Ultrasonic-Induced Synthesis And Characterization Of Rare Earth Metal Nanomaterials

In recent years, ultrasonic-induced synthesis has been attracting increasing interest in chemistry. An ultrasonic-induced process has been established for the synthesis of Ceria-zirconia solid solutions and MWO₄ (M= Fe, Mn, Pb, Zn) nanomaterials in the present thesis. A hydrothermal method has also been employed for the comparison. These as-prepared nanostructures were characterized by scanning election microscopy(SEM), transmission election microscopy(TEM), Energy Dispersive Spectroscopy (EDS), X-ray diffraction(XRD), UV-vis spectroscopy, fourier transform infrared(FT-IR), thermogravimetry (TG) and other techniques. The main results obtained in this thesis have been summarized as the following:1. The nanomaterials such as CeO₂, ZrO₂, CeO₂-ZrO₂ solid solutions, CeO₂-ZrO₂/MWCNTs complex, FeWO₄, MnWO₄, PbWO₄ and ZnWO₄ has been synthesized via sonochemical process and hydrothermal method. It is indicated that the ultrasonic-induced method is a facile, mild, efficient and environmental friendly method.2. CeO₂-ZrO₂ solid solutions freshly prepared by PEG-assisted sonochemical method exhibit remarkably high surface area of 226 m2·g-1, and could be kept as high as 190 m2·g-1 even after calcined at 773 K. It is suggested that CeO₂-ZrO₂ prepared by PEG-assisted sonochemical method possesses good thermal stability, and can keep their size and do not easily recrystalline. The addition of PEG-600 in the sonochemical process can enhance the thermal resistance of CeO₂-ZrO₂ solid solutions.3. The potential oxygen storage capacity (OSC) of CeO₂-ZrO₂ solid solutions adsorbed on MWCNTs prepared by hydrothermal method and sonochemical method are 0.59% and 0.85%, which are higher than the products without MWCNTs(0.37% and 0.45%). It is indicated that, the addition of MWCNTs can enhance the oxygen storage capacity (OSC) of CeO₂-ZrO₂ solid solutions. This character could make CeO₂-ZrO₂ solid solutions find its way in their practical applications especially for used as catalysis in TWCs.4. FeWO₄, MnWO₄, PbWO₄ and ZnWO₄ nanostructures with different morphologies such as particles and porous films have been synthesized via a simple and fast EG-assisted ultrasonic-induced approach. The possible growth mechanism of surfactant-assisted formation of FeWO₄ and MnWO₄ was put forward: The crystal growth is an in situ self-seeding progress. The concentration of surfactant EG plays a key role on the morphology of product.5. When the content of EG increases to 70%, porous FeWO₄ films, MnWO₄ films and ZnWO₄ films have been fabricated. The high content of EG suppresses the agglomeration of the FeWO₄, MnWO₄ and ZnWO₄ particles and induces the formation of porous films structures during the calcinations process. The phase, thickness, and crystallinity of the films were controllable by adjusting the reaction conditions.6. The optical properties such as UV-Vis spectra and FTIR spectra of FeWO₄ and MnWO₄ were examined. It is indicated that the surfactant EG is a good soft template for the preparation of FeWO₄ and MnWO₄. This may promote the wider application of surfactant EG in the synthesis of other inorganic materials with unique properties.In conclusion, ultrasonic-induced method has many advantages in the synthesis of nanomaterials such as morphology control, size control, good dispersion and narrow size distribution etc.