Synthesis And Characterization Of ε-MnO₂ Microparticules

ε-MnO2 microparticules are widely applications in supercapacitors, VOCs treatment, water treatment and magnetic materials, due to its unique physical and chemical properties. The main challenge in this area is how to synthesis beautiful and neat morphologies and unique structure of ε-MnO2, which may serve as a powerful tool for the tailoring of physical and chemical properties of materials. The main points of this thesis can be summarized as follows:1. The cube-, sphere- and ellipsoid-like ε-MnO2 microparticules were prepared using co-precipitation method or hydrothermal method to synthesis MnCO3 precursors, and then calcined in air at 400℃ for 6h. The microparticules were characterized by XRD, Raman, SEM, TEM, BET, TG-DSC, XPS and H2-TPR techniques. The morphologies are neat and controllable. The cube- and sphere-like ε-MnO2 microparticules both have diameters of ～1.5μm, ellipsoid-like ε-MnO2 microparticule has long axis lengths of ～2μm and short axis lengths of～1.4 μm. The cube-, sphere- and ellipsoid-like ε-MnO2 microparticules have large specific surface area (88.51,137.19,79.66 m2/g, respectively), and the pore size is 7.78nm, 6.29nm and 7.12nm, respectively, which instructions that they are mesoporous materials. The cube-, sphere- and ellipsoid-like ε-MnO2 microparticules show excellent reducibility and catalytic activity. Their catalytic activities for the combustion of toluene were studied, T50%(the temperature acquired for 50% toluene conversion) is 193℃,191℃,203℃, respectively, and T90%(the temperature acquired for 90% toluene conversion) is 199℃, 194℃,209℃, respectively. Furthermore, their catalytic degradation methylene blue were studied, the degradation efficiency is 88.54%,90.82%,80.76% after 120min. The catalytic activity decreases in the following order:sphere>cube>ellipsoid-like ε-MnO2. The sphere-like ε-MnO2 microparticule has the best catalytic activity, because it has the highest surface area, the highest Mn3+/Mn4+ atomic ratio and best low-temperature reducibility.2. The ellipsoid-like ε-MnO2 core-shell structure microparticule were prepared using hydrothermal method to synthesis MnCO3 precursors, and then treated with KMnO4 to oxidate for 12h at 80℃ and added HCl to etch for 1h at room temperature, at last calcined at 400℃ for 6h. The oxidation time, etching concentration and time are the key steps to control the core-shell structure. The ellipsoid-like ε-MnO2 core-shell structure microparticule was characterized by XRD, SEM, TEM, BET and H2-TPR techniques. The ellipsoid-like s-MnO2 core-shell structure microparticule is neat and controllable, its specific surface area is 155.14 m2/g and the pore size is 10.52nm,also it has excellent reducibility, which instructions that it has better catalytic activity than ellipsoid-like ε-MnO2 microparticules. The catalytic degradation methylene blue were studied, the degradation efficiency is 85.82% after 120min.