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

Abstract

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 scattering (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 α-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 agglomeration 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.