V2O5 Nanorods Research Articles

V2O5 nano-rods using low temperature chemical pyrophoric reaction technique: The effect of post annealing treatments on the structural, morphological, optical and electrical properties

Synthesis of high purity V2O5 nano-rods using chemical pyrophoric reaction process under the pyrophoric conditions has been demonstrated to successfully synthesis at 180°C for 24h. Their nanostructure has been characterized by XRD, HR-SEM, HR-TEM, XPS, UV, FT-IR, TG-DTA and I–V characteristics, respectively. XRD results confirmed that the complete conversion of as-prepared sample V4O9 phase changes to V2O5, for all annealing temperature. HRSEM and TEM studies shows that the V2O5 sample having dense, smooth and some random distribution of nano-rods at 600°C. Standard oxygen peak 530.2eV was found as expected for vanadium bonded oxygen in XPS spectrum. The decomposition process of this system is investigated by thermo-gravimetric and differential thermal analysis (TG-DTA). From I–V characteristics, the deviation of ohmic behavior at lower voltage range towards the non-ohmic at higher voltage range is due to the high voltage induced temperature effects in the sample. The conduction mechanism is discussed qualitatively on the basis of small polaron model. Activation energies have been found to be 0.45eV at 600°C for 1h.

Reduced graphene oxide enwrapped vanadium pentoxide nanorods as cathode materials for lithium-ion batteries

Novel reduced graphene oxide/vanadium pentoxide (rGO/V2O5) nanocomposites were fabricated by coassembly between negatively charged graphene oxide and positively charged oxide nanorods. A series of characterization including X-ray diffraction, Raman spectrum, scanning electron microscopy and transmission electron microscopy indicated that the V2O5 nanorods with the width of about 50nm and the length from a few hundred nanometers to several micrometers were enwrapped by rGO layers to form core–shell nanostructures. Compared with the pristine V2O5 nanorods, the as-prepared rGO/V2O5 nanocomposites with 13wt% rGO showed a significantly enhanced electrochemical performance with high reversible capacities, good cycling stabilities and excellent rate capabilities as a cathode material for lithium batteries. The rGO/V2O5 nanocomposites electrodes delivered a stable discharge capacity around 140mAhg−1 at a current density of 150mAg−1 for 100 cycles in the voltage range of 2.5–4.0V. Furthermore, the nanocomposites electrodes delivered discharge capacities of 287mAhg−1 and 207mAhg−1 during the first and 50th cycles in the voltage range of 2.0–4.0V at a current density of 100mAg−1, respectively. The as-synthesized nanocomposites are promising candidates for electrical energy storage applications.

Thermochromic VO2 nanorods made by sputter deposition: Growth conditions and optical modeling

Reactive dc magnetron sputtering onto glass-based substrates yielded deposits of thermochromic VO2 with well-developed nanorods and nanowires. Their formation was promoted by high substrate temperature (above ∼500 °C), sufficient film thickness, proper inlet of the reactive gas, dispersed gold “seeds,” and pronounced substrate roughness. Rutherford back scattering ascertained mass thicknesses, scanning electron microscopy depicted the nanostructures, and glancing incidence X-ray diffraction proved that single-phase VO2 was normally formed. Spectrophotometric measurements of total and diffuse transmittance and reflectance on VO2 thin films, at room temperature and ∼100 °C, allowed us to determine complex dielectric functions below and above the “critical” temperature for thermochromic switching (∼68 °C). These data were then used in computations based on the Bruggeman effective medium theory applied to randomly oriented prolate spheroidal structural units to derive the optical properties of the deposits. Experimental and computed data on spectral absorptance were found to be in good qualitative agreement.

Mesoporous vanadium oxide nanostructures: Hydrothermal synthesis, optical and electrochemical properties

VO2(B) nanoplates and nanorods have been successfully synthesized via a hydrothermal process by using V2O5 as vanadium source and HO–(CH2)n–OH (with n=3 and 5) as reducing and structure directing agents. The morphology, the structure, the crystallinity and the composition of the materials were investigated by X-ray diffraction (DRX), scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption/desorption isotherms respectively have been used. The optical properties of the as-synthesized VO2(B) were investigated by UV–visible absorption and photoluminescence. Electrochemical measurements have revealed reversible redox behavior with charge–discharge cycling corresponding to the reversible lithium intercalation/deintercalation.

