Tungstic Acid Research Articles

One-step ball-milling synthesis of cesium tungsten bronze nanoparticles and near-infrared shielding performance

Tungsten bronze (MxWO3) materials have been widely used as thermal insulation for architectural glass because of their higher near-infrared (NIR) light shielding capacity. To solve the problems encountered in solvothermal preparation with high costs and low yields, this study has developed a facile, eco-friendly, effective, but low-cost method, with no need for any annealing process, for promoting the large-scale fabrication of cesium tungsten bronze (CsxWO3, x = 0.32) nanomaterials for potential thermal insulation windows applications. In the proposed ball-milling process, the tungstic acid material could be reduced to hydro tungsten bronze (HxWO3) by cellulose, while the cesium ions (Cs+) could be gradually incorporated into the interspace until the formation of Cs0.32WO3 (Cs/W atomic ratio = 0.32), with an average particle size of ∼33 nm after a 15 h ball-milling process. The reaction mechanism has been investigated in detail via particle structural analysis and optical performance characterization. The obtained Cs0.32WO3 nanoparticles are dispersed in a solution composed of surfactant (s) and polymer (s) which can form a thin film with a thickness of about 2 μm on a glass substrate, by a spinning coating or casting method, to exhibit high visible (Vis) light transmittance (T566nm = 72.6%), and excellent NIR-shielding capability (T1388nm = 5.3%), reflected by good heat-insulating performance in practice use. This work will pave a new path for large-scale production of Cs0.32WO3 nanomaterials with low costs and high performance, beneficial for practical applications in energy-saving glass coatings.

An effective and eco‐friendly sonochemical multicomponent synthesis of trisubstituted imidazoles via modified silica‐coated cobalt ferrite nanoparticles by tungstic acid

This research is providing a method for the synthesis of 2,4,5‐trisubstituted imidazole derivatives based on pursuing the green chemistry principles. Therefore, a one‐pot multicomponent cyclocondensation reaction through aldehyde interaction with ammonium acetate and 1,2‐diketone was carried out in EtOH:H2O solvent under ultrasound irradiation. This protocol was utilized as an eco‐effective synthetic route by applying CoFe2O4@SiO2@(‐CH2)3OWO3H nanocomposite as a nanocatalyst. The stabilized tungstic acid on 3‐chloropropyl anchored to SiO2‐coated CoFe2O4 magnetic nanoparticles was designed, prepared, and applied as a recyclable heterogeneous acid catalyst to attain high product yields and short reaction times. The structure of nanocatalyst was confirmed by using Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), energy dispersive spectroscopy (EDS), vibrating sample magnetometer (VSM), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) techniques, and the obtained organic derivatives were examined through melting point, FT‐IR, and 1H NMR analyses.

Tungstic Acid: A Simple and Effective Solid Catalyst in Terpene Alcohol Oxidation Reactions with Hydrogen Peroxide

In this work, we report for the first time, the tungstic acid-catalyzed oxidation of terpene alcohols with hydrogen peroxide. This simple, solid, and commercially available catalyst efficiently promoted the conversion of borneol, geraniol and nerol to camphor and epoxide products, respectively. Effects of main reaction parameters, such as catalyst load, the molar ratio of oxidant to the substrate, time, and reaction temperature were investigated. Conversions and selectivity greater than 90% were achieved using 1.0 mol % of H2WO4 after 2 h of reaction at 90 °C. The activation energy was equal to 66 kJmol−1. We propose a reaction mechanism based on the experimental results. This solid catalyst was easily recovered and reused without loss of activity. As far as we know, it is the first time that tungstic acid was used as the catalyst in the oxidation reactions of terpene alcohols.

An efficient and eco-compatible multicomponent synthesis of 2,4,5-trisubstituted imidazole derivatives using modified-silica-coated cobalt ferrite nanoparticles with tungstic acid.

