Vanadate Phase Research Articles

Silver vanadate and cerium oxide decorated graphene oxide ternary heterostructure nanocomposites: structural, electrochemical, and optoelectrical properties

In the present work, we synthesized a novel ternary heterostructure nanocomposite comprising Silver Vanadate and Cerium Oxide Decorated Graphene Oxide (AgVO3-CeO2/GO) using a straightforward and cost-effective method. Six samples, including GO, CeO2, CeO2/GO, AgVO3, AgVO3/GO, and CeO2-AgVO3/GO, were prepared. The structural, morphological, electrochemical, and optoelectrical properties of these samples were thoroughly investigated. X-ray diffraction (XRD) demonstrated the presence of graphene oxide, cerium oxide, and silver vanadate phases, while transmission electron microscopy (TEM) showed the single crystalline nature of AgVO3 and the dispersion of CeO2 and AgVO3 nanoparticles within the GO matrix. The heterojunctions between different components facilitated efficient charge transfer and enhanced optoelectronic performance. External quantum efficiency was measured using a 532 nm laser beam, and the electrical properties were evaluated under dark and illuminated conditions with a two-point probe setup. The inclusion of CeO2 and AgVO3 nanoparticles in the GO matrix improved charge transport and interfacial charge transfer processes. These findings highlight the potential of these materials for various optoelectronic applications, including photodetection, sensing, and energy harvesting, with further optimization potentially leading to high-performance devices with enhanced functionality and efficiency.

SrTiO3-SrVO3 Ceramics for Solid Oxide Fuel Cell Anodes: A Route from Oxidized Precursors.

Perovskite-type Sr(Ti,V)O3-δ ceramics are promising anode materials for natural gas- and biogas-fueled solid oxide fuel cells, but the instability of these phases under oxidizing conditions complicates their practical application. The present work explores approaches to the fabrication of strontium titanate-vanadate electrodes from oxidized precursors. Porous ceramics with the nominal composition SrTi1-yVyOz (y = 0.1-0.3) were prepared in air via a solid state reaction route. Thermal processing at temperatures not exceeding 1100 °C yielded composite ceramics comprising perovskite-type SrTiO3, pyrovanadate Sr2V2O7 and orthovanadate Sr3(VO4)2 phases, while increasing firing temperatures to 1250-1440 °C enabled the formation of SrTi1-yVyO3 perovskites. Vanadium was found to substitute into the titanium sublattice predominantly as V4+, even under oxidizing conditions at elevated temperatures. Both perovskite and composite oxidized ceramics exhibit moderate thermal expansion coefficients in air, 11.1-12.1 ppm/K at 30-1000 °C, and insignificant dimensional changes induced by reduction in a 10%H2-N2 atmosphere. The electrical conductivity of reduced perovskite samples remains comparatively low, ~10-1 S/cm at 900 °C, whereas the transformation of oxidized vanadate phases into high-conducting SrVO3-δ perovskites upon reduction results in enhancement in conductivity, which reaches ~3 S/cm at 900 °C in porous composite ceramics with nominal composition SrTi0.7V0.3Oz. The electrical performance of the composite is expected to be further improved by optimization of the processing route and microstructure to facilitate the reduction of the oxidized precursor and attain better percolation of the SrVO3 phase.

Vanadium Speciation in Ancient Shales Revealed through Synchrotron-Based X-ray Spectroscopy

Redox-sensitive trace elements, such as vanadium, are frequently used as paleoredox proxies to infer the redox status of ancient marine depositional environments. When applied to vanadium, this approach relies on an accurate understanding of vanadium geochemistry in marine sediments. This, in turn, requires the application of analytical techniques capable of providing reliable chemical information on vanadium host phases of vanadium and thus the ability to distinguish authigenic from detrital phases. The increasing availability of synchrotron-based X-ray spectroscopic techniques capable of providing chemical speciation information at both the bulk and micro-scale presents an opportunity to refine our understanding of vanadium geochemistry in ancient marine sediments. Here, we show the utility of synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy and scanning X-ray fluorescence microscopy (SXFM) for investigating vanadium host phases in ancient marine sediments. The studied samples from the 1400 Ma Xiamaling Formation came from strongly contrasting depositional settings (ranging from oxic to euxinic) with a wide range of vanadium enrichments (enrichment factors from 0.7 to 9.6), yet vanadium speciation determined by XANES was consistently found to be phyllosilicate-hosted vanadium (III). High-resolution elemental imaging by SXFM coupled with global statistical colocalization analyses revealed strong associations between vanadium and potassium, consistent with vanadium hosted by potassium-rich clay minerals. These findings, while demonstrating the power of synchrotron-based X-ray methods, imply that differentiating authigenic and detrital vanadium in ancient marine sediments is unlikely to be possible given that post-depositional processes result in similar chemical speciation for both fractions. This will also limit the reliability of vanadium isotope system studies that depend on differentiating authigenic and detrital fractions using selective extraction procedures.

