Active Tungsten Oxide Research Articles

Solar-light active tungsten oxide coated ceramic membrane with unique surface wettability fabricated by RF magnetron sputtering: Remediation of oily wastewater and photo-catalytic self-cleaning

A thin film monoclinic WO3 was coated on porous alumina ceramic membrane by RF magnetron sputtering (RFMS), and used as a self-cleaning filtering medium for the remediation of oily water (oil-in-water emulsion). An optimum concentration of oxygen vacancy was introduced in WO3 lattice by optimizing the sputtering parameters. The excess of electron concentration arises from the introduction of oxygen vacancy enabled the induction of highly polar hydroxyl radicals on the membrane surface and this enhanced the water affinity of the surface. The resulting WO3 coated porous alumina ceramic membrane exhibited a unique combination of surface wettability: super hydrophilic in air with static contact angle 0°, super oleophilic in air with contact angle 0°, and super oleophobic under the water with contact angle close to 159.5°. These favorable wetting conditions was utilized to develop an efficient membrane for water passing oil water separation system which eventually exhibited substantially increased oil water separation efficiency, permeate flux, and critical pressure to withstand the higher applied trans-membrane pressure. In addition to the efficient oil water separation, the novelty of the membrane is its self-cleaning capability, where the organic pollutants that clogged the membrane pore during its operation was photo-catalytically removed under the natural sunlight. The self-cleaning feature of the membrane was possible also due to the presence of high concentration of electrons, comparable to that of noble metal introduced by oxygen vacancy in WO3 lattice. The collective oscillation of electron constellation resonates with the irradiated light source and resulted in surface plasmonic resonance (SPR), and consequent anomalous light absorption for efficient photo-catalytic self-cleaning of the membrane under natural sunlight. It was found that after a prolonged use, the WO3 coated porous alumina ceramic membrane showed a sharp decline of permeate flux due to clogged pores, and this was rectified and initial flux wad restored by simply exposing the used membrane to sun light.

Microgravimetric study of electrochemical properties of PEDOT/WO3 composite films in diluted sulfuric acid

Poly-3,4-ethylenedioxythiophene composite films with tungsten oxide (PEDOT/WO3) were obtained by potentiodynamic deposition of tungsten oxide from acidic metastable solution of isopolytungstates into poly-3,4-ethylenedioxythiophene film, pre-deposited on an Au-quartz crystal. The electrochemical deposition of tungsten oxide into poly-3,4-ethylenedioxythiophene was investigated by electrochemical quartz microgravimetry (EQCM), the masses of PEDOT and tungsten oxide deposits were estimated. The electrochemical behavior of PEDOT/WO3 composite films with different masses of deposited tungsten oxide was studied by cyclic voltammetry and EQCM in the 0.5 M sulfuric acid electrolyte. The change of the fraction of tungsten oxide in the PEDOT/WO3 composite film results in the change of the slope of the Δf–E dependency in the potential region, corresponding to WVI/WV redox process. It is due to an oppositely directed mass transport (anion and cation) during the redox process in the composite film. The average molar mass of transferred species involved in the redox process in tungsten oxide was estimated to be 26 ± 4 g mol−1. It was shown that the fraction of electrochemically active tungsten oxide deposit is dependent on its mass in the composite, with increase of the mass of tungsten oxide in PEDOT/WO3, the fraction of electroactive tungsten oxide WO3 decreases due to decrease in its active area.

MgF2-Based Luminescing Ceramics

Results of investigation at 300 K of photo- and cathodoluminescence of the high-temperature optical ceramics synthesized for the first time based on MgF2 activated tungsten oxide are presented.

Highly Active Tungsten Oxide Nanoplate Electrocatalysts for the Hydrogen Evolution Reaction in Acidic and Near Neutral Electrolytes.

