Titanium Alkoxide Research Articles

Low-Temperature Photochemical Conversion of Organometallic Precursor Layers to Titanium(IV) Oxide Thin Films

Thin layers of titanium(IV) ethoxide [Ti(OEt)4] as a metal–organic precursor were spin-coated onto silicon wafers under inert conditions and subsequently photochemically converted to thin titanium(IV) oxide (TiOx) films employing vacuum ultraviolet (VUV) radiation from a xenon excimer lamp. The photochemical conversion was performed below 35 °C and at ambient pressure in a nitrogen atmosphere with an optimized content of oxygen. Ti(OEt)4 decomposition and its kinetics were monitored and analyzed by gas chromatography and infrared spectroscopy. Precursor layers with a thickness between 270 and 1060 nm could be converted into much thinner TiOx films (40–165 nm). The decrease in thin film thickness was found to coincide with the removal of organic side chains and densification to a compact oxide network. For precursor layers with a thickness of up to 550 nm, VUV irradiation with a moderate radiant exposure (He) of 2.3 J cm–2 led to almost carbon-free amorphous layers with a composition close to stoichiometri...

Titania-coated manganite nanoparticles: Synthesis of the shell, characterization and MRI properties

Novel procedure for coating of oxide nanoparticles with titania, employing hydrolysis and polycondensation of titanium alkoxides under high-dilution conditions and cationic surfactants, is developed and applied to magnetic cores of perovskite manganite. Bare particles of the ferromagnetic La0.65Sr0.35MnO3 phase, possessing high magnetization, M10kOe(4.5K) = 63.5emug−1, and Curie temperature, TC = 355K, are synthesized by sol-gel procedure and subsequently coated with titania. Further, a comparative silica-coated product is prepared. In order to analyse the morphology, colloidal stability, and surface properties of these two types of coated particles, a detailed study by means of transmission electron microscopy, dynamic light scattering, zeta-potential measurements, and IR spectroscopy is carried out. The experiments on the titania-coated sample reveal a continuous though porous character of the TiO2 shell, the nature of which is amorphous but can be transformed to anatase at higher temperatures. Finally, the relaxometric study at the magnetic field of 0.5T, performed to quantity the transverse relaxivity and its temperature dependence, reveals important differences between the titania-coated and silica-coated nanoparticles.

Preparation of Bragg mirrors on silica optical fibers and inner walls of silica capillaries by employing the sol–gel method, and titanium and silicon alkoxides

The paper presents results on sol–gel preparation and characterization of multilayered coatings, Bragg mirrors, on silica slides, silica fibers, and inner walls of silica capillaries. In the coatings titania was employed for high-index layers and silica for low-index ones. Coatings with up to three pairs of titania and silica layers have been fabricated from alkoxide input sols. A sol based on tetramethylorthosilicate with RW = 1.75 and tetramethylorthosilicate concentration of 2 mol/l for used for silica layers. A sol of titanium butoxide with RW and alkoxide concentration of 1.58 and 0.315 mol/l, respectively, was employed for titania layers. Modified dip-coating techniques have been developed for the application of gel layers from the sols onto fibers or inside silica capillaries. Single gel layers were dried at 200 °C, final coatings were heat-treated at 450 °C. Relative velocities of substrates and sols have been controlled to obtain layers with an optical thickness of about 140 nm. Prepared single layers have been characterized by measuring their thicknesses by optical profilometry and refractive indices of titania layers by spectral ellipsometry. Homogeneity and appearance of multilayered coatings have been characterized by scanning electron microscopy and morphology of coatings by X-ray spectrometry. Optical properties of coatings on silica slides have been determined from their UV–VIS-NIR transmission and reflection spectra. Transmission optical properties of coated optical fibers and capillaries have been characterized by angular distributions of the output power from the fibers at a wavelength of 650 nm and by measuring their transmission spectra. Obtained results show that Bragg mirrors fabricated on silica slides can exhibit a minimal transmittance of about 17 % around a wavelength of 650 nm and that prepared fibers and capillaries provided with Bragg-mirror coatings are capable of guiding light and have lowest transmission losses around a wavelength of 550 nm.