Heterogeneity of the vanadia phase dispersed on titania. Co-existence of distinct mono-oxo VOx sites.

The structural and configurational characteristics of the species comprising the (VOx)n phase dispersed on TiO2(P25) are studied under oxidative dehydration conditions by in situ molecular vibrational spectroscopy (Raman, FTIR) complemented by in situ Raman/18O isotope exchange and Raman spectroscopy under static equilibrium at temperatures of 175-430 °C and coverages in the 0.40-5.5 V nm-2 range. It is found that the dispersed (VOx)n phase consists of distinct species with different configurations. At low coverages of 0.40 and 0.74 V nm-2, isolated (monomeric) species prevail. Two distinct mono-oxo species are found: (i) a majority Species-I, presumably of distorted tetrahedral OV(-O-)3 configuration with VO mode at 1022-1024 cm-1 and (ii) a minority Species-II, presumably of distorted octahedral-like OV(-O-)4 configuration with VO mode at 1013-1014 cm-1. Cycling the catalysts in the 430 → 250 → 175 → 430 °C sequence results in temperature-dependent structural transformations. With decreasing temperature, a Species-II → Species-I transformation with concomitant surface hydroxylation takes place by means of a hydrolysis mechanism mediated by water molecules retained by the surface. A third species (Species-III, presumably of di-oxo configuration with νs/νas at ∼995/985 cm-1) occurs in minority and its presence is increased when further lowering the temperature according to a Species-I → Species-III hydrolysis step. Species-II (OV(-O-)4) shows the highest reactivity to water. For coverages above 1 V nm-2, an association of VOx units takes place leading to gradually larger polymeric domains when the coverage is increased in the 1.1-5.5 V nm-2 range. Polymeric (VOx)n domains comprise building units that maintain the structural characteristics (termination configuration and V coordination number) of Species-I, Species-II, and Species-III. The terminal VO stretching modes are blue-shifted with increasing (VOx)n domain size. A lower extent of hydroxylation is evidenced under static equilibrium forced dehydrated conditions, thereby limiting the temperature dependent structural transformations and excluding the possibility of incoming water vapors as the cause for the temperature dependent effects observed in the in situ Raman/FTIR spectra. The results address open issues and offer new insight in the structural studies of VOx/TiO2 catalysts.

Performance analysis of three distinct NixV2Oy single-phase nano self-assemblies for asymmetric supercapacitor fabrication and effective detection of low-concentration hazardous herbicide.

Single-phase inorganic nanostructures with multiple applications are required for cost-effective, sustainable applications to save the environment from toxic activities. Nickel vanadate (NixV2Oy), possessing three phases, such as NiV2O6, Ni2V2O7, and Ni3V2O8, acts as an effective electrode material and potential electrochemical sensors. Nickel vanadate phases (NiV2O6, Ni2V2O7, and Ni3V2O8) were synthesized through the gel-matrix technique, and their phase purity, crystallinity, morphology, optical properties, etc., were evaluated and studied. Electrochemical studies infer that NiV2O6 exhibits the highest specific capacity of 251 C g-1 (69.7 mA h g-1) at 1 A g-1 compared to the other nickel vanadate phases and provides better cyclic stability of 80.19% for 5000 cycles. The asymmetric supercapacitor device fabricated from NiV2O6 results in a specific capacity of 189 C g-1 (52.5 mA h g-1), energy density of 59.06 W h kg-1, and a power density of 1125 W kg-1 with a capacitive retention rate of 74.91% and coulombic efficiency of 99.61% for 10 000 cycles. The electrochemical detection potential of NixV2Oy in bifenox herbicide has been studied with all the synthesized nanostructures. Among them, NiV2O6-based sensor probes demonstrated excellent characteristics, including high sensing current and low detection limits of 0.6 nM with a linear range of 1-57 nM. The real-time herbicide detection of NiV2O6 in live samples was checked with freshly harvested potatoes. This advancement further enhances the utilization of NixV2Oy materials for electrochemical applications.

