Tungstic Acid Research Articles

Durability improvement of electrochromic WO3 thin films by deposition of an ultra-thin Al2O3 layer via atomic layer deposition

Introduction of an ultra-thin Al2O3 protective layer via atomic layer deposition (ALD) significantly enhances the durability and performance of amorphous tungsten trioxide (a-WO3) thin films for electrochromic devices. The Al2O3 layer, despite being less than 4 nm thick, effectively suppresses the dissolution of WO3 that typically occurs through hydration reactions forming WO3·H2O and tungstic acid (H2WO4). XRD and XPS analyses confirmed the presence of Al2O3 and its minimal impact on the amorphous structure of WO3 thin films. Optical transmittance measurements showed that the Al2O3-protected a-WO3 thin films maintained a higher transmittance modulation (ΔT) compared to bare a-WO3 thin films, with the ALD30 sample retaining 87.9 % of its initial transmittance modulation after 1000 cycles, in contrast to the rapid degradation observed in unprotected films. Microstructural analysis revealed significantly fewer surface cracks and reduced thickness loss in Al2O3-coated films after 100 cycles. Additionally, ICP-MS analysis indicated a much lower W concentration in the electrolyte for Al2O3-protected samples, confirming reduced dissolution.

One-Pot Fabrication of Copper-Doped WO3·H2O Opto-Functional Layered Device using Submerged Photosynthesis of Crystallites.

This study introduces a one-pot, submerged photosynthesis of crystallites (SPsC) method for fabricating monohydrate tungstic acid (WO3·H2O) nanoplates directly integrated onto a stainless steel mesh, offering a simplified production and enhanced device stability for optical functional applications. The fabricated devices demonstrate exceptional broadband light absorption across the ultraviolet (UV), visible (Vis), and near-infrared (NIR) ranges. Notably, 1% Cu doping significantly boosts the NIR absorption, yielding a high solar utilization efficiency of 81.40%. In solar water evaporation experiments, the devices exhibit a maximum temperature increase of 13 °C under 1-Sun (100 mW/cm2) illumination, achieving an energy conversion efficiency of 32.5%. Moreover, electrochemical characterization reveals light-induced conductivity changes and enhanced current density, suggesting potential applications in rectifying devices. This versatile and environmentally conscious SPsC fabrication method holds promise for the sustainable development of diverse nanodevices.

Insight into the chemistry of Folin’s test for uric acid

Folin developed an analytical technique for uric acid spectroscopic determination. It is based on the interaction of uric acid with sodium tungstate in phosphoric acid. This produces an intense blue colour after alkalinization, whose concentration is measured. However, the structure of the organic product obtained was not mentioned. The present communication gives the references related to each reaction step, as well as information about the reaction products obtained in uric acid oxidations carried-out in acidic or in alkaline mediums. The reaction route is as follows: addition of tungstic acid to the C-C double bond, acidolysis of the organo-metallic ester, producing tungstic subacid and an epoxide. Oxirane opening to vicinal diol after reaction with water. Two carbinolamines result, which are broken by protonation at the nitrogen; carbonyl groups are formed at C-4 and C-5 with concomitant elimination of a urea molecule. This way alloxan monohydrate is formed. The blue products obtained are described.

Cs-Doped WO3 with Enhanced Conduction Band for Efficient Photocatalytic Oxygen Evolution Reaction Driven by Long-Wavelength Visible Light.

