Search Results (25)

Gel precursors were formed by reacting bismuth nitrate pentahydrate, acetic acid, sodium metavanadate, and NaOH. pH was adjusted using NaOH solution followed by calcination to obtain bismuth vanadate (BiVO₄) photocatalysts. During synthesis, pH directly influenced the formation and structure of the gel network. Therefore, the effects of pH on the microstructure and photocatalytic activity of BiVO₄ were investigated. At pH 3, the sample consisted of microspheres formed by tightly packed small particles. At pH 5, the microspheres transformed into aggregated flakes. Photocatalytic performance was evaluated through methylene blue (MB) degradation, revealing the sample prepared at pH 7 (7-BVO) demonstrated the highest efficiency. The electronic band structure, bandgap, and band edge positions of 7-BVO were probed by density functional theory (DFT) and UV-vis absorption spectra. Furthermore, photoluminescence spectroscopy, electrochemical measurements, active species trapping experiments and liquid chromatography mass spectrometry technique collectively revealed the possible mechanistic pathways for MB photodegradation by 7-BVO. Full article

Vanadium-based cathodes are promising for aqueous zinc-ion batteries (ZIBs) due to the large interlayer distance. However, the poor stability of electrode materials due to the dissolution effects has severely hindered the commercial development. To address this challenge, we propose an in situ NH₄⁺ pre-intercalation strategy to enhance the electrochemical performance of Na_0.76V₆O₁₅ (NaVO), thereby optimizing its structural stability and ionic conductivity. Moreover, NH₄⁺ pre-intercalation introduced a large number of oxygen vacancies and defects into the material, causing the reduction of V⁵⁺ to V⁴⁺. This transformation suppresses the dissolution and enhances its conductivity, thereby significantly improving the electrochemical performance. This modified NaNVO cathodes deliver a higher capacity of 456 mAh g⁻¹ at 0.1 A g⁻¹, with a capacity retention of 88% after 140 cycles and a long lifespan, maintaining 99% of its initial capacity after 2300 cycles. This work provided a new way to optimize the cathode for aqueous zinc-ion batteries. Full article

The elimination of absorbance of excess dye by selective oxidation was first proposed for analytical methods using the formation of ion-association complexes (IAs). On this basis, a new sensitive and selective spectrophotometric method for the determination of phosphate in the form of the IA of 11-molybdovanadophosphate with diindodicarbocyanine (DIDC) was developed. Symmetric diindodicarbocyanine and diindotricarbocyanine dyes can be completely oxidized by sufficiently strong oxidizing agents such as permanganate, dichromate, cerium (IV), and vanadate. Of the three dyes investigated (DIDC, N,N’-dipropyldiindodicarbocyanine, and diindotricarbocyanine), the best results were obtained with DIDC. A mixture of molybdate, vanadate, and nitric acid was preferably used as an oxidizing agent. Selective decolorization of only free dye ions, as well as changes in the IA spectrum compared to the dye spectrum, were explained by the isolation of the dye due to the formation of poorly soluble IA nanoparticles and changes in the redox potential of the dye due to its aggregation. The following optimal conditions for phosphate determination were found: 0.3 M nitric acid, 0.43 mM sodium molybdate, 0.041 mM sodium vanadate, 0.015 mM DIDC, and 18 min for the reaction time. The molar absorptivity of the IA was 1.86 × 10⁵ mol⁻¹·L·cm⁻¹ at 600 nm, and the detection limit for phosphate was 0.013 µM. The developed method was applied to the determination of phosphate in natural water samples. Full article

