On a new calcium vanadate: synthesis, structure and Li insertion behavior

A synthetic form of the mineral hewettite was prepared via a new route in aqueous medium, starting either from the crystalline compound Li_1.1V₃O₈, or from its amorphous precursor. The anhydrous, crystalline derivative Ca_0.5V₃O₈ was obtained by heating the synthetic hewettite at 250°C under dynamic vacuum. The diffraction studies show that the 2D structure of Ca_0.5V₃O₈ involves the same V₃O₈ layers as in the hewettite or in Li_1+αV₃O₈. The stacking of the layers is similar to that in the metahewettite. A structural model is proposed, where the Ca²⁺ ions occupy octahedral sites in the interlayer space. The electrochemical behavior of Ca_0.5V₃O₈ vs. lithium insertion is presented. It is original and reveals particularly good performances in terms of stability during cycling at C/5 rate. The homologues obtained with Mg or Ba, instead of Ca, are briefly presented.     

联二脲氧化生成偶氮二甲酰胺反应的钒催化机理

在钒催伦剂存在下，用氯酸钠氧化联二脲制成偶氮二甲酰胺，从钒催化剂的单晶培养和结构解析入手，通过反应动力学研究，用ＥＳＲ检测反应过程中四价钒的生成，用分光光度法（分别以钛钛试剂和硫氰酸铵为显色剂）确定了反应过程中三价钒的生成和变化情况，从而提出了可能的催化机理，还利用量化计算从热力学角度证实了所提出的包括四价钒铬离子歧化过程在内的钒催化机理的合理性。     

Rb7[SiO4][VO4]: ein Ortho‐Silicat‐Vanadat(V)

Rb₇[SiO₄][VO₄]: an Ortho‐Silicate‐Vanadate(V) Rb₇[SiO₄][VO₄] has been obtained from a redox reaction between CdO and vanadium metal in the presence of Rb₂O and SiO₂ at 600 °C in an Ag container as yellow‐greenish transparent single crystals. The crystal structure determination (IPDS data: P2₁/c, a = 637.6(1) pm, b = 1039.7(1) pm, c = 2076.8(4) pm, β = 93.21(2)°, Z = 4, wR2 = 0.1319) reveals the presence of isolated complex anions, [SiO₄]^4— and [VO₄]^3—.     

Cu2(bipy)2V6O17: A new type of layered inorganic–organic hybrid copper(II) vanadate

Hydrothermal reaction of copper(II) acetate, 2,2′-bipyridine (bipy) and NH₄VO₃ at 170 °C lead to a new layered polyoxovanadate with organically covalent-bonded copper(II) complex, Cu₂(bipy)₂V₆O₁₇ (1). Cu₂(bipy)₂V₆O₁₇ (1) is a new copper(II) vanadium(V) oxide featuring a new layered architecture, in which the V₂O₇ dimeric units and the cyclic tetranuclear V₄O₁₂ cluster units are interconnected via corner sharing into a unique one-dimensional {V₆O₁₇}⁴⁻ anionic chain, such chains are further bridged by {Cu(bipy)}²⁺ complex cations into a 010 organic–inorganic hybrid layer.     

IR-spectral investigation of the structure of glasses in the Fe2O3-V2O5 system

The structure of glasses in the Fe₂O₃-V₂O₅ system in the 0–50 mol% Fe₂O₃ range is studied by IR-spectroscopy. It is found that the introduction of Fe₂O₃ favours the transformation of the VO₅-groups into VO₄ ones. This effect may be shown with the aid of IR-spectra, owing to the fact that these glasses are characterized by two high-frequency bands at 1020 and 930 cm^–1. The first is determined by the vibrations of the short V=O nonbridging bonds in the VO₅-groups, while the second is assigned to the vibrations of the V—O-bonds in deformed VO₄-tetrahedra.

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IR-spektroskopische Strukturuntersuchung von Gläsern des Systems Fe₂O₃-V₂O₅

Zusammenfassung Die Struktur von Gläsern des Systems Fe₂O₃-V₂O₅ in dem Bereich von 0–50 Molprozent Fe₂O₃ wurde mit Hilfe der IR-Spektroskopie untersucht. Zusatz von Fe₂O₃ begünstigt die Umwandlung der VO₅- in VO₄-Gruppen. Das kann in den IR-Spektren durch zwei Banden bei 1020 und 930 cm^–1 festgestellt werden. Die erste wird durch Schwingungen der kurzen V=O-Nichtbrücken-bindungen in den VO₅-Gruppen verursacht, die zweite wird auf Schwingungen der V—O-Bindungen in dem deformierten VO₄-Tetraeder zurückgeführt.

