Preparation And Growth Mechanism Of Manganese Oxides Nanomaterials

With the rapid development of modern society, energy and environment problem havearoused more and more attention, however, new approaches and chances to solve theseproblems are provided by the fast development of nanoscience and nanotechnology.Manganese oxides with excellent properties have wide applications in various fields, forexample, catalysts, absorbers, ion exchange, communication, microwave ferrite, softmagnetic ferrite, gas sensor, humidity sensors and many other fields. Here, our attention isfocused on its applications in the following two fields, energy and environmental protectionIt does not only has the advantages of low prices, high energy density and high safety, butalso has no harm to the environment as the cathode material of lithium-ion secondarybatteries. It can also eliminate the electron magnetic pollution caused by various kinds ofelectronic devices as an microwave absorber, thus purifies the human living environment.Therefore, with the call for environmental protection as the times background, the rapiddevelopment of nanoscience and technology as the scientific background and the respect ofits applications in the fields of lithium-ion secondary batteries and microwave absorption,the preparation, growth mechanism and morphology control of the low dimensionalmanganese oxides nanomaterials were investigated. Moreover, its application as microwaveabsorber was primarily studied which lays a solid foundation for further investigations.The content, results and originalities of this research are as follows:1.3D self-assembled flowerlike hierarchical spheres of MnO₂ andγ-MnOOH nanobelts were prepared by a simple hydrothermal method, using KMnO₄ and H₂O as reactants, without any templates and surfactants. Morphology and structure of the product were characterized. A growth mechanism was proposed for the first time, which involved two competitive factors, temperature and Coulomb interaction, to understand the formation mechanism of the product. A simple morphology control method to obtain products of uniform morphology and their proportion in the product, which deduced from the proposed mechanism was supported by parallel experiments, thus the morphology of the product can be controlled.2. Manganese oxde film on Si substrate was obtained by hydrothermal method, using KMnO₄ and H₂O as reactants, without the assistance of any templates and surfactants. The as-prepared film consists of a porous surface layer which was composed of many single crystal nanosheets, and one or more amorphous bottom layers. In-depth characterization was carried out. Results showed that the porous surface layer was Birnessite MnO₂ and the amorphous bottom layers might containγ-MnOOH,γ-Mn₃O₄,γ-MnO₂,α-MnO₂, and -OH bonded Mn and Si ions and SiO₂ might existed in the interface between the substrate and bottom layers. To understand formation mechanism of the as-prepared manganese oxide film, a complex mechanism involved the coexistence of internal stress and chemical reaction was proposed, and the formation mechanism and process of the film were well understood.3. Hydrohausmannite (β-MnOOH andγ-Mn₃O₄),Mn₃O₄ nanoparticles and 3D porous network were prepared by hydrothermal method and subsequent heat treatments. The formation process of the 3D porous network was studied. The microwave absorption properties of the samples were tested, and the effect of particles size, temperature and duration of the heat treatment were also investigated. Comparation of microwave absorption properties of nanomaterials and bulk materials were made. For the future application of manganese oxide in microwave absorption, microwave absorption mechanism of the samples was discussed in detail.