This work presents a facile and green method using Citrus aurantifolia fruit extract for the biosynthesis of magnetite nanoparticles (MNs). The effects of some effective parameters such as temperature, reaction time and the ratio of
Citrus aurantifolia extract to sodium borohydride on the synthesis were investigated. The synthesized Fe3O4 nanoparticles were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), energy-dispersive X- ray spectroscopy (EDX), transmission scanning electron microscopy (TEM), and vibrating sample magnetometer (VSM). The results showed that the MNs were well-monodisperse with the mean size of 50 nm and superparamagnetism value of 40.1 emu/g. Adsorption of Cr(VI) in aqueous solution at pH 2.5 using MNs reached 94.9% for removal of Cr(VI). The main contribution of this work was the synthesis of MNs in an economical and environmental friendly way, achieving size-controlled MNs at mild conditions. A possible mechanism of MNs synthesis was also presented.