The Studies On The Synthesis And Characterization Of NaBir And The Misfit-layered Compounds

In this thesis we have studied the layered-structure birnessite and the misfit-layered compounds. By viewing a lot of literatures I have cognized the layered-compounds, and known the characteristics of the misfit-layered compounds in its'composition, structure as well as its'existence in the nature. I have also comprehended the synthesis methods and potential applications of these compounds. Based on this, I have investigated birnessite and misfit-layered compounds.we have firstly studied the synthesis of birnessite. Birnessite is distributed abroad in natural soil. However, birnessite occurred in nature is in poor crystallization and the composition is uncertain. So synthesis of birnessite is the basis for the further study and application of this material. There are two main methods for the synthesis of birnessite reported in the domestic literatures at present. One is the oxidation of Mn(II) in basic condition, the other one is the deoxidization of Mn(VII) in acidic condition. These two methods are not ideal, because either the conditions are rigor and uneasy to be controlled, or the product is not layered compound. After reviewing some literatures, I have chosen one method reported in literature. However, I have failed in the synthesis of birnessite with this method. So I have carefully studied the literatures on the one hand, on the other hand I have done a lot of experiments to improve the method. Finally we have synthesized the single-phase layered birnessite which crystallization has been increased greatly. This improved method is superior to the method reported in the literature. Furthermore, this method possesses the advantages of the simpleness, economy and repeatability. The synthesis of birnessite is pouring a mixed solution of 3% H₂O₂ and 0.6 M NaOH (1000 mL) into a solution of 50% Mn(NO₃)2 or MnCl₂ (35 mL)under strong stirring. This suspension was aged in the mother solution at room temperature for 2 days.The second work we have done is to improve the crystallization of the birnessite further by hydrothermal treatment. By doing lots of experiments, I have found the basis conditions for increasing the crystallization of birnessite by the hydrothermal treatment. The best conditions are: the reaction time is 7h, the reaction temperature is 180℃, the sample mass is 1g, and NaOH concentration is 2M.The other important work we have done is the preparation of the misfit-layered compounds. I have prepared and obtained NMO and MMO. The synthesis of the misfit layered compounds usually needs higher temperature and longer time. We have adopted the low temperature hydrothermal synthesis and obtained the mixed layered compounds. I have done many experiments in the intercalation of Ni(OH)₂ into the birnessite. With the intercalation, the space of the interlayer of the birnessite increases and a kind of misfit-layered compounds with two sublattices is formed. The synthesis of NMO is as follows: a certain NaBir was dispersed into NiCl2 solution, after one day stirring, 0.5M NaOH solution was added until pH =9-10, then the mixture was filtered and washed with distilled water for many times until pH=7, and was autoclaved in distilled water at 160°C for 2-3 days, repeated hydrothermally treatment for 2-4 times.In the synthesis of NMO I have found that the original birnessit is favorable the formation of NMO with more Ni(OH)₂ a bit while the hydrothermally-treated birnessite is favorable the formation of pure NMO. We have studied the birnessite and the misfit layered compounds with the XRD, IR, SEM, ICP, DTA-TG, ISP etc. methods. I have investigated the relationships among the synthesis method, the structure and the properties of the compounds. I have educed some conclusions which would be helpful for the further studies in this field.