Low Vanadium Content Research Articles

Electrodeposition of titanium\u2013vanadium alloys from chloride-based molten salts: influence of electrolyte chemistry and deposition potential on composition, morphology and microstructure

In the present study, we demonstrate co-deposition of titanium and vanadium from a eutectic LiCl–KCl electrolyte enriched with VCl3 and TiCl2 at 700 K. While the addition of metallic titanium to the electrolyte caused vanadium depletion by a displacement reaction, metallic vanadium addition created and stabilized divalent vanadium ions in the melt, which are supposed to positively affect the deposition process. Various electrochemical experiments were carried out with different electrolyte concentrations, and a relationship between applied potential, electrolyte concentration and composition of the deposit was established. The composition and the morphology of the obtained deposits were strongly affected by the electrolysis conditions. Electrodeposited vanadium-rich Ti–V alloys were found to grow as dendrites, whereas the titanium-rich alloys exhibited a dense cauliflower-like surface morphology. In contrast to deposits of the single elements, which are composed of comparably large faceted crystals, the Ti–V alloys obtained in this study were very fine grained, especially those with vanadium contents around 10–15 at%. Transmission electron microscopy revealed that, depending on the composition of the deposit, either a biphasic α + β microstructure in the case of low vanadium contents or β-(V,Ti) with small amounts of ω phase for high vanadium contents were found.Graphic abstract

Changes in the SO2 Level and PM2.5 Components in Shanghai Driven by Implementing the Ship Emission Control Policy.

This study aims to understand the effect of the Domestic Emission Control Area (DECA) policy on ambient SO2 and particle components in Shanghai. Online single particle analysis and SO2 measurements from 2015 to 2017 were compared to analyze the long-term variations before and after the DECA policy. Our study showed that there was a significant decrease in SO2 by 27-55% after the implementation of the DECA policy. The number fraction of ship-emitted particles increased along with the increase in ship traffic activity, but the particles tended to contain lower-vanadium content. The elemental carbon component decreased, while the organic carbon components increased after switching oil. One thousand and ninety four ship fuel oil samples were collected. The oil sample analysis confirmed the ambient particle results; sulfur content decreased in domestic ship heavy fuel oils from 2013 to 2018; in the low sulfur fuel oils used after the DECA policy, vanadium was still highly correlated with sulfur as it was in high-sulfur fuels. Our results suggested that heavy fuel oil is still a major part of the low-sulfur ship oils in use. The multiple-component control including organic pollutants regarding low sulfur fuel oils may be necessary for preventing air pollution from ship emissions.

Multi-spectroscopic and elemental characterization of southern Australian asphaltites

Strandings of various types of bitumen along the coast of southern Australia are long known. Among these, brittle, angular lumps termed ‘asphaltites’ are possibly sourced from Cretaceous source rocks linked to an oceanic anoxic event (OAE), but the exact source remains unclear. The unusual chemical composition of these asphaltites and their survival during transport and shoreline stranding suggest that they formed by nearby submarine seepage of asphaltene-rich crude oils. Here, we provide a detailed organic and inorganic geochemical characterization of asphaltites to constrain their origin and age. High-pressure hydropyrolysis (HyPy) of asphaltene fractions from ten asphaltites released similar assemblages of macromolecularly bound compounds, suggesting a common source for all asphaltites. Comprehensive gas chromatography–time-of-flight mass spectrometry (GC×GC-TOFMS) was used to compare these asphaltene-derived compounds with the maltene fractions, while compound specific isotope analysis (CSIA) was used to compare δ13C and δ2H of n-alkanes and isoprenoids. A large offset between the δ2H of the n-alkanes and isoprenoids suggests oil generation and expulsion at low thermal maturity. The mean concentrations of isorenieratane and chlorobactane, carotenoid derivatives indicative of photic zone euxinia (PZE), in the asphaltites were 8.8 ± 0.8 SEMµgg−1 and 1.4 ± 0.1 SEMµgg−1, respectively. A mean Aryl Isoprenoid Ratio of 0.75 (SD = 0.17) is accompanied by Pr/Ph of ∼1.2. These features strongly support persistent PZE conditions at the level expected for an OAE. Trace metal contents of the asphaltites, including low selenium and high vanadium concentrations, also support anoxic conditions. Rhenium-osmium (Re-Os) analyses constrain the age of asphaltite generation to 103 ± 22 Ma, with a relatively low initial 187Os/188Os ratio of 0.44 ± 0.18. Integrating local geologic knowledge with organic and inorganic geochemistry and Re-Os isotopic results, we identify a Cretaceous unit associated with OAE1a (∼125 Ma) as the most likely source of the asphaltites. Alternative scenarios involving source rocks deposited during OAE1b (∼112 Ma) are possible, but require rapid burial of organic-rich sediments to reach required maturation levels in a shorter time.

