Nitrate adsorption using green iron oxide nanoparticles synthesized by Eucalyptus leaf extracts: Kinetics and effects of pH, KCl salt, and anions competition

This research investigated the colloidal stability and reactivity of green iron oxide nanoparticles for removing NO3- ions from polluted water. These nanoparticles were synthesized by Eucalyptus globulus leaf extract (EL-Fe NPs). Transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and dynamic light scat-tering (DLS) were utilized to characterize EL-Fe NPs. The effect of contact time, different pH, KCl salt, and anions (PO43-, SO42-, HCO3-, Cl-), on NO3- adsorption using EL-Fe NPs were evaluated. Based on the results, Fe3O4 and a-Fe2O3 nanoparticles were encapsulated by polyphenols and have irregular nano-particulate structures. After 30 min, the maximum adsorption capacity of 1.5 g L-1 EL-Fe NPs dispersed in 50 mg L-1 NO3- solution with a pH of 3.7 was acquired at about 12.91 mg/g. Adsorption of NO3- on EL-Fe NPs was strongly pH dependent, and at pH > 6.6 no significant adsorption occurred. KCl salt by agglom-eration of EL-Fe NPs, the mean particle size varied between 25.6 nm and 63 nm, and NO3- adsorption decreased dramatically. It was observed that EL-Fe NPs significant affinity to adsorb PO43-ions. As a result, no significant adsorption of NO3- ions onto EL-Fe NPs was detected in the presence of phosphate ions. The experimental data were reasonably fit to a pseudo-second-order kinetic model (R2 = 0.992), which can be concluded that the primary mechanism of NO3- adsorption is electrostatic. This work indicated that the removal of NO3- using EL-Fe NPs was influenced by the type and concentration of accompanying cations and anions. (c) 2023 Elsevier B.V. All rights reserved.