A novel homogenous in-situ generated ferrihydrite nanoparticles/polyethersulfone composite membrane for removal of lead from water: Development, characterization, performance and mechanism

Nanocomposite adsorptive membranes with nanosorbents incorporated have become a promising material for the treatment of heavy metal-containing water, but their practical applications have been limited by the aggregation of nanosorbents in the membrane matrix. In this study, a homogenous in-situ generated ferrihydrite nanoparticles (NPs)/polyethersulfone (PES) adsorptive membrane was prepared for the removal of lead from water for the first time. The XRD, TEM and XPS results showed that ferrihydrite particles with the size smaller than 10 nm were successfully introduced into the composite membrane. The SEM-EDS result indicated a homogenous distribution of the in-situ generated ferrihydrite NPs in PES membrane. With more generated NPs, the membrane structure varied from a larger finger-like macro-void structure (i.e. M3, M6) to a suppressed finger-liker macro-void structure, due to the contributions of viscosity hindrance and thermodynamic enhancement to the demixing rate. Besides, the surface hydrophilicity and water flux increased gradually. The membrane M9 was stable for treating lead-contaminated water at pH above 3.0, with the optimal adsorption pH at 5.5. Furthermore, the M9 displayed the highest adsorption capacity of Pb2+ of 64.77 mg/g, high selectivity toward Pb2+, and excellent reusability without significant loss of adsorption of Pb2+. In filtration process, the M9 can effectively remove Pb2+ mainly by adsorption via cation exchange between Pb2+ and H+ in the presence of ferrihydrite NPs in membrane. More importantly, the presence of humic acid can significantly enhance Pb2+ removal by M9 via adsorption and size exclusion mechanisms (caused by either chelation with HA or barrier effect caused by HA filter cake). Therefore, the present nanocomposite adsorptive membrane can be used as a promising material for treatment of heavy metal-containing water.