Photocatalysis by titanium complexes of the reaction of ClO4 −, ions with alcohol molecules

In the photolysis of perchloric acid solutions of titanium(IV) with additions of ethanol, the formation of titanium(III) compounds was detected. Irradiated solutions ([HClO₄]=0.8 M) at 77K are characterized by an anisotropic ESR signal with parameters g ₁=1.994, g ₁=1.904, which correspond to pseudo-octahedral aqua-complexes of titanium(III). With the passage of time, the signal intensity of the titanium(III) compounds decreases, which is explained by their oxidation by ClO₄ ions. During prolonged photolysis of titanium(IV) compounds in 7 M HClO₄ with an addition of ethanol, a multicomponent signal of the paramagnetic chlorine oxide ClO₂ with parameters g _xx=2,004, a _xx(³⁷Cl)=6.0. mTl a _xx(³⁵Cl)=7,30 mTl, is recorded instead of the signal of titanium(III) compounds. Evidently ClO₂ is formed as a result of a rapid dark reaction between compounds of trivalent titanium (products of the photochemical step) and chlorate ions, which are accumulated in the solution as a result of successive photochemical and dark redox conversions of the titanium compounds, perchlorate ions, arid free radicals from the alcohol molecules. The formation of free radicals in the system was established by the ESR method after irradiation of frozen solutions.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 6, pp. 679–686, November–December, 1986.     

Carrier influence on the paramagnetic and catalytic properties of supported titanium complexes

Alumina-silica possessing various Al₂O₃/SiO₂ ratios was used as a carrier of surface titanium complexes. The systems obtained were examined as models for the investigation of the macroligand (inorganic gel) influence on the physicochemical properties of supported transition metal complexes. The titanium complexes were prepared first by the reaction of CpTiCl₃, with the hydroxyl groups of the gel and then reduced by an excess of BuLi. The influence was established of the basic gel properties on: (a) the amount of titanium(IV) and titanium(III) complexes on the alumina-silica gel surfaces; (b) the symmetry of the surface Ti^III surface complexes; (c) the electron density around the surface-Ti^III ions, ionic or covalent bonds character in a complex; and (d) the catalytic activity in olefin hydrogenation.     

Reversible double insertion of aryl isocyanates into the Ti-O bond of titanium(IV) isopropoxide

The insertion of phenyl isocyanate into titanium isopropoxide leads to the formation of a dimeric complex [Ti(OⁱPr)₂(μ-OⁱPr){C₆H₅N(OⁱPr)CO}]₂ (1) which has been structurally characterized. Reaction of titanium isopropoxide with two and more than 2 equiv. of phenyl isocyanate is complicated by competitive, reversible insertion between the titanium carbamate and titanium isopropoxide. The ligand formed by insertion of phenyl isocyanate into the titanium carbamate has been structurally characterized in its protonated form C₆H₅N{C(OⁱPr)O}C(O)N(H)C₆H₅ (3aH). Insertion into the carbamate is kinetically favored whereas insertion into isopropoxide gives the thermodynamically favored product.     

The roles of oxidation state,Lewis acid cocatalyst and solvent polarity in activating titanium compounds for olefin polymerization

The polymerization activity of the following three catalyst systems towards ethylene has been investigated and compared: 1) methyltitanocene chloride-Me₂AlCl 2) η³-allyltitanocene-Me₂AlCl and 3) titanium dichloride tetrahydrofuranate-Me₂AlCl. The first two catalysts formed homogeneous phases and produced linear polymer; the last catalyst functioned in a heterogeneous medium and formed crosslinked polymer. The titanium(IV) catalyst was about 30 times more active than the titanium(III) system and the titanium(II) catalyst on MgCl₂ could be made 8 times more active than the titanium(IV) system. A novel mechanism is proposed to explain the behavior and activity of the titanium(II) system.     

Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. XLI. Darstellung und Thermolyseprodukte von Methyltitanhalogeniden

Contributions to the Chemistry of Transition Metal Alkyl Compounds. XLI. Preparation and Thermolysis Products of Methyl Titanium Halides (CH₃)_nTiX_{4 ? n} derivatives (X = Cl, Br, I) can be prepared by comproportionation reactions of tetramethyl titanium with titanium tetrahalides at deep temperature. Furthermore, the methyl titanium iodides are formed from tetramethyl titanium and iodine. Thermolysis of CH₃TiX₃ derivatives yields titanium(III) halides. At decomposition of the (CH₃)₂TiX₂ compounds in ether solution titanium(II) halides are obtained in a fine-distributed, very reactive form.     

