V2O5 nanoparticles obtained from a synthetic bariandite-like vanadium oxide: Synthesis, characterization and electrochemical behavior in an ionic liquid

Control of crystal size tailors the electrochemical performance of α-V2O5 as a Mg2+ intercalation host

α-V₂O₅ has been extensively explored as a Mg²⁺ intercalation host with potential as a battery cathode, offering high theoretical capacities and potentials vs. Mg²⁺/Mg. However, large voltage hysteresis is observed with Mg insertion and extraction, introducing significant and unacceptable round-trip energy losses with cycling. Conventional interpretations suggest that bulk ion transport of Mg²⁺ within the cathode particles is the major source of this hysteresis. Herein, we demonstrate that nanosizing α-V₂O₅ gives a measurable reduction to voltage hysteresis on the first cycle that substantially raises energy efficiency, indicating that mechanical formatting of the α-V₂O₅ particles contributes to hysteresis. However, no measurable improvement in hysteresis is found in the nanosized α-V₂O₅ in latter cycles despite the much shorter diffusion lengths, suggesting that other factors aside from Mg transport, such as Mg transfer between the electrolyte and electrode, contribute to this hysteresis. This observation is in sharp contrast to the conventional interpretation of Mg electrochemistry. Therefore, this study uncovers critical fundamental underpinning limiting factors in Mg battery electrochemistry, and constitutes a pivotal step towards a high-voltage, high-capacity electrode material suitable for Mg batteries with high energy density.

Time-dependent DFT and experimental study on visible light photocatalysis by metal oxides of Ti, V and Zn after complexing with a conjugated polymer

Tuning the photoactive behavior of transition metal oxide (Ti₂O₄, V₂O₅, Zn₃O₃) cluster units by structural modifications with polythiophene.

A Rare Example of Four-Coordinate Nonoxido Vanadium(IV) Alkoxide in the Solid State: Structure, Spectroscopy, and Magnetization Dynamics

The distorted tetrahedral [V(OAd)₄] alkoxide (OAd = 1-adamantoxide, complex 1) is the first homoleptic, mononuclear vanadium(IV) alkoxide to be characterized in the solid state by X-ray diffraction analysis. The compound crystallizes in the cubic P4̅3 n space group with two highly disordered, crystallographically independent molecules in the asymmetric unit. Spin Hamiltonian parameters extracted from low temperature X- and Q-band electron paramagnetic resonance (EPR) experiments performed for polycrystalline samples of 1, both in the concentrated (bulk) form and diluted in the diamagnetic [Ti(OAd)₄] analogue, reveal a fully axial system with g _z < g _x, g _y and A _z ≫ A _x, A _y. Complex 1 has also been characterized by alternate current susceptometry with varying temperature (3-30 K) and static magnetic field (up to 8.5 T), showing field-induced slow relaxation of the magnetization with relaxation times ranging from ca. 3 ms at 3 K to 0.02-0.03 ms at 30 K, in line with relevant results described recently for other potential molecular quantum bits. Pulsed EPR measurements, in turn, disclosed long coherence times of ca. 4 μs at temperatures lower than 40 K, despite the presence of the H-rich ligands. The slow spin relaxation in 1 is the first observed for a tetracoordinate nonoxido vanadium(IV) complex, and results are compared here to those generated by square-pyramidal V^IV(O)²⁺ and trigonal prismatic V⁴⁺ with oxygen donor atom sets. Considering that the number of promising d¹ complexes investigated in detail for slow magnetization dynamics is still small, the present work contributes to the establishment of possible structural/electronic correlations of interest to the field of quantum information processing.

Redox-active ligand controlled selectivity of vanadium oxidation on Au(100)

Metal-organic coordination networks at surfaces, formed by on-surface redox assembly, are of interest for designing specific and selective chemical function at surfaces for heterogeneous catalysts and other applications. The chemical reactivity of single-site transition metals in on-surface coordination networks, which is essential to these applications, has not previously been fully characterized. Here, we demonstrate with a surface-supported, single-site V system that not only are these sites active toward dioxygen activation, but the products of that reaction show much higher selectivity than traditional vanadium nanoparticles, leading to only one V-oxo product. We have studied the chemical reactivity of one-dimensional metal-organic vanadium - 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (DPTZ) chains with O2. The electron-rich chains self-assemble through an on-surface redox process on the Au(100) surface and are characterized by X-ray photoelectron spectroscopy, scanning tunneling microscopy, high-resolution electron energy loss spectroscopy, and density functional theory. Reaction of V-DPTZ chains with O2 causes an increase in V oxidation state from VII to VIV, resulting in a single strongly bonded (DPTZ2-)VIVO product and spillover of O to the Au surface. DFT calculations confirm these products and also suggest new candidate intermediate states, providing mechanistic insight into this on-surface reaction. In contrast, the oxidation of ligand-free V is less complete and results in multiple oxygen-bound products. This demonstrates the high chemical selectivity of single-site metal centers in metal-ligand complexes at surfaces compared to metal nanoislands.

