Vanadium Oxide Nanotubes Research Articles

Impregnating ionic Pt species on vanadium oxide nanotubes

Vanadium oxide nanotubes (VNT) have drawn increasing attention as vanadium compounds may be used in a wide range of applications. In this contribution, VNT was synthesized by a hydrothermal treatment from V 2O 5 using hexadecylamine as template. XRD, FTIR, SEM, TEM/HRTEM and TG analyses were used to investigate their chemical stability and suitability to adsorb platinum ionic species without damaging the nanostructure. It was shown that the nanostructures are open-ended multiwalled nanotubes, formed by 13–16 layered walls, with inner diameter of 30–50 nm and outer diameter of 150–200 nm. The impregnation of Pt was found to be feasible but their structure and morphology are sensitive to the pH of the impregnation media.

Photoinduced reentrant insulator-metal-insulator transitions in vanadium oxide nanotubes

We report photoinduced reentrant insulator-metal-insulator transitions in a low-dimensional nanoscale system of vanadium oxide nanotubes, a Mott insulator in the dark with no metal-insulator transitions. The nature of the spatially inhomogeneous intermediate metallic phase was elucidated by the photocurrent decay analysis of the system.

Synthesis and characterization of layered and scrolled amine-templated vanadium oxides

In order to fully understand the formation mechanism, structure, and role of structural curvature of vanadium oxide nanotubes (VONTs), two isostructural materials (one planar and the other curved)—ethylenediammonium (enH2) intercalated V7O16 and vanadium oxide nanourchins (VONUs)—were synthesized and characterized via X-ray diffraction (XRD), electron microscopy, thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy, and magnetic measurements. The synthesis route to (enH2)V7O16 is developed using vanadium pentoxide as a starting material and employing pH control. VONUs are synthesized using n-dodecylamine as an amine template for the first time. We demonstrate that the structure of the vanadium oxide layer in these compounds is similar to that of VONTs and their magnetic properties all fit to the same model including the temperature-independent, Curie–Weiss, and spin ½ antiferromagnetic dimer contributions. The vanadium oxidation state in tubular structures appears to be higher than in planar compounds such as (eH2)V7O16 and BaV7O16. The role of the template and vanadium reduction in the formation of nanotubes is discussed.

Structure and electronic properties of Li-doped vanadium oxide nanotubes

The influence of Li-doping on the mixed-valent vanadium oxide nanotubes has been investigated using electron energy loss spectroscopy. In particular, the electron diffraction profiles and the vanadium L excitation edges have been studied. We observe that the structure of the vanadium oxide nanotubes is stable against electron transfer upon Li-doping. Excitations at the vanadium L edges show features which are associated with a reduction of the vanadium valency.

Surfactants in the formation of vanadium oxide nanotubes

The role of long-chain surfactants in the formation of vanadium oxide nanotubes from V 2 O 5 –organic additive hybrid nanocomposites seems to be connected with enforcing crystalline V 2 O 5 to transform into a layered precursor giving then nanoscrolls under hydrothermal conditions.

Sensor properties of vanadium oxide nanotubes

Vanadium oxide nanotubes synthesised with hexadecylamine-1 as a structure-directing template were tested as gas sensitive elements for oxygen, nitrogen oxide, triethylamine (TEA) and dimethylmethylphosphonate (DMMP).

Synthesis of Ag modified vanadium oxide nanotubes and their antibacterial properties

Vanadium oxide nanotubes (VOx-NTs) modified by highly dispersed Ag nanoparticles have been synthesized via a facile silver-mirror reaction. The crucial factors that affected the preparation of the Ag modified vanadium oxide nanotubes (Ag/VOx-NTs) have been also studied. The dispersion and structure of Ag nanoparticles in the obtained materials were characterized by transmission electron microscopy (TEM), electron diffraction (ED) and X-ray diffraction (XRD). The results showed the distribution and size of the formed Ag particles were greatly influenced by the concentration of AgNO3 solution. Typically, Ag nanoparticles were well dispersed on the VOx-NTs with the size range from 3 to 10nm. The corresponding antibacterial tests demonstrated the as-synthesized Ag/VOx-NTs exhibited strong antibacterial activity against Escherichia coli (E. coli).