Synthesis, characterization and formation mechanism of metastable phase VO2(A) nanorods

Pure phase VO2(A) nanorods were synthesized via the reduction of V2O5 by oxalic acid during the hydrothermal treatment. Two sets of samples were prepared by varying both system temperature and reaction time under a filling ratio of 0.40 for observing the formation and evolution of VO2(A) nanorods. Structures were characterized by X-ray diffraction, scanning and transmission electron microscopies, respectively. It was found that VO2(B) was firstly formed and then transformed into VO2(A) as the increasing system temperature or extending reaction time. An assembling and following crystal adjustment was proposed for explanation the formation process of VO2(A) from VO2(B). For VO2(A) nanorods, the phase transition temperature of 169.7°C was higher than that of the VO2(A) bulk, it might be ascribed to the lower crystallinity or nonstoichiometry in VO2(A) nanorods. VO2 nanostructures with controllable phases and properties should find their promising applications in a single VO2 nanodevice.

Optical and electrical properties of V2O5 nanorod films grown using an electron beam

An electron beam irradiation method is suggested for growing V2O5 nanorods. V2O5 nanorods with an orthorhombic structure (α-V2O5) were well grown by electron beam irradiation and the nanorod growth was greatly enhanced by inserting a buffer layer. The X-ray diffraction pattern of V2O5 nanorods grown at a dose rate of 800kGy considerably changed due to an increase in structural inhomogeneity formed by vanadyl–oxygen vacancies. The transition temperature increased due to the increasing surface resistance and was steeply enhanced by the increase in crystallinity with growing nanorods. Two photoluminescence peaks were observed at 530nm and 710nm for the V2O5 nanorods grown at a dose rate of 800kGy due to oxygen vacancies and a band edge transition.

Core-shell VO2@TiO2 nanorods that combine thermochromic and photocatalytic properties for application as energy-saving smart coatings

Vanadium dioxide (VO2) is a Mott phase transition compound that can be applied as a thermochromic smart material for energy saving and comfort, and titanium dioxide (TiO2) is a well-known photocatalyst for self-cleaning coatings. In this paper, we report a VO2@TiO2 core-shell structure, in which the VO2 nanorod core exhibits a remarkable modulation ability for solar infrared light, and the TiO2 anatase shell exhibits significant photocatalytic degradation of organic dye. In addition, the TiO2 overcoating not only increased the luminous transmittance of VO2 based on an antireflection effect, but also modified the intrinsic colour of VO2 films from yellow to light blue. The TiO2 also enhanced the chemical stability of VO2 against oxidation. This is the first report of such a single nanoparticle structure with both thermochromic and photocatalytic properties that offer significant potential for creating a multifunctional smart coating.

Influence of growth ambient on the surface and structural properties of vanadium oxide nanorods

The influence of growth ambient on the surface and structural properties of vanadium oxide nanorods have been studied by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (RS). The vanadium oxide nanorods, which were synthesized through an ambient controlled vapor transport process, exhibit different surface electronic properties depending upon the growth ambient. The Raman data indicates that the as-grown samples are orthorhombic V2O5 phase with a small variation of stoichiometry. Under highly oxidative conditions, nearly stoichiometry sample can be grown. If the samples were grown under less oxidizing conditions, an increase of structural disorder was observed. The observed V 2p core level spectra of both samples showed a single peak with chemical shifts corresponding to the V5+ and V4+. XPS results suggested that the highly oxidized vanadium ions (V5+) are gradually reduced to lower oxidation state (V4+) with the decreases of ambient oxygen levels during growth. The results clearly show that surface non-stoichiometry may be correlated with structural disorder of V2O5 nanorods. The growth ambient and post-annealing may influence the vanadium oxidation state and subsequent surface reactivity significantly.

Carbon nanocage supported synthesis of V2O5 nanorods and V2O5/TiO2 nanocomposites for Li-ion batteries

We present the facile synthesis of crystalline V2O5 nanorods and V2O5/TiO2 nanocomposites structures by a carbon nanocage (CNC)-assisted growth process, using vanadium triisopropoxide oxide and titanium isopropoxide precursors in air at 500 °C. The diameters of the resultant V2O5 nanorods ranged between ∼10 and 70 nm, while the crystalline V2O5/TiO2 nanocomposite structures adopted a unique morphology, due to both crystallisation and templating processes, with V2O5 adopting small-diameter nanowire and nanorod morphologies surrounded by sub-30 nm TiO2 nanoparticles. The V2O5 nanorods and V2O5/TiO2 nanocomposites were characterised by electron microscopy and X-ray diffraction techniques and subsequently reviewed as positive Li-ion electrodes. The phase-pure V2O5 nanorod structures exhibited appreciable Li+ storage properties over the potential range of 2.0–4.0 V vs. Li/Li+, displaying capacities of up to 288 mA h g−1 with appreciable cyclic behaviour at test rates of up to ∼1 C. The crystalline V2O5/TiO2 nanocomposite structures displayed similar Li+ storage properties, however, increasing molar fractions of TiO2 led to a decline in the overall capacity versus the single-phase V2O5 counterparts. Interestingly, the Li+ insertion behaviour of the V2O5/TiO2 nanocomposite displayed character more-typical of amorphous V2O5, which was ascribed to a structural buffering effect of the inactive TiO2 phase.

