WO3 Content Research Articles

A novel process on preparation of ammonium metatungstate solution using bipolar membrane electrodialysis

ABSTRACTAn industrial (NH4)2WO4 solution was used to directly prepare ammonium metatungstate solution using bipolar membrane electrodialysis. The effects of current density, initial concentrations of NH4HCO3 and WO3 in feeds, temperature and pH of product solution on the process were investigated. A continuous running test was carried out under the optimum conditions and the results showed that the direct recovery of WO3 reached 99.97% with average current efficiency of 72.5% and power consumption of 0.877 kWh kg−1 WO3 using a feed solution containing 172.3 g L−1 WO3 and a base solution containing 1.5 mol L−1 NH4HCO3 with a current density of 700 A m−2 and a solution pH in salt compartment of 2.8 at 31°C for 600 min, indicating easy and stable operation of the bipolar membrane electrodialysis process.

Multi-property improvement of TiO2-WO3 mixed oxide films deposited on 316L stainless steel by electrophoretic method

Titanium dioxide (TiO2) is widely employed in many domains, such as photo-catalysis, self-cleaning and bio-medical applications due to its photocatalytic properties and high chemical stability. However, its mechanical and tribological properties as well as its resistance to corrosion can be improved by the addition of the other elements. The aim of the present work is to study the impact of adding WO3 in TiO2-WO3 composites coating on the mechanical and tribological properties as well as on the corrosion resistance. In this work, TiO2-WO3 composites were obtained with using different amounts of WO3. Structural properties of the coatings were analyzed using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDXS) and scanning electron microscopy (SEM). Besides, mechanical properties were investigated by nano-indentation measurements. Micro-scratch tester was performed to evaluate the tribological properties. Potentiodynamic polarization and electrochemical impedance spectroscopy of composite coating were measured through electrochemical tests. Obviously, thin film with the highest amount of tungsten (Ti50W50)Ox was characterized by the best mechanical properties compared to the result obtained for the pure TiO2 coating. In addition, the increase of the WO3 content in the coating allowed improving the tribological properties.

Synthesis and properties of nanocomposites of WO3 and exfoliated g-C3N4

Abstract The nanocomposites of WO3 nanoparticles and exfoliated graphitized C3N4 (g-C3N4) particles were prepared and their properties were studied. For this purpose, common methods used for characterization of solid samples were completed with dynamic light scattering (DLS) method and photocatalysis, which are suitable for study of aqueous dispersions. The WO3 nanoparticles of monoclinic structures were prepared by a hydrothermal method from sodium tungstate and g-C3N4 particles were prepared by calcination of melamine forming bulk g-C3N4, which was further thermally exfoliated. Its specific surface area (SSA) was 115 m2 g−1. The nanocomposites were prepared by mixing of WO3 nanoparticles and g-C3N4 structures in aqueous dispersions acidified by hydrochloric acid at pH = 2 followed by their separation and calcination at 450 °C. The real content of WO3 was determined at 19 wt%, 52 wt% and 63 wt%. It was found by the DLS analysis that the g-C3N4 particles were covered by the WO3 nanoparticles or their agglomerates creating the nanocomposites that were stable in aqueous dispersions even under intensive ultrasonic field. Using transmission electron microscopy (TEM) the average size of the pure WO3 nanoparticles and those in the nanocomposites was 73 nm and 72 nm, respectively. The formation of heterojunction between both components was investigated by UV–Vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photocatalysis and photocurrent measurements. The photocatalytic decomposition of phenol under the LED source of 416 nm identified the formation of Z-scheme heterojunction, which was confirmed by the photocurrents measurements. The photocatalytic activity of the nanocomposites decreased with the increasing content of WO3, which was explained by shielding of the g-C3N4 surface by bigger WO3 agglomerates. This study also demonstrates a unique combination of various characterization techniques working in solid and liquid phase.