An efficient, cost-effective, and earth-abundant catalyst that could drive the production of hydrogen from water without or with little external energy is the ultimate goal toward hydrogen economy. Herein, nanoplates of tungsten oxide and its hydrates (WO3·H2O) as promising electrocatalysts for the hydrogen evolution reaction (HER) are reported. The square-shaped and stacked WO3·H2O nanoplates are synthesized at room temperature under air in ethanol only, making it as a promising green synthesis strategy. The repeated electrochemical cyclic voltammetry cycles modified the surface of WO3·H2O nanoplates to WO3 as confirmed by X-ray photoelectron and Auger spectroscopy, which leads to an improved HER activity. Hydrogen evolution is further achieved from distilled water (pH 5.67) producing 1 mA cm–2 at an overpotential of 15 mV versus the reversible hydrogen electrode. Moreover, WO3·H2O and WO3 nanoplates demonstrate excellent durability in acidic and neutral media, which is highly desirable for practical application. Improved hydrogen evolution by WO3(200) when compared to that by Pt(111) is further substantiated by the density functional theory calculations.

Development and analyses of self-passivating tungsten alloys for DEMO accidental conditions

Tungsten is considered the main candidate material for the first-wall in DEMO due to its high melting point, low erosion yield and low tritium retention. Nevertheless, it can cause a substantial safety issue in a loss-of-coolant accident (LOCA) in combination with air ingress into the plasma vessel, due to the formation and sublimation of volatile neutron activated tungsten oxide. Self-passivating tungsten alloys introduce a passive safety mechanism by forming a stable chromic oxide scale on the surface acting as a diffusion barrier for oxygen and preventing the formation of tungsten oxide. Self-passivating tungsten alloys optimized for oxidation resistance containing ∼12wt.% Cr and ∼0.6wt.% Y are investigated under conditions of argon–oxygen, humid argon and humid air atmospheres at different partial pressures and temperatures ranging from 1073 to 1273K. Thin films with ∼3.5μm thickness produced by magnetron sputter deposition are used as a model system. The oxidation resistance of these films in an argon–20vol.% oxygen atmosphere is sufficient to prevent formation and release of tungsten oxide at temperatures of from 1073 to 1273K. The sublimation of Cr in nitrogen–oxygen–water atmosphere at T≥1273K is discussed. A deeper understanding of the governing processes for oxygen/Cr diffusion under different atmospheres is gained, supported by SEM/EDX in combination with FIB cross-section and TGA measurements.

Effect of Deposition Temperature on the Growth of Tungsten Oxide Layer Deposited on Polyethylene Terephthalate Fibers

Photocatalytically active tungsten oxide (WOx) layer were deposited on polyethylene terephthalate (PET) fibers using sol gel method in order to minimize the lost of WOx into flowing water during photocatalysis process. This helped to reduce the deterioration of photocatalytic performance of WOx over time as well as the formation of secondary pollutant by WOx particles. In this work, the optimum deposition condition of WOx layer was achieved using 90 ̊C deposition temperature. The photocatalytic activity of WOx layer in removal of Rhodamine B (RhB) dye followed first order kinetics. As much as 60.04%, and 32.18% of RhB dyes were removed using WOx layer grown on PET surface under UV light and visible light irradiation, respectively. Under UV light exposure and continuous circulation of RhB solution with a flow rate of 35mL/min, the wastewater purifier loaded with WOx layer based PET fibre showed 54.18% photodegradation efficiency. The repeated cycles of single WOx layer on PET fibers upon photodegradation of RhB observed good stability and reusability. Scavenger tests indicated that the holes and hydroxyl radicals were the dominant reactive species in photocatalytic degradation of RhB dye. Based on these findings, the photodegradation mechanism of RhB dye by WOx layer was proposed.

Comparison of Indium Tin Oxide and Indium Tungsten Oxide as Transparent Conductive Substrates for WO3-Based Electrochromic Devices

We compare two different transparent conducting oxides (TCO), namely indium tin oxide (ITO) and indium tungsten oxide (IWO), as substrates for the preparation of electrochromically active tungsten oxide (WO3) thin films by ultrasonic spray pyrolysis. The ITO- and IWO-coated glass substrates were prepared by magnetron sputtering at low temperatures, an interesting alternative to chemical vapor deposition at high temperatures. We report the electrochemical and electrochromic characteristics of WO3 deposited on the ITO- and IWO-coated glass substrates. Due to the application of WO3 as electrochromic material, particular attention was paid to the electron and ion transport, the cycling response, and the coloration/bleaching optical modulation and kinetics of the WO3 layer. The results are discussed in relation with the morphology, crystallinity and conductivity of the ITO/IWO layer.

From liquid to thin film: colloidal suspensions for tungsten oxide as an electrode material for Li-ion batteries

Using a colloidal suspension, electrochemically active tungsten oxide thin films (150 nm) have been prepared via ultrasonic spray deposition using two different current collectors, namely TiN and Pt.

