Showing papers on "Vanadate published in 2017"

Relationship between structures and activities of supported metal vanadates for the selective catalytic reduction of NO by NH3

Abstract: Transition and rare earth metal vanadates are potential active phases for the selective catalytic reduction (SCR) of nitric oxide by ammonia for exhaust gas emission control. In this work, various metal vanadates mixed with SiO2-WO3-TiO2 (TWS) were compared to vanadia-based SCR catalysts. FeVO4-based catalysts were found to be the most active metal vanadates, followed by CeVO4 and ErVO4. In depth analysis using XRD, BET, H2-TPR, DRUV and DRIFTS demonstrated that the vanadates partly decomposed above 600–750 °C to the corresponding single metal oxides, the decomposition temperature correlating with their relative stability. The activity and the estimated fraction of freed VOx from the vanadate decomposition strongly correlated with vanadia-based catalysts at comparable V-loading. Based on these findings, the enhanced thermal stability of the vanadate-based catalysts was correlated to an overall lower amount of free VOx species compared to vanadia-based catalysts. The released VOx species are responsible for the activity of the metal vanadate-based SCR catalysts and are of similar nature to those of vanadia-based catalysts. Therefore, the claimed high temperature stability advantage of supported metal vanadates is merely an effect of the degree of vanadate decomposition and is not related to their intrinsic stability.

Shape Controlled Synthesis of Copper Vanadate Platelet Nanostructures, Their Optical Band Edges, and Solar-Driven Water Splitting Properties.

Abstract: We report the morphological and size tailored rational and facile synthesis of copper vanadate nanostructures via sonication assisted sol gel method. Field emission scanning electron microscopy (FESEM), indicated irregular and nanoflakes morphologies for the as synthesized copper vanadate (CV-120) and copper vanadate calcined at 250 °C (CV-250). The semispherical platelets shaped morphology revealed for the copper vanadate calcined at 550 °C (CV-500). The XRD patterns confirm the monoclinic and triclinic crystal phases for CV-250 and CV-500, respectively. The optical properties of CV-250 and CV-500 via UV-DRS showed significant absorption in the visible regime at λ = 565 nm and 670 nm with band gap 2.2 eV and 1.84 eV, respectively as calculated from Kubelka-Munk (KM) equation via Tauc’s plot. The values of band edge positions of CV-250 and CV-550 straddle with the hydrogen (HER) and oxygen evolution reaction (OER) potentials. The photoelectrodes of CV-250 and CV-500 fabricated by adsorption desorption method to test their photoelectrochemical (PEC) water splitting performance in the three-electrode cell. The onset photocurrent potential is observed at ~0.42 V, which reached to saturation at 1.05 V. The photocurrent density at saturation is ~0.65 mA/cm2 for CV-250 and CV-500, respectively.

Europium-doped GdVO4 nanocrystals as a luminescent probe for hydrogen peroxide and for enzymatic sensing of glucose

Abstract: The authors describe the preparation of Eu 3+ -doped GdVO 4 nanocrystals (NCs) by precipitation of the Gd 3+ (Eu 3+ )-citrate complex which was then converted to the respective vanadate by dialysis. The fractions of Eu 3+ ranged from 5 to 100 mol%. The NCs were characterized by XRD, TEM, ICP-OES and dynamic light scattering which revealed that they possess superior colloidal stability in aqueous solutions in that no precipitation can be observed even after several months. The NCs display red and largely red-shifted fluorescence (peaking at 618 nm) on photoexcitation at around 300 nm. Fluorescence is strongly quenched by hydrogen peroxide. It is also shown that the fraction of doping with Eu 3+ strongly affects quenchability. Most efficient quenching by H 2 O 2 is observed if the NCs are doped with 50% of Eu 3+ . The findings were exploited to develop a fluorometric assay for H 2 O 2 that works in the 5 to 250 μM concentration range, with a limit of detection as low as 1.6 μM (at a signal-to-noise ratio of 3). The probe was further employed to design a highly sensitive enzymatic assay for glucose via measurement of the quantity of H 2 O 2 formed as a result of the catalytic action of glucose oxidase.

