Chlorine-resistant loose nanofiltration membranes based on interface quaternization of hexamethylenetetramine

Facile preparation of loose nanofiltration membranes (LNMs) with good chlorine resistance is highly demanded for water purification. Here, we reported the preparation of LNMs via the interfacial quaternization of hexamethylenetetramine (HMTA) with 1,3,5-benzenetricarbonyl trichloride (TMC). Both the macrocyclic structure of HMTA and the relatively low reactivity of tertiary amines are beneficial for the formation of loose structures with high permeance. The resulting HMTA/TMC LNMs showed high water permeance (71.0 L m−2 h−1 bar−1) combined with good Evans Blue (EB)/NaCl selectivity (EB rejection: 98%, NaCl rejection: 12.7%). Notably, the LNMs features quaternary amide structure that contains no active hydrogen, thus the high separation performance was maintained during 20-days immersion of the membrane in 200 ppm NaClO solution. Furthermore, chlorine resistance of the membrane was retained at varied pH conditions, and separation performance of the fouled membranes could be restored by NaClO cleaning. Considering these beneficial properties, the membrane holds great promise in dye/salt separation.