Preparation of TiO2 Sol Using TiCl4 as a Precursor

A titanium dioxide sol with narrow particle size distribution was synthesized using TiCl₄ as the starting material. The sol was prepared by a process where HCl was added to a gel of hydrated titanium oxide to dissolve it. The resulting aqueous titanic acid solution was heated to form titanium dioxide sol. The effects of preparation parameters were investigated. TiCl₄ was slowly added to distilled water at 5°C. Aqueous solution of sodium hydroxide was added to adjust the pH of the system to 8–12. After aging for a period of time, the peptized sol was filtered and sufficiently washed. The filtered cake was repulped in water. Hydrochloric acid was slowly added to the solution with stirring. After condensation reaction and crystallization, a transparent sol with suspended TiO₂ was formed. XRD results show that the crystalline phase was anatase. The suspended TiO₂ particles were rhombus primary particles with the major axis ca. 20 nm and the minor axis ca. 5 nm. The TiO₂ particles prepared at pH 8 had the largest surface area of 141 cm³/g and it was microporous. The compositions of the solution which yielded the smallest suspended TiO₂ particles were TiO₂:HCl (35% HCl) = 1:1 (molar ratio), concentration of TiO₂ = 10%. Hydroxypropyl cellulose with viscosity of 150–400 cps was added as a dispersant. The sol was excellent in dispersibility and long-term stability. Transparent thin films could be obtained through dip-coating glass substrate in the sol. The dip-coating on glass can be less than three times to have one monolayer TiO₂. The transparent TiO₂ thin film had strong hydrophilicity after being illuminated by UV light.     

Preparation of titania colloids by thermal hydrolysis of urea and densification behavior of the collid-derived monolithic titania gels

Hydrous titania colloids with different sizes and shapes were prepared from urea-containing TiCl₄ solutions by controlled thermal hydrolysis of urea. Very small colloidal particles (Sw=280–290 m²/g) with anatase structure were precipitated from aqueous HCl solutions of [TiCl₄] <1.0 mol/dm³ and [urea] >16.6 mol/dm³. Sols containing such colloids could be converted to translucent monolithic gels. A decrease in urea concentration ([urea]=8.3 mol/dm³) caused the production of aggregated rutile-type particles with a large aspect ratio, from which only titania powder was obtained. Heating of a monolithic gel above 500°C resulted in the accelerated densification of the gel. A highly densified titania with 96% of theoretical density was produced from the monolithic gel after heating at 700°C for 6 h.     

Preparation and characterization of SiO2/TiO2 composite microspheres with microporous SiO2 core/mesoporous TiO2 shell

SiO₂/TiO₂ composite microspheres with microporous SiO₂ core/mesoporous TiO₂ shell structures were prepared by hydrolysis of titanium tetrabutylorthotitanate (TTBT) in the presence of microporous silica microspheres using hydroxypropyl cellulose (HPC) as a surface esterification agent and porous template, and then dried and calcined at different temperatures. The as-prepared products were characterized with differential thermal analysis and thermogravimetric (DTA/TG), scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption. The results showed that composite particles were about 1.8 μm in diameter, and had a spherical morphology and a narrow size distribution. Uniform mesoporous titania coatings on the surfaces of microporous silica microspheres could be obtained by adjusting the HPC concentration to an optimal concentration of about 3.2 mmol L⁻¹. The anatase and rutile phase in the SiO₂/TiO₂ composite microspheres began to form at 700 and 900 °C, respectively. At 700 °C, the specific surface area and pore volume of the SiO₂/TiO₂ composite microspheres were 552 and 0.652 mL g⁻¹, respectively. However, at 900 °C, the specific surface area and pore volume significantly decreased due to the phase transformation from anatase to rutile.     