Characterisation of carnotite and tyuyamunite using Raman, luminescence and laser-induced breakdown spectroscopy

Among the wide range of natural uranium minerals, uranyl vanadates have attracted particular attention due to the economic viability of co-producing uranium and vanadium for industrial applications The typically remote locations of the ore deposits favour in situ analytical techniques offering rapid, minimally destructive characterisation wherever possible. This study reports on the use of luminescence, Raman and laser-induced breakdown spectroscopy to characterise the two most commonly found uranyl vanadates in nature, carnotite (K2(UO2)2V2O8·3H2O) and tyuyamunite (Ca(UO2)2V2O8·5–8H2O); the first attempt to use all three laser-based techniques in tandem for these phases. Significant differences in the luminescence emission signal intensity along with a noticeable shift in the resolved emission peak positions enable carnotite and tyuyamunite to be readily distinguished. Extraction of the band spacing from luminescence emission spectra provides confirmation of the position of the equivalent Raman uranyl symmetric stretch, ν1(UO2)2+, vibration for each mineral. Raman itself, was unable to differentiate carnotite and tyuyamunite owing to the weak signals obtained; however, the degree of splitting in the vanadate symmetric stretch, ν1(VO3)3-, feature and, to a lesser extent, the position of the ν1(UO2)2+ peak might be used to distinguish between tyuyamunite and metatyuyamunite, although further studies are required for confirmation. Compositional LIBS analysis was successful in identifying minor quartz, gypsum, Mg- and Fe-bearing inclusions, subsequently confirmed by optical and scanning electron microscopy. The findings indicate that multiple laser-based techniques offer the potential for real-time characterisation of uranyl vanadate phases where intrusive sampling, transportation and ‘off-site’ laboratory analysis is impracticable.

Enhanced optical properties of yttrium aluminum garnet with the yttrium vanadate impurity phase

Yttrium aluminum garnet doped with europium with an additional impurity phase of yttrium vanadate doped europium has been prepared in different ways: synthesized by a sol-gel route and mechanically mixed in a mortar. The obtained samples were characterized by X-ray diffraction analysis, and scanning electron microscopy. Photoluminescence spectra were recorded to understand the role of the impurity phase in the garnet's optical properties. The impurity phase showed a significant contribution to the optical properties of Y3Al5O12:1%Eu.

Mixed Ionic and Electronic Conduction in TeO2-ZnO-V2O5 Glasses towards Good Dielectric Features.

The melt-quenching technique was used to synthesize tellurite glasses of the chemical composition 80TeO2-(20-x) ZnO-xV2O5. X-ray diffraction (XRD) patterns indicate the amorphous nature of the prepared glasses. Raman and FTIR measurements demonstrate a progressive substitution of the Te-O-Te linkages by the Te-O-V bridges and the formation of VO4 and VO5 units by a change of the vanadium coordination due to the higher number of oxygens incorporated by further addition of V2O5. The AC conductivity was investigated in the frequency range of 40 Hz to 107 Hz between 473 K to 573 K. A good coherence of the AC conductivity was found using a model correlating the barrier hopping (CPH) and the dominant conduction process changes from ionic to polaronic with the addition of V2O5. The dielectric constant exhibits high values in the range of lower and medium frequencies. Both variations of the electric modulus and the dielectric loss parameters with frequency and temperature showed a relaxation character mainly assigned to the vanadate phases. The electric modulus displays a non-Debye dielectric dispersion and a relaxation process. The present results open the door to future zinc-tellurite glasses-doped vanadium exploitation as a potential electrolyte-based material for solid-state batteries.

Dual-phase high-entropy (FeCoNiZn)xV2Oy oxides with promising microwave absorption properties

Dual-phase high entropy oxide (HEO) ceramics (FeCoNiZn)xV2Oy were prepared using a simple sintering process. Vanadium oxide was selected due to the characteristics of reduction ability and multiphase transformation under different conditions. The crystal structure, microstructure, elemental chemical state, magnetic property and microwave absorption (MA) properties of HEO ceramics were studied. The results show that the two-phase structure is spinel phase and vanadate phase, and there are oxygen vacancies in the samples. Magnetic properties can be promoted with high content of spinel phase. Lots of oxygen vacancies were found in the sample sintered at 900 °C, which exhibited good MA ability. The minimum reflection loss (RL) of −36.5 dB was obtained at 10.72 GHz with a thickness of 2.2 mm, while the effective bandwidth reached 2.77 GHz. Large number of oxygen vacancies can speed up the migration of electrons or ions, thereby improving the dielectric loss capability.

