Self assembled V2O5 nanorods for gas sensors

Hollow spheres of vanadium pentoxide made up of self assembled nanorods have been prepared successfully by solvothermal method. The calcinated samples of V₂O₅ nanorods exhibit orthorhombic structure as determined through XRD analysis. The nanorods are found to self assemble into hollow sphere like structures which can be clearly seen in SEM images. The diameter of the hollow spheres were around 2–3 μm, while the nanorods forming the micro spheres were with diameters in the range of 100–200 nm and are of few hundreds of nanometers in length. The change in the resistance of the V₂O₅ nanorod sensing element with respect to the test gas concentration was measured by noting down the resistance at each concentration for various time intervals. Sensitivity of the material linearly increased with different concentration of ethanol and ammonia. It is clearly seen that the V₂O₅ nanorods have more sensing response for ethanol when compared to that of ammonia.     

Facile synthesis of Nb2O5 nanorod array films and their electrochemical properties

Nb₂O₅ nanorod array films were synthesized by a facile hydrothermal process using niobium metal foil and NH₄F as precursors. The Nb₂O₅ nanorods stand on the niobium metal foil substrate and are less than 100 nm in diameter and about 1 μm in length. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) characterizations indicate that these nanorods have orthorhombic structure and grew longitudinally along 〈0 0 1〉 direction. The nanorod growth mechanism was discussed. Thermal annealing at a temperature below 500 °C did not change the microstructure of nanorods but improve the crystallinity. The Nb₂O₅ nanorod array films have been tested as cathode material for lithium battery, which showed a good specific capacity up to 380 mAh g⁻¹ even after 50 charge/discharge cycles.     

X-RAY PHOTOELECTRON SPECTROSCOPY STUDY ON ELECTROCHROMIC V2O5 THIN FILM

Nanocrystalline V₂O₅ thin films were reactively radio-frequency magnetron-sputtered under optimal deposition parameters. Their electrochemical and electrochromic characteristics were investigated by cyclic voltammetry and in-situ monochromatic transmittance measurements. Upon lithium intercalation, V₂O₅ thin films showed a double electrochromic behavior depending on the wavelength and the intercalation extent. X-ray photoelectron spectroscopy results showed that part of the V⁵⁺ in V₂O₅ was reduced to V⁴⁺ during the Li⁺ intercalation process.     

Vertical aligned V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanoneedle arrays grown on Ti substrate as binder-free cathode for lithium-ion batteries

V₂O₅ nanoneedle arrays were grown directly on titanium (Ti) substrate by a facile solvothermal route followed with calcination at 350 °C for 2 h. The as-prepared V₂O₅ nanoneedles are about 50 nm in diameter and 800 nm in length. The electrochemical behavior of V₂O₅ nanoarrays as binder-free cathode for lithium-ion batteries (LIBs) was evaluated by cyclic voltammetry and galvanostatic discharge/charge tests. Compared with V₂O₅ powder electrode, V₂O₅ nanoneedle arrays electrode exhibited improved electrochemical performance in terms of high discharge capacity of 262.5 mA h g^?1 between 2.0 and 4.0 V at 0.2 C, and high capacity retention up to 77.1% after 100 cycles. Under a high current rate of 2 C, a discharge capacity of about 175.6 mA h g^?1 can be maintained. The enhanced performance are mainly due to the intimate contact between V₂O₅ nanoneedle active material and current collector, which enable shortened electron transfer pathway and improved charge transfer kinetics, demonstrating their potential applications in high rate electrochemical storage devices.     