Preparation of spherical spinel LiMn2O4 cathode material for lithium ion batteries

A novel process is proposed for synthesis of spinel LiMn₂O₄ with spherical particles from the inexpensive materials MnSO₄, NH₄HCO₃, and NH₃H₂O. The successful preparation started with carefully controlled crystallization of MnCO₃, leading to particles of spherical shape and high tap density. Thermal decomposition of MnCO₃ was investigated by both DTA and TG analysis and XRD analysis of products. A precursor of product, spherical Mn₂O₃, was then obtained by heating MnCO₃. A mixture of Mn₂O₃ and Li₂CO₃ was then sintered to produce LiMn₂O₄ with retention of spherical particle shape. It was found that if lithium was in stoichiometric excess of 5% in the calcination of spinel LiMn₂O₄, the product had the largest initial specific capacity. In this way spherical particles of spinel LiMn₂O₄ were of excellent fluidity and dispersivity, and had a tap density as high as 1.9 g cm^–3 and an initial discharge capacity reaching 125 mAh g^–1. When surface-doped with cobalt in a 0.01 Co/Mn mole ratio, although the initial discharge capacity decreased to 118 mAh g^–1, the 100th cycle capacity retention reached 92.4% at 25°C. Even at 55°C the initial discharge capacity reached 113 mAh g^–1 and the 50th cycle capacity retention was in excess of 83.8%.     

Thermal annealing synthesis of titanium-dioxide nanowire-nanoparticle hetero-structures

Crystalline TiO₂ nanowire-nanoparticle hetero-structures were successfully synthesized from titanium foils by using a simple thermal annealing method with the aid of CuCl₂ at the atmospheric pressure. Nanowires were grown from Ti foils by simply annealing Ti foils at 850 °C. Then, TiCl₄ was delivered to TiO₂ nanowires so as to precipitate TiO₂ nanoparticles on nanowire surfaces. At 750 °C reaction temperature, nanoparticles of tens of nanometers in diameter were well distributed on pre-grown nanowire forests. Nanoparticles were likely to be precipitated by TiCl₄ decomposition or oxidation and that require high temperatures above ∼650 °C. Electron microscopy, X-ray diffraction, and UV-vis spectroscopy analyses show they have the rutile polycrystalline structure with a slightly enlarged bandgap compared to that of bulk TiO₂. The influence of key synthesis parameters including reaction temperature, reaction time, and quantity of supplied materials on the incorporating nanoparticles was also systematically studied. The optimum reaction condition in the present paper was identified to be 750 °C annealing with repetitive 20 min reactions. A higher reaction temperature yielded larger diameter particles, and higher loading of Ti produced dense particles without changing the particle size. Finally, this method could be utilized for synthesizing other metal oxide nanowires-nanoparticle hetero-structures.     

Synthesis of hollow spherical silica with MCM-41 mesoporous structure

Hollow spherical mesoporous silica was synthesized by using sodium silicate as a precursor and a low concentration of cetyltrimethylammonium bromide (CTAB) (0.154 mol dm^–3). The resulting hollow spherical particles were characterized with scanning electron microcopy (SEM), small-angle X-ray diffraction (SXRD), transmission electron microscopy (TEM), and N₂ gas adsorption and desorption techniques. The results showed that regular spherical mesoporous silica could be obtained only if the molar ratio of propanol to CTAB was in the range of approximately 8:1–9:1. The spherical particles were hollow (inside), and the shell consisted of smaller particles with a pore structure of hexagonal symmetry. With an increase of the molar ratio of propanol to CTAB, the distance (a value) between centers of two adjacent pores increased, and the pore structure of mesoporous silica became less ordered. N₂ adsorption–desorption curves revealed type IV isotherms and H1 hysteresis loops; with an increase of the molar ratio of propanol to CTAB, the pore size with Barrett–Joyner–Halenda (BJH) diameter of the most probable distribution decreased, but the half peak width of the pore size distribution peak increased     

Extraction characteristics of pertechnetate with tetraphenylarsonium in the presence of chloride,nitrate and perchlorate anions

Selected extraction systems of TcO ₄ ^– –(H,Na)A–H₂O/R(TcO₄,A)–CHCl₃, C₆H₅NO₂ type, where A=Cl^–, NO ₃ ^– , ClO ₄ ^– , R=(C₆H₅)₄As⁺, were studied. The solvent extraction of sub- and super-stoichiometric ratio of TcR was performed. The solubility of (C₆H₅)₄AsTcO₄ in water, chloroform and nitrobenzene were determined too. The results of the extractions are presented in the form of TcO ₄ ^– distribution dependencies on the phase composition and the extraction constants of individual TcO ₄ ^– , Cl^–, NO ₃ ^– , ClO ₄ ^– anions and TcO ₄ ^– -Cl^–, TcO ₄ ^– –NO ₃ ^– , TcO ₄ ^– –ClO ₄ ^– ion pairs.     