The aim of this study has been to offer a method for the synthesis of 2,4,5-trisubstituted imidazole derivatives based on green chemistry principles. Therefore, a one-pot multicomponent cyclocondensation reaction through aldehyde interaction with ammonium acetate and 1,2-diketone under solvent-free conditions was utilized as an eco-effective synthetic route using CoFe2O4@SiO2@(-CH2)3OWO3H NPs as the catalyst. The stabilized tungstic acid on 3-chloropropyl-anchored SiO2-coated CoFe2O4 magnetic nanoparticles was designed, prepared, and applied as a recyclable heterogeneous acid catalyst to attain high product yield in a short reaction time. The nanocatalyst structure was confirmed using FT-IR, Raman, XRD, FE-SEM, EDX, VSM, and TGA techniques, and the organic product structures were examined by melting point, FT-IR and 1H NMR analyses.

Enhanced Anticarcinogenic and Antimicrobial Response of Synthesized Tungsten Oxide Nanoparticles

In the present study, we fabricated tungsten trioxide nanoparticles (WO3 NPs) from a tungsten complex [W(C13H10NO)3] of ligand N-salicylideneaniline with tungstic acid as the precursor. Nanoparticles were synthesized using the direct thermal decomposition method. These nanoparticles were evaluated for cytotoxicity influence on human breast cancer MCF7 cell line (adenocarcinoma). The observed results suggested that WO3 can destroy 50 % of viable cells after 24 h of incubation at 37 °C. Based on these results, we concluded that WO3 nanoparticles could be a potential drug carrier candidate against human breast cancer cells based on the amount of the drug. In addition, WO3 nanoparticles exhibited significant antimicrobial and antifungal activity.

Visible-light-induced superhydrophilicity of crystallized WO3 thin films fabricated by using a newly isolated W6+ complex salt of citric acid.

Transparent tungsten trioxide thin films, which demonstrated visible-light (Vis-light)-induced superhydrophilicity, with thicknesses of 100-120 nm, adhesion strengths greater than 49 MPa, bandgap energies of 2.8-2.9 eV, and haze values of 0.4-0.5%, were fabricated using a solution-based process on quartz glass substrates. The precursor solution was prepared by dissolving a W6+ complex salt isolated from a reacted solution of tungstic acid, citric acid, and dibutylamine in H2O, in ethanol. By heating the spin-coated films in air for 30 min at temperatures higher than 500 °C, crystallized WO3 thin films were obtained. The O/W atomic ratio was evaluated to be 2.90, based on the peak area analysis of X-ray photoelectron spectroscopy spectra of the thin-film surfaces, indicating the co-presence of W5+ ions. The water contact angle on film surfaces, which was approximately 25° prior to light irradiation, decreased to less than 10° upon irradiation with 0.06 mW cm-2 Vis-light for only 20 min at 20-25 °C and a relative humidity (RH) of 40-50%. By comparing the contact angle changes at RH values of 20-25%, it was revealed that the interaction between ambient water molecules and the partially O-deficient WO3 thin films plays an important role in achieving photoinduced superhydrophilicity.

Production of fine-dispersed tungstic acid

The paper presents the results of studies of fine-grained tungstic acid synthesis and research of tungsten trioxide obtained from it. A literature analysis was performed and the direction of the study was formulated. A method of precipitation of tungstic acid from sodium tungstate solutions by hydrochloric acid solution has been proposed. To produce tungstic acid, a continuous operation unit that provided the required draining rates of sodium tungstate and hydrochloric acid solutions, the temperature of draining solutions and their concentrations, was created. The dependence of the specific surface of the obtained tungstic acid on the concentration of the used hydrochloric acid was investigated, and the optimum concentration of hydrochloric acid at 430 grams per liter was determined. Using the mathematical method of simplex-planning experiments, the effect of three parameters on the specific surface area of tungstic acid — the concentration of sodium tungstate solution, the ratio of volume rates of drained solutions, and the temperature of drained solutions, was investigated. The following, close to optimum parameters have been received: concentration of sodium tungstate solution of 35–40 grams per liter, ratio of concentrated (430 g/l) hydrochloric acid to the volume of sodium tungstate solution is (1.9–2.0):1, temperature of solutions is 15–20 °С. Tungstic acid with a specific surface area of 60 m2/gram was obtained. It is determined that for the preparation of tungsten trioxide with a high specific surface area, the heating rate of tungsten acid in its drying must be 40–50 degrees per hour and the final drying temperature must be equal to 400 °C. Figures illustrating the dependence of the specific surface of the obtained tungstic acid on the concentration of sodium tungstate solution, the ratio of the volume velocities of the drained solutions and the temperature of the drained solutions are presented.

