Synthesis And Properties Of Vanadium Compounds Nanomaterials

Since vanadium and vanadium oxide resource are rich in our contry, it is very important to effectively utilize vanadium resource, and explore vanadium oxide–dependent solid luminescent materials and highly active photocatalysts. Intensive investigation has been done including the exploration of preparation methods, properties, reaction mechanism and application of the vanadium oxides and vanadates crystal. Nowadays, the synthetic methods mainly include solid reaction process, vapor deposition process, hydrothermal method, etc. Although all these methods have their own advantages, most of them involve high vacuum, a high temperature, high pressure, high cost, complex process, or low purity, and so on. Therefore, developing new methods to synthesize vanadium oxide and vanadates nanocrystals is siginifiacant for fully utilization of vanadium resource.In the thesis, different morphology of V₃O₇·H₂O、V₃O₇、AgVO₃、Pb₅（VO₄）₃OH、Ba₃V₂O₈、NdVO₄ micro- and nano-crystals were synthesized by hydrothermal method, composite-hydroxide-mediated method and composite-salt-mediated method. And, their thermal, photoelectric, magnetic, luminescent and photocatalytic properties have been studied. The main contents can be summarized as follows:①The NdVO₄ nanowires were synthesized by a facile composite molten salt method. The XRD, SEM and HRTEM results show that NdVO₄ nanowires with tetragonal phase are connected together in bases, rooted in one center, and have typical diameter of 100 nm and length up to 3μm. The UV-vis spectrum shows that NdVO₄ nanwires have four strong absorption peaks from UV to near infrared region. The photocatalytical degradation of Rhodamine B dye and methyl orange under visible light irradiation using the NdVO₄ nanowiresis were investigated, which shows an excellent catalytic degradation activity to RhB and suggests its possible application in the organic pollutant treatment under visible light irradiation. The electron density states of the NdVO₄ were calculated with the Vienna ab initio simulation package, by which we can explain the light absorption and photodegradation properties.②Lead vanadium oxide hydroxide nano- and micro-crystals have been synthesized by a simple composite-hydroxide-mediated （CHM） method. The morphology of the product could be tuned from separate rods to rod bunches by simply controlling the reaction parameters. The UV-visible spectrum shows that the band gap of the Pb₅（VO₄）₃OH is 2.92 eV. The photoluminescence have been investigated in the temperature range 10-300 K. The results indicate a blue luminescence （430 nm） at room temperature and a strong red luminescence （623 nm and 672 nm） at low temperatures under excitation of 325 nm laser. The luminescent mechanism of the Pb5（VO4）3OH was discussed.③The flower-shaped barium vanadate has been obtained by the composite hydroxide mediated （CHM） method from V₂O₅ and BaCl₂ at 200℃for 13 h. XRD and XPS spectrum of the as-synthesized sample indicate it is hexagonal Ba₃V₂O₈ with small amount of Ba₃VO_4.8 coexistence. Scan electron microscope and transmission electron microscope display that the flower-shaped crystals are composed of nanosheets with thickness of ²0 nm. The UV-visible spectrum shows that the barium vanadate sample has two optical gaps （3.85 eV and 3.12 eV）. Photoluminescence spectrum of the barium vanadate flowers exhibits a visible light emission centered at 492 and 525 nm which might be attributed to VO4 tetrahedron with Td symmetry in Ba₃V₂O₈. The ferromagnetic behavior of the barium vanadate nanoflowers has been found with saturation magnetization of about 83.50×10^-3 emu/g, coercivity of 18.89 Oe and remnant magnetization of 4.63×10^-3 emu/g, which is mainly due to the presence of a non-orthovanadate phase with spin S=1/2. Meanwhile, Eu³⁺ doped barium vanadate nanoflowers were also synthesized by the same method, and luminescent and magnetic properties of doped barium vanadate were investigation at room temperature.④V₃O₇·H₂O nanobelts have been synthesized via a hydrothermal route. The synthesized products were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The V₃O₇·H₂O nanobelts are of orthorhombic phase and single crystalline nanobelts with width of 100-500 nm and length up to 100μm. Thermogravimetry was used to determine thermal decomposition temperature of V₃O₇·H₂O nanobelts. Monoclinic V₃O₇ nanobelts could be obtained by thermal decomposition of V₃O₇·H₂O nanobelts at 400℃. Light sensitivity in exposure to a simulated sunlight in different intensity and biases have been investigated on the electrode made from the V₃O₇·H₂O and V₃O₇ nanobelts. The photocurrent responses of the V₃O₇·H₂O and V₃O₇ nanobelts are fully reversible and periodic. The results show that the photocurrent intensity of the V₃O₇ nanobelts is much larger than that of the V₃O₇·H₂O nanobelts.⑤Ag decoratedβ-AgVO3 nanowires were synthesized by the hydrothermal method. The synthesis yields nanowires with a monoclinic phase structure. Typical nanowires have diameter of about 200-700 nm and length up to 300μm with some Ag nanoparticles attached on their surface. Theβ-AgVO₃ nanowires have a band gap of 2.25 eV. Photocatalytic degradation of Rhodamine B dye is investigated. Under the visible light irradiation, about 64% of RhB can be effectively photodegraded by the catalysis of the Ag decoratedβ-AgVO₃ nanowires within 150 min. It is found that the Ag decoratedβ-AgVO₃ nanowires possess excellent catalytic degradation activity owing to its effective visible light absorption, heterojunction structure and well crystallization.