Tungsten Oxide Nanostructures Research Articles

Quasi‐One‐Dimensional Bismuth Tungsten Oxide Nanostructures Templated by Cotton Fibers

Using cotton fibers as templates, quasi‐one‐dimensional bismuth tungsten oxide (Bi2WO6) nanostructures were successfully synthesized using a combination of solution dipping and calcinating at 500°C. The Bi2WO6 nanostructures were characterized using X‐ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and N2 adsorption and desorption measurements. Their optical property was studied using a UV‐vis spectrum, and the photocatalytic activity was investigated by degrading the organic compound. It was found that the Bi2WO6 nanostructures maintained the quasi‐one‐dimensional morphology of the cotton fibers and were composed of nanoparticles about 40 nm in size. The mechanism of formation of the quasi‐one‐dimensional Bi2WO6 nanostructures was also discussed. Moreover, the quasi‐one‐dimensional Bi2WO6 nanostructures exhibited good visible light absorption and could efficiently decompose rhodamine B under visible light irradiation.

Tunable Generation and Adsorption of Energetic Compounds in the Vapor Phase at Trace Levels: A Tool for Testing and Developing Sensitive and Selective Substrates for Explosive Detection

Among various methods for landmine detection, as well as soil and water pollution monitoring, the detection of explosive compounds in air is becoming an important and inevitable challenge for homeland security applications, due to the threatening increase in terrorist explosive bombs used against civil populations. However, in the last case, there is a crucial need for the detection of vapor phase traces or subtraces (in the ppt range or even lower). A novel and innovative generator for explosive trace vapors was designed and developed. It allowed the generation of theoretical concentrations as low as 0.24 ppq for hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in air according to Clapeyron equations. The accurate generation of explosive concentrations at subppt levels was verified for RDX and 2,4,6-trinitrotoluene (TNT) using a gas chromatograph coupled to an electron capture detector (GC-ECD). First, sensing material experiments were conducted on a nanostructured tungsten oxide. The sensing efficiency of this material determined as its adsorption capacity toward 54 ppb RDX was calculated to be five times higher than the sensing efficiency of a 54 ppb TNT vapor. The material sensing efficiency showed no dependence on the mass of material used. The results showed that the device allowed the calibration and discrimination between materials for highly sensitive and accurate sensing detection in air of low vapor pressure explosives such as TNT or RDX at subppb levels. The designed device and method showed promising features for nanosensing applications in the field of ultratrace explosive detection. The current perspectives are to decrease the testing scale and the detection levels to ppt or subppt concentration of explosives in air.

Removal of Rhodamine 6G induced by laser and catalyzed by Pt/WO3 nanocomposite

The present study deals with the surface modification of nano-structured tungsten oxide (WO 3 ) with nanoparticles of platinum (Pt) by applying a novel laser-based photocatalytic process. Microscopic studies revealed that Pt particles were homogeneously dispersed with narrow size distribution (2–4 nm) onto the surface of WO 3 within a short time of laser irradiation while XPS studies indicated that the deposited Pt nanoparticles were in the metallic form. Nano-structured bimetallic assemblies that consisted of WO 3 and Pt particles showed enhanced photocatalytic removal of Rhodamine 6G as compared to pure WO 3 . Influence of laser irradiation time and platinum content has been studied. The Pt/WO 3 nanocomposites were also prepared using conventional setup and the resulting photocatalytic activity of the catalysts were compared under both the light sources.

Tantalum–tungsten oxide thermite composites prepared by sol–gel synthesis and spark plasma sintering

Energetic composite powders consisting of sol–gel derived nanostructured tungsten oxide were produced with various amounts of micrometer-scale tantalum fuel metal. Such energetic composite powders were ignition-tested and the results show that the powders are not sensitive to friction, spark and/or impact ignition. Initial consolidation experiments, using the High-Pressure Spark Plasma Sintering (HPSPS) technique, on the sol–gel derived nanostructured tungsten oxide produced samples with higher relative density than can be achieved with commercially available tungsten oxide. The sol–gel derived nanostructured tungsten oxide with immobilized tantalum fuel metal (Ta–WO 3) energetic composite was consolidated to a density of 9.17 g cm −3 or 93% relative density. In addition, those samples were consolidated without significant pre-reaction of the constituents, thus retaining their stored chemical energy.