Preparation of uniform rhodamine B-doped SiO2/TiO2 composite microspheres

Uniform rhodamine B (RB)-doped SiO₂/TiO₂ composite microspheres with catalytic and fluorescent properties were prepared by an easy and economical method in this paper. The composite microspheres were built up with well-dispersed silica particles as the cores, RB as both the doped agent and stabilizer, and the TiO₂ shells were obtained through the hydrolysis of TiCl₄ in water bath. The morphology and structure of the particles were characterized by scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The characterization results indicate that composite particles are all in spherical shape and have a narrow size distribution. The composite particles calcined above 500 °C reveal clear crystalline reflection peaks of the rutile TiO₂ which exhibits well catalytic property. The photocatalytic experiment was carried out in order to examine the catalytic property of composite microspheres. The fluorescent property of particles was also investigated. Dye-leakage test indicates that RB molecules entrapped in the composite particles by this method are stable inside the particles.     

Preparation of TiO2 coating films containing Pd fine particles by sol-gel method

TiO₂ coating films of 0.3–0.4 m in thickness that contain fine Pd particles have been prepared by sol-gel method using Ti(OC₃H ₇ ⁱ )₄ and PdCl₂ as starting materials in an attempt to obtain optical materials that show surface plasma resonance in the visible range. A temperature higher than 900°C was required for formation of Pd metal particles when the heat-treatment was conducted in air. Heat-treatment of pre-heated amorphous films in air at 800°C resulted in precipitation of PdO particles, the size of which could be varied by changing the time of heat-treatment, and subsequent heat-treatment in H₂/Ar gas converted the PdO particles into Pd metal particles. Heat-treatment of pre-heated amorphous films in H₂/Ar gas also resulted in precipitation of Pd metal particles. The size of the Pd metal particles precipitated in the films was 6 to 90 nm, depending on the conditions of heat-treatment. The resultant TiO₂ films containing Pd metal particles were brownish grey in color and showed optical absorption in the visible range over 400 nm, which is attributed to surface plasma resonance of Pd metal particles.     

1,1,1,1-Tetrakis(o-fluorophenylamino)silane tris[titanium(IV) chloride]. Evidence for a new titanium cation [Ti2Cl7]+

Si(NHC₆H₄F-o)₄ · 3TiCl₄ (1) has been obtained from the disproportionation of (CF₃CH₂O)₃SiNHC₆H₄F-o and TiCl₄ in petroleum ether (40–60 °C) at –10 °C. The analytical (elemental analysis, molar conductance) and spectral (i.r., ¹H- and ¹⁹F-n.m.r.) data suggested that (1) behaves as [Si(NHC₆H₄F-o)₄ · Ti₂Cl₇]⁺ [TiCl₅]^–. The presence of these ions has been confirmed by characterising the products of metathetical reactions of (1) with R₄NX (R = Bu and Et; X = I and Br) and with AgNO₃. The data suggest the presence of a new titanium cation [Ti₂Cl₇]⁺.     

