Vanadium Pentoxide Sol Research Articles

One-step synthesis and characterization of poly(o-toluidine) nanofiber/metal nanoparticle composite networks as non-enzymatic glucose sensors

Composite networks of poly(o-toluidine) (POT) nanofibers (NFs) and gold (Au)/copper (Cu) nanoparticles (NPs) were facilely synthesized through a one-step seeding polymerization reaction and a redox/complexation process that took place between monomers and corresponding metal salt cations in aqueous medium at ambient temperature. In order to ensure the polymeric NF morphology formation and to enhance the overall oxidative potential of the different reaction media, vanadium pentoxide (V2O5) sol–gel NFs were played critical roles both as well-known seeding agents and also as the auxiliary oxidative agent. The homogenous embedment/distribution of Au and Cu NPs within 1D POT NF matrix enhanced the electron transfer process and prevented the possible catalyst NPs deformation. Furthermore, without the need of glucose oxidase (GOx) enzyme, POT-Au/Cu nanocomposites exhibited excellent bio sensitivity for glucose within a wide linear operation range of 1–30mM (R=0.99846). Multiple electrochemical cycling stability, high tolerance for chloride (Cl−) ions and high selectivity for glucose were also achieved by the these nanocomposites, since their electrodes showed negligible response to the common interfering reagents, i.e. uric acid (UA), l-ascorbic acid (AA) and 4-acetamidophenol (AP), at their physiological levels. Thus, this facile and effective seeding polymerization approach via one-step redox/complexation process can be utilized as a general methodology and effective fabrication tool to synthesize metal NP embedded nanofibrous conducting polymer (CP) networks as the building blocks for new generation non-enzymatic biosensors.

CORRELATION BETWEEN WATER-BATH TEMPERATURE, SOLUTION VISCOSITY AND OPTICAL PROPERTIES OF SOL–GEL DERIVED V2O5 THIN FILMS

Thin films of V 2 O 5 were deposited on glass substrates by dip-coating technique using sol–gel route. The vanadium pentoxide sol was prepared by dissolving V 2 O 5 powder in H 2 O 2 solution. The solutions were kept in water bath and heated at five different temperatures for 30 min. The samples were annealed at 150°C for 60 min. The optical, structural, and morphological measurements were performed for characterization of samples. The effect of viscosity on optical constants (n, k, and Eg) of V 2 O 5 were studied. The indirect optical band gap energy of sol–gel V 2 O 5 thin films are about 2.33 eV and independent of viscosity within the error limits. The results show that the water-bath temperature strongly influences the viscosity of sol. The viscosity of sol was changed from 12.5 to 75 m Pa s. with increasing water-bath temperature from 50 to 90°C. The XRD measurements show that the structure of the V 2 O 5 films and powders is polycrystalline after annealing at 450°C. A correlation exists between the viscosity, morphology, and optical characteristics.

Layer-by-layer composite films of polyaniline and vanadium pentoxide sol gels studied by electrochemical surface plasmon spectroscopy

Electroactive multilayer films of polyaniline (PAni) and vanadium pentoxide (V2O5) sol-gels were prepared on gold surfaces by means of the layer-by-layer (LBL) method. The stepwise buildup and the optoelectrochemical behaviour of the composite films were investigated in-situ by electrochemical surface plasmon spectroscopy (ESPS). A thickness increment of 2.3 nm per deposited bilayer was obtained by modelling the surface plasmon spectra. The composite multilayer films display charging-discharging characteristics similar to a bare vanadium pentoxide xerogel network along with an optoelectrochemical response which is dominated by the conducting polymer component. Electrochemical impedance spectroscopy (EIS) experiments confirm the findings from ESPS with regard to the presence of different conductive states of the composite.

Structural and optical properties of vanadium pentoxide sol–gel films

The V 2O 5 films were obtained using sol–gel procedure. The composition and mesostructure of the layers were investigated with the UV and Raman spectroscopy, as well as with electron microscopy. We showed that the changes in the properties of thin layers accompanying the variation of film thickness are connected with the changes in the microstructure of the film rather than with changes in its composition. The thin V 2O 5 layers obtained in the present study are composed of disordered clusters; their mean size is 4–13 nm.

