Monodispersed Co, Ni-Ferrite Nanoparticles with Tunable Sizes:  Controlled Synthesis, Magnetic Properties, and Surface Modification

Ferrite (CoxNiyFe3-x-yO4, x = 0.6, 0.3, 0.2, 0, y = 0, 0.6, 0.7, 0.8) nanoparticles monodispersed in nonpolar solvents have been prepared with different Co, Ni, and Fe compositions by heating mixtures of inorganic salts and sodium dodecylbenzenesulfonate (SDBS) in n-octanol. The as-prepared nanoparticles were characterized in detail by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), selective area electron diffraction (SAED), infrared (IR), thermal-gravimetric (TG) analysis, and other techniques. The nanoparticle sizes could be tuned by adjusting the reaction time. The formation mechanism of the nanoparticles during the solvothermal process is proposed based on the experimental results. The effects of size and composition of the nanoparticles on magnetic properties were investigated, and the magnetic properties of nanoparticles with the same size but different compositions were compared. Furthermore, water-dispersible nanoparticles were obtained by simply washing the as-prepared nanoparticles with acetic acid.