Cesium doped WO3 (Cs-WO3) photocatalyst with high and stable oxidation activity was successfully synthesized by a one-step hydrothermal method using Cs2CO3 as the doped metal ion source and tungstic acid (H2WO4) as the tungsten source. A series of analytical characterization tools and oxygen precipitation activity tests were used to compare the effects of different additions of Cs2CO3 on the crystal structure and microscopic morphologies. The UV-visible diffuse reflectance spectra (DRS) of Cs-doped material exhibited a significant red shift in the absorption edge with new shoulders appearing at 440-520 nm. The formation of an oxygen vacancy was confirmed in Cs-WO3 by the EPR signal, which can effectively regulate the electronic structure of the catalyst surface and contribute to improving the activity of the oxygen evolution reaction (OER). The photocatalytic OER results showed that the Cs-WO3-0.1 exhibited the optimal oxygen precipitation activity, reaching 58.28 µmol at 6 h, which was greater than six times higher than that of WO3-0 (9.76 μmol). It can be attributed to the synergistic effect of the increase in the conduction band position of Cs-WO3-0.1 (0.11 V) and oxygen vacancies compared to WO3-0, which accelerate the electron conduction rate and slow down the rapid compounding of photogenerated electrons-holes, improving the water-catalytic oxygen precipitation activity of WO3.

Nanomaterials functionalized acidic ionic organosilica as highly active catalyst in the selective synthesis of benzimidazole via dehydrogenative coupling of diamines and alcohols

An acidic tungstate-based zwitterionic organosilica drived simple self-condensation of tungstic acid and zwitterionic organosilane (PMO-IL-WO42−), was remarkably demonstrated to be highly efficient and environmentally friendly catalyst for directly selective synthesis of benzimidazoles from benzyl alcohols under atmpshpheric air pressure and without any additional oxidant. The one-pot synthesis of benzimidazoles from benzyl alcohols and 1,2-phenylenediamine was efficiently achieved via direct dehydrogenative reaction using a low amount of recoverable PMO-IL-WO42− nanocatalyst in water under ambient conditions with a conversion efficiency of more than 90%. Enhancements in yield and selectivity of benzimidazole formation were observed when water was utilized as the solvent. Furthermore, the PMO-IL-WO42− nanocatalyst exhibited exceptional stability, demonstrating the ability to be effortlessly separated and reused for at least eight reaction cycles without any noticeable loss in activity or product selectivity. This method supports an eco-friendly atom economy and provides a sustainable approach to accessing benzimidazoles directly from benzyl alcohols under mild conditions, demonstrating its potential for practical applications in organic synthesis.

Physicochemical Properties of Tungsten Trioxide Photoanodes Fabricated by Wet Coating of Soluble, Particulate, and Mixed Precursors

Advanced oxidation processes are emerging technologies for the decomposition of organic pollutants in various types of water by harnessing solar energy. The purpose of this study is to examine the physicochemical characteristics of tungsten(VI) oxide (WO3) photoanodes, with the aim of enhancing oxidation processes in the treatment of water. The fabrication of WO3 coatings on conductive fluorine-doped tin oxide (FTO) substrates was achieved through a wet coating process that utilized three different liquid formulations: a dispersion of finely milled WO3 particles, a fully soluble WO3 precursor (acetylated peroxo tungstic acid), and a combination of both (applying a brick-and-mortar strategy). Upon subjecting the WO3 coatings to firing at a temperature of 450 °C, it was observed that their properties exhibited marked variations. The fabricated photoanodes are examined using a range of analytical techniques, including profilometry, thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), and voltammetry. The experimental data suggest that the layers generated through the combination of particulate ink and soluble precursor (referred to as the brick-and-mortar building approach) display advantageous physicochemical properties, rendering them suitable for use as photoanodes in photoelectrochemical cells.

Tungstic acid integrated metal–organic frameworks for efficient oxygen evolution reaction

Mimicking the isolated and encapsulated active manganese sites within proteins in nature through the integration of NiFe sites and tungstic acid nanoparticles in an ordered open framework in an isolated manner.