Vanadium precipitation is the key step in producing vanadium products from vanadium solution. The sustainable development of the vanadium industry requires new environmentally friendly processes for vanadium precipitation. In this study, NaVO₃ solution was pretreated with manganese salt to preliminarily separate the vanadium and sodium components. The product of vanadium extraction by manganese salt was dissolved by acid to produce manganese vanadate solution. After vanadium precipitation by hydrolysis, manganese removal, and calcination, the target product V₂O₅ was obtained. Scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma emission spectrometry (ICP-OES), and atomic absorption spectrometry (AAS) were used to perform the characterization and analyses. The results showed that vanadium and manganese have a strong binding ability. The rate of vanadium extraction by manganese salt reached 99.75%, and the product of vanadium extraction by manganese salt was Mn₂V₂O₇, with a sodium content of only 0.089%, confirming the effective separation of vanadium and sodium. The acid dissolution rate of the vanadium extraction product reached 99.95%, and the rate of vanadium precipitation by hydrolysis reached 97.87%. After manganese removal and calcination, the purity of the V₂O₅ product reached 98.92%. In addition, the recyclability of manganese sulfate and ammonium sulfate was analyzed. The process reduced the production of ammonia–nitrogen wastewater, laying a foundation for researching new technologies for extracting vanadium from vanadium slag. Full article

Na₅V₁₂O₃₂ is an attractive cathode candidate for aqueous zinc-ion batteries (AZIBs) by virtue of its low-cost and high specific capacity (>300 mAh g⁻¹). However, its intrinsically inferior electronic conductivity and structural instability result in an unfavorable rate performance and cyclability. Herein, K-doped Na₅V₁₂O₃₂ (KNVO) was developed to promote its ionic/electronic migration, and thus enhance the Zn²⁺ storage capability. The as-produced KNVO displays a superior capacity of 353.5 mAh g⁻¹ at 0.1 A g⁻¹ and an excellent retentive capacity of 231.8 mAh g⁻¹ after 1000 cycles at 5 A g⁻¹. Even under a high mass of 5.3 mg cm⁻², the KNVO cathode can still maintain a capacity of 220.5 mAh g⁻¹ at 0.1 A g⁻¹ and outstanding cyclability without apparent capacity decay after 2000 cycles. In addition, the Zn²⁺ storage kinetics of the KNVO cathode is investigated through multiple analyses. Full article

In order to expand the application of bismuth vanadate (BiVO₄) to the field of photoelectrochemistry, researchers have explored the potential of BiVO₄ in catalyzing or degrading organic substances, potentially presenting a green and eco-friendly solution. A study was conducted to investigate the impact of electrolytes on the photocatalysis of benzyl alcohol by BiVO₄. The research discovered that, in an acetonitrile electrolyte (pH 9) with sodium bicarbonate, BiVO₄ catalyzed benzyl alcohol by introducing saturated V⁵⁺. This innovation addressed the issue of benzyl alcohol being susceptible to catalysis in an alkaline setting, as V⁵⁺ was prone to dissolution in pH 9 on BiVO₄. The concern of the photocorrosion of BiVO₄ was mitigated through two approaches. Firstly, the incorporation of a non-aqueous medium inhibited the formation of active material intermediates, reducing the susceptibility of the electrode surface to photocorrosion. Secondly, the presence of saturated V⁵⁺ further deterred the leaching of V⁵⁺. Concurrently, the production of carbonate radicals by bicarbonate played a vital role in catalyzing benzyl alcohol. The results show that, in this system, BiVO₄ has the potential to oxidize benzyl alcohol by photocatalysis. Full article

Na-V-P-Nb-based materials have gained substantial recognition as cathode materials in high-rate sodium-ion batteries due to their unique properties and compositions, comprising both alkali and transition metal ions, which allow them to exhibit a mixed ionic–polaronic conduction mechanism. In this study, the impact of introducing two transition metal oxides, V₂O₅ and Nb₂O₅, on the thermal, (micro)structural, and electrical properties of the 35Na₂O-25V₂O₅-(40 − x)P₂O₅ − xNb₂O₅ system is examined. The starting glass shows the highest values of DC conductivity, σ_DC, reaching 1.45 × 10⁻⁸ Ω⁻¹ cm⁻¹ at 303 K, along with a glass transition temperature, T_g, of 371 °C. The incorporation of Nb₂O₅ influences both σ_DC and T_g, resulting in non-linear trends, with the lowest values observed for the glass with x = 20 mol%. Electron paramagnetic resonance measurements and vibrational spectroscopy results suggest that the observed non-monotonic trend in σ_DC arises from a diminishing contribution of polaronic conductivity due to the decrease in the relative number of V⁴⁺ ions and the introduction of Nb₂O₅, which disrupts the predominantly mixed vanadate–phosphate network within the starting glasses, consequently impeding polaronic transport. The mechanism of electrical transport is investigated using the model-free Summerfield scaling procedure, revealing the presence of mixed ionic–polaronic conductivity in glasses where x < 10 mol%, whereas for x ≥ 10 mol%, the ionic conductivity mechanism becomes prominent. To assess the impact of the V₂O₅ content on the electrical transport mechanism, a comparative analysis of two analogue series with varying V₂O₅ content (10 and 25 mol%) is conducted to evaluate the extent of its polaronic contribution. Full article