Mo-doped V<Subscript>2</Subscript>O<Subscript>5</Subscript> hierarchical nanorod/nanoparticle core/shell porous microspheres with improved performance for cathode of lithium-ion battery

Mo-doped V₂O₅ hierarchical nanorod/nanoparticle core/shell porous microspheres (MVHPMs) were prepared via a simple hydrothermal approach using ammonium metavanadate and ammonium molybdate as precursors followed by a thermal annealing process. The samples were characterized by XRD, SEM, TEM, EDS, and XPS carefully; it confirmed that porous microspheres with uniform Mo doping in the V₂O₅ matrix were obtained, and it contains an inner core self-assembled with 1D nanorods and outer shell consisting of nanoparticles. A plausible growth mechanism of Mo-doped V₂O₅ (Mo-V₂O₅) porous microspheres is suggested. The unique microstructure made the Mo-V₂O₅ hierarchical microspheres a good cathode material for Li-ion battery. The results indicate the synthesized Mo-V₂O₅ hierarchical microspheres exhibit well-improved electrochemical performance compared to the undoped samples. It delivers a high initial reversible capacity of 282 mAh g^?1 at 0.2 C, 208 mAh g^?1 at 2 C, and 111 mAh g^?1 at 10 C, and it also exhibits good cycling stabilities; a capacity of 144 mAh g^?1 is obtained after 200 cycles at 6 C with a capacity retention of >?82%, which is much high than that of pure V₂O₅ (95 mAh g^?1 with a capacity retention of 72%).

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Graphical Abstract Mo-doped V₂O₅ hierarchical porous microspheres with improved LIB performance

     

Synthesis and characterization of TiO2/Fe2O3 core-shell nanocomposition film and their photoelectrochemical property

TiO₂/Fe₂O₃ core-shell nanocomposition film has been fabricated via two-step method. TiO₂ nanorod arrays are synthesized by a facile hydrothermal method, and followed by Fe₂O₃ nanoparticles deposited on TiO₂ nanorod arrays through an ordinary chemical bath deposition. The phase structures, morphologies, particle size, chemical compositions of the composites have been characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and ultraviolet-visible (UV-vis) spectrophotometer. The results confirm that Fe₂O₃ nanoparticles of mean size ca. 10 nm coated on the surface of TiO2 NRs. After depositing Fe₂O₃, UV-vis absorption property is induces the shift to the visible-light range, the annealing temperature of 600 °C is the best condition for UV-vis absorption property of TiO₂/Fe₂O₃ nanocomposite film, and increasing Fe content, optical activity are enhanced one by one. The photoelectrochemical (PEC) performances of the as-prepared composite nanorods are determined by measuring the photo-generated currents under illumination of UV-vis light. The TiO₂ NRs modified by Fe₂O₃ show the photocurrent value of 1.36 mA/cm² at 0 V vs Ag/AgCl, which is higher than those of unmodified TiO₂ NRs.     

V<Subscript>2</Subscript>O<Subscript>5</Subscript>-SiO<Subscript>2</Subscript> hybrid as anode material for aqueous rechargeable lithium batteries

V₂O₅-SiO₂ hybrid material was fabricated by heat-treating a mixture of H₂SiO₃ and V₂O₅. SEM, TEM, XRD, and N₂ isotherm analyses were performed to characterize the morphology and structure details of the as-prepared V₂O₅-SiO₂. The possibility of using the as-prepared V₂O₅-SiO₂ as anode material for aqueous lithium-ion batteries was investigated. Potentiostatic and galvanostatic results indicated that the intercalation/de-intercalation of Li⁺ in this material in aqueous electrolyte was quasi-reversible. It was also found that a discharge capacity of up to 199.1 mAh g^?1 was obtained at a current density of 50 mA g^?1 in aqueous solution of 1 M Li₂SO₄, a value which is much higher than the available reported capacities of vanadium (+5) oxides in aqueous electrolytes.     

Size effect on multiferroicity of GdMn2O5 nanorods

Four GdMn₂O₅ nanorod samples of various axial lengths (〈L_C〉) along the c axis were synthesized. The antiferromagnetic and ferroelectric ordering disappeared as 〈L_C〉 decreased to 66 and 55 nm. Various ferroic critical sizes were observed for the two types of domain sizes. Between T = 18 and 26 K, a charge ordering X-ray diffraction peak appeared at 〈L_C〉 = 79 nm. This peak was associated with structural distortion and axial length. The broken multiferroicity of the GdMn₂O₅ nanorods limits their practical application. For applications in memory devices, the estimated maximal capacity is approximately 650 Gbits/in².     