Sodium-pillared vanadium oxides as next-gen materials: Does co-inserted water control the cyclic stability of vanadates in an aqueous electrolyte?

Layered vanadium oxides are, due to their adaptable interlayer distance and a multivalent state of vanadium, interesting electrode materials for various kinds of metal-ion batteries with both aqueous and nonaqueous electrolytes. In this study, a precursor solution adjusted for hydrothermal synthesis of sodium vanadate Na2V6O16, is modified by addition of carbon nanopowder Vulcan XC72, and this suspension is used for an one-pot hydrothermal synthesis of sodium vanadate/C composite. XRD analysis evidenced that the obtained composite is the mixture of two vanadate phases: Na2V6O16 and NaV6O15, instead of expected single-phase vanadate. SEM and TEM observations of composite revealed that these vanadate phases emerge in a form of both nanowires and nanospheres. The heterogeneity of phases and morphology of the composite is attributed to the directional action of carbon nanoparticles as a nucleation seed. The composite, used in aqueous Li-ion battery with LiFe0.95V0.05PO4/C cathode and LiNO3 electrolyte, displayed improved charge storage (220 mAh g−1 at current rate 150 mA g−1 in the initial discharge), after dc charging, in comparison to NaV6O15 or Na2V6O16 nanowire anodes. Furthermore, versatile insertion capability of this heterostructured composite towards mono (Li+, Na+) and multivalent (Ca2+, Mg2+, Al3+) ions in aqueous electrolytes is demonstrated by Cyclic Voltametry method, where the capacity stability depends on the type of cation, following the order Al3+, Li+, Mg2+, Ca2+. Upon 100 potentiodynamic chaging/discharging cycles, Ca2+ions display much better capacitance retention than Li+ ions (i.e., 64 vs. 13% of the initial value). The coinserted electrolyte constituents, H2O and OH− species, are considered to be responsible for the improved capacity retention, making vanadium ions less strained and less soluble. The pH, the concentration of the electrolyte and the type of anion are found to influence the cyclic behavior of observed vanadate composite in Ca-containing electrolyte. These results open a new directions in vanadate electrochemistry towards more sustainaible and cheaper aqueous batteries.

(Digital Presentation) Vanadium Intercalated Cobalt Trimesic MOF Composite for Enhanced Solid-State Asymmetric Supercapacitor Storage

