Ti Alkoxide Research Articles

Back Cover: Macromol. Rapid Commun. 8/2005

Back Cover: The cover shows the use of the TiCp2Cl‐catalyzed radical ring opening (RRO) of epoxides in the living ring opening polymerization of cyclic esters. Zn reduction of TiCp2Cl2 (red) produces the TiCp2Cl metalloradical (green) which upon epoxide RRO generates novel Ti alkoxide initiators (orange‐blue) and provides access to a variety of epoxide‐derived polymer chain ends. Further details can be found in the Communication by A. D. Asandei* and G. Saha on page 626.

Synthesis, Characterization and Photocatalytic Activity of TiO2 Powders Prepared Under Different Gelling and Pressure Conditions

Homogeneous TiO2 gel powders were prepared by hydrolysis and condensation of titanium(IV) isopropoxide with HCl or SnCl2 catalysts, by working under reduced pressure or in air. Ti(IV) alkoxide was previously modified by reaction with formic or acetic acid, used as chelating ligands, when gelation was performed in acidic catalysis. Crude TiO2 xerogels were purified by water reflux treatment in order to induce a low temperature crystallisation to the anatase phase. Both crude and purified TiO2 samples were characterised by XRD, FT-IR, SEM, and N2 adsorption analysis. Thermoanalyses (TG, DTA, DTG, TG-MS, TG-GC-MS) were carried out to quantify the residual organic components in the crude TiO2 gels and to obtain stoichiometric formulas to describe their chemical compositions. XRD data of purified TiO2 powders were processed by means of a Rietveld refinement procedure to determine TiO2 polymorphs, crystallite sizes and cell parameters, before their use in photocatalytic tests. The photoactivity of the purified TiO2 anatase powders was studied by using 4-nitrophenol degradation as “probe” reaction carried out in a batch and/or a membrane photoreactor. Samples prepared by using formic acid or SnCl2 were the most photoactive, whereas specimens gelled under vacuum treatment showed detrimental effects.

Combination of two catalytic sites in a novel nanocrystalline TiO2–iron tetrasulfophthalocyanine material provides better catalytic properties

Mesoporous titania nanocrystals containing iron tetrasulfophthalocyanine (FePcS) have been synthesised by a one-pot hydrolytic process from a modified Ti alkoxide; the novel hybrid catalyst was efficient in heterogeneous oxidation of 2,3,6-trimethylphenol and β-isophorone suggesting a cooperative effect between TiO2 and FePcS catalytic sites.

Synthesis and nanostructure characterization of carbon base hybrid ceramics derived from Si–H containing resin–alkoxide mixtures

Si–H containing thermosetting resin, poly[(phenylsilylene)-ethynylene-1,3-phenylene ethynylene] which shows high ceramic yield after pyrolysis, was modified with various metal (Ti, Ta, Zr, Si and Al) alkoxides. The modified resins were shaped to sheet form by solution casting and pyrolyzed at high temperatures to give amorphous materials with Si–M(metal elements in alkoxides)–C–O compositions. The small angle X-ray scattering (SAXS) analysis was performed to give nanostructure information on the pyrolyzed sheets, in which metal oxide particles are considered to be dispersed in carbon rich matrix. The size and distribution of particles derived from the SAXS pattern fittings depended on kinds of the used alkoxide and the pyrolysis temperature. For the practical application for these hybridized gel systems, the flow coating of precursor solutions on stainless steels were attempted. The coated layer on the substrate showed black and glassy surface with no obvious cracks even after pyrolysis at 1073 K with a coating thickness of 2–3 μm.

Synthesis of mesoscopic barium titanate single crystals incorporating a cuboid-shaped hollow core

Mesoscopic barium titanate (BaTiO 3) single crystals with dimensions of 10–15 nm that incorporated a cuboid-shaped hollow core were synthesized by a sol–gel method using a highly-concentrated Ba–Ti alkoxide precursor solution combined with a surfactant templating approach. In this synthesis route, perovskite BaTiO 3 nanocrystals were formed directly by a polycondensation reaction of the gel framework during aging at room temperature. Hollow-core nanocrystals were contained in the product, which was obtained by firing the crystalline gel at 500 °C in flowing oxygen. The cuboid-shaped hollow cores of the nanocrystals were about 0.2 nm in size and had {1 0 0} inner surfaces. In addition, it was also found that some kind of ordered structure was formed on a mesoscale with an interplaner spacing of 14 nm before and after firing at 500 °C.