V2O5 aerogel-like lithium intercalation host

Thin self-standing films and powders of highly amorphous V₂O₅ have been prepared via a combined sol-gel and solvent exchange procedure. The amorphous V₂O₅ is a highly interconnected porous material with very thin solid walls and shows a unique lithium intercalation behavior. Electrochemical tests performed on composite cathodes made by mixing the material with carbon particles demonstrated a very high lithium insertion capacity.     

Sub-10 nm V2O5 Crystals on Carbon Nanosheets for Advanced All-Solid-State Lithium Metal Batteries

V₂O₅, as a lithium-free cathode material, has inherent defects such as sluggish kinetics and volume change and, at the same time, requires a lithium metal anode that tends to form dendrites in liquid electrolytes. Both the lithium dendrite and the flammable electrolyte solvent bring longtime safety issues. This work introduces nonflammable inorganic–organic composite solid electrolyte to inhibit the growth of the lithium dendrite and suppress the instability caused by V₂O₅ nanometerization. However, the long-term cycling and rate performances are still insufficient even when reducing V₂O₅ size to about 50 nm. As an improvement, sub-10 nm V₂O₅/C nanosheets are designed and prepared using corn stalks as precursors through simple impregnation and calcination process. The V₂O₅/C offers a much better electrode/electrolyte contact and interface stability than bulk V₂O₅ and commercial V₂O₅ in the inorganic–organic composite solid electrolyte. The discharge capacity is 228 mAh g⁻¹ at 0.1 C after 50 cycles and ≈110 mAh g⁻¹ at 2.0 C.     

Ultrafast laser assisted fabrication of ZnO nanorod arrays for photon detection applications

Orderly aligned ZnO nanorod arrays were grown by the ultrafast laser assisted ablation deposition method. These nanorod arrays were further used to make efficient p-n heterojunction photodetector arrays, which have the potential to have nanoscale spatial resolution for imaging, unique incident polarization discrimination capability, and much improved quantum efficiency as well as detection sensitivity. Both front- and back-illumination photodetection schemes were demonstrated by growing those ZnO nanorod arrays on p-type silicon and p-type Zn_0.9Mg_0.1O-coated Al₂O₃ (0 0 0 1) substrates, respectively. Typical diode rectification behavior and photosensitivity were observed in both designs through I-V and photocurrent measurements.     

Synthesis of VO2 (B) nanorods for Li battery application

Vanadium dioxide nanorods were synthesized through a hydrothermal reaction from V₂O₅ xerogel, poly(vinyl pyrrolidone) (PVP) and lithium perchlorate (LiClO₄). The prepared samples were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical discharge–charge cycling in lithium battery. SEM images reveal the nanorods to have dimensions on the order of 1–3 μm in length and 10–50 nm in diameter. The measured initial discharge capacity of the lithium battery with a cathode made of VO₂ (B) nanorods was 152 mA h/g.     

Nanophase ZnV2O4 as stable and high capacity Li insertion electrode for Li-ion battery

Spinel ZnV₂O₄ nanoparticles are synthesized by a hydrothermal method and its properties are characterized using XRD, SEM, TEM, and electrochemical test. The structural and morphological characterizations show that ZnV₂O₄ sample has high purity and well crystallization with crystal size less than 20 nm. The as prepared electrode shows stable capacity over 660 mAh g⁻¹ in the voltage range of 0.01–3.0 V at 50 mA g⁻¹. The reaction mechanism with lithium ion is also investigated through ex-XRD and -TEM. It shows that the pristine ZnV₂O₄ is transformed to isostructural spinel Li_xV₂O₄ (x close to 7.6) and metal Zn phase during the first lithiation process. Then the spinel Li_xV₂O₄ seems to perform a topotactic intercalation reaction mechanism and that the in-situ formed Li_xV₂O₄ can still keep its spinel matrix while allowing more than 5.7 lithium reversibly into/out over 50 cycles.     

