VO2 Nanostructures Research Articles

A simple method to synthesize V2O5 nanostructures with controllable morphology for high performance Li-ion batteries

V2O5 nanostructures have been synthesized through an environmental friendly and simple solvent-free solid-state chemical reaction. By changing the calcination temperature in air, V2O5 nanostructures with different morphologies, such as hierarchical nanosheets, nanosheets, and hierarchical nanobelts, have been obtained. Electrochemical testing results show that hierarchical V2O5 nanobelts exhibit high specific discharge capacity and excellent cycle stability, which display high discharge specific capacities of 240mAhg−1 at 1C, whereas high discharge specific capacities of 174mAhg−1 at 8C. The delivered capacity at 1C can maintain 91% of its initial capacity (the 2nd cycle) after 100 cycles. The V2O5 nanobelts show good electrochemical performance due to its special hierarchical structure that reduces the contact resistance between the ions and materials, adjust the volume change, and relieve the pressure of large deformation in the charging/discharging process. The hierarchical V2O5 nanobelts display promising application prospects as an excellent cathode material for lithium ion batteries.

Structural and toxic effect investigation of vanadium pentoxide

A facile inorganic complex synthesis route has been developed to synthesis V2O5 nanostructures. The effects of varying incubation time on the crystallinity and morphology of the V2O5 phase has been investigated. The obtained XRD result clearly revealed the pure orthorhombic V2O5 crystalline phase. Raman antiphase bridging VO and chaining VO stretching modes peaks at 686 and 521cm−1 attributed orthorhombic V2O5 characteristics. The V2p3/2 peak at the binding energies of 517eV and V2p1/2 peak at 524eV assigned to V5+ oxidation state. Bioinspired V2O5 nanostructures as a biocompatible material for anticancer agents show excellent cytotoxicity at higher V2O5 concentration.

Nanoscale contact resistance of V2O5 xerogel films developed by nanostructured powder

Here we report the synthesis of V2O5 nanostructures by a fast, simple, cost-effective, low-temperature chemical process; followed by the deposition of V2O5 xerogel thin films on a glass substrate by a sol–gel route. Phase analysis, phase transition, microstructural and electronic characterization studies are carried out by x-ray diffraction, texture coefficient analysis, field emission scanning electron microscopy, transmission electron microscopy (TEM), related selected area electron diffraction pattern (SAED) analysis, Fourier transform infrared spectroscopy, thermogravimetry and differential thermal analysis, differential scanning calorimetry, and x-ray photoelectron spectroscopy techniques. Confirmatory TEM and SAED data analysis prove further that in this polycrystalline powder there is a unique localized existence of purely single crystalline V2O5 powder with a preferred orientation in the (0 1 0) direction. The most interesting result obtained in the present work is that the xerogel thin films exhibit an inherent capability to enhance the intrinsic resistance against contact induced deformations as more external load is applied during the nanoindentation experiments. In addition, both the nanohardness and Young’s modulus of the films are found to be insensitive to load variations (e.g. 1 to 7 mN). These results are explained in terms of microstructural parameters, e.g. porosity and structural configuration.

Precursor-mediated synthesis of double-shelled V2O5hollow nanospheres as cathode material for lithium-ion batteries

Hollow micro-/nanostructures have a wide range of applications in catalysis, rechargeable batteries, drug delivery, and gas sensors, as well as energy storage and conversion. Herein, we report a facile, template-free, precursor-mediated method to synthesize V2O5 nanomaterials with three different architectures: double-shelled hollow nanospheres, single-shelled hollow nanospheres and nanoparticles. These V2O5 nanostructures are obtained via a simple thermal treatment in air of a “pre-synthesized” vanadyl glycerolate precursor, and their morphologies can be easily tuned by varying the thermal treatment temperatures. Electrochemical studies show that the double-shelled V2O5 hollow nanospheres as a cathode material for lithium-ion batteries deliver an initial capacity of 256.7 mA h g−1 with a Coulombic efficiency of nearly 100%, and their capacity is superior to the two other V2O5 nanostructures (i.e., single-shelled hollow nanospheres and nanoparticles), mainly due to their unique double-shelled hollow structure.

Controllable synthesis of VO2(D) and their conversion to VO2(M) nanostructures with thermochromic phase transition properties

VO2(M) nanostructures with lower thermochromic phase transition temperature and narrower thermal hysteresis width were synthesized by a hydrothermal-calcination method, making them suitable candidates for smart windows.