Hydrothermal preparation of reduced graphene oxide/tungsten trioxide nanocomposites with enhanced electrochemical performance

A series of rGO/WO3 nanocomposites have been synthesized in this study using the single-step hydrothermal approach by varying the concentration of WO3 for supercapacitor applications. Accordingly, the effect of different WO3 contents on the electrochemical performance of rGO/WO3 was extensively studied. It was noteworthy that rGO/WO3 nanocomposite with mass ratio of 1:100 showed the highest specific capacitance (i.e., 274 F g−1 at current density of 0.7 A g−1) at 150 °C with a reaction time of 20 h. By careful control of the synthesis parameters, rGO/WO3 with fibers-like structure could be obtained. Correspondingly, this structure can lower the resistance and shorten the diffusion pathway coupled with offering more reactive sites for electrolyte. A possible growth mechanism of WO3 deposited on rGO was also proposed in the presence work. Additionally, this piece of work also provided a better understanding the roles of fiber-like WO3 anchored on rGO/WO3 nanocomposites for efficient electrochemical capacitor.

Evaluation of physical, structural properties and shielding parameters for K2O–WO3–TeO2 glasses for gamma ray shielding applications

In the present work, a series of ternary glasses in the K2O–WO3–TeO2 system have been synthesized by conventional melt quenching technique. Glass formation range of the selected glass system was determined and physical, structural and radiation shielding properties of the glasses were investigated. Density (ρ), molar volume (VM), oxygen molar volume (VO), oxygen packing density (OPD), average cross-link density (nc¯), the number of bonds per unit volume (nb) and Poisson's ratio (μcal) values were evaluated for the interpretation of physical and structural properties. Fourier transform infrared (FTIR) spectra of the glasses were analyzed in order to obtain the information on the structural transformations in the glass network following the equimolar substitution of TeO2 by K2O + WO3 and changing K2O or WO3 at constant TeO2. Increasing K2O at constant TeO2 decreases the network connectivity due to the formation of non-bridging oxygen sites and the glass network became less tightly packed. On the other hand, equimolar substitution of TeO2 with WO3+K2O in these glasses resulted in a more compact glass network. The mass attenuation coefficients have been computed using WinXCom program and the obtained values were used to calculate the half value layer, the effective atomic number and the electron density. In addition, the macroscopic effective removal cross-section for fast neutron values are also evaluated. The variation of shielding parameters was discussed for WO3 variation in the glass composition and photon energy. From the derived results, it was found that K30W60T10 is the best glass in terms of shielding effectiveness among all the studied glasses due to higher values for mass attenuation coefficient, effective atomic number, and electron density and lower values of half value layer. These glasses show potentiality to be used as shielding materials and for an improved shielding effectiveness of the K2O–WO3–TeO2 glasses, a large WO3 content would be required.

Structural, magnetic and electromagnetic wave absorption properties of WO3–CuFe2O4: a novel nanocomposite

Novel WO3–CuFe2O4 nanocomposites with significantly higher electromagnetic wave absorption properties have been synthesized. The synthesized nanocomposites exhibit coexistence of both phases at higher WO3 concentrations without impurity phases as confirmed by XRD and FTIR studies. TEM micrographs demonstrate the formation of CuFe2O4 nanoparticles embedded in WO3 shells. FTIR results reveal the presence of characteristic stretching and vibration modes associated with WO3 and CuFe2O4. The magnetic measurements show the ferromagnetic behavior of all studied samples. However the saturation magnetization has shown a decreasing behavior while coercivity increases with the concentration of incorporated WO3. The WO3 concentration up to 30 wt% enhances the microwaves absorption properties (−26.32 dB at frequency 6.6 GHz) and shifts the absorption maximum curve to higher frequency.

Compositional dependence of thermal, optical and mechanical properties of oxyfluoride glass

Tungsten oxyfluoride glasses are characterized by low phonon energy. This is due to the presence of fluoride ions that have low phonon energy and formation of low phonon energy WO6 units. Oxyfluoride glasses based on WO3–BaF2–RF, where RF = LiF, NaF or mixed (LiF–NaF) have been prepared by melt quenching technique. The density and molar volume of the prepared glasses show a decrease with the increase of RF instead of WO3 content. The glass transition temperature Tg is found to decrease with increasing RF content. The refractive index increases with the addition of heavy polarizable fluorides. The decrease of the elastic moduli and microhardness of these glasses may be due to the decrease in density and the depolymrization effect. The Poisson’s ratio increases with increasing RF content due to the structural changes and formation of (NBOs) and (NBF) units. The aim of this work is to prepare a glass host with low phonon energy to be an efficient host with good luminescence properties, when doped with rare earth ions, and to study its structural, thermal, optical and mechanical properties.