Titanium Dioxide Nanoparticles: Synthesis, X-Ray Line Analysis and Chemical Composition Study

TiO2 nanoparticleshave been synthesized by the sol-gel method using titanium alkoxide and isopropanolas a precursor. The structural properties and chemical composition of the TiO2 nanoparticles were studied usingX-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy.The X-ray powder diffraction pattern confirms that the particles are mainly composed of the anatase phase with the preferential orientation along [101] direction.The physical parameters such as strain, stress and energy density were investigated from the Williamson- Hall (W-H) plot assuming a uniform deformation model (UDM), and uniform deformation energy density model (UDEDM). The W-H analysis shows an anisotropic nature of the strain in nanopowders. The scanning electron microscopy image shows clear TiO2 nanoparticles with particle sizes varying from 60 to 80nm. The results of mean particle size of TiO2 nanoparticles show an inter correlation with the W-H analysis and SEM results. Our X-ray photoelectron spectroscopy spectra show that nearly a complete amount of titanium has reacted to TiO2.

Nontemplate sol–gel synthesis of catalytically active mesoporous titanosilicates

A method for the nontemplate sol–gel synthesis of micro-mesoporous and mesoporous titanosilicates is developed using commercially available raw materials (a mixture of oligomer esters of orthosilicic acid (Ethylsilicate-40) and a water–alcohol solution of titanium(IV) ethoxide). The effect of the pH values of the reaction mixture on sol–gel synthesis is studied using the characteristics of the porous structure of titanosilicates. Samples of amorphous structure with different textural characteristics are obtained by varying the pH in the range of 3–10: specific surface area, 320–740 m2/g; micropore volume, 0.04–0.15 cm3/g; and mesopore volume, 0–0.92 cm3/g. It is shown that a sample of mesoporous titanosilicate obtained with alternating pH values has maximum catalytic activity in the oxidation reaction of 4-tert-butylphenol (TBP) in aqueous solutions of hydrogen peroxide. (Conversion of 4-tert-butylphenol, 45 wt %; selectivity of the formation of 4-tert-butylcatechol, 66 wt %. Conditions: 10 wt % of titanosilicate; TBP/H2O2 = 1/2; 75°C; 1 h).

Anodic dissolution behavior of zirconium in Bun4NBr-containing isopropanol solution

Anodic dissolution behavior of zirconium in Bun4NBr-contaning isopropanol solution was investigated using cyclic voltammetry, linear sweep voltammetry and chronoamperometry, complemented with a scanning electron microscope (SEM). The voltammograms did not exhibit active dissolution until the breakdown of passive layer induced by aggressive bromide anions. SEM images confirmed the existence of pits on zirconium surface. The depth and breadth of pits were intensified with increasing potential. The pitting potential shifted negatively as either temperature or Bun4NBr concentration was increased, while it increased with increasing scan rate. The corrosion current density increased with increasing temperature. The apparent activation energy of anodic dissolution of zirconium was 21.88 kJ/mol. The chronoamperometry revealed that increasing Bun4NBr concentration shortened the incubation time for passivity breakdown and accelerated the pit nucleation and growth. The experimental results were helpful to obtain the optimum conditions for electrosynthesis of zirconium isopropoxide.

