Synthesis And Application Of Nano-manganese Oxides

The system of manganese oxides is relatively complex, which include MnO, Mn2O3, Mn3O4, MnO2, etc. Manganese oxides are rich in natural resources, low cost, environmentally friendly, and have the special structure, so they have widely applicable value, such as in areas of super capacitors, catalysts, sensors, batteries, electronics and optoelectronics. The same species of manganese oxides prepared by different method will be different in the morphology and the crystalline form, which will seriously affect their functions and uses. In order to broaden the application of manganese oxides, the study of new preparation method to prepare manganese oxides with special morphology have become hotspots.In this thesis, amorphous nano-structured manganese dioxide has been successfully prepared by a new method-homogeneous redox method from an aqueous solution of potassium permanganate and hexamethylenetetramine. The major morphology of as-prepared MnO2 was a loose spherical structure with a size range of 50 nm to 150 nm. Electrochemical characterization was performed using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance measurements in 6 mol·L?1 KOH aqueous electrolyte. Results showed that, amorphous nano-structured manganese dioxide was a good candidate for an electrochemical capacitor. A specific capacitance of 321.31 F·g-1 was obtained at the current density of 0.50 A·g?1.With Mn2+ as a source of manganese and ammonium nitrate as an oxidant, MnO2 nanowires with large aspect ratio were successfully synthesized via a new low-temperature hydrothermal route in absence of any surfactant or template. MnO2 nanowires gradually thickened and eventually became rods with small aspect ratio by extending the reaction time or increasing the Mn2+ concentration. Moreover, the crystal form of MnO2 was changed fromαorγintoβ. The results of electrochemical performance test showed that MnO2 nanowires and nanorods are not suitable for electrochemical capacitor. The formation mechanism of manganese dioxide was explored.Using manganese nitrate, ammonia and H2O2 as raw materials, special appearanceβ-MnO2 nanorods were successfully synthesized via a simple low- temperature hydrothermal route in absence of mineralizer. The catalytic decomposition of products on H2O2 were studied. And the results showed that the preparedβ-MnO2 was a good catalyst for the decomposition of H2O2. The catalytic efficiency was up to 0.90 s-1·g-1, which is higher than commercial MnO2.Have studied the conditions of preparation of manganese oxide through the ethanol-water mixed solvothermal method, found that with 50% solution of manganese nitrate as raw material, and ethanol-water as solvent, by adjust the ratio of solvent, Mn2O3 and Mn3O4 with special morphology were prepared respectively. This paper also studied the catalytic decomposition of products on H2O2. The results showed that the prepared Mn3O4 had poor catalytic efficiency on decomposition of H2O2, but the prepared Mn2O3 had high catalytic activity on the decomposition of H2O2. The catalytic efficiency of the prepared Mn2O3 was up to 1.73 s-1·g-1, which is higher than commercial MnO2.