Low temperature preparation of mesoporous TiO2 films for efficient dye-sensitized photoelectrode by chemical vapor deposition combined with UV light irradiation

A new method for fabricating plastic film-based mesoporous TiO 2 electrodes for efficient dye-sensitized solar cells is described. TiO 2 nanocrystalline layers electrophoretically deposited on indium-tin-oxide (ITO)-coated polyethylene terephthalate (PET) film was post-treated with chemical vapor deposition (CVD) of Ti alkoxide followed by UV light irradiation at temperatures below 110 °C. UV-assisted CVD treatment drastically enhanced dye-sensitized photocurrent and improved photovoltage up to 750 mV. A film electrode bearing Ru complex (Ru 535-bis TBA) dye-sensitized TiO 2 on ITO–PET yielded solar energy conversion efficiency of 3.8%.

Aqueous Titanate Sols from Ti Alkoxide- -Hydroxycarboxylic Acid System and Preparation of Titania Films from the Sols

Aqueous titanate sols were prepared by reactions of titanium tetraisopropoxide (TIP) with α-hydroxycarboxylic acids in water. IR and Raman spectra, and elemental analyses of the precipitates obtained from the sols revealed that the carboxylates were chelated to titanium but the Ti species were polymerized to form a cluster that had a colloidal nature. Spin-coating of titania (TiO2) thin films from these sols was also examined. Interestingly, it was found that (004) preferentially oriented anatase films with refractive index of 2.54 were obtained from TIP-lactic acid-NH3 (1:1:1, molar ratio) aqueous sol. This crystallographic orientation was characteristic of the TIP-lactic acid-NH3 (1:1:1) system, and was not affected by the kinds of substrates used and the heating rate of the film. TEM observation indicated that small anatase grains had already formed at 200°C. Therefore, the crystallographic orientation might depend strongly on the structure of the chemical species of the precursor solutions.

Low temperature preparation of mesoporous TiO 2 films for efficient dye-sensitized photoelectrode by chemical vapor deposition combined with UV light irradiation

A new method for fabricating plastic film-based mesoporous TiO 2 electrodes for efficient dye-sensitized solar cells is described. TiO 2 nanocrystalline layers electrophoretically deposited on indium-tin-oxide (ITO)-coated polyethylene terephthalate (PET) film was post-treated with chemical vapor deposition (CVD) of Ti alkoxide followed by UV light irradiation at temperatures below 110 °C. UV-assisted CVD treatment drastically enhanced dye-sensitized photocurrent and improved photovoltage up to 750 mV. A film electrode bearing Ru complex (Ru 535-bis TBA) dye-sensitized TiO 2 on ITO–PET yielded solar energy conversion efficiency of 3.8%.

Electrochemical Properties of Nanostructured Amorphous, Sol-gel-Synthesized TiO2 / Acetylene Black Composite Electrodes

Amorphous titanium oxide was prepared by a sol-gel route employing Ti(IV) alkoxide as a starting agent. The average size of the primary particles was about 4 nm, and the Brunauer-Emmett-Teller specific surface area was 390 m2 g−1. Addition of acetylene black in synthesis allowed us to obtain the composite of titania and carbon materials. The composite materials could be galvanostaticly discharged and charged around 2 V vs. After thermal treatment at 330°C the composite showed specific capacity above 125 mA h g−1, even under large discharge current of 10 A g−1. Based on the relationship between specific capacity and current density, the chemical diffusion coefficient of lithium was estimated to be © 2004 The Electrochemical Society. All rights reserved.