Spontaneous and Self-Assembled Line Formations on Silicon Substrates with Vanadium Pentoxide Sol−Gels

A simple one-pot method has been developed to deposit discreet nanometer line formations on silicon substrates without any surface pretreatment starting with vanadium pentoxide sol-gels. These vanadium suspensions were made by hydrolyzing amorphous V2O5 in water. The properties of the vanadium clusters were determined through X-ray diffraction, elemental analyses, pH calculations, and concentration calculations. Morphology of the lines was examined with optical microscopy, atomic force microcoscopy, and scanning electron microscopy. Infrared spectroscopy was used to inspect the organic components. The vanadium sol-gel used formed discreet and regular lines with high reproducibility and on the same order of magnitude as other patterning techniques. Previous research with a low solubility, 8 g/L, metal oxide for line, ring, or helix formation has not been found in the literature; this work could lead to novel applications of metal oxides such as porous catalysts, battery materials, and resistive electronic materials.

The influence of anchoring energy on the prolate shape of tactoids in lyotropic inorganic liquid crystals

A model was constructed to describe the prolate shape of anisotropic regions, tactoids, coexisting with the isotropic phase in lyotropic inorganic liquid crystals. The elastic energy of the tactoid, the surface energy, and the interaction energy between the director field and the boundary of the tactoid were taken into account. Large-sized tactoids were shown to be prolate because of the competition between the elastic energy of the nematic phase of the tactoid and the surface energy. Small-sized tactoids were prolate because of the competition of the surface energy with the anchoring energy between the director and the boundary of the tactoid. The suggested model was applied to experimental data to determine the ratio of the elastic constants K 3/K 1 and the ratio between the anchoring energy W and the surface tension σ depending on the “time of aging” of vanadium pentoxide sols in water.

Mg Intercalation Properties into V 2 O 5 gel/Carbon Composites under High-Rate Condition

carbon composites were prepared from a homogeneous suspension in which vanadium pentoxide sol and acetylene black powder were mixed with acetone acting as a surfactant. The composite was loaded on indium-tin oxide (ITO)-coated glass, and then the magnesium intercalation property and the high-rate charge-discharge performance were evaluated in an electrolyte of acetonitrile at room temperature. In cyclic voltammetry, two main peaks of a reversible redox reaction were observed. It was determined that 1.84 mol of Mg per mol of were inserted in the first cycle at a relatively slow sweep rate of 0.1 mV s−1, which corresponds to a specific capacity of 540 mAh Galvanostatic charge-discharge tests at various current densities showed a high capacity of about 600 mAh at a current density of 1.0 A and about 300 mAh was maintained even at 20 A © 2003 The Electrochemical Society. All rights reserved.

Physical properties of vanadium pentoxide sol gel films

Vanadium pentoxide films were prepared by an inorganic sol-gel method. Optical absorption study of V 2O 5 yielded a direct band gap of 2.4 eV. The temperature coefficient of resistance, β T was 2% K −1, which indicated that V 2O 5, could be used as a resistor. The thermoelectric power showed n-type semi-conduction. The small changes in the Seebeck coefficient indicated suitability as a thermistor. The activation energies calculated from the first heating–cooling cycle, were 0.1 and 0.37 eV, which indicated two types of conduction. X-Ray diffraction of V 2O 5 films showed the three characteristic peaks at ‘ d’ spacing of 0.34, 0.27 and 0.217 nm. Annealing at 573 and 673 K improved the crystallinity of the films and decreased the localized states in the band gap.

Vanadium Pentoxide Sol and Gel Mesophases

Colloidal suspensions of V2O5 ribbon-like particles display optical textures typical of lyotropic nematic phases. Tactoids (small nematic droplets) and then isotropic phases are formed as these systems are diluted. Nematic suspensions can be oriented by applying a magnetic or an electric field. Such a liquid crystal behavior is mainly due to the highly anisotropic shape of vanadium oxide colloidal particles. Acid dissociation at the oxide/water interface gives rise to surface electrical charges and electrostatic repulsion should also be responsible for the stabilization of the nematic phases. Anisotropic xerogel layers are formed when these gels are deposited and dried onto flat substrates. X-ray diffraction patterns of such coatings exhibit a series of 00l harmonics due to the turbostratic stacking of the oxide particles. Dehydration is reversible and fluid mesophases are again obtained via a swelling process when water is added to the xerogel.