In-situ construction of g-C3N4/WO3 heterojunction composite with significantly enhanced photocatalytic degradation performance

g-C3N4/WO3 heterojunction composites were synthesized via an in-situ method by thermal polymerizing the mixture of dual precursors (urea and thiourea with molar ratio of 3:1) and different amount of tungstic acid. The as-synthesized g-C3N4/WO3 composites, with lamellar and rod-like nano-porous structure, were mainly composed of g-C3N4 and monoclinic WO3, in which the crystal size of WO3 was about 5–10 nm. The specific surface area of the composite increased gradually with the tungstic acid dosage and reached 79.41 m2/g when the addition amount of tungstic acid was 1 wt%. The in-situ construction of g-C3N4/WO3 heterojunction contributed to the reduction of band gap, improvement of the visible response range as well as the acceleration of the separation and migration of the photogenerated carriers. As the dosage of tungstic acid increased, the photocatalytic degradation performance of g-C3N4/WO3 composite towards tetracycline improved gradually and achieved the optimum when the addition amount of tungstic acid was 0.1 wt% (CN/WO3-10). CN/WO3-10 (0.05g) degraded 83 % of tetracycline molecules (100 mL, 20 mg/L) after photocatalysis for 100 min, whose degradation rate constant was 10.1 and 1.48 times that of pure WO3 and g-C3N4, respectively. Moreover, g-C3N4/WO3 composite exhibited excellent stability and reusability for the photocatalytic degrading tetracycline. This work provides a facile and practicable approach for the preparation of g-C3N4/WO3 composite.

Hydrothermal synthesis of hierarchical microstructure tungsten oxide/carbon nanocomposite for supercapacitor application

A hierarchical nanocomposite of carbon microspheres decorated with tungsten oxide (WO3) nanocrystals resulted from the hydrothermal treatment of a precursor solution containing glucose and tungstic acid. The dehydration of glucose molecules formed oligosaccharides, which consequently carbonized, turning into carbon microspheres. The carbon microspheres then acted as a spherical nucleus onto which WO3 nanocrystals grew via heterogeneous nucleation. The reaction product showed a phase junction of orthorhombic and monoclinic WO3, which transitioned to mix-phase of tetragonal and monoclinic WO3 after a subsequent heat treatment at 600 °C in an inert condition. The electrochemical tests showed that incorporating WO3 onto the carbon (WO3/C) resulted in a three-fold increase in the specific capacitance compared to WO3 alone and a high coulombic and energy efficiencies of 98.2% and 92.8%, respectively. The nanocomposite exhibited supercapacitance with both Faradaic and non-Faradaic charge storage mechanisms. Electrochemical impedance spectroscopy showed a lower charge transfer resistance for the composite at Rct = 11.7Ω.

Defect Driven Opto-Critical Phases Tuned for All-Solar Utilization.

Materials imbued with uniformly dispersed, photo-responsive nanoparticles are instrumental in sustainable energy and photonic applications. Conventional methods, however, constrain their all-solar response. An innovative alternative is proposed: submerged photo-synthesis of crystallites (SPsC). It is shown that strategic doping with copper and oxygen vacancies can induce opto-critical phases from the non-stoichiometric tungstic acids (WO3 ·H2 O). These opto-critical phases enable a dynamic equilibrium shift in lattice defect stabilization, facilitating an unprecedented a whole solar wavelength response. This response manifests as photothermal, photo-assisted water evaporation, and photo-electrochemical characteristics. Harnessing all-solar energy, this one-pot SPsC strategy may steer the design and development of advanced oxide materials, enhancing functionality across diverse application domains. This article is protected by copyright. All rights reserved.

Breaking the C[sbnd]C bond of glucose on tungsten oxide-based catalysts in aqueous phase

In chemistry, selective activation of CC bonds enables the direct production of valuable chemicals from widely available and inexpensive natural materials but remains a fundamental challenge due to their kinetic inertness. The selective cleavage of CC bond in glucose by tungsten oxide-based catalysts in aqueous phase pioneers a path for converting cellulose biomass into valuable ethylene glycol. However, debates regarding the active phase and how it selectively breaks the C6 into C2 fragments have persisted for over a decade. In this study, we present a comprehensive mechanistic investigation by modeling three potential active phases, i.e. the reduced WO3-x surface, the dissolved tungstic acid, and tungsten bronze, in explicit solvent waters. By constrained molecular dynamics simulations, we have demonstrated that the low-coordinated W center can chelate with glucose, forming a metallacyclic complex with a 5-membered ring after the protonation of carbonyl group. The formation of 5-membered ring serves as the premise for the selectivity to C2 fragments via homolytic cleavage of CC bond. Furthermore, the reduced W5+ center is suggested to be crucial in facilitating the cleavage process by stabilizing the dissociated C4 intermediates via a redox process. In conclusion, we propose that the surface decoration of reduced and low-coordinated W sites can act as active heterogeneous catalysts for the selective conversion of cellulose in aqueous phase. These recent findings have the potential to provide valuable insights and strategies for CC bond activation in both biomass conversion and organic synthesis.