Morphology-controlled synthesis of highly adsorptive tungsten oxide nanostructures and their application to water treatment

A facile route to control the morphology of tungsten oxide hierarchical hollow structures was demonstrated. The morphology of the tungsten oxide nanostructures could be tuned from size-controlled hollow urchins to nanowires by adjusting the concentration of the tungsten precursor, with no need for catalysts, surfactants, or templates. The tungsten oxide nanostructures were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and nitrogen adsorption–desorption measurements. The as-prepared tungsten oxide hierarchical hollow nanostructures showed a very high specific surface area and demonstrated an excellent ability to remove organic pollutants. The adsorption capability of our tungsten oxide hierarchical hollow nanostructure was much higher than those of previously reported transition metal oxide nanostructures including Mn3O4, Fe2O3, and MnO2 as well as other alternative adsorbents such as MCM-22, fly ash, and red mud. This study provides a simple strategy for template/surfactant-free synthesis of hierarchical hollow nanostructures. Also, the as-prepared products are expected to be new promising materials for environmental remediation.

Synthesis of Nanostructured Tungsten Oxide Thin Films: A Simple, Controllable, Inexpensive, Aqueous Sol−Gel Method

Among the available metal oxide nanostructures, tungsten oxide has remained, at times, troublesome to fabricate, with many synthetic methods often requiring exotic equipment and or reagents. In this work, we present a systematic investigation demonstrating a new method for the deposition of anhydrous and hydrated nanostructured tungsten oxide thin films via spin coating. The attributes of these materials include the following: high surface area, controllable deposition, and compatibility with existing semiconductor fabrication infrastructure making this method a suitable candidate for application in the manufacture of gas sensors and dye sensitized solar cells. We will show that it is possible to form micrometer thick highly crystalline nanostructured thin films and, using Raman, SEM, XRD, XPS, and TEM analysis, will prove that these nanostructures can be rendered into anhydrous or partially or fully hydrated tungsten oxides. We further demonstrate the application of these materials in the fabrication of ...

Synthesis of Nanostructured Tungsten Oxide (WO2.9) Fibers and Discs

Evaporation of WO3.0 powder during transmission electron microscopy resulted in the formation of nanofibers of WO2.9, which deposited on adjacent cooler regions of the carbon substrate. Controlled experiments using the inert gas condensation method were performed to investigate the formation mechanism of the nanofibers. Depending on the growth conditions, different morphologies of WO2.9 phase were observed. Structural characterization was carried out using analytical electron microscopy techniques. On the basis of these observations, a qualitative growth model is proposed.

Micro-Structural, Electrical and Spectroscopic Investigations of Pulsed Laser Ablated Palladium Incorporated Nanostructured Tungsten Oxide Films

Pure and Pd incorporated (0.5, 1 and 5 wt%) WO3 films are prepared on quartz substrates using pulsed laser ablation (PLD) technique in an oxygen ambient of 0.12 mbar, at a substrate temperature (Ts) of 873 K. Palladium incorporation effects on the microstructure, optical and electrical properties of tungsten oxide films are systematically investigated using techniques like X-ray diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), micro-Raman spectroscopy, UV-Vis absorption spectroscopy and temperature dependent electrical resistivity measurements. The micro-structural analysis by XRD and micro-Raman indicates that Pd addition can perturb the tungsten oxide lattice and suppress the grain growth. Optical band gap values of the films increases from 3.17 eV for pure WO3 to 3.29 eV for 5 wt% Pd incorporated WO3 films. All the films present high transparency in the visible spectral range. The electrical resistivity studies of the pure and Pd incorporated films done at room temperature and for the range of temperature; 170-450 K reveal that Pd addition can lower the resistivity of the WO3 thin films. Room temperature resistivity as well as activation energy of the film decreases exponentially with Pd incorporation concentration. Highly transparent, nanocrystalline and semiconducting WO3 films with low resistivity obtained by Pd incorporation can make WO3 suitable for microelectronics industry and for gas sensing applications.

