Ternary deep eutectic solvent enhanced the diffusion control of amine monomer for highly permeable and anti-fouling polyamide nanofiltration membranes

Thin-film composite nanofiltration (TFC NF) membranes have been widely used in water treatment, while the common active polyamide (PA) separation layer suffers the problems of excessive mass transfer resistance and fouling. In this work, a novel ternary deep eutectic solvent (DES) of citric acid/choline chloride/glycol as an additive in the aqueous phase was focused on regulating the formation of PA layer. The ternary DES can interact with piperazine (PIP) via hydrogen bonding and electrostatic interaction, synergistically enhancing the diffusion control of PIP with viscosity modulation during interfacial polymerization. Notably, a thinner and rougher separation layer with a cellular-like structure was obtained by optimizing the ratio of citric acid in ternary DES. Accordingly, the optimized TFC10%-3 membrane maintained an excellent Na2SO4 rejection (98.8 %) and a 104.7 % increase in pure water permeance (39.5 L·m−2·h−1·bar−1) compared to the original membrane, outperforming commercial membranes and the most NF membranes reported in the literature. Besides, the introduction of citric acid in PA layer increased the surface hydrophilicity and electronegativity of TFC10%-3 membrane, resulting in a higher flux recovery rate (FRR = 93.2 %) of TFC10%-3 membrane than that of TFC10%-0 membrane (FRR = 83.9 %). This study provides a feasible design strategy for the preparation of highly permeable and anti-fouling TFC NF membranes and enrichs the application of ternary DES in water treatment.