Metal organic framework (MOF) is a supramolecular coordination material composed of metal ions coordination, nodes, and organic ligands. MOFs were used as active materials for chemical capacitors to realize the high electrochemical performance, providing adequate redox sites and accelerating ion diffusion rate. Using MOF as a template to fabricate a novel platform can deliver large specific surface areas and abundant oxidation-active sites to augment electrical conductivity. The electrode material based on a MOF has a unique morphology that can significantly shorten charge transport paths to alleviate the electron transport and diffusion, thus strengthening the catalytic performance of the electrode materials. Also, the incorporation of vanadium in the intermediate leads to a broad impact on the morphology and the electrochemical energy storage of Cobalt-Trimesic matrix worked as a base for fabricating the composite. The DMF is a solvent to prepare the vanadium cobalt oxide composite derived using the MOF matrix. Trimesic acid is used as an initial organic linker precursor to initiate the formation of MOF of cobalt in DMF solvent. Then the vanadium ion is integrated into the same material matrix. In this study, the impact of organic system precursors and the integration of annealing play a pivotal role in alleviating the enhanced electrochemical storage response. After analyzing through XRD, the corresponding MOF crystal peaks are prominently affirmed. The high intensified peaks in the obtained patterns symbolize the oxide phase of cobalt vanadium and confirm the formation derived from MOF. The FTIR spectroscopy investigation depicted the proper presence of cobalt, vanadium, carbon, and nitrogen. The observed FESEM morphology illustrated the dissimilar structure and involved in the charge storage likewise. The morphology significantly impacts surface-dependent charge storage with having porosity introduced. High-temperature annealing also consists of the crystal orientation of the bi-metallic MOF matrix and creates porosity on the effective surface area.The Co-MOF-V oxide composite is thoroughly investigated individually in three-electrode arrangements for analyzing the electrochemical charge storage in 2MKOH represented in Fig.1 (c-d). Firstly, the oxide is scrutinized as working positive electrodes and measured in the potential window of -0.2 to 0.6 V w.r.t the saturated calomel reference electrode. The accomplished specific capacitance value from the cyclic voltammetry plot is 549 F/g at 2mV/s scan rate. Furthermore, the charge-discharge analysis of the composite delineated an admirable discharge time at 3mA/cm2 current density. It portrayed 349 F/g specific capacitance, leading to higher specific energy and specific power of 31.02Wh/kg and 159.53W/kg at the value of the same current density. The Nyquist plot corroborates that the electrode resistance, electrode-electrolyte interfacing resistance, and the value of diffuse layer resistance are significantly less. This study can bestow a greater pathway of ion transportation from the electrolyte to active electrode material that abetted to conversate superior storage using complete morphology. The transition metal possesses a variational oxidation state that directly contributes to this MOF composite's pseudocapacitive charge storage process. Alternatively, comparable analysis is directed over anode material that is lignocellulose derived activated porous carbon. It is depicted in Fig.1(e-f) in the potential window of -1 to 0v w.r.t the Ag/AgCl electrode in 2M KOH. The gained specific capacitance from the cyclic voltammetry analysis is 426 F/g at a 2mV/s scan rate. Besides, the charge-discharge study of the same carbon depicted admirable discharge time at 0.5A/g current density and portrayed 565 F/g specific capacitance. The specific energy and power of 78.47Wh/kg and 282W/kg at the same current density. Also, the integrated porous system with the high active surface area, which significantly comes from the MOF matrix, provides an added phase to strengthen the amount of storage like EDLC formation.Furthermore, combining both of those active materials, the asymmetric supercapacitor storage is made up [Fig.1 (g-h)]. That system works upon 0 to 1.4V windows. The attained areal capacitance is 0.54 F/cm2, and volumetric capacitance is 0.68 F/cm3 in the current density of 4mA/cm2. The Ragone plot shows its perfect positioning in the region of asymmetric storage. This ASC system delineated coulombic efficiency 79% of capacitive retention 75% after the 10,000 long cycle stability study. From the electrochemical impedance spectroscopy analysis, the obtained interfacing and electrode resistance diffuse layer resistance is found significantly lesser and upwards. Figure 1

Synthesis of Phase-Pure Thermochromic VO2 (M1).

A highly reproducible, simple, and inexpensive synthesis method for obtaining phase-pure thermochromic monoclinic VO2 (M1) is presented. Vanadium(III) oxide and ammonium metavanadate were used as starting materials and no additional reducing agents are required. Heating a mixture of these two components under an argon atmosphere at 750 °C for 2-4 h provides the direct formation of VO2 (M1) without detectable impurity phases. The formation reaction of VO2 (M1) was studied using in situ powder X-ray diffraction (PXRD), where a pressed pellet of the precursor material was heated during the continuous collection of PXRD data on a two-dimensional detector. The formation takes place via at least two crystalline intermediate phases where the first forms at 170-185 °C (likely an ammonium and oxygen deficient (NH4)1-δVO3-δ phase), and the second at 230 °C (likely a more disordered phase due to the increased background intensity). We assume that the solid-state reaction between the unknown but likely disordered vanadate phase and vanadium(III) oxide starts at 395 °C in concert with the appearance of several other unknown crystalline phases. At 610-750 °C, phase-pure rutile VO2 (P42/mnm) is obtained, which upon cooling converts to monoclinic VO2 (M1). The product composition, microstructure, and homogeneity are characterized by Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The synthesized VO2 (M1) has a sharp reversible insulator-to-metal transition at 71.3 °C during heating and 59.5 °C during cooling, as characterized using differential scanning calorimetry, and resistivity and magnetic property measurements.

