Thermal Decomposition Of Ammonium Metavanadate Research Articles

Oxygen vacancy-enriched V2O5·nH2O nanofibers ink for universal substrates-tolerant and multi means-integratable NH3 sensing

Universal substrates-tolerant and multi means-integratable ammonia (NH3) sensing is highly desired in future Internet of Things in environmental monitoring, food security and early diagnosis of human diseases, however, is still less than satisfactory. Here, an oxygen vacancy-governed NH3 sensing has been developed with V2O5·nH2O nanofibers (NFs) ink, via combined thermal decomposition of ammonium metavanadate and dilution. As-obtained NH3 sensing ink takes on red colloids, in which the V2O5·nH2O NFs around 14 nm in diameter are interconnected. Beneficially, the fabric fiber decorated with V2O5·nH2O NFs ink displays excellent selectivity and ppb-concentration detection limit. Remarkably, V2O5·nH2O NFs ink is integrated over “hard” and “flexible” substrates such as glass, wood, paper, leaf and fabric with excellent tolerance by multi-integratable means such as writing, dipping and sewing. Theoretically, such NH3 sensing is interpreted that the bonding between V2O5 NFs and H2O modulates oxygen vacancy and thus adsorption sites, and the incorporation between crystal water and free one contributes to stable ink. Practically, a sensing device built with V2O5·3.1H2O NFs ink has been simulated to communicate with a smartphone with reliable NH3 sensing.

Structural control of V2O5 nanoparticles via a thermal decomposition method for prospective photocatalytic applications

BackgroundRecently, transition-metal oxides have represented an exciting research topic, especially their fundamental and technological aspects. Here, vanadium pentoxide nanoparticles (V2O5-NPs) were synthesized through the thermal decomposition of ammonium meta-vanadate. In the current study, we investigated the photocatalytic activity of V2O5-NPs to develop and regulate the V2O5 structure for adsorption applications.ResultsThe obtained nanoparticles were inspected by X-ray diffraction, scanning electron microscope, transmission electron microscope, and differential thermogravimetric analysis, which proved the formation of the nanorod structure. The ultraviolet–visible absorption spectra revealed a 2.26 eV band gap for V2O5-NPs that correlates with indirect optical transitions. The photocatalytic activity of the V2O5-NPs was investigated by methylene blue (MB) degradation in aqueous solutions. An initial concentration of 25 ppm, a temperature of 40 °C, 40 mg of adsorbent mass, and 1 h of contact time were the optimal conditions for the efficient removal of MB that could reach up to 92.4%. The mechanism of MB photocatalytic degradation by V2O5-NPs is explained.ConclusionsThe photodegradation data better fit with the Langmuir isotherm model. The thermodynamic parameters indicated that the adsorption was spontaneous and endothermic. The reaction kinetics followed the pseudo-second-order model. Thermally prepared V2O5-NPs offer a simple and efficient approach for selective MB removal from an aqueous medium.Graphical abstract

Structural and optical properties of V2O5 nanostructures grown by thermal decomposition technique

Vanadium pentoxide (V2O5) is a widely used industrial catalyst and a promising substitute to the acidic and hygroscopic PEDOT: PSS hole transport layer in organic solar cells. In this work, V2O5 nanostructures were synthesized by thermal decomposition of ammonium metavanadate (NH4VO3) at various temperatures. Structural and morphological studies confirmed the formation of orthorhombic structure of V2O5 nanorods. The UV–Vis–NIR reflectance spectra show a temperature dependent red-shift in band gap corresponding to indirect optical transitions. The peaks corresponding to band edge emissions were obtained from photoluminescence spectra. From Fourier-transform infrared (FTIR) studies, the vibrational modes involved in V2O5 nanostructures were identified. Temperature dependence of the precursor NH4VO3 was evaluated from thermogravimetric–differential (TGA/DTA) curves.