Cobalt, nickel, manganese and zinc vanadates were synthesized by a hydrometallurgical two-phase method. The extraction of vanadium (V) ions from alkaline solution using Aliquat^® 336 was followed by the production of metal vanadates through precipitation stripping. Precipitation stripping was carried out using solutions of the corresponding metal ions (Ni (II), Co (II), Mn (II) and Zn (II), 0.05 mol/L in 4 mol/L NaCl), and the addition time of the strip solution was varied (0, 1 and 2 h). The time-dependent experiments showed a notable influence on the composition, structure, morphology and crystallinity of the two-dimensional vanadate products. Inspired by these findings, we selected two metallic vanadate products and studied their properties as alternative cathode materials for nonaqueous sodium and lithium metal batteries. Full article

Volatile organic compounds (VOCs) are a notable group of indoor air pollutants released by household products. These substances are commonly employed as solvents in industrial operations, and some of them are recognized or suspected to be cancer-causing or mutagenic agents. Due to their high volatility, VOCs are typically present in surface waters at concentrations below a few micrograms per liter. However, in groundwater, their concentrations can reach levels up to thousands of times higher. This study analyses the applicability of the photoelectrochemical (PEC) sensing of VOCs in aqueous medium. Tungsten oxide and bismuth vanadate photoanodes were tested for PEC sensing of xylene, toluene, and methanol in sodium chloride and sodium sulfate electrolytes. The crystalline structure and morphology of coatings were analyzed using XRD and SEM analyses. Photoelectrochemical properties were evaluated using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The results of the study show that aromatic compounds tend to block the surface of the photoelectrode and interfere with the PEC sensing of other substances. WO₃ photoanode is found to be suitable for the PEC sensing of methanol under the mild conditions in aqueous electrolytes; however, electrode engineering and assay optimization are required to achieve better detection limits. Full article

Soil salinity is a worldwide problem that adversely affects plant growth and development. Soil salinization in Xinjiang of China is very serious. Ping’ou hybrid hazelnut, as an important ecological and economic tree species, as well as a salt-tolerant plant, has been grown in Xinjiang for over 20 years. Understanding the salt-tolerance mechanism of Ping’ou hybrid hazelnut is of great significance for the breeding of salt-tolerant varieties and the rational utilization of salinized land. In this study, ‘Liaozhen 7’, a fine variety of Ping’ou hybrid hazelnut, was selected as test material, and seedlings were treated with 0 (control), 50, 100 and 200 mM NaCl. Subsequently, the pattern of NaCl-induced fluxes of Na⁺, K⁺ and H⁺ in the root meristematic zone and their response to ion transport inhibitors were studied using non-invasive micro-test technology (NMT). Different concentrations of NaCl stress significantly increased the Na⁺ concentration in roots, while K⁺ concentration decreased first and then increased with the increase of NaCl concentration. Meanwhile, NaCl stress induced a significant decline in K⁺/Na⁺ ratio. Control and 200 mM NaCl-induced Na⁺ and K⁺ fluxes in roots exhibited an outward efflux, whereas an inward flux was observed for H⁺. Under 200 mM NaCl stress, the average rates of net Na⁺ and K⁺ efflux, as well as H⁺ influx in roots were significantly increased, which were 11.6, 6.7 and 2.3 times higher than that of control, respectively. Furthermore, pharmacological experiments showed that 200 mM NaCl-induced Na⁺ efflux; H⁺ influx was significantly suppressed by amiloride, an inhibitor of plasma membrane (PM) Na⁺/H⁺ antiporter, and sodium vanadate, an inhibitor of PM H⁺-ATPase. Net Na⁺ efflux and H⁺ influx induced by NaCl decreased by 89.9% and 135.0%, respectively. The NaCl-induced Na⁺ efflux was mediated by a Na⁺/H⁺ antiporter using energy provided by PM H⁺-ATPase. The NaCl-induced K⁺ efflux was significantly restricted by tetraethylamine chloride, a K⁺ channel inhibitor, and promoted by sodium vanadate, which decreased by 111.2% and increased by 80.8%, respectively, indicating that K⁺ efflux was regulated by depolarization-activated outward-rectifying K⁺ channels and non-selective cation channels (NSCCs). In conclusion, NMT data revealed that NaCl stress up regulated the root Na⁺/H⁺ antiporter and H⁺ pump (an activity of PM Na⁺/H⁺ antiport system) of ‘Liaozhen 7’, which compelled the Na⁺/H⁺ exchange across the PM and restricted K⁺ loss via depolarization-activated K⁺ channels and NSCCs simultaneously, thereby maintaining the K⁺/Na⁺ homeostasis and higher salt tolerance. Full article