Three-Dimensional TiO2 Structures Incorporated with Tungsten Oxide for Treatment of Toxic Aromatic Volatile Compounds

This study assessed 3D WO3–TiO2 nanoflowers (WTNF) synthesized by a combined hydrothermal–ultrasonication–impregnation method for their applicability to the treatment of aromatic volatile compounds under visible-light illumination. The scanning electron microscopy exhibited the formation of 3D structures in the prepared WTNF samples. The X-ray diffraction patterns and energy dispersive X-ray results indicated a successful incorporation of WO3 into TNF structures. The UV-visible spectroscopy showed that the prepared WTNF samples can be functioned under visible light irradiation. The output-to-input concentration ratios of toluene and o-xylene with WTNF samples were lower than those of TiO2 nanoflowers. These findings were illustrated on the basis of charge separation ability, adsorption capability, and light absorption of the sample photocatalysts. The input-to-output concentration ratios of the target chemicals were lowest for 10 M NaOH and highest for 5 M NaOH. The photocatalytic degradation efficiencies of WTNF sample photocatalysts increased with increasing WO3 content from 0.1% to 1.0%, and dropped gradually with increasing WO3 content further to 4.0%. Light-emitting-diodes (LEDs) are a more highly energy-efficient light source compared to a conventional lamp for the photocatalytic degradation of toluene and o-xylene, although the photocatalytic activity is higher for the conventional lamp.

Effects of phosphoric acid and ageing time on solvent extraction behavior of phosphotungstic acid

A sulfuric-phosphoric acid leaching process for scheelite was developed. In the process, tungsten exists as a soluble phosphotungstic acid in the leachate. Thus, extracting tungsten from the solution is necessary. Considering the advantages of solvent extraction with oxygen-containing solvents, 2-octanol and tri-butyl phosphate (TBP) were employed to extract tungsten from phosphotungstic-sulfuric acid solutions. The impacts of phosphoric acid and ageing time on the extraction were primarily investigated. It was determined that for H3PW12O40 solution with high H2SO4 (49.71g/L S) content, the WO3 content in raffinates remained as low as 0.01g/L after a single stage extraction even if the ageing time increased. However, if such solution contained high H3PO4 (113.95g/L P), the remaining WO3 content increased to approximately 0.29g/L after aged for 0.5h. And, it further increased to 1.06 and 2.16g/L after ageing for 24h and 14days. It indicated that phosphoric acid and ageing time played an anti-synergistic effect on the extraction. Furthermore, for the solution with abundant H3PO4 aged for 0.5h, the 31P NMR results showed there were only the characteristic peak of H3PW12O40 (δ=−16.24ppm) and the peak of H3PO4 (δ=−0.96ppm). However, an unknown peak (δ=−2.80ppm) appeared in the spectrum of such solution aged for two weeks and that of its raffinate. This finding implies that the combination reaction between phosphoric and phosphotungstic acid creates another species that is difficult to extract. Therefore, to obtain satisfactory extraction efficiency, the dosage of phosphoric acid should be controlled during the mineral decomposition stage.

Green synthesis of UV and visible light active TiO2/WO3 powders and films for malachite green and ethylene photodegradation

Powder nanocomposites of TiO2/WO3 are prepared by a simple solid-state thermal procedure from commercial oxide powders and cast thereafter as a film coating on TLC substrate. The WO3 content in the powder composites is varied from 0.5 to 50%. The phase composition and morphology of titania/tungsten composites and films is characterized by SEM and X-ray analysis. The photocatalytic activity of TiO2/WO3 powders is tested in the degradation of malachite green dye in aqueous solutions under UV and visible light irradiation. The effect of preparation temperature on the photocatalytic activity is also investigated. It is found out that the mixed powder of 5%WO3 manifests the best photocatalytic performance. The prepared powder photocatalyst is deposited as a film coating on TLC sheet for gas-phase application. The as-obtained composite coated photocatalysts with 5%WO3 are tested for air purification from ethylene contamination under UV and visible light illumination. The TiO2/WO3 coated photocatalysts show always a higher efficiency in comparison to that of the pure TiO2.