Synthesis, Mechanism, and Gas‐Sensing Application of Surfactant Tailored Tungsten Oxide Nanostructures

AbstractWidely applicable nonaqueous solution routes have been employed for the syntheses of crystalline nanostructured tungsten oxide particles from a tungsten hexachloride precursor. Here, a systematic study on the crystallization and assembly behavior of tungsten oxide products made by using the bioligand deferoxamine mesylate (DFOM) (product I), the two chelating ligands hexadecyltrimethylammoniumbromide (CTAB) (II) and poly(alkylene oxide) block copolymer (Pluronic P123) (III) is presented. The mechanistic pathways for the material synthesis are also discussed in detail. The tungsten oxide nanomaterials and reaction solutions are characterized by Fourier transform IR, 1H, and 13C NMR spectroscopies, powder X‐ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high‐resolution TEM, and selected‐area electron diffraction. The indexing of the line pattern suggests WO3 is in its monoclinic structure with a = 0.7297 nm, b = 0.7539 nm, c = 0.7688 nm, and β‐i; = 90.91 °. The nanoparticles formed have various architectures, such as chromosomal shapes (product I) and slates (II), which are quite different from the mesoporous one (III) that has internal pores or mesopores ranging from 5 to 15 nm. The nanoparticles obtained from all the synthetic procedures are in the range of 40–60 nm. The investigation of the gas‐sensing properties of these materials indicate that all the sensors have good baseline stability and the sensors fabricated from material III present very different response kinetics and different CO detection properties. The possibility of adjusting the morphology and by that tuning the gas‐sensing properties makes the preparation strategies used interesting candidates for fabricating gas‐sensing materials.

Structural and electrochromic properties of tungsten oxide prepared by surfactant-assisted process

By virtue of gemini surfactant template, nanostructured tungsten oxides thin films were prepared from the modified tungsten hexachloride sol–gel techniques. Temperature was varied as it is an important factor for crystallization, surface morphology and microstructure of tungsten oxides, from the studies of X-ray diffractions, scanning electron microscopy and transmission electron microscopy. The mesoporous sample calcined at 300 °C has tri-dimensional vermicular mesopores with nanocrystallites embedded in the pore wall, while such uniform structure would be destroyed by higher calcination temperature of about 400 °C. X-ray photoelectron spectroscopy was used for analyzing the surface-binding states and the stoichiometry for the oxides. Electrochromic characterization was implemented by simultaneous voltametric and spectrophotometric measurements of tungsten oxides/indium tin oxide (ITO) electrodes. The investigation results showed that organized pore-wall nanostructure has strong effects on the electrochemical and chromogenic properties depending on the specific surface area and the impacts from the evolved crystallization.

Synthesis and characterization of WO 3 nanostructures prepared by an aged-hydrothermal method

Nanostructures of tungsten trioxide (WO 3) have been successfully synthesized by using an aged route at low temperature (60 °C) followed by a hydrothermal method at 200 °C for 48 h under well controlled conditions. The material was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Specific Surface Area (S BET) were measured by using the BET method. The lengths of the WO 3 nanostructures obtained are between 30 and 200 nm and their diameters are from 20 to 70 nm. The growth direction of the tungsten oxide nanostructures was determined along [010] axis with an inter-planar distance of 0.38 nm.

The evolution of tungsten oxide nanostructures from nanowires to nanosheets

The self-synthesis of tungsten oxide (W18O49) nanowires/nanosheets on sputtering-deposited tungsten films was obtained by thermal annealing in nitrogen under the thermal budgets of 750 °C for ≥2 h or ≥850 °C for 0.5 h. Experimental evidence of the nanomorphology transformation of tungsten oxide nanostructures from nanowires to nanosheets was presented, which can be attributed to the formation and re-crystallization of an amorphous interface layer between two neighboring parallel-growth nanowires linked together with a low angle misalignment along their growth directions.