Preparation of textured bismuth titanate ceramics through templated grain growth combined with spark plasma sintering

ABSTRACTTextured bismuth titanate (Bi4Ti3O12), the simplest and best known compound among the bismuth layer-structure ferroelectrics is interesting because of its peculiar switching behavior which results from a small c-axis component of the spontaneous polarization and a small coercive force. We prepared Bi4Ti3O12 ceramics through the templated grain growth (TGG) method combined with the spark plasma sintering (SPS) method. The TGG method was developed to provide a simpler way of creating textured ceramic microstructures. The SPS method enables a compact powder to be sintered under uniform heating to a high density at relative low temperatures and with much shorter sintering periods than with conventional sintering.We obtained a Bi4Ti3O12 precursor powder through a co-precipitation method with Ti alkoxide and Bi oxide as raw materials. Platelet Bi4Ti3O12 was synthesized from the precursor powder through a flux method using NaCl and KCl. The obtained platelet Bi4Ti3O12 had a high aspect ratio. The ceramics were prepared by SPS treatment using a mixture of the platelet Bi4Ti3O12 and the amorphous precursor powder. As a result, dense ceramics could be easily obtained without crystalline amorphous precursors and grain growth was not observed during the sintering. After heat treatment of the ceramics, we obtained highly textured, high density Bi4Ti3O12 ceramics. The ceramics showed high orientation, above 70%, for the c-axis direction and high density of over 85%.

TiCp2Cl-Catalyzed Living Radical and Ring Opening Polymerizations Initiated from Epoxides and Aldehydes in the Synthesis of Linear, Graft and Branched Polymers

ABSTRACTTi(III)Cp2Cl-catalyzed radical ring opening (RRO) of epoxides or single electron transfer (SET) reduction of aldehydes generates Ti alkoxides and carbon centered radicals which add to styrene, initiating a radical polymerization. This polymerization is mediate in a living fashion by the reversible termination of growing chains with the TiCp2Cl metalloradical. In addition, polymers or monomers containing pendant epoxide groups (glycidyl methacrylate) can be used as substrates for radical grafting or branching reactions by self condensing vinyl polymerization. In addition, Ti alkoxides generated in situ by both epoxide RRO and aldehyde SET initiate the living ring opening polymerization of ε-caprolactone. Thus, new initiators and catalysts are introduced for the synthesis of complex polymer architectures.

Influence of hydrolysis conditions of the acetate sol–gel process on the stoichiometry of PZT powders

[Pb(Zr,Ti)(OAc) x(OR) y] acetate-alkoxide precursor was prepared by chelating from organic Pb, Zr and Ti alkoxides by their dissolution in various amounts of acetic acid (AcOH). Sols were formed by hydrolysis of acetate-alkoxides with ethylene glycol and transformed by polycondensation to a gel at 80 °C. The final stoichiometry of prepared PZT gels was determined by chemical analysis after their filtration and calcination at 500 °C. As results from the DTA/TGA, IR and XRD analysis, the optimum mole ratio of (Pb+Zr+Ti) to AcOH for preparation of viscous polycondensed stoichiometric gel is 1:7 and a pure perovskite phase is formed at 500 °C. The stoichiometric ratio in PZT calcinate was degraded after increasing the added amount of AcOH. At a low AcOH concentration, two-phase (pyrochlore and perovskite) regions are formed during gellation. At 700 °C, the decomposition of a pyrochlore phase and the formation of a perovskite phase takes place despite significant cation nonstoichiometry in PZT powders.

Novel electro-rheological nanocrystalline dielectric particles modified with or embedded in organics

Inorganic-organic materials consisting of dielectric particles and organics were synthesized through in-situ processing of metal-organic precursors. BaTiO 3 precursor was synthesized from barium metal, titanium isopropoxide and 4-octyloxyphenol (OP). The modified Ba–Ti alkoxide could successfully afford OP-modified BaTiO 3 nano-particles below 100 °C. KNbO 3 precursor was synthesized by the reaction control of potassium ethoxide, niobium ethoxide and acetoacetoxyethyl methacrylate. The organic matrix included nanometer-sized crystalline particles depending upon the hydrolysis conditions. The nanocrystalline particles were identified by XRD, electron diffraction and energy dispersive X-ray analysis. The hybrid nanocomposites revealed an interesting electrorheological (ER) behavior on applying DC field. The yield stress increased with increasing applied voltage and volume ratio of nano-particles. The hybridization of nanocrystalline particles and organic matrix was found to give a pronounced effect on ER properties.

