Preparation And Characterization Of Spinel Ferrite Hollow Nanospheres

Magnetic nanostructure materials have gained great interests for their novel physicochemicalproperties and widely applications in various fields. Up to now, magnetic nanostructure, for examples,magnetic nanorods, nanowire, nano-hexagon, nano-triangle, nanocube, nanosolid/hollow spheres have beenprepared. Among these nanostructures, magnetic hollow nanospheres, particularly ferrite hollownanospheres received special attentions for the applications in drug-delivery, catalysis, high-densitymagnetic storage, magnetic fluid, optional electronic devices, magnetic response imaging, andelectrophotographic development and so on. Now, the general approaches to obtain magnetic hollownanospheres are template method （hard and soft templates）, reverse micelles, and Ostwald ripeningapproaches, hard templates approaches getting hollow structures by corrosion or calcinations often makethe the hollow structures collapse, soft method is hard to control, and the hollow structures are nonuniform,the reverse micelle methods are rare to hollow structures, however, Ostwald ripening approaches are simpleand could get monodisperse samples, and become a popular method. In this thesis, we got the ferrite hollownanospheres by a green, powerfrugal and simple method based on hydrothermal method.First, we got the Fe₃O₄magnetic hollow nanospheres by solvothermal method, the chemicalcomposition and morphologyes were characterized by X-ray powder diffraction （XRD）, fourier transforminfrared spectroscopy（FT-IR）, scaning and transmission electron microscopy（SEM/TEM）, further more, themagnetic properties were measured by superconducting quantum interference device （SQUID）. The resultsshow, with the reaction time going on, the160nm solid nanospheres transformed to180-250nm hollownanospheres. Compared with the samples obtained by solvothermal （glycol）, the reaction temperature waslower, and the samples have a good dispercivity, and water-solubility. In addition, the hollow nanospheresshowed a superparamagnetic property at a rather low temperature （130K）, which extended the servicetemperature range of the hollow nanospheres.Hydrothermal method can obtained nanostructure materials, while sonochemistry can accelerate thereaction rate and synthesize the nanomaterials at room temperature. Based on theses features; γ-Fe₂O₃hollow nanospheres were prepared by hydrothermal/sonochemistry two-steps. By studying the reactionmechanism, kekendare effect was used to interpret the formation process, and the saturation magnetization of the obtained sample is obviously higher than common γ-Fe₂O₃nanoparticles, and the γ-Fe₂O₃hollownanospheres were superparamagnetic at room temperature.Summarized the characteristics of the above two methods, the ferrite hollow nanospheres have anunobvious hollow structure, what′s more, and some of the nanospheres have not hollow structure. To solvethis problem, hydrothermal reduction approach was applied to synthesize the ferrite （MF₂O₄; M=Fe, Co, Zn,Mn） nanospheres with obvious hollow structure. The diameter and shell thickness of these hollownanospheres could be tuned by the dosage of the alkali. The samples exhibited ferromagnetism at roomtemperature and have a rather high saturation magnetization. Further more, the surface of these hollownanospheres feature water-soluble groups, which conduce to the coupling of biologically active molecules,and thus thse hollow nanospheres have a goog prospects for biological application. In addition, due to itsown chemical properties and large surface area, these ferrite hollow nanospheres will have broadapplication prospects in the fied of water-treatment.