Room‐Temperature Ferromagnetism in MoTe2 by Post‐Growth Incorporation of Vanadium Impurities

AbstractPost‐synthesis doping of 2D materials is demonstrated by incorporation of vapor‐deposited transition metals into a MoTe2 lattice. Using this approach, vanadium doping of 2H‐MoTe2 produces a 2D ferromagnetic semiconductor with a Curie temperature above room temperature (RT). Surprisingly, ferromagnetic properties can be induced with very low vanadium concentrations, down to ≈0.2%. The vanadium species introduced at RT are metastable, and annealing to above ≈500 K results in the formation of a thermodynamically favored impurity configuration that, however, exhibits reduced ferromagnetic properties. Doping with titanium, instead of vanadium, shows a similar incorporation behavior, but no ferromagnetism is induced in MoTe2. This indicates that the type of impurities in addition to their atomic configuration is responsible for the induced magnetism. The interpretation of the experimental results is consistent with ab initio calculations, which confirm that the proposed vanadium impurity configurations exhibit magnetic moments, in contrast to the same configurations with titanium impurities. This study illustrates the possibility to induce ferromagnetic properties in layered van der Waals semiconductors by controlled magnetic impurity doping and thus to add magnetic functionalities to 2D materials.

Combinatorial optimization and synthesis of multiple promoted MoVNbTe catalysts for oxidation of propane to acrylic acid

New MoVTeNb multi-component catalysts (so-called M1 phase) were designed and tested using combinatorial and high-throughput methods. An international team of academic institutes and industrial partners has cooperated to understand the chemistry occurring during the hydrothermal synthesis and crystallization of the M1 phase of the MoVTeNb mixed oxide. With this information, the optimization of this catalyst system could be targeted with the aim of improving catalyst performance for short chain alkane – ethane and propane - oxidation reactions.Beside the elements responsible for the formation of the M1 phase (Mo, V, Te, and Nb) and promoters found to be advantageous in our previous work (Mn, Ni, W and citric acid), the following components were added to the synthesis mixture: Ce, Cu, Co, Cr and ethylene glycol. Contrary to the previous approach in this study, the V/Mo, Te/Mo and Nb/Mo ratios were kept constant. Consequently, the experimental space had nine variables. The discrete levels of variables are established in such a way that the number of the potential experimental points in the multi-dimensional experimental space was in the range of 200 000. Five new generations were designed using an optimization platform consisting of holographic optimization algorithm and artificial neural networks. Altogether 250 catalysts were prepared and tested. A complex objective function was created consisting of two independent catalytic performance characteristics – conversion and product selectivity – as well as the expected production costs and prices of the target product acrylic acid (AA) and export steam. The AA production costs were estimated assuming a recycle scheme for such a future AA plant with standard downstream equipment. The best catalysts in the group of catalysts with low vanadium content gave acrylic acid yields of 58% in the high throughput tests after five generations. On the bases of holographic maps, correlations between the composition of the synthesis mixtures and the yields of AA were visualized allowing to see the cross effect between components. Mn and Co had a positive effect, while Cu and Ce resulted in negative effect on the yield of AA. The analysis of the correlation between conversions vs. product yields allowed figuring out the main reaction routes leading to acrylic acid and CO2 in a consecutive reaction scheme.Following this successful high throughput development, the hydrothermal method using the newly identified synthesis aids was further optimized and successfully scaled up to 40 l autoclaves using the cheapest available chemicals, the oxides. This now renders possible the large-scale production of that complex MoVNbTe mixed oxide catalyst.