Sol-Gel Synthesis and Phase Evolution Behavior of Sterically Stabilized Nanocrystalline Zirconia

Nanocrystalline as well as submicron sized, non-agglomerated, spherical ZrO₂ particles have been successfully synthesized using the sol-gel technique utilizing hydroxypropyl cellulose (HPC) as a polymeric steric stabilizer. The effect of various parameters such as the ratio of molar concentration of water and alkoxide (R), the molar concentration [HPC] and the molecular weight (MW_HPC) of HPC polymer as well as the calcination temperature on ZrO₂ nanocrystallites size and their phase evolution behavior is systematically studied. The phase evolution behavior of nanocrystalline ZrO₂ is explained and correlated with the adsorption behavior of HPC polymer on ZrO₂ nanoparticles surface, which is observed to be a function of R, [HPC], MW_HPC and the calcination temperature. Optimum synthesis parameters for obtaining 100% tetragonal phase in nanocrystalline ZrO₂ are identified for the present sol-gel method of synthesizing nanoparticles.     

Gelation of tenuous titania gels in a reverse micellar medium

Tenuous gels of TiO₂ are synthesized from titanium isopropoxide in a reverse micellar medium. The volume fraction of TiO₂ in these gels is equal to 0.2%. The chemical and aggregative mechanisms are studied using ¹H NMR, small-angle X-ray scattering, dynamic and static light scattering. The alkoxide hydrolysis occurs at the first stage of the gelation. Small clusters (70–80 Å) are produced. The aggregation induces mass fractal structures with fractal dimensions depending on the solvent used in the synthesis: 1.4<D _f<1.9. The interpretation of these results is based on interactions between the growing inorganic chains and the surfactant molecules.     

Insect pheromones and their analogues. XVI. Practical synthesis of hexadec-9Z-enal — A component of the sex pheromone of the cotton bollwormHeliothis armigera

A synthesis of hexadec-9Z-enal — a component of the sex pheromone of the cotton boll-wormHeliothis armigera (Hübner) — based on cyclooctene (I) is proposed. Through a solution of 22 g of (I), 250 ml of cyclohexane, and 40 ml of MeOH is passed (at 5°C) 0.2 M O₃/O₂, the solution is decanted off, and the precipitated ozonide is dissolved in 200 ml of MeOH and is reduced with 19 g of NaBH₄ (40°C) with the isolation, after the usual working up, of 23.4 g of octane-1,8-diol (II). From 0.5 mole of (II) and 0.6 mole of 45% HBr 8-bromooctan-1-ol (III) is obtained and this is converted into 1-(2-THPL)oxy)-8-bromooctane (IV). The condensation of (IV) with oct-1-yne (Ar, LiNH₂, HMPTA, 10°C, 1 h, and then 55°C, 10 h) leads to 1-(2-THPL-oxy)hexadec-9-yne (V) the hydrolysis of which (MeOH, H₂O, p-TsOH, 20°C for 20 h) yields hexadec-9-yn-ol (VI). The reduction of (VI) (Et₂O, iso-BuMgBr, Cp₂TiCl₂, 0°C, 15 min, then 20°C, 1 h) yieldshexadec-9Z-en-l-ol (VII). The oxidation of (VII) (PyHCrO ₃ ⁺ Cl^–, CH₂Cl₂, 20°C, 2 h) gives hexadex-9Z-enal (VIII). Characteristics of the compounds (yield (%), n _D ^{20 (25)}: (II) – 80, mp 61–62°C; (III) – 75, 1.4807; (IV) – 99, —; (V) – 52, 1,4650; (VI) – 85, 1.4657; (VII) – 99, 1.4650; (VIII) – 98, 1.4600. Characteristics of the IR and PMR spectra of compounds (V–VII) are given.Institute of Chemistry, Bashkir Branch, Academy of Sciences of the USSR, Ufa. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 286–289, March–April, 1987.     

Electrical Properties of Transparent Doped Oxide Films

In the present study n-type and p-type transparent conductive TiO₂ films were prepared by using sol-gel method. The n-type TiO₂ films were obtained by using Ti(OC₃H ₇ ⁱ )₄ solutions co-doped with Ru and Ta. The films were uniform and transparent in all the conditions, and their crystalline phases were anatase when HCl or HNO₃ was used as a catalyst. The resistivity decreased with increasing Ta content and increased with increasing Ru content. Most of the films showed resistivity minima at a heat-treatment temperature of 700°C. The lowest resistivity of 10¹ 10² cm was attained. The p-type TiO₂ films were obtained by using Ti(OC₃H ₇ ⁱ )₄ solutions co-doped with Co and Nb (Sb). The films were also uniform and transparent when AcAc was used, while samples heat-treated at 800°C became opaque when HCl was added. Rutile single phase appeared when the films were heat-treated at 700°C. Logarithmic resistivity of films co-doped with Co and Nb was directly proportional to the reciprocal absolute temperature. On the other hand, the slopes for films co-doped with Co and Sb were different below and above 200°–220°C. The activation energy at the low-temperature region is as low as 0.17 eV, and the resistivity at room temperature is 10⁴ 10⁵ cm.     

