Antifouling low-pressure highly permeable single step produced loose nanofiltration polysulfone membrane for efficient Erichrome Black T/divalent salts fractionation

Nanofiltration (NF) membranes are effective in treating wastewater containing organics, dyes, and divalent salts; however, lacking the capability of fractionating the dyes/divalent salts, which is crucial for the treatment of the textile wastewater. Loose NF with excellent permeability is highly required to effectively fractionate the dye and divalent salts. Herein, a facile surface modification of ultrafiltration (UF) membranes with the loose layer of nanosilver immobilized polydopamine have been reported. The self-initiated dopamine polymerization on the polysulfone (PS) coordinated with the silver (Ag) to form a loosely held layer of the silver immobilized polydopamine functionalized polysulfone membrane (L-Ag-PDA-PS-membrane). The original polysulfone membrane had a contact angle of ~ 65° that was reduced to ~ 25° after nanosilver immobilization. Fabricated membranes were thoroughly investigated by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), Atomic force microscopy (AFM), and contact analyzer. High rejection of 99.9% of Eriochrome Black T (EBT) was witnessed with the exceptionally high permeation flux of 39.2 LMH using L-Ag-PDA-PS-membrane. The polydopamine (PDA)-silver modified membranes showed higher permselectivity than the PDA-only counterparts, the former rejecting the dye altogether while letting most of the divalent ions (Mg2+, SO42-) pass through. Long-term fouling runs in the presence of bovine serum albumin (BSA) showed that the presence of Ag/PDA slowed down the rate of flux decline considerably, and flux decline was only 15.6% after 6 h of continuous operation in the presence of the foulants. The designed membrane is an excellent example for fractionating the dye and divalent salts.