Na2WO4 Solution Research Articles

Unusual enhancement of the radical production in the X-ray irradiated aqueous-organic systems containing W(VI) in homogeneous and nanoparticle forms

The metal and oxide nanoparticles (NPs) containing various elements with high atomic number (Z) are considered as prospective sensitizers for the production of radicals upon X-ray irradiation of aqueous solutions, which can be used for different applications in medical treatment and material modification. The common basis for the sensitizing effect in oxygen-free systems is concerned with increase of the absorbed dose due to the presence of high-Z atoms (known as physical enhancement, relatively insensitive to the NP size). In this work we report the first experimental evidence for extra enhancement of the radical yield in a model oxygen-free aqueous organic system irradiated with X-rays (45 kVp) in the presence of W(VI) compounds, both in homogeneous solutions of Na2WO4 and in the form of ultra-small NPs of WO3. Meanwhile, in the case of larger WO3 NPs the radical yield is consistent with physical enhancement mechanism. In the case of systems containing HfO2 NPs only physical enhancement was observed, independent of the NP size. Unusually large enhancement of radical production and size effect for W(VI) in homogeneous and NP forms was tentatively attributed to the radiation-chemical processes involving intermediate formation of metastable W(V) due to reactions of hydrated electron.

Modeling of equilibria in acidified solutions of sodium orthotungstate in the presence of calcium(II) ions

The interactions of the Ca2+–WO42––H+–H2O system initially acidified to the molar ratio (acidity) Z=(H+)/(WO42–)=1.00 were studied by the methods of pH-potentiometry, mathematical modeling and conductometry in the interval Z=0.60–2.00 at 2980.1 K with NaNO3 (I=0.05–0.30 moll–1) as the supporting electrolyte. The logarithms of the equilibrium concentration constants were calculated by the Newton's method, and previously unknown logarithms of the thermodynamic constants and Gibbs energy of the reactions of the formation of ion associates Ca2+,[W4O14(OH)2]4–; Ca2+,[W6O20(OH)2]6–; Ca2+,[W12O40(OH)2]10–; Ca2+,H[W12O40(OH)2]9–; Ca2+,H2[W12O40(OH)2]8–; Ca2+,H3[W12O40(OH)2]7–; [W12O38(OH)2]6–; and H[W12O38(OH)2]5– were calculated using the Pitzer method. The formation of particles with a ratio of Сa2+:[W12O40(OH)2]10–=1:1 and Сa2+:[W6O20(OH)2]6–=1:1 in the solutions was shown by the conductometric titration method. The crystals of calcium paratungstate B Ca5[W12O40(OH)2]30H2O were synthesized from Na2WO4 solution acidified to acidity Z = 1.00. By using ATR-FTIR and Raman spectroscopies, it was shown that the isopolyanion in the composition of the salt belongs to the structural type of paratungstate B. The structure of Ca5[W12O40(OH)2]30H2O was determined by single crystal X-ray diffraction: monoclinic, P21/n, a=15.3619(4) Å, b=11.7537(3) Å, c=18.1471(5) Å, =109.2950(10)0, V=3092.58(14) Å3, R1=0.0298, wR(F2)=0.1387.

Preparation ultrafine WC based on the new tungsten metallurgy system of “no ammonia transformation - no hydrogen reduction”

The preparation of ultra-fine tungsten carbide (WC) is a difficult and hot topic in tungsten industry. The industrial production process requires the need to transform tungsten concentrates to produce ammonium paratungstate (APT) intermediate products followed by hydrogen reduction to produce W, and finally carburization to produce WC. Due to the formation of H2O in the hydrogen reduction process, it is difficult to obtain <100 nm tungsten powder materials. Therefore, in this study, a novel method was introduced that synthesizes ultrafine WC via hydrothermal synthesis of ZnWO4 followed by a carbothermic reduction–carburization process. The findings of this study showed that ZnWO4 with a particle size of 29 nm was synthesized from Na2WO4 solution. This can solve the problem of ammonia‑nitrogen wastewater discharge in the process of APT preparation, and prepare nano-scale raw material. In addition, zinc is volatile at high temperature, which has been widely used in the field of recycling waste cemented carbide. Based on this, the WC mixed powder was obtained by carbothermic reduction of ZnWO4 under the condition of excess C addition, which can inhibit the agglomeration of particles and avoid the production of H2O. Then the single-phase WC with a particle size of 60 nm was obtained by a carburization reaction process at 1300 °C for 3 h. The research intersects tungsten metallurgy with tungsten material preparation, shortens the production process and reduces waste water discharge.