Three-Dimensionally Branched Titanium Dioxide with Cheek-Brush Morphology: Synthesis and its Application to Polymer Composites

Nanofiber bundles of TiO2 with a unique cheek-brush morphology were prepared by simple, rapid, one-pot, single-step, and template-free solvothermal treatment of a titanium alkoxide and aromatic ester in methanol. The solvothermal reaction was performed by heating a mixture of titanium tetraisopropoxide and dimethyl phthalate in methanol to 300 °C. The precursor solution had to be kept at room temperature for 20 min before heating the solution to obtain a cheek-brush morphology. The heating rate (5–6 °C/min), final reaction temperature (300 °C), and holding time at the final temperature (10 min) were also crucial for formation of the cheek-brush morphology. A systematic study of additives in the precursor solution showed that aromatic esters such as diethyl phthalate and methyl benzoate gave cheek-brush morphologies. The cheek-brush TiO2 assemblies were used to crosslink a poly(N-isopropylacrylamide) hydrogel; the brushes enhanced the physical adhesion properties of the hydrogel. The hydrogel prepared from a 20wt% polymer containing 0.02wt% of the cheek-brush TiO2 assemblies had an 11 % and 9.1 % higher ultimate tensile strength and elongation ability, respectively, compared with a prototype hydrogel without a crosslinker. A hydrogel prepared using TiO2 spheres of a similar size had an 11 % and 18 % lower ultimate tensile strength and elongation ability, respectively, compared with the prototype hydrogels.

Room temperature synthesis of TiO2 supported chitosan photocatalyst: Study on physicochemical and adsorption photo-decolorization properties

The room temperature in-situ sol gel technique was used to synthesize TiO2 supported chitosan (CS) nanocomposites. The effect of calcination was assessed in the context of its physicochemical and adsorption-photodecolorization properties. During sol gel, hydrolysis and condensation of titanium alkoxide was conducted under acidic conditions, which resulted in the formation of crystalline anatase phase in TiO2-CS (TC) composite at room temperature. Furthermore, calcination treatments (100°C, 300°C, 500°C) gradually increased the charge carrier recombination rates, due to the thermal degradation of Chitosan. Photocatalytic activity was assessed using Methyl orange, which resulted in 100% decolorization within 90min of UV exposure with un-calcined nanocomposite. Hence, the reactive OH and NH2 functional groups on the surface of CS are responsible for the adsorption-photodecolorization process. Overall, this study provides comprehensive data on the effective modification of TiO2 with Chitosan and the effect of calcination on the physicochemical and adsorption-photodecolorization properties of the TC nanocomposite.

Nanodomains within bicontinuous silicone/water microemulsions retard TiO2 nanoparticle aggregation

Nanoparticles of TiO2 are used in a variety of applications because of their high refractive index and photocatalytic behaviour. We report that both the interactions between the surfactant and titanium alkoxide and templating provided by a microemulsion significantly retard the formation of visible TiO2 aggregates. TiO2 nanoparticles (<30nm) were prepared under mild, neutral conditions within water-in-oil and bicontinuous silicone microemulsions. The particles aggregated only slowly, as shown by UV absorption spectroscopy transmission electron microscopy, and particle sizing. Retarded particle growth is ascribed primarily to constricted domains provided by self-organization within a water/surfactant/silicone microemulsion.

Optical properties of metal oxynitride thin films grown with atmospheric plasma deposition

Thin films of tantalum oxynitride (TaOxNy) and titanium oxynitride (TiOxNy) are deposited using atmospheric plasma deposition and a suite of optical properties are reported. Tantalum and titanium ethoxide are introduced into the afterglow of a radio-frequency capacitively coupled plasma, facilitating the growth of oxynitride films on silicon and polycarbonate at temperatures below 180 °C. The plasma power and nitrogen flow within the plasma are varied between 60 and 120 W and between 0.1 and 0.3 LPM respectively. We use spectroscopic ellipsometry to show that the optical properties of the metal oxynitride films grown in this study are comparable to those synthesized with sol–gel methods. Measurement of both the extinction coefficient and the transmission on polycarbonate substrates indicates good transparency in the visible wavelengths of light. Additionally, the refractive index increases when increasing the number of reactive nitrogen species within the discharge. We use x-ray photoelectron spectroscopy to correlate the higher indexes observed at large secondary gas flows to the presence of metal oxynitride bonding. Single layer anti-reflection coatings are deposited on silicon, with a five-fold and seven-fold reduction in reflection for TaOxNy and TiOxNy coatings, respectively. In total, we have found that the modulation of nitrogen concentration within the plasma discharge results in good control over optical constants. In addition, we observe similarities between films deposited with atmospheric plasma and those reported for sol–gel, indicating an alternative processing route where solution chemistries are currently applied.

