Synthesis of vanadium oxide nanotubes from V2O5 sols

Vanadium oxide nanotubes (VO_x-NTs) were prepared by using V₂O₅ sols as precursor for the first time with hexadecylamine (HDA) as structure-directing template via a modified sol–gel method followed by hydrothermal treatment. Structure and morphology of the nanotubes were investigated by XRD, SEM, HRTEM, TGA, FT-IR and XPS. The obtained nanotubes were found having outer diameters from 30 to 100 nm and inner diameters from 10 to 30 nm with length up to several micrometers. It is also confirmed that water molecules enter vanadium oxide layers together with structure-directing template and the low valence vanadium occurs in the VO_x-NTs.     

Phase Separation Derived Core/Shell Structured Cu11V6O26/V2O5 Microspheres: First Synthesis and Excellent Lithium‐Ion Anode Performance with Outstanding Capacity Self‐Restoration

Novel amorphous vanadium oxide coated copper vanadium oxide (Cu₁₁V₆O₂₆/V₂O₅) microspheres with 3D hierarchical architecture have been successfully prepared via a microwave‐assisted solution method and subsequent annealing induced phase separation process. Pure Cu₁₁V₆O₂₆ microspheres without V₂O₅ coating are also obtained by an H₂O₂ solution dissolving treatment. When evaluated as an anode material for lithium‐ion batteries (LIBs), the as‐synthesized hybrid exhibits large reversible capacity, excellent rate capability, and outstanding capacity self‐recovery. Under the condition of high current density of 1 A g^?1, the 3D hierarchical Cu₁₁V₆O₂₆/V₂O₅ hybrid maintains a reversible capacity of ≈1110 mA h g^?1. Combined electrochemical analysis and high‐resolution transmission electron microscopy observation during cycling reveals that the amorphous V₂O₅ coating plays an important role on enhancing the electrochemical performances and capacity self‐recovery, which provides an active amorphous protective layer and abundant grain interfaces for efficient inserting and extracting of Li‐ion. As a result, this new copper vanadium oxide hybrid is proposed as a promising anode material for LIBs.     

Thermochromic VO2 nanorods and other vanadium oxides nanostructures

Thermochromic VO₂ nanorods were prepared via thermal conversion of the metastable VO₂–B phase synthesized by hydrothermal methods. We observe an increased thermochromic transition temperature to ∼75–80 °C by variable-temperature infrared spectroscopy. Nano- and sub-micron structures of other vanadium oxides (V₃O₇, (NH₄)_0.5V₂O₅, and V₂O₅) were obtained simply by varying the starting materials in the hydrothermal synthesis. We also obtained nanostructures of the high temperature tetragonal rutile phase of VO₂ by thermolysis of single-source vanadium (IV) precursors.     

A one-step hydrothermal way for the synthesis of vanadium oxide nanotubes containing the phenylpropylamine as template obtained via non-alkoxide route

Vanadium oxide nanotubes (VO_x-NTs) with high crystallinity were synthesized by using the crystalline V₂O₅ as precursor for the first time with 3-phenylpropylamine as structure-directing template via one-step hydrothermal way. Structure and morphology of the nanotubes were investigated by Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray powder diffraction, Thermal analysis and Infrared. The inner and the outer of the obtained nanotubes vary respectively between 15 to 25 nm and 70 to 100 nm with a length up to 4 μm.     

Hydrothermal synthesis and magnetic property of Cu3(OH)2V2O7·nH2O

Copper vanadium oxide hydroxide hydrate (Cu₃(OH)₂V₂O₇·nH₂O) nanoparticles with mean size of about 100 nm were successfully synthesized by a simple hydrothermal method. The structure and morphology of the as-synthesized products were characterized by X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Raman spectra, and Fourier transform infrared spectra (FTIR). The composition and purity of the as-synthesized Cu₃(OH)₂V₂O₇·nH₂O nanoparticles were characterized by Energy disperse spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The magnetic property of the as-synthesized Cu₃(OH)₂V₂O₇·nH₂O nanoparticles was characterized by vibrant sample magnetometer. Magnetic hysteresis curve indicate that the as-synthesized nanoparticles are of weak ferromagnetic property at room temperature.     

