The Hydrothermal Synthesis Of Nano Manganese Oxide And Study On Its Growth Mechanism

Due to the special tunnel structures and the layer structure, manganese oxides are important transitional metal oxides, which have a wide range of applications in the catalysis, electrochemistry, ion exchange and molecular adsorption. The performance of nano manganese oxide will be improved more effectively by control of manganese oxide crystal form, size and morphology in the nanoscale with the special effect of nano materials. And then, how to control of the size and morphology of nano manganese becomes the research hot spot. The hydrothermal method is widely used in the study because of easy operation and low cost, when there are more and more preparation ones. Therefore, how to prepare the controlled crystal form and morphology of nano manganese oxide has become an important research direction in the research field of nano manganese oxide.As the most common reactant, potassium permanganate was the precursor of the research. The nano manganese oxides with different crystal form and morphology had been prepared through the hydrothermal method. The hydrothermal conditions of this research included the types of reactants, reactant concentration ratio, the types of surfactant, surfactant concentration and ph value of solution. The impact of these conditions on the preparing nano manganese oxides was researched. To determine the crystal form and observe the morphology, the main detection and analysis methods were used in the experiment: the X ray diffraction analysis(XRD) and scanning microscopic analysis(SEM). The research results were as follows:The concentration ratio potassium permanganate and manganese sulfate was changed with unchanged concentration of manganese element in the absence of surfactant. β-Mn O2 nanorod、α-Mn O2 nanowire and δ-Mn O2 nanoflower had been produced by increasing the concentration of potassium permanganate and reducing the concentration of manganese sulfate. Potassium ion of Potassium permanganate had the important influence on the nucleation of nano manganese dioxide. The growth speed of the more stable tunnel structure direction was quicker. The reason of the collapse of nanowall and formation of nanoflower was the combined action of the metastable nanoplates and the decreasing tendency of surface energy.The concentration of potassium permanganate kept stable when sodium citrate was added. The formation and collapse of Mn OOH nanowires were related to the reducibility and the alkaline of sodium citrate in the solution. Sodium citrate adsorbed on the surface of Mn3O4 crystal using its dispersibility to suppress the growth of the grain to produce the zero dimensional Mn3O4 nanoparticles.The concentration of potassium permanganate kept stable when CTAB was added. The different micelle shapes were formed when the CTAB critical micelle concentration was reached. Spherical micelles promoted the formation of the Mn OOH nanowires. Lamellar micelles adsorbed on the {111} surface of the octahedrons to reduce its surface energy and the Mn3O4 octahedrons formed finally. But in neutral aqueous solution, the formation of spherical micelles cannot be inhibited and pure Mn3O4 octahedrons cannot form. When the p H value of the initial solution, p H<7, Mn3O4 was dissolved in hydrochloric acid and cannot nucleate; p H>7, spherical micelles didn’t form. In the p H=10, pure Mn3O4 nano octahedral structure had formed.