The Synthesis And Characterization Of Manganses Dioxide And Its Properties Of Photo-catalytic And Capacitance

With the development of modern science and nanotechnology, the nanomaterials with single performance can not completely meet the needs of the people. Among numerous nanomaterials, transition metal oxides(TMOs) in general exhibit high electrochemical energy storage ability and excellent optical performance. As a typical TMO, manganese dioxide is popular in the fields of supercapacitor and photo-catalysis because of the low cost, environmental-friendly, high theoretical specific capacitance and unique catalytic activity. In this work, manganese dioxide with different morphologies and structures were synthesized by the hydrothermal method. Scanning electron microscopy(SEM), transmission electron microscopy(TEM), Raman spectroscopy(Raman), X ray diffraction(XRD) and specific surface area test were used to study the morphology and microstructure of the as-synthesized products. By adjusting the experimental parameters, different results were obtained and the possible growth mechanism based on these results was proposed. The capacitive and photocatalytic properties of MnO2 were investigated. The main content of this work summarized as follows:1. Uniform MnO2 nanorods were synthesized successfully via a facile and effective hydrothermal approach. Scanning electron microscope images showed that the average diameter of the as-synthesized nanorods is about 30 nm and the length of that is about 5 m, respectively. Photocatalytic experimental results indicate that Congo red can be degraded nearly completely(over 97%) after visible light irradiation of 120 min,demonstrating potential applications of such nanorod structures for waste water purification.2. A simple hydrothermal route was developed for the synthesis of uniformα-MnO2 nanowires using a controllable redox reaction in a MnCl2–KMnO4 aqueous solution system. Electrochemical properties of the resulting products as an electrode were investigated. The electrode can provide a specific capacitance of 180 F·g-1 at a current density of 1.0 A·g-1. After 2000 cycles, the specific capacitance was maintained above 78%. Besides, the as-synthesized products were also used as the photocatalyst forthe photocatalytic degradation of several dye molecules. The results show almost complete degradation(~99%) of Congo red dye molecules in 30 min. Such ultralong MnO2 nanowires are expected to have potential applications in waste water treatment and energy storage.3. MnO2 with α-, β- and δ-type structures was controllably synthesized by hydrothermal treatment of an acidic solution of KMnO4 containing different concentrations of ions at 160 oC. The effects of metallic cations, H+ and anions on the structures and morphologies of MnO2 were investigated systematically. The experimental results indicated that cations played a significant part in the formation of MnO2 with different structures. Possible formation mechanisms are proposed based on a series of controlled experiments. The electrochemical properties of supercapacitors based on different types of MnO2 electrodes were investigated in detail. The specific capacitance measured for MnO2 strongly depended on the crystallographic structure and decreased in the order α-MnO2(535 F·g-1)> δ-MnO2(464 F·g-1)> β-MnO2(155 F·g-1) at a current density of 0.5 A·g-1. β-MnO2 was more stable in cycle test compare the other two types of MnO2. After 3000 cycles, β-MnO2 showed good stability, maintaining a cycling efficiency of 80%.