Hydrolysis Of VO Research Articles

From VO2 (B) to VO2 (A) nanobelts: first hydrothermal transformation, spectroscopic study and first principles calculation

The phase transition process from VO(2) (B) to VO(2) (A) was first observed through a mild hydrothermal approach, using hybrid density functional theory (DFT) calculations and crystallographic VO(2) topology analysis. All theoretical analyses reveal that VO(2) (A) is a thermodynamically stable phase and has a lower formation energy compared with the metastable VO(2) (B). For the first time, X-ray absorption spectroscopy (XAS) of the V L-edge and O K-edge was performed on different VO(2) phases, and the differences in the electronic structure of the two polymorphic forms provide further experimental evidence of the more stable VO(2) (A). Consequently, transformation from VO(2) (B) to VO(2) (A) is much easier to be realized from a dynamical point of view. Notably, the transformation of VO(2) (B) into VO(2) (A) show the sequence VO(2) (B)-high-temperature VO(2) (A(H)) phase-low-temperature VO(2) (A) phase, which was achieved by hydrothermal treatment, respectively. Also, an alternative synthesis route was proposed based on the above hydrothermal transformation, and VO(2) (A) was successfully prepared via the simple one-step hydrothermal method by hydrolysis of VO(acac)(2) (acac = acetylacetonate). Therefore, VO(2) nanostructures with controlled phase compositions can be obtained in high yields. Through elucidating the structural evolution in the crystallographic shear mechanism, we can easily guide the design of other metal oxide nanostructures with controllable phases.

Sol–gel synthesis of vanadium pentoxide nanoparticles in air- and water-stable ionic liquids

Vanadium pentoxide (V2O5) nanoparticles were synthesized at moderate reaction temperatures by hydrolysis of VO[OCH(CH3)2]3 in two different air- and water-stable ionic liquids with the same anion: 1-butyl-1-methyl pyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4]Tf2N) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIM]Tf2N) via the sol–gel method using acetone and isopropanol either as refluxing solvents or as co-solvents. The cation type of the ionic liquid affects the crystallinity, morphology, and surface area of the produced nanoparticles: [Py1,4]Tf2N gave products with higher crystallinity especially with acetone as a refluxing and co-solvent, while [EMIM]Tf2N gave a clear mesoporous morphology with isopropanol as a refluxing solvent. Ionic liquids affect the key factors (morphology and surface area) that make V2O5 an attractive material as catalyst and/or cathodic material for lithium ion batteries.

Interaction of oxovanadium(IV) with carboxylic ligands in aqueous solution: A thermodynamic and visible spectrophotometric study

The hydrolysis of VO 2+ and the complex with sulfate were studied potentiometrically, spectrophotometrically and calorimetrically, in NaCl aqueous solution (0 < I ≤ 1 mol L − 1 ) and at t = 25 °C. The formation of two hydrolytic species VO(OH) + and VO 2(OH) 2 2+ and one complex with sulfate was found, with log β = − 5.65 for the reaction VO 2+ + H 2O = VO(OH) + + H +, log β = − 7.02 for the reaction 2VO 2+ + 2H 2O = (VO) 2(OH) 2 2+ + 2H + and log K = 1.73 for VOSO 4 0 species (at I = 0.1 mol L − 1 and t = 25 °C). For these species, using calorimetric data, Δ H and TΔ S values were also obtained. By using the above values, interactions of VO 2+ with acetate ( ac), malonate ( mal), succinate ( suc), 1,2,3-propanetricarboxylate ( tca) and 1,2,3,4-butanetetracarboxylate ( btc) ligands were studied potentiometrically and spectrophotometrically. The formation of ML +, ML 2 0 and MLOH 0 for ac; ML 0, MLH +, ML 2 2− and ML 2H − for mal; ML 0, MLH + and MLOH − for suc; ML − and MLH 0 for tca and ML 2−, MLH − and MLH 2 0 for btc were found. Formation constants are reported at I = 0.1 mol L − 1 , together with SIT parameters for the dependence on ionic strength. By visible spectrophotometric measurements, λ max and ε max values for the relevant species in solution were determined.

A Combinatorial Approach for the Synthesis and Characterization of Polymer/Vanadium Oxide Nanocomposites

Vanadium pentoxide xerogels were prepared by the hydrolysis of VO(OC3H7)3 by the sol−gel process. The generation of V2O5 was optimized by a combinatorial approach incorporating rapid screening by Raman spectroscopy. The latter revealed crystallites of vanadium oxide. Subsequently poly(p-ethylphenol) (PEP)/V2O5 nanocomposites were prepared by the sol−gel process at the optimized molar ratio of VO(OC3H7)3/H2O/acetone = 1/45/300. Evidence from Raman spectra indicated that the presence of PEP did not interfere in the formation of crystalline V2O5 in the composites. FTIR also exhibited interaction between PEP and V2O5. TEM showed a fibrous V2O5 structure dispersed in the PEP matrix.