Selectively extracting H2WO4 of high purity from the H2SO4 decomposition product of scheelite through hydrogen peroxide coordination followed by purification using ion-exchange and solvent extraction and thermal decomposition

The discharge of ammonium-containing wastewater and saline wastewater, which are among the main sources of water pollution in China, is difficult to avoid in traditional tungsten extraction processes. Sulfuric acid decomposition of scheelite can address the issue of saline wastewater discharge, but effectively dissolving tungsten from the sulfuric acid decomposition product without causing ammonia pollution remains a challenge. To tackle these problems, this work proposes a novel process of selectively extracting tungsten from sulfuric acid decomposition products using hydrogen peroxide coordination. Under the optimum preparation conditions, 99.0% of tungsten in scheelite was transformed into tungstic acid. The extraction efficiency of tungsten from the product by hydrogen peroxide reached 99.4%, while tungsten content in residue is <1%. The conversion of tungsten from the product to peroxotungstic acid was investigated. After the purification using ion-exchange and solvent extraction, high-purity tungstic acid was obtained through thermal decomposition, with the content of each impurity element being lower than 15 mg/l. This study offers a new approach to producing high-purity tungstic acid from the sulfuric acid decomposition product of scheelite while eliminating the issues of ammonium-containing wastewater and saline wastewater.

A comparative study on sPEEK‐based composite membranes with various inorganic fillers using different preparation routes for DMFCs

AbstractIn this study, proton‐conducting sulfonated polyether ether ketone (sPEEK) membranes including tungstic acid, organically modified montmorillonite, and silicon dioxide were prepared using solution casting method for direct methanol fuel cells. All obtained composite membranes had adequate thermal stability for fuel cells, and their surfaces became more hydrophilic due to the incorporation of additives. The ion exchange capacities of the composite membranes were found to be very close to the sPEEK membrane. While the proton conductivity of the sPEEK membrane was 8.6 mS cm−1, the addition of additives led to an enhancement in the proton conductivity values. Among the prepared composite membranes, sPEEK‐H2WO4‐5 had the highest proton conductivity (36.5 mS cm−1) which was comparable to Nafion117 in water at room temperature. On the other hand, the methanol permeabilities of the composite membranes were in the same order compared to sPEEK but showed minor changes depending on the added materials and their compositions. Among the membranes obtained by solution casting, sPEEK‐H2WO4‐5 was found to be the best composite membrane due to its high proton conductivity and acceptable methanol permeability. Layer‐by‐layer modified sPEEK membranes were also obtained in the study for comparison and it was found that sPEEK‐PAH/H2WO4‐2 displayed the best selectivity value.

Chronoamperometry-induced transmittance changes approach to detect aqueous sodium ion solutions using tungsten oxide thin films

A simple, inexpensive method to detect sodium ions from aqueous solutions is reported in this paper. The method of detection based on transmittance changes observed in tungsten oxide films on.Tungsten oxide is deposited on ITO glass substrate by continuous electrodeposition method from Peroxo Tungstic Acid precursor. Chronoamperometry at a cathodic potential of −1V was performed on the sample in different concentrations (10 mM-150 mM) of NaCl solutions prepared in TRIS buffer solvent. UV–VIS-NIR transmittance in NaCl solutions was measured for the sample before and after chronoamperometry, and the corresponding transmittance changes (ΔT) were recorded. Due to the formation of tungsten bronze, the transmittance of the sample decreases during chronoamperometry. It was observed that the transmittance change increases with the NaCl concentration, and in the NIR wavelength range, the transmittance change observed was maximum. The sensor has a linear response in the range of 10 to 150 mM Na+ and excellent selectivity towards N+ as compared to interfering ions K+ and Ca2+. Its straightforward design, higher response, and selectivity make sodium detection in food sectors and health monitoring possible.

