| The mixted metal oxides (MMO) material, derived from Layered double hydroxides (LDHs) precursor after thermal treatment under high temperature, has potentially been used in many fields such as catalysis, magnetic, opticals and so on. The properties preformed by the MMO material are closely related with the microstructure, the composition and the morphology transformation from LDHs precursor. In the present thesis, we discuss the transformation mechanism of LDHs precursors under high temperature, and then focous on the relationship between the properties and the coupling interaction on the interface of different phases of the MMO material. Firstly, ZnAl-LDHs were chosed and studied the microstructure as well as composition transformation during the transformation process, and the transformation mechanism was proposed based on the experimental results. Then coupling effects on the properties of the MMO material, including the photocatalytic and magnetic properties were studied respectively. Moreover, considering the controversy about LDHs material in the photocatalytic field, we discuss the real cause of the removal of organic dye molecules using pristine LDHs materal. We believe that our work can be regarded as theorical and experimental basis for the understanding of the transformation mechanism from LDHs precursors to MMO material, and it also can provide some information for the structural design as well as the property regulation of the MMO material according to the actural requirments.The innovation of this thesis and results are as follows:Fristly, aiming at the point about the transformation mechanism under high temperature, the ZnAl-LDHs precursors were firstly chosed, and the transformation process to the ZnO/ZnAl2O4 nanocomposites were studied based on the various characterization methods including high resolution transmission electron microscope (HRTEM). The final results indicated that, the ZnAl-LDHs underwent three stages under different thermal treatment condition, includingâ…°) the destruction of the LDHs precursors and the formation of ZnO crystal nucleus;â…±) the orientional growth of ZnO andâ…²) the formation of ZnO/ZnAl2O4 nanocomposites. The transformation mechanism was proposed and it also has been proved to show good university.Secondly, based on the structural feature of the ZnO/ZnAl2O4 nanocomposites derived from ZnAl-LDHs precursors, the photocatalytic properties of the ZnO/ZnAl2O4 were discussed. After the thermal treatment, the nanoheterjunction structure was formed on the interface between the ZnO and ZnAl2O4 phases, and the strong coupling interaction between the two semiconductors made for the separation of photo-induced electron-hole pairs. Therefore, compared with single phase ZnO or similar ZnO/ZnAl2O4 fabricated by other physiochemical methods, the ZnO/ZnAl2O4 derived from ZnAL-LDHs precursors showed higher photocatalytic activity.Thirdly, in order to beat "superparamagnetic limit" of ferromagnetic nanoparticles, the NiO/NiFe2O4 nanocomposites were fabricated from NiFe-LDHs precursors after the topotactic transformation under high temperature. The strong ferromagnetic (FM)-antiferromagnetic (AFM) coupling interaction between the NiO and NiFe2O4 phases leads to the obvious improvement of the magnetic stability of the NiFe2O4 nanoparticles. The blocking temperature of NiFe2O4 nanoparticles in NiO/NiFe2O4 nanocomposite film increased more than 200 K than that for pure NiFe2O4 nanoparticles with similar size.Finally, considering the extensive use of LDHs in the field of removal of organic dye molecules in the solution, the reaction essence was discussed. Representative MgAl-LDHs and ZnCr-LDHs were chosed; then series of experiments under/without visible light irradiation and density functional computation have been done. The real reason for the removal of different organic dye molecoules from the solution with the MgAl-LDHs and ZnCr-LDHs were discussed. |
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