V2O5 Content Research Articles

Controlled synthesis of mesoporous zinc oxide containing oxygen vacancies in low annealing temperature for photoelectrochemical biosensor

Abstract In this work, a mesoporous zinc oxide containing different concentrations of oxygen vacancies (VO) was controlled synthesized via low temperature annealing. XPS, Raman spectroscopy and electron paramagnetic resonance spectroscopy were employed to investigate the changes of VO concentrations following the increase of annealing temperature. According to the experiment, the highest concentration of VO was obtained at the annealing temperature of 350 °C. The relationship between photoelectrochemical biosensor performance and VO concentration was discussed in detail in terms of electrochemical measurements and VO characterization. Results showed that increasing the VO could result in high carrier intensity, active sites and catalytic rate constant. In addition, the performance toward glucose detection could be improved by increasing VO.

Thermally Stable Amorphous Oxide-based Schottky Diodes through Oxygen Vacancy Control at Metal/Oxide Interfaces

Amorphous oxide semiconductor (AOS)-based Schottky diodes have been utilized for selectors in crossbar array memories to improve cell-to-cell uniformity with a low-temperature process. However, thermal instability at interfaces between the AOSs and metal electrodes can be a critical issue for the implementation of reliable Schottky diodes. Under post-fabrication annealing, an excessive redox reaction at the ohmic interface can affect the bulk region of the AOSs, inducing an electrical breakdown of the device. Additionally, structural relaxation (SR) of the AOSs can increase the doping concentration at the Schottky interface, which results in a degradation of the rectifying performance. Here, we improved the thermal stability at AOS/metal interfaces by regulating the oxygen vacancy (VO) concentration at both sides of the contact. For a stable quasi-ohmic contact, a Cu-Mn alloy was introduced instead of a single component reactive metal. As Mn only takes up O in amorphous In-Ga-Zn-O (a-IGZO), excessive VO generation in bulk region of a-IGZO can be prevented. At the Schottky interfaces, the barrier characteristics were not degraded by thermal annealing as the Ga concentration in a-IGZO increased. Ga not only reduces the inherent VO concentration but also retards SR, thereby suppressing tunneling conduction and enhancing the thermal stability of devices.

Aquation reaction of iminodiacetate complex of oxidovanadium(IV) with 2,2’-bipyridine induced by Fe(III) ions: Kinetic studies

The kinetics of the aquation reaction of the [VO(ida)(bipy)]·2H2O (VO(ida)(bipy)) complex (where ida = iminodiacetate anion and bipy = 2,2’-bipyridine) promoted by [Fe(H2O)6]3+ ions were investigated in aqueous solutions. Spectrophotometric studies were carried out at different temperatures in the range of 293.15–313.15 K. The concentration of the [Fe(H2O)6]3+ (Fe3+) ions was kept within the range of 2 × 10–4 to 8 × 10–4 mol L–1, and the concentration of VO(ida)(bipy) was 1 × 10–3 mol L–1. The values of the observable reaction rate constants were calculated based on the Glint computer program. Furthermore, the mechanism for the aquation of VO(ida)(bipy), induced by Fe(III) ions, has been proposed.

Oxygen vacancy mediated conductivity and charge transport properties of epitaxial Ba0.6La0.4TiO3− δ thin films

We report on the effects of the oxygen vacancy (VO) regarding the microstructure, conductivity, and charge transport mechanisms of epitaxial Ba0.6La0.4TiO3−δ (BLTO) films. The VO concentration can be largely regulated from 21.5% to 37.8% by varying the oxygen pressure (PO2) during film deposition. Resistivity-temperature and Hall effect measurements demonstrate that the BLTO films can be tuned remarkably from an insulator to a semiconductor, and even to a metallic conductor by regulating the VO concentration. The role of VO concentration in the charge transport mechanism is clarified. For films with low VO concentration, the charge transport is dominated by variable range hopping (VRH) at low temperatures, and it shows small polaron (SP) hopping at high temperatures. For films with high VO concentration, the carrier transport remains VRH at low temperatures, while it changes to SP hopping at moderate temperatures, and is dominated by thermal phonon scattering at high temperatures. Furthermore, the lower starting temperature of SP hopping for films with higher VO concentrations indicates that VO favors electron-phonon coupling. Different charge transport mechanisms are assumed to be due to different VO-induced defect energy levels in the BLTO films, which has been verified by their soft x-ray absorption spectroscopy results.