Surface modification of WO3 nanoparticles with Pt and Ru for VOCs sensors

• WO3 nanoparticles were fabricated by the thermolysis method, Pt and Ru as the active catalysts are loaded with the wet impregnation method. • The Pt/Ru-WO3 indicated the significant enhanced for sensitive response to acetone. • The power-law response to oxygen was observed. Ru is dominated by electron sensitization, while a major for Pt is reflected in its catalytic sensitization. • This study provides beneficial information and insights into the sensitization mechanism of bimetallic nanoparticles on MOS materials. The production of a large number of metal oxide semiconductor materials is more for design needs, while theoretical exploration is relatively less concerned. In this work, WO 3 nanoparticles were prepared by the tungstic acid thermolysis method, and the catalysts of Pt and Ru were loaded on the surface of nanoparticles with a wet impregnation method. As expected, the sensitive responses were enhanced significantly with the additional loading of Pt, which revealed that bimetallic loading could achieve better properties with a smaller loaded amount than single metal. According to the power-law response to oxygen and H 2 -TPR results, the sensitization mechanism of noble metals loaded WO 3 to acetone as the typical VOCs was investigated. The results showed that the sensing processes were dominated by oxygen adsorption behavior and there was no difference with the loading of Ru. Furthermore, the power-law coefficient n became smaller with Pt loading. It is proposed that oxygen adsorbates on the surface become more active due to Pt. We would like to propose further a perspective, i.e., polymetallic loading that utilizes the properties of different metals to achieve synergism. In this work, WO 3 nanoparticles were prepared by the tungstic acid thermolysis method, and the catalysts of Pt and Ru were loaded on the surface of nanoparticles with a wet impregnation method. Sensor devices were fabricated by the screen-printing technique, and the schematic drawing of sensor structure and a photograph of MOS sensor device were presented in graphical abstracts. The powders were mixed with prepared organic solutions and adhesive to obtain a printable paste, which was deposited on an aluminum substrate with interdigitated Au microelectrodes on the front side and Pt microheater on the backside. As expected, the sensitive response was enhanced significantly with the additional loading of Pt, which revealed that bimetallic loading could achieve better properties with a smaller loaded amount than single metals. The results showed that the sensing processes were dominated by oxygen adsorption behavior and there was no difference with the loading of Ru. Furthermore, the power-law coefficient n became smaller with Pt loading. It is proposed that oxygen adsorbates on the surface become more active due to Pt. We demonstrated that the sensing mechanism of the Ru-WO 3 and Pt/Ru-WO 3 sensors is not identical, and Ru is dominated by electron sensitization, while a major for Pt is reflected in its catalytic sensitization. Loaded metals combine with WO 3 to form a heterojunction layer, which enhances the ability of sensitive materials to regulate electrons. The catalytic activity of both metals was enhanced due to the synergistic effect of the bimetals. Consequently, this study provides beneficial information and insights into the sensitization mechanism of bimetallic nanoparticles on MOS materials, which can help us to tune further the bimetallic composition and catalytic activity for specific applications and pave the way for polymetallic loading studies.