Enhancing the Rate of Organic Material Decomposition Photo Catalyzed by High Performance Visible Light Activated Tungsten Oxide

We report a novel approach for increasing the rate of organic material decomposition photo-catalyzed by visible light activated tungsten oxide (WO3). It was confirmed that photo-catalysis by WO3 nano-particles fabricated by gas phase method and annealed at 600 °C for 1 hour achieves 30 times higher decomposition rate compared to photo-catalysis by commonly reported nitrogen doped titanium dioxides (TiO2). 1) The high decomposition rate in the presence of WO3 nano-particles could be attributed to their high crystalline quality and large surface area. It was also found that the decomposition rate can further be doubled by addition of metal oxides such as zirconium oxide (ZrO2) or TiO2. Furthermore, it is shown that immersing WO3 nano-particles mixed with ZrO2 or TiO2 in Pt colloid or Ru ionic solutions achieve complete decomposition of organic material to CO2 and H2O. These novel methods are already in the mass production stage.

Enhancing the Rate of Organic Material Decomposition Photo Catalyzed By High Performance Visible Light Activated Tungsten Oxide

We report a novel approach for increasing the rate of organic material decomposition photo-catalyzed by visible light activated tungsten oxide (WO3). It was confirmed that photo-catalysis by WO3 nano-particles fabricated by gas phase method and annealed at 600 °C for 1 hour achieves 30 times higher decomposition rate compared to photo-catalysis by commonly reported nitrogen doped titanium dioxides (TiO2). 1) The high decomposition rate in the presence of WO3 nano-particles could be attributed to their high crystalline quality and large surface area. It was also found that the decomposition rate can further be doubled by addition of metal oxides such as zirconium oxide (ZrO2) or TiO2. Increased adsorbability of organic material by the WO3 nano-particles as a result of ZrO2 or TiO2 addition could explain the observed enhancement in the decomposition rate. Furthermore, it is shown that immersing WO3 nano-particles mixed with ZrO2 or TiO2 in Pt colloid or Ru ionic solutions achieve complete decomposition of organic material to CO2 and H2O. This is made possible by the catalytic effect of Ru and Pt, which decreases the activation energy required for breaking down C-C bonds. These novel methods are already in the mass production stage.Experiment and ResultIt is well known that photo-catalyst activity improves with higher specific surface area and/or better crystallinity.In order to achieve higher surface area and improved crystallinity we fabricated nano-sized WO3 particles from vapor phase, followed by annealing at atmospheric conditions. A TEM image of the WO3 nano particles obtained from the ammonium paratungstate vapor is shown in Figure 1. The grain size was about 10 nm before annealing and about 20 nm after one hour 600°C annealing. The Raman spectra are shown in Figure 2. Before annealing the WO3 peaks at 700 and 800 cm-1 are broad, and the W=O terminating group peak appears in 930 cm-1. After annealing and at higher annealing temperatures the former two peaks become sharper, while the latter almost disappears. The peaks at 140, 270 and 320 cm-1 belong to monoclinic WO3 crystals and indicate improved cristallinity with monoclinic structure at higher annealing temperatures.2)3) With these WO3 nano particles organic material decomposed at a 30 times higher rate as compared to decomposition catalyzed by commonly reported nitrogen-doped titanium dioxides.(Fig. 3) Comparing the measured decrease of organic material concentration in the presence of WO3 with the reaction rate equations for the processes involved indicates that the decomposition rate is controlled by the speed of organic adsorption at the photocatalyst surface. To increase the adsorbability of the organic materials, metallic oxides such as ZrO2 and TiO2were added. As a result, the decomposition rate can further be doubled by addition of metal oxides.The remaining issue is the weaker oxidizing ability of WO3 as compared to TiO2. This diminishes WO3’s capability for decomposition of some organic molecules, e.g. acetic acids. As a solution to this problem it is proposed to add ruthenium or platinum by immersing the WO3 nano-particles mixed with ZrO2 or TiO2 in Pt colloid or Ru ionic solutions. These results suggest that complete decomposition of acetic acid with WO3photocatalyst may be possible, too. (Fig. 4)It is believed that the synthesized photocatalyst reported here, can be used as indoor deodorant.1) R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, Y. taga, Science, 293, 269 (2001)2) M. Boulova and G. Lucazeau, J. Solid State Chem. 167, 425(2002)3) A. G. Souza-Filho, V. N. Freire, J. M. Sasaki, J. Mendes Filho, J. F. Juliao, U.U. Gomes, J. Raman Spectrosc. 31, 451(2000)