Structure,properties, and MEMS and microelectronic applications of vanadium oxides

Vanadium oxides have for many decades attracted much attention for their rich and unique physical properties which pose intriguing questions as to their fundamental origins as well as offering numerous potential applications for microelectronics, sensors, and microelectromechanical systems (MEMS). This paper reviews the unique structure and properties of the two most common vanadium oxides which have entered into microfabricated devices, VO₂ and V₂O₅, and some of the past and future device applications which can be realized using these materials. Two emerging new materials, sodium vanadium bronzes and vanadium oxide nanotubes are also discussed for their potential use in new microelectronic devices.     

W doped vanadium oxide nanotubes: Synthesis and characterization

W doped vanadium oxide nanotubes (VONTs) were prepared via a rheological phase reaction followed by self-assembling process. The nanotubes were characterized by elemental analysis, IR, XRD, SEM, TEM, HRTEM, SAED and XPS. Elemental analysis, IR, XRD, SAED and XPS could confirm the crystalline characteristic of the W doped VONTs, while the SEM, TEM, and HRTEM confirmed their morphology and microstructure.     

Synthesis and structural characterization of mesoporous V2O5 thin films for electrochromic applications

Mesoporous vanadium pentoxide (V₂O₅) films have been synthesized by hydrolysis of vanadium tri-isopropoxide (VO(OC₃H₇)₃) in the presence of polyethylene glycol (PEG) as a structure-directing agent. The structure, the stoichiometry and the morphology of the films have been studied as a function of the thermal annealing by X-ray diffraction (XRD), micro-Raman spectroscopy, optical microscopy, scanning electron microscopy and atomic force microscopy. XRD patterns and Raman spectra show the presence of two previously unreported crystalline phases. The PEG:V₂O₅ molar ratio affects the temperature of phase formation, the amount and even the order in which the phases appear. The morphological characterization underlines the role of the surfactant to promote porous networks, formed by micrometric clusters of controlled shapes and patterns embedded in a homogeneous host matrix.     

Processing,characterization, and bactericidal activity of undoped and silver-doped vanadium oxides

Vanadium oxide (V) and silver-doped vanadium oxide (Ag-V) powders were prepared via sol–gel processing. Structural evolution and bactericidal activity was examined as a function of temperature ranging from 250, 350, 450 and 550 °C. Powders were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Raman spectroscopy. Results from all techniques showed vanadium pentoxide (V₂O₅) is the predominant phase regardless of heat treatment temperature or the addition of silver (Ag). XRD analysis suggests Ag is present as AgCl in samples heat treated to 250, 350, and 450 °C and as AgV₆O₁₅ at 550 °C. Bactericidal activity was evaluated against Escherichia coli using the agar disk diffusion method considering both Ag-V and undoped, V powders. While the addition of Ag significantly increased bactericidal properties, the specific Ag valency, or crystal structure and morphology formed at higher temperatures, had little effect on functionality.     

Synthesis and modification of micro-and nanorods of vanadium oxides

A method for the gas-phase synthesis of single-crystalline micro-and nanorods of vanadium pentoxide (V₂O₅) has been developed based on the thermal decomposition of vanadium chloride vapor. Using this technique, it is possible to obtain separate micro-and nanorods (with thicknesses ranging from 50 nm to 5 μm and a length of up to 7 mm), planar arrays, and three-dimensional structures. The temperature dependence of the resistance of individual microrods of vanadium oxides in various degrees of oxidation has been measured.     

