Green synthesized iron nanoparticles by green tea and eucalyptus leaves extracts used for removal of nitrate in aqueous solution

Since water pollution associated with high concentrations of nitrate poses serious threats to aquatic ecosystems and can eventually lead to eutrophication, the removal of nitrate, particularly in a large scale context is still a challenge. To address it, this study proposed that iron nanoparticles (Fe NPs) synthesized by green tea (GT-Fe) and eucalyptus leaves (EL-Fe) extracts, which regarded as cleaner productions can be used for the efficient removal of nitrate. Scanning electron microscopy (SEM) and X-ray energy-dispersive spectrometer (EDS) confirmed the successful synthesis of spheroidal iron nanoparticles. Meanwhile, X-ray diffraction (XRD) and Fourier Transform Infrared spectrometer (FTIR) indicated the formation of Fe0-iron oxide core-shell NPs with polyphenols as a capping/stabilizing agent. Batch experiment showed that 59.7% and 41.4% of nitrate was removed by GT-Fe and EL-Fe NPs, compared to the 87.6% and 11.7% that was removed using zero-valent iron nanoparticles (nZVI) and Fe3O4 nanoparticles, respectively. Nevertheless, reactivity of nZVI decreased 2.1-fold after being aged in air for two months, whilst GT-Fe and EL-Fe NPs almost remain the same. Additionally, the kinetics study indicated that the nitrate removal process better fitted to the pseudo-second-order adsorption model, where the qe was 13.06 mg/g for GT-Fe and 9.698 mg/g for EL-Fe NPs. Based above, a removal mechanism dominated by adsorption and co-precipitation process with subsequently reduction was proposed. Finally, applications of these as-prepared green Fe NPs in swine wastewater demonstrated a promising environmental pollution management option for large scale eutrophic wastewater treatment.