Synthesis, characterisation and catalytic performance of a mesoporous tungsten silicate: W-TUD-1

Tungsten containing TUD-1 catalysts with Si/W ratios of 10–50 were synthesised by a two-step impregnation method and a direct one-step sol–gel method. The one-step method yielded finely dispersed catalytically active tungsten oxide nano-particles (<1nm) (at Si/W ratio above 20), while the two-step method yielded both tungsten oxide nano-particles and bulk tungsten oxide. This was established using INAA, N2 physisorption, powder XRD, Raman spectroscopy, TEM, diffuse reflectance UV–vis, FT-IR, H2-TPR and NH3-TPD analysis. Both types of catalyst preparation resulted in active acidic catalysts for the Prins cyclisation of citronellal. It was demonstrated that the finely dispersed tungsten oxide nano-particles were responsible for the catalytic activity.

Fine Cemented Carbide Particles Prepared with Activated Tungsten Oxide

Fine cemented carbide in the diameter of less than 1 μm is obtained activated tungsten oxide. The samples are characterized by laser particle size analyze, electron microscope and sclerometer. The experimental results show that the size of tungsten particles and tungsten carbide prepared with activated tungsten becomes small remarkably, and coarse tungsten particles decrease. The properties of cemented carbide prepared with activated tungsten oxide are better than those of cemented carbide made with blue tungsten oxide. Especially, the hardness of cemented carbide prepared with activated tungsten oxide increases by about 7 %.

Visible Light Activated Tungsten Oxide Sensors for NO2 Detection at Room Temperature

The sensing characteristics of tungsten oxide (WO3) gas sensors under visible light illumination have been investigated at room temperature. Sensing measurements were performed on sputtered (thin-film) and screen-printed (thick film) WO3 layers towards sub-ppm NO2. Light sources with different wavelength were employed to illuminate the WO3 sensors. The results showed that the light illumination effectively improved the NO2 sensing properties and the 475 nm light (blue colour) was the most effective for the WO3 sensors.

Sensing properties of Pt/Pd activated tungsten oxide films grown by simultaneous radio-frequency sputtering to reducing gases

1 at% platinum activated tungsten oxide (Pt–WO3) and 1 at% palladium activated WO3 (Pd–WO3) films were grown on Al2O3 substrates by a simultaneous radio-frequency sputtering process. The as-sputtered films were thermally treated at 450 °C for 24 h. Phase structure and chemical composition of the as-sputtered and thermally treated films were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. Sensing characteristics of the Pt–WO3 and Pd–WO3 films, as well as a pure WO3 film, were characterized with 25–200 ppm H2, 25–200 ppm CO and 0.62–5 ppm NH3 at various working temperatures and relative humidity of target gases. Effects of Pt and Pd on sensing characteristics of the sensors were compared and studied.

Using co-sputtered platinum or palladium activated tungsten oxide films to detect reducing gases

WO3, activated by 1% Pt or 1% Pd, was deposited by radio frequency co-sputtering process. The as-sputtered films were thermally-treated at 450°C for 24h after co-sputtering. The microstructure, crystal structure and chemical composition of the as-sputtered and thermally-treated films were analyzed by SEM, XRD and XPS. The sensing characteristics of the Pt or Pd activated WO3 films, as well as the pure WO3 films, were characterized with 25-200ppm H2, 25-200ppm CO and 0.62-5ppm NH3 at 50-300°C in air with different humidity.

Direct solid-state synthesis of tungsten carbide nanoparticles from mechanically activated tungsten oxide and graphite

Solid-state carbothermic reduction of tungsten oxide (WO 3) to nano-sized tungsten carbide (WC) particles was achieved by calcining mechanically activated mixtures of WO 3 and graphite at 1215 °C under vacuum condition. By experiments and thermodynamic calculations, the intermediate phases, WO 2.72, WO 2 and metallic tungsten (W), were observed at 741 °C, which decomposed to synthesize the final product (WC). Homogeneity increase and associated decrease in the diffusion path by mechanical milling and formation of these intermediates are mainly responsible for the successful production of WC. The process indicates that solid-state synthesis of WC nanoparticles directly from as-milled mixtures of tungsten oxide and graphite powder is possible.