Sol–Gel Chemistry of Titanium Alkoxide toward HF: Impacts of Reaction Parameters

The sol–gel chemistry of titanium-based oxide prepared in a fluorinated medium leads to an oxy-hydroxyfluorinated framework owing to the occurrence of both hydrolysis and fluorolysis reactions. Here, a systematic study was carried out to investigate the impact of the sol–gel synthesis parameters on the reaction of titanium alkoxides and HF. This study provides comprehensive insights into the sol–gel process in a fluorinated medium. Depending on the extent of fluorination, two types of structures can be stabilized including an anatase Ti1–x–y□x+yO2–4(x+y)F4x(OH)4y and a fluoride-rich hexagonal-tungsten-bronze (HTB) Ti1–x□xO1–4x(F,OH)2+4x phases, where □ refers to titanium vacancies. The reactivity of titanium alkoxide in alcohol toward HF has been shown to mostly depend on the solvent characteristics highlighting an alcohol interchange reaction between the titanium precursor and the solvent. Increasing the fluorine concentration leads to a structural change from the anatase to the fluoride-rich HTB phase, ...

A facile general route for ternary Fe2O3@TiO2@nanometal (Au, Ag) composite as a high-performance and recyclable photocatalyst

A modified sol–gel reaction of alkoxy-terminated magnetite (Fe3O4) with titanium alkoxide afforded core–shell nanostructure with titania capsule. Ambient-air calcination of core–shell nanostructure resulted in the formation of Fe2O3@TiO2 with photocatalytic activity, the degree of which depended on the calcination temperature (500–800°C). The Fe2O3@TiO2 (700°C) with higher oxygen vacancies exhibited enhanced photocatalytic activity than that of Fe2O3@TiO2 (500°C) with fair magnetism, despite its lower surface area. Au nanometal deposition enhanced the photocatalytic activity of recyclable Fe2O3@TiO2 (500°C) due to the increased charge separation, whereas Ag nanometal deposition induced the slight increase in the photocatalytic activity of Fe2O3@TiO2@Ag.

Group 4 complexes of salicylbenzoxazole ligands as effective catalysts for the ring-opening polymerization of lactides, epoxides and copolymerization of ε-caprolactone with L-lactide

A series of salicylbenzoxazole pro-ligand 2-(5-X-benzoxazol-2-yl)-6-R1-4-R2-phenol, L1H-L4H were subjected to reaction with titanium, zirconium and hafnium alkoxides. The substituents (R1, R2, X) present in the pro-ligand back bone are (H, H, H) for L1H; (H, H, Cl) for L2H; (Br, Br, H) for L3H; and (Cl, Cl, H) for L4H. The mononuclear Ti complexes, 1a-4a of [M(L)2(OiPr)2] formulation were prepared by combining the pro-ligands L1H-L4H with Ti(OiPr)4 in dry toluene. However, with the addition of H2O (0.5 M equiv.), the controlled hydrolysis of Ti complex 4a in a mixed solvent of THF/toluene produced oxo-bridged dinuclear Ti complex 5a having [M(μ-O)(L)2(OiPr)]2 formulation in good yield (≥75%) using L4H as the pro-ligand. The composition of the mononuclear Zr and Hf complexes of L1H-L4H are found to be quite similar to that of the Ti complexes. Additionally, mononuclear Zr complexes 1b-4b and Hf complexes 1c-4c were prepared. The oxo-bridged dinuclear Zr and Hf complexes 5b and 5c were isolated from the controlled hydrolysis reactions of mononuclear Zr and Hf complexes 4b and 4c. All these complexes were well characterized and crystal structure of six of the fifteen complexes were determined. These complexes were used as initiators for the ring-opening polymerization (ROP) of rac-LA, copolymerization of L-LA with ε-CL and homopolymerization of rac-epoxides. In particular, the dinuclear Zr complex (5b) was found to exhibit extremely high activity in these polymerization studies. Iso-enriched polymers were observed upon using the Zr and Hf complexes of the pro-ligands L3H or L4H as the initiator. DFT studies have been carried out on the ROP of lactides initiated by the Ti, Zr and Hf complexes 1a, 1b and 1c. The results indicated that the activation barrier to reach the transition state using Zr complexes is lower and hence facile as compared to the Ti and Hf complexes.

