Study on the Synthesis and Properties of Superparamagnetic Monodisperse Fe_3O_4 Nanoparticles

There are extensive applications for superparamagnetic Fe3O4 nanoparticles in the field of biomaterials. Superparamagnetic magnetite nanoparticles coated with oleic acid were prepared in the refluxing mixed system of water,ethanol alcohol and toluene at 74℃. The effect of the OH-concentration on the surface properties,size,dispersion and magnetic properties of magnetite nanoparticles was studied systematically. The properties of magnetite nanoparticles were tested by X-ray diffraction (XRD),fourier transform infrared (FTIR),dynamic light scattering (DLS),transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The results show that when the molar ratio of NaOH to Fe(Ⅱ) is less than 8,magnetite nanoparticles coated with oleic acid can be dispersed easily in nonpolar solvents. The addition of NaOH has no obvious influence on the size and the saturation magnetization of magnetite nanoparticles. While the molar ratio of NaOH to Fe(Ⅱ) is more than 8,magnetite nanoparticles can only be dispersed in polar solvents,such as water. Although the saturation magnetization increases to 40A·m2/kg,magnetite nanoparticles are polydisperse and easy to agglomerate in water.