Outperformed electrochromic behavior of poly(ethylene glycol)-template nanostructured tungsten oxide films with enhanced charge transfer/transport characteristics

Porous tungsten oxide films of nanocrystalline tungsten oxide embedded in an amorphous tungsten oxide matrix have been synthesized via poly(ethylene glycol) (PEG)-template sol-gel technique with peroxopolytungstic acid precursor. The effects of PEG addition on the microstructure and electrochromic performance of the tungsten oxide films are investigated. Charge transfer/transport properties in the tungsten oxide films are studied by electrochemical impedance spectroscopy (EIS) as well. Triclinic tungsten oxide film is formed in the absence of PEG. The PEG-template tungsten oxide film demonstrates an electrochromic performance superior to that of the crystalline tungsten oxide film, including larger transmittance modulation and coloration/bleaching efficiency as well as faster response times. EIS measurements indicate that faster charge-transfer rates at the tungsten oxide/electrolyte interface and larger Li(+) diffusion coefficients in tungsten oxide are achieved in the PEG-template film. We suggest that the PEG-template tungsten oxide film with a porous crystalline/amorphous nanostructure provides an effective means for charge transfer/transport to encourage its superior electrochromic performance.

Tungsten Oxide Nanostructures Growth in HFCVD System by Slow Positron Beam

Tungsten oxide (WOx) nanostructures were prepared by a hot filament chemical vapor deposition (HFCVD) system. Two series of samples were synthesized by adjusting filaments temperature (Tf) and oxygen gas concentration (OGC). The crystallinity and stoichiometry were highly related to Tf and OGC. The evolution of stoichiometry and types of defects was illuminated by slow positron implantation spectroscopy (SPIS). A turning point of Tf=1750°C was found that at this point the crystallinity and stoichiometry natures were the best. In order to develop the chemical phase from substoichiometric to stoichiometric, the oxygen gas concentration in the mixture gas during deposition should be raised to an appropriate level.

Synthesis of Nanostructured Tungsten Oxide Thin Films

A facile and inexpensive method to produce thin films of nanostructured tungsten oxide is described. A nanocrystalline tungstite (WO3·H2O) film is spontaneously formed when a tungsten substrate is immersed in nitric acid at elevated temperatures. The resulting thin film is composed of plate-like tungstite crystals with edges preferentially directed out from the substrate surface. The tungstite can easily be transformed into WO3 by annealing. Patterned WO3·H2O/W structures can be obtained by a combination of lithographic techniques and etching. In this study, the effect of exposure time, acid concentration, and temperature on the microstructure of the films has been investigated. The potential of this inexpensive synthesis method to produce large-area coatings of nanostructured tungsten oxide as well as patterned films makes it interesting for several different applications, such as batteries, gas sensors, and photocatalysts.

Hydrothermal synthesis and characterization of self-assembled h-WO 3 nanowires/nanorods using EDTA salts

One-dimensional (1D) self-assembled single-crystalline hexagonal tungsten oxide (h-WO 3) nanostructures were synthesized by a hydrothermal method at 180 °C using sodium tungstate, ethylenediaminetetraacetic (EDTA) salts of sodium or ammonium, and sodium sulfate. Controlled morphological modification of h-WO 3 nanowire bundles was achieved and hierarchical urchin-like structures were produced by simply substituting the sodium ions with ammonium ions in the EDTA salt solution. Self-assembled h-WO 3 nanowire bundles and nanorods that formed urchin-like structures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. 1D self-assembled h-WO 3 nanowire bundles of ∼100 nm diameter and 1–2 μm length were comprised of several individual uniform nanowires of 4–6 nm diameter. These individual nanowires served as building blocks of the bundles. Raman, cyclic voltammetry (CV), and photoluminescence (PL) spectroscopy studies revealed their structure, electrochemical response, and luminescence properties. The synthesis of 1D self-assembled h-WO 3 nanowire bundles and urchin-like structures was differentiated by means of Na +- and NH 4 +-based EDTA salt solutions.