A new process for extracting vanadium by direct calcification using the heat of molten vanadium slag

A novel technology for extracting vanadium from molten converter vanadium slag was studied at the laboratory scale by oxidation and calcification. The effect of the cooling method, CaO addition, and reaction time on the phases of calcified vanadium slag was studied. Under the action of oxygen and CaO, the molten vanadium slag underwent calcification reaction to form acid-soluble calcium vanadate phase and the feasibility of its main chemical reaction was calculated by Factsage8.1. The calcified vanadium slag was leached by H2SO4 solution and characterized by the XRF, XRD, SEM, and EDS techniques. Compared with the traditional process, the new process saved much energy, and it was faster and more efficient. The XRD results showed that CaV2O5, Ca7V4O17, and Ca3V2O8 were gradually formed in the molten vanadium slag with increasing CaO addition. However, when too much CaO was added, Ca2SiO4 and CaTiO3 were also formed. These phases wrapped part of the vanadium and reduced the leaching rate of vanadium. When the mass ratio of Ca to V was 0.75, under the optimal acid leaching conditions (particle size of calcified vanadium slag less than 0.075 mm, leaching temperature 90 ?, H2SO4 concentration 200 g.L-1, liquid-to-solid ratio 6:1 ml.g-1, leaching time 60 min, and stirring speed 300r.min-1), the leaching rate of vanadium from calcified vanadium slag could exceed 90%. The new process not only saved energy and reduced emissions, but also reached the average level of the existing vanadium extraction process.

Exploring the role of fuel on the microstructure of VOx/MgO powders prepared using solution combustion synthesis

We report findings of a structural characterization of VOx/MgO powders prepared by a stoichiometric solution combustion synthesis using five different fuels. Characterization of the synthesized powders was done using X-ray diffraction, Raman spectroscopy, Inductively Coupled Plasma Emission Spectroscopy, Scanning Electron Microscopy and Aberration Corrected Transmission Electron Microscopy. It was found that the microstructure and extent of vanadate phase formation and dispersion, for each powder, were influenced by the selection of fuel used. By correlating experimentally extracted microstructural parameters to calculated thermodynamic parameters we demonstrate the important role of the fuel in controlling the reaction kinetics. Specifically, we highlight the role of a fuel's reducing valency in regulating the maximum temperature and heating rate of a reaction. Based on the findings we propose a model of formation for the material system, demonstrating the potential of this novel one-step method for the controlled synthesis of VOx/MgO powders for catalytic applications.

First principles studies of the electronic and structural properties of the rutile VO2(110) surface and its oxygen-rich terminations

We present a density functional theory (DFT) study of the structural and electronic properties of the bare metallic rutile VO2 (110) surface and its oxygen-rich terminations. Due to the polyvalent nature of vanadium and abundance of oxide phases, the modelling of this material on the DFT level remains a challenging task. We discuss the performance of various DFT functionals, including PBE, PBE + U (U = 2 eV), SCAN and SCAN + rVV functionals with non-magnetic and ferromagnetic spin ordering, and show that the calculated phase stabilities depend on the chosen functional. We predict the presence of a ring-like termination that is electronically and structurally related to an insulating V2O5 (001) monolayer and shows a higher stability than pure oxygen adsorption phases. Our results show that employing the spin-polarized SCAN functional offers a good compromise, as it offers both a reasonable description of the structural and electronic properties of the rutile VO2 bulk phase and the enthalpy of formation for oxygen rich vanadium phases present at the surface.

Boosting the Electrochemical Performance of V2 O3 by Anchoring on Carbon Nanotube Microspheres with Macrovoids for Ultrafast and Long-Life Aqueous Zinc-Ion Batteries.

Zinc-ion batteries (ZIBs) are next-generation energy storage systems with high safety and environmental friendliness because they can be operated in aqueous systems. However, the search for electrode materials with ideal nanostructures and compositions for aqueous ZIBs is in progress. Herein, the synthesis of porous microspheres, consisting of V2 O3 anchored on entangled carbon nanotubes (p-V2 O3 -CNT) and their application as cathode for ZIBs is reported. From various analyses, it is revealed that V2 O3 phase disappears after the initial charge process, and Zn3+ x (OH)2+3 x V2- x O7-3 x ∙2H2 Oand zinc vanadate (Zny VOz ) phases undergo zinc-ion intercalation/deintercalation processes from the second cycle. Additionally, the electrochemical performances of p-V2 O3 -CNT, V2 O3 -CNT (without macrovoids), and porous V2 O3 (without CNTs) microspheres are compared to determine the effects of nanostructures and conductive carbonaceous matrix on the zinc-ion storage performance. p-V2 O3 -CNT exhibits a high reversible capacity of 237mA h g-1 after 5000 cycles at 10 A g-1 . Furthermore, a reversible capacity of 211mA h g-1 is obtained at an extremely high current density of 50 A g-1 . The macrovoids in V2 O3 nanostructure effectively alleviate the volume changes during cycling, and the entangled CNTs with high electrical conductivity assist in achieving fast electrochemical kinetics.

