A novel polyester-amide loose composite nanofiltration membrane for effective dye/salt separation: The effect of long molecule on the interfacial polymerization

Loose nanofiltration (LNF) membrane with exclusively high dye rejection and inorganic salt permeation are remarkable method to treatment dye/salt wastewater for the achievement of zero liquid discharge. Herein, a long molecule bis-tris propane with amines and hydroxyl groups was firstly chosen as aqueous monomer in interfacial polymerization to fabricate a novel polyester-amide LNF membrane. Noteworthily, the investigation of morphology characterization and preparation conditions revealed that the size of molecule was a vital influence factor for the formation mechanism of unique loose structure of LNF made by long molecule. A new insight about the size of long molecule to form ultrathin thickness of self-repression layer on the formation mechanism of LNF was proposed in this work to replenish the previous theory. A series of characterization verified that the polyester-amide layer is negatively charged and hydrophilic due to the carboxyl and hydroxyl groups on the surface. Meanwhile, the tailored 0.3-LNF exhibited high water permeability (114.9 L m(-2) h(-1)), dye rejection (98.83% RB 5) and low salt rejection (11.72% NaCl) under 0.5 MPa, which displayed good performance for the fractionation of dye/salt mixtures. In addition, the polyester-amide LNF membrane possesses a superior anti-fouling and stability performance.