Synthesis and optical properties of vanadium dioxide nanoparticles in nanoporous glasses

A method for the synthesis of vanadium dioxide (VO₂) nanoparticles in nanoporous silicate glass matrices with a pore size of 17 and 7 nm has been developed. According to this, vanadium pentoxide (V₂O₅) nanoparticles are initially grown in the pores, and then V₂O₅ is reduced to VO₂ in hydrogen. The optical transmission spectra of 1-mm-thick VO₂-modified glass samples have been measured. The temperature dependence of the transmission coefficient has been studied in the course of the semiconductor-metal phase transition in VO₂ nanoparticles.     

Periodic microsyntaxy in VnO2n−1

A new long period Magnéli phase V₁₃O₂₄ has been found in a vanadium oxide specimen in the composition range of V₆O₁₁ and V₇O₁₃ prepared by a chemical vapor transport technique. Based on the lattice images, the new phase should rather be interpreted as a product of periodic microsyntactic intergrowth of V₆O₁₁ and V₇O₁₃. This is the first observation of the periodic intergrowth of two Magnéli phase compounds having a common (121) CS plane.     

Microstructure and microhardness of vanadium oxides in the range VO<Subscript>0.57</Subscript>-VO<Subscript>1.29</Subscript>

X-ray diffraction and optical microscopy data are presented which demonstrate that substoichiometric vanadium oxide (VO_0.57-VO_0.97) consists of a cubic phase with the B1 structure (sp. gr. Fm \(\bar 3\) m) and an ordered monoclinic phase of composition V₁₄O₆ (sp. gr. C2/m). The content of the latter phase decreases with increasing oxygen content. The superstoichiometric vanadium oxide VO_1.29 is shown to contain trace amounts of V₅₂O₆₄. Vickers microhardness data for nonstoichiometric vanadium oxides in the range VO_0.57-VO_1.29 show that, with increasing oxygen content, their H _V has a tendency to decrease, from 18 to 12 GPa. Their microhardness is shown for the first time to have a maximum near the stoichiometric composition VO_1.00.     

Structural Investigation of Catalytically Grown Carbon Nanotubes

Carbon nanotubes (CNTs) having diameters in the range of 30–50 nm and few micrometers in length were synthesized in one step through a chemical-reduction route under autogenous pressure of H₂/CO₂. The synthesized materials prepared under different experimental conditions were characterized using different techniques. Results showed that V₂O₅ used as a catalyst for the nucleation of CNTs become carburized to vanadium carbide (V₈C₇) and provides a site for growth of CNTs. At high temperature, carbide particles thus formed become encapsulated at the tip of nanotube followed by the growth of CNTs through the tip-growth mechanism. Thermogravimetric analysis results showed that the CNTs obtained after the longer reaction time are more stable at high temperatures. Raman analysis showed a well-ordered graphite structure.     

The preparation,characterization and optical properties of Cd2V2O7 and CdCO3 compounds

Cadmium vanadium oxides (Cd₂V₂O₇) and Cadmium carbonates (CdCO₃) were synthesized via a facile hydrothermal method. X-ray diffraction (XRD), Raman spectroscopy, infrared spectrometer (IR), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the structure, morphology and chemical state of the samples, respectively. The photoluminescence (PL) properties of the as-synthesized Cd₂V₂O₇ and CdCO₃ were measured at room temperature using an excitation wavelength of 325 nm. The Cd₂V₂O₇ shows two visible light emission centers located at 589 and 637 nm, which are supposed to be relevant to local defects in Cd₂V₂O₇. The CdCO₃ shows three emission centers located at 408, 530 and 708 nm, which are supposed to be relevant to the electron transition from the conduction band to valence band and defect related energy level.     