Study on the hydrothermal reaction of FeCl<Subscript>3</Subscript> solution in the presence of poly(vinyl alcohol)

A 0.5 dm³ aqueous solution of 0.1 M FeCl₃ dissolving 1 wt% poly(vinyl alcohol) (PVA) was treated hydrothermally in a stainless steel autoclave at various temperatures (T _h=110–200 °C). Highly ordered red corpuscle-like hematite particles around 2 m in diameter were produced after aging the solution at T _h=110 °C for 7 days, though large numbers of spherical PVA microgels around 2–4 m in diameter were produced together with the red corpuscle-like particles at T _h120 °C. The number of red corpuscle-like hematite particles decreased but that of spherical PVA microgels increased with increasing T _h, leading to the proposal that the method carried out in the present study will become a new synthetic method of polymer microgels. The ferric ions acted as a cross-linking agent to make PVA insoluble in water. The red corpuscle-like hematite particles produced at T _h=110 °C had high specific surface areas and showed high mesoporosity. The mesoporosity appeared to be more pronounced after evacuating the particles above 300 °C. The diameter of the mesopores after evacuation above 300 °C ranged from 2 to 20 nm, with a maximum at around 5–6 nm. The H₂O and N₂ adsorption experiments revealed that there are no ultramicropores in the particles. The H₂O and CCl₄ adsorption experiments further disclosed that the surface hydrophobicity of the particles is low even though PVA molecules remain after evacuation of the particles at 100–400 °C. Furthermore, the micropores produced after evacuation of the particles at 400 °C exhibited a high size restriction effect, i.e., the micropores produced were accessible to H₂O (diameter 0.253 nm) and N₂ (diameter 0.318 nm) molecules but not to CCl₄ (diameter 0.514 nm).     

Nucleation of Titania Nanocrystals in Silica Titania Waveguides

SiO_{2(1 – x)}-TiO_2(x) monomode waveguides at 632.8 nm, with x in the range 0.07–0.2 and thickness of about 0.4 m, were deposited on silica substrates by a dip-coating technique. Nucleation of TiO₂ nanocrystals and the growth of their size by thermal annealing up to 1300°C were studied by waveguided Raman scattering in the SiO_2(0.8)-TiO_2(0.2) composition. In the low frequency region (5–50 cm^–1) of the VV and HV polarized Raman spectra the symmetric and quadrupolar acoustic vibrations are observed. The mean size of the titania particles are obtained from the frequencies of the Raman peaks. The results are compared with those obtained from the measure of the linewidths in the X-ray diffraction spectra. Nanocrystals with a mean size in the range 4–20 nm are obtained by thermal annealing in a corresponding range of 700–1300°C.     

A direct hydrogen-1, carbon-13, and nitrogen-15 NMR study of lutetium(III)-isothiocyanate complexation in aqueous solvent mixtures