Dependence of device behaviours on oxygen vacancies in ZnSnO thin-film transistors

ZnSnO thin-film transistors (TFTs) were fabricated by pulsed laser deposition in different oxygen partial pressures. It is found that the oxygen vacancy (VO) contents in ZnSnO films can be readily modified by the oxygen pressures in the growth process. The dependence of behaviors of ZnSnO films and TFTs on relative VO concentration was studied in detail. The relative VO concentration was determined by XPS spectra. The optical band-gap energies of ZnSnO films showed a negative correlation with VO concentration. The strong relation can also be identified for the electrical performances of ZnSnO TFTs. The threshold voltage, subthreshold swing, and density of interfacial trap states increased with the VO concentration in general. The field-effect mobility had a maximum value of 23.6 cm2 V−1 s−1 at oxygen pressure of 6 Pa, which is ascribed to the competitive factors of VO at different chemical states. It is expected that this work would gain a better understanding of oxygen vacancy in ZnSnO TFTs for practical applications.

K+ deactivation of V2O5-WO3/TiO2 catalyst during selective catalytic reduction of NO with NH3: Effect of vanadium content

The effect of vanadium content on the resistance to K+ deactivation of V2O5-WO3/TiO2 SCR catalyst in biomass-fired flue gas was investigated. Catalytic activity and ammonia oxidation were measured, and the properties of fresh and K+-deactivated catalysts were characterized by XRD, N2 physisorption, H2-TPR, NH3-TPD and NH3-DRIFT. The BET surface area decreases with increased vanadium content for both fresh and K+-poisoned samples, but it is not responsible for catalyst deactivation. Ammonia oxidation starts from 300 °C and becomes more important with increasing vanadium content and at higher temperature. K+ can inhibit ammonia oxidation, but inactivates the newly generated NO2 to be reduced. The increase of vanadium content reduces mainly the Lewis acid sites, while the amount of BrØnsted acid sites increases. Monomeric and polymeric vanadium are the dominant species on the TiO2 support, and the amount of isolated vanadyl (V = O) species decreases with V2O5 content while the amount of V-OH species in polymeric vanadia increases. Isolated vanadyl species are advantageous to high-temperature catalytic activity while polymeric vanadia species increase ammonia and K+ adsorption. The (3 wt% V2O5)-WO3/TiO2 catalyst shows the best performance for both NO reduction and K+ resistance due to it containing both monomeric and polymeric vanadia species (or V = O and V-OH). Catalysts with 3 wt% V2O5 are preferable for flue gases with high alkali metal contents. Finally, the mechanism of reaction for different vanadium contents and corresponding K+-poisoning are also discussed.