Study of the morphological evolution of vanadium pentoxide nanostructures under hydrothermal conditions

A detailed study on the morphological evolution of one-dimensional (1D) vanadium pentoxide (V2O5) nanostructures was performed. Small-angle X-ray scattering (SAXS) and electron microcopy techniques were used for the analyses of the influence of synthesis parameters on a hydrothermal synthesis method of V2O5 nanostructures based on the degradation of a peroxocomplex precursor. A mechanism that explains the morphological evolution under different experimental conditions is proposed and the role of the dehydration process as well as the importance of the oriented attachment (OA) mechanism is discussed.

Effect of post-growth annealing on the structural, optical and electrical properties of V2O5 nanorods and its fabrication, characterization of V2O5/p-Si junction diode

We report the synthesis of V2O5 nanorods by utilizing simple wet chemical strategy with ammonia meta vanadate (NH4VO3) and polyethylene glycol (PEG) exploited as precursor and surfactant agent, respectively. The effect of post-annealing on structural, optical and electrical properties of V2O5 nanorods was characterized by XRD, HRSEM-EDX, TEM, FT-IR, UV (DRS), PL, TG–DTA and DC conductivity studies. The X-ray diffraction analysis revealed that the prepared sample annealed at 150°C for 5h which exhibited anorthic phase of V5O9 and annealed at 300–600°C showed the anorthic phase change to orthorhombic phase of V2O5 due to the post-annealing effect. The surface morphology results indicated that increasing temperature caused a change from microrods to a nanorods shape in the morphology of V2O5. FT-IR spectrum confirmed that the presence of V2O5 functional groups and the formation of V–O bond. The optical band gap was found in the range 2.5–2.48eV and observed to decreases with various annealed temperature. The DC electrical conductivity was studied as a function of temperature which indicated the semiconducting nature. Further, the potential of V2O5 nanostructures were grown on the p-Si substrate using the nebulizer spray technique. The junction properties of the V2O5/p-Si diode were evaluated by measuring current (I)–voltage (V) and AC characteristics.

First-principles insights on electron transport in V2O5 nanostructures

Abstract The present report is on the electron transport properties of V2O5 nanostructures, investigated using density functional theory. As the band structure of V2O5 exhibits semiconducting nature, the V2O5 nanostructures are designed as molecular device and the transport properties are studied. The density of electrons is found to be more in the oxygen sites than in vanadium sites. The device density of states shows that the density of electrons in the energy intervals depends on the applied bias voltage. The transmission spectrum gives the insight on the transport property of V2O5 molecular device. The bias voltage drives the electrons across V2O5 scattering region, where the transmission along V2O5 molecular device mainly depends on the bias voltage. The findings of the present work give insights to fine-tune the transport property of V2O5 molecular device upon varying the bias voltage.

Hydrothermal synthesis and electrochemical properties of V2O5 nanomaterials with different dimensions

In the work, four types of typical morphologies of differently dimensional pure V2O5 nanostructures including nanoflowers, nanoballs, nanowires and nanorods were synthesized through a simple hydrothermal method. The morphology of the product depends on the types of solvent and acid. Hierarchical nanoflowers and zero-dimensional (0D) nanoballs of V2O5 nanocrystals were obtained when using C2H5OH as solvent. One dimensional (1D) nanowires and nanorods were obtained if H2O was used to participate in the reaction. The morphology and structure of the samples were characterized by XRD and SEM, respectively. The electrochemical behaviors of nanoflowers, nanoballs, nanowires and nanorods as electrodes in a supercapacitor device were tested using cyclic voltammetry (CV) curves and galvanostatic charge–discharge (GCD) curves. The electrochemical test results indicate that the rod-like structure leads to a significant improvement of storage capacity, electrochemical kinetics and rate capability. And 1D V2O5 nanorods show the largest specific capacitance of 235Fg−1 at the current density of 1Ag−1 when used as supercapacitor electrode in 1mol/L Na2SO4 electrolyte. It turns out that 1D V2O5 nanorod is an ideal material compared with other morphologies for supercapacitor electrode.

Substrate-mediated strain effect on the role of thermal heating and electric field on metal-insulator transition in vanadium dioxide nanobeams.

Single-crystalline vanadium dioxide (VO2) nanostructures have recently attracted great attention because of their single domain metal-insulator transition (MIT) nature that differs from a bulk sample. The VO2 nanostructures can also provide new opportunities to explore, understand, and ultimately engineer MIT properties for applications of novel functional devices. Importantly, the MIT properties of the VO2 nanostructures are significantly affected by stoichiometry, doping, size effect, defects, and in particular, strain. Here, we report the effect of substrate-mediated strain on the correlative role of thermal heating and electric field on the MIT in the VO2 nanobeams by altering the strength of the substrate attachment. Our study may provide helpful information on controlling the properties of VO2 nanobeam for the device applications by changing temperature and voltage with a properly engineered strain.