Effect of Solution pH on the Synthesis of Two-Dimensional Molybdenum–Tungsten Sulfide Nanostructures

Compared with binary transition-metal dichalcogenides (TMDCs), ternary alloys or heterojunctions have more abundant properties. The spin-coating method has been widely used in the synthesis of TMDCs. However, there is still a lack of research on the effect of acidity and alkalinity of precursor solutions on the epitaxial growth of TMDCs. It is found that the MoxW1–xS2 ternary alloy is formed when an acidic solution of (NH4)2MoO4 and (NH4)2WO4 is used for spin-coating, while the MoS2/WS2 lateral heterojunction with a sharp boundary is formed when an alkaline solution of Na2MoO4, Na2WO4, and NaOH is used. According to the calculation, under alkaline conditions, sulfur atoms preferentially bind to MoO42– due to lower energy and finally form a lateral heterojunction. However, under acidic and neutral conditions, MoO42– and WO42– in the precursor solution will undergo a complex reaction, respectively. Because there is no significant difference in the binding energy of the reaction between the sulfur atom and two complexes, a ternary alloy will be formed. The controllable synthesis of different types of TMDCs can be achieved by regulating acidity and alkalinity.

Modeling of equilibria in an acidified solution of sodium orthotungstate in the presence of barium(II) ions

Interactions in the Ba2+–WO42––H+–H2O system, that was acidified to the molar ratio (acidity) Z=(H+)/(WO42–)=1.00, in the range of Z=0.60–2.00 at 2980.1 K with NaNO3 as the background electrolyte (I=0.1–0.3 mol•l–1), were studied by the methods of pH-potentiometry, mathematical modeling and conductometry. Logarithms of concentration constants of equilibrium were calculated by Newton's method. Previously unknown logarithms of thermodynamic constants and Gibbs energies of formation reactions for some ion pairs (BaOH+,[W12O40(OH)2]10–; Ba2+,[W12O40(OH)2]10–; Ba2+,H2[W12O40(OH)2]8–; Ba2+,H3[W12O40(OH)2]5–; Ba2+,[W12O18(OH)2]6–; and Ba2+,H[W12O18(OH)2]5–) were calculated by Pitzer's method. The formation of particles with a Ba2+:[W12O40(OH)2]10–=1:1 ratio in solutions was established by conductometric titration method. A scheme of interconversions between ion pairs in an aqueous solution was proposed. From acidified to different Z values aqueous solutions of Na2WO4, the normal and double barium(II) paratungstates B Ba5[W12O40(OH)2]30H2O (Z=1.17), Na4Ba2[W12O40(ОН)2]28Н2О (Z=1.25), and Na2Ba4[W12O40(ОН)2]25Н2О (Z=1.33) were synthesized. The data of FTIR spectroscopy showed that the isopoly anion in the salts' composition belongs to the paratungstate B structural type.

Sustainable extraction of tungsten from the acid digestion product of tungsten concentrate by leaching-solvent extraction together with raffinate recycling

Acid digestion of tungsten concentrates has attracted more and more attention in recent years, sustainable extraction of tungsten from acid digestion product of tungsten concentrates to obtain (NH4)2WO4 solution with low impurity content is the key for ammonium paratungstate production. In this work, a process of extracting tungsten from acid digestion product by leaching-solvent extraction together with raffinate circulation was introduced. The acid digestion product was firstly leached by Na2CO3, and the leaching efficiency was 99.47% with circulation of Na2CO3 solution converted from the raffinate of solvent extraction. The tungsten in pure Na2WO4 solution with 121.26 g/L WO3 could be almost completely extracted by solvents containing 15% N235 or 15% Alamine 308 in one stage. The extraction mechanism of N235 and Alamine 308 was the same, while Alamine 308 showed better performance and higher saturated loading capacities for tungsten extraction. The loaded tungsten was stripped from organic phases using NH3·H2O with stripping efficiency of 99.98%, obtaining (NH4)2WO4 solutions with WO3 concentration above 260 g/L and low impurity content. The raffinate containing high Na2SO4 concentration was converted to Na2CO3 solution by adding BaCO3 and recycled for the leaching of digestion product, which could significantly reduce the discharge of sodium salt wastewater. The presented work provides a cleaner production route for preparing pure (NH4)2WO4 solution from acid digestion product of tungsten concentrates.

