Synthesis, Characterization And Properties Of VO_X And M-V-O Nanaomaterials

Vanadium oxide and vanadate nanomaterials with uniform size and shape are of special interest from both theoretical and practial perspectives because of their special structures and intrinsic properties. This thesis focuses on the morphology-controllable synthesis of the lanthanide vanadate nanocrystals and VOx nanotubes. The structures, morphologies, and composition are characterized by using multi spectroscopic techniques such as powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared absorption spectra (FT-IR), X-ray photoelectron spectroscopy (XPS) and Raman spectra, etc. In addition, the possible application of the prepared products in photo-catalysis, photo-luminesce are also studied. According to consecution and corresponding experimental results, this thesis is divided into three parts:1. Hydrothermal Synthesis, Characterization and Photocatalytic Activity of Doped CeVO4nanocrystalsSingle-crystalline CeVO4and CeVO4:Ca2+nanocrystals (NCs) were prepared via a hydrothermal method in the absence of any surfactant or template. TEM, HRTEM, XRD and ICP were used to characterize the morphology and structure of the products. The substitution of aliovalent cation Ca2+changed the stoichiometry in order to preserve the charge neutrality. XPS and solid state51V NMR spectra have confirmed that there is a valence change from Ce3+to Ce4+for a fraction of cerium atoms whereas the vanadium atoms remain in the pentavalent state V5+upon the substitution of Ca2+into CeV04. Raman spectroscopy is used to monitor the effects of the doping ion on CeVO4lattice contraction and distortion. The appearance of the shifted or broadened Raman peaks for the doped CeVO4is understood by theoretical calculations based on Vienna ab initio simulation package. The redox properties of these nanocrystals have also been investigated by TPR techniques, and the different photocatalytic activity on degradation of methylene blue is investigated.2. Synthesis and Photoluminescence properties of LaVO4:Eu3+nanocrystalsLaVCO4and Eu3+doped LaV04nanorod and nanocubic are synthesized by using hydrothermal method. The dimensions and morphologies of the products could be effectively controlled by adjusting experimental conditions. And the effects of different synthetic conditions on the morphologies, structures and photoluminescence properties of products are investigated. For Eu3+ions doped phosphors, the structure of the host and the lattice site of Eu3+ions are very important factors that affect emission efficiency, and the transformation from monazite to the zircon structure resulted in a remarkable improvement of the luminescent properties. Quantum efficiency of nanostructured LaVO4:Eu3+is also discussed.3. High efficient synthesis of VOx nanotubes by cooperation of tetramethylamine hydroxide and tetradecylamineA simple, rapid and highly effectient method for the synthesis of uniform vanadium oxide nanotubes with the cooperation of tetramethylammonium hydroxide (TMAOH) and tetradecylamine are successfully developed. The cooperation between TMA+and C14H29NH3+under ultrasound for the delamination of V2O5layered vanadium oxide is a more efficient procedure than the ones used before. Thin VOX nanosheet can be formed easily and the followed scrolling procedure under hydrothermal treatment requires a shorter period of time. Structure and morphology of the nanotubes are characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), small angle X-ray diffraction (SAXRD) and Fourier transform infrared (FT-IR). The surfactants are successfully removed during Soxhlet extraction for about10h, and the VOx nanotubes without surfactants are reported for the first time. This new approach to the synthesis of VOx nanotube opens up a range of possible applications in the preparation of nanocomposites with novel properties and morphologies.