Liquid Crystal Behavior of V2O5·nH2O Gels

AbstractMost liquid crystals are made of organic molecules, very few of them are based on mineral compounds. Vanadium pentoxide gels and sols have been shown to give mesophases. They are made of ribbon-like polymeric particles of vanadium pentoxide dispersed in water. Ansitropic xerogel layers are formed when these gels are deposited and dried onto flat substrates. Dehydration is reversible and fluid phases are again obtained via a swelling process when water is added to the xerogel.When observed by polarized light microscopy, colloidal suspensions of V2O5 ribbons display defects typical of lyotropic nematic phases. Dilute nematic suspensions can even be oriented by applying a magnetic field of about 0.5 Tesla. Such a liquid crystal behavior is mainly due to the highly anisotropic shape of vanadium oxide colloidal particles. Acid dissociation at the oxide/water interface gives rise to surface electrical charges and electrostatic repulsions should also be responsible for the stabilization of the nematic phase.

Effects of aging time on V2O5 sol-gel coatings

Abstract : Vanadium pentoxide (V2O5) sols have been used in conductive coatings and related applications. From cryo-Transmission Electron Microscopy (TEM) and Nuclear Magnetic Resonance (NMR) spectroscopic studies of the gelation, there are several intermediate structures and reactions in this process, but no information is yet available on the effects of aging on the dependent properties of viscosity, conductance, and film morphology in the coating process. This study observed the changes in these properties over a 30 day period by means of rheological measurements and microscopic observation of the dried coatings obtained. The study found that the sol viscosity and ability to wet substrates is related to the initial decomposition of the precursors in solution and the start of the polymerization process. Distinct differences were observed in coating morphology as later aggregation and agglomeration processes occurred.

Molecular aspects of tactoid formation in man and animals.

Annals of the New York Academy of SciencesVolume 241, Issue 1 p. 623-637 MOLECULAR ASPECTS OF TACTOID *: FORMATION IN MAN AND ANIMALS Makio Murayama, Makio Murayama National Institutes of Health Bethesda, Maryland 20014Search for more papers by this author Makio Murayama, Makio Murayama National Institutes of Health Bethesda, Maryland 20014Search for more papers by this author First published: November 1974 https://doi.org/10.1111/j.1749-6632.1974.tb21919.xCitations: 1 * A tactoid is an elongated particle, such as vanadium pentoxide sol, tobacco mosaic virus, myosin, fibrin, or deoxygenated sickle cell hemoglobin, which appears as a spindle-shaped body under the polarizing microscope and which occurs in a thready liquid crystal phase. “Nematic tactoid” and “nematic liquid crystal” will be used interchangeably in this discussion. Tactoids are anisotropic, as revealed by the polarizing microscope, which indicates that they are composed of oriented particles, and that the direction of orientation coincides with the long axis of the tactoid. For additional information see Brown, Doane, and Neff. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume241, Issue1Hemoglobins: Comparative Molecular Biology Models for the Study of DiseaseNovember 1974Pages 623-637 RelatedInformation

The influence of ultrasonic waves on the viscosity and stability of vanadium pentoxide sol

The vanadium pentoxide sol when exposed to ultrasonic waves shows an increased value of hydrogen ion concentration and conductivity. It is postulated that this change is due to either supersaturation of metavanadic acid in presence of the high frequency waves or to the production of peroxyvanadic acid under the influence of hydrogen peroxide which is known to be formed in traces under these conditions. The change in viscosity of vanadium pentoxide sol in presence of electrolytes under the influence of ultrasonic waves has also been recorded.