Assessment of possibility of obtaining alloying components in the process of desalting of heavy hydrocarbon raw materials. Part 2

Earlier, the authors had already successfully proposed a method for extracting minerals from crude oil as a first step, to be further developed in this second step in the direction of obtaining solid (metallic and / or oxide) phases of nickel and vanadium. The scientific, practical and strategic importance of the work is clearly-underlined with a general depletion of vanadium and nickel ores. In the current situation of mineral resources with a general depletion of vanadium and nickel ores, it becomes necessary to search for new and alternative resources to obtain these strategic and important metals and their compounds from available resources. Taking into account that vanadium and nickel ores are practically absent in the raw material resources base of some countries, such as Middle East’s countries. Thus, a high percentage of imports of this metal product remains, which worsens the economic situation that has developed during political conflicts. The scientific approach was based on a combination of hydrometallurgical and electrometallurgical experiments, consistently carried out through the processes of sorption and desorption during cathodic electrodeposition. Sorption processes for vanadium and nickel were carried out using a mixture of Syrian sorbing materials (incense-type resins and surface-activated natural clays) with finely ground glass SiO2. Cathodic electrodeposition experiments were carried out on a copper cathode plate, and on the other hand, an insoluble glassy carbon electrode was used as the anode. All batch experiments were carried out to determine the best conditions for vanadium and nickel sorption by studying six different parameters affecting the sorption capacity of vanadium and nickel. As a result, the maximum sorption capacity of vanadium and nickel was 87.5 % and 91.3 % consistently under the predetermined conditions. Eventually, 7.6 % Ni (with a purity of 97 %) was recovered from the solution after the desorption process by the electrolytic method (during electrolysis); 15.6 % (99.3 % pure) V2O5 and 11.5 % (79 % pure) NiO chemically.

One-pot in situ fabrication of Cu-coupled rugby-shaped BiVO4 sosoloid for enhancing photocatalytic activity with SPR effect via ultrasonic hydrothermal strategy

One-pot wet chemistry strategy via an ultrasonic hydrothermal in situ procedure has been applied to construct a serial of monoclinic Cu-coupled rugby-shaped hierarchical BiVO4 sosoloids with diverse Cu coupling amount. The SEM and TEM images indicate that the coupled copper content had no effect on the crystalline phase of bismuth vanadate, but it had an important effect on its morphology, which changed from seed shape to rugby shape. As demonstrated by XRD and XPS analysis, it was found parts of Cu2+ doped into the BiVO4 monoclinic lattice to make it self-assemble into a rugby-shaped solid solution and another part of Cu loaded on the surface of BiVO4 sosoloids. Under visible light illumination (>420 nm), as-obtained 1.5% Cu-BiVO4 sosoloid had a degradation rate reached 99% for RhB within 50 min, and its photodegradation activity was 5.6 times higher than that of pure BiVO4. and remained above 96% after 5 cycles. The enhanced photocatalytic efficiency of xCu-BiVO4 sosoloids may be mainly attributed to the superior Cu-coupled rugby-shaped BiVO4 sosoloid microstructures with large specific surface area. During the ultrasonic hydrothermal process, the doping Cu2+ can effectively replace V5+ ions to form a virtual energy level accompanied by V4+, which can become a trapping center and capture the excitation electrons on the conduction band. The surface plasmon resonance (SPR) effect of copper can effectively expand the range of visible light response. On the other hand, d orbital electrons of Cu can quickly transfer to the BiVO4 conduction band according to Fermi energy level, so as to promote the interfacial charge transfer process, thus inhibiting the recombination of photo-generated carriers and improving the photocatalytic activity. Based on the synergetic effects of components in degradation of organic contaminants, this study provides a promising photocatalytic material driven by visible light for environmental remediation and protection.