A new metallate phase of V2O5 crystalline microstructure achieved in a facile route: synthesis, characterization, and measurement in catalytic reactions

Experiencing a series of complicated changes, abundant orange crystals of novel metallic phase of vanadium pentoxide were obtained by a mild chemical method, the formula of which is defined as [V3(μ3-O)2⋅(μ1-OH)⋅O5]⋅H2O. Differ from the synthesis methods of vanadium oxide published, we have adopted a simple solution method that mixed starting materials are refluxing in the system of ethanol-water under a relatively lower temperature. Symmetry of the crystals is Monoclinic, with cell unit dimensions: a=4.9978(10)Å, b=8.4273(17)Å, c=7.8669(16)Å, β=96.44(3)° and space group of P2₁/m. The structure of the complex was characterized by elemental analysis, IR, UV-vis spectroscopy and single-crystal diffraction analysis. Powder X-ray diffraction (PXRD) was used to detect the purity of the crystals, and crystal morphology was detected by the scanning electron microscope (SEM). In addition, in order to extend application of oxidovanadium complexes, bromination catalytic activity about the complex in a single-pot reaction of the conversion of phenol red to bromophenol blue in a mixed solution of H2O-DMF at a constant temperature of 30±0.5 °C with a buffer solution of NaH2PO4Na2HPO4 (pH=5.8) was evaluated firstly, indicating that the complex can be considered as a potential functional model of bromoperoxidase, in the meantime, we have conducted the bromination catalytic reaction to simulate and measure the changes in reaction process indirectly. Besides, catalytic oxidation activity of the complex is also evaluated in the oxidation of cyclohexane (Cy) and cyclopentane with hydrogen peroxide promoted under mild conditions, showing potential catalytic activity of the complex by comparing TON (total turnover number) ratios of CyO/CyOH (CyO is the abbreviation of cyclohexanone and CyOH represents cyclohexanol) in the oxidation results.

A comprehensive review on synthesis methods for transition-metal oxide nanostructures

Recent developments of transition-metal oxide nanostructures with designed shape and dimensionality, including various synthesis methods and applications, are presented.

Rapid hydrothermal synthesis of VO2 (B) and its conversion to thermochromic VO2 (M1)

The present study provides a rapid way to obtain VO2 (B) under economical and environmentally friendly conditions. VO2 (B) is one of the well-known polymorphs of vanadium dioxide and is a promising cathode material for aqueous lithium ion batteries. VO2 (B) was successfully synthesized by rapid single-step hydrothermal process using V2O5 and citric acid as precursors. The present study shows that phase-pure VO2 (B) polytype can be easily obtained at 180 °C for 2 h and 220 °C for 1 h, that is, the lowest combination of temperature and duration reported so far. The obtained VO2 (B) is characterized by X-ray powder diffraction, high-resolution scanning electron microscopy, and Fourier transform infrared spectroscopy. In addition, we present an indirect way to obtain VO2 (M1) by annealing VO2 (B) under vacuum for 1 h.

Surface-Enhanced Raman Scattering of the Bariandite Oxide Layer on a Vanadium Dioxide Crystal

Variable-temperature (25–100°C) Raman spectra of a crystal of commercial VO2 have revealed surface-enhanced Raman scattering (SERS) of the V=O stretching mode of the bariandite-like vanadium oxide species, V10O24·9H2O, that is formed on the surface of the crystal. Upon passing through the semiconductor-to-metal phase transition of VO2 at 68°C, there is an approximately three to five-fold increase in Raman intensity of the V=O stretching mode. This effect is reversible with hysteresis upon decreasing the temperature. The temperature dependence of the Raman spectra at temperatures below the transition suggest that even the semiconductor phase has some SERS effect.

Stability Criteria of Fullerene-like Nanoparticles: Comparing V₂O5 to Layered Metal Dichalcogenides and Dihalides

Numerous examples of closed-cage nanostructures, such as nested fullerene-like nanoparticles and nanotubes, formed by the folding of materials with layered structure are known. These compounds include WS₂, NiCl₂, CdCl₂, Cs₂O, and recently V₂O₅. Layered materials, whose chemical bonds are highly ionic in character, possess relatively stiff layers, which cannot be evenly folded. Thus, stress-relief generally results in faceted nanostructures seamed by edge-defects. V₂O₅, is a metal oxide compound with a layered structure. The study of the seams in nearly perfect inorganic "fullerene-like" hollow V₂O₅ nanoparticles (NIF-V₂O₅) synthesized by pulsed laser ablation (PLA), is discussed in the present work. The relation between the formation mechanism and the seams between facets is examined. The formation mechanism of the NIF-V₂O₅ is discussed in comparison to fullerene-like structures of other layered materials, like IF structures of MoS₂, CdCl₂, and Cs₂O. The criteria for the perfect seaming of such hollow closed structures are highlighted.