High performance loose nanofiltration membranes obtained by a catechol-based route for efficient dye/salt separation

Loose nanofiltration membranes with excellent dye rejection and high inorganic salt transmission are promising for dye/salt separation. Herein, a mussel-inspired organic solvent-free method was chosen to prepare loose nanofiltration membranes with tunable surface structures and properties. A low-cost material, 1,2-dihydroxybenzene (catechol), was used to replace dopamine for the mussel-inspired surface coating strategy. With the assistance of CuSO4/H2O2, a catechol/PEI coating layer was formed on the polyethersulfone (PES) substrate in only 10 min. Through constructing the coating layer based on polyethylenimine (PEI) with different molecular weights, catechol/PEI ratios and solution deposition times, different membranes were obtained. The separation performance of the membrane is tested by a lab-scale crossflow setup under the pressure of 4 bar. Especially, LNM-3 have an ultrahigh water permeability (24.5 LMH bar−1) and an extremely low rejection for both NaCl and Na2SO4 in the concentrations between 1.0 and 50.0 g L−1. Meanwhile, LNM-3 shows superior rejection for different types of dyes, demonstrating their great potential in practical applications. Overall, such an approach enabled by an organic solvent-free process and low-cost chemicals may offer a new strategy for the environmental-friendly and economical manufacturing of multifunctional loose nanofiltration membrane.