Influence of capping agents additives on morphology of CeVO4 nanoparticles and study of their photocatalytic properties

Abstract: In this paper, cerium vanadate (CeVO4) nanoparticles were synthesized via a precipitation method on the reaction between cerium nitrate hexahydrate and ammonium metavanadate in water. Besides, three capping agents such as glucose, lactose and starch were used to investigate their effects on the morphology and particle size of CeVO4 nanoparticles. According to the vibrating sample magnetometer, cerium vanadate (CeVO4) nanoparticles indicated a paramagnetic behavior at room temperature. To evaluate the catalytic properties of nanocrystalline cerium vanadate, the photocatalytic degradations of methyl orange under ultraviolet light irradiation were carried out. The structural, morphological, magnetic, and optical properties of as-obtained products were characterized by techniques such as XRD, SEM, EDX, VSM, and UV–Vis spectroscopy.

V2O5-WO3/TiO2 catalysts under thermal stress: Responses of structure and catalytic behavior in the selective catalytic reduction of NO by NH3

Abstract: V2O5-WO3/TiO2 catalysts of compositions typically used in SCR applications were subjected to calcinations in air at temperatures between 873 K and 1023 K for different durations, starting from a mildly calcined state in which species structure originating from wet preparation had been fixed by calcination at 623 K for 1 h. After calcination, samples were examined with respect to their SCR activity and to structural changes by nitrogen physisorption, XRD, Raman spectroscopy, EPR, temperature-programmed reduction, XPS and Low-Energy Ion Scattering (LEIS). Driven by loss of BET surface area, samples exhibited a complex behavior with up to three well-separated maxima of SCR activity before final deactivation. While the first of these maxima depended on the calcination rate (temperature), the other two maxima occurred at specific ranges of the BET surface area. During calcination, tungstate was segregated from the support surface forming WO3 under more severe conditions. Observations in the EPR spectra are in conflict with assignments of observed SCR activities to isolated vanadate sites. Assuming major contributions of dimeric vanadate to the catalytic performance, a model was proposed, which explains the first two activity maxima while the origin of the third one remains to be elucidated. In this model, segregation of tungstate results in formation of active V-O-V structures from less active isolated vanadate species previously separated by excessive amounts of tungstate. The main role of tungstate is to provide optimum sizes of vanadate ensembles, but a direct favorable influence of tungstate on vanadate is not excluded.

Resveratrol Ameliorates Tau Hyperphosphorylation at Ser396 Site and Oxidative Damage in Rat Hippocampal Slices Exposed to Vanadate: Implication of ERK1/2 and GSK-3β Signaling Cascades

Abstract: The objective of this study was to investigate the effect of resveratrol (a natural polyphenolic phytostilbene) on tau hyperphosphorylation and oxidative damage induced by sodium orthovanadate (Na3VO4), the prevalent species of vanadium (vanadate), in rat hippocampal slices. Our results showed that resveratrol significantly inhibited Na3VO4-induced hyperphosphorylation of tau at the Ser396 (p-S396-tau) site, which is upregulated in the hippocampus of Alzheimer’s disease (AD) brains and principally linked to AD-associated cognitive dysfunction. Subsequent mechanistic studies revealed that reduction of ERK1/2 activation was involved in the inhibitory effect of resveratrol by inhibiting the ERK1/2 pathway with SL327 mimicking the aforementioned effect of resveratrol. Moreover, resveratrol potently induced GSK-3β Ser9 phosphorylation and reduced Na3VO4-induced p-S396-tau levels, which were markedly replicated by pharmacologic inhibition of GSK-3β with LiCl. These results indicate that resveratrol could suppre...

Vanadate complexation to ferrihydrite: X-ray absorption spectroscopy and CD-MUSIC modelling

Abstract: The mobility of vanadium in the environment is influenced by sorption to metal (hydr)oxides, especially those containing iron. The aim of this study is to understand the adsorption behaviour of van ...

Lanthanoid-Doped Phosphate/Vanadate Mixed Hollow Particles as Ratiometric Luminescent Sensors.

