Study On The Synthsis, Formation Mechanism And Properties Of Nano/Micro-Materials Of Rare Earth Compounds Via A Solution Route

Due to their novel optical, electronic and magnetic properties, nano/micro- materials of lanthanide compounds have great potential applications in many fields, such as photoluminescence, optical fibers, humidity sensors, catalysts, magnetic materials and antibacterial materials. Stimulated by both the promising application and the interesting properties, much attention has been devoted to the controlled synthesis of lanthanide nanomaterials with different morphologies and the investigation of their size/shape-dependent properties. On the other hand, the abundant resource of rare earth in our country enables us to extend the applications of lanthanide nanomaterials in the above mentioned fields. In this work, a series of nano/micro-materials of lanthanide with uniform size and morphology have been successfully synthesized via a solution route. The main contents of this thesis are summarized as following:(1) LnPO4·nH2O (Ln = La-Gd) (n = 0～1) and Ln(OH)3 (Ln = La-Gd) one-dimensional nanomaterials are fabricated without using any surfactant or template at room temperature. The formation of one-dimensional nanomaterials can be attributed to the anisotropic growth of light lanthanide phosphate and light lanthanide hydroxide. The aspect ratios of one-dimensional nanomaterials can be effectively controlled by adjusting the reaction time and pH value of the reaction system. Under the similar reaction conditions, the monoclinic YPO4·2H2O and Eu3+-doped LaPO4 nanowires are also obtained. The optical properties of the doped nanomaterials prepared at different reaction time and Eu(OH)3 are related to the morphology and the crystalline degree. The light lanthanide not only have similar chemical property and shape but also demonstrate own unique character.(2) Monodisperse YVO4 (DyVO4, ErVO4) architectures with persimmon-like, cube-like and nanoparticle shape have been synthesized via a complexing agent-assisted solution route. The shape and size of these as-prepared architectures can be tuned effectively by controlling the reaction conditions, such as reaction time, the molar ratio of complexing agent/Y3+, the structure of the complexing agent and rare earth precurors. As a typical morphology, the growth process of monodisperse nanopersimmons has been examined. The interaction between rare earth ion and the complexing agent is crucial for the morphology of the as-synthesized lanthanide orthovanadate. The optical properties of YVO4 nanopersimmons are relevant to their size and shape.(3) The different kinds of yttrium fluoride have been prepared via a simple hydrothermal method in the presence of sodium nitrate. The morphology and chemical composition of the as-obtained product can be controlled by varying factors, such as the concentration of the starting salt in solution, the temperature and reaction time and rare earth precursors. The product composition variation from Na(Y1.5Na0.5)F6 andα-NaYF4 to YF3, and corresponding morphological transformation from spherical aggregation to octahedron have been observed under the different reaction conditions. Further studies reveal that the morphology and composition of the as-synthesized lanthanide fluoride are also determined by the ionic radius of rare earth. It is reasonable to believe that sodium nitrate plays double roles in the reaction. One is to serve as chelating ligand to kinetically control the reaction rate, and the other is to act as surfactant to affect the facet growth and the shape of the product.(4) Different ceria morphologies have been obtained with two reaction system. First,cubic-like CeO2 nanocrystals have been synthesized through a facile solvothermal process in toluene using hexadecylamine as capping agent and CeCl3·7H2O as precursor. The water content, the concentration of ligand and the structure of the aliphatic amine are critical to the formation of the monodisperse nanocub. The growth of ceria nanocubes is strongly dependent on the intrinsic crystal structure and the kinetic factors employed during the synthetic course. The electrochemical properties of the obtained samples reveal its potential application as anode material in lithium-ion batteries. The photocatalytic properties of the obtained samples present the size/shape-dependent properties. Second, Monodisperse CeCO3OH architectures with water caltrop-like shape have been synthesized by a complexing agent-assisted solution route. The anisotropic growth of light CeCO3OH and a complexing agent have great influence on the formation of architectures. The shape and size of CeCO3OH architectures can be controlled effectively by adjusting the reaction conditions, such as reaction time, the molar ratio of complexing agent/Ce3+ and reaction temperature. Ceria (CeO2) architectures with caltrop-like shape have been obtained by a thermal decomposition oxidation process at high temperature using as-synthesized CeCO3OH.