A direct, low-temperature hydrogen-1, carbon-13, and nitrogen-15 nuclear magnetic resonance study of lutetium(III)-isothiocyanate complex formation in aqueous solvent mixtures has been completed. At –100°C to –120°C in water-acetone-Freon mixtures, ligand exchange is slowed sufficiently to permit the observation of separate¹H,¹³C, and¹⁵N NMR signals for coordinated and free water and isothiocyanate ions. In the¹³C and¹⁵N spectra of NCS^–, resonance signals for five complexes are observed over the range of concentrations studied. The¹³C chemical shifts of complexed NCS^– varied from –0.5 ppm to –3 ppm from that of free anion. For the same complexes, the¹⁵N chemical shifts from free anion were about –11 ppm to –15 ppm. The magnitude and sign of the¹⁵N chemical shifts identified the nitrogen atom as the binding site in NCS^–. The concentration dependence of the¹³C and¹⁵N signal areas, and estimates of the fraction of anion bound at each NCS^–:Lu³⁺ mole ratio, were consistent with the formation of [(H₂O)₅Lu(NCS)]²⁺ through [(H₂O)Lu(NCS)₅]^2–. Although proton and/or ligand exchange and the resulting bulk-coordinated signal overlap prevented accurate hydration number measurements, a good qualitative correlation of the water¹H NMR spectral results with those of¹³C and¹⁵N was possible.     

Electronic structures of tetrahedral CrO 4 2− , VO 4 3− and TiCl4

The electronic structures of the tetrahedral systems CrO ₄ ^2– , VO ₄ ^3– and TiCl₄ are discussed on the basis of semiquantitative LCAO MO calculations.

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Zusammenfassung Die Elektronenstrukturen der Tetraedersysteme CrO ₄ ^2– , VO ₄ ^3– und TiCl₄ werden an Hand halbquantitativer LCAO-MO Rechnungen diskutiert.

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Résumé Discussion des structures électroniques des systèmes tétraédriques CrO ₄ ^2– , VO ₄ ^3– et TiCl₄ sur la base de calculs semi-quantitatifs LCAO MO.

     

Dissociation constants of the ampholyte glycine in 50 mass % methanol-water from 5 to 55°C,with related thermodynamic quantities

The two thermodynamic dissociation constants of glycine at 11 temperatures from 5 to 55°C in 50 mass % methanol-water mixed solvent have been determined from precise emf measurements with hydrogen-silver bromide electrodes in cells without liquid junction. The first acidic dissociation constant (K ₁)for the process HG⁺H⁺+G^± is expressed as a function ofT(^oK) by the equation pK ₁ = 2043.5/T – 9.6504 + 0.019308T. At 25°C, pK ₁is 2.961 in the mixed solvent, as compared with 2.350 in water, with H°=1497 cal-mole^–1, G°=4038 cal-mole^–1, S°=–8.52 cal-°K^–1-mole^–1, and C _p ^o =–53 cal-°K^–1-mole^–1. The second acidic dissociation constant (K ₂)for the process G^±H⁺+G^– over the temperature range studied is given by the equation pK ₂ = 3627.1/T – 7.2371 + 0.015587T. At 25°C, pK ₂is 9.578 in MeOH–H₂O as compared with 9.780 in water, whereas H° is 10,257 cal-mole^–1, G° is 13,063 cal-mole^–1, S° is –9.41 cal-°K^–1-mole^–1, and C _p ^o is –43 cal-°K^–1-mole^–1. The protonated glycine becomes weaker in 50 mass % methanol-water, whereas the second dissociation process becomes stronger despite the lower dielectric constant of the mixed solvent (=56.3 at 25°C).     

Dissociation quotient of benzoic acid in aqueous sodium chloride media to 250°C

The dissociation quotient of benzoic acid was determined potentiometrically in a concentration cell fitted with hydrogen electrodes. The hydrogen ion molality of benzoic acid/benzoate solutions was measured relative to a standard aqueous HCl solution at seven temperatures from 5 to 250°C and at seven ionic strengths ranging from 0.1 to 5.0 molal (NaCl). The molal dissociation quotients and selected literature data were fitted in the isocoulombic (all anionic) form by a six-term equation. This treatment yielded the following thermodynamic quantities for the acid dissociation equilibrium at 25°C and 1 bar: logK_a=–4.206±0.006, H _a ^o =0.3±0.3 kJ-mol^–1, S _a ^o =–79.6±1.0 J-mol^–1-K^–1, and C _p;a ^o =–207±5 J-mol^–1-K^–1. A five-term equation derived to describe the dependence of the dissociation constant on solvent density is accurate to 250°C and 200 MPa.