Hydrothermal Synthesis Of MnO₂Nanomaterials And Their Electrochemical Properties

In recent years, manganese oxides are of considerable importance in technological applications,including lithium-ion battery, ion-exchange, molecular adsorption, zinc-manganese dioxide batteries,biosensors, catalysis, magnetic materials, and electrochemical capacitors due to their structural flexibilitycombined with novel chemical and physical properties. The science and technology workers begin todevelop material on the nanometer scale since the1990s, for nanotechnology permeates to the field ofelectrochemistry. Furthermore, MnO₂as many advantages, such as excellent electrochemistry property, lowcost and environmental friendly. So the material exhibited extensive application prospect in the fields ofindustrial production, biosensor and home appliances et al. In this thesis, we developed our work focusingon synthesis, characterization, constructing electrochemical sensor based on direct transfer of MnO₂nanorods and nanowires, and theirs application in Supercapacitor.1. One-pot Hydrothermal Synthesis of Uniform β-MnO₂Nanorods for Nitrite SensingA simple hydrothermal method was developed for the synthesis of uniform single-crystal β-MnO₂nanorods only using potassium permanganate and sodium nitrite in acidic solution, without any seed ortemplate. The as-prepared β-MnO₂nanorods have the average diameter of300±20nm and a length up to1.2±0.2μm. Moreover, the effects of pH, temperature, and reactant molar ratios on the morphology of thefinal product were studied in detail. In addition, the catalytic ability of the as-prepared β-MnO₂nanorodswas tested for the electrooxidation of nitrite. The resulting sensor showed a wide linear range from0.29μMto26.09mM （R=0.9986）, high sensitivity （1.21μA·mM-1）, low detection limit （0.29μM, S/N=3）, andfast response （less than5s）.2. A Hydrogen Peroxide Sensor Based on β-MnO₂NanorodsA novel hydrogen peroxide （H2O₂） sensor was fabricated based on the synthesized β-MnO₂nanorods.The β-MnO₂nanorods were constructed by a facile hydrothermal method, which were characterized byscanning electron microscopy and X-ray diffraction. Electrochemical techniques like cyclic voltammetrywere used to evaluate the electrochemical performance of the β-MnO₂nanorods modified glassy carbonelectrode by casting. The resulting sensor exhibited excellent catalytic activity toward the oxidation ofH2O₂with wide linear range from2.45μM to42.85mM （R=0.9993）, high sensitivity （21.74μA·mM-1）, low detection limit of2.45μM （S/N=3）, and fast response （within5s）.3. Hydrothermal Synthesize MnO₂Nanowire for High-Performance SupercapacitorA simple hydrothermal method was developed for the synthesis of uniform single-crystal γ-MnOOHnanowires only using potassium permanganate and hexamethylene tetramine (C₆H₁₂N₄), without any seedor template. β-MnO₂nanowires is made by calcining as–prepared γ-MnOOH in a muffle furnace at300℃for2h. Moreover, the effects of temperature, and reactant molar ratios on the morphology of the finalproduct were studied in detail. Electrochemical properties of the resultant were investigated by testing thecharge/discharge curves and cyclic voltammetry of a three-electrode system, in which working electrodewas made from the β-MnO₂nanowire. Cyclic voltammograms （vs. SCE） gave ideal capacitor behaviorbetween0V and0.8V in1.0mol·L-1Na2SO4with a constant specific capacitance about262.7F·g-1at5mV·s-1. Electrode made of resultant powder can provide a specific capacitance of120F·g-1at scan rate of50mV·s-1. After150cycles, the specific capacitance maintains above95%.