Effect of water intercalation onVOxlayers in dodecylamine-intercalated vanadium oxide nanotubes

Dodecylamine-intercalated vanadium oxide nanotubes were obtained by distinct synthesis processes. Water intercalation in the nanotube structure was identified in a marked manner by the distortion of the $\mathrm{V}{\mathrm{O}}_{x}$ layers in the x-ray diffraction patterns and enhanced ${\mathrm{V}}^{4+}\mathrm{O}$ absorption in the Fourier-transform infrared spectra. Our electron spin resonance measurements sensitively reflect changes in the microscopic structure and magnetic interactions introduced by the water intercalation in the vanadium oxide nanotubes.

Magnetic characterization of vanadium oxide/polyaniline nanotubes

We present a magnetic study of vanadium oxide nanotubes (VO x -NTs) with polyaniline (PAni). Transmission electron microscopy (TEM) shows the tubular shape and the multi-wall structure of the nanotubes. The static magnetic susceptibility measured at different magnetic fields shows a Curie behavior, while the magnetization versus magnetic field presents a non-linear dependence at low temperatures. Both experiments can be explained by the presence of paramagnetic ions with S = 1/2. Using Electron Paramagnetic Resonance technique, we identified as V 4+(3d 1) the paramagnetic ions present in the nanostructures. All the experimental results can be explained by a fraction between 14% and 18% of V 4+ with respect to the total V atoms in the system.

Effects of synthetic conditions on the structure and morphology of open-ended vanadium oxide nanotubes and study of their growth mechanism

Vanadium oxide nanotubes (VOx-NTs) have been synthesized by using n-butylamine as structure-directing template and V2O5 as precursor under hydrothermal conditions. XRD, FTIR, SEM, TEM, BET and TG-DTA characterizations have been performed to both optimize the synthetic conditions and understand the growth mechanism of VOx-NTs. The results showed that open-ended VOx-NTs were obtained under the optimized conditions (hydrothermal temperature: 150–160°C, hydrothermal time: 5–7 d, the molar ratio of V2O5 to n-butylamine is 1:1) with diameters ranging from about 30 to 100 nm and several micrometers in length. The BET surface area and the desorption cumulative pore volume of pores of the as-synthesized sample were about 27.4609 m2/g and 0.191087 cm3/g, respectively. The result presents that the synthesis of VOx-NTs is controlled by the “rolling” mechanism and temperature is primary driving force for rolling.

Hydrothermal Synthesis of Vanadium Oxide Nanotubes from Oxide Precursors

Vanadium oxide nanotubes were synthesized as the main product by a direct hydrothermal treatment of oxide precursors and long chain amines as structure-directing templates. The morphology and structure of nanotubes was characterized by powder X-ray diffraction, electron microscopy, and thermal analysis. Nanotubes of high aspect ratio with layered structures were found to grow together in the form of bundles. The paper also discusses the chemistry issues involved in synthesizing nanostructured vanadium oxides.

Synthesis, structure, and properties of vanadium pentoxide nanotubes

Vanadium oxide nanotubes are synthesized by the hydrothermal method with the use of polycrystalline vanadium oxide V2O5 and 1-hexadecylamine as a structural template. The structure of the vanadium oxide nanotubes is investigated using small-angle X-ray diffraction and transmission electron microscopy. It is demonstrated that the structure of the vanadium oxide nanotubes is characterized by a combination of fragments with different interlayer distances associated with the twisting of oxide layers in the form of “nanorolls.” The thermal stability, morphology, and surface properties of the nanotubes, as well as the role of the organic template in the formation of their structure, are discussed.

Metal cations inserted in vanadium-oxide nanotubes

Vanadium-oxide nanotubes (VOx-NTs) consist of nanosize cylinders of thin, easily bent vanadyl (VOx) wall chains, which are open at both ends. Surfactant molecules (e.g. C12H27N) can be easily trapped in the interior of the nanotube walls. The structure of as-synthesized VOx-NTs are observed to collapse to an amorphous vanadium oxide at temperatures greater than 250°C. This happens, even under a protective atmosphere. This property makes the VOx-NTs unusable as a catalyst at temperatures between 400–500°C, which is the temperature range where many applications would exist. In order to increase the thermal stability of VOx-NTs several exchange reactions have been used to modify the original nanotubes. In these reactions metallic cations (Cd2+, Co2+, Mn2+ or Zn2+) were introduced. It was observed that that the morphology of the nanotubes remained unchanged after the exchange reactions were performed. In order to characterize the exchanged VOx-NTs the following analytic techniques were used: scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared, particle-induced X-ray emission and Rutherford backscattering spectrometry. The results showed that the VOx-NTs exchanged with metallic cations have preserved their tubular morphology. However, it has not been possible to fully perform a 100% efficient exchange reaction.

