A novel dimer - Heteropolytungstate with a vanadium atom as the centre - Synthesis and structural characterization of (H3O)(4)[VW12O40Na (H2O)(4)](2)

A novel dimer-tungstovanadate, (H3O)(4)[VW12O40Na (H2O)(4)](2), was hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction, IR spectra, TGA-DSC thermal analysis and polarograpy. The yellowish crystal crystallized in the triclinic system, space group P1, a = 1.464 5(3) nm, b = 1.468 6(3) nm, c = 1.411 1(3) nm, alpha = 111.82(2)degrees, beta = 93.17(3)degrees, gamma = 117.47(3)degrees, V = 2.210 6(8) nm(3), Z = 1, D-c = 4.552 g . cm(-3), lambda (Mo K alpha) = 0.071 073 nm, mu = 31.402 mm(-1) F(000) = 2 6481 R = 0.078 0. The title compound consists of two Keggin structure units linked together with two hydrated sodium cations to form a dimer with a porous structure with the pore dimension of 0.766 nm X 0.778 5 nm.

Polishable amperometric hydrogen peroxide sensor based on sol-gel-derived conductive composite containing vanadium-17-molybdodiphosphate

A new kind of conductive vanadium-17-molybdodiphosphate/graphite/methylsilicate composite was firstly prepared by the sol-gel technique and used as electrode material for the fabrication of amperometric hydrogen peroxide sensor. The remarkable advantage of the sensor is its excellent reproducibility of surface renewal by simple mechanical polishing.

Electrochemical quartz crystal microbalance study for vanadium hexacyanoferrates: monitoring of film growth and ion effects during redox reactions

An electrochemical quartz crystal microbalance was employed to monitor directly the growth of vanadium hexacyanoferrate (VHF) films on platinum substrates during electrodeposition and interfacial coagulation in the solution containing sulfuric acid electrolyte, vanadium(IV) and hexacyanoferrate(III). Mass changes of the gold/crystal working electrode were correlated with cyclic voltammetry data. Effects of cations (NH4+, Li+, Na+ and K+), anions (SO42- and NO3-) and solvent during redox reactions of the films were studied. The results show that cations were incorporated into the film during reduction and expelled from the film during oxidation. Solvent also participates in VHF electrochemistry, and its role cannot be neglected. Anions play no role in VHF electrochemistry. (C) 1997 Elsevier Science S.A.

Electrochemistry of vanadium hexacyanoferrate film

Two stable redox couples, accompanying clear color switches between yellow green and blue, can be observed when the VHCF-coated film platinum electrodes are cyclic potential scanned in 3.6 M H2SO4 and 0.2 M K2SO4 electrolyte solution. Electrochemical results and in situ Fourier transfer infrared (FT-IR) spectroscopy demonstrate that the redox reaction of the electroactive iron sites is related to the first redox couple (E-1/2 = 0.81 V) while the second redox couple (E-1/2 = 1.01 V) is due to the redox reactions of the electroactive vanadyl ions. Under the proper conditions, such as in high acidic solutions or thin films (deposition time is less than 2 min) and so on, the third redox couple (E-1/2 = 0.89-0.94 V) can be observed on the cyclic voltammograms, which originates from the redox reactions of the interstitial vanadyl ions. This electrochemical reaction mechanism is investigated by in situ probe beam deflection technique, exchange of K+ ions accompanies with redox reaction of the iron sites, but for redox reaction of the vanadyl ions, both H+ ions, K+ ions and water molecules are involved.

Binary alloys of nylon 1010 and ethylene-propylene copolymer: Chemical, morphological, and mechanical analysis

The modification of ethylene-propylene copolymer (EPM) has been accomplished by melt grafting of maleic anhydride (MAH) molecules promoted by radical initiators. The resulting EPM-g-MAH and EPM have been used to obtain binary nylon 1010/EPM or nylon 1010/EPM-g-MAH blends by melt mixing. It was found that the EPM-g-MAH copolymer used as the second component has a profound effect upon the properties of the resulting blends. This behavior has been attributed to a series of chemical and physicochemical interactions taking place between the two components. The interactions are due to the presence of the anhydride functionality on the copolymer and do not occur when this functionality is absent. The interaction has been confirmed by Fourier-transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, and scanning electron microscopic.

ELECTROCHEMICAL STUDY OF ISOPOLY AND HETEROPOLY ANION TRANSFER ACROSS THE WATER NITROBENZENE INTERFACE .2. VANADIUM-CONTAINING HETEROPOLYTUNGSTATE ANIONS

The electrochemical transfer behaviour of vanadium-containing heteropolytungstate anions [PW12-xVxO40]((3+r)-) (x = 1-4) across the water \nitrobenzene interface has been investigated by cyclic voltammetry and chronopotentiometry with cyclic linear current scanning. The transfer of PW11V1O404-, HPW10V2O404-, H2PW10V2O403-, H3PW9V3O403- and H4PW8V4O(40)(3-) across the water \nitrobenzene interface can be observed within the potential window. The effects were observed of pH in the water phase on the transfer behaviour and the formation of vanadium-containing heteropolytungstate anions in solution. Heteropolytungstate anions become more stable due to their involving the vanadium atom. The degree of protonation and the dissociation constant of the trivalent vanadium-containing heteropolytungstate anion of protonation increase with increasing vanadium content. The transfer processes are diffusion-controlled The standard transfer potential, the standard Gibbs energy and the dissociation constant for vanadium-containing heteropolytungstate anions have been obtained and the transfer mechanisms are discussed.

INVESTIGATION OF THE ELECTRICAL AND MAGNETIC-PROPERTIES OF YSR2-XCAXV3O9-Y

All the members of the solid solution of YSr2-xCaxV3O9-y have the orthorhombic symmetry. Their electrical and magnetic properties have been studied. The magnetic susceptibility and electrical resistivity increase gradually with x. The system shows paramagnetic behavior both at 300 K and at 77 K. It is shown that a change of valence state of vanadium obviously affects the electrical and magnetic properties of the solid solution.

TRANSPORT OF ELECTROACTIVE SPECIES FE-2+ THROUGH THIN-FILMS OF VANADIUM HEXACYANOFERRATE

It is demonstrated that the electroactive species Fe~(2+) ion can transport easily through the thin films of vanadium hexacyanoferrate (VHF) to the underlaying glassy carbon (GC)electrode surface to be oxidized directly at less positive potential and that it can also be oxidized at the film at more positive potential through the media- tion of redox sites in the film. These two processes yield sequentially clearly distinguished first and second wave in stationary current-potential curves resulting...