Photoinduced Formation of Colloidal Silver in Nitrocellulose Solutions Containing Titanium Alkoxides

The study shows the possibility of photo-induced reduction of silver nitrate and formation of stable colloidal silver particles in an isopropanol-N,N-dimethylacetamide solution of titanium alkoxide (polybutyl titanate) stabilized by nitrocellulose. It is established that titanium alkoxide and the products of its partial hydrolysis in the liquid composition play the role of a photocatalyst for the reduction of silver ions; the introduction of nitric or acetic acid additives to the composition significantly increases its photosensitivity. The films deposited from the liquid composition, previously irradiated with visible or UV light, consist of hydrated titanium dioxide and nitrocellulose with incorporated colloidal silver. Thermal treatment of the films at 150–245°C leads to the decomposition of nitrocellulose and an increase in the absorption by silver particles.

Atomic Insights into Nanoparticle Formation of Hydroxyfluorinated Anatase Featuring Titanium Vacancies

Anatase TiO2 with exposed highly reactive (001) surface is commonly prepared using solution-based synthesis in the presence of a fluorinating agent acting as a structure-directing agent. Recently, the solvothermal reaction of titanium tetraisopropoxide in the presence of aqueous HF has resulted in the stabilization of an oxyhydroxyfluorinated anatase phase featuring cationic vacancies. In the present work, we have studied its formation mechanism, revealing a solid-state transformation of a highly defective anatase phase having a hydroxyfluoride composition that subsequently evolves through an oxolation reaction into an oxyhydroxyfluoride phase. Importantly, this work confirms that titanium alkoxide precursors can react with HF via a fluorolysis process yielding fluorinated molecular precursors, which further condense to produce new composition and structural features deviating from a well-ordered anatase network.

Improved Process for Preparation of tert-Butanesulfinyl Ketimines of Hindered Ketones under Nitrogen Flow

An improved process for tert-butanesulfinyl ketimines formation using titanium(IV) alkoxides is described. This new protocol gives better results especially for sterically hindered ketones compared to classical conditions where titanium(IV) isopropoxide is found to be only moderately effective. We found that removal of isopropanol or ethanol from the reaction mixture either under a nitrogen flow or under vacuum dramatically increased reaction rate, extent of conversion, and yield of the reaction. This methodology has been exemplified on several substrates reported in the literature to be difficult.

Alumina coating with TiO2and its effect on catalytic photodegradation of phenol andp-cresol