     

A revisit of photoluminescence property for vanadate oxides AVO3 (A:K, Rb and Cs) and M3V2O8 (M:Mg and Zn)

We revisited the vanadium oxide phosphors, AVO₃ (A:K, Rb, and Cs) and M₃V₂O₈ (A:Mg and Zn) for a revaluation of possibility of these compounds for lighting applications, and the internal quantum efficiency (η) and luminescent colour properties for AVO₃ (A:K, Rb, and Cs) and M₃V₂O₈ (A:Mg, and Zn) have been presented. The AVO₃ showed the broadband emission from 380 to 800 nm, and the η for the KVO₃, RbVO₃ and CsVO₃ were 4%, 79% and 87%, respectively. The CIE colour coordinates are located at white region on the chromaticity diagram. The M₃V₂O₈ (A:Mg and Zn) also exhibited a quite broadband emission between 410 and 900 nm, indicating yellow luminescent colour. The Zn₃V₂O₈ showed high η value, 52%, compared to that of the Mg₃V₂O₈ (η=6%). This enhancement of η in the Zn₃V₂O₈ could be due to the increasing exciton diffusion assisted by the hybridizations of Zn 3d and O 2p orbitals for the valence band, and Zn 4s and Ti 3d orbitals for the conduction band.     

Na2O＊B2O3＊V2O5玻璃的^51V核磁共振研究

本文应用~(51)V核磁共振研究了Na_2O·B_2O_3·V_2O_5玻璃的结构,结果表明: 1)R<0.5+K时,随着R的增加,依次形成NaV_3O_8、NaVO_3和NaVO_3-B结构。 2)R=0.5+K时,全部的V_2O_5转化为NaVO_3和NaVO_3-B结构。 3)R>0.5+K时,由于硼酸盐中非桥氧数的增加,NaVO_3-B结构逐步消失,并推测NaVO_3-B结构中的B原子为四配位结构。     

One-dimensional GdVO4:Ln (Ln=Eu, Dy, Sm) nanofibers: Electrospinning preparation and luminescence properties

One-dimensional GdVO₄:Ln³⁺ (Ln=Eu, Dy, Sm) nanofibers have been prepared by a combination method of sol-gel process and electrospinning technology. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL), quantum efficiency (QE), and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. The XRD, FT-IR, and TG-DTA results show that GdVO₄:Ln³⁺ nanofibers samples crystallize at 700 °C. SEM images indicate that the as prepared precursor fibers are smooth. After being calcined at 700 °C for 4 h, the fibers still maintain their fiberlike morphology with rough surface. TEM image further manifests that the GdVO₄:Ln³⁺ nanofibers consist of nanoparticles. Under ultraviolet excitation and low-voltage electron beam excitation, GdVO₄:Ln³⁺ phosphors showed their strong characteristic emission due to an efficient energy transfer from vanadate groups to dopants. The optimum doping concentration of Ln³⁺ in the GdVO₄ nanofibers also has been investigated.     

Remobilization of pentavalent antimony and vanadium from a granular iron hydroxide material--a comparative study of different leaching systems

The remobilization of antimony and vanadium from previously loaded commercial granular ferric-hydroxide GEH material (intended for water treatment) was examined by using a sequential extraction procedure and three different leaching systems to evaluate their physicochemical mobility and potential availability under different simulated environmental conditions. A classical batch extraction, an extraction cell (EC) and rotating-coiled columns (RCC) were used as extraction systems.For each system it could be shown that the content of ion-exchangeable antimony and vanadium in previously loaded material is negligible (<1.5%). The oxyanions were sorbed strongly and could be predominantly remobilized through reducing agents, which means through dissolution of the iron (hydr)oxide matrix.The major advantages of dynamic systems in comparison to batchwise fractionation technique are the drastically reduced extraction time and the possibility of generating information to the leaching kinetics. It is shown that the efficiency of the three leaching systems is quite different employing Wenzel's sequential fractionation protocol. Only by working with RCC, the iron (hydr)oxide matrix was completely dissolved within four steps resulting in the total mobilization of antimony and vanadium. EC seems to be less suitable for leaching studies of Sb and V sorbed on iron(hydr)oxide. The remobilizable proportion of the several fractions was lower in comparison to batch and RCC and seems to be a result of an agglomeration of the GEH in the EC device.