Electrochemical synthesis of tetragonal oxide tungsten bronze nanofilms on platinum

We are the first to synthesize nanofilms of tetragonal oxide tungsten bronze (OTB) on a Pt(110) substrate by the electrolysis of the K2WO4–Na2WO4–WO3 melt at 700 and 750°C. The composition and the morphology of OTB are shown to depend on the deposition potential and the WO3 concentration in the melt. The laws of formation of tetragonal OTB films are discussed. The synthesized OTB samples are found to have a good thermal stability in the temperature range 20–800°C.

Enhancing the Corrosion Inhibition Behaviour of Epoxidized Natural Rubber-Polyaniline Dodecylbenzenesulfonate Blend via the Incorporation of WO3

Electrically-conductive (in the region of 10−3 S.cm−1) epoxidized natural rubber-polyaniline dodecylbenzenesulfonate [ENR-PAni.DBSA] blend was prepared, and the effect of incorporation of WO3 on its corrosion inhibition behaviour for carbon steel was assessed for the first time. It was found that the electrical conductivity of this blend could be enhanced by up to an order of magnitude for WO3 loadings of 20.0–22.5 wt.%. From both total immersion and electrochemical corrosion tests, ENR-PAni.DBSA blends with 20.0–22.5 wt.% of WO3 were found to be the best corrosion inhibitors for carbon steel, in both acid and artificial brine environments. However, a blend containing a higher WO3 content (i.e. 25.0 wt.%) showed a significant poorer corrosion inhibition behaviour for carbon steel due to its more severe phase separation and porosity between the ENR host matrix and WO3.

Hydrothermal fabrication of WO3-modified TiO2 crystals and their efficiency in photocatalytic degradation of FCF

WO3-modified TiO2 polyscale crystals were fabricated successfully using the hydrothermal technique. The as-prepared samples were characterized using powder X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, photoluminescence spectroscopy and UV–vis spectroscopy. The photocatalytic application of these synthesized samples was confirmed by photocatalytic degradation of fast green dye solution under sunlight and UV irradiation. The degradation efficiency was analyzed by measuring the parameters such as percent transmittance, chemical oxygen demand and percent decomposition of the dye solution. It was noted that the photodegradation efficiency of the samples varies with added amounts of WO3 content. The highest photodegradation efficiency was obtained using 2WT sample where the pace of decomposition was 70.5% under UV light and 81.3% under sunlight.

Mixed Ion-Polaron Glasses as New Cathode Materials

Electrical transport in mixed ion-polaron glasses has been investigated in four series of glasses containing transition metal oxides (TMO) namely WO3/MoO3, and Na+/Ag+ ions with the composition xWO3- (30-0.5x)Na2O-(30-0.5x)ZnO-40P2O5, xWO3-(30- 0.5x)Ag2O-(30-0.5x)ZnO-40P2O5, xMoO3-(30-0.5x)Na2O- (30-0.5x)ZnO-40P2O5, and xMoO3-(30-0.5x)Ag2O-(30- 0.5x)ZnO-40P2O5, 0 ≤ x ≤ 60 (mol%). The DC conductivity of Na-glasses up to 30 mol% of WO3 and MoO3 is almost identical due to the dominance of ionic conductivity. In this compositional region, the introduction of tungstate and molybdate units increases the mobility of sodium ions and compensates the decrease in sodium number density. On the other hand, with increasing WO3 and MoO3 content and decreasing Ag+ ion concentration in Ag-glasses the DC conductivity decreases for few orders of magnitude. A significant difference in conductivity is observed for glasses with higher WO3 and MoO3 content. While for glasses containing WO3 the conductivity rapidly increases due to a huge polaronic contribution indicating a turnover from predominantly ionic to polaronic transport, the conductivity for MoO3- glasses decreases in the entire mixed compositional range suggesting dominant ionic transport. The changes in the conduction mechanism with the systematic alternation of the glass composition have been analyzed in correlation with the structural modifications and variations of molybdenum and tungsten in different oxidation states.