Abstract: Rare earth (RE) phosphates and vanadates are structurally similar compositions that display distinct but complementary luminescent properties. The properties of these phosphors can be combined in REPO4-REVO4 heterostructures during the development of new sensing technologies for biological applications. This work presents the synthesis of hollow RE phosphate/vanadate colloidal particles and evaluates their applicability as luminescent markers. Hydrothermal treatments of RE hydroxycarbonate particles in the presence of the PO43– and VO43– precursors afforded the final REPO4–REVO4 solids in a two-step template synthesis. We converted precursor hydroxycarbonate particles into the final heterostructures and characterized their structure and morphology. According to our detailed study into the spectroscopic properties of Eu3+-doped particles and their luminescence response to several species, the presence of the phosphate and vanadate phases in a single particle provided different chemical environments and ena...

Thermodynamic investigation of uranyl vanadate minerals: Implications for structural stability

Abstract: Understanding the crystal chemistry, materials properties, and thermodynamics of uranyl minerals and their synthetic analogs is an essential step for predicting and controlling the long-term environmental behavior of uranium. Uranyl vanadate minerals are relatively insoluble and widely disseminated within U ore deposits and mine and mill tailings. Pure uranyl vanadate mineral analogs were synthesized for investigation using high-temperature drop solution calorimetry. Calculated standard-state enthalpies of formation were found to be −4928.52 ± 13.90, −5748.81 ± 13.59, and −6402.88 ± 21.01, kJ/mol for carnotite, curienite, and francevillite, respectively. Enthalpies of formation from binary oxides for uranyl vanadate minerals exhibit a positive linear correlation as a function of the acidity of oxides. Normalized charge deficiency per anion (NCDA) is presented to relate bonding requirements of the structural units and interstitial complexes. An exponential correlation was observed between NCDA and energetic stability (enthalpy of formation from binary oxides) for the studied minerals. Additionally, NCDA and oxide acidity exhibit an exponential correlation where decreasing oxide acidity results in an exponential decrease in NCDA. The number of occurrences of uranyl vanadate mineral species are found to correlate with both enthalpy of formation from oxides and NCDA.

Mechanism of Enhancing Extraction of Vanadium from Stone Coal by Roasting with MgO

Abstract: In this paper, the extraction of vanadium from stone coal by roasting with MgO and leaching with sulfuric acid has been investigated, and the mechanism analysis of stone coal roasting with MgO was studied. The results indicated that under the conditions that the mass fraction of the particles with grain size of 0–0.074 mm in raw ore was 75%, the roasting temperature was 500 °C, the roasting time was 1 h, MgO addition was 3 wt %, the sulfuric acid concentration was 20 vol %, the liquid-to-solid ratio was 1.5 mL/g, the leaching temperature was 95 °C, and leaching time was 2 h, resulting in a vanadium leaching efficiency of 86.63%, which increased by 7.73% compared with that of blank roasting. The mechanism analysis showed that the degree of calcite decomposition was low and, thus, magnesium vanadate was more easily formed than calcium vanadate below 500 °C. Moreover, magnesium vanadate was easier to dissolve than calcium vanadate during the sulfuric acid leaching process. Thus, the vanadium leaching efficiency was enhanced by using MgO as a roasting additive below 500 °C. Additionally, at high temperature the formation of tremolite would consume calcium oxide produced from the decomposition of calcite, thus, the formation of calcium vanadate was hindered, and V2O5 would react with MgO to form magnesium vanadate. Therefore, the vanadium leaching efficiency of roasting with MgO was higher than that of blank roasting at high temperature.

Corrosion inhibition of AA6063 alloy by vanadates in alkaline media

Abstract: Vanadium aqueous compounds are considered as promising environmentally friendly inhibitors for heterogeneous aluminium alloys. In this study, mechanism of corrosion inhibition of AA6063 in alkaline media by vanadate inhibitors is presented. A combination of weight loss and open circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy was used to compare corrosion behavior of AA6063 alloy in aerated pH 10 0.05 M sodium chloride solutions in the absence and presence of 0.003 mol/l sodium orthovanadate. Tetrahedrally coordinated mono- and polyvanadates, that are main forms in such solutions, cause a decrease in corrosion current density and significantly increase amplitude of impedance spectra and impedance modulus |Z| values due to mixed cathodic-anodic inhibition effect mainly associated with the formation of adherent surface film on cathodic and anodic intermetallic particles of alloy.