Bandgap renormalization in titania modified nanostructured tungsten oxide thin films prepared by pulsed laser deposition technique for solar cell applications

Pure and titania modified WO3 films are prepared using pulsed laser ablation technique in an oxygen ambient of 0.12mbar at a substrate temperature of 873K. Titania incorporation effects on the microstructure, optical, and electrical properties on the tungsten oxide films are systematically investigated using techniques such as x-ray diffraction, atomic force microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, micro-Raman spectroscopy, and UV-visible absorption spectroscopy measurements. The resistivity measurements of the pure and titania modified WO3 films are done at room temperature. The variation of resistivity with temperature for the range of 170–450K is also investigated. The microstructural analysis indicates that titania addition strongly perturbs the tungsten oxide lattice and suppresses the grain growth. Optical measurements revealed a bandgap renormalization in tungsten oxide films for higher titania concentrations. Bandgap values of the films decrease from 3.17eV for pure WO3 to 2.7eV for 10wt% TiO2 modified WO3 films. The shifting of photoresponse of WO3 films to visible range by titania incorporation throw light on the feasibility of their application in visible-light-driven photocatalysis and in solar cells. All the films show semiconducting behavior in their temperature dependence of resistivity.

The influence of filament temperature and oxygen concentration on tungsten oxide nanostructures by hot filament metal oxide deposition

Tungsten oxide (WOx) nanostructures were prepared by a hot filament chemical vapour deposition system and the temperature of the hot tungsten filaments was changed by steps of degrees. The morphology and average growth rate were indicated by scanning electron microscopy which showed that the morphology was highly related to the filament temperature (Tf) and the distance between the filaments and the polished Si (1 0 0) substrates (df). The influence of Tf on the crystalline nature was studied by x-ray diffraction and Raman spectroscopy. The evolution of stoichiometry and types of defects was indicated by x-ray photoelectron spectroscopy and slow positron implantation spectroscopy. When Tf was up to 1750 °C, tungsten oxide nanostructure was synthesized. A turning point of Tf was found at which the nature of crystallinity and of stoichiometry was the best. As Tf increased to 2100 °C or df decreased, the film crystallinity decreased; correspondingly, the component ratio of stoichiometry WO3 decreased and lots of vacancy agglomerates were present. In order to develop the chemical phase from substoichiometry to stoichiometry, the oxygen gas concentration in the mixture gas during deposition should be raised to an appropriate level.

HFCVD and CSVT techniques working together to produce nanostructured tungsten oxide

Hot Filament Chemical Vapour Deposition (HFCVD) was used to deposit tungsten oxide clusters on a graphite surface using a tungsten filament as source. These clusters were subsequently transported onto quartz and Si substrates where they transformed into WO 3 − X nanowires. The transport of tungsten species from source to substrate was made through the Close Spaced Vapour Transport (CSVT) technique. The synthesized nanostructures were characterized by means of SEM, EDS, XRD techniques as well as by Raman spectroscopy. The results show that the nanowires have a monoclinic structure, a diameter about 100 nm and they were extended many tenths of micrometers.

Nanostructured tungsten oxide thin films by the reactive pulsed laser deposition technique

Preparation of nanostructured tungsten oxide thin films using the reactive pulsed laser ablation technique is reported. The structural, morphological, optical and electrical properties of deposited films are systematically studied by changing the ambient oxygen pressure (pO2). Structural dependence of tungsten oxide films on ambient oxygen pressure is discussed using grazing incidence X-ray diffraction (GIXRD) and micro-Raman spectra. The section analysis using atomic force microscopy exposed the smooth surface features of the deposited films. The blue shift in optical bandgap with an increase in ambient oxygen pressure is expounded in terms of electronic band structure of tungsten oxide. The influence of oxygen pressure on optical constants like extinction coefficient, band edge sharpness, refractive index and optical bandgap is also conveyed. The temperature variation of electrical resistance for films deposited at 0.12 mbar furnishes evidence for its semiconducting nature.