Catalytic Activity and Surface Characteristics of WO3-doped MnOx-TiO2 Catalysts for Low-temperature Selective Catalytic Reduction of NOx with NH3

The effect of added WO₃ on the catalytic activity and surface characteristics of the MnOx-TiO₂ system was investigated for the low-temperature selective catalytic reduction of NOx with NH₃. Based on physio-chemical characterizations, the specific surface areas of the WO₃-MnOx-TiO₂ catalysts increased from 76.12m²/g to 90.29m²/g as the WO₃ content increased, and crystallinity of the anatase TiO₂ phase decreased. The NOx conversion efficiency of the WO₃-MnOx-TiO₂ catalysts with WO₃ contents was over 70% at 200 °C, and their efficiency was over 90% at 300 °C. The results of Fourier transform infrared spectroscopy indicated that the 1438 and 1632 cm-1 values, which were assigned to Lewis and Bronsted acid sites, increased with the increase in WO₃ content. The enhanced catalytic acidity originated from changes to the physical and chemical structures on the surface. MmOx formed on the TiO₂ surface of the 15 wt% WO₃-doped MnOx-TiO₂, and amorphous state Mn2O3 (Mn3+) and WO3 (W6+) existed on the surface, which led to the improved Lewis and Bronsted acid sites, respectively.

Ambient pressure drying synthesis of Cs0.33WO3/SiO2 composite aerogels for efficient removal of Rhodamine B from water

A novel Cs0.33WO3/SiO2 composite aerogel was synthesized by ambient pressure drying process using hexamethyldisiloxane/HCl for the surface modification of the wet gel. The influences of Cs0.33WO3 content on the microstructure, pore characteristics and adsorption/photocatalytic activity of the composite aerogels were investigated. The as-prepared composite aerogels exhibited higher specific surface area with 265–465m2/g and pore volume with 1.11–1.86cm3/g. After being heat-treated at 550°C, the composite aerogels transformed from hydrophobicity to hydrophilicity without changing the main phase of Cs0.33WO3, which indicated that the outer SiO2 aerogel could improve the oxidation resistance of Cs0.33WO3 greatly. Furthermore, the specific surface area and pore volume of the composite aerogels with appropriate composition even have an increasing trend after heat-treatment. The adsorption mechanism of Rhodamine B on the Cs0.33WO3/SiO2 composite aerogels with different Cs0.33WO3 content was studied using kinetic adsorption models, and the photocatalytic degradation of Rhodamine B was evaluated. The results indicated that the adsorption kinetics of the composite aerogels followed the pseudo-second-order model with the adsorption process being mainly based on chemical adsorption and physical adsorption playing a role as assistance. The composite aerogels exhibited excellent adsorptivity/photocatalytic degradation performance and higher recycling efficiency for the pollutant Rhodamine B.

Construction of solid-state Z-scheme carbon-modified TiO2/WO3 nanofibers with enhanced photocatalytic hydrogen production

Abstract Carbon-layer-coated TiO 2 /WO 3 nanofibers (WTC) were fabricated by combining the electrospinning technique (for TiO 2 /WO 3 nanofibers) and hydrothermal method (for carbon shell). The structure characterization results showed that TiO 2 /WO 3 nanofibers (WT) were encased within an uniform carbon shell about 10 nm in thickness. By adjusting the content of WO 3 , the graphitization degree of carbon layer could be controlled, and the WTC nanofibers had remarkable light absorption in the visible region. Furthermore, the photoelectrochemical performance and photocatalytic activity were investigated systematically. As expected, the H 2 -generation rate of the as-prepared composite materials was greatly enhanced compared with pure TiO 2 nanofibers (TNFs), TiO 2 /WO 3 nanofibers (WT) and TiO 2 @carbon core/shell nanofibers (TC). The enhanced activities were mainly attributed to the multichannel-improved charge-carrier photosynthetic heterojunction system with the carbon layer on the surface of TiO 2 as an electron collector and WO 3 as a hole collector, leading to effective charge separation on these components, which were evidenced by photoluminescence spectroscopy (PL), electrochemical impedance spectroscopy (EIS) and photocurrent analysis. Besides, the addition of WO 3 promoted the graphitization of carbon layer, which in turn improved transport of electrons in the carbon layer and also contributed to the performance improvement.

