Study On The Preparation And Properties Of ZnMn₂O₄ Micro/Nano-Structure

Mn-based transition metal oxides have caused much attention due to their novel properties and applications in lithium ion batteries, capacitors, sensors, and so on. ZnMn₂O₄ has been widely applied due to its environmental friendly, low price, rich sources. ZnMn₂O₄ nanostructures with various forms have been fabricated, such as nanoballs, nanoflowers, nanorods, nanotubes, etc. As the electrode material, the structure and morphology of ZnMn₂O₄ have great effects on the study of electrochemical properties. It is important to improve the structure and performance, simplify growth method.Many groups have reported different morphology of ZnMn₂O₄ nanostructure and its application in the field of catalysis and electrochemistry. However, there are few reports about Mg/Cd-doped ZnMn₂O₄ nanostructures, ZnMn₂O₄ compound nanostructure and its photoluminescent properties. ZnMn₂O₄ nanostructure has been fabricated with various methods so far, such as electrostatic spinning, urea combustion, sol-gel, template and hydrothermal method, etc. However, it is still key how to improve the properties and control the morphology of the sample. ZnMn₂O₄ with typical spinel structure is ternary composite transition metal oxides, so there are binary oxides in the reaction process., It is important to control the high efficiency Mg/Cd-content for improving the performance of ZnMn₂O₄.In the paper, ZnMn₂O₄ nanostructures with different conditions have been fabricated by hydrothermal method, and the ZnMn₂O₄ porous microball has been fabricated with optimal condition. Their electrochemical property has been studied in detail. The Mg/Cd-doping ZnMn₂O₄ and ZnMn₂O₄/Zn MgO compounds have also been prepared. Finally, the results are analyzed detaily. The main results are as follows:?1? ZnMn₂O₄ micro/nanostructure with different reaction temperature and time has been fabricated by hydrothermal method. The influence of reaction temperature and time on structure, morphology and properties of the sample is analyzed. The results show that the crystallization and morphology of samples becomes better with the increase of reaction time, but the crystallization and morphology of samples become worse when the reaction time changes from 24 h to 32 h. The sample with the growth time of 24 h has good catalytic effect, which is related to the grain size and specific surface area. Compared the samples with different reaction temperature at the same time, the sample with the condition of 140 ? has good crystal and purity. The results about the electrochemical performance show that the sample grown on nickel foam substrate has good cycle performance and frequency response.?2? ZnMn₂O₄ porous microsphere structure has been prepared by solvothermal method. ZnMn₂O₄ powder was prepared at the first, and then the samples were fabricated on the different substrate. The results show that ZnMn₂O₄ with good crystallinity and high purity has a novel porous structure. The electrochemical investigation results show that different substrate has a great influence on the electrochemical properties of ZnMn₂O₄ sample, and the sample grown on the nickel foam substrate have higher specific capacitance?128 Fg-1? and small resistance, suggesting that sample has a very good lattice matching with the substrate and little lattice defects in the sample.?3? The influence of Mg/Cd-doping on the structure, morphology and properties of ZnMn₂O₄ is studied systematically. The XRD results show that ZnMn₂O₄ sample with flocculent structure is still typical spinel structure, but the diffraction peaks become intensity and narrow, showing that the sample has a good crystallinity and smaller size. PL spectra show that there is only a green light peak in the visible range. This may be caused by more oxygen vacancy due to the Mg-doping, and the electronic transition can be occurred from the oxygen vacancy. The results of Cd-doping samples show that the morphology is microstructure with smooth surface, and the Cd atoms are in the form of embedding into the crystal lattice. The sample has high purity and high specific capacitance?364 Fg-1?, which is associated with the ions insert and embedded layer. The expansion ratio of the sample increases and the size of the working electrode changes because of Cd-doping.?4? Mg-doping ZnO nanostructures have been successfully fabricated with different Mg-contents by hydrothermal method and CVD method, respectively. ZnMn₂O₄/Mg-doped ZnO composite structure has been prepared with optimal condition for improving the photocatalytic performance of the sample. The samples were characterized by SEM, XRD, PL and photocatalytic performance. The results show that the sample is microstructure with a high crystallinity, but the sample begins to grow along the?112? crystal orientation. This is may be caused that there is intense stress along the?112? direction orientation during complex. PL spectra show that there are strong peaks in the visible range, which is related to the bound excitons in the sample.