Effect of vanadium and nickel on iron-rich ash fusion characteristics

Ash fusibility is the key parameter related with ash slagging in gasifier. The ash fusibility of coal blended with petroleum coke is significantly influenced by vanadium and nickel from petroleum coke. The effects of vanadium (V) and nickel (Ni) on iron-rich ash, such as coal ash with ferrum-based flux addition, are lack of study. This study investigates the effect of vanadium pentoxide (V2O5), nickel monoxide (NiO) and VNiO (V2O5 and NiO) on iron-rich ash fusibility under a reducing atmosphere. X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and X-ray photoelectron spectroscopy (XPS) were used to study the mineral transformation, surface morphology and valence state of vanadium in ash and slag at high temperatures. The results show that high-melting coulsonite (FeV2O4) is generated in slag with the increasing V2O5 content, and FeV2O4 transforms into the karelianite (V2O3) at 1400 °C. The content of iron in liquid slag is reduced for the formation of coulsonite and V-rich spinel in the primary fusion stage. These cause the continuously linear increase of AFTs with the increasing V2O5 content. NiO in ash is reduced to metallic Ni, which promotes metallic Fe precipitation and forms Fe-Ni alloy to agglomerate into spherical particles. The precipitation of Fe reduces the content of iron into liquid slag, leading to increase AFTs slowly. The AFTs also increase significantly with the increase of VNiO content. The interaction between V-containing matter and metallic Ni is not found, and there is not obvious synergistic effect of V2O5 and NiO on AFTs. Besides, the good linear relationships are shown between the AFTs and the contents of V2O5, NiO and VNiO, and R2 of the fitting lines is as high as 0.99. These can be used to guide co-gasification of petroleum coke and iron-rich coal.

Hydrothermal Synthesis and Characterization of Mn-Doped VO2 Nanowires

AbstractMonoclinic VO2 is a known polymorph of vanadium dioxide that has received much attention due to its oxidative capabilities, geometric configuration, and promising applications in functional windows. VO2 can usually be obtained through a hydrothermal method under high pressure. In this work we report a synthesis of VO2 doped with Manganese using a rapid single-step hydrothermal process with V2O5, manganese (II) acetate and citric acid as precursors. Different syntheses were carried out in which the concentration of V2O5 and citric acid remained constant whereas the concentration of manganese (II) acetate was varied. The reactants underwent a stirring phase for 30 minutes before being loaded into a hydrothermal reactor for 2.5 hours at 200°C. The resultant was washed three times to remove the residual precursors. Imaging and spectroscopy characterizations such as TEM, SEM and UV-VIS-NIR have been performed on different doping concentration and the results display a dependence on doping concentrations.

Detailed understanding on the relation of various pH and synthesis reaction times towards a prominent low temperature H2S gas sensor based on ZnO nanoplatelets

Abstract An unceasing scientific challenge to monitor the emissions of toxic and flammable gases in a selective approach is of great importance for safety of human health. As a result, herein, we report on the detailed study of the gas sensing characteristics of ZnO nanostructures prepared at various reaction pH and times. The findings revealed that the variation of synthesis reaction pH and times play a vital role on the morphology and structure. The ZnO-4h@10.5 pH based sensor demonstrated a low response when exposed to reducing gases (CO, CH4 and NH3), volatile organic compounds (ethanol, acetone, benzene and toluene) and oxidizing gas (NO2), while exposed to H2S gas unpreceded and reproducible response (i.e. 3 times more than the interfering gases) at low operating temperature of 75 °C was observed. The exceptional response (i.e. resistance ratio) observed at the low operating temperature towards 40 ppm H2S was elucidated by the improved gas accessibility and relative concentration of VO induced by structural transformation, which induced change in oxygen adsorption. The high H2S gas selectivity was ascribed to the reactivity of H2S and low temperature decomposition to participate in a reaction with a ZnO nanoplatelets-based sensor. The fundamental gas-sensing mechanism associated to the ZnO response and point defects at low operating temperature is evaluated in detail.

Recovery of vanadium from secondary tailing of iron ore by salt roasting-alkaline leaching and solvent extraction processes

In this paper, the recovery of vanadium from the secondary tail deposits of iron ore by salt roasting-alkaline leaching and solvent extraction has been investigated. To extract the vanadium, after the characterizations studies (XRF, SEM, and EPMA analyzes), preliminary leaching was performed using HCl to reduce lime. Subsequently, the solid that was gained from this stage was put in the oven for palletizing and salt roasting (sodium carbonate) at the temperature of 850°C. This sample was leached in the presence of sodium bicarbonate (NaHCO3), under certain conditions. Solvent extraction experiments were carried out on the solution of carbonated leaching under different conditions. According to SEM studies, the dominant are calcium, vanadium, and phosphorus in the sample. The percentage of Vanadium (V), according to EPMA results in the 20 selected points, was determined as 0.65%. XRF analysis showed that V2O5 and CaO contents of sample were 2.04% and 51.72%, respectively. Lime was reduced to 32.59% after initial leaching with HCl. The carbonate leaching resulted in a total recovery of 93.46% at 85 °C for 60 minutes and with 40 g /l of sodium bicarbonate. In addition, under the optimum conditions of pH=6, the ratio Vaq/Vorg=1 and the organic phase concentration of 0.5 M using the anionic Aliquat 336 extractant, Vanadium can be recovered effectively (extraction efficiency=97%) from alkaline leaching solution in the form of decavanadate or and the anions in the form of or in one stage.

