Abstract: In this paper,monodisperse Fe3O4 nanoparticles with the size of 6-10 nm were synthesized via co-precipitation method.As-synthesized Fe3O4 were characterized by X-ray diffraction (XRD),Fourier transform infrared (FT-IR) spectrometer and transmission electron microscope (TEM).The effect of hydrochloric acid (HC1) amount on products was investigated by TEM and UV-vis absorption spectra.The results indicated that HCl could commendably modulate dispersity of nanometer Fe3O4.A possible generated mechanism of Fe3O4 crystals was proposed in virtue of Zeta potential,it demonstrates that the particles'dispersion and stability changed with the diffusion bilayer.Besides,the magnetic properties of as-synthesized Fe3O4 are detected and the results prove that the modified magnetic nanoparticles exhibit good superparamagnetic property.

Key words: In this paper,monodisperse Fe3O4 nanoparticles with the size of 6-10 nm were synthesized via co-precipitation method.As-synthesized Fe3O4 were characterized by X-ray diffraction (XRD),Fourier transform infrared (FT-IR) spectrometer and transmission electron microscope (TEM).The effect of hydrochloric acid (HC1) amount on products was investigated by TEM and UV-vis absorption spectra.The results indicated that HCl could commendably modulate dispersity of nanometer Fe3O4.A possible generated mechanism of Fe3O4 crystals was proposed in virtue of Zeta potential,it demonstrates that the particles'dispersion and stability changed with the diffusion bilayer.Besides,the magnetic properties of as-synthesized Fe3O4 are detected and the results prove that the modified magnetic nanoparticles exhibit good superparamagnetic property.