Effect of Strontium-Doped Lanthanum Vanadate on Crystal Structure, Conductivity and Vanadium Valence State of a La 1−x Sr x VO 3 Anode in a Reducing Environment

Abstract: La1−xSrxVO3 (where x = 0, 0.1, 0.3, 0.5, 0.7, and 1) exhibits a transition from an antiferromagnetic insulator to a paramagnetic metallic conductor and has been synthesized as a potential anode material for solid oxide fuel cells (SOFCs). La1−xSrxVO3 was synthesized by a solid-state reaction process followed by heat treatment under a reducing atmosphere (Ar:80/H2:20). X-ray diffraction (XRD) results indicate that LaVO3 was substituted with various amounts of Sr2+ in the cation sublattice. Pure LaVO3 shows an orthorhombic structure. After Sr2+ substitution, a more symmetrical cubic perovskite structure was obtained because the tolerance factor is close to 1. The valence state of the vanadium ions of the La1−xSrxVO3 was further verified by x-ray photoelectron spectroscopy (XPS). According to the XPS results, when the lanthanum ion was substituted by a strontium ion, the negatively charged defect, SrLa’, was compensated for by changing the valence of vanadium from a trivalent to a tetravalent or pentavalent state. The dependence of conduction behavior of La1−xSrxVO3 on the amount of Sr addition is discussed in terms of the hopping process with super/double exchange interaction and a charge transfer mechanism.

Nanorods of FeVO4: An efficient heterogeneous catalyst for chemoselective oxidation of benzylic alcohols

Abstract: Controllable fabrication of iron vanadate (FeVO4) was achieved by the hydrothermal approach. The excellent catalytic activity of the prepared nanorods of iron vanadate for the oxidation of benzylic alcohols as well as its potential for oxidation of the benzylic sp3 C-Hs in the presence of urea hydrogen peroxide (UHP) as oxidant was reported. The prepared nanorods and nanospheres were fully characterized by FT-IR, XRD, EDAX, ICP-AES, SEM, and TEM. In the presence of the catalyst, alcohols chemoselectively (100%) convert to the corresponding aldehydes/ketones, giving a total turnover number about 380 for 10 consecutive runs.

Simultaneous speciation of chromate, arsenate, molybdate and vanadate in alkaline samples by HPLC-ICP-MS at different concentration levels of vanadate

Abstract: Flay ash, cement and electric arc furnace (EAF) dust are frequently mixed in building composites. From them, chromium (Cr), arsenic (As), molybdenum (Mo) and vanadium (V) may be leached. Concentrations of V in leachates may be significantly higher than those of Cr, As and Mo, making simultaneous speciation analysis particularly difficult. In this work, a high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) procedure was used for simultaneous speciation of chromate, arsenate, molybdate and vanadate. First, the behaviour of Cr, As, Mo and V species in different oxidation states was studied during their separation under acidic (pH 5) and alkaline (pH 12) conditions. At alkaline pHs chromate, arsenate, molybdate and vanadate were simultaneously separated and eluted at retention times from 390 to 450 s, 230 to 270 s, 340 to 430 s and 270 to 380 s, respectively and detected on-line by ICP-MS, recording m/z 52, 75, 95 and 51, respectively. When V species were leached in significantly higher concentrations than Cr, Mo and As, their detection was possible at the low abundance (0.25%) 50V isotope, which is also the mass of the 50Cr isotope (abundance 4.345%), due to selective separation between V and Cr species. Good repeatability of measurement (RSD better than ±3.0%) and quantitative elution of elemental species (column recoveries 99–105%) were obtained. Finally, the procedure was applied in the simultaneous speciation analysis of chromate, arsenate, molybdate and vanadate in highly alkaline aqueous leachates from composites consisting of fly ash, cement and EAF dust that contained a wide range of concentrations of vanadate.