Microbially influenced tungsten mobilization and formation of secondary minerals in wolframite tailings

Wolframite [(Fe,Mn)WO4] tailings represent a hazardous waste that can pose a threat to the environment, humans, animals and plants. The present study aims to conduct a high-resolution depth profile characterization of wolframite tailings from Wolfram Camp, North Queensland, Australia, to understand the biogeochemical influences on W mobilization. Several indigenous Fe- and S-oxidizing bacteria (e.g., Streptococcus pneumoniae and Thiomonas delicata) in wolframite tailings were found highly associated with W, As, and rare earth elements. Biooxidation of metal sulfides, i.e., pyrite, molybdenite and bismuthinite, produced sulfuric acid, which accelerated the weathering of wolframite, mobilizing tungstate (WO42-). Using synchrotron-based X-ray fluorescence microscopy (XFM) and W L-edge X-ray absorption near-edge spectroscopy (µ-XANES) analysis, wolframite was initially transformed into Na- and Bi- tungstate as well as tungstic acid (partial weathering) followed by the formation of Ga- and Zn- tungstate after extensive weathering, i.e., the wolframite had disappeared. While W (VI) was the major W species in wolframite tailings, minor W(0) and W(II), and trace W(IV) were also detected. The major contaminant in the Wolfram Camp tailings was As. Though wolframite tailings are hazardous waste, the toxicity of W was unclear. Tungsten waste still has industrial value; apart from using them as substitution material for cement and glass production, there is interest in reprocessing W waste for valuable metal recovery. If the environmental benefits are taken into consideration, i.e., preventing the release of toxic metals into surrounding waterways, reprocessing may be economic.

Preparation of hexagonal boron nitride supported phosphomolybdic tungstic acid catalysts with different alkyl substituted imidazolium cations: Insight into hydrophobicity and electron transfer

In this study, a series of hexagonal boron nitride (h-BN) supported phosphomolybdic tungstic acid (POM) catalysts with different alkyl substituted imidazolium cations were successfully synthesized. The oxidative desulfurization (ODS) performance of the different catalysts was evaluated. The ODS of benzothiophene (BT), dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (4,6-DMDBT) and actual diesel was conducted by using [C12mim]3PMo6W6O40/h-BN as the catalyst and H2O2 as the oxidant. The [C12mim]3PMo6W6O40/h-BN catalyst was analyzed by FT-IR, XPS, XRD, TEM, contact angle testing, and nitrogen adsorption–desorption. In addition, DBT was converted completely in 20 min under the optimum conditions. We also showed evidence that electron transfer between [C12mim]3PMo6W6O40 and h-BN can promote oxidative desulfurization. In addition, even after 20 cycles, the activity of the catalyst did not decrease obviously. Finally, the catalytic mechanism occurring during the ODS process was investigated.

Quantitative Evaluation of the Diffusion Coefficients of Aqua Ions in Hydrogels via Iron Corrosion

A method to quantitatively evaluate the diffusion coefficient of aqua ions, viz. protons and hydroxide ions, in hydrogels using iron corrosion was developed. In this paper, the locations of the anode and cathode formation, which dominate iron corrosion, were experimentally controlled using pseudosacrificial corrosion protection with conductive anticorrosion ink. First, hydrogen (atomic) generation during the process was confirmed by a chromic gel with iron-doped tungstic acids. Then, the diffusion of aqua ions generated from them was visualized using a BTB-agar hydrogel with BTB (bromothymol blue), and the diffusion coefficient of aqua ions was evaluated using Fick’s law by reading the time variation of luminance. The temperature dependence of the diffusion coefficient was also examined, and the activation energies were evaluated as 19.0 ± 5.9 and 25.9 ± 3.3 kJ/mol for hydroxide ions and proton, respectively. Furthermore, the experimentally evaluated diffusion coefficients of aqua ions were used in a computer simulation to solve the diffusion equation to predict the pH distribution. The diffusion behaviors of aqua ions by the experiment are almost consistent with the simulation results and demonstrate the feasibility of the present method.

Hydrothermal Synthesis of Co-Exposed-Faceted WO3 Nanocrystals with Enhanced Photocatalytic Performance.