DFT predictions of vibrational spectra of titanium tetramethoxide oligomers and the structure of titanium tetraalkoxides in liquid and solid phases

Plausible structures of the titanium tetramethoxide trimer were optimized at the B3LYP/6-31+G^* level. From the four types of structures of the Ti₃O₁₂ cage found earlier for the Ti(OH)₄ trimer only two isomers were found as energy minima on the Ti₃(OMe)₁₂ potential energy surface. One isomer (I), belonging to the C_i point group, is built from three interconnected titanium oxide tetrahedra with a linear arrangement of titanium atoms. This structure have a titanium oxide skeleton similar to that of Ti₃(OH)₁₂. The other isomer (II), of C₂ symmetry, is built by edge sharing TiO₆ groups. Theoretical IR spectra of these isomers are compared with reported experimental IR spectra of solid titanium tetramethoxide and newly obtained Raman spectra of commercial powders. It was shown that the number and position of observed bands in the CO stretching region of the IR spectra of the so-called modification A of solid titanium tetramethoxide are in a good agreement with the predicted vibrational spectrum of trimer I. The equilibrium structure and IR and Raman spectra were also obtained for the Ti₄(OMe)₁₆ tetramer. The comparison of the predicted vibrational spectrum with the experimental IR spectra of modification B as well as of the Raman spectrum of solid titanium tetramethoxide allows us to confirm the tetrameric structure of this modification and to propose the similar structure for commercial samples.     

二氧化钛纳米晶溶胶内渗透电极对染料敏化太阳能电池的光伏性能的提高

以自制的过氧钛酸(PTA)水溶液为前驱体,用水热法制备了透明锐钛矿相二氧化钛溶胶.无需有机添加剂可得到直径小于7 nm的棒状二氧化钛纳米晶溶胶.通过将溶胶内渗透到染料敏化太阳能电池(DSSCs)的多孔二氧化钛电极后,消除了多孔电极内的大孔并改善了电极内纳米晶之间的连通性.用扫描电子显微镜(SEM)和光学轮廓仪对溶胶内渗透后的光阳极进行了表征.结果表明:小颗粒棒状二氧化钛纳米晶附着在多孔的二氧化钛表面,填充了电极由于烧结产生的大孔,并在多孔的二氧化钛内部形成了有利于电子传输的网络结构.与未经处理的多孔电极相比,改性后的光阳极组装成染料敏化太阳能电池后光电转化效率提高了64%.     

Synthesis of rutile titanium dioxide from Russian raw materials

The conditions of the structure formation of rutile titanium dioxide from titanium dioxide (anatase) and titanium hydroxide isolated by thermolysis from the titanium compound (NH₄)₂TiO(SO₄)₂ · H₂O and by thermal hydrolysis of a titanium sulfate(IV) solution, respectively, were studied. It was shown that the mechanical activation of the studied powders causes, in addition to a decrease in the initial grain size, deep destructuring with the formation of the transition phase, which, in the process of the subsequent high-temperature treatment, functions as a matrix for the formation of rutile. The research results will be used for the development of a new variant of the technology for the synthesis of titanium dioxide, which is an important component of compositions for polymeric materials—in particular, the K-300-61 and K-153 adhesives.     

Synthesis of TiC-C fiber from titanium isopropoxide treated phenolic resin fiber

Precursor fibers for titanium carbide-carbon fibers were synthesized by reacting phenolic resin fibers with titanium isopropoxide (TIP). In this system, titanium oxide gel coated fiber was prepared by hydrolyzing TIP infiltrated resin fiber. The precursor fibers obtained after the hydrolysis were converted into titanium oxide-carbon fibers (TiO₂-C fibers) by pyrolysis at 1273 K. The TiO₂-C fibers were converted into titanium carbide-carbon fibers (TiC-C fibers) by heat treatment at 1373–1973 K. The mechanisms of the conversion from TiO₂-C fibers to TiC-C fibers were characterized by TGA.     