Ultra-long VO2 (A) nanorods using the high-temperature mixing method under hydrothermal conditions: synthesis, evolution and thermochromic properties

Well-crystallized, ultra-long VO2 (A) nanorods were synthesized using a facile high-temperature mixing method (HTMM) under hydrothermal conditions. The as-obtained products were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-Vis-NIR, differential scanning calorimetry and Fourier transform infrared spectroscopy. The effect of W doping on the phase-transition properties of VO2 (A) was also studied. The results indicate that the optimal synthesis condition of VO2 (A) using the HTMM is hydrothermal treatment at 240 °C for 48 h with a 3 : 1 molar ratio of the reducing agent to the vanadium source. The reason why the polymorphic forms of VO2 show different colors is that the light in the visible region reflected by the samples is different. The phase-transition temperature of the pure VO2 (A) is 154.75 °C, which is significantly lower than the 162 °C reported previously. When a small amount of W is doped, VO2 (A) will be transformed into other polymorphic forms, which indicates that the crystal structure of VO2 (A) is highly sensitive to limited doping. Importantly, the as-obtained pure VO2 (A) shows good thermochromic properties and optical-switching characters. A crystal growth mechanism for VO2 (A), oriented-attachment–exfoliation–recrystallization–oriented-attachment, is proposed and described in detail.

Effect of annealing and electrochemical properties of sol–gel dip coated nanocrystalline V2O5 thin films

Nanocrystalline vanadium pentoxide (V2O5) thin films were deposited on glass substrates by a simple and cost effective sol–gel dip coating method. The effect of annealing on microstructure and optical properties of V2O5 thin films were investigated. Formation of nanorods with the average diameter of 500–750nm after annealing is observed by scanning electron microscopy. X-ray diffractometry indicates that an orthorhombic structured thin film is transformed to β-V2O5 nanorods by subsequent annealing at 500°C. It was also confirmed that the growth of nanorods strongly correlates with annealing conditions; nanorod formation can be explained by surface diffusion phenomenon. The electrochemical performance of the V2O5 nanorods was investigated by cyclic voltammetry.

Time-based investigation of the growth of VO2(B) micro- and nanostructures on vanadium by hydrothermal synthesis

In an autoclave partly-filled with water wherein a V metal strip is placed 70° to the horizontal we observed that VO2 nanorods and exfoliated microspheres were generally grown on the portion of the strip above the water surface while parallelepiped-like structures were generally grown on the portion below. XRD, HRTEM, showed that VO2 structures produced were monoclinic and base centred in crystal structure. FT-IR, Raman Spectroscopy and XPS suggested that V metal was oxidized by hydrothermal synthesis in water to yield two oxides, V2O3, and VO2, with VO2 forming the bulk of the product. A time-based investigation of the synthesis of VO2 micro-nanostructures on V metal by hydrothermal synthesis suggests that the nucleation and growth of VO2/V2O3 micro-nanostructures is temperature-controlled and not kinetics/diffusion-controlled, with optimal temperatures for the synthesis being in the vicinity of 185–190 °C and growth of these oxides taking place in 2 h as opposed to 7 days in previously reported work [L. Jiang et al., VO2 rods with a rectangular cross-section, Journal of Crystal Growth, 310 (2008) 4301–4304]. We propose here a mechanism for the growth of the two types of micro/nanorods above water and the parallelepiped-like structures grown on V metal found below the water level.

Synthesis of γ-LiV2O5 nanorods as a high-performance cathode for Li ion battery

One-dimension γ-LiV2O5 nanorods were synthesized using VO2(B) nanorods as precursor in this study. The as-prepared material is characterized by X-ray diffraction, X-ray photoelectron spectrometry, Fourier-transform infrared, transmission electron microscopy (TEM), cyclic voltammetry, and charge–discharge cycling test. TEM results show that LiV2O5 nanorods are 90–250 nm in diameter. The nanorods deliver a maximum discharge capacity of 284.3 mAh g−1 at 15 mA g−1 and 270.2 mAh g−1 is maintained at the 15th cycle. Good rate performance is also observed with the discharge capacity of 250.1 and 202.6 mAh g−1 at 50 and 300 mA g−1, respectively. The capacity retention at 300 mA g−1 is 84.2% over 50 cycles. The Li+ diffusion coefficient of LiV2O5 is calculated to be 10-10–10−9 cm2 s−1. It is demonstrated that the nanorod morphology could greatly facilitate to shorten lithium ion diffusion pathways and increase the contact area between active material and electrolyte, resulting in high capacity and rate performance for LiV2O5.