Vanadium ionic species from degradation of Ti-6Al-4V metallic implants: In vitro cytotoxicity and speciation evaluation

Among the metallic materials used in biomedical industry, the most common choice for orthopedics and dental implants is titanium (Ti) and its alloys, mainly due to their superior corrosion and tribocorrosion resistance and biocompatibility. Under different conditions in vivo, such as different pH levels, composition of body fluid and mechanical loads, metallic materials may suffer from degradation, resulting in the release of undesired wear particles and ions. In particular, the Ti-6Al-4V system represents almost half of the production of Ti as a biomaterial and many concerns have been raised about titanium, aluminum and vanadium ions releasing. This work evaluates the cytotoxic effects of vanadium ionic species generated from Ti-6Al-4V surfaces regarding mouse pre-osteoblasts and fibroblasts. In our cell viability tests, we noticed a significant decrease in the fibroblasts' cell viability with vanadium concentrations (23 μM) close to those previously reported to be observed in vivo in patients with poor functioning of their medical devices based on Ti-6Al-4V (30 μM). Speciation modelling was carried-out, for the first time, to this system. Results of the modelling reveal that vanadates(V), namely H2VO4− and HVO42−, are the main species present in cell culture media. Otherwise, in synovial fluids of individuals with poorly functioning implants, wherein the concentration of vanadium may go up to ca. 30 μM, the tentative theoretical speciation data indicates a high occurrence probability for VV- and VIV-species bound to albumin and hyaluronic acid. In conclusion, even though relatively low concentrations of vanadium may be released from Ti-6Al-4V implants in vivo, the continuous contact with peri-implant cells for long periods of time may represent a potentially hazardous situation.

Ab Initio Metadynamics Study of the VO2+/VO2+ Redox Reaction Mechanism at the Graphite Edge/Water Interface.

Redox flow batteries (RFBs) are promising electrochemical energy storage systems, for which development is impeded by a poor understanding of redox reactions occurring at electrode/electrolyte interfaces. Even for the conventional all-vanadium RFB chemistry employing V2+/V3+ and VO2+/VO2+ couples, there is still no consensus about the reaction mechanism, electrode active sites, and rate-determining step. Herein, we perform Car-Parrinello molecular dynamics-based metadynamics simulations to unravel the mechanism of the VO2+/VO2+ redox reaction in water at the oxygen-functionalized graphite (112̅0) edge surface serving as a representative carbon-based electrode. Our results suggest that during the battery discharge aqueous VO2+/VO2+ species adsorb at the surface C-O groups as inner-sphere complexes, exhibiting faster adsorption/desorption kinetics than V2+/V3+, at least at low vanadium concentrations considered in our study. We find that this is because (i) VO2+/VO2+ conversion does not involve the slow transfer of an oxygen atom, (ii) protonation of VO2+ is spontaneous and coupled to interfacial electron transfer in acidic conditions to enable VO2+ formation, and (iii) V3+ found to be strongly bound to oxygen groups of the graphite surface features unfavorable desorption kinetics. In contrast, the reverse process taking place upon charging is expected to be more sluggish for the VO2+/VO2+ redox couple because of both unfavorable deprotonation of the VO2+ water ligands and adsorption/desorption kinetics.

Surface Reactivity of Titania\u2013Vanadia Mixed Oxides Under Oxidizing Conditions

The surface structure and reactivity of TiO2(110) with 1–15% of admixed vanadium were studied using thermal desorption spectroscopy, scanning tunneling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy with the methanol partial oxidation as the reactivity test reaction. Prior to the experiments the sample was oxidized at elevated temperatures with O2 of different pressures up to 10−6 mbar. As shown in a preceding publication (Song et al. in Surf Sci 653:181–186, 2016), vanadium leads to an increased reducibility of the mixed oxide, which resulted in the simultaneous presence of reduced and oxidized structural elements at the surface. At low vanadium concentrations (a few percent) small vanadia clusters with V4+ form above the fivefold Ti rows at the surface together with short vanadium decorated strands along [001]. These types of structure promote the partial oxidation of methanol towards formaldehyde at 550 K. At higher vanadium concentrations the vanadia aggregates at the surface contain V5+ in addition to V4+. They produce formaldehyde already at 480 K and below. The oxidized TiO2(110) layer with admixed vanadium releases QMS-detectable amounts of O2 already at a temperature of about 450 K, which is about 80 K below the corresponding temperature for TiO2(110) without vanadium. This is attributed to the increased reducibility of rutile with admixed vanadium.