Ohmic-rectification conversion that is tuned using H2O2 for enhanced rectification and optoelectronic performance in MoS2/ZnO nanorod devices

The characteristics of a p–n junction that consists of MoS₂ thin films and ZnO nanorods grown on heavily-doped n-type Si substrate are reported. The current–voltage characteristics for MoS₂/ZnO nanorod devices exhibit ohmic conduction. The measured current is limited by thermionic emission in MoS₂/ZnO nanorod devices that are treated with H₂O₂. H₂O₂ treatment results in the modification of the MoS₂–ZnO interface, so the rectification performance for MoS₂/ZnO nanorod devices is improved. H₂O₂ treatment also increases the responsivity of MoS₂/ZnO nanorod devices to solar irradiation. This phenomenon is caused by induced ohmic-rectification conversion due to H₂O₂ treatment.     

Enhanced ethanol sensing properties of TiO2/ZnO core–shell nanorod sensors

TiO₂-core/ZnO-shell nanorods were synthesized using a two-step process: the synthesis of TiO₂ nanorods using a hydrothermal method followed by atomic layer deposition of ZnO. The mean diameter and length of the nanorods were ～300 nm and ～2.3 μm, respectively. The cores and shells of the nanorods were monoclinic-structured single-crystal TiO₂ and wurtzite-structured single-crystal ZnO, respectively. The multiple networked TiO₂-core/ZnO-shell nanorod sensors showed responses of 132–1054 % at ethanol (C₂H₅OH) concentrations ranging from 5 to 25 ppm at 150 ^°C. These responses were 1–5 times higher than those of the pristine TiO₂ nanorod sensors at the same C₂H₅OH concentration range. The substantial improvement in the response of the pristine TiO₂ nanorods to C₂H₅OH gas by their encapsulation with ZnO may be attributed to the enhanced absorption and dehydrogenation of ethanol. In addition, the enhanced sensor response of the core–shell nanorods can be attributed partly to changes in resistance due to both the surface depletion layer of each core–shell nanorod and the potential barriers built in the junctions caused by a combination of homointerfaces and heterointerfaces.     

Tailoring of electrochemical properties of V2O5 thin films grown on flexible substrates using plasma-assisted activated reactive evaporation

The vanadium pentoxide (V₂O₅) thin films have been deposited using home built activated reactive evaporation technique on indium tin oxide-coated flexible Kapton substrates and investigated their microstructural and electrochemical properties. X-ray diffraction pattern displayed predominant (001) orientation designating the orthorhombic structure of the films deposited at optimised growth conditions. The surface of the films is observed to be composed of vertical elliptical-shaped grains of size 98 nm distributed uniformly over the surface of the films provided with root mean square surface roughness of 9 nm as evidenced from atomic force microscopy studies. As-deposited V₂O₅ thin films demonstrated constant discharge capacity of about 60 μAh/(cm² _?μm) for 10 cycles at room temperature in the potential window of 4.0–2.5 V. The influence of silver (Ag) interlayer on electrochemical properties of V₂O₅ films was investigated and observed appreciable improvement in electrochemical performance of ‘V₂O₅/Ag/V₂O₅’ films. The multilayered V₂O₅/Ag/V₂O₅ films exhibited a discharge capacity of about 75 μAh/(cm² _?μm) provided with enhanced cycliability.     

Lithium intercalation in α′-NayV2O5 synthesized via the hydrothermal route

Vanadium bronzes Na_yV₂O₅ are synthesized via the hydrothermal route from a mixture of V₂O₅ and NaOH in the presence of a reducing agent. Fine crystalline powders made of needle-like particles are obtained that exhibit the layered structure typical of the α′-Na_yV₂O₅ phase (y≈1). Electron delocalization arises from a hopping process of unpaired electrons between V⁴⁺ and V⁵⁺. Alkaline cations are intercalated between the oxide layers and discharge curves show that up to one Li⁺ ion per vanadium can be reversibly inserted between the [V₂O₅] layers in the 3.3–0.5 V range. Chemical diffusion coefficient of Li ions in Li_xNaV₂O₅ is found to be dependent on the degree of intercalation. D⁺ varies from 1×10⁻¹⁰ up to 5×10⁻¹⁰ cm²/s for 0≤×≤2. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Controlled growth of standing Ag nanorod arrays on bare Si substrate using glancing angle deposition for self-cleaning applications