Vanadium-oxide nanotubes: Synthesis and template-related electrochemical properties

The electrochemistry of mixed-valent-containing vanadium-oxide nanotubes (VO x -NTs) is first reported. Using dodecylamine and hexadecylamine as templates, two kinds of VO x -NTs were synthesized and characterized. Both VO x -NTs contain V 2O 3, VO 2 and V 2O 5 species. Dodecylamine-templated VO x -NTs (C 12-VO x -NTs) are much more stable than hexadecylamine-templated VO x -NTs (C 16-VO x -NTs). C 12-VO x -NTs demonstrate stable redox behavior at ∼−0.2 V, which is arising from the electrochemical transfer between V(III) and V(IV), whereas C 16-VO x -NTs exhibit unstable and weak redox peaks. In both cases, the reduction reaction of V(V)–V(IV) is never observed. The oxidation peak for V(IV) appeared only after a relatively long time immersion, suggesting that some small molecules such as water intercalate into the layered nanostructures before the electrochemical reaction. The difference may be an origin of the different template-induced the electroactivity of vanadium-oxide species in the nanotube-microenvironment.

Spectroscopic and microscopic study of vanadium oxide nanotubes

V 2 O 5 nanotubes synthesized via the sol-gel route has been studied by electron energy loss spectroscopy (EELS), x-ray absorption spectroscopy (XAS), and energy dispersive x-ray analysis, in order to understand the local structure of vanadium in the nanotubes. Contrary to our expectation, all the features of the XAS and EELS spectra of the V2O5 nanotubes are in line with that of bulk layered vanadium oxide revealing that vanadium is present in the 5+ oxidation state in the nanotubes. However, V2O5 nanotubes exhibit additional surface states in their electronic structure in comparison with bulk V2O5. A comparison of measured and calculated spectra allows us to distinguish single-wall from multiwall V2O5 nanotubes.

Synthesis and Electrochemical Performance of Ag-Containing VONTs

The Ag-containing VO x nanotubes were synthesized from V 2 O 5 , Ag 2 O and hexadecylamine. The nanotubes were characterized by SEM, TEM, XRD, electrochemical investigation, etc. The results show that the presence of the silver stabilizes the structure of vanadium oxide nanotubes for electrochemical redox reactions with lithium.

Electrochemical Synthesis of Vanadium Oxide Nanotube Thin Film Electrodes for High Power Energy Storage Devices

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Effects of synthesis methods of vanadium oxide nanotubes on the inter layer distances

Vanadium oxide nanotubes were synthesized via two methods: (1) Adding a template to vanadium oxide gels, (2) Grinding mixture of a template and vanadium oxide by using a ball mill. Influence of preparation method on structure of vanadium oxide nanotubes has been investigated. Vanadium oxide nanotubes has been characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM) techniques.

Atomic Layer Structure of Vanadium Oxide Nanotubes Grown on Nanourchin Structures

Science Foundation Ireland (SFI grant no. 02/IN.1/172); Fondo Nacional de Desarrollo Cientifico y Tecnologico, Chile ( FONDECyT grants 1050344, 1030102, 7050081); University of Chile; Universidad Tecnologica Metropolitana, Chile

Hydrothermal synthesis of vanadium oxide nanotubes by a facile route

Vanadium oxide nanotubes were synthesized by hydrothermal treatment from V 2O 5· nH 2O sols as precursor and dodecylamine as structure-directing template. The morphology and structure of the nanotubes were characterized by SEM, TEM, XRD, TG-DTA and FTIR. The experimental results reveal that the duration of the hydrothermal treatment is of importance for obtaining VO x -NTs which have a layered structure. TG-DTA study indicates that V 5+ cations in nanotubes are partially reduced to V 4+ cations. The results from FTIR spectra indicate the difference in V-O vibrations between before and after hydrothermal treatment. From the results, it suggests that during hydrothermal treatment, the rearrangement of the vanadium oxide structure leads to the formation of VO x nanotubes from lamellar structure because of the presence of V 4+ species.