Fabrication Of Manganese-based Miro/Nanomaterials And Their Catalytic Performances

This paper includes three parts:the fabrication and characterization of Mn2O3 Nano-flakes, 1D nanostructured Mn2O3 and MnCO3 hierarchical microstructures. Besides, we focused on controlled synthesis of Mn3O4 Nano-flakes, manganese carbonate and manganese oxide (Mn2O3) micro-/nano-structures by liquid-phase methods and also study the impact factors. Nano-flakes and a series of micro-structure including squid-like, fan-shaped, hierarchical spheres what else nanowires were prepared. Meanwhile, we focus on studying the preparation, formation mechanism, structural characterization and performance test and application, etc. Content involved the control synthesis of rhodochrosite structured MnCO3 and cubic bixbyite-typed Mn2O3; CO Catalytic oxidation performance; the formation mechanism of the Hierarchical polymorphic MnCO3 series under one-pot hydrothermal route through control cobalt ion’s doping content; the growth of nanowires in the mixed solvent of H2O and N, N-dimethylformamide, and the doping mechanism for improving the performance of CO catalytic oxidation. The full text aims at the control for synthesis of micro-and nano-structured (size, shape, etc) materials; at characterization, and exploring effective methods for constructing micro-and nano-structured materials.1. Study on the factors of one step solvothermal synthesis of Mn3O4 and its influence of the reaction systemIn the weak base solvent DMF, we selected Mn(NO3)2 as manganese source, polyvinylpyrrolidone (PVP) as the structure directing agent, to carry out hydrothermal reaction under a certain temperature for some time. The single variable method was used to study the influencing factors of the experiment, including temperature, time, quantity of Mn(NO3)2 aqueous solution, amount of DMF. The effects are controllable that the reaction time and temperature have on the oxidation product of Mn3O4. As a result, we can design the experimental program to achieve effective control on the morphology and composition of the precipitate.2. Study on Mn2O3 nanowires’s controlled synthesis and the performance of catalytic oxidation of COMn(NO3)2 is a metal source, mixed solvents are DMF and H2O (v 2:1), surfactant are PVP and EDTA. Nanowire structures can be obtained with insulation at 180℃ for 21 h. Nanowire morphology remains unchanged with Ni2+, Co2+ ions doped by one-step hydrothermal methods. XRD showed that the crystals of the products are Ni-Mn-O solid solution and Co-Mn-O solid solutions. Raman, and H2-TPR, Mapping and other characterizations show that Ni2+, Co2+ has entered the Mn2O3 lattice. The improved activity of CO catalytic oxidation has a close relationship to lattice defects produced after Ni2+/Co2+ doping and increased oxygen vacancy. In addition, pure Mn2O3 nanowires were modified by Au loading experiment. The experimental results show that the gold product obtained by co-precipitation method in glucose solution can obviously enhance the catalytic capability.3. Controllable preparation of the hierarchical polymorphic Co2+ doped MnC03 series under solvothermal conditionsMn(NO3)2 is selected as the source of manganese, PVP as surfactant, N, N-dimethylformamide as solvent, kept in surroundings at 210℃ with a ramp rate of 2 ℃/min-1 for 18 h, and Hierarchical polymorphs of manganese carbonate was succeeded in synthesizing. Adding Co(AC)2·4H2O as doped cobalt sources to the reaction solution at beginning, morphology of flower-like, fan-shaped, half-spherical and hierarchical micro-sphered structure can be obtained through adjusting cobalt doping content at 0%,5%,10%,15%,20% respectively. Scanning electron microscopy (SEM) observations showed the controllable novel morphology, good decentralization and uniformity. This provides a new method for the synthesis of other doped nano-materials. Through the track observations at different reaction time by transmission electron microscope image of the sample (TEM), we believe that the formation of hierarchical micro-sphered structure is the result of cobalt ion guided directional aggregation, cobalt ion as a guide for accelerated crystal nucleation, directional accumulation and growth. All these illustrate cation dopant have an important influence on the morphology of the products. The results of CO Catalytic oxidation show that Cobalt doping have effect on the improvement catalytic performance compared with -pure manganese carbonate, because doping increases the surface area of the product; besides 15% Co2+ doped samples performed the highest catalytic activity, suggesting that a best doping value exist on the improvement.