Synthesis and properties of polypyrrole–vanadium oxide hybrid aerogels

Vanadium pentoxide/polypyrrole aerogel composites were synthesized by two sol–gel routes. The first utilized simultaneous polymerization of pyrrole and vanadyl alkoxide precursors. Hydrolysis of VO(OC 3H 7) 3 using pyrrole/water/acetone mixtures over a range of compositions yielded monolithic green–black gels. Supercritical drying yielded aerogels (150–257 m 2/g, 0.1–0.2 g/cm 3). These polypyrrole/V 2O 5 `nanocomposites' exhibited lower electrical conductivity with increased polypyrrole content. The second method involved oxide gel formation in the presence of a dispersion of preformed colloidal polypyrrole. SEM studies of the resulting `microcomposites' aerogels (80–140 m 2/g) show the presence of polypyrrole particles encapsulated in the fibrous V 2O 5 network. These materials exhibit conductivity equivalent to that of vanadium pentoxide. The interaction between polypyrrole and V 2O 5 in the materials was probed using infrared spectroscopy.

Fabrication, microstructure and electrical conductivity of V 2O 5 ceramics

V 2O 5 gels corresponding to the formula V 2O 5· nH 2O with n = 2.07, 0.5, and 0.2 have been prepared by the hydrolysis of VO(OC 2H 5) 3, followed by washing and drying. After dehydration, V 2O 5 crystallizes at 310° to 400°C. V 2O 5 powders with strip-like particles are produced after heating at 630°C. Well-densified V 2O 5 ceramics (97.7% of theoretical) have been fabricated by the combined use of hot pressing (630°C/2h/30MPa) and hot isostatic pressing (630°C/1h/196MPa). The texture is of a plate structure, the grain being ≈ 30 μm long and ≈ 6 μm wide. Electrical conductivities have been measured in the temperature range of 25° to 600°C. Activation energies are determined to be 0.09 and 0.18 eV for initial and final stages, respectively.

Vanadium Oxide/Polypyrrole Aerogel Nanocomposites

Vanadium pentoxide/polypyrrole aerogel (ARG) nanocomposites were prepared by hydrolysis of VO(OC{sub 3}H{sub 7}){sub 3} using pyrrole/water/acetone mixtures. Monolithic green-black gels with polypyrrole/V ratios ranging from 0.15 to 1.0 resulted from simultaneously polymerization of the pyrrole and vanadium alkoxide precursors. Supercritical drying yielded high surface (150--200 m{sup 2}/g) aerogels, of sufficient mechanical integrity to allow them to be cut without fracturing. TEM studies of the aerogels show that they are comprised of fibers similar to that of V{sub 2}O{sub 5} ARG`s, but with a much shorter chain length. Evidence from IR that the inorganic and organic components strongly interact leads them to propose that this impedes the vanadium condensation process. The result is ARG`s that exhibit decreased electronic conductivity with increasing polymer content. Despite the unexpected deleterious effect of the conductive polymer on the bulk conductivity, at low polymer content, the nanocomposite materials show enhanced electrochemical properties for Li insertion compared to the pristine aerogel.

Structure and physical properties of V 2O 5 gels containing GeO 2

Monolithic gels of V 2O 5 containing up to 9.5 mol% GeO 2 were obtained by the hydrolysis of VO(C 2H 5O) 3 and Ge(C 2H 5O) 4 in ethanol solution. The gels were fiber-like, less than 10 nm in thickness, and became shorter with addition of GeO 2. Fracture surfaces of the xerogels containing GeO 2, dried at room temperature, were glassy. However, broad peaks of X-ray diffraction were observed for the gels which suggested a layer-like structure. The crystallization temperature of the xerogels increased with increasing GeO 2 content. The bulk xerogels were electrically isotropic, and the dc conductivity decreased with increasing GeO 2 content. The refractive indices measured by ellipsometry also decreased with increasing GeO 2 content.

Synthesis and Characterization of Vanadium Oxide Gels from Alkoxy-Vanadate Precursors

ABSTRACTVanadium oxide gels are synthesized through vanadium oxo-alkoxide hydrolysis condensation processes. Different precursors and hydrolysis conditions lead to different sorts of gels. V0(0Amt)3hydrolyzed with a large excess of water results in red jammy gels with a layered structure. They exhibit electronic and ionic behavior comparable to vanadium pentoxide gels from inorganic precursors. Hydrolysis of VO(OPrn)3in an alcoholic medium, leads to orange transparent monolithic gels. They have a highly branched polymeric structure. Controlled hydrolysis of vanadium oxo-alkoxide precursors has the further advantage of giving good adherent thin films.