Highly efficient tungsten trioxide containing mesocellular silica foam catalyst in the O-heterocyclization of cycloocta-1,5-diene with aqueous H2O2

Abstract WO 3 -containing mesocellular silica foam (MCF) catalysts have been synthesized via an in situ method by using tetraethyl orthosilicate (TEOS) and sodium tungstate as the precursors and via a traditional impregnation method. All catalysts are highly efficient in the O -heterocyclization of cycloocta-1,5-diene (COD) (see Scheme 1 in Section 3.2) to 2,6-dihydroxy-9-oxabicyclo[3.3.1]nonane ( 1 ) and 2-hydroxy-9-oxabicyclo[3.3.1]nonane-6-one ( 2 ) with a COD conversion up to 100% and ( 1 + 2 ) selectivity up to 98%. The WO x species are well dispersed in the W-containing catalysts via the in situ method with the WO 3 loading up to 20 wt.%, as proved by XRD, TEM, Raman, and UV–vis DRS. TPR and XRD results show that the WO 3 –MCF catalysts derived from the in situ method show much stronger interactions between active tungsten oxide species and the MCF support than the WO 3 /MCF obtained by the traditional impregnation method. The in situ method-derived catalyst also shows far better stability than the impregnation one according to the results from the recycling experiment.

High coloration performance of electrochromic devices assembled with electrolytes based on a branched boronate ester polymer and lithium perchlorate salt

An amorphous, colorless, and highly transparent polymer containing boron atoms in its branched chain architecture was synthesised from boron trioxide, poly(ethylene glycol) (PEG) and methoxy end-capped PEG. Electrolytes based on this polymer and different concentrations of lithium perchlorate (LiClO 4) were prepared and characterised by impedance spectroscopy, calorimetry and thermogravimetry. The results showed a thermal stability up to at least 150 °C, and conductivities reaching 10 − 4 S cm − 1 at room temperature. The latter value was much lower than that measured for a reference liquid electrolyte based on propylene carbonate (PC) and LiClO 4. The boron-containing electrolytes were further evaluated in electrochromic devices fabricated using transparent and electronically conducting SnO 2/F electrodes and electrochromically active tungsten oxide (WO 3) films. Their performance was compared with corresponding devices assembled using liquid and gel electrolytes based on LiClO 4 salt and PC. The best coloration performance was observed for the electrochromic device incorporating the boron-containing electrolyte having a molar ratio of [B]/[ClO 4] equal to 3:1. The value of the coloration efficiency was 59 cm 2 C − 1 for this device. Cyclic voltammetry further showed that the performance of this device was not affected by continuous cycling, and that 34 times less injected electric charge was needed in order to obtain the same coloration level compared to the device containing the liquid electrolyte (0.31 mC and 10.5 mC, respectively). In addition, improved durability and optical properties were observed for the former device when the coloration voltage was increased to 4 V, at which the device showed a very high contrast ratio of 7700.

Synthesis of highly active tungsten(VI) oxide photocatalysts for oxygen evolution by hydrothermal treatment of aqueous tungstic acid solutions

Tungsten(VI) oxide (WO3) powders of monoclinic crystal structure with high crystallinity have been synthesized by hydrothermal treatment (HTT), at 523 or 573 K, of aqueous tungstic acid (H2WO4) solutions prepared from sodium tungstate by ion-exchange (IE) with a proton-type resin. HTT and/or calcination of home-made and commercial H2WO4 solids of tungstite structure also produced WO3. These WO3 powders with various physical properties were used as photocatalysts for evolution of oxygen (O2) from an aqueous silver sulfate solution, and the correlation between their physical properties and photocatalytic activity was examined. WO3 powders of high crystallinity, e.g., IE-HTT-WO3 synthesized at 573 K, gave the highest O2 yield, suggesting that the crystallinity of WO3 is a key factor in its high activity for this reaction system. Calcination at <1073 K improved the crystallinity of some WO3 powders, resulting in increases in their activities; however, calcination at a higher temperature reduced the activity, presumably due to formation of oxygen vacancies acting as recombination centers.