E. V. Polyakov

Metatitanic Acid: Synthesis and Properties

Features of proton-for-lithium ion substitution in monoclinic and pseudocubic lithium titanate are studied by X-ray diffraction, NMR spectroscopy, and Raman spectroscopy. Proton incorporation into the lithium titanate structure decreases the parameter ac of the pseudocubic unit cell from 8.28 Å in Li2TiO3 to =8.15 Å in H2TiO3. Metatitanic acid, like hydrous titania, has weak acid properties, but unlike titania, it sorbs hydrolyzable multicharged cations from aqueous solutions.

Electronic structure and the optical and photocatalytic properties of anatase doped with vanadium and carbon

The electronic structures of undoped anatase and anatase doped with carbon and vanadium have been calculated using the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) method in the LSDA + U approximation. It has been shown that the doping of TiO2 leads to the formation of narrow bands of the C and Vimpurity states in the band gap. The calculations of the imaginary part of the dielectric function have made it possible to estimate the intensity of the optical absorption. It has been established that the doping with vanadium and carbon leads to optical absorption in the visible range and to an increase in the absorption in the ultraviolet range up to 4 eV. This should result in an increase in the photocatalytic activity on the surface of the doped anatase. The experimental determination of the photocatalytic activity of whiskers of the anatase doped with carbon and vanadium in the reaction of hydroquinone oxidation has confirmed the increase in the activity of the doped materials under exposure to ultraviolet, visible, and blue light. The phenomenon of dark catalysis in the anatase doped with carbon and vanadium has been interpreted within the concept of low-energy electronic excitatio ns between the impurity levels of carbon.

Synthesis and properties of titanium glycolate Ti(OCH2CH2O)2

A new efficient method for the synthesis of extended micro-and nano-sized crystals (whiskers, fibers) of titanium glycolate Ti(OCH2CH2O)2 has been suggested. The method implies the reaction of hydrated titanium dioxide with ethylene glycol on heating in air. Thermolysis of Ti(OCH2CH2O)2 in air gives titanium dioxide as anatase (400–500°C) and rutile (T > 700°C), the morphology of titanium glycolate crystals being inherited by the oxide. The pseudocrystals of the thermolysis product in an inert gas medium (T = 500–950°C) represent aglomeration of nano-sized titanium dioxide particles and amorphous carbon. At temperatures up to 1300°C, the formation of the TiO2−xCx phase with a rutile structure is probable. In a wet air environment, titanium glycolate is partially hydrolyzed to give TiOx(OCH2CH2O)2−2x(OH)2x·xH2O (0 ≤ x ≤ 1) and on keeping in water at room temperature, ethylene glycol is completely displaced from the crystals. This process is also not accompanied by changes in the particle morphology.

Synthesis and photocatalytic activity of Ti[1 − x]VxO[2 − y]Cy whiskers in hydroquinone oxidation in aqueous solutions

Ti1−xVxO2−yCy (0 ≤ x ≤ 0.10 and x = 0.50) whiskers having the anatase structure were synthesized via thermolysis of vanadium-doped titanium glycolate of composition Ti1−xVx(OCH2CH2O)2 (0 ≤ x ≤ 0.10 and x = 0.50). The starting reagents used to prepare Ti1−xVx(OCH2CH2O)2 were mixtures of coprecipitated titanium and vanadyl hydroxides, which were heated in ethylene glycol at T ≤ 200°C: (1 − x)TiO(OH)2 + xVO(OH)2 + 2HOCH2CH2OH = Ti1−xVx(OCH2CH2O)2 + 3H2O↑. Thermolysis of vanadium-doped titanium glycolate in various gas media over a wide range of temperatures is useful to prepare titania samples doped with both vanadium and carbon to form a phase of the general composition Ti1 − xVxO2 − yCy whiskers prepared by thermolyzing Ti1 − xVx(OCH2CH2O)2 in air at 450°C were found to have a high photocatalytic activity in hydroquinone oxidation in aqueous solutions irradiated in the UV spectral range; the photocatalyst’s activity increases with increasing vanadium concentration. When hydroquinone was irradiated in the blue, the maximal catalytic activity was discovered in a sample of composition Ti0.50V0.50O2−yCy. Quantum-chemical calculations support experimental data that the double doping of titania (Ti1−xVxO2−yCy) enhances its photocatalytic activity compared to undoped anatase or anatase doped in one sublattice: Ti1−xVxO2 and TiO2−yCy.