Study of the retention mechanism of uranium on titanium oxide

We have studied the phenomenon of retention of uranium, as a carbonato complex UO₂(CO₃) ₃ ⁴⁻ on titanium oxide. We first proposed a method for preparing titanium oxide whose ion-exchange capacities (2.9 meq Na⁺/g, 0.11 meq UO ₂ ²⁺ /g) and physical properties (mechanical resistance and granulometry) make it quite suitable for liquid chromatography and particularly for the extraction process of uranium from sea-water. We prepared the sodium tricarbonatouranate, the major form of uranium in sea-water. We studied the retention of this compound on titanium oxide. From a thermodynamic study of the retention equilibrium we proposed a retention mechanism of the ligang-exchange type: uranyl is retained on titanium oxide, surrounded with two CO ₃ ²⁻ ligands and two ≥TiO⁻ ligands. We shown that 2/3 of the exchanged hydroxyl groups have pK_H1=4.9 and 1/3 of them have pK_H2=9.3.     

Modelling of substitutional defects in the structure of Ti-bearing hibonite

A local atomic structure around titanium positions in Ti-bearing hibonite (CaAl₁₂O₁₉) has been studied. The structural models of substitution of different substitution defects Ti–Al in hibonite by titanium atoms have been considered. Optimization of structural models of hibonite has been done by means of density functional theory calculations using pseudopotential approximation as implemented in VASP 5.3 code. Gibbs free energies analysis has shown that models of substitution of M2 and M4 aluminum positions by titanium atoms are the most probable. For the most probable structural models of Ti-bearing hibonite theoretical X-ray absorption near-edge structure (XANES) spectra near the titanium K edge have been calculated. Significant differences in theoretical XANES spectra calculated for different structural models with non-optimized and optimized atomic structure have been demonstrated. Changes in the intensity of pre-edge structure of TiK XANES spectra for different substitution models of aluminum by titanium have been observed which relate to different titanium coordination in structural models. Energy shift of spectral features towards lower energy for optimized models implies increase of interatomic distances in local surroundings of Ti absorbing atoms.     

Photochemical properties of peroxo complexes of titanium,intermediate products in the photocatalytic liquid-phase oxidation of alcohols

A study has been made of the photochemical reactions of titanium(IV) peroxo complexes formed in the reaction of titanium tetrachloride with hydrogen peroxide in alcoholic solutions and which are characterized by intense charge transfer bands at 360–425 nm. Irradiation of the solutions with light of = 254 nm leads to the decomposition of the titanium(IV) peroxo complexes, the formation of titanium(III) compounds, as well as the oxidation of the alcohol to aldehyde. In the irradiated frozen solutions associated complexes of titanium(III), organic free radicals formed from the alcohol molecule, as well as peroxy radicals have been identified by EPR. Irradiation with light corresponding to the longwave band of the peroxo complexes leads to their decomposition but titanium(III) compounds and alcohol oxidation products are not formed in this case. In irradiated frozen solutions the formation of paramagnetic titanium(IV) complexes containing the fragment Ti...O ₂ has been established, as well as other paramagnetic particles identified tentatively as coordinated Ti...O ₂ ^· radicals or radical pairs. It is shown that the decomposition of hydrogen peroxide in the presence of titanium(IV) compounds is photocatalytic.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 24, No. 1, pp. 67–74, January–February, 1988.     

FT-IR Spectroscopy of Acid-Modified Titanium Alkoxides: Investigations on the Nature of Carboxylate Coordination and Degree of Complexation

Modification of titanium butoxide by acetic acid has been studied by means of FT-IR spectroscopy. A deconvolution procedure was carried out to give further insight concerning the coordination modes of acetate ligands in Ti_aO_b(OBu)_c(OAc)_d complexes. From these results, molecular structures of the acetic acid modified precursor in a stoichiometric Ti(OBu)₄/AcOH (1:1) were proposed. On the basis of ATR spectroscopic data, the degree of complexation in Ti_aO_b(OBu)_c(OAc)_d oligomers as a function of the molar ratio Ti/AcOH was also estimated. Organic/inorganic hybrids were prepared from titanium butoxide and acrylic terpolymers bearing active acid groups via the sol-gel process. The interactions between the acid groups of the polymer and titanium butoxide were investigated by FT-IR spectroscopy and the carboxylate coordination modes were compared with the coordination modes in the acetato complexes.     

