Glycolate Ti1 − x Fe x (OCH2CH2O)2 − x/2 as a precursor for the preparation of quasi-one-dimensional (1D) solid solutions Ti1 − x Fe x O2 − 2x/2 (0 ≤ x ≤ 0.1)

Quasi-one-dimensional (1D) solid solutions Ti_{1 ? x} Fe _x (OCH₂CH₂O)_{2 ? x/2} (0 < x ≤ 0.1) with the structure of anatase were prepared by heating the glycolate Ti_{1 ? x} Fe _x (OCH₂CH₂O)_{2 ? x/2} in an atmosphere of air at a temperature of >450°C. The conditions of formation and the properties of the new glycolate Ti₃Fe₂(OCH₂CH₂O)₉ were described. It was found that the synthesized Ti_{1 ? x} Fe _x O_{2 ? 2x/2} solid solutions exhibit photocatalytic activity in the reaction of hydroquinone oxidation in an aqueous solution on irradiation with UV light. A correlation between the rate of oxidation of hydroquinone and the concentration of iron in the catalyst was established. A procedure for the preparation of titanium dioxide with the structure of anatase doped with iron and carbon (Ti_{1 ? x} Fe _x O_{(2 ? x/2) ? yCy)} and also composites on its basis, which contain an excess amount of carbon, was proposed.     

Anatase–rutile transformation at the synthesis of rutile pigments (Ti,Cr,Nb)O2 and their color properties

Synthesis of rutile pigments is based on solid state reaction and on Hedvall effect, i.e., phase transformation from anatase to rutile. Therefore, it is important to know the thermal behavior of these compounds (the temperature of this change). The goal was to prepare rutile pigments of type Ti_1?3xCr_xNb_2xO_2+x/2 by conventional solid state method from titanium dioxide TiO₂ (AV-01, anatase), to determine an influence of composition (x = 0, 0.05, 0.10, 0.20, 0.30, 0.50) and calcination temperature (850; 900; 950; 1,000; 1,050; 1,100; 1,150 °C) on color properties of these compounds and to analyze other starting compounds of titanium (hydrated anatase paste TiO₂·nH₂O, titanyl sulfate dihydrate TiOSO₄·2H₂O (VKR 611), hydrated sodium titanium oxide paste Na₂Ti₄O₉·nH₂O) and their reaction mixtures for x = 0.05 by simultaneous TG–DTA analysis. According to the highest chroma C of color, the optimal conditions for synthesis of these pigments are concentration x = 0.05 and calcination temperature 1,050 °C and higher. It was observed that initial temperature 760–830 °C is needful for a formation of rutile structure. This temperature is the lowest for hydrated Na₂Ti₄O₉ paste (760 °C) and similar for other starting compounds of titanium.     

The influence of concentration of doping elements on anatase–rutile transformation at the synthesis of rutile pigments (Ti,Cr,Nb)O2 and their pigmentary properties

An analysis of the effects of dopants concentration and different starting titanium compounds on the anatase to rutile phase transformation at the synthesis of rutile pigments Ti_1?3xCr_xNb_2xO_2±δ is presented in this study. The main goal was to analyze reaction mixtures for x = 0.05 (previous study) and 0.30 by simultaneous TG–DTA analysis and to determine the temperature of anatase–rutile transition. For x = 0.05, initial temperatures 760–830 °C are needful for a formation of rutile structure. The temperature is the lowest for the hydrated Na₂Ti₄O₉ paste (760 °C) and similar for other starting compounds of titanium. But for x = 0.30, the anatase–rutile transition begins at higher temperatures 910–1,030 °C because of high-Nb content, which is the inhibitor of this modification change. In addition, we found the influence of calcination temperatures (850, 900, 950, 1000, 1050, 1100, and 1150 °C) on color properties and particle size distribution of these materials prepared from anatase TiO₂ and with x = 0.30. Selected pigments were also analyzed by X-ray powder diffraction.     