Polyaniline-supported tungsten-catalyzed oxidative deoximation reaction with high catalyst turnover number

Polyaniline-supported tungsten (W@PANI) was easily prepared by immersing polyaniline (PANI) in the aqueous solution of Na2WO4. It was found to be an efficient catalyst for oxidative deoximation reaction, the very important transformation for pharmaceutical industry. Besides the green features, the method employed very few of catalytic tungsten (0.048 mol% vs. oxime substrates), resulting in the high turnover numbers (TONs) of the catalyst (ca. 103 mol/mol) and the low metal residues in product (<0.1 ppm). The reaction is applicable for a variety of substrates, including those containing heterocycles, which are key intermediates in medicine synthesis. It has also been successfully magnified to kilogram scale production to afford the desired carbonyl products smoothly.

Orthophosphoric acid solutions of sodium orthovanadate, sodium tungstate, and sodium molybdate as potential corrosion inhibitors of the Al2Cu intermetallic phase

Orthophosphoric acid solutions of sodium orthovanadate, sodium tungstate, and sodium molybdate are tested as potential corrosion inhibitors of the Al2Cu intermetallic phase. Corrosion inhibition is observed for 0.2 M solutions of Na3VO4 and Na2WO4 by increasing the pH to > 2. When the pH is < 2, the aforementioned salts increase the corrosion rate of the intermetallic phase. A 0.2 M solution of Na3VO4 causes the precipitation of vanadium phosphate on the surface of the Al2Cu phase at pH = 1.

Controllable Syntheses of Hierarchical WO3 Films Consisting of Orientation-Ordered Nanorod Bundles and Their Photocatalytic Properties

A series of hierarchical hexagonal WO3 (h-WO3) films consisting of orientation-ordered nanorod bundles paralleling the fluorine-doped tin oxide (FTO) glass substrate were synthesized through a hydrothermal reaction of Na2WO4 solution (pH 2.30). By varying the Na2WO4 concentration, the aspect ratios of the h-WO3 nanorods and the shapes of the orderly stacked nanorod bundles can be conveniently adjusted, which then influence the morphology of the resultant hierarchical h-WO3 films on the FTO substrate. With enhancing the Na2WO4 concentration, the nanorod bundles are changed from a flat shape into a fusiform one to form h-WO3 film with a relatively smaller porosity and smoother surface. Compared with the h-WO3 film with fusiform-shaped nanorod bundles, the h-WO3 film with flat-shaped ones exhibits better photocatalytic O2 generation activity as the direct consequences of its larger specific surface area, higher roughness, and better light absorption property.

Взаємодія в системі Ce3+ – WO42– – H+ – H2O за різної кислотності.

