Effect of Anions on Removal Efficiency of Green Synthesized Iron Nanoparticles

Iron nanoparticles (FeNPs) were synthesized using a one-step green method with pomegranate leaf extract (PG) as a reducing and stabilizing agent. The effects of different anions in the iron salt precursor on the synthesis of FeNPs and their impact on the removal efficiency of malachite green (MG) were studied using characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Zeta potential, X-ray photoelectron spectroscopy (XPS), and BET. The results showed that the removal efficiency of MG by FeNPs synthesized with different anions follows the order: RPG-Fe₂(SO₄)₃>RPG-Fe(NO₃)₃, RPG-FeCl₃>> RPG-FePO₄. The strong electrostatic interaction between PO₄^3- and Fe³⁺ prevented the complexation of polyphenols in PG with FePO₄, resulting in the lowest activity of PG-FePO₄. The coordination and reduction of phenolic hydroxyl groups in PG extract led to the formation of amorphous (Fe(Ⅱ)/Fe(Ⅲ)-polyphenol) complexes for FeNPs synthesized with other anions. Uniform size and smaller particle size of FeNPs played a key role in enhancing the removal efficiency of MG, while the surface elemental composition and Zeta potential had little impact.