Facile preparation of Z-scheme WO3/g-C3N4 composite photocatalyst with enhanced photocatalytic performance under visible light

Visible-light-driven WO3/g-C3N4 composites photocatalysts were synthesized via a facile one-step simultaneously heating procedure with urea as the main precursor. These prepared catalyst samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), transmission electron microscopy (TEM), N2 adsorption, ultraviolet-visible diffuse reflection spectroscopy (UV–vis), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and electrochemical impedance spectroscopy (EIS). The photocatalytic activity of the WO3/g-C3N4 composites was evaluated by the photo-degradation of Rhodamine B (RhB) under visible light irradiation. The results indicated that the composites with 25wt.% WO3 content exhibited highest photocatalytic activity compared to pure WO3, bare g-C3N4 and other WO3/g-C3N4 composites. The favorable photocatalytic activity of WO3/g-C3N4 composites was mainly attributed to the excellent surface properties, enhanced visible-light absorption and the desirable band positions. A possible Z-scheme photocatalytic mechanism was proposed based on structure and electrochemical characterizations results, which can well explain the enhanced migration rate of photogenerated electrons and holes in WO3/g-C3N4 heterojunctions.

V<sub>2</sub>O<sub>5</sub>-WO<sub>3</sub>/TiO<sub>2</sub> Catalysts for Low Temperature NH<sub>3</sub> SCR: Catalytic Activity and Characterization

A systematic investigation of the effect of WO3 loading over V2O5/TiO2 catalysts was carried out for the selective catalytic reduction of NO by NH3. The characteristics were examined use BET surface area , X-ray diffractometry (XRD) , Temperature programmed desorption (TPD) of NH3 . It was fund that the WO3 species could interact with the TiO2 anatase phase to exhibits a high activity. With increasing WO3 content ,the activity of V-W/TiO2 for the selective catalytic reduction of NO by NH3 was improved at low temperatures in the range of 3～7%. The results showed that the adding of WO3 to V2O5/TiO2 could result in exposing acid sites of catalysts doped WO3 at low temperature. Furthermore, especially the catalytic activity of VW7Ti showed higher than 80% at 180 °C. However, the catalytic BET surface area and the mass of acid sites not play a leading role for improving low-temperature activity of VWTi in this paper.

Solar photocatalytic degradation of sulfamethoxazole over tungsten – Modified TiO2

Ten x% W-P25(T) composite catalysts were synthesized, characterized and tested for the photocatalytic degradation of antibiotic sulfamethoxazole (SMX), where x=1–6wt.% is the WO3 content and T=600–900°C is the calcination temperature applied for the preparation of catalysts. Modification of TiO2 with tungsten results in materials with higher anatase content and specific surface area, compared to undoped samples calcined at the same temperature, and in a small shift of the absorption threshold toward the visible region.Screening experiments showed that the 4% W-P25(700) catalyst was the most active for SMX degradation (350μg/L) under simulated solar irradiation enhancing the rate of pristine P25-TiO2 by 50%; this catalyst was used in subsequent kinetic and mechanistic experiments.The rate of degradation increases with increasing catalyst concentration in the range 10–250mg/L, while experiments at varying SMX concentration show a transition from first (at 200μg/L) to zeroth (at 1000μg/L) order kinetics. Degradation in actual matrices (wastewater and drinking water) is slower than in pure water due to the presence of non-target organics and anions; nonetheless, the presence of electron acceptors such as hydrogen peroxide or sodium persulfate enhances considerably degradation rates.SMX degradation proceeds through the formation of several primary and secondary transformation by-products (TBPs) as evidenced by LC-TOF-MS analysis. Based on the identified TBPs and their temporal evolution profiles, transformation pathways are proposed. The antimicrobial activity of SMX and its TBPs was tested against Escherichia coli and Enterococcus faecalis reference strains, showing that toxicity partially decreases upon oxidation.