不同形貌二氧化锰纳米材料的制备及其电容性能研究

【作者】 何学侠；

【导师】 刘宗怀；

【作者基本信息】 陕西师范大学 ， 无机化学， 2010， 硕士

【摘要】 随着现代社会的飞速发展,环境和能源问题越来越突出。锰的价格低廉、无毒、对环境友好、结构多样化且其自然资源丰富,这使得氧化锰材料在能源、环境、催化、吸附、离子交换和通讯等诸多领域都有广泛的应用。因此,本论文以二氧化锰材料为对象,研究了具有特殊形貌二氧化锰材料的制备及其电容性能,利用XRD、SEM、TEM、CV等手段,表征了所制备材料的结构、形貌和电化学性质。全文包括综述和实验二大部分。第一章综述部分主要论述了二氧化锰的结构特征、合成方法、性质及其应用。实验部分以高锰酸钾和硫酸锰为反应体系,制备了空心微球型二氧化锰(第二章)和星型纳米簇状二氧化锰(第三章)；以SBA-15为模板制备了二氧化锰介孔材料(第四章)。在探讨了制备材料生长机理的基础上,研究了制备材料的电化学性质。第五章为全文的结论。主要研究内容、研究成果及创新点如下：1.在无模板剂或表面活性剂辅助条件下,以高锰酸钾和硫酸锰的氧化还原反应体系为研究对象,采用水热反应制备了三维海胆型和空心微球二氧化锰纳米材料。高锰酸钾和硫酸锰摩尔比为6：1时,酸性体系中直接水热反应20 min得到了海胆型二氧化锰；高锰酸钾和硫酸锰摩尔比为6：1的反应体系中加入适当量的三价铁离子,得到了空心微球型二氧化锰。应用XRD、SEM、TEM、N2吸附和元素分析,对所制备材料进行了表征。结果表明海胆型和空心微球型二氧化锰纳米材料都是由纳米棒组装而成,铁离子对合成空心微球型二氧化锰纳米材料具有关键作用,空心微球型二氧化锰的生长机理遵循奥斯特瓦尔德熟化机制。空心微球型二氧化锰纳米材料在1 mol/L的Na2SO4溶液中,扫描速度为5 mV／s时显示了较高的比电容,其比电容量达到106 F/g。同时,该材料具有好的电化学可逆性及循环稳定性,是较理想的超级电容器电极材料。2.在无模板剂或表面活性剂辅助条件下,以摩尔比为5：3的高锰酸钾和氯化锰为研究体系,向体系中添加不同价态金属离子,如钠离子,镁离子,铁离子,研究结果发现,反应体系中存在的不同金属离子能显著影响制备产物的形貌。不加金属离子时,产物为不均匀纳米棒,当加入上述离子时,其形貌分别变为花瓣状,均匀棒状和星型二氧化锰纳米簇。星型纳米簇状二氧化锰材料在1 mol/L的Na2SO4溶液中,扫描速度为5 mV／s时所得循环伏安曲线对称性良好,测试电势范围内无氧化还原峰出现,可以满足超级电容器快速充放电的需求。3.采用模板辅助法合成介孔二氧化锰材料。以介孔分子筛SBA-15为模板,高锰酸钾和硝酸锰为锰源,采用水热反应制备了二氧化锰负载的SBA-15中间体。该中间体用氢氧化钠溶掉模板,形成了具有介孔结构的二氧化锰材料。研究结果表明,用SBA-15模板制备的二氧化锰具有介孔孔道和大的比表面积,但该材料比电容较小。更多还原

【Abstract】 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.更多还原