| With the rapid development of modern society, environmental and energy issues are becoming increasingly prominent. Manganese oxides are cheap, non-toxic, environmentally friendly, structural diversification and rich in natural resources, these excellent properties result in manganese oxides having a wide range of applications in many fields, such as energy, environment, catalysis, adsorption, ion exchange, and communication and so on. In this thesis, manganese dioxides with different morphologies are prepared and the electrical properties are discussed. Meanwhile, the structure, morphology and the chemical composition of the obtained materials were characterized by XRD, SEM, BET and AAS.This paper mainly consists of two sections, the review section and the experimental part. The crystal structure, synthesis methods, properties and applications of manganese dioxide are reviewed in Chapter 1. Manganese oxides with hollow microsphere and star-like nanocluster morphologies are prepared in Chapter 2 and Chapter 3 on the basis of the reaction system of KMnO4 and MnSO4, respectively. The prepared manganese oxides with different morphologies have been characterized and a possible growth mechanism of hollow MnO2 microspheres is studied on the basis of the experimental results. In addition, the mesoporous manganese oxide has been prepared by using SBA-15 as a sacrifice template in Chapter 4. Finally, the research conclusion is presented in Chapter 5.The contents, experimental results and originalities of this research are as follows:1. Without the assistance of any templates or surfactants, manganese oxides with hollow microsphere morphology and urchin morphology are successfully prepared via a simple hydrothermal method at 150℃within 20 minutes on the basis of the reaction system of KMnO4 and MnSO4, respectively. Manganese oxides with urchin morphology is obtained with a molar ratio of KMnO4/MnSO4=6:1 in a acid solution while hollow structured MnO2 microspheres can be obtained only when Fe3+ions are added in the same reaction system. The prepared materials are systemically characterized by XRD, SEM, TEM, N2 adsorption-desorption and element analyses. The research results show that Fe3+ions are crucial in controlling the growth of hollow structured MnO2 microspheres, and the obtained manganese oxides with different morphologies are consisted of nanorods. Hollow MnO2 microspheres are formed according to the Ostwald ripening process. The electrochemical performance of the obtained samples with different morphologies indicates that the hollow structured MnO2 microspheres show an ideal capacitive behavior and good cycling stability. In compare with manganese oxide with urchin morphology, the specific capacitance of hollow structured MnO2 microspheres is 106 F/g at a sweep rate of 5 mV/s in 1 mol/L Na2SO4 solution, and the t Fe3+ions enhance markedly the specific capacitance of the obtained material.2. Without assistance of any templates or surfactants, by adding different mental ions, such as Na+, Mg+, Fe3+to a system of KMnO4/MnCl2 with a molar ratio of 5:3, manganese oxide with petal-like, nanorods, star-like nanocluster morphology is obtained. The experimental results show that the metal ions existed in the reaction system affluence the morphology of the obtained materials, manganese oxide with star-like nanocluster morphology is obtained by adding Fe3+ions into the reaction system. The experimental results show that the cyclic voltammetry curve of the synthesized material has good symmetric characteristic and non-redox peaks are observed at a sweep rate of 5 mV/s in 1 mol/L Na2SO4 solution.3. Mesoporous manganese oxide is synthesized by using SBA-15 as sacrifice template, KMnO4 and Mn(NO3)2 as manganese source by a hydrothermal treatment. The experimental results show that the prepared mesoporous manganese dioxide material has a large surface area and good mesoporous characteristic, but its electrochemical performance is not good due to the existence of SiO2 as an impurity. |
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