纳米锰氧化物水热法合成及其生长机理的探究

发布时间：2018-01-24 23:20

本文关键词： 锰氧化物纳米材料表面活性剂生长机理　出处：《重庆大学》2015年硕士论文　论文类型：学位论文

【摘要】：锰氧化物是重要的过渡金属氧化物,因其晶体结构具有特殊的隧道结构和片层结构,在催化、电化学、离子交换和分子吸附方面都有着广泛的应用。利用纳米材料的特殊效应,在纳米尺度范围内,控制锰氧化物的晶型、尺寸和形貌,能更有效地提高纳米锰氧化物的性能。进而,如何控制纳米锰氧化物的尺寸和特殊形貌成为了研究热点。制备纳米锰氧化物的方法越来越多,水热法因操作简便、成本低廉在研究中得到广泛应用。因此,在纳米锰氧化物的研究领域内,如何通过水热法来制备可控晶型和形貌的纳米锰氧化物成为了一个重要的研究方向。本文选择最常见的反应物锰酸钾,作为水热反应的前驱体。通过水热反应,制备得到具有不同的晶型和形貌的纳米锰氧化物。研究水热反应的反应物种类、反应物浓度比、表面活性剂的种类、表面活性剂的浓度及溶液的酸碱度,对制备纳米锰氧化物的影响。实验中使用的主要检测和分析手段有:X射线衍射分析(XRD)和扫描显微分析(SEM),对水热反应得到的产物进行晶型的确定和形貌的观察,结合现有理论和以往的研究,得到研究结果如下:在无表面活性剂添加的前提下,控制锰元素的浓度不变,改变高锰酸钾和硫酸锰的浓度比,随着高锰酸钾浓度的增加,硫酸锰浓度的降低,得到了β-Mn O2纳米棒状结构、α-Mn O2纳米线状结构和δ-Mn O2纳米花状结构。高锰酸钾电离出的钾离子对纳米二氧化锰结晶形核有重要的影响。形核后,形成的隧道结构晶体会沿着形成的隧道结构更加稳定的方向加速生长;形成片层状的纳米片的亚稳定结构和表面能降低的趋势的共同作用下促使纳米片组成的纳米墙瓦解,形成纳米花状结构。加入表面活性剂柠檬酸三钠,保持高锰酸钾浓度不变。柠檬酸三钠电离在溶液中呈碱性,具有还原性,对Mn OOH纳米线形成与瓦解有重要的影响。柠檬酸三钠具有分散性,在部分锰元素还原为正二价的时候,会吸附在形成的Mn3O4晶体表面,抑制其晶粒的生长,最终得到了零维Mn3O4纳米颗粒。加入表面活性剂CTAB,保持高锰酸钾浓度不变,CTAB达到临界胶束浓度形成不同形状的胶束。CTAB形成球状胶束的时候,促进Mn OOH纳米线的形成;形成层状胶束的时候,吸附在其形成的纳米颗粒八面体的{111}面上降低{111}表面能,使暴露出来的{111}面继续生长,最终形成Mn3O4纳米八面体结构。但在中性水溶液中,无法抑制球状胶束的形成,进而无法得到纯净的Mn3O4八面体。改变初始溶液的酸碱度,p H7,Mn3O4溶于盐酸,无法形核;p H7,球状胶束无法形成。在p H=10的时候,形成了纯净的Mn3O4纳米八面体结构。
[Abstract]:Manganese oxide is an important transition metal oxide, its crystal structure has a special structure of tunnel and lamellar structure in catalysis, electrochemistry, ion exchange and molecular adsorption has been widely used. The use of special effect of nanomaterials at nanometer scale, crystal control of manganese oxide, size and morphology that can effectively improve the performance of nano manganese oxide. Then, how to control the size of nano manganese oxide and special morphology has become a research hotspot. The preparation of nano manganese oxide method is more and more, the hydrothermal method has simple operation and low cost in research has been widely used. Therefore, in the research field of nano manganese oxide how, for controlled synthesis of nano manganese oxide crystal structure and morphology has become an important research direction by a hydrothermal method. The most common reaction of potassium manganate, as hydrothermal reaction Should be the precursor. By hydrothermal reaction, preparation of nano manganese oxides with different crystal phase and morphology. Research on hydrothermal reaction of reactants, concentration of reactant ratio, surfactant type, concentration and surfactant solution pH, the effect of preparation of nano manganese oxide. The experiment mainly used in detection and analysis methods: X ray diffraction (XRD) analysis and scanning electron microscope (SEM), were observed and determined the crystal morphology of product from hydrothermal reaction, combined with the existing theory and previous research, the results obtained are as follows: in the absence of surfactant added under the premise of concentration control of the Mn concentration change unchanged, Potassium Permanganate and manganese sulfate ratio, with the increase of the concentration of Potassium Permanganate, reduce the concentration of manganese sulfate, beta -Mn O2 nanorods were obtained, a -Mn O2 nanowire structure and -Mn nano O2 The flower like structure. The Potassium Permanganate ionized potassium has an important influence on the crystal nucleation of nano manganese dioxide. After nucleation, crystal formation of tunnel structure along the tunnel structure form more stable direction of the accelerated growth; interaction trend of metastable structures forming sheet nano lamellar and surface can reduce the the nano film composed of nano wall collapse, the formation of flower like nanostructures. Adding surfactant citric acid three sodium, keep Potassium Permanganate concentration constant. Three citric acid sodium ionization is basic in solution, is reductive, has an important influence on the formation and collapse of Mn OOH nanowires. Three citric acid sodium with dispersion when part of the manganese reduction, is two of the price, can be adsorbed on the surface of Mn3O4 crystal formation, inhibit the grain growth, finally got zero dimensional Mn3O4 nano particles. The addition of surfactant CTAB, keep high The potassium permanganate concentration unchanged,.CTAB CTAB micelle reached the critical micelle concentration of different shapes are formed when the formation of spherical micelles, promote the formation of Mn OOH nanowires; when the formation of lamellar micelle adsorption, reduce the surface energy of {111} nanoparticles in the formation of the eight face of {111} on the surface of the {111} surface exposed to growth. The final formation of nanometer Mn3O4 eight structure. But in neutral aqueous solution, the formation of spherical micelles could not suppress, and cannot get the pure Mn3O4 eight surface. Changing the initial pH value of solution, P H7, Mn3O4 dissolved in hydrochloric acid, not p nucleation; H7, spherical micelles cannot be formed when p H=10. The formation of pure Mn3O4 eight nano structure.

【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1;O614.711

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