In this paper, rod-shaped, cuboid-shaped, and irregular WO3 nanocrystals with different co-exposed crystal facets were prepared for the first time by a simple hydrothermal treatment of tungstic acid colloidal suspension with desired pH values. The crystal structure, morphology, specific surface area, pore size distribution, chemical composition, electronic states of the elements, optical properties, and charge migration behavior of as-obtained WO3 products were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), fully automatic specific surface area and porosity analyzer, UV–vis absorption spectra, photoluminescence (PL) spectra, and electrochemical impedance spectroscopy (EIS). The photocatalytic performances of the synthesized pHx-WO3 nanocrystals (x = 0.0, 1.5, 3.0, 5.0, and 7.0) were evaluated and compared with the commercial WO3 (CM-WO3) nanocrystals. The pH7.0-WO3 nanocrystals with co-exposed {202} and {020} facets exhibited highest photocatalytic activity for the degradation of methylene blue solution, which can be attributed to the synergistic effects of the largest specific surface area, the weakest luminescence peak intensity and the smallest arc radius diameter.

Fabrication of an Efficient N, S Co-Doped WO3 Operated in Wide-Range of Visible-Light for Photoelectrochemical Water Oxidation.

In this work, a highly efficient wide-visible-light-driven photoanode, namely, nitrogen and sulfur co-doped tungsten trioxide (S-N-WO3), was synthesized using tungstic acid (H2WO4) as W source and ammonium sulfide ((NH4)2S), which functioned simultaneously as a sulfur source and as a nitrogen source for the co-doping of nitrogen and sulfur. The EDS and XPS results indicated that the controllable formation of either N-doped WO3 (N-WO3) or S-N-WO3 by changing the nW:n(NH4)2S ratio below or above 1:5. Both N and S contents increased when increasing the nW:n(NH4)2S ratio from 1:0 to 1:15 and thereafter decreased up to 1:25. The UV-visible diffuse reflectance spectra (DRS) of S-N-WO3 exhibited a significant redshift of the absorption edge with new shoulders appearing at 470–650 nm, which became more intense as the nW:n(NH4)2S ratio increased from 1:5 and then decreased up to 1:25, with the maximum at 1:15. The values of nW:n(NH4)2S ratio dependence is consistent with the cases of the S and N contents. This suggests that S and N co-doped into the WO3 lattice are responsible for the considerable redshift in the absorption edge, with a new shoulder appearing at 470–650 nm owing to the intrabandgap formation above the valence band (VB) edge and a dopant energy level below the conduction band (CB) of WO3. Therefore, benefiting from the S and N co-doping, the S-N-WO3 photoanode generated a photoanodic current under visible light irradiation below 580 nm due to the photoelectrochemical (PEC) water oxidation, compared with pure WO3 doing so below 470 nm.

Characterisation of novel microbial strains Proteus mirabilis and Bordetella avium for heavy metal bioremediation and dye degradation.

The entitled study focuses on exploring the microbial diversity and its applicability in the remediation of metal contaminated soil using microbes, which is a reliable and cost effective technique. Tungsten enriched soil of Kuhi-Agargaon-Khobna region (Nagpur, India) were analysed by XRF method to detect heavy metals. The traditional microbiological techniques were used to isolate tungsten tolerant microbes. Applicability of these microbes in bioremediation and Azo dye degradation was mainly studied. The two novel bacterial strains, Proteus mirabilis (RS2K) and Bordetella avium (RS3K), were isolated and identified to show the tolerance to tungsten, using 16S rDNA and phylogenetic analysis. These novel strains have also shown the tolerance to other metallic salts viz., (sodium) tungsten, tungstic acid, ammonium metaparatungstate, mercuric chloride, cobalt chloride and azo dye. These microbes were found to accumulate tungsten intracellularly as confirmed through ICP-MS and SEM-EDS analyses. Microbes exhibited well-equipped cellular mechanisms for metal tolerance to survive in heavy metal-laden ecology. Current study contains substantial potential in bioleaching of heavy metals and green mining along with Nano bioremediation for heavy metal pollution.