Photo-production of hydrogen over the CdS–TiO 2 nano-composite particulate films treated with TiCl 4

Nanosize CdS and TiO 2 sol were prepared by precipitation reaction of Cd(NO 3) 2 and Na 2S aqueous solutions and by sol–gel reaction of Ti alkoxide, respectively. They were mixed together mechanically with variation of the mole ratio ( r) of TiO 2/(CdS+TiO 2). Then, the CdS−TiO 2 mixed sols were further treated with the hydrothermal processing at the temperatures of 120–240°C. CdS–TiO 2 composite particulate films were thus prepared by casting the resulting sol onto F:SnO 2 conducting glass and a subsequent heat-treatment at 400°C under air. Again, the physical properties of these films were controlled by the surface treatment with TiCl 4 aqueous solution. With the hydrothermal treatment, the crystallinity of both CdS and TiO 2 particles increased, and CdS particles were seen to be surrounded homogeneously by TiO 2 particles. Hydrogen photo-production rates measured under the present experimental conditions varied according to the mole ratio ( r) and showed the maximum value at r=0.8, which were in consistent with the photocurrent trend of the composite films, suggesting the importance of effective distribution and contacts among the particles. Also, the film surface treatment with TiCl 4 aqueous solution caused a considerable improvement in photocatalytic activity and photocurrent of the films, probably as a result of closer contacts between the primary particles by the etching effect of TiCl 4.

Atom Transfer Radical Polymerization with Ti(III) Halides and Alkoxides

Ti(III) compounds (halides and n-butoxide) along with several mono-, bi-, and tridentate ligands have been studied for the first time in the atom transfer radical polymerization (ATRP) of styrene. The important advantage of titanium compounds is the white color of the Ti(IV) ions (Ti in the highest and air stable oxidation state) which ensures the absence of coloring in the final polymer. The better control over polymerization was realized when conditions increasing the reactivity of the intermediate Ti(IV) species and decreasing their steady state concentration were maintained. This occurred when chlorides were replaced with bromides (which decreased the bond strength), and when ligands with low donor ability were employed. Using a sulfide complex of Ti(III) chloride and 1,2-bis(hexylthio)ethane allowed styrene polymerization with kinetic and molecular weight characteristics inherent to ATRP.

The effects of titanium precursors on hydriding properties of alanates

An overview is presented of recent advances in the development of new and improved alanates for applications and in the fundamental understanding of how Ti-doping enhances hydrogen absorption. Sample materials were produced using approaches based on direct-synthesis and dry Ti-doping methods. It is desirable to introduce Ti through non-reactive processes to avoid the hydrogen capacity loss that occurs through the formation of inactive byproducts (for example Na–halide from the decomposition of Ti–halides and Na–oxides from the decomposition of Ti–alkoxides). We show, for the first time, that alanates can be Ti-doped using TiH2 or through indirect-doping by pre-reacting TiCl2 with LiH. Both methods result in enhanced kinetics. However, improved rates were achieved only after a prolonged activation period of about a 10 cycles, suggesting that cycling leads to Ti diffusion and substitution into the alanate lattice which provides the mechanism through which Ti-doping enhances kinetics. Thus, the reactive decomposition of Ti–halide and alkoxide precursors in the doping process serves an important but not necessarily required function.

Preparation and Characterization of Ti-Pillared Clays Using Ti Alkoxides. Influence of the Synthesis Parameters

AbstractTitanium was introduced into the clay structure by cation exchange with polymeric Ti cations which were formed by partial hydrolysis of Ti alkoxide in HCl. X-ray diffraction, N2 adsorption-desorption, chemical analysis, thermogravimetric analysis, differential thermal analysis, temperature-programmed desorption of ammonia and temperature-programmed reduction were used to characterize the resulting Ti-pillared clays (Ti-PILCs). Titanium methoxide allows the synthesis of a solid with a large basal spacing (26 Å), a large surface area (360 m2/g), a significant amount of micropore surface area (90%), and notable acidity. Moreover, Ti-PILCs obtained from methoxide were found to be thermally stable up to 500°C. A correlation between the increase in acidity and the increases in both microporosity and Ti content was observed. The surface area, the micropore volume, the acidity and the d001 peak intensity all increased upon increasing the amount of Ti added to the preparation (up to ∼15 mmoles of Ti/g clay). The use of an aqueous suspension of 0.13 wt.% of clay yielded the best structural and textural properties in terms of subsequent use of the clay as a catalyst.