Facile synthesis of nanostructured vanadium oxide as cathode materials for efficient Li-ion batteries

Homogeneous VO2 (B) nanorods approximately 100 nm in width and 1–2 μm in length have been fabricated via the hydrothermal process, and are then transformed into irregularly shaped V2O5 nanoparticles of several hundreds nanometers large and 20–30 nm thick after annealing the precursor material at 500 °C for 30 min. Both the V2O5 sheet-like nanoparticles and VO2 (B) nanorods were tested as active cathode materials for Li-ion batteries. The V2O5 sheet-like nanoparticles delivered a high discharge capacity of 281 mA h g−1 at 50 mA g−1 and 191 mA h g−1 at 2400 mA g−1; the material also demonstrated good cyclic stability with a small capacity loss of 35 mA h g−1 after 40 cycles. The VO2 (B) nanorods and V2O5 sheet-like nanoparticles prepared by the straightforward, environmental friendly and high yield route investigated in this study could prove to be promising candidates for efficient Li-ion batteries.

Thermally driven V2O5nanocrystal formation and the temperature-dependent electronic structure study

The temperature sensitive crystallization behavior of amorphous V2O5 films on glass and silicon substrates was investigated. Results indicated that after annealing in oxygen ambience, the as-sputtered amorphous V2O5 films on glass substrates dramatically transformed to standing β-phase V2O5 nanorods and flat-lying nanoslices, while large V2O5 particles with α-phase were obtained on Si substrates. Thermally driven surface diffusion was considered as the crystal growth mechanism and different crystallization behavior on the glass or silicon substrate was attributed to the distinct initial surface microstructures. The temperature dependent electronic properties of V2O5 on glass were investigated by synchrotron radiation, which clearly shows the anisotropic structure characteristics of crystallized V2O5 compound.

A Facile Fabrication of VO2(A) Micro-nanostructures with Controlled Shape and Its Electrochemical Behavior in Lithium Ion Batteries

Abstract VO2(A) micro-nanostructures have been synthesized via a facile hydrothermal method by hydrolysis of oxidovandium(2+) ethylene glycolate in malonic acid solution. The novel morphologies of VO2(A) could be readily tuned by altering the concentrations of malonic acid and reaction temperature. It is revealed that malonic acid played an important role as a structure directing agent helping the alternative formation of VO2(A). Furthermore, their electrochemical properties were investigated, which reveal that the as-prepared VO2(A) nanorods exhibit a relatively higher first discharge capacity than other VO2(A) morphologies.

Nanofiber-to-nanorod transformation during annealing of electrochemically deposited vanadium oxide nanofibers

Na0.33V2O5 nanorods with high aspect to ratio have been obtained from Na+ intercalated V2O5 nanofibers in a one step annealing process. The solid state transformed nanorods present lengths of microns and widths around 400nm. X-ray diffraction measurements (XRD) and selected area electron diffraction analysis (SAED) indicate that the nanorods are in essence single crystals grown along the [010] direction with surface dominated by the (001) atomic planes. The morphology transformation is discussed in terms of a solid state transformation driven by a mass transport mechanism from nanofibers in order to form the nanorods. The results demonstrated the possibility to produce high crystalline Na0.33V2O5 nanostructures with potential application as cathode for energy storage devices.

Synthetic beta-K0.33V2O5 Nanorods: A Metal-Insulator Transition in Vanadium Oxide Bronze

We found a linear relationship between the metal-insulator transition (MIT) temperature and the A(+) ionic radius of the beta-A(0.33)V(2)O(5) bronze family, leading our attention to beta-K(0.33)V(2)O(5) which has been neglected for a long time. We have introduced a facile hydrothermal method to obtain the single-crystalline beta-K(0.33)V(2)O(5) nanorods. As expected, both the temperature-dependence of the resistivity and magnetization demonstrated MITs at about 72 K for beta-K(0.33)V(2)O(5), thus matching well with the linear relationship described above. The beta-K(0.33)V(2)O(5) was assigned as a new member of the beta-A(0.33)V(2)O(5) bronze family for their similar crystal and electronic structures and their MIT property; this addition enriches the beta-A(0.33)V(2)O(5) bronze family.

Structural and Optical Properties of V2O5 Nanorod Films

Structural and Optical Properties of V2O5 Nanorod Films

Effect of annealing on the microstructure and optical properties of ZnO/V2O5 composite

Vanadium pentoxide (V2O5) films capped with a thin ZnO layer were prepared by magnetron sputtering at room temperature. The effect of annealing on the microstructure and optical properties of films was systematically investigated. Results indicated that the initially smooth films transformed to porous composite nanocrystals at 500 °C and then further to agglomerated nanoslices at 550 °C. This microstructure transformation is attributed to the distinct temperature-sensitive crystallization of V2O5. The annealed films exhibited enhanced visible photoluminescence, which was attributed to the coupling between V2O5 nanorods and ZnO nanoparticles as well as the improved V2O5 crystallinity.