Tungsten extraction from scheelite hydrochloric acid decomposition residue by hydrogen peroxide

• W was leached from crude tungstic acid or residue by an efficient and clean method. • H 2 O 2 dissolved W from crude tungstic acid or residue selectively. • The W leaching ratio exceeded 96% for crude tungstic acid and 99% for the residue. • Pure tungstic acid was obtained from peroxotungstic acid solution. • More than 99.6% of W was precipitated from peroxotungstic acid solution. To reduce the amount of ammonia wastewater produced during traditional tungsten metallurgy, a novel method has been developed. Hydrogen peroxide was first used to selectively dissolve tungsten from crude tungstic acid and scheelite hydrochloric acid decomposition residue. Then, the peroxotungstic acid solution obtained was heated to prepare pure tungstic acid through thermal decomposition . The results showed that when the temperature was 40–45 °C, the molar ratio of hydrogen peroxide to tungstic acid was 2:1, and the reaction time was 60 min, more than 96 % of the crude tungstic acid was dissolved. Tungsten was easily leached from the hydrochloric acid decomposition residue under the conditions of a hydrogen peroxide concentration of 1.95 mol/L, 60 min, and 30 °C. The tungsten leaching ratio was 99.4 %. Using a decomposition temperature higher than 95 °C, seed addition amount more than 2.5 g/L, an acid concentration of 1 mol/L, and a reaction time of 120 min, the final W concentration in the mother liquor was 0.5 g/L and the decomposition ratio of peroxotungstic acid was more than 99.6 % with the product being WO 3 ·H 2 O. This research showed that hydrogen peroxide could dissolve tungstic acid and scheelite hydrochloric acid decomposition residue, and that the peroxotungstic acid obtained was readily decomposed into tungstic acid, which made it possible to leach scheelite cleanly and efficiently.

Efficient dissolution of tungstic acid by isopolytungstate solution based on the polymerization theory of tungsten

The rare metal tungsten is a very important strategic metal. The traditional tungsten ore alkaline process has many problems, including the generation of alkali residue, ammonia‐nitrogen wastewater, and industrial wastewater during ion exchange. The feasibility of decomposing scheelite with sulfuric acid has been confirmed due to the economic and environmental pressures faced by scheelite decomposition; however, extracting tungsten from the decomposition residue is a difficult process. This study was based on the polycondensation theory of tungsten, in which tungstic acid (H2WO4) rapidly dissolves in isopolytungstate solution during the acid adjustment process of sodium tungstate solution. Taking advantage of the different polymerization morphologies, a new idea in which tungstic acid selectively enters the solution after the polycondensation reaction between tungstic acid and isopolytungstate is proposed. In this work, the dissolution of tungstic acid in isopolytungstate solution under different experimental conditions were studied. The results indicated that isopolytungstate solution can undergo polycondensation reaction with tungstic acid, and the dissolution of W reached 0.37 g/g under suitable dissolution conditions. Additionally, the residue formed in sulfuric acid decomposition had a satisfactory leaching effect of tungsten in the isopolytungstate solution with a WO3 leaching efficiency of about 98.8%. Tungsten in the hydrochloric acid decomposition residue could also be extracted efficiently in the form of an isopolytungstate solution with a WO3 leaching yield >99%. This work proposes a cleaner and more efficient idea for the selective dissolution of tungsten from the acid decomposition residue of scheelite.

The Synthesis of h-BN-Modified Z-Scheme WO3/g-C3N4 Heterojunctions for Enhancing Visible Light Photocatalytic Degradation of Tetracycline Pollutants.

