Fabrication And Magnetic Properties Of Ferrite Nanostructure (Hollow) Microspheres

Magnetic nanomaterials have gained technological significance after they became known as a variety of biomedical applications, for example, contrast agents in magnetic resonance imaging, drug delivery to tumor cells and cancer treatment by hyperthermia, and cell separation and purification. It is essential and necessary to optimize the physicochemical properties of magnetic nanomaterials to fulfill their functions in biomedical fields.Superparamagnetic microspheres are a kind of the important magnetic materials, the diameter, magnetic content, saturation magnetization and surface property of magnetic nanospheres play important roles in their biomedical applications and determine their moving speed in the solution, signal intensity and conjugation with drug or biomolecules. Among various magnetic nanoparticles, ferrites, such as magnetite (Fe₃O₄) and cobalt ferrite (CoFe₂O₄) have been considered as ideal candidates for these bio-related applications owing to their good biocompatibility and stability in physiological conditions and low cytotoxicity. In addition, the superparamagnetic behavior, high magnetization, and high water dispersibility make them ideal candidates for various important applications. Herein, monodispersed CoFe₂O₄ microspheres and Fe₃O₄ hollow microspheres were fabricated, in which the mechanism of formation of the microspheres and hollow microspheres were discussed.At first, based on a low-temperature route, monodispersed CoFe₂O₄ microspheres (MSs) were fabricated through aggregation of primary nanoparticles. The microstructural characteristics of the as-prepared MSs were characterized by X-ray diffraction/photoelectron spectroscopy, scanning/transmitting electron microscopy, and magnetic properties were carried out by using Quantum Design Superconductor Quantum Interference Device (SQUID) and VSM. The results indicate that the diameters of CoFe₂O₄ MSs with narrow size distribution can be tuned from over 200 to 330 nm. Magnetic measurements reveal these MSs exhibit superparamagnetic behavior at room temperature with high saturation magnetization.Superparamagnetic Fe₃O₄ hollow microspheres with an average diameter of 240 nm have been solvothermally synthesized where each of them are composed of primary nanoparticles with the size of 10–14 nm. The magnetism investigation indicates that the as-prepared samples remain room-temperature superparamagnetic behavior with a high saturation magnetization (up to 83.5 emu/g), approaching to correspondent bulk single-crystal Fe₃O₄ (92 emu/g). A thin PVP layer in this work was actually formed on the surface of the Fe₃O₄ primary NPs, which has potentially useful for surface modification. The excellent products may lead to many promising for various technological applications.