Synthesis And Microwave Absorption Properties Of Hollow Magnetite Nanostructures And Their Composites

With the rapid development of wireless communication, electromagnetic wave interference (EMWI) and pollution has become a big headache for the human beings. The EMWI not only reduces the communication quality between people but also poses potential threat to the health of human beings. In order to solve the problem, researchers have investigated the various kinds of electromagnetic wave absorbers with thin, light and wide properties. Up to now, the magnetic materials and dielectric materials are attracting the most research efforts, but the researches demonstrate that magnetic materials would be the most promising candidates as microwave absorption materials.Magnetite, as a ferromagnet, has a wide application prospect in the fields of magnetofluids, magnetic recording materials, catalysts supports and bio-medicines due to its unique magnetic and electronic properties. Besides, because of its good antioxidation capacity, high thermal stability and low weight, magnetite has been proved an excellent microwave absorption candidate. In this paper, we choose magnetite as the research target, focusing on the hydro-thermal synthesis of the hollow magnetite spheres, investigating the formation mechanism of the hollow structured nanomaterials and evaluating their magnetic properties as well the microwave absorption ability. In addition, we also prepared the hollow Fe3O4@ZnO@TiO2core-shell structures in order to increase their permittivity thus improving the microwave absorption property. The main contents of this research can be summarized as follows:(1) With FeCl3·6H2O, EG, PVP, CO(NH2)2as raw materials, we synthesized the hollow magnetite spheres through hydro-thermal route at the temperature of473K. By varying the amount of added raw materials and sampling at different intervals, we investigated the formation mechanism of the hollow magnetite spheres. XRD characterization demonstrated that the synthesized hollow magnetite spheres are of high purity, well-crystallized and have the cubic face-centered phase. SEM and TEM images showed that the monodispersed hollow magnetite spheres with the diameter of around500nm have hollow nature, and the hollow interior has a diameter of around200nm. The hollow magnetite spheres exhibited high saturation magnetization value of90.6emu/g and coercivity of300Oe at room temperature. The epoxy resin composites with68wt%hollow magnetite spheres provided good electromagnetic wave absorption performance (RL<-20dB) in the range of1.6-3.0GHz with the absorber thickness of5-9mm.(2) Hollow Fe3O4@ZnO@TiO2core-shell structured spheres have been successfully synthesized through a simple two-step sol-gel method and the synthesis process is illustrated as an explicit schematic diagram. Surfactant cetyltrimethylammonium bromide (CTAB) was employed to realize the mesoporous TiO2shell on the surface of Fe3O4@ZnO composite spheres, which will enlarge the specific surface area thus improving the microwave absorption properties. Electron microscopy examinations indicate that the composite core-shell structured hollow spheres have a homogeneous ZnO interlayer and an anatase TiO2shell outside the ZnO layer, both of which have a thickness of about20nm. The magnetization hysteresis curves of the samples show that the core-shell structured composites have a magnetic saturation value of41.5emu/g.