Preparation And Properties Of MnO <2> 2 + 2 + 2 + -Fe ^{3 +} LDHs Porous Materials The Study

Layered double hydroxides (LDHs), also well-known as hydrotalcite-like compounds, are typical anionic layered compounds. They have been paid to wide attention in structure and property and showed a wide range of applications in catalysts, anion exchangers, acid absorbents, bioactive nanocomposites, electroactive and cathode materials of supercapacitor. Manganese oxides are considered as the most potentially material for supercapacitor due to their low cost, high electrochemical activity and environment friendliness. Also, layered doubled hydroxides consisted of transition metals such as Co, Ni, Fe and so on, have been widely studied in recent years because of their potential applications in anion exchangers, heterogeneous catalysts, adsorbents, electro-and photoactive materials, and so on. Therefore, it is very important to research the preparation, characterization and property of LDHs materials consisted of transition metals and metal oxide pillared LDHs materials. In this thesis, Co2+-Ni2+-Fe3+-CO32-LDHs material with high crystallinity and well regular shape is hydrothermally synthesized by using trisodium citrate (TSC) as a complexing agent. Then, MnO2-pillared Co2+-Ni2+-Fe3+LDHs is obtained by ion exchange technique and followed by redox reaction. The porosity and electrochemical property of MnO2-pillared Co2+-Ni2+-Fe3+LDHs porous nanocomposite have been studied. The main works are as follows:(1) Preparation of MnO2-pillared Co2+-Ni2+-Fe3+layered double hydroxide porous nanocompositeBy a complexing agent assisted homogeneous precipitation method, Co2+-Ni2+-Fe3+-CO32-LDHs materials with Co2+/Ni2+/Fe3+molar ratio of0.5/3/1is hydrothermally prepared at150℃for2days. Sample Co2+-Ni2+-Fe3+-CO32-LDHs is firstly converted to Co2+-Ni2+-Fe3+-Cr--LDHs through an ion exchange reaction in NaCl-HCl salt-acid mixed solution, and then it is converted into sample Ni2+-Fe3+-MnO4-LDHs in KMnO4solution for1day. Sample Co2+-Ni2+-Fe3+-MnO4"-LDHs is treated with a MnCL; solution, MnO4-ions intercalated in the interlayer are reduced to MnO2particles, and MnO2pillared Co2+-Ni2+-Fe3+LDHs nanocomposite is obtained. The structure, morphology and composition of the obtained materials at different stages are characterized by XRD, SEM, TEM, TR, AAS, and XPS analyses. The obtained materials at different stages maintain the layer structure, suggesting that both the ion exchange reaction and oxidation-reduction reaction can not cause the destruction of the layer structure.(2) Study on the property of MnO2-pillared Co2+-Ni2+-Fe3+layered double hydroxides porous nanocompositeMnO2pillared Co2+-Ni2+-Fe3+LDHs is heat-treated in air at different tempatures (100℃,200℃,300℃, and400℃) for4h, the thermal stability and the N2adsorption-desorption properties are investigated. The research results show that the structure and property of the calcinated materials are affected by the calcination temperature. The layered structures of MnO2pillared Co2+-Ni2+-Fe3+LDHs can be remained to200℃, and it will collapse and form metal oxide when the caicination temperature is higher than300℃. The specific surface area of145m2g-1is obtained for MnO2-LDHs (200℃). The electrochemical property of as-prepared samples at different stages has been investigated by cyclic voltammetry in1mol L-1KOH solution at a voltage of-0.2-0.4V. MnO2pillared Co2+-Ni2+-Fe3+LDHs heat-treated at200℃not only exhibits a high specific capacitance of389F g-1at a scan rate of5mV s-1, but also shows relatively good cycle stability (92.3%capacitance retention after500cycles at a scan rate of20mV s-1), which make it have a potential application as electrode material for supercapacitor.