Aqueous citrato-oxovanadate(iv) precursor solutions for VO₂: synthesis, spectroscopic investigation and thermal analysis

Abstract

An aqueous precursor solution, containing citrato-VO(2+) complexes, is synthesized for the formation of monoclinic VO2. With regard to the decomposition of the VO(2+) complexes towards vanadium oxide formation, it is important to gain insights into the chemical structure and transformations of the precursor during synthesis and thermal treatment. Hence, the conversion of the cyclic [V4O12](4-) ion to the VO(2+) ion in aqueous solution, using oxalic acid as an acidifier and a reducing agent, is studied by (51)Vanadium nuclear magnetic resonance spectroscopy. The citrate complexation of this VO(2+) ion and the differentiation between a solution containing citrato-oxalato-VO(2+) and citrato-VO(2+) complexes are studied by electron paramagnetic resonance and Fourier transform infra-red spectroscopy. In both solutions, the VO(2+) containing complex is mononuclear and has a distorted octahedral geometry with a fourfold R-CO2(-) ligation at the equatorial positions and likely a fifth R-CO2(-) ligation at the axial position. Small differences in the thermal decomposition pathway between the gel containing citrato-oxalato-VO(2+) complexes and the oxalate-free gel containing citrato-VO(2+) complexes are observed between 150 and 200 °C in air and are assigned to the presence of (NH4)2C2O4 in the citrato-oxalato-VO(2+) solution. Both precursor solutions are successfully used for the formation of crystalline vanadium oxide nanostructures on SiO2, after thermal annealing at 500 °C in a 0.1% O2 atmosphere. However, the citrato-oxalato-VO(2+) and the oxalate-free citrato-VO(2+) solution result in the formation of monoclinic V6O13 and monoclinic VO2, respectively.

Self‐Assembled Monolayer Stabilized Gold‐Vanadate Nanoflute for Water Splitting Reactions

“…The presence of such signal for Au(0)/Au(I) couple clearly suggested that the Au particles in the material was mostly in zero oxidation state and was in accordance with the XRD and DRS study . The other dominant cathodic peak at −1.1 V and its corresponding anodic peak almost at the same potential was due to the [VO 2 ] 2− /[VO 2 ] 3− couple (Figure S2b) . The quasi‐reversible couple appearing at −0.74 V was for VO 2 2+ /VO 2 3+ couple and the peak at 0.69 V was for V (V)/V (IV) couple (Figure S2b) .…”

Silver‐Sulphur Oxido‐Vanadium Cluster: A Newly Born Catalyst for Direct Reduction of Aryl Carboxylic Acids to Aldehydes via Mars and van Krevelen Mechanism

“…Low angle PXRD pattern of the AgVT catalyst is shown in Figure . PXRD shows the characteristic plane for both silver sulphides and silver vanadates indicating linkage between silver and vanadium through thioglycolic acids . Diffraction peaks observed nearly at 2θ=6.11 is characteristics of those observed in materials with interlayer spacing and the peaks below 2θ=20° may be attributed to the VO 2 + unit …”

Kinetic Analysis of the Redox Reaction in an Aqueous Vanadium–Oxalate System

“…At this stage of the synthesis, the vanadium oxidation state equals +V. The reduction of dioxovanadium(V) to oxovanadium(IV) using oxalic acid occurs in a two-step mechanism, 6,7 starting by the coordination of oxalate anions to dioxovanadium(V), with formation constant K f :…”

“…Furthermore, the complete reduction of dioxovanadium(V) to oxovanadium(IV) has been shown to be essential for the sol(ution)−gel synthesis of thermochromic vanadium(IV) oxide. 6,7 This exercise can therefore be combined conveniently with the feature article of Parkin and Manning focusing on thin-film deposition of vanadium dioxide and its applications. The method of initial rates is used to determine the rate equation of the redox reaction.…”

“…This laboratory practice is compatible with various aspects in the curriculum of an undergraduate chemistry course, and prior to the experiments, the students should be acquainted with the theoretical concepts of the crystal field theory and reaction kinetics. Furthermore, the complete reduction of dioxovanadium­(V) to oxovanadium­(IV) has been shown to be essential for the sol­(ution)–gel synthesis of thermochromic vanadium­(IV) oxide. , This exercise can therefore be combined conveniently with the feature article of Parkin and Manning focusing on thin-film deposition of vanadium dioxide and its applications …”