Effects of V2O5 on elastic, structural, and optical properties of mixed ionic–electronic 20Na2O–20CaO–(60 − x)B2O3–xV2O5 glasses

Glass samples [20Na2O–20CaO–(60 − x)B2O3–xV2O5, where 0 ≤ x ≤ 2.5 mol%] were prepared using melt-quenching method to study the mixed ionic–electronic (MIE) effect on the elastic and optical properties of the glasses. Ultrasonic velocities, elastic moduli, hardness, and Debye temperature decreased to a minimum at x = 1.5 mol%. The initial decrease in the elastic moduli may have been caused by the increase in the number of non-bridging oxygen (NBO). In this process, V2O5 acted as a modifier at low vanadium concentration but changed to a network former at x > 1.5 mol%. The FTIR spectra showed the presence of VO4, VO5, BO3, and BO4 vibration groups, and this result confirmed that V2O5 played a dual role in the glass network. Considerable decrease in dc conductivity (x = 1.5 mol%) signified a blocking effect on the ionic current in the MIE glasses. Interestingly, the observed anomaly in the elastic moduli coincided with the dc conductivity minima, indicating possible influence of the MIE effect on the elastic anomaly. Quantitative analysis using ideal bulk compression and ring deformation models showed a decrease in Kbc/Ke at x > 1.5 mol% which implies that ring deformation was reduced in the region. Furthermore, the MIE effect also influenced the optical properties of the investigated glasses. The optical band gap (E opt) and refractive index exhibited minimum and maximum values, respectively, at x = 1.5 mol%. The increase in concentration of NBOs and the defect states elucidated the significant changes in the E opt of the glasses.

Vanadium removal by organo-zeolites and iron-based products from contaminated natural water

Natural water with a high specific ultraviolet absorbance (SUVA) value (4.3) and high vanadium concentration (1.2–1.9 mg/l) was investigated for vanadium(V) removal through sorption using solid sorbents and co-precipitation with a ferric sulphate coagulant. Although there are studies on vanadium removal by sorption and co-precipitation, the removal of vanadium in the presence of natural organic matter has not been adequately addressed. In the sorption method, hexadecyltrimethylammonium bromide (HDTMA) modified clinoptilolite (Cp) and synthetic zeolite (Na-P1), and ferric oxyhydroxide (CFH-12) were tested as sorbents. In the co-precipitation method, vanadium removal may occur simultaneously with the coagulation process of humic substances. Co-precipitation with iron was proven to be more efficient than sorbent-based processes. A ferric sulphate coagulant dosage (as product) of 75 mg/l resulted in a residual vanadium concentration of 70–80 μg/l and vanadium removal closely followed the removal of humic substances. This might be related to the binding of vanadium by the humic substances. Regarding sorbents, 1–2 g/l dosages of Na-P1 (at pH ∼6) and CFH-12 (pH 3.7–4.7) were required to reach a low vanadium concentration. A much higher dosage was required for Cp, which can be explained by the lower loading of HDTMA on the zeolite surface. Na-P1 increased the pH of the treated water whereas CFH-12 decreased the pH. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses revealed that the pH change was due to the leaching of hydroxides and calcite from the Na-P1 and jarosite from the CFH-12. The organo-zeolites exhibited fast kinetics. The surface binding of vanadium and vanadium-humic substances can be regarded as the main mechanism. For CFH-12, the diffusion of vanadium into pores was a significant, albeit slow mechanism, in addition to the sorption on the external surface. The humic substances present in natural water significantly affected the mechanism of vanadium uptake. The XPS data confirmed the strong binding of organic matter on CFH-12 whereas organic matter was only weakly bound to the organo-zeolites.

Properties of vanadium-loaded iron sorbent after alkali regeneration.

The aim of this research was to investigate the regeneration and reuse of a commercial granular iron sorbent (mainly goethite) when used in vanadium removal. A regeneration rate of 3 M NaOH was the highest (85%) achieved, followed by 2 M NaOH (79%) and 1 M NaOH (68%). The breakthrough curves show that the regenerated material can be reused. The BET (Brunauer-Emmett-Teller) surface area increased by 35-38% and the total pore volume increased by 123-130% as a consequence of NaOH treatment. The results indicated that sodium hydroxide could be used for the regeneration of iron sorbent although the regeneration was incomplete. This may be explained by the fact that vanadium diffusion into pores is a significant sorption mechanism in addition to complex formation with surface functional groups. As a consequence, vanadium desorbability from pores is not as effective as the regeneration of surface sites. X-ray photoelectron spectroscopy analyses confirmed a very low vanadium content on the surface of the NaOH-treated iron sorbent.