The Thermal Decomposition of Ammonium Meta-Vanadate under Restricted Flow Conditions

The products obtained during the thermal decomposition of ammonium meta-vanadate depend on the configuration of the container, the mass of the sample, the heating rate and the composition of the carrier gas. The decomposition in an uncapped container produced (NH4)2V4O11, NH4V3O8, and V2O5 as the apparent stable products while the products in a capped container were NH4V3O8, and V2Ox where x was between 4 and 5. These differences are attributed to the different amounts of the evolved gases in the cell. EGA-FTIR clearly established that the reduced final product in the capped cell resulted from a reaction between NH3 and the V2O5 formed during the decomposition. A pre-equilibrium kinetics model where the rate of the reverse reaction depends on the partial pressure of the gaseous products in the cell could explain the different reaction intermediates. This model provides a possible explanation for the different apparent activation energies that have been reported for the thermal decomposition of other compounds where a reversible step could occur in the decomposition mechanism.

Kinetics of Thermal Dissociation of Ammonium Metavanadate

The solid products of thermal decomposition of ammonium metavanadate can be used as catalysts in many important processes, and a knowledge of the dynamics of these processes is therefore essential. The thermal dissociation of ammonium metavanadate was studied under non-isothermal conditions in air atmosphere. This process occurred in three steps under the applied experimental conditions, and was associated with the elimination of ammonia and water below 330°C and with the formation of nitrogen oxides above 330°C. The kinetics of particular stages of (NH4)2OV205 decomposition was evaluated from the dynamic mass loss data by means of the integral method, with applycation of the Coats and Redfern approximation. The first stage of decomposition to ammonium hexavanadate is governed by a random nucleation model, the second step by a three-dimensional diffusion or contracting volume model, and the last stage again by a random nucleation model. The apparent activation energies found for the particular stages were 144.97, 378.31 or 184.40 and 260.65 kJ mol−1, respectively.

Mechanisms for the thermal decomposition of NH4VO3into V6O13, V3O7and V2O5

The thermal decomposition of ammonium metavanadate, NH4VO3, has been studied by differential scanning calorimetry (DSC), mass spectrometry (MS) and X-ray diffraction (XRD) in the temperature range 50–500 °C. Different experimental conditions (heating rate and atmosphere) have been explored in various combinations. Different types of reaction mechanisms leading to crystalline V6O13 and V3O7 can be identified. The formation of V2O5 is also discussed briefly.

Thermal decomposition of ammonium metavanadate in a fluidized bed reactor

Studies on the decomposition of ammonium metavanadate (AMV) in the presence of O 2 were carried out in a fluidized bed reactor. The ammonia gas thus released was passed directly into hydrochloric acid solution of known initial pH and the change in pH of the solution was monitored as a function of time and temperature. The degree of decomposition α was calculated at intermediate stages of the reaction. The overall decomposition pattern was found to fit well into the ‘Power-law’ kinetic equation. The fluidized bed reactor was found to be effective in achieving a substantial reduction in both the time and temperature required for the complete decomposition of AMV to V 2O 5. The activation energy and rate constant for the overall reaction were determined to be 12.54 ± 0.44 kJ mol −1 and 1.4 × 10 −3 s −1 respectively. The value of the activation energy suggests that the process is surface-area controlled.

Influence of Al2O3 support on the thermal decomposition of ammonium metavanadate

The thermal decomposition of ammonium metavanadate (AMV) supported on aluminium oxide was investigated using differential thermal analysis, thermogravimetry, infrared and X-ray diffraction techniques. The results obtained revealed that the decomposition of AMV supported on alumina proceeded in three decomposition stages. Alumina was found to enhance only the decomposition of the intermediate ammonium hexavanadate to produce V2O5. In addition, the values of activation energies of the various decomposition stages were accompanied by a significant decrease on decreasing the concentration of AMV. The infrared spectra indicated that the band corresponds to the surface site V=O strongly affected by the presence of Al2O3. Finally, an interaction between Al2O3 and V2O5 occurred at 660 °C giving well-crystallized AlVO4.