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

Ti_1−x V _x O_2−y C _y (0 ≤ x ≤ 0.10 and x = 0.50) whiskers having the anatase structure were synthesized via thermolysis of vanadium-doped titanium glycolate of composition Ti_1−x V _x (OCH₂CH₂O)₂ (0 ≤ x ≤ 0.10 and x = 0.50). The starting reagents used to prepare Ti_1−x V _x (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 = Ti_1−x V _x (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 Ti_{1 − x} V _x O_{2 − y} C _y whiskers prepared by thermolyzing Ti_{1 − x} V _x (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 Ti_0.50V_0.50O_2−y C _y . Quantum-chemical calculations support experimental data that the double doping of titania (Ti_1−x V _x O_2−y C _y ) enhances its photocatalytic activity compared to undoped anatase or anatase doped in one sublattice: Ti_1−x V _x O₂ and TiO_2−y C _y .     

Thermal stability of anatase TiO2 aerogels

Titanium dioxide (TiO₂) aerogels were prepared with sol–gel ambient pressure drying method by using titanium tetrachloride (TiCl₄) as precursor and tetraethoxysilane as modifier, calcinated at different temperature and characterized by X‐ray diffraction, transmission electron microscopy and small angle X‐ray scattering. The results showed that the TiO₂ aerogels remained amorphous under 500 °C, changed to anatase from 600 °C and further changed to rutile from 900 °C. Between 60 °C and 500 °C, the primary particles within the samples concentrated mainly upon small sizes, enlarged and diverged remarkably above 600 °C. The crystalline grains grew and agglomerated with the rise of the calcination temperature. The TiO₂ aerogels at a temperature higher than 800 °C have better stability than anatase because of the formation of partial Ti―O―Si bonds. Copyright © 2016 John Wiley & Sons, Ltd.     

Phase relations and exsolution phenomena in the system NiOTiO2

The phase relations in the system NiOTiO₂ were studied between 1000 and 1600°C using quenched powder specimens, DTA runs, and single crystal diffusion couples. Quenching experiments establish the stable phases TiO₂ (rutile), NiTiO₃ an ilmenite structure type, Ni_2(1+x)Ti_1?xO₄ (x ≥ 0.16), a cation-excess spinel, and Ni_1?2xTi_xO (rocksalt structure type). DTA runs reveal the existence of an additional nonstoichiometric ilmenite phase Ni_1?2xTi_1+xO₃ (x ≤ 0.03) above 1260°C. In quenched (1500, 1450°C) or slowly cooled single crystal diffusion couples, mutual oriented exsolutions occur in the rutile crystal and in the ilmenite diffusion zone. Orientation relations are: {101}_rutile{1120}_ilmenite; ∥010〉_rutile∥00.1〉_ilmenite. The cation-excess spinel decomposes below 1375°C into oriented intergrowth of NiTiO₃ (ilmenite) and NiO: {111}_NiO{0001}_NiTiO3; ∥110〉_NiO∥21.0〉_NiTiO3.     

Etude thermodynamique des oxydes TiO2−x a 1050°C

g_O2^M (O/Ti) and h z (O/Ti) have been directly measured at 1050°C within the whole homogeneity range of the rutile phase TiO_2?x, respectively, using the method of equilibration between oxides and buffer gaseous mixtures and by means of a high temperature microcalorimeter. These results are discussed in terms of point defects.     

DSC investigation of nanocrystalline TiO<Subscript>2</Subscript> powder

The aim of the article is to investigate the influence of particle size on titanium dioxide phase transformations. Nanocrystalline titanium dioxide powder was obtained through a hydrothermal procedure in an aqueous media at high pressure (in the range 25–100 atm) and low temperature (≤200 °C). The as-prepared samples were characterized with respect to their composition by ICP (inductive coupled plasma), structure and morphology by XRD (X-ray diffraction), and TEM (transmission electron microscopy), thermal behavior by TG (thermogravimetry) coupled with DSC (differential scanning calorimetry). Thermal behavior of nanostructured TiO₂ was compared with three commercial TiO₂ samples. The sequence of brookite–anatase–rutile phase transformation in TiO₂ samples was investigated. The heat capacity of anatase and rutile in a large temperature range are reported.     