Kinetic studies at carbon felt electrodes for vanadium redox-flow batteries under controlled transfer current density conditions

In this work we present a combination of mathematical modeling and experimental kinetic characterization of carbon felt electrodes in positive electrolyte (PE) and negative electrolyte (NE) of vanadium redox-flow batteries. The mathematical model is applied to check for homogeneous transfer current density within a radially connected carbon electrode intensively flown through by the electrolyte. Transfer current homogeneity depends mainly on electrolyte conductivity, electrode thickness and charge transfer coefficient. The transfer current inhomogeneity of the investigated electrode samples is below 5%, when single layers of carbon electrodes (415μm thickness at 89% porosity and 210μm thickness at 75% porosity) are applied and high electrolyte conductivities (>800mS∙cm−1) are maintained by low vanadium concentrations (<15mM). Experimental results show charge transfer coefficients for high overpotentials of 0.26±0.03 for the reduction reaction in NE and 0.37±0.04 for the oxidation reaction in NE. The charge transfer coefficients of the PE are 0.13±0.02 for reduction and 0.30±0.04 for the oxidation reaction. Application of the Butler-Volmer equation to describe the polarization behavior shows adequate agreement with the experimental results at states of charge between 25% and 75%. The rate constants for the PE reaction are nearly two times higher than for the NE reaction.

ORGANIC GEOCHEMISTRY OF THE LOWER SILURIAN TANEZZUFT FORMATION AND BIOMARKER CHARACTERISTICS OF CRUDE OILS FROM THE GHADAMES BASIN, LIBYA

The Ghadames Basin of NW Libya contains more than 10 B brls oil‐equivalent in Palaeozoic siliciclastic reservoirs which are charged by organic‐rich “hot shales” in the Lower Silurian (Rhuddanian) Tanezzuft Formation. Geochemical analysis of 85 shale samples and ten oils from three fields (NC2, NC4 and NC7) in the central and northern part of the basin provides a robust description of the Tanezzuft – Mamuniyat/Acacus petroleum system in this region, and of the associated source facies and oil families. The shale samples underwent total organic carbon (TOC) analysis and Rock‐Eval pyrolysis, and the ten crude oil samples were analysed by gas chromatography – flame ionization detection (GC‐FID) and GC‐mass spectrometry (GC‐MS) of the saturated and aromatic hydrocarbon fractions, accompanied by stable carbon isotopic analysis. Organic matter ranges from Type II to mixed Type II/III kerogen with varying oil and gas generation potential in the early to main stages of the oil generation window.The analysed oils are characterised by low sulphur, nickel and vanadium contents, and relatively high API gravity (34.9–46.8oAPI). Biomarkers suggest that they were generated from marine shales containing abundant Type II to mixed Type II/III kerogen deposited in mildly anoxic – suboxic conditions with a dominance of C29 over C27 or C28 steranes, indicative of a source rich in brown algae and cyanobacteria. Their close stratigraphic association and biomarker characteristics support a Tanezzuft “hot shales” source for the Mamuniyat and Acacus oils in the three fields. Maturity‐related parameters based on terpanes, steranes, aromatic hydrocarbons and low molecular‐weight hydrocarbons, suggest generation from marine shales in the early to peak oil‐generation window. The ZE3‐NC7, A19‐NC7 and A20 NC7 oils from the NC7 oil field are significantly more mature than those from the NC2 and NC4 fields. This indicates a difference in expulsion timing and may be related to the presence of two “hot shales” or to fault‐triggered vertical migration preceding and during the Neogene.

Synthesis method and substrate influence on TiO2 films doped with low vanadium content

Titania films doped with low amount of vanadium were deposited on different substrates (microscope glass, microscope glass covered with SiO2 barrier layer, and silicon wafer with a thermally grown layer of SiO2) by dip coating from solutions prepared by sol-gel and microwave (MW) assisted sol-gel syntheses. The selected molar composition was 99.95:0.05 which corresponds to 0.03at% of V. The films were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray diffraction (XRD) and Spectroscopic Ellipsometry (SE). The deposited films thermally treated at 450°C, presented homogeneous and continuous nanostructured surfaces and good adherence to the substrates used. All samples crystallized in anatase phase and have good optical properties. The highest transmission value was obtained for the V-doped TiO2 films (T > 90%) deposited from solutions prepared by microwaves assisted sol-gel method. Based on the obtained results it was concluded that the method of preparation has higher influence on the properties of the resulted films than the substrates used.