聚吡咯/钒氧纳米管复合阴极材料的制备及其电化学行为研究

以V2O5粉末和过氧化氢为原料,十六烷基胺为模板剂,利用水热合成法制备钒氧纳米管,然后结合阳离子交换技术,用导电聚合物聚吡咯修饰替换钒氧纳米管中的有机模板剂,成功制备了聚吡咯/钒氧纳米管复合材料。借助透射电子显微镜和傅里叶红外光谱观察和分析了修饰前后纳米管的形貌和结构变化,实验结果证实聚吡咯不但成功修饰替换了钒氧纳米管中的有机模板剂,而且还很好地保持了纳米管的管状结构。采用恒流充放电和循环伏安分别测试了修饰前后样品的电化学性能,测试结果表明导电聚合物聚吡咯的修饰替换极大地提高了电极材料的首次充放电比容量和循环稳定性,循环伏安结果和20次循环后的表面形貌分析也进一步证实了这一结论。由于聚吡咯具有高的电导率和良好的柔韧性,不仅提高了复合纳米管材料的电导率,而且还改善了复合纳米管材料的结构稳定性。     

Sodium vanadate-induced corrosion of nickel and MCrAIY coatings on Inconel 600

The vanadate-induced corrosion of M Cr AIY coatings (M = Ni/Fe) on Inconel alloy 600 has been studied by using samples with preformed vanadate deposits. The samples were exposed to oxygen at 650 to 800°C for a maximum of 25 h in a thermobalance. The presence of molten vanadate ((Na₂O)_x·V₂O₅) on the surface causes accelerated corrosion. The corrosion rates increase with increasing V₂O₅ content of the vanadates. In the presence of molten vanadate, protective scales of Cr₂O₃-Al₂O₃ fail to develop; rather the oxide layer next to the coating consists of the oxides of all components in the coating and of vanadium both as vanadate and as vanadium sesquioxide. In most cases the molten vanadate phase fluxes the oxide scale and particularly the NiO phase in the oxide layer. Under these conditions the corrosion is probably governed by inward transport of oxygen (or oxygen species) in the vanadate melt. When the NiO concentration in the oxide layer next to the metal is high (as on nickel-base coatings with more than 75 wt-%Ni) a Ni₃(VO₄)₂ layer gradually develops between the oxide and the melt. This is accompanied by compositional changes in the oxide layer beneath the vanadate and results in a slow oxidation rate. MST/510     

Synthesis,characterization, and thermodynamic parameters of vanadium dioxide

A novel process was developed for synthesizing pure thermochromic vanadium dioxide (VO₂) by thermal reduction of vanadium pentoxide (V₂O₅) in ammonia gas. The process of thermal reduction of V₂O₅ was optimized by both experiments and modeling of thermodynamic parameters. The product VO₂ was characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TG), and differential scanning calorimetry (DSC). The experimental results indicated that pure thermochromic VO₂ crystal particles were successfully synthesized. The phase transition temperature of the VO₂ is approximately 342.6 K and the enthalpy of phase transition is 44.90 J/g.     

Facile synthesis of single crystalline vanadium pentoxide nanowires and their photocatalytic behavior

High quality single crystalline vanadium pentoxide (V₂O₅) nanowires were grown on sapphire and ITO coated glass substrates using spin coating followed by annealing process. The nanowires formed by this method are found to be approximately 5 μm long with an average diameter of 100 nm. The thickness of the spin coated vanadium precursor film played a vital role to form uniform seed layers which are essential for the growth of high quality V₂O₅ nanowires. The growth mechanism was investigated with respect to temperature and thickness of the precursor film. The synthesized nanowires have been proven to be a potential photocatalyst for the degradation of toluidine blue O dye under ultraviolet irradiation.     

Studies on V2O5 induced hot corrosion

Nickel samples coated with a monitored thickness of vanadium pentoxide were oxidized at 900°C under various oxygen pressures. The microstructures of the thin film grown on nickel were studied by X-ray diffraction, A E S, M E B and energy dispersive X-ray analyses. A nickel vanadium oxide is assumed to be located in the short-circuits of the growing oxide NiO leading to a rapid diffusion of nickel ions unless a vanadate precipitates. This mechanism allows us to forecast a way of protection against V₂O₅ induced hot corrosion. Thus, AISI 310 coated with magnesium is much less attacked by V₂O₅, because magnesium and vanadium react to form solid Mg₃V₂O₈.