Formation and Aging of Precipitates. VII. Habit of Crystals in Vanadium Pentoxide Sols by Electron Microdiffraction Method

Abstract The crystals in Biltz-, Müller-, and ion-exchange sols were all identified with vanadium pentoxide by the electron diffraction method. The crystals in aged Biltz sol were fiber-like. The specimen prepared ordinarily gave rise to the Debye-Scherrer pattern and that of the tactoid corresponded to the fiber pattern. The fiber axis of the fibrous crystal was decided to be the b-axis.

Formation and Aging of Precipitates. VI. Morphology of Crystals in Various Vanadium Pentoxide Sols by Electron Microscopy

Abstract Vanadium pentoxide sols were prepared by Biltz’, Müller’s and ion exchange method, and the crystals in the sols were observed with an electron microscope. The crystals in Biltz sol were small fibrils at first, but they grew into long fibrous crystals upon aging. The crystals in Müller and ion exchange sols were fibrils and needles respectively and hardly grew at all. The growth of the fibrous crystals in Biltz sol is likely to be due to the recrystallization of the fibrils.

Electron Microscopy and Diffraction Studies of Vanadium Pentoxide Sols

Vanadium pentoxide sols were prepared by the method using the cation exchange resin and Biltz method and studied with an electron microscopy and diffraction method. The sol prepared by the ion exchanger contained capillary crystals and the particles did not grow by aging. The Biltz sol grew like fibre by aging. These sols were confirmed to be vanadium pentoxide by the electron diffraction.The fibres of Biltz sol, about one year old, could be arranged in parrallel with each other and was investigated by the selected area electron diffraction method. The diffraction pattern was a typical fibre pattern with many layer lines and the fibre axis was confirmed to be b-axis.

Preparation of vanadium pentoxide sols by ion exchange

The most widely used method for the preparation of vanadium pentoxide sols involves addition of an acid to ammonium vanadate, washing the precipitated oxide until it begins to peptize and then suspending in water until dispersion is complete (1).2 The sols contain a variable amount of molecular vanadium pentoxide, depending on their age (5). The molecular fraction passes through dialyzing membranes and, since it is in equilibrium with the colloidal particles, purification of the system by dialysis is accompanied by continuous loss of vanadium. The preparation of a sol of low electrolyte content has been reported by Prandtl and Hess (4). The method consisted of hydrolyzing the tertiary butyl ester of orthovanadic acid followed by distillation of the alcohol. This report describes the preparation of a relatively pure vanadic acid system from ammonium vanadate by the method of ion exchange. A batch procedure has been employed because of the low solubility of the starting material.

Investigation of Flow in Liquids by Use of Birefringent Colloidal Solutions of Vanadium Pentoxide

Abstract The author, engaged on hydrological research on the Bosphorus (1) and interested in diffusion and turbulence as biological environmental factors, was first induced to try a flow-birefringence method on a macroscopic scale, as a result of reading a paper on the shape of protein molecules (2). The use of vanadium-pentoxide sols as a birefringent medium for the demonstration of fluid flow was so successful that Prof. J. C. Bliss, Dean of the Engineering School at Robert College, encouraged the author to write a preliminary publication emphasizing the possibility of engineering application. On account of the pressure of other work, the manuscript was not ready until the beginning of September, 1945. It appears that, unknown to the author, the method of flow birefringence has been in use for some time. In a recent article by Walter Leaf (3) the following statement is made: “This process was developed in the chemical-engineering department of the Massachusetts Institute of Technology by D. R. Dewey, 2nd, under the direction of Dr. E. A. Hauser about 4 years ago.” The process involves the use of the birefringent properties of bentonite clays (named from Fort Benton, Wyoming). Jerome Alexander (4), writing in 1925, quotes a report of Edgar T. Wherry to the effect that “under the microscope, between crossed nicols, the grains (of bentonite) show distinct double refraction.…. the grains being of visible dimensions in two dimensions,…. yet of colloidal dimensions in the third.” The isolation of Istanbul during the war period perhaps accounts for the fact that the M.I.T. work was overlooked. On account of this, the title and a number of sections in the original manuscript of this paper have been modified or omitted, because their inclusion after the appearance of Leaf’s publication would have been redundant. More particularly, sections on the use of polarized light, see Taylor (5), and on the construction of experimental apparatus have either been omitted entirely or reduced to a minimum. However, it seemed in place to leave a little of the theory upon which the method is based, and to emphasize the suitability of vanadium-pentoxide sols as a birefringent medium, particularly where photographic recording is desirable.