Polyoxometalate Archetype-Boosted Stability and Charge Storage of 2D Graphene Nanosheets

In this study, the potential of impregnation of phosphotungstic acid (PTA), a polyoxometalate in enhancing specific capacitance (C sp) and diminishing the well-known restacking phenomenon of graphene nanosheets was explored. Graphene nanosheets were prepared chemically from graphite powder through the formation of graphene oxide (GO) and then the subsequent reduction of GO to the reduced GO (rGO). Impregnation of PTA in rGO-PTA (rGP) composites was carried out by simply dispersing rGO and PTA derived from tungstic acid. Scanning electron microscopy, X-ray diffraction analysis, UV–vis reflectance spectroscopy, and Fourier-transform infrared spectroscopy were used to analyze the elemental composition, microstates, and morphology of the composites. The charge-storing capacity and stability of the prepared rGP composites casted on a graphite electrode were examined with cyclic voltammetric, chronopotentiometric, and electrochemical impedance techniques. The effect of ions on the charging capacity of the electrodes was verified using electrolytes with different ion sizes. About 100% enhancement of C sp of rGO with 87% capacitance retention for 2000 charging-discharging cycles was achieved by impregnating rGP composites with only 1% PTA.

Characterization of W-Er2O3 alloy prepared by co-deposition method and spark plasma sintering

Oxide dispersion strengthened tungsten (ODS-W) alloys are promising plasma facing material in future fusion reactors. In this study, composite powders of W-Er2O3 were prepared by co-deposition method and hydrogen reduction, and then consolidated by spark plasma sintering (SPS). Microstructure evolution during co-deposition process was investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and Fourier transform infrared spectrometer (FTIR). Also, simulation using DMol3 module in Materials Studio was carried out to understand the co-deposition mechanism. The results showed that H+ of W-OH bond in white tungstic acid was replaced by Er3+ due to coordination reaction during co-deposition process, leading to formation of ring-like chelate of (WO)nEr. This indicates that doping of Er3+ was achieved at a molecular level. Consequently, Er2O3 particles were relatively uniformly distributed in W-Er2O3 alloy, and the hardness and compressive strength reached 627 ± 19 HV and 1640 ± 40 MPa, respectively.

Temperature-Controlled Transformation of WO3 Nanowires into Active Facets-Exposed Hexagonal Prisms toward Efficient Visible-Light-Driven Water Oxidation.

A unique transformation of WO3 nanowires (NW-WO3) into hexagonal prisms (HP-WO3) was demonstrated by tuning the temperature of the (N2H4)WO3 precursor suspension prepared from tungstic acid and hydrazine as a structure-directing agent. The precursor preparation at 20 °C followed by calcination at 550 °C produced NW-WO3 nanocrystals (ca. <100 nm width, 3-5 μm length) with anisotropic growth of monoclinic WO3 crystals to (002) and (200) planes and a polycrystalline character with randomly oriented crystallites in the lateral face of nanowires. The precursor preparation at 45 °C followed by calcination at 550 °C produced HP-WO3 nanocrystals (ca. 500-1000 nm diameter) with preferentially exposed (002) and (020) facets on the top-flat and side-rectangle surfaces, respectively, of hexagonal prismatic WO3 nanocrystals with a single-crystalline character. The HP-WO3 electrode exhibited the superior photoelectrochemical (PEC) performance for visible-light-driven water oxidation to that for the NW-WO3 electrode; the incident photon-to-current conversion efficiency (IPCE) of 47% at 420 nm and 1.23 V vs RHE for HP-WO3 was 3.1-fold higher than 15% for the NW-WO3 electrode. PEC impedance data revealed that the bulk electron transport through the NW-WO3 layer with the unidirectional nanowire structure is more efficient than that through the HP-WO3 layer with the hexagonal prismatic structure. However, the water oxidation reaction at the surface for the HP-WO3 electrode is more efficient than the NW-WO3 electrode, contributing significantly to the superior PEC water oxidation performance observed for the HP-WO3 electrode. The efficient water oxidation reaction at the surface for the HP-WO3 electrode was explained by the high surface fraction of the active (002) facet with fewer grain boundaries and defects on the surface of HP-WO3 to suppress the electron-hole recombination at the surface.