The process of vanadium migration and silicon extraction by alkaline leaching from high silicon stone coal under reduction conditions

It is difficult to utilize stone coal with a vanadium grade of below 0.7%. With the aim of effectively utilizing the silicon and vanadium in stone coal, the vanadium concentration and silicon extraction processes by alkaline leaching under reducing conditions were investigated. The effect of NaOH mass fraction, temperature and the amount of hydrazine hydrate on the leaching process was researched. Moreover, the laws of phase transformation and the migration process of vanadium were revealed. The results show that the dissolution of quartz resulted in the exposure of muscovite and goldmanite, but the phase of muscovite and goldmanite was not damaged. Under the optimal operation conditions (25% mass fraction of NaOH, liquid-solid ratio 2:1 at 200 °C for 4 hours), 90.14% of silicon was removed. At the same time, the modulus of sodium silicate product reached 1.88 and the content of V2O5 enriched from 0.5% to 2.51%. In addition, V(IV) was partially reduced to V(III) by adding hydrazine hydrate in an amount of 10% by mass. V(IV) migrated from the liquid phase to the alkali leaching slag, and the recovery of vanadium increased from 89.48% to 94.43%. All the obtained results suggest an efficient process for separation and extraction of vanadium and silicon.

Influence of oxygen vacancies on the spontaneous polarisation and piezoelectricity of ZnO: a first-principles study

By using the Berry phase method, influence of oxygen vacancy (Vo) on the polarisation property of ZnO has been investigated. Calculated results indicate that the spontaneous polarisation, the piezoelectric constants e31 and e33 are very sensitive to the concentration and distribution of Vo. The absolute values of them decrease nonlinearly as Vo concentration increases. At the same concentration, non-uniform distribution of Vo is favoured in energy, and can enhance the impact on spontaneous polarisation and e31. 1.56% Vo-Vo complex can even reverse the orientation of the spontaneous polarisation, while the case for e33 is opposite, the influence is weakened. These findings suggest that the polarisation property of ZnO might be adjusted by controlling the point defects.

Influence of oxygen vacancies on the spontaneous polarisation and piezoelectricity of ZnO: a first-principles study

By using the Berry phase method, influence of oxygen vacancy (Vo) on the polarisation property of ZnO has been investigated. Calculated results indicate that the spontaneous polarisation, the piezoelectric constants e31 and e33 are very sensitive to the concentration and distribution of Vo. The absolute values of them decrease nonlinearly as Vo concentration increases. At the same concentration, non-uniform distribution of Vo is favoured in energy, and can enhance the impact on spontaneous polarisation and e31. 1.56% Vo-Vo complex can even reverse the orientation of the spontaneous polarisation, while the case for e33 is opposite, the influence is weakened. These findings suggest that the polarisation property of ZnO might be adjusted by controlling the point defects.