Structure and photocatalytic properties of materials based on titanium dioxide and silver nanoparticles

Phase composition and structure of mesostructured materials, titanium dioxide and titanium dioxide modified with silver nanoparticles, have been studied by X-ray diffraction analysis. Introduction of Ag(I) ions into the initial composition and variation of the annealing temperature over the 500–950°C range allows controlling the anatase to rutile crystal phase ratio in the samples. The photocatalytic activity of TiO₂ and TiO₂/Ag samples has been demonstrated using the methyl orange degradation reaction. The catalytic properties of the materials have been found to depend on the anatase to rutile phase ratio and on the presence of silver nanoparticles.     

Preparation of nanocrystalline anatase TiO2 using basic sol-gel method

Nanocrystalline titanium dioxide particles with anatase structure and high thermal stability have been synthesized using the basic sol-gel method. The particle size and morphology were refined under hydrothermal conditions in the presence of different concentrations of tetramethylammonium hydroxide (TMAH) at 210°C and 230°C. XRD and TEM analysis showed that the TiO₂ particles obtained were homogeneous and monodispersive at low contents of TMAH. All intense peaks, clearly observed in the XRD patterns, were assigned to the anatase phase and no rutile phase was observed. At high contents of TMAH, nanoscale small (10–30 nm) and larger (>100 nm) TiO₂ particles were one-pot synthesized. The nanocrystalline TiO₂ particles synthesized by this method have good thermal stability. With the sintering temperature of up to 650°C, all the XRD peaks maintained good agreement with the anatase reference data.     

The products of the reaction of the hydroxyl radical with 2-ethoxyethyl acetate

The gas-phase reaction products of the OH radical with 2-ethoxyethyl acetate (EEA, CH₃C(O)OCH₂CH₂OCH₂CH₃) have been investigated. 1,2-Ethanediol acetate formate (EAF, CH₃C(O)OCH₂CH₂OC(O)H) and ethyl formate (EF, HC(O)OCH₂CH₃) were identified as the two main products. A third product, ethylene glycol diacetate (EGD, CH₃C(O)OCH₂CH₂OC(O)CH₃), was also observed. EAF, EF, and EGD formation yields were determined to be 0.37 ± 0.03 and 0.328 ± 0.018 and 0.040 ± 0.005, respectively. Proposed reaction mechanisms are discussed and compared with these data. © 1996 John Wiley & Sons, Inc.     

Nitrogen-doped TiO2 from TiN and its visible light photoelectrochemical properties

Homogeneous titanium nitride (TiN) thin film was produced by simple electrophoreic deposition process on Ti substrate in an aqueous suspension of nanosized TiN powder. Nitrogen-doped titanium dioxide (TiO_2−xN_x) was synthesized by oxidative annealing the resulted TiN thin film in air. Photoelectrochemical measurements demonstrated visible light photoresponse for the electrode of annealed electrophoreic deposited TiN samples. It is found that the synthesized TiO_2−xN_x electrode showed higher photo potential under white and visible light illumination than the pure TiO₂ electrode. The photocurrent under visible light illumination was also observed, which increased with the increase of deposition time of TiN thin films.     

Solvothermal synthesis of TiO2: anatase nanocrystals and rutile nanofibres from TiCl4 in acetone

This work reports a new synthetic approach for single‐phase TiO₂ nanomaterials by solvothermal treatment of titanium tetrachloride in acetone at 80–110 °C. Small, uniform, and yet size‐tunable (5–10 nm) anatase titania nanocrystallites were obtained using a low concentration of TiCl₄ in acetone (i.e., at molar ratios of TiCl₄/acetone ≤ 1:15) in the temperature range of 80–110 °C, while rutile nanofibers were synthesized using a high concentration of TiCl₄ (e.g., TiCl₄/acetone = 1:10) at 110 °C. Copyright © 2007 John Wiley & Sons, Ltd.     