Investigating the Optical Properties of Electrodeposited Tungsten Oxide Thin Films for Selective Sodium-Ion Detection

A novel method of sodium ion detection from aqueous solutions based on a change of optical transmittance is proposed. Tungsten oxide-coated ITO samples for selective sodium ion detection are prepared from varying concentrations of Peroxo Tungstic Oxide precursors using a simple cathodic electrodeposition method. The optical property changes were recorded in the UV-VIS-NIR range for the samples in aqueous solutions of NaCl in TRIS/DI water solvent. It was observed that transmittance increases with NaCl concentration in a particular wavelength range. A detailed material characterization was performed to support this observation and study Na+ ion diffusion-induced structural changes. The sensor deposited from Peroxo Tungstic Acid precursor of molarity 45 mM, at a cathodic potential of -0.45 V, showed a better response. The sensor exhibits good selectivity towards N+ as compared to K+ and Ca2+ ions and linear response in the range of 10 mM to 150 mM Na+. Simple construction, higher response, and selectivity make it a promising method for sodium sensing in food industries and health monitoring.

On the mechanism of the Folin test for uric aci

The mechanism of the interaction of uric acid with sodium tungstate in phosphoric acid (Folin test) is described. This insight involves the following steps: addition of tungstic acid to the carbon-carbon double bond in uric acid. Protolysis of the organometallic ester gives rise to dihydroxyoxotungsten and an epoxide, via a concerted mechanism. Acid catalyzed ring opening of the oxirane produces a vicinal diol via reaction of the intermediate carbocation with water. Isomerization of the resulting carbinolamide groups is enhanced by the resonance of the ureido group. Breaking of the second carbinolamide gives urea and alloxan, 5-ketobarbituric acid hydrate. Uric acid oxidation in strong acidic medium like phosphoric acid produces alloxan, whereas oxidation in alkaline, neutral, or slightly acidic medium, gives allantoin.

Hierarchical Structures Formed in an Atmospheric Pressure Plasma Jet by Polymerization from an Aerosol of Oxalic Acid Stabilized WO3–x Nanosheet Colloids: Toward High-Performance Electrochemical Devices and Sensors

The development of microstructures which combine high total surface area and high porosity is crucial for technologies such as electrocatalysis, electrochromics, and sensors. High deposition rate, composition control of deposition, and low processing temperature to retain active compositions are also desirable. To this end, this study describes combining colloidal sol chemistry with a nonthermal atmospheric pressure dielectric barrier discharge plasma jet to print hybrid inorganic/organic tungsten trioxide/oxalic acid (WO3–x/OA) microspheres. Injection of an aerosol of oxalic acid stabilized colloidal tungstic acid into an atmospheric pressure plasma jet results in the deposition of spherical structures in which the colloid is trapped within a plasma-polymerized organic shell. Subsequent low-temperature sintering produces hierarchical spherical shell-like structures comprising tungsten oxide nanosheets. Alteration of the gas flow rate changes the composition of the deposited material. The method has promise for the general preparation from colloidal precursors of porous materials of controlled morphology and composition with hierarchical microstructures, such as are required for applications in electrochemical devices and sensors which need a high ratio of surface area to volume and connectivity throughout the structure, yet also need a microstructure which is open for rapid exchange of reactants.