Electroless chemical aging of carbon felt electrodes for the all-vanadium redox flow battery (VRFB) investigated by Electrochemical Impedance and X-ray Photoelectron Spectroscopy

Electroless chemical aging of commercially available, porous carbon felt electrodes for the all-vanadium redox flow battery (VRFB) was investigated by full-cell and half-cell measurements in a beaker set-up and a cell with flow-through geometry at different states of charge and different temperatures. Changes in the charge transfer resistance and the double layer capacitance due to chemical aging were determined by electrochemical impedance spectroscopy (EIS) and correlated with ex-situ X-ray photoelectron spectroscopy (XPS). EIS measurements revealed that the aging of the carbon electrodes was dependent on the temperature for low vanadium concentrations and independent on the temperature for high vanadium concentrations. This indicates that the electroless aging of the electrodes occurs due to a chemical reaction with the sulfuric acid and with the vanadium. XPS measurements revealed an increase of the amount of surface functional groups on the carbon felt electrodes by a factor of 1.5 to 1.8 after 8days of mere contact with electrolyte. Moreover, the conducting sp2-hybridized layer was diminished by a factor of 2 or more. It appears that the negative half-cell [V(II)/V(III)] is more strongly affected by chemical aging than the positive half-cell [V(IV)/V(V)]. Electroless aging was found to be inevitable for all the carbon felts used.

Microstructure, mechanical properties and friction behavior of magnetron-sputtered V-C coatings

This study describes reciprocating sliding friction experiments of three types of magnetron-sputtered vanadium carbide/amorphous carbon nanocomposite coatings, VC1−x/a-C, against alumina counterparts under unlubricated conditions. It links micro- to macroscale tribology in order to provide a better understanding of the sliding mechanisms of these nanocomposite coatings with varying constitution and microstructure (i.e. by varying the C/V concentration ratio between 1.2 and 2.9). Correspondingly, the volume fraction of the amorphous carbon phase (a-C) increases with increasing the carbon content as shown by electron microprobe studies, X-ray diffraction and Raman spectroscopy; simultaneously, the volume fraction of nanocrystalline vanadium carbide (VC1−x) decreases, and the crystallite size and crystallinity of the thin films decrease with increasing carbon content. These constitution and microstructure changes have an impact both on the mechanical and the tribological properties of the coatings. Mechanical properties characterization shows that the indentation hardness (H) and the reduced modulus (Er) of the coatings decrease with increasing the carbon concentration (i.e. H ranges between 15 and 33GPa and Er ranges between 239 and 391GPa for the low and high vanadium concentration respectively). A similar behavior was also observed with the results on the critical load of failure obtained from scratch tests, where the coatings with the highest vanadium concentration exhibits higher critical load of failure and thus, better coating adhesion. However, reciprocating micro- and macroscale tribological tests performed at a relative humidity level of 45±5% (i.e. normal load in the microtribological experiments is between 100mN and 1N and for the macroscale tribometry the normal load is 20N) reveal higher friction values and increased wear with the high vanadium content coatings. This sliding behavior is attributed to differences in the third body formation (i.e. carbon based transfer- and tribo-film) and velocity accommodation modes, which are analyzed ex situ by means of X-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy and atomic force microscopy.

