A new insight into the transformation mechanism between reactivity of aqueous monomer and chlorine resistance of polyester-amide nanofiltration membrane

Polyester-amide (PEA) thin film composite (TFC) nanofiltration (NF) membranes were widely researched due to their excellent chlorine resistance properties. However, the underlying transformation mechanism between the reactivity of monomers during membrane preparation and chlorine resistance effect of the membrane was still unclear. Herein, 2-Hydroxyethylhydrazine (2Hyd) and N-(2-Hydroxyethyl) ethylenediamine (N2Hyd) were respectively selected to react with trimesoyl chloride (TMC) for preparing PEA-TFC-NF membranes by interfacial polymerization. The characterization and multiscale simulations results revealed that the differences in monomer reactivity affected the crosslinked pathways of their amine and hydroxyl groups, leading to variations in the chlorine resistance of PEA active layer. Although the reactivity of 2Hyd was higher than N2Hyd, which was demonstrated by ∆E_(HOMO-LUMO), the chlorine resistance of NF-2Hyd membrane made by 2Hyd was worse. More polyamide bonds rapid formation on the surface of NF-2Hyd membrane due to 2Hyd with the higher activity, which limited the formation of more polyester crosslinked structures, resulting the poor chlorine resistance for NF-2Hyd. Meanwhile, the lower HOMO-LUMO energy and Stronger interaction energy with CIO⁻ of the NF-2Hyd membrane also verified the weaker chlorine resistance. Overall, this work could provide a new insight into the selection of specific monomers for developing high chlorine resistance NF membranes.