Effect of doping by boron, carbon, and nitrogen atoms on the magnetic and photocatalytic properties of anatase

The effect of doping of titanium dioxide with the anatase structure by boron, carbon, and nitrogen atoms on the magnetic and optical properties and the electronic spectrum of this compound has been investigated using the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) band-structure method in the local spin density approximation explicitly including Coulomb correlations (LSDA + U) in combination with the semiempirical extended Hückel theory (EHT) method. The LSDA + U calculations of the electronic structure, the imaginary part of the dielectric function, the total magnetic moments, and the magnetic moments at the impurity atoms have been carried out. The diagrams of the molecular orbitals of the clusters Ti3X (X = B, C, N) have been calculated and the pseudo-space images of the molecular orbitals of the clusters have been constructed. The effect of doping on the nature and origin of photocatalytic activity in the visible spectral range and the specific features of the generation of ferromagnetic interactions in doped anatase have been discussed based on the analysis of the obtained data. It has been shown that, in the sequence TiO2 − yNy → TiO2 − yCy → TiO2 − yBy (y = 1/16), the photocatalytic activity can increase with the generation of electronic excitations with the participation of impurity bands. The calculated magnetic moments for boron and nitrogen atoms are equal to 1 μB, whereas the impurity carbon atoms are nonmagnetic.

Lithium chloride sorption by zinc hexacyanoferrate(II) from a nonaqueous medium

Mechanisms of lithium chloride sorption by zinc hexacyanoferrate(II) Zn2Fe(CN)6 · 2.5H2O in a nonaqueous medium (ethanol) were studied by chemical analysis, X-ray powder diffraction, wide-line 7Li and 1H NMR, vibrational spectroscopy, and impedance spectroscopy. The physicochemical properties of sorption products are reported. Lithium ions in the sorption products were found to be in a hydrated form. The accommodation of molecularly sorbed Li+ aq · Cl− ion pairs in the bores of channels in the crystal structure results in the formation of a continuous network of hydrogen bonds and changes the proton transport mechanism. As the lithium chloride concentration increases in the temperature range 22–150°C, the conductivity (σ) of sorption products increases three to four orders of magnitude to reach 10−3 S cm−1.

Precursor-based synthesis of nanosized tungsten carbide WC and WC: n Co nanocomposites

Tungsten carbide (WC) is a ceramic material ofgreat industrial importance owing to the unique set ofproperties, the key of them being extraordinary hardness, wear resistance, and thermal shock resistance.These properties account for its wide use for fabricating abrasives and various cutting devices [1]. Amongthe most important functional properties of WC andWC:

Thermally Stimulated Transformation of Micellar Tungsten Glycolate into Nanodisperse Tungsten Carbide

154 The increasingly strict requirements for the quality and performance of metalworking tools stimulate the development of new methods for synthesizing nano disperse WC powders and hard alloys on their basis [1]. Among these methods are high energy grinding [2], spray conversion of homogeneous solutions of a pre cursor [1, 3], and various gas phase [4] and plasma chemical [1, 5] synthesis methods. The recrystalliza tion of the synthesis products is suppressed by various variants of hot isostatic and electric pulse pressing and high frequency induction heating [1, 6]. For the same purpose, WC grain growth inhibitors, such as vana dium and chromium carbides and Group IV and V metal carbonitrides, are introduced into the initial WC–Co hard alloy mixtures [7]. To this effect, the usual fine WC–Co reaction mixture is also diluted by nanoparticles of the carbide phase. Note, however, that addition of WC nanoparticles to the initial mix ture, i.e., transition to a bimodal size distribution of WC grains, typically gives rise to various inhomogene ities in a sintered composite and favors the develop ment of pore and crack formation processes [1].