Identification of selective oxidation of TiC/SiC composite with X-ray diffraction and Raman spectroscopy

Open cell 3D titanium carbide/silicon carbide (TiC/SiC) composite was oxidised to titanium oxide/silicon carbide (TiO₂/SiC) following different temperature profiles in a thermal gravimetric analysis (TGA) instrument in continuous air-flow and static air (oven) environments. The TiC oxidation to anatase, starting at temperatures over 450°C, was confirmed by Raman spectroscopy and X-Ray diffraction (XRD). By increasing the temperature, the mass fraction of anatase diminished, while the mass fraction of rutile increased. SiC oxidation started at 650°C when a mixture of TiO₂/SiO₂/SiC could be observed by Raman, XRD and HRTEM.     

The investigation of sodium titanates by the hydrothermal reactions of TiO2 with NaOH

The hydrothermal reactions of TiO₂ with NaOH were performed in the molar range of Na₂O from 0 to 30% between 250 and 530°C. The compounds obtained were TiO₂ (rutile, brookite, and anatase), Na₂O·nTiO₂ (n = 3, 4, 6, and 9) and Na_xTiO₂, the formation ranges for which are shown in a reaction diagram. The roles of water in this hydrothermal system are investigated, to discuss the differences among the known and the present reaction diagrams and to raise a reliability of diagrams. From the present reaction diagram, phase relations in the system TiO₂Na₂O are estimated taking account of direct or indirect actions of hydrothermal water on solid phases.     

Synthesis and structure of quasi-one-dimensional zinc oxide doped with manganese

Nanotubes of manganese-doped zinc oxide Zn_{1 − x} Mn _x O (0 ≤ x ≤ 0.2) were synthesized by heating the Zn_{1 − x} Mn _x (HCOO)(OCH₂CH₂O)_1/2 precursor in air at 500°C. The precursor with extended crystals was synthesized by a solvothermal method based on heat treatment of a mixture of Zn_{1 − x} Mn _x (HCOO)₂ · 2H₂O with an ethylene glycol excess at 100–130°C. The tubular morphology of Zn_{1 − x} Mn _x O particles was identified by transmission electron microscopy. Tubular quasi-one-dimensional particles were shown to have a nanodispersed polycrystalline structure, the size of separate crystallites being from 5 to 20 nm. X-ray photoelectron spectroscopy suggested that the manganese distribution on the outer surface layer of Zn_{1 − x} Mn _x O nanotubes is nonuniform.     

The effect of annealing temperatures on surface properties,hydroxyapatite growth and cell behaviors of TiO2 nanotubes

Well‐ordered TiO₂ nanotubes were prepared by the electrochemical anodization of titanium in an ethylene glycol electrolyte containing 1 wt% NH₄F and 10 wt% H₂O at 20 V for 20 min, followed by annealing. The surface morphology and crystal structure of the samples were examined as a function of the annealing temperature by field emission scanning electron microscopy (FE‐SEM) and X‐ray diffraction (XRD), respectively. Crystallization of the nanotubes to the anatase phase occurred at 450 °C, while rutile formation was observed at 600 °C. Disintegration of the nanotubes was observed at 600 °C and the structure vanished completely at 750 °C. Electrochemical corrosion studies showed that the annealed nanotubes exhibited higher corrosion resistance than the as‐formed nanotubes. The growth of hydroxyapatite on the different TiO₂ nanotubes was also investigated by soaking them in simulated body fluid (SBF). The results indicated that the tubes annealed to a mixture of anatase and rutile was clearly more efficient than that in their amorphous or plain anatase state. The in vitro cell response in terms of cell morphology and proliferation was evaluated using osteoblast cells. The highest cell activity was observed on the TiO₂ nanotubes annealed at 600 °C. Copyright © 2010 John Wiley & Sons, Ltd.     

