofiltration (NF) membranes by interfacial polymerization, for dye removal. The preparation parameters of the NF membrane were optimized by investigating the effects of the concentrations of two monomers, the soaking time of the carrier in aqueous solution of monomer, and the polymerization time on the membrane performance. The surface roughness of optimized membrane was found to be only 5.08 nm, and the stabilized contact angle was about 25°, indicating very high hydrophilicity. When the pH was in the range from 3 to 10, the membrane surface became electronegative, which resulted in a high rejection rate toward various negatively charged dyes. For the congo red dye solution, the membrane showed a flux of 36.81 L m⁻² h⁻¹ and a rejection rate of 99%. The rejection rate of the other two negatively charged dyes investigated herein was also above 95%. Moreover, the filtration experiment of bovine serum albumin solution showed that the flux recovery rate of the membrane was up to 89.85%, indicating good stability and antifouling performance.