Controllable Synthesis Of Manganese-based Oxides And Their Electrochemical And Catalytic Properties

Nanomaterials have broad application prospects in the 21st century. The manganese-oxide nanomaterials possess the particular advantages than other oxides due to its unique electronic configuration. Manganese oxides are considerable important in many technological applications such as electronics industries, magnetics, chemical industry, catalysis, environmental etc. Hence, it is necessary to research the synthesis of manganese-oxide nanomaterials and controlled factors. In this paper, we synthesized Mn₃O₄ and MnOOH by a novel oxidation precipitation method, and the effects of preparing conditions on the phase and morphology were studied; The effect of additives on the size of products was studied. A type of magnetic composite materials core-shell Fe₃O₄ / FeMnOx was synthesized by impregnation and oxidation methods, and its electrochemical properties and catalytic oxidation performance were studied.The main research contents and results are listed as follows.(1) The preparation of Mn3O4 and MnOOH by a oxidation–precipitation method.Mn₃O₄ and MnOOH were prepared by a oxidation–precipitation method, and the effect of different reaction conditions such as the temperature(room temperature and hydrothermal process),the dripping speed of NaOH solution,the effects of surfactant (sodium dodecyl benzene sulfonate)and the adding order of reactant were discussed. The results show that the higher temperature was favourable the crystallization and maturation of the product. In the presence of SDBS, the phase and morphology of the products were both determined by the dripping speed of NaOH solution, single phase of Mn₃O₄ nanoparticles can be prepared by the dripping NaOH solution to the solution of MnCl₂ and H₂O₂ at 1ml/L, and Mn3O4 nanorods can be obtained at 6ml/min. While single phase of MnOOH nanorods can be obtained by pouring the NaOH solution into the reaction system quickly or changing the adding order of H₂O₂ and NaOH. At the dripping speed rate of 6ml/min of NaOH solution. MnOOH can be synthesized by adding the NaOH solution before H₂O₂; conversely, Mn₃O-4 can be got.(2) The influence of additives on Mn₃O₄ morphology. Mn (NO₃)₂, NH₃·H₂O and H2O2 were used as raw material, precipitator and oxidant, respectively. We studied the effects of nine agents on size of Mn₃O₄, including CTAB, ethanol, glutamate, polyethylene glycol, oxalic acid, EDTA, glucose, citric acid, tartaric acid. The results showed that tartaric acid, citric acid and glucose have the biggest influence on the size of Mn₃O₄, the product size became smaller with increasing the adding mount of those agents. The surface and capacitance of the preduct increased significantly with decreasing its particle size.(3) Synthesis and catalytic properties of core-shell structure Fe-Mn compsite oxide Fe₃O₄/FeMnO_x。Epigranular and ferromagnetic Fe3O4 were successfully prepared by a coprecipitation method. The diameter of particles were about 30-50 nm. Core/shell Fe₃O₄/FeMnO_x nanoparticles were synthesized by the oxidation-reduction reaction between MnO₄- and Fe²+ on the surface of Fe₃O₄. During reaction process, the pH of the solution is mantained at 7-8. Fe₃O₄/FeMnO_x was found to be an effective and stable heterogeneous catalyst for the discoloration of methylene blue (MB) in aqueous solution with H2O2. The characterization studies verified that Fe₃O₄ core was coated with a layer of Fe–Mn composite oxide. The coated shell not only increased the surface hydroxyl groups, but also enhanced the interfacial electron transfer, thus causing the higher activity. The discoloration of MB could be due to the decomposition of H₂O₂ into ?OH and the adsorption of MB on Fe₃O₄/FeMnO_x.