An Environment-Friendly Process Featuring Calcified Roasting and Precipitation Purification to Prepare Vanadium Pentoxide from the Converter Vanadium Slag

Converter vanadium slag is a byproduct of the iron making process when the vanadium titanomagnetite is used as iron raw material. A cleaner process including calcified roasting, dilute acid leaching, precipitation purification, vanadium precipitation with ammonium salt, followed by thermal decomposition was proposed to extract vanadium resource from this slag. And then vanadium pentoxide with purity over 98% was prepared, which can be used as additives for high strength low alloy steel production. A total vanadium recovery beyond 80% was achieved in this whole process. Since no sodium and potassium salt was introduced, wastewater generated was closed-circulating after removing the enriched impurities of P, Si, Ti and Cr with adding powder CaO. The content of V2O5 in residues after vanadium extraction was lower than 1.2 wt.%, while other valuable metals like Fe, Mn, Cr and Ti were concentrated. With no alkaline metal salts added in this process, the metal resources of Fe, Mn, Cr and Ti in the residues were more feasible to be recovered with pyrometallurgy processes.

Morphological Modification and Analysis of ZnO Nanorods and Their Optical Properties and Polarization.

We report on the effect of the morphological modification on optical properties and polarization of ZnO nanorods (NR). Here, the morphology and structure of the ZnO NR were modified by introducing different annealing temperatures. The increase of length and diameter and change in density of the ZnO NR were clearly observed by increasing the annealing temperature. We found that the samples show different oxygen vacancy (VO) and zinc interstitial (ZnI) concentrations. We suggest that the different concentrations of VO and ZnI are originated from morphological and structural modification. Our results reveal that optical absorption and polarization of ZnO NR could be enhanced by producing a high concentration of VO and ZnI. The modification of VO and ZnI promotes a decrease in the band gap and coexistence of high optical absorption and polarization in our ZnO NR. Our findings would give a broad insight into the morphological modification and characterization technique on ZnO NR. The high optical and polarization characteristics of ZnO NR are potential for developing the high-performance nanogenerator device for multitype energy harvesting.

The effect of N-doped form on visible light photoactivity of Z-scheme g-C3N4/TiO2 photocatalyst

The reasons for the difference of visible light activity between the direct contact g-C3N4/TiO2 Z-scheme composites obtained by one-step or two-step calcination process were investigated in detail by XRD, TEM, XPS, Raman and ESR technologies. TEM results showed that only g-C3N4 obtained by two-step calcination (denoted as CN-TSC) presented the porous structure which was in favor of the light absorption. XPS analysis indicated that interstitial doped N species formed in one-step calcination composite (denoted as CT-OSC) while substitutional N would appear in two-step calcination composite (denoted as CT-TSC). Nevertheless, interstitial N located at the higher position in the band gap of TiO2 and usually acted as the strong capture center of holes which was unfavorable to charge transfer. ESR and Raman results indicated that CT-TSC with some concentration of surface Vo and lower concentration of bulk Vo had excellent charge separation efficiency, according to the surface-enhanced Raman scattering (SERS) results of photo-induced charge-transfer (PICT) enhancement mechanism. And as a result, the visible-light activity for propylene oxidation of CT-TSC was twice higher than that of CT-OSC.

Fine-Tunable Self-Activated Luminescence in Apatite-Type (Ba,Sr)5(PO4)3Br and the Defect Process.

Intrinsic defect-related luminescence has recently been attracting more research interest for the modification of phosphors. However, the connection between defect formation and crystal structure has never been considered. In this work, we report that in the absence of an impurity activator, under a reducing atmosphere, apatite-type compound M5(PO4)3X (M = Ca, Sr, or Ba; X = F, Cl, or Br) can emit tunable colors ranging from blue to orange depending on the content of M and X. To better understand the cause, Ba5- mSr m(PO4)3Br (BSPOB; m = 0-5) solid solutions were analyzed in detail. The dependency of self-activated luminescence on atmospheric conditions and solid solution compositions was investigated by combining experimental characterizations and theoretical calculations using density functional theory. Crystal structures of these solid solutions were verified by X-ray diffraction patterns as well as Rietveld refinements. With the defect formation energy and electron paramagnetic resonance measurement, we propose that an oxygen vacancy (VO) should be mainly responsible for the peculiar super wide band emission. Moreover, the enhanced distortion of solid solution crystal structures augments VO concentrations and leads to luminescence intensities in solid solutions that are higher than that in end point compounds. Variations of the electronic structure of BSPOB matrices with gradual tuning of the Sr/Ba ratio were also investigated. As a result, the introduction of VO defect levels within the band gap leads to the formation of donors and acceptors, allowing for a modulation of the photoluminescence throughout the visible part of the spectrum. As the first report in the literature to demonstrate fine-tunable emissions over a wide wavelength range as a consequence of native defective levels in a series of continuous apatite-type solid solutions, our results illustrate the feasibility of defect-meditated systems by carefully tailoring defect chemistry and nonstoichiometric chemical composition under controlled conditions to engineer phosphor properties.