Acetonitrile mediated facile synthesis and self-assembly of silver vanadate nanowires into 3D spongy-like structure as a cathode material for lithium ion battery

Abstract: We report the facile, one-step acetonitrile-mediated synthesis and self-assembly of β-AgVO3 nanowires into three-dimensional (3D) porous spongy-like hydrogel (~ 4 cm diameter) as cathode material for lithium ion battery of high performance and long-term stability. 3D structures made with superlong, very thin, and monoclinic β-AgVO3 nanowires exhibit high specific discharge capacities of 165 mAh g−1 in the first cycle and 100 mAh g−1 at the 50th cycle, with a cyclic capacity retention of 53% at a current density of 50 mA g−1. 3D structures are synthesized by reaction between ammonium vanadate and silver nitrate solution containing 5 mL of acetonitrile followed by a hydrothermal treatment at 200 °C for 12 h. Acetonitrile (used here for the first time in the silver vanadate synthesis) plays an important role in the self-assembly of the silver vanadate nanowires. A tentative growth mechanism for the 3D structure and lithium ions intercalation into β-AgVO3 nanowires has been discussed and described.

Controllable synthesis of SmVO4 nanoparticles with different morphologies by wet chemical route

Abstract: In this work various morphologies of samarium vanadate (SmVO4) nanostructures were synthesized via chemical reaction between samarium nitrate hexahydrate and ammonium metavanadate. The effect of different surfactants such as sodium dodecyl sulfate, ethylene diamine tetraacetic acid and polyvinylpyrrolidone on the morphology of samarium vanadate nanostructures was investigated. Photo-catalytic property of SmVO4 was examined by degradation of methyl orange as organic pollutant in water under UV light irradiation. Nanostructures were characterized by X-ray diffraction, energy dispersive X-ray microanalysis, diffuse reflectance spectroscopy and scanning electron microscopy. According to the vibrating sample magnetometer result, SmVO4 nanoparticles indicated a paramagnetic behavior at room temperature.

Highly conductive barium iron vanadate glass containing different metal oxides

Abstract: Abstract 20BaO·5ZnO·5Fe2O3·70V2O5 glass annealed at 450°C for 30 min showed a marked decrease in the electric resistivity (ρ) from 4.0×105 to 4.8 Ωcm, while 20BaO·5Cu2O·5Fe2O3·70V2O5 glass from 2.0×105 to 5.0 Ωcm. As for the conduction mechanism, it proved that n-type semiconductor model in conjugation with the small polaron hopping theory was most probable. Since ZnII and CuI have a 3d10-electron configuration in the outer-most orbital, Ga2O3- and GeO2-containing vanadate glasses were explored in this study. 20BaO·5Ga2O3·5Fe2O3·70V2O5 glass showed a less remarkable decrease of ρ from 4.5×105 to 100 Ωcm, and 20BaO·5GeO2·5Fe2O3·70V2O5 glass from 3.3×106 to 400 Ωcm. Activation energies for the conduction (Ea) of GeO2- and Ga2O3-contaning glasses before the annealing were respectively estimated to be 0.42 and 0.41 eV. It proved that barium iron vanadate glass with a smaller Ea value could attain the higher conductivity after the annealing at temperaures higher than the crystalization temperature.

Vanadate-Dependent Peroxidases in Macroalgae: Function, Applications, and Environmental Impact

Abstract: Vanadate(V)-dependent haloperoxidases VHPOs in marine macroalgae catalyze the 2e- oxidation, by H2O2, of bromide and iodide (X-) to X+ species such as HOX, X2 and X3-. Several other substrates, including sulfides, are also oxidized. In the active center, H2VO4- is covalently attached to the Ne of a histidine residue, an arrangement that has successfully been modeled with synthetic analogs of the active center. Vanadium acts as a Lewis acid, forming an intermediate peroxido/hydroperoxido complex. The X+ species generated by the VHPOs halogenates organics present in seawater, from which halomethanes CH4-nXn (n is chiefly 2 or 1) evolve. Additionally, the hypohalous acids can protect the algae against biofilm formation. Prospective applications point towards this biocidal (anti-bacterial) potential of the peroxidases. The seaweeds further exploit the haloperoxidase activity in the synthesis of a multitude of brominated bio-functional molecules. Algal bromoperoxidase activity may account for up to 25% of the atmospheric bromine load. Bromomethanes and iodine released from the aqua- into the atmosphere substantially contribute to ozone depletion, and thus indirectly also to the oxidative conversion of (atmospheric) dimethyl sulfide and nitric oxide.