Artificial Aging of Vanadium Pentoxide Sol

Artificial Aging of Vanadium Pentoxide Sol

The Role of Attractive and Repulsive Forces in the Formation of Tactoids, Thixotropic Gels, Protein Crystals and Coacervates

The formation of tactoids from thixotropic sols, of Schiller layers from iron-oxide sols, the separation of tobacco virus solutions and bentonite sols into two liquid layers and the crystallization of proteins are regarded as examples of unipolar coacervation (micelles having like charges) which must involve attractive forces. Kallmann, Willstätter, Freundlich, De Boer, Hamaker, Houwink and others have assumed that the attraction is due to van der Waals forces. They have also analyzed the stability of colloid systems by diagrams giving the potential energy as a function of the distance between micelles. It is now shown that the Coulomb attraction between the micelles and the oppositely charged ions in the solution gives an excess of attractive force which must be balanced by the dispersive action of thermal agitation and another repulsive force. Thus there is no need to assume long range van der Waals forces. The past use of energy diagrams is criticized because it has ignored the effect of the thermal agitation and the attraction of the ``gegenions'' in solution. Instead of potential energy it is proposed that osmotic pressure p be used, which includes these previously neglected factors. A maximum in p as the colloid concentration increases is the condition for the separation into two phases (coacervation). The Debye-Hückel theory (1st approximation) for the osmotic pressure of electrolytes takes into account both these factors and permits a rough calculation of the conditions under which coacervation occurs. The 2nd approximation, which considers particle size, does not agree as well with experiment as the first approximation. The reasons for this lack of agreement are discussed. The micelles in unipolar coacervates are not in contact, but are separated by relatively large distances (10–5000A). Either a specific repulsive force or a decrease in the Coulomb attraction as the concentration increases (due to decreased charges on micelles) can account for stable coacervates. The assumption of a definite ζ-potential, rather than a definite charge on the micelles, gives automatically just such a decrease in attraction. The general mathematical theory of coacervation presents great difficulties because the approximations of the Debye-Hückel theory cannot be used. However, the one-dimensional problem of the forces acting between parallel colloidal platelets can be solved rigorously in terms of elliptic integrals. For highly charged particles in sufficiently dilute solutions of electrolytes, the pressure p in the liquid between the two plates is given by p = (π/2)D(kT/eb)2 = 8.9×10—7/b2 dynes/cm2 where b is the distance in cm between the plates and D is the dielectric constant (81 for water at T = 293°K). This pressure which tends to force the plates apart is independent of the charge on the plates and on the electrolyte concentration (univalent ions only). Polyvalent ions decrease the force. This force is of the right magnitude to account for the stability of unipolar coacervates. It also furnishes a quantitative explanation of the Jones-Ray effect, by which low salt concentrations decrease the capillary rise in surface tension experiments with water. Experimental determinations were made of the relaxation times τ for the decay of birefringence in bentonite and vanadium pentoxide sols, after stirring was stopped. In one sample of bentonite, τ varied with the 22nd power of the concentration, while in V2O5 sols the exponent was 1.8. The temperature coefficients of τ were also measured and the activation energies were calculated. A theory of the relaxation of birefringence was developed, according to which the micelles in dilute thixotropic bentonite sols are arranged normally in a cubic lattice (isotropic). Temporary shear in the liquid orients the micelles and produces birefringence although the lattice remains cubic. The experimental data confirm the theory and indicate that the energy barrier opposing reorientation of micelles in a particular bentonite sol varied with the inverse 20th power of the distance between the micelles. With V2O5 this exponent was about 4. Further support for the theory was obtained by experiments which gave ``angles of isocline'' for bentonite particles in a flowing sol that varied from 65° to 78°. In bipolar coacervates (which contain micelles of unlike polarities) the electric fields and the charges on the micelles increase as the micellar concentration increases. When a certain concentration is reached, the field rises to a value so high as to cause increased hydration which holds the micelles apart and gives stability to the coacervate.