Formation of Ce(III)-containing isopoly tungstates in acidified to different acidity Z = ν(H+)/ν(WO42–) = 0.00, and 1.00–1.364 solutions of the Na2WO4 – HNO3 – CeCl3 – H2O system was studied.Formation of cerium(III) orthotungstate Ce2(WO4)3·9H2O from non-acidified solution of Na2WO4 (Z = 0.00) was determined by the chemical analysis, XRD, and FTIR spectroscopy. Obtaining of an individual Ce2(WO4)3 phase after Ce2(WO4)3·9H2O calcination at 500 ºC was confirmed by X-ray diffraction analysis. Absence of tetrahedral surrounding of tungsten atoms by oxygen atoms in Ce2(WO4)3∙9H2O salt anion was established by the analysis of FTIR spectroscopy data. From the solution with Z = 1.00 the cerium heptatungstate Ce2W7O24·20H2O was synthesized. Presence of Ce4W9O33 and WO3 phases in products of Ce2W7O24·20H2O thermal decomposition were identified by X-ray diffraction analysis. Conditions for Ce5[HW7O24]3·56H2O synthesis from the Na2WO4 – HNO3 – CeCl3 – H2O system with Z = 1.17 were elaborated. Presence of only WO3 phase in products of Ce5[HW7O24]3·56H2O thermal decomposition at 500 ºC was identified by X-ray diffraction analysis. Crystallization of Ce4W9O33 phase in products of Ce5[HW7O24]3·56H2O thermal decomposition was observed after calcination at 700 ºC. Conditions for the synthesis of Cerium(III) salts with paratungstate B anion, Ce10[W12O40(OH)2]3·94H2O and Na10Ce20[W12O40(OH)2]7·180H2O, from the Na2WO4 – HNO3 – CeCl3 – H2O system with Z = 1.17, and 1.29 respectively were established. Presence of [W12O40(OH)2]10– anion was detected by FTIR spectroscopy. Procedure for the double sodium-cerium(III) salt Na2Ce2[Ce2(H2O)10W22O72(OH)2]·35H2O synthesis from the solution with Z = 1.364 was elaborated. Presence of lacunary metatungstate anion in the salt composition was determined by FTIR spectroscopy. Two Cerium(III) сations in [Ce2(H2O)10W22O72(OH)2]8– are coordinated to polyoxotungstate anion additionally stabilizing two Keggin-type lacunary metatungstate anions, connected by two μ2-O vertices.

ChemInform Abstract: Two 1‐D Krebs‐Type Heteropolyoxotungstates Based on [X2W21O72Na(OH)2]13‐ (X: SbIII, BiIII) Units.

Abstract[Me2NH2]2Na11 [X2W21NaO72(OH)2] ·34H2O (X: SbIII (I), BiIII (II)) are prepared by a one‐pot self‐assembly of aqueous solutions of Na2WO4, NaOAc, and Me2NH2Cl to which a HCl solution of SbCl3 (or Bi(NO3)3 and Zr(NO3)4 for (II)) is added dropwise.

ChemInform Abstract: [Ni(OH)3W6O18 (OCH2)3CCH2OH]4‐: The First Tris‐Functionalized Anderson‐Type Heteropolytungstate.

AbstractThe title compound, Na2(Me4N)2 [Ni(OH)3W6O18 (OCH2)3CCH2OH]·9H2O is synthesized from an aqueous solution of Na2WO4, Ni(NO3)2, and HNO3 (pH 6.5, 25 °C, 10 d) followed by addition of C(CH2‐OH)4 (reflux, 80 °C, 5 h), and Me4NCl (55% yield).

Efficient recycling of WC-Co hardmetal sludge by oxidation followed by alkali and sulfuric acid treatments

We present a process to recycle strategic metals, viz. tungsten and cobalt, from a WC-Co hardmetal sludge (WCHS) via oxidation followed by a two-step hydrometallurgical treatment with alkali and acid solutions. The oxidation of WCHS was investigated in the temperature range of 500 to 1000 °C and optimized at 600 °C to transform the maximum WC into an alkali-soluble WO3. The conditions for the selective dissolution of WO3 in stage-I were optimized as follows: 4.0 M NaOH, pulp density of 175 g/L, and temperature of 100 °C for 1 h, yielding maximum efficacy. Subsequently, in the second step, the optimal conditions for cobalt leaching from the alkali-treated residue were established as follows: 2.0 M H2SO4, 25 g/L pulp density, and 75 °C temperature for 30 min. Downstream processing of the obtained metal ions in solutions was also easier, as the only impurity of dicobaltite ions with the Na2WO4 solution was precipitated as Co(OH)3 under atmospheric O2; meanwhile, the CoSO4 solution obtained through the second step of processing can be treated via electrolysis to recover the metallic cobalt. The present process is simpler in operation, and the efficient use of eco-friendly lixiviants eliminates the previously reported disadvantage.