Studies on the syntheses of polymetalloxanes and their properties as a precursor for amorphous oxide. IV. Properties of SiO2–TiO2 oxide fibers from polytitanosiloxane

From polytitanosiloxanes (PTS), SiO₂–TiO₂ oxide fibers with fairly good tensile strength were prepared, and their mechanical and thermal properties were investigated. The precursor fibers PTS-0.5 and PTS-1.0 were obtained by dry spinning of a highly viscous PTS solution which were formed as the reaction mixture of silicic acid (SA) with bis(2,4-pentanedionato)titanium diisopropoxide (PTP) in the molar ratios (SA/PTP) of 0.5 and 1.0. The precursor fibers PTS-0.5 were too brittle to measure their tensile strength, whereas PTS-1.0 and the heat-treated fibers were found to have tensile strength of 130 (precursor), 540 (500°C), and 450 (900°C) MPa, respectively. Heat-treatment of the fibers PTS-1.0 at above 1000°C forms anatase and rutile of titanium dioxide. The crystallization is resulted from the unreacted PTP which is not incorporated into the polymer network.     

Crystal Structure of a Trinuclear Titanium(IV) Complex with (rac)‐3,3′‐Bis(methoxymethyl)‐BINOLate

Reaction of (rac)‐3,3′‐bis(methoxymethyl)‐BINOL [H₂(CH₃OCH₂)₂BINO] with excess Ti(OⁱPr)₄ and one equivalent of H₂O in CH₂Cl₂ affords a trinuclear titanium(IV) complex [{(CH₃OCH₂)₂BINO}Ti₃(μ₃‐O)(OiPr)₆(μ₂‐OiPr)₂]. By dissolving it in dichloromethane and hexane and cooling to 0 °C, plate‐like pale yellow single crystals (monoclinic, P2₁/n, a = 12.605(3), b = 21.994(5), c = 19.090(4) Å, β = 92.764(8)°, V = 5286.2(19) ų, T = 293(2) K) were obtained. Each oxygen atom at 2 or 2′ position of the (CH₃OCH₂)₂BINO ligand bonds to only one titanium atom. There is no interaction between the third Ti atom and the two oxygen atoms of 3,3′‐bis(methoxymethyl)‐BINOLate.     

Thermal and Microchemical Characterisation of Sol-Gel SiO2, TiO2 and xSiO2–(1–x)TiO2 Ceramic Materials

Amorphous SiO₂, TiO₂ and xSiO₂–(1–x)TiO₂ ceramic materials with selected values of x 0.5, 0.7 and 0.9, have been prepared via sol-gel process using silicon tetraethoxysilane (TEOS) and titanium tetraisopropoxide Ti(OPri)₄. By means of the combined use of differential thermal analysis (DTA),thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM),X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy(XAES), the surface microchemical structure and morphology of the sol-gel materials have been studied as a function of thermal treatments carried out in air up to 1200°C. In the range of temperature from 50 to 450°C, DTA-TG results evidence a remarkable mass loss due to the evaporation of organic solvents entrapped in the sol-gel materials and of the remnant organic components of the precursor metal alkoxides. In the range of temperature from 400 to about 1000°C, by means of the combined use of DTA, XRD, XPS and XAES techniques as a function of temperature and of chemical composition, it is possible to evidence the formation of crystalline phases such as quartz, anatase and rutile. Furthermore, line shape analysis of O1s XPS peak allows to distinguish between single O–Ti and O–Si bonds and also to disclose the presence of cross linking Si–O–Ti bonds, that act as bridges between SiO₂and TiO₂ moieties. As a function of temperature, Si–O–Ti bonds are broken and the formation of new Ti–O and Si–O bonds as in TiO₂ and SiO₂takes place as well as a silica segregation phenomenon. This revised version was published online in July 2006 with corrections to the Cover Date.