Thermal decomposition of ammonium metavanadate doped with Fe, Co or Ni hydroxides

The thermal decomposition of pure ammonium metavanadate (AMV) and of AMV doped with Fe3+,Co2+ or Ni2+ ions was investigated by TG, DTA, IR and X-ray diffraction. The results obtained revealed that the presence of these dopants enhances the formation of the intermediate compounds V2O5 solid. Some of the V5+ ions of the V2O5 lattice seemed to be reduced to V4+ ions. The activation energies of the different decomposition stages for all samples were calculated. The doped solids calcined at 450°C were characterized by the determination ofSbet and by electrical conductivity measurements. The mechanisms by which these ions affect the properties of the solids produced are discussed in relation to the defect structure created by the doping process.

ChemInform Abstract: Thermal Decomposition of Ammonium Metavanadate(V) in Open and Closed Systems.

AbstractIt is found that thermal decomposition of NH4VO3 (I) in a closed high‐pressure system involves the redox reaction between V(V) and NH3 to yield with increasing temp. the compounds (NH4)2V6O12(OH)2, VO2‐x(OH)x, and V2nO2n‐1.

Electron optical studies of the thermal decomposition of ammonium metavanadate (NH 4VO 3)

The thermal decomposition of ammonium metavanadate (AMV), up to 400°C in air was studied by differential thermal analysis, thermogravimetric analysis, infrared spectroscopy and X-ray diffraction. The possible identities of the decomposition products are discussed. Complementary morphological and structural investigations were made by scanning and transmission electron microscopy. The parent material and its calcination products were found to be subject to radiation damage in the transmission electron microscope. High resolution lattice imaging, combined with the minimum dose technique, has allowed a correlation to be made with the structural features of AMV, intermediate products and final vanadium pentoxide catalyst material.

The Thermal Decomposition of Ammonium Metavanadate(V) in Open and Closed Systems

The thermal decomposition of ammonium metavanadate(V) has been studied at atmospheric pressure, at hydrothermal, and high-pressure conditions, respectively. In a closed high-pressure system a redox reaction between vanadium(V) and ammonia takes place, to yield with increasing temperature the compounds (NH4)2V6O12(OH)2, VO2-δ(OH)δ, and V2nO2n-1 the composition of the product eventually approaching V2O3 at 1100 °C. All these compounds can easily be converted into V2O5 by heating in air. The mid-infrared spectra of the decomposition products obtained by slow heating of NH4VO3 in air, are virtually identical and show that ammonium hexavanadate(V), (NH4)2V6O16, is the most important, and perhaps only, intermediate in the “non-reduction” case. On further heating, (NH4)2V6O16 may not only loose ammonia and water to form V2O5 but could as well partially be reduced by ammonia. This could explain the diversity of intermediate “compounds” described in the literature. Hydrothermal reaction of NH4VO3 yielded (NH4)0.5V2O5, (NH4)2V3O8, and V2O3 at rather low temperatures.

Electron optical studies of the formation of vanadium pentoxide catalyst

The oxides of vanadium, especially vanadium pentoxide, have been extensively studied because of their interesting physical properties particularly in catalysis. Vanadium pentoxide is generally used in the oxidation and ammoxidation of hydrocarbons.This catalyst has been prepared via the thermal decomposition of ammonium metavanadate (AMV) in air. Thermogravimetric analysis (TGA), infrared spectroscopy (IRS) and x-ray diffraction (XRD) techniques together with high resolution electron microscopy (HREM) and scanning electron microscopy (SEM) have enabled us to elucidate the physicochemical changes occurring during the decomposition process.According to TGA results, the decomposition of AMV commences at 150°C and is complete by 320°C leading to vanadium pentoxide by loss of ammonia and water with the formation of two intermediate compounds, namely at 190°C, ammonium bivanadate: (NH4)2V4 O11, and at 230°C, ammonium hexavanadate AHV: (NH4)2V6O16 . Samples for structural correlation studies were prepared by heating AMV in a stream of air for 2 hours at selected temperatures of 140, 190, 230, 320 and 400°C.