Morphological investigations of nanostructured V2O5 over graphene used for the ODHP reaction: from synthesis to physiochemical evaluations

Several V2O5 nanostructures, including the rod or belt-like, tube-like, needle-like and flower-like, were synthesized via the reflux and hydrothermal processes utilizing different templates such as monoamine, diamine, aromatic and alcoholic amines

Pulsed Laser Deposition of Metal Oxide Nanoparticles, Agglomerates, and Nanotrees for Chemical Sensors

Pulsed laser deposition (PLD) was used to prepare WO3, ZnO-modified SnO2, and V2O5 nanostructures as gas sensing materials on top of commercial SGX Sensortech MEMS microheater platforms. The layers were formed of different types of nanostructures including nanoparticles, agglomerates, and nanotrees with fractal-like growth. Clear dependency between the deposition parameters, structural morphology, and gas sensing performance was found. The sensing materials were found to be sensitive to different types of gaseous species, so that WO3 and SnO2 had very good response up to 600% to 50ppm NO, and V2O5 up to -35% to 20ppm NH3, respectively.

Solid-state transformation of single precursor vanadium complex nanostructures to V₂O₅ and VO₂: catalytic activity of V₂O₅ for oxidative coupling of 2-naphthol.

A vanadium complex, [(C5H5N)2V2O3·H2O], of different morphologies has been obtained via a modified hydrothermal procedure using pyridine and VOSO4 salt as the starting material. The evolved [(C5H5N)2V2O3·H2O] nanobelts are of 50-200 nm in width and of a length up to several millimeters. At higher temperatures (600 °C), the solid [(C5H5N)2V2O3·H2O] nanostructures are converted to vanadium pentoxide (V2O5) and vanadium dioxide (VO2) when heated in air and nitrogen atmosphere, respectively. During growth, the mechanism of the evolution of octahedra, truncated octahedra, and hollow truncated octahedra of [(C5H5N)2V2O3·H2O] are reported for the first time. These types of well-structured morphology are also isolated while V2O5 and VO2 are evolved. The as-grown belt-like and octahedral morphologies of [(C5H5N)2V2O3·H2O] are retained during the solid-state transformation, suggesting a route to evolve crystalline nanomaterials. Again, the morphological evolution of the [(C5H5N)2V2O3·H2O] nanostructures has been examined to be pyridine and precursor vanadyl sulfate (VS) concentration dependent. Thus, we are able to isolate truncated octahedra as an intermediate during the formation of [(C5H5N)2V2O3·H2O] nanobelts and nanoflowers with a high pyridine (Py) concentration. Interestingly, longer reaction times successively featured the transformation of truncated octahedra into nanobelts. Nanobelt evolution is not observed at low pyridine concentrations. However, the formation of octahedral morphology takes place at low pyridine concentration. All of the nanostructures were critically examined and characterized thoroughly by various physical techniques to ascertain their purity, structure and composition. An interesting, thermodynamically stable, single crystalline product from DMF soluble [(C5H5N)2V2O3·H2O] has been characterized, which indirectly supports the composition of [(C5H5N)2V2O3·H2O]. Selectively, vanadium pentoxide nanobelts have been found to be an efficient catalyst for the oxidative coupling of 2-naphthol to binaphthols under a molecular oxygen atmosphere.

Size effects on metal-insulator phase transition in individual vanadium dioxide nanowires.

We report the size effects on the metal-insulator phase transition of vanadium dioxide (VO2) nanowires prepared by chemical vapor deposition. The phase transition temperature can be tuned from 67 °C in the bulk VO2 to as low as 29°C by reducing the diameter of VO2 nanowires to nanoscale. Temperature-dependent Raman spectra display a clear dynamic picture on the metal-insulator phase transition process of the VO2 nanowires. Whilst, Raman study shows no remarkable strain effect on the phase transition behaviors of our samples. The increasing surface defect density with reducing nanowire size facilitates the decreasing phase transition temperature. In addition, the polarized-photocurrent effect was observed, resulting from the anisotropy of the photoresponse and also caused by the reduced dimensionality.Our results indicate that size of VO2 nanostructures can dominate their thermoelectric and photoelectrical properties.

Scalable hydrothermal synthesis of free-standing VO₂ nanowires in the M1 phase.