Influence of Vanadate Structure on Electrochemical Surface Reconstruction and OER Performance of CoV2O6 and Co3V2O8

The increase in global population and modernization of the world created a surge in the energy demand. Currently, carbon-based fossil fuels like coal, petroleum, natural gases etc., are the most widely used energy sources. However, they are limited in resources, and the burning of these fuels produces greenhouse gases which create a harmful impact on the environment. Wind, solar, geothermal energies are considered efficient, clean energy sources, but their intermittent nature restricts their real-life applications [1]. In this regard, Hydrogen is increasingly envisaged as an alternative fuel due to its highest gravimetric energy density (142 MJ/kg) and environmentally benign nature. Electro-catalytic water splitting is a promising method to produce hydrogen in a sustainable manner. For efficient water splitting, the oxygen evolution reaction (OER) at the anode acts as a bottleneck due to its four-electron/proton-coupled mechanism. To facilitate OER, catalysts are generally employed, but most are based on expensive metals, such as Ir, Rh etc. This has enthused researchers to develop cheaper transition metal based catalysts. Although many transition metal based catalysts have been developed, cobalt vanadate systems as OER catalysts are less explored [2]. This enthused us to synthesize pure phase Co3V2O8 and CoV2O6 by thermal co-precipitation followed by calcination. We could able to get these two different phases of cobalt vanadate by altering the reaction conditions slightly. Among these materials, CoV2O6 showed higher geometric electrocatalyst activity towards OER. The overpotential requirement to attain the benchmark current density of 10 mA/cm2geo was 360 mV, whereas Co3V2O8 required 510 mV overpotential to reach 10 mA/cm2geo current density. In addition, we have investigated the factors responsible for the superior phase-dependent electrocatalytic OER activity of two different crystalline cobalt vanadate phases. Vanadates as a class of oxometallates can exist as discrete as well as polymeric ions. For example, while orthovanadate is a discrete [VO4]3− ion, metavanadate ([VO3]n)n− can be visualized as a polymeric network of VO3 units. Earlier reports on cobalt vanadate as OER catalyst have ascribed activity difference to optimal metal-oxygen bond strength. In contrast, we found out that the etching of vanadate moieties from the precatalyst during the electrochemical activation plays a pivotal role [3]. Further, we observed that the polymerization of vanadate ions significantly affects the etching process. CoV2O6 has a polymeric structure consisting of chains of [VO3]−, formed via corner-shared VO4 tetrahedra, corner-shared VO6 octahedra, and edge-shared VO6 octahedra, whereas in Co3V2O8 vanadate ions only exist as discrete [VO4]3- tetrahedral. Due to the polymeric structure of metavanadate, its etching from the material would tear off a long chain of vanadate, thereby aiding the transformation of the material to its active phase. In contrast, the etching of orthovanadate is structurally constrained and, thus, much slower in nature. The resulting higher surface reconstruction exposes a higher number of catalytically active cobalt sites that otherwise lay inactive due to their position in bulk. Cobalt vanadates with polymeric vanadates (CoV2O6) showed better OER over monomeric orthovanadates (Co3V2O8) due to higher vanadate etching. Further, this work validates that etching can happen even from lattice positions, where bonding between constituents are strong.

Influence of vanadium content on structure and activity of V2O5–ZrO2–SiO2 catalyst for propane dehydrogenation

In order to create alternative vanadium oxide-supported catalysts for the process of non-oxidative propane dehydrogenation to propylene, we studied the effect of the increased content of vanadium oxide in the V2O5–ZrO2–SiO2 composition on its structure and catalytic properties. Zirconium silicate hydrogel in the form of finished spherical granules with the SiO2 content of more than 50% was prepared by direct sol-gel synthesis from zirconium oxychloride and sodium metasilicate using the droplet coagulation technology. Catalysts were fabricated by impregnation of hydrogel with an aqueous solution of vanadyl sulfate salt, hydrothermal treatment and calcination in air. By using scanning electron microscopy, X-ray diffraction analysis and low-temperature nitrogen adsorption/desorption method, we showed that amorphous samples with a developed mesoporous structure (with the pore diameter of ~6 nm and the specific surface area of ~300 m2 g–1) were formed when the content of the supporting V2O5 on zirconium silicate was 10, 20, 25, and 30 wt.%. In the course of temperature increase in the propane dehydrogenation reaction, the catalyst samples crystallized in the reaction mixture propane–inert gas with the formation of tetragonal zirconia. When the content of V2O5 was 25% or 30%, additional phases of reduced vanadium oxides and traces of the zirconium vanadate phase were formed. After the reaction, the specific surface area of the catalysts decreased significantly and the average pore size of the samples with 25% and 30% V2O5 increased to ~30 nm. The propylene yield reproducibly observed on the samples with 25% and 30% V2O5 was lower than that on the samples with 10% V2O5; however, it remained quite high, which was probably due to the expanded diameter of the pores and the appearance of additional ZrV2O7 sites that are active with respect to the dehydrogenation of light alkane.