The results of the processing of ash from the combustion of fuel oil after roasting with the addition of Na₂CO₃ followed by aluminothermic melting are presented. As a result, metallic nickel and vanadium slag were obtained. Studies of slag, metal, and deposits on the electrode were carried out. The resulting metal contains about 90 wt% Ni. The main phases of scurf on the electrode are a solid solution based on periclase (Mg_{1–x–y–z}Ni_xFe_yV_zO), sodium-magnesium vanadate (NaMg₄(VO₄)₃), and substituted forsterite (Mg_2–x–yFe_xNi_ySiO₄). The processing of ash made it possible to significantly increase the concentration of vanadium and convert it into more soluble compounds. Vanadium amount increased from 16.2 in ash to 41.4–48.1 V₂O₅ wt% in slag. The solubility of vanadium was studied during aqueous leaching and in solutions of H₂SO₄ and Na₂CO₃. The highest solubility of vanadium was seen in H₂SO₄ solutions. The degree of extraction of vanadium into the solution during sulfuric acid leaching of ash was 18.9%. In slag, this figure increased to 72.3–96.2%. In the ash sample, vanadium was found in the form of V⁵⁺, V⁴⁺ compounds, vanadium oxides VO₂ (V⁴⁺), V₂O₅ (V⁵⁺), and V₆O₁₃, and nickel orthovanadate Ni₃(VO₄)₂ (V⁵⁺) was found in it. In the slag sample, vanadium was in the form of compounds V⁵⁺, V⁴⁺, V³⁺, and V^(0÷3)+; V⁵⁺ was presented in the form of compounds vanadate NaMg₄(VO₄)₃, NaVO₃, and Ca_xMg_yNa_z(VO₄)₆; V³⁺ was present in spinel (FeV₂O₄) and substituted karelianite (V_{2–x–y–z}Fe_xAl_yCr_zO₃). In the obtained slag samples, soluble forms of vanadium are due to the presence of sodium metavanadate (NaVO₃), a phase with the structure of granate Ca_xMg_yNa_z(VO₄)₆ and (possibly) substituted karelianite (V_{2–x–y–z}Fe_xAl_yCr_zO₃). In addition, spinel phases of the MgAl₂O₄ type beta-alumina (NaAl₁₁O₁₇), nepheline (Na_4–xK_xAl₄Si₄O₁₆), and lepidocrocite (FeOOH) were found in the slag samples. Full article

