Organic salt modulated preparation of ultra-thin and loose polyamide nanofiltration membranes with enhanced performance

Polyamide (PA) membranes prepared by interfacial polymerization (IP) show bright prospects for nanofiltration applications. Modulation of the IP process can effectively regulate the structures and properties of PA separation layer. Reducing thickness and increasing looseness of PA layer’s structure are effective strategies for improving membrane permselectivity. Herein, an organic salt of 4-hydroxybenzenesulfonic acid sodium salt (HBSA) was chosen as a modulator to regulate the IP process which interacts with amine monomer through electrostatic interaction and hydrogen-bonding interaction. The diffusion of amine-reactive monomers can be effectively slowed down by the electrostatic interaction between HBSA and amine monomers, resulting in an ultrathin membrane structure. Moreover, the homogeneous hydrogen-bonding network around the amine-reactive monomers inhibited the IP reaction, resulting in a loose PA structure with nearly 2 times higher porosity than that of the pristine PA. The above two effects led to improvement both in water permeance up to 34.4 L m−2 h−1 bar−1 and Na2SO4 rejection up to 99.1%, overcoming the permeability-selectivity trade-off.