Cyclic voltammetry analysis of copper electrode performance in Na2WO4 solution and optical property of electrochemical synthesized CuWO4 nanoparticles

The electrochemical behavior of copper electrode in sodium tungstate (Na2WO4) solution has been studied through cyclic voltammetry (CV). CV results informed that CuWO4 was formed in kinds of electrochemical processes followed with chemical reaction. A cationic exchange membrane-assisted electrolysis method was developed to synthesize optical nanoparticle CuWO4 for the first time. Anode chamber collected CuWO4 was calcined at 500 °C based on the thermogravimetry test result. The X-ray diffraction (XRD) pattern of calcined CuWO4 showed no impurities. Microstructure of CuWO4 was characterized by transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM). The fourier transform infrared spectroscopy (FTIR) of the sample further confirmed the formation of pure CuWO4 nanoparticle. Furthermore, the optical property of the nanomaterial was studied by ultraviolet visible diffuse reflectance spectrophotometer (UV–vis) and photoluminescence (PL).

ChemInform Abstract: Following the Reaction of Heteroanions Inside a {W18O56} Polyoxometalate Nanocage by NMR Spectroscopy and Mass Spectrometry.

AbstractThe Dawson‐like “Trojan horse” cluster (Me2NH2)8 [W18O56(HPO3)2 (H2O)2]·20H2O is isolated from an aqueous solution of Na2WO4, H3PO3, and Me2NH (pH 2.8, stirring under heating).

In Situ Formation of Efficient Cobalt-Based Water Oxidation Catalysts from Co(2+)-Containing Tungstate and Molybdate Solutions.

Replacing rare and expensive noble-metal catalysts with inexpensive and earth-abundant ones is of great importance to split water either electrochemically or photoelectrochemically. In this study, two amorphous cobalt oxide catalysts (Co-W film and Co-Mo film) with high activity for electrocatalytic water oxidation were prepared by fast, simple electrodeposition from aqueous solutions of Na2WO4 and Na2MoO4 containing Co(2+). In solutions of Na2WO4 and Na2MoO4, sustained anodic current densities up to 1.45 and 0.95 mA cm(-2) were obtained for Co-W film at 1.87 V versus a reversible hydrogen electrode (RHE) and Co-Mo film on fluorine-doped tin oxide (FTO) substrates at 1.85 V versus RHE. For the Co-W film, a much higher current density of 4.5 mA cm(-2) was acquired by using a stainless-steel mesh as the electrode substrate. Significantly, in long-term electrolysis for 13 h, the Co-W film exhibited improved stability in cobalt-free buffer solution in comparison with the previously reported Co-Pi film.

ChemInform Abstract: A Noble‐Metal‐Free, Tetra‐Nickel Polyoxotungstate Catalyst for Efficient Photocatalytic Hydrogen Evolution.

AbstractNa6K4 [Ni4(H2O)2 (PW9O34)2]·32H2O is synthesized by refluxing an aqueous solution of Na2WO4, Na2HPO4, and Ni(OAc)2 for 2.5 h, followed by addition of KOAc (73% yield).

ChemInform Abstract: High Adsorption Capacity for Cationic Dye Removal and Antibacterial Properties of Sonochemically Synthesized Ag2WO4 Nanorods.

AbstractThe title nanorods with an average diameter of 15—25 nm and a surface area of about 115 m2/g are synthesized by irradiation of an aqueous solution of Na2WO4 and AgNO3 under air for 1.5 h with high intensity ultrasonic radiation at 40 kHz.

ChemInform Abstract: Synthesis and Characterization of a New Keggin Anion: [BeW12O40]6‐.

AbstractThe title anion is hydrothermally synthesized from an aqueous solution of Na2WO4, Be(NO3)2, and HNO3 (Parr digestion bomb, pH 3.5, 160 °C, 7 d) followed by filtration.

ChemInform Abstract: Solvothermal Synthesis of Pyrochlore‐Type Cubic Tungsten Trioxide Hemihydrate and High Photocatalytic Activity.

AbstractPyrochlore‐type cubic WO3·0.5H2O is prepared by solvothermal processing of an aqueous solution of Na2WO4, urea, and HCl in H2O/acetone (autoclave, 140 °C, 3 d).