Polymerization of propylene by the three-component system comprising titanium(III) chloride,ethylaluminum sesquichloride,and sodium sulfate

Sodium sulfate increases the polymerization activity of the titanium(III) chloride (AA)–ethylaluminum sesquichloride system for the polymerization of propylene. The reaction of ethylaluminum sesquichloride with sodium sulfate at mild conditions isolates diethylaluminum chloride, which is responsible for the polymerization activity. The reaction of these components at severe conditions forms an organometallic compound containing sulfate, (C₂H₅)₄Al₂SO₄, and this compound is a powerful activator for titanium(III) chloride.     

The structure of polypropylene-TiO2 organoinorganic nanocomposites prepared via solvent crazing

A method is developed for crazing-based production of mechanically strong hybrid polypropylene film composites containing amorphous titanium dioxide nanophase (up to ～30 wt %). As a whole, the morphology of the composite represents an interpenetrating network in which the inorganic component (TiO₂) is distributed in the nanoporous structure of a polypropylene matrix. The structure and composition of amorphous titanium dioxide present an ensemble of TiO₂ nanoparticles with a size of ～1 nm (20 wt %) included in a loose network of titanium oxopolymers (80 wt %) containing ～30 wt % side OC₃H₇ and OH groups bonded to titanium atoms.     

Formation of the structure of cerium oxide-modified titanium dioxide

The formation of the structure of titanium dioxide containing 3–15 wt % CeO₂ in a wide temperature range (300–850°C) has been investigated by X-ray powder diffraction, electron microscopy, and adsorption methods. Modification of titanium dioxide with cerium oxide causes the formation of nanostructured Ce-Ti-O compounds consisting of incoherently intergrown fine anatase crystallites. The crystallites are separated by interblock boundaries in which cerium ions are stabilized. The nanostructure formed in the Ce-TiO₂ oxide system stabilizes the anatase phase, prevents the sintering of anatase particles at high temperatures, and allows modified anatase to retain a larger specific surface area and a higher porosity upon heat treatment than pure titanium dioxide does.     

Specific features of etching of ultrafine- and coarse-grained titanium in base and acid solutions of hydrogen peroxide

The character and kinetics of chemical etching of nanostructured titanium in base (NH₄OH/H₂O₂) and acid (H₂SO₄/H₂O₂) solutions of hydrogen peroxide (Piranha) were studied. A study of the etching kinetics showed that the etching rate of the nanostructured titanium is not constant and tends to decrease, but in the case of the sulfuric acid solution the decrease is smoother owing to the growth of the oxide layer. The etching rate for ultrafine-grained titanium is higher than for the coarse-grained sample. The applied significance of the study is associated with the fact that Piranha solutions show promising for cleaning, hydrophilizing, and making rough the titanium surface for use in medical implants.     

Electrolytic coating of titanium onto iron and nickel electrodes in the molten LiF + NaF + KF eutectic

The electrolytic reduction of Ti(III) species in LiF+NaF+KF eutectic on iron and nickel, studied using voltammetric techniques, proceeds reversibly in the 600–700°C temperature range. No interaction occurs between the iron electrode and the titanium coating, whereas the solubility of titanium in nickel has been proved. Chronoamperometric measurements at constant potentials more positive than the Ti(III)/Ti equilibrium potential indicate that the electrochemical incorporation of titanium in nickel is controlled by intermetallic diffusion.Coatings of pure titanium 20 to 30 μm thick were produced on iron at 700°C and on nickel at 600 and 700°C; they were homogeneous and well-crystallized. X-ray fluorescence analysis showed that the pure titanium coating is joined to the nickel supporting metal by a multilayer zone consisting of Ti₂Ni, TiNi and TiNi₃ definite compounds.     

Effect of yttrium oxide on the formation of the phase composition and porous structure of titanium dioxide

The formation of the structure of TiO₂ (anatase) doped with 1–5 mol % Y₂O₃ is reported. The dopant changes the anatase structure from regular to nanocrystalline. The nanocruystalline structure consists of incoherently intergrown 5- to 7-nm anatase crystallites (500°C) separated by interblock boundaries accommodating yttrium ions. The formation of the nanocrystalline anatase structure stabilizes small anatase crystallites and raises the anatase-to-rutile phase transition temperature above 900°C. Owing to this structure, the developed specific surface area and fine porous texture of yttrium oxide-doped titanium dioxide survive up to higher temperatures than those of undoped titanium dioxide.