During the discharge of Na–O₂ batteries, O₂ is reduced and combines with Na⁺ to form an insulating solid sodium oxide on the cathode, which severely hinders the mass transfer path, resulting in high polarization voltage, low energy efficiency, and short battery life. Hereby, we proposed a novel illumination-assisted Na–O₂ battery in which bismuth vanadate (BiVO₄) with few defects and high surface areas was used as the catalyst. It showed that the charge overpotential under photo assistance reduced by 1.11 V compared with that of the dark state one. Additionally, the insolating sodium oxide discharge products were completely decomposed, which was the key to running Na–O₂ batteries over 200 cycles with a charge potential of no more than 3.65 V, while its counterpart (under dark condition) at 200 cycles had the charge potential higher than 4.25 V. The experiment combined with theoretical calculation shows that few defects, high surface areas, the altered electron transfer kinetics, and the low energy gap and low oxygen absorption energy of the (040) crystal face of monoclinic BiVO₄ play an important role in catalyzing oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Full article

In this study, diffusion coefficients of ammonium vanadate at tracer concentrations in artificial saliva with and without sodium fluoride, at different pH values, were measured using an experimental model based on the Taylor dispersion technique. Ternary mutual diffusion coefficients (D₁₁, D₂₂, D₁₂, and D₂₁) for four aqueous systems {NH₄VO₃ (component 1) + β-cyclodextrin (β-CD) (component 2),} {NH₄VO₃ (component 1) + β-cyclodextrin (HP-β-CD) (component 2)}, {NH₄VO₃ (component 1) + sodium dodecyl sulphate (SDS) (component 2)} and {NH₄VO₃ (component 1) + sodium hyaluronate (NaHy) (component 2)} at 25.00 °C were also measured by using the same technique. These data showed that diffusion of ammonium vanadate was strongly affected in all aqueous media studied. Furthermore, a significant coupled diffusion of this salt and β-CD was observed through the non-zero values of the cross-diffusion coefficients, D₁₂, allowing us to conclude that there is a strong interaction between these two components. This finding is very promising considering the removal, from the oral cavity, of vanadium resulting from tribocorrosion of Ti-6Al-4V prosthetic devices. Full article

Aluminum anodization in an aqueous solution of formic acid and sodium vanadate leads to the formation of alumina/carbon composite films. This process was optimized by varying the concentrations of formic acid and sodium vanadate, the pH, and the processing time in constant-voltage (60–100 V) or constant-current mode. As estimated, in this electrolyte, the anodizing conditions played a critical role in forming thick, nanoporous anodic films with surprisingly high carbon content up to 17 at.%. The morphology and composition of these films were examined by scanning electron microscopy, ellipsometry, EDS mapping, and thermogravimetry coupled with mass spectrometry. For the analysis of incorporated carbon species, X-ray photoelectron and Auger spectroscopies were applied, indicating the presence of carbon in both the sp² and the sp³ states. For these films, the Tauc plots derived from the experimental diffuse reflectance spectra revealed an unprecedentedly low bandgap (E_g) of 1.78 eV compared with the characteristic E_g values of alumina films formed in solutions of other carboxylic acids under conventional anodization conditions and visible-light absorption. Full article

Calcium vanadate (CaV₂O₆), a new product of vanadium precipitation, was obtained from vanadium slag by sodium roasting-water leaching and calcium precipitation. The separation behavior of vanadium and silicon in vanadium slag during sodium roasting and water leaching was systematically studied, and micro-morphology and valence migration behavior of vanadium and Fe in vanadium slag, roasting slag, and residue were revealed. The Na₂CO₃ was added to the vanadium slag at 20% mass fraction, roasted at 790 °C, and kept for 120 min, the roasted sample was added to the deionized aqueous solution with a liquid-solid ratio of (L/S) 5mL/g, and then heated at 90 °C for 60 min, 89.54% vanadium and 1.96% chromium were extracted. Sodium carbonate tends to combine with vanadium to form sodium vanadate, while silicon is easy to combine with Fe and Na to form acmite (NaFeSi₂O₆). When the molar ratio of N (Ca/V) is 0.6 and CaO, is added to adjust the pH of vanadium leaching solution to 6.7 ± 0.1 and precipitate 90 min at 90 °C, vanadium is precipitated in the form of CaV₂O₆ with a purity of 95.69%, under these conditions, the precipitation ratio is 95.03%. Full article