ChemInform Abstract: Thermal Decomposition of Ammonium Metavanadate Supported on Al2O3.

AbstractThe results obtained by DTA, TG, and X‐ray diffraction techniques reveals that ammonium vanadate decomposes according to the scheme.

Thermal decomposition of ammonium metavanadate supported on Al 2O 3

The thermal decomposition of ammonium metavanadate supported on aluminium oxide was investigated using DTA, TG and X-ray diffraction techniques. The results obtained revealed that ammonium vanadate decomposed at 225–250°C giving an intermediate compound ((NH 4) 2V 6O 16) which decomposed readily at 335–360°C producing V 2O 5. Alumina was found to chance the formation of the intermediate compound and retard its decomposition. Some of the V 5+ ions of V 2O 5 lattice seemed to be reduced into V 4+ and V 3+ ions by heating in air at 450°C in the presence of Al 2O 3. Such a reaction was attributed to dissolution of some Al 3+ ions in the V 2O 5 lattice via location in interstitial positions and/or in cationic vacancies. Al 2O 3 was found to interact with V 2O 5 at 650° C giving well-crystalline A1VO 4 which decomposed at about 750°C forming well-crystalline δ-Al 2O 3 and V 2O 5,. Pure Al 2O 3, heated in air at 1000°C, existed in the form of the κ-phase which, on mixing with V 2O 5 (0.5 V 2O 5:1 Al 2O 3) and heating in air at 1000°C, was converted entirely to the well-crystalline α-Al 2O 3 phase.

ChemInform Abstract: THERMAL DECOMPOSITION OF AMMONIUM METAVANADATE

AbstractDie Produkte der thermischen Zersetzung von NH4‐metavanadat werden bei verschiedenen Temperaturen zwischen 100 und 700°C durch Röntgenbeugung, IR‐ und ESR‐Spektren untersucht.

Thermal Decomposition of Ammonium Metavanadate

X-Ray, infrared, and electron spin resonance (e.s.r.) studies were made on the samples prepared by the thermal decomposition of ammonium metavanadate at various temperatures between 100 and 700 °C. A new intermediate compound has been identified to be formed between 100 and 150 °C. This new compound is stable up to 200 °C, and is a complex ammonium–vanadyl compound, since while the infrared studies showed the presence of an NH4 group, and V—N bond, the e.s.r. gave the signal of VO2+ ions (V4+ + O2− = VO2+). A mechanism of the decomposition of ammonium metavanadate has been given.

The thermal decomposition of ammonium metavanadate, III

The kinetics and thermodynamics of the thermal decomposition of ammonium metavanadate (AMV) are combined with the structural information available for AMV, for the important decomposition intermediate, ammonium hexavanadate (AHV), and for vanadium pentoxide, the product of the decomposition in non-reducing atmospheres, to enable the atomic movements involved in the course of decomposition to be discussed in detail. The decomposition of AMV involves scission of the V-G chains in the AMV structure (accompanied by simultaneous evolution of gaseous ammonia and water) with subsequent rearrangement and cross-linking of discrete units, based on V3O 8 − , to form AHV. Further decomposition to V2O5 is a similar but less ordered process.

The thermal decomposition of ammonium metavanadate, I

The stoichiometry of the various stages involved in the thermal decomposition of ammonium metavanadate has been shown to correspond to a stepwise decrease in the ratio of ammonia and water to V2O5, with V2O5 being the final product in vacuum, in air and in argon. In ammonia, VO2 is formed. The actual stages and intermediates are dependent upon the prevailing atmosphere. Chemical analyses, together with infrared absorption spectra and X-ray powder data, have enabled the intermediates and products to be characterized and the structural changes involved in the decomposition to be discussed.