Synthesis of Novel Titanasiloxanes with Ring and Cage Structures Using Sterically Demanding Substituents

Novel oligomeric titanasiloxanes have been synthesized in good yields by reaction of sterically demanding organosilanetriols with titanium alkoxides. The silanetriols Bu-t(2)(Me3Si)FlSi(OH)(3) (5), (Me3Si)FlSi(OH)(3) (6), and MeFlSi(OH)(3) (7) and the titanium alkoxides Ti((OEt)-Et-i)(4), Ti((OPr)-Pr-i)(4), and Ti((OPr)-Pr-i)(2)(acac)(2) have been used as starting materials (Fl = fluorenyl). Quite different structures are obtained by only small modifications of the organic substituents of the substrates. Thus, the condensation reactions result in the formation of the polyhedral titanasiloxanes [Bu-t(2)(Me3Si)FlSi](4)O-12[TiOEt](4) (8), [(Me3Si)FlSi](2)O-5[Ti(OEt)](4) /mu(2)-OEt](6) [mu(4)-O] (9), ([Bu-t(2)(Me3Si)FlSi](3)O-10[Ti((OPr)-Pr-i)](4) [mu(2)-OiPr](2) [mu(3)-O]Ti)(2)O (10), and [MeFlSi](2)O-8[Ti((OPr)-Pr-i)](6)(-) [mu(2)-(OPr)-Pr-i](4)[mu(3)-O](2)[PhNH2](2) (11) and the cyclic titanasiloxane [MeFlSi((OPr)-Pr-i)](2)O-4[Ti(acac)(2)](2) (12). A 1:1 stoichiometry of the starting materials leads to 8 and 12 in quantitative yield, while 9-11 are isolated in minor quantities. If the appropriate substrate ratio is used, the latter compounds can also be obtained in high yields. All titanasiloxanes have been characterized by X-ray crystallography, NMR, IR, and elemental analysis.

Catalytic Effect of Chemically Modified Metal Alkoxides on Hydrolysis and Condensation Reactions of Methyl- and Phenyl-Ethoxysilanes

The catalytic effect of chemically modified metal alkoxides on the hydrolysis and condensation reactions of methylethoxysilanes and phenylethoxysilanes was investigated by 29 Si nuclear magnetic resonance spectroscopy and gel permeation chromatography. Metal alkoxides such as Al(O-sec-C 4 H 9 ) 3 , Ti(O-iso-C 3 H 7 ) 4 and Nb(OC 2 H 5 ) 5 modified with ethyl acetoacetate accelerated not only the condensation reactions but also the hydrolysis reactions of methyl- and phenyl-alkoxysilanes. The catalytic effect of these metal alkoxides was found to be different between methyl- and phenyl-alkoxysilanes. The catalytic activity increases in the order of Nb < Al<Ti alkoxides in the case of methyl-ethoxysilanes, whereas in the case of phenyl-ethoxysilanes it increases in the order of Nb < Ti < Al alkoxides. The difference in catalytic activity was discussed on the basis of the partial charge of M in metal alkoxide, the difference in electronegativity between M and Si and the difference between the coordination number and valence of M.

Evolution of the Si-condensed species in a multicomponent polymeric system

Alcoholic sol-gel systems were prepared using a pre-hydrolyzed tetraethyl orthosilicate (TEOS) sol as the main component. Ti and Zr alkoxides were also introduced in order to provide properties of technological interesttowards producing the final ceramics. The molar ratios Si:Ti:Zr were 82:7:11, respectively. Six potential chelating molecules were used as modifying agents in order to control the reactivity of Ti and Zr, avoiding precipitation. The products were characterized by spectroscopic techniques including Small Angle X-ray Scattering (SAXS), 29Si NMR, UV-Vis and Fourier Transform Infrared (FTIR) spectroscopies. The radial distribution functions (RDF) of the gels and calcined solids were obtained; in addition, the porosimetry study of the solids calcined at 873 K in air was performed. The results are mainly discussed in terms of the condensation of the Si species; however, the influence of Ti, Zr and the modifying agent structures is also considered.