A facile approach to manipulate the hydrophobicity of surface by controlled growth of standing Ag nanorod arrays is presented. Instead of following the complicated conventional method of the template-assisted growth, the morphology or particularly average diameter and number density (nanorods cm^?2) of nanorods were controlled on bare Si substrate by simply varying the deposition rate during glancing angle deposition. The contact angle measurements showed that the evolution of Ag nanorods reduces the surface energy and makes an increment in the apparent water contact angle compared to the plain Ag thin film. The contact angle was found to increase for the Ag nanorod samples grown at lower deposition rates. Interestingly, the morphology of the nanorod arrays grown at very low deposition rate (1.2 Å?sec^?1) results in a self-cleaning superhydrophobic surface of contact angle about 157° and a small roll-off angle about 5°. The observed improvement in hydrophobicity with change in the morphology of nanorod arrays is explained as the effect of reduction in solid fraction within the framework of Cassie–Baxter model. These self-cleaning Ag nanorod arrays could have a significant impact in wide range of applications such as anti-icing coatings, sensors and solar panels.     

Solution‐Based Phototransformation of C60 Nanorods: Towards Improved Electronic Devices

A modified liquid–liquid interface precipitation synthesis of C₆₀ nanorods, effects and opportunities following an in situ photochemical transformation in the liquid state, and an electronic characterization using a field‐effect transistor (FET) geometry are reported. The nanorods feature a high aspect ratio of ≈10³ and a notably small average diameter of 172 nm. Interestingly, it is found that a decreased nanorod diameter appears to correlate with distinctly improved electronic properties, and an average electron mobility of 0.30 cm² V^?1 s^?1, as measured in a FET geometry, is reported for as‐grown nanorods, with the peak value being an impressive 1.0 cm² V^?1 s^?1. A photoexposure using green laser light (λ = 532 nm) is demonstrated to result in the formation of a polymer‐C₆₀ shell encapsulating a monomer‐C₆₀ bulk; such photo‐transformed nanorods exhibit an electron mobility of 4.7 × 10^?3 cm² V^?1 s^?1. It is notable that the utilized FET geometry only probes the polymer‐C₆₀ nanorod surface shell, and that the monomer‐C₆₀ bulk is anticipated to exhibit a higher mobility. Importantly, photoexposed nanorods can be conveniently processed as a stabile dispersion in common hydrophobic solvents, and this finding is attributed to the insoluble character of the polymer‐C₆₀ shell.     

Reaction mechanism of elemental mercury oxidation to HgSO4 during SO2/SO3 conversion over V2O5/TiO2 catalyst

Experiments and density functional theory calculations were conducted to uncover the reaction chemistry of Hg⁰ oxidation during SO₂/SO₃ conversion over V₂O₅/TiO₂ catalyst. The results show that SO₂ promotes Hg⁰ oxidation over V₂O₅/TiO₂ catalyst with the assistance of oxygen. The promotional effect is dependent on the reaction temperature, and is associated with the bimolecular reaction between Hg⁰ and SO₃ over V₂O₅/TiO₂ catalyst. SO₂ can be oxidized to SO₃ which has high oxidation ability for Hg⁰ oxidation. SO₂/SO₃ conversion proceeds through a three-step reaction process in the sequence of SO₂ adsorption → SO₂ oxidation → SO₃ desorption. SO₂ oxidation presents an activation energy barrier of 223.84 kJ/mol. HgSO₄ species is formed from the bimolecular reaction between Hg⁰ and SO₃ over V₂O₅/TiO₂ catalyst. Hg⁰ oxidation by SO₃ over V₂O₅/TiO₂ catalyst occurs through three reaction pathways, which are energetically favorable for HgSO₄ formation. SO₂* → SO₃* is identified as the rate-determining step of HgSO₄ formation. During Hg⁰ oxidation by SO₃ over V₂O₅/TiO₂ catalyst, HgSO₄ desorption is a highly endothermic reaction process and requires a higher external energy. The proposed skeletal reaction network can be used to well understand the reaction mechanism of Hg⁰ oxidation during SO₂/SO₃ conversion over V₂O₅/TiO₂ catalyst.