The photocatalytic performance of common photocatalysts is limited by their low surface area, insufficient absorption of light energy, and fast photogenerated electron–hole recombination rate. The introduction of Z-scheme photocatalysts decorated with hexagonal boron nitride (h-BN) has already been confirmed to be an effective way to extend the surface area and increase the charge separation, thereby enhancing the photocatalytic performance. In this study, a hexagonal boron nitride (h-BN)-decorated WO3/g-C3N4 heterojunction photocatalyst was successfully synthesized via an in situ method using tungstic acid, melamine, and hexagonal boron nitride as the precursors. The physical and chemical properties of the resulting samples were thoroughly characterized. The surface, morphological, and optical properties of the resulting materials were thoroughly characterized by XRD, XPS, SEM, TEM, UV–vis DRS, BET surface areas, PL, and ESR analysis. The WO3/g-C3N4/BN composite exhibited a much higher photocatalytic activity for tetracycline degradation under visible light irradiation than pure g-C3N4, WO3, and BN. The favorable photocatalytic activity of WO3/g-C3N4/BN composites can be ascribed to the increased surface area and enhanced separation efficiency of photogenerated electron–hole pairs by adding h-BN nanosheets and forming the WO3/g-C3N4 heterojunction. This work indicates that the WO3/g-C3N4/BN photocatalyst is a promising material in wastewater treatment.

Reclamation of tungsten from spent HDS catalyst: a detailed study

ABSTRACT The awareness of the depletion of high grade ore is of paramount importance now-a-days for all the metallurgical industries and researchers. For the conservation of resources, processing of low and lean grade ores is very much essential. Moreover, the recycling and reuse of the secondaries must be the core strength in that context. The spent catalyst obtained from a petroleum refinery was having 20.33% WO3 and 49.14% Al2O3 as major part of the matrix. The spent catalyst was devolatilized at 650°C to remove the oils, organics and other volatile matter. The devolatilized spent catalyst was processed treated with 8% NaOH at 90°C for 3 h to dissolve tungsten as sodium tungstate. The W bearing liquor was treated with H2SO4 to precipitate tungstic acid at pH 1.0. and subsequent production of tungsten trioxide by roasting at 700°C and tungsten metal with 99.91% purity by reduction roasting by H2 gas has also been reported. The alkali leached residue was leached with 10% sulphuric acid at 80°C for 2 h so as to extract nickel and later on precipitated as nickel hydroxide.

Photo- & radio-chromic iron-doped tungstic acids fabricated via submerged photosynthesis

Chromism-based detection by materials composed of both organic and inorganic materials has been exploited in various ways in sensors and smart windows because the optical properties of such materials can be reversibly changed. High-energy radiation beams may induce chromism via both ionizing and non-ionizing effects, but inherently chromic materials that can detect various types of radiation beams are not well understood. To be useful for high-energy radiation detection, a material must be safe; stable under radiation, exhibiting little radiation damage and radioactivation; and useable in various material forms. In the present study, we show that iron-doped tungstic acids of Fe-WO3·nH2O (n = 0.33, 1, 2), which is for the first time fabricated by submerged photosynthesis with hydrogen peroxide, can be used as a chromic solution to detect various radiation beams as well as ultraviolet non-ionizing radiation. The coupling redox reactions between Fe and W ions in Fe-WO3·nH2O have been proposed as the chromic mechanism. The prepared chromic solution exists as an aqueous liquid containing nanoparticles but can be easily gelatinized or sheeted and used in various forms as a detection material. Thus, our chromic solution of iron-doped tungstic acids is suitable for comprehensive radiation detection.

Sub-stoichiometric tungsten oxide by the stearic acid method

The synthesis of tungsten oxide by peroxotungstic route presents challenges, such as low solubility of tungstic acid in water and the fact that calcination product is a mixture of polytungstates. We propose a new route to obtain sub-stoichiometric tungsten oxides, using stearic acid, a non-toxic and low-cost material, as the dispersing and structuring agent for tungstic acid. The interaction between the precursor and the structuring agent was evaluated through chemical and structural analyses. Calcination of the stearic acid/tungstic acid systems produces vacant-rich monoclinic and orthorhombic tungsten oxides. Stearic acid plays a role of growth-directing agent and higher concentration of stearic acid promoted the growth of structures with plaque-shaped morphology in the samples, contributing to obtain sub-stoichiometric tungsten oxides, desired materials for visible light absorption.