Polyamide nanofiltration membranes modified with Zn–Al layered double hydroxides for natural organic matter removal

Zn–Al layered double hydroxides (LDH) modified polyamide (PA) nanofiltration (NF) membranes were successfully fabricated by interfacial polymerization of 1,3-Phenylene diamine (MPD) and 1,3,5-Benzenetricarbonyl trichloride (TMC) monomers. Compared to raw PA membranes, the LDH incorporated membranes showed denser PA layers with more leaf-like folds, rather than ridges and valleys, according to images from field emission scanning electron microscopy (FESEM) and atomic force microscope (AFM). Higher hydrophilicity (with the contact angle decreased from 70.33° to 55.66°) and water permeability (with pure water flux enhanced from 6.76 to 9.48 L/m2 h, measuring approximately 40.2% improvement) were achieved by PA membranes embedded with Zn–Al LDH nanoparticles. The rejection ability of different membranes was evaluated using Aldrich-humic acid (HA) and water from the Huangpu River; the results indicated that PA/LDH membranes exhibited a higher removal efficiency of natural organic matter (NOM). Excitation–emission matrix (EEM) fluorescence spectroscopy was also used in analysing raw natural water and permeate to investigate the removal mechanism toward different types of organic matters; better antifouling properties were observed for modified PA membranes.