EPR studies on VO2+doped sodium –borate glasses synthesized by microwave method

Electron paramagnetic resonance (EPR) of VO2+ions in sodium borate glass system has been studied over a wide range of composition. The EPR spectra exhibited hyper fine splitting (hfs) due to considerable weakening of interaction between vanadium ion concentrations. The hfs is seen between 10 and 35 mol% of vanadium concentration. The appearance of hfs is due to the interaction of 3d1 electron spin of 51V ion with its nuclear spin, which increases with increasing concentration till 35 mol%. The spin -Hamiltonian parameters (g and A), the dipolar hyperfine coupling parameter (P) and Fermi contact interaction parameter (k) have also been evaluated. The values of spin-Hamiltonian parameters indicate that VO2+ ions are in octahedral coordination with a tetragonal compression which can be attributed to the structural changes taking place with the increasing concentration of V2O5

Effect of V2O5 concentration on the structural and optical properties and DC electrical conductivity of ternary semiconducting glassy nanocomposites

Transition metal oxide–doped glassy nanocomposites of the form xV2O5-(1 − x) (0.05CdO-0.95ZnO) with x = 0.3, 0.5, 0.7, and 0.9 were prepared by the melt quenching route. Their microstructure was studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, transmission electron microscopy, and optical absorption spectroscopy. The absorption bands at around 640–756 cm−1 are attributed to the antisymmetric stretching vibrations of VO2 groups. Physical attributes such as density, molar volume, oxygen molar volume, oxygen packing density, number of bonds per unit volume, and the average stretching force constant were evaluated. The XRD patterns reveal distinct diffraction peaks indicating crystallinity in the sample with x = 0.3, whereas significantly broadened patterns are observed in samples with x = 0.5, 0.7, and 0.9, reflecting a dominant amorphous nature. Different peaks in the XRD patterns indicate the formation of Zn2V2O7, ZnV2O6, CdV2O6, Cd2V2O7, and CdVO3 nanocrystallites, which are dispersed in the as-prepared glassy matrices. The optical absorption spectra show indirect transitions. With a rise in the concentration of V2O5, the optical transmission cutoff wavelength moves to higher wavelength. DC electrical conductivity was studied at various temperatures from 60–650 °C. The establishment of small polaron hopping was anticipated from the DC electrical conductivity data. DC conductivity was inferred with use of Mott's and Greaves's variable range hopping models.

Modeling and interpretation of UV and blue luminescence intensity in β-Ga2O3 by silicon and nitrogen doping

Temperature-dependent cathodoluminescence spectra of (2¯01) Si-doped β-Ga2O3 single crystals and (010) N-doped epitaxial films were comprehensively shown to investigate their electronic structure and defect states. The decrease in the self-trapped exciton (STE) emission at low temperatures in heavily Si-doped crystals implied the Debye-Hückel screening of STEs with the critical charge density larger than 2 × 1018 cm−3. The analysis based on the rate equation model suggested a significant influence of the donor-acceptor-pair recombination involving a SiGa donor on the UV luminescence band in the Si-doped crystals. The blue luminescence band was suppressed for the heavily N-doped epitaxial films with a N concentration of 1 × 1018 cm−3, implying the decrease in the oxygen vacancy (VO) concentration by N doping. The increase in the NO acceptor concentration as well as the decrease in the VO concentration were found to contribute to the compensation of residual Si donors resulting in high resistivity of N-doped epitaxial films.