Preparation of ZnO nanoparticles: Structural study of the molecular precursor

The structure of zinc acetate derived precursor currently used in the sol-gel synthesis of ZnO nanoparticles is described. The reaction products obtained before and after reflux of ethanolic zinc acetate solution have been studied by UV-Vis, photoluminescence, FTIR and EXAFS at the Zn K edge. EXAFS results evidence for both precursor solutions a change from the octahedral coordination sphere of oxygen atoms characteristic of the solid zinc acetate dihydrate compound into a four-fold environment. The EXAFS spectra of precursor solutions can be satisfactorily reproduced using the molecular structure reported for Zn4O(Ac)(6) (Ac = COOCH3). UV-Vis and FTIR measurements are also in agreement with the formation of this oligomeric precursor. The structural modification is more pronounced after reflux at 80degreesC, because the increase of the Zn4O(Ac)(6) amount and the formation of nearly 3.0 nm sized ZnO nanoparticle.

Strontium titanate films prepared by spray pyrolysis

Strontium titanate thin films were prepared by spray pyrolysis technique. Deposition parameters, such as solution concentration, time and temperature of deposition, and flow rate of carrier gas were optimized to obtain dense films without cracks. Films with different thicknesses were prepared through the control of deposition time. Prepared thin films were homogeneous, well crystallized, with uniform grain size. (C) 2003 Elsevier Ltd. All rights reserved.

Local structure and near-infrared emission features of neodymium-based amine functionalized organic/inorganic hybrids

Nd3+-based organic/inorganic hybrids have potential application in the field of integrated optics. Attractive sol-gel derived di-urea and di-urethane cross-linked poly (oxyethylene) (POE)/siloxane hybrids (di-ureasils and di-urethanesils, respectively) doped with neodymium triflate (Nd(CF3SO3)(3)) were examined by Fourier transform mid-infrared (FT-IR), Raman (FT-Raman), Si-29 magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and photoluminescence spectroscopies, and