Synthesis And Characterization Of CoFe₂O₄/Hollow Glass Microspheres Composites

In this paper, the composite of hollow glass microspheres coated by CoFe2O4 nanoparticles has been successfully prepared via coprecipitation method. And CoFe₂O₄ nanoparticles have been synthesized in the presence ofβ-cyclodextrin at different temperatures by coprecipitation method. The resultant composites were characterized by X-ray diffraction, field emission scanning electron microscope, transmission electron micrographs, energy dispersion X-ray spectroscopy and vibrating sample magnetometer.We report the composite of hollow glass microspheres coated by CoFe₂O₄ nanoparticles prepared using different precipitators via coprecipitation technique; study the effect of different precipitators on morphology of the coating layer. The samples were prepared using NaOH as precipitator instead of CO(NH₂)₂ . CoFe₂O₄ coated layer was directly formed in the reaction solution, thus no further calcinations were done. The CoFe2 O4 coating layer prepared using urea as precipitator is better than using NaOH as precipitator. It is uniform and continuous. According to analysis about XRD patterns and FESEM and EDS pictures above, we would like to propose a surface reaction and the CoFe2O4 coatinglayernucleation- growth model on the surface of hollow glass microspheres about how this coating layer was formed. The most uniform and entire CoFe₂O₄ coating layer with thickness ca. 200–300 nm has been synthesized under the urea concentration of 0.7 M. The saturation magnetization values of the samples increase with the thickness of the CoFe₂O₄ coating layer increasing. The coercivity of samples first increases with the increasing thickness of the CoFe₂O₄ coating layer and then decreases. The saturation magnetization and coercivity values of the samples are significantly lower than the pure CoFe2O4 nanoparticles. This behavior may be attributed mainly to the contribution of the volume of the non-magnetic hollow glass microspheres to the total sample volume. The microwave absorption property of the composites resulted high absorption than the pure CoFe₂O₄ nanoparticles.The density of absorbent decreases. The mechanism of microwave absorption is that after the microwave reflects many times in the hollow glass microspheres, the CoFe2O4 layer brings on repetitious loses to the microwave, thus it greatly enhanced the microwave absorption efficiency.The hollow glass microspheres coated with CoFe₂O₄ nanoparticles mechanism: when hollow glass microspheres are added into urea aqueous solution, large numbers of OH- react with the surface of hollow glass microspheres to form the amount of _OH function groups as the nucleation sites on their surface. Then the added CoCl 2 .6 H2 O and FeCl 3 .6 H2 O provide Co²⁺ and Fe³⁺ would be absorbed by _OH functional groups through electrostatic interaction to form precursors Co(OH)₂ and Fe(OH)₃ on the surface of the modified-hollow glass microspheres. After the thermal treatment, CoFe₂O₄ coating layer on the surface of hollow glass microspheres is achieved.CoFe₂O₄ nanoparticles have been synthesized in the presence ofβ-cyclodextrin at different temperatures by coprecipitation method. The effects ofβ-cyclodextrin and reaction temperature on the particle size and magnetic properties of the nanoparticles have been studied. XRD patterns and TEM micrographs show the particle size is about 2～5 nm with the changing reaction temperature in tne presence ofβ-cyclodextrin. The results of VSM indicate that the CoFe₂O₄ nanoparticles synthesized in the presence ofβ-cyclodextrin at different temperatures have superparamagnetic property.