Morphology Controllable Syntheses Of Nano-/microstructures Of Tungsten And Molybdenum (Composite) Oxides And Their Application In Photoluminescent Phosphor And Lithium-ion Battery

3 nanocrystal, NaLa(WO4)2 micro/nanocrystal, MoO2 hollow microsphere and MoO2 hollow nanosphere were successfully synthesized through hydrothermal method. The morphology and size of NaLa(WO4)2 as well as the inner void space of MoO2 hollow microsphere could be successfully modulated. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) were employed to characterize the crystal phase, structure, size and morphology of the as-obtained products. The formation mechanisms for the as-obtained micro/nanostructures were proposed on the basis of a series of time-dependent experiments. Finally, the photoluminescent and lithium ion anode properties of the as-obtained products were investigated by PL emission and excitation spectra, electrochemical workstation and battery test system. Moreover, the intrinsic relationships between product properties and structures were detailedly disclosed. The main contents are summarized as follows:1. Pure-phase La2(WO4)3:Eu3+ nanocrystals and spindle-like NaLa(WO4)2: Yb3+/Er3+ nano-/microcrystals:selective synthesis, morphologies and photoluminescent propertiesThe selective synthesis of pure-phase La2(WO4)3 nanocrystals and uniform spindle-like NaLa(WO4)2 nano-/microcrystals with tunable size based on one reaction system has been reported for the first time. The sodium ion is crucial for the selective synthesis of La2(WO4)3 and NaLa(WO4)2. An additional hydrothermal treatment has a great effect on the morphology of La2(WO4)3, while the hydrothermal temperature and time, and the amount of glycerine significantly influence the morphology and size of NaLa(WO4)2. Based on the time-dependent experiments, it is proposed that the Ostwald ripening is the formation mechanism of the spindle-like NaLa(WO4)2. The resultant La2(WO4)3:Eu3+ nanocrystals can emit a bright red color with a high purity under the excitation of 467 nm (blue region) and, more importantly, it can be easily dispersed in distilled water. The up-conversion emission intensity of NaLa(WO4)2: Yb3+/Er3+ is increased rapidly with the Yb3+ concentration under 980 nm laser excitation, suggesting the efficient energy transfer from Yb3+ to Er3+. Moreover, the emission color can be tuned from chartreuse to green by increasing the Yb3+ concentration. These unique properties of La2(WO4)3 and NaLa(WO4)2 are closely related with their distinctive crystal structures.2. Morphology controllable synthesis of NaLa(WO4)2:morphology dependent photoluminescent property and single-phased white light emission of NaLa(WO4)2:Eu3+/Tb3+/Tm3+Uniform single-crystalline NaLa(W(WO4)2 microspindles were successfully prepared via a hydrothermal method in combination with a post annealing process by adding an extremely small amount of EDTA-2Na into the reaction system. Meanwhile, the product morphology could also be tuned into microplates, nanocrystals, submicrodumbbells and connected twin-microspheres by simply altering the amount of additive used and ratio of mixed solvents. The photoluminescent (PL) performance of NaLa(WO4)2:Eu3+ microspindles and microplates was investigated and it was found that NaLa(WO4)2:Eu3+ microspindles had a much more intensive emission, and furthermore, the possible reasons responsible for the improved photoluminescent performance of microspindles were discussed. More importantly, due to the efficient energy transfer from Tm3+, Tb3+ to Eu3+, a novel single-phased and near-UV-pumped white-light-emitting phosphor NaLa(WO4)2:Eu3+/Tb3+/Tm3+ was also successfully fabricated through optimizing the molar ratio among Eu3+, Tb3+and Tm3+ in NaLa(WO4)2 microspindle host.3. Monodisperse Mo02@C hollow microspheres with remarkably improved lithium-ion battery anode propertiesMonodisperse MoO2 hollow microspheres with tunable inner space have been facilely synthesized through a hydrothermal process using MoO3 microbelts instead of bulk MoO3 as the precursor. It was found that the reactant morphology has a great impact on the product morphology and the inner space could be tuned by changing the amount of NaOH aqueous solution. The possible formation mechanism was proposed and discussed. One layer of amorphous carbon was subsequently coated on the surface of MoO2 hollow microspheres through a simple hydrothermal approach followed by annealing in argon. As the anode material for lithium ion batteries, MoO2@C hollow microspheres manifest high specific capacity and Coulombic efficiency, excellent cycling stability and superior rate capability. The significantly enhanced performance of MoO2@C hollow microspheres can be attributed to its desirable structure designs such as nanoscaled primary building blocks, carbon coating, hollow structure, and especially the synergy between the carbon coating and hollow structure.4. Facile Synthesis of Uniform Mo02@C Hollow Nanospheres with Superior Lithium-ion Storage PropertiesUniform MoO2@C hollow nanospheres with the size of 200nm are facilely synthesized through a soft-templated hydrothermal method combined with an annealing process. This approach effectively integrates material fabrication and carbon coating into one step, which is beneficial to the industrialization. Because of its well-designed structure (such as nanoscaled building blocks, hollow structure, carbon coating), MoO2@C hollow nanospheres have exhibted superior lithium-ion storage properties, such as high specific capacity (909.8 mAh·g-1), long cycle stability and excellent rate capability.