Investigation of spectral interference effects on determination of uranium concentration in phosphate ore by inductively coupled plasma optical emission spectroscopy

Abstract Effects of spectral interferences on determination of the uranium concentration in phosphate ore were investigated by inductively coupled plasma optical emission spectroscopy (ICP-OES). Eleven high intensity emission lines including four lines recommended by ICP-OES apparatus were chosen to determine the uranium concentration. The ore samples were collected from phosphate acid producing industry in the south of Iran. Three different acid combinations [(HNO3:HCl:HF-2:6:2), (H3PO4:H2SO4:HF-3:3:3), (HNO3:H2O2:HF-4:2:2)] used in microwave digestion method to explore the spectral interference effects in different solvent environments. The results showed that the trusty uranium concentration, obtained in the 367.007 nm, 386.592 nm, 389.036 nm and 409.014 nm by second acid digestion method which were 0.665 ppm, 0.972 ppm, 0.670 ppm and 0.801 ppm, respectively. Although the line of 409.014 nm was reported as the best line for determining of the uranium concentration in several literatures, the results showed that this line has a significant spectral interference with vanadium in some ores which should be considered in determining of the uranium concentration. Spectral interference effects of some elements which have high concentrations in the phosphate ore including Ca, Fe, Mg, Pb, V, Mn, and Ti on the line intensities were also investigated. Results indicated that the chosen elements affect emission intensities of all of 11 lines. They also indicated that the line of 409.014 nm provides a trusty precision in the determination of the uranium concentration in the ore sample with low vanadium concentration (at least, U/V ratio of 1:5). Results show that the line of 409.014 nm provides acceptable precision with some corrections in comparison with other selected lines. For instance in high concentrations of other elements including Fe and Ti in the ore samples, strong influences on the line intensities of the 367.007 nm (by Fe self-absorption), 386.592 nm (by Ti in high concentration), and 389.036 nm (by Fe self-absorption) were considered.

Effect of the vanadium concentration on structural and photoluminescence of YP1−xVxO4: 1 at. % Tb3+ nanophosphors

Simple sol-gel method was used to synthesize nanoscale yttrium phosphate-vanadates with general formula YP1−xVxO4: 1 at. % Tb3+ (x = 0–1.0). The nanopowder samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and room temperature steady and time resolved photoluminescence spectroscopy. The structural analysis reveals that the volume, the crystallite size of the nanophosphors increases with increasing vanadium content and their morphologies, changes from spherical, for low vanadium content, to rods for high content. Blue and green PL emissions of Tb3+and (VO4)3− were observed in YP1−xVxO4 and investigated in details. In addition, the role of Inter-Valence Charge transfer IVCT band in the quenching process of Tb3+ emission in YP1−xVxO4 is highlighted.

Effect of vanadium admixing on the surface structure of TiO2(110) under non-oxidizing conditions

Single crystalline Ti+V mixed oxide layers have been prepared by doping vanadium into TiO2(110) thin films on TiO2(110) single crystal substrates with a Ti+Ta mixed oxide interlayer between the film and the substrate. The interlayer prevents the diffusion of vanadium into the substrate and also the diffusion of Ti3+ between substrate and overlayer. Mixing vanadium into the TiO2 lattice increases the reducibility of the host oxide as concluded from an appreciable degree of reduction produced by comparatively mild annealing. A high density of bridging oxygen vacancies was identified at the surface of films with a low vanadium content (2%) while a (1×2) reconstruction as also known for massively reduced TiO2(110) was observed for layers with 8% of vanadium. Studies of methanol adsorption indicate that the vanadium atoms are mostly located below the surface since there is no indication of a vanadium-methanol interaction. We provide evidence that the reducibility of the vanadium ions in the thin film is higher than that of the titanium ions and we suggest that this is the origin of the increased reducibility of the mixed oxide.

Hydrogen production by steam reforming of DME over Ni-based catalysts modified with vanadium

Dimethyl ether steam reforming (DME-SR) for hydrogen production has been studied over VNi/Al2O3 catalysts as part of an investigation aimed at the development of effective technology based on second generation of biofuels. Methanol steam reforming (MeOH-SR) was investigated as a step of the DME-SR process. High activity in the MeOH-SR was observed and two different mechanism depending on temperature and influenced by the vanadium content (0.5, 1 and 3%) was evidenced: direct methanol decomposition to CO and H2 was observed at low temperature and low vanadium content and methanol steam reforming reaction occurs majorly to give an almost stoichiometric H2/CO2 ratio at moderate to high temperature (400 °C) over 3VNi. DME conversion is complete at 500 °C over VNi catalysts in DME-SR, as a two steps reaction: DME hydrolysis and MeOH-SR giving an H2 rich gas reformate generated with a H2 selectivity c.a. 60–70% over 0.5VNi and 3VNi, values maintained during 4.5 h of activity in the same reaction conditions with no signs of deactivation or significant coke formation over catalyst surface.