BACKGROUND This study is focused on the peptization of Boehmite and titanium alkoxide (modified sol–gel method) to obtain Al2O3–TiO2 mixed oxides taking advantage of the physicochemical properties of TiO2 and Al2O3. TiO2 is an important semiconductor and the most active photocatalyst. Al2O3 is an insulator with high surface area and thermal, chemical and mechanical resistance. It is possible to produce high surface area materials, where TiO2 is dispersed on the alumina surface for photodegradation of pollutants. RESULTS γ-Al2O3–TiO2 (5, 10 and 15 wt% TiO2) mixed oxides presented stabilization of the anatase phase. Rietveld studies showed incorporation of the Al3+ into the TiO2 anatase and Ti4+ into the Al2O3. They exhibit higher specific surface area than pure TiO2. The TiO2-coated alumina surface with small TiO2 particles produced a large number of active sites on the surface. The sample with 15 wt% of TiO2 presented the highest photodegradation of p-cresol and phenol. CONCLUSION The addition of TiO2 to the alumina improved the photoactivity of pure TiO2 producing materials with higher surface area covered with TiO2. Alumina delayed the recombination of photogenerated electron–hole pairs favoring the formation of highly reactive •OH radicals. The photodegradation of p-cresol and phenols increased with TiO2 loading increase. © 2016 Society of Chemical Industry

Synthesis of PLGA using a C 3-symmetric Zr (IV) amine tris(phenolate) alkoxide initiator and the effects of gamma radiation on its properties

In this paper, we report the preparation and characterisation of poly(lactic-co-glycolic) acid (PLGA) using a C 3-symmetric Zr (IV) amine tris(phenolate) alkoxide initiator. Although the zirconium alkoxide initiator is slower than the most commonly used Sn(Oct)2, relatively high molecular weights were obtained at a temperature of 130 °C, for a monomer to initiator ratio of 1000/1 (24 h) and 5000/1 (48 h). The degree of racemisation also depends on the initiator used. The reactions performed with the zirconium initiator showed a higher degree of racemisation when compared to those performed with Sn(Oct)2. A slight increase in the racemisation with time was also observed. The effects of gamma radiation on PLGA were also studied. Doses commonly applied to sterilise materials for biomedical applications were employed—10, 18, 25 and 50 kGy. The molecular weight of all samples irradiated decreased in a dose-dependent fashion—up to 56 % loss for 10 kGy and 72 % for 50 kGy—but were less pronounced for higher doses. Changes in thermal properties, such as melting point, glass transition temperature and enthalpy of crystallisation and fusion, were also observed after irradiation.

Low-cost composites based on porous titania–apatite surfaces for the removal of patent blue V from water: Effect of chemical structure of dye

Hydroxyapatite/titania nanocomposites (TiHAp) were synthesized from a mixture of a titanium alkoxide solution and dissolution products of a Moroccan natural phosphate. The simultaneous gelation and precipitation processes occurring at room temperature led to the formation of TiHAp nanocomposites. X-ray diffraction results indicated that hydroxyapatite and anatase (TiO2) were the major crystalline phases. The specific surface area of the nanocomposites increased with the TiO2 content. Resulting TiHAp powders were assessed for the removal of the patent blue V dye from water. Kinetic experiments suggested that a sequence of adsorption and photodegradation is responsible for discoloration of dye solutions. These results suggest that such hydroxyapatite/titania nanocomposites constitute attractive low-cost materials for the removal of dyes from industrial textile effluent.

Terminal-Selective Transesterification of Chlorine-Capped Poly(Methyl Methacrylate)s: A Modular Approach to Telechelic and Pinpoint-Functionalized Polymers.

Terminal-selective transesterification of chlorine-capped poly(methyl methacrylate)s (PMMA-Cl) with alcohols was developed as a modular approach to create telechelic and pinpoint-functionalized polymers. Being sterically less hindered and electronically activated, both the α-end ethyl ester and ω-end methyl ester of PMMA-Cl were efficiently and selectively transesterified with diverse alcohols in the presence of a titanium alkoxide catalyst, while retaining the pendent esters intact, to almost quantitatively give various chlorine-capped telechelic PMMAs. In sharp contrast to conventional telechelic counterparts, the telechelic polymers obtained herein yet carry a chlorine atom at the ω-terminal to further work as a macroinitiator in living radical polymerization. The iterative process of living radical polymerization and terminal-selective transesterification successfully afforded unique pinpoint-functionalized polymers where a single functional monomer unit was introduced into the desired site of the polymer chains.