VO2 nanostructures derived from solution-phase methods are often plagued by broadened and relatively diminished metal-insulator transitions and adventitious doping due to imperfect control of stoichiometry. Here, we demonstrate a stepwise scalable hydrothermal and annealing route for obtaining VO2 nanowires exhibiting almost 4 orders of magnitude abrupt (within 1 °C) metal-insulator transitions. The prepared nanowires have been characterized across their structural and electronic phase transitions using single-nanowire Raman microprobe analysis, ensemble differential scanning calorimetry, and single-nanowire electrical transport measurements. The electrical band gap is determined to be 600 meV and is consistent with the optical band gap of VO2, and the narrowness of differential scanning calorimetry profiles indicates homogeneity of stoichiometry. The preparation of high-quality free-standing nanowires exhibiting pronounced metal-insulator transitions by a solution-phase process allows for scalability, further solution-phase processing, incorporation within nanocomposites, and integration onto arbitrary substrates.

Synthesis of V2O5 Nanoflakes on PET Fiber as Visible-Light-Driven Photocatalysts for Degradation of RhB Dye

The visible-light-driven semiconductor photocatalysts are the current research focus techniques used to decompose organic pollutants/compounds. The photodegradation efficiency of organic compounds by photocatalyst is expected to be better compared to UV-light-driven semiconductor photocatalysts technique since the major components of our solar energy are visible light (~44%). However, as most of the previous research work has been carried out using semiconductor photocatalysts in the form of powder, extra steps and costs are needed to remove this powder from the slurry to prevent secondary pollution. In this research work, we will explain our fabrication technique of V2O5 nanoflakes by growing radially on PET fibers. By utilizing the flexibility and high surface area of polymeric fibers as novel substrate for the growth of V2O5 nanoflakes, the Rhodamine B (RhB) could be degraded under visible light irradiation. The photodegradation of RhB solution by V2O5 nanoflakes followed the 1st order kinetic with a constant rate of 0.0065 min−1. The success of this research work indicates that V2O5 nanoflakes grown on PET fibre could be possibly used as organic waste water purifier under continuous flow condition. A photodegradation mechanism of V2O5 nanostructures to degrade RhB dye is proposed based on the energy diagram.

VO2 nanostructures based chemiresistors for low power energy consumption hydrogen sensing

Mott-type VO2 oxide nanobelts are demonstrated to be effective hydrogen gas sensors at room temperature. These nanobelts, synthesized by hydrothermal process and exhibiting the VO2 (A) crystallographic phase, display room temperature H2 sensitivity as low as 0.17 ppm. The nanobelts (ultralong belt-like) nanostructures could be an ideal system for fully understanding dimensionally confined transport phenomena in functional oxides and for building functional devices based on individual nanobelts.

In situ probing of doping- and stress-mediated phase transitions in a single-crystalline VO₂ nanobeam by spatially resolved Raman spectroscopy.

We demonstrate an experimental in situ observation of the temperature-dependent evolution of doping- and stress-mediated structural phase transitions in an individual single-crystalline VO₂ nanobeam on a Au-coated substrate under exposure to hydrogen gas using spatially resolved Raman spectroscopy. The nucleation temperature of the rutile R structural phase in the VO₂ nanobeam upon heating under hydrogen gas was lower than that under air. The spatial structural phase evolution behavior along the length of the VO₂ nanobeam under hydrogen gas upon heating was much more inhomogeneous than that along the length of the same nanobeam under air. The triclinic T phase of the VO₂ nanobeam upon heating under hydrogen gas transformed to the R phase and this R phase was stabilized even at room temperature in air after sample cooling. In particular, after the VO₂ nanobeam with the R phase was annealed at approximately 250 °C in air, it exhibited the monoclinic M1 phase (not the T phase) at room temperature during heating and cooling cycles. These results were attributed to the interplay between hydrogen doping and stress associated with nanobeam-substrate interactions. Our study has important implications for engineering metal-insulator transition properties and developing functional devices based on VO₂ nanostructures through doping and stress.

Self-assembled hairy ball-like V2O5 nanostructures for lithium ion batteries

Hairy ball-like nanostructures assembled from nanowires, are synthesized by a hydrothermal method. The reaction time has a significant effect on the morphologies of the products. After calcination at 360 °C, the precursor can be transformed to hairy ball-like V2O5 nanostructures, which present an excellent electrochemical performance for lithium ion batteries.

Competitive growth texture of pulsed laser deposited vanadium dioxide nanostructures on a glass substrate

We report on the crystal structure and morphology of vanadium dioxide (VO2) nanostructures synthesized by pulsed laser deposition on soda-lime glass substrates. The VO2 nanostructures exhibit sharp a-axis diffraction peaks, characteristic of the VO2 monoclinic phase, which implies that highly a-axis textured VO2 was formed. A detailed description of the growth mechanisms and the substrate–film interaction is given, and the characteristics of the electronic transition and hysteresis of the phase transition are described in terms of the morphology and grain boundary structure. The sharpness of the transition and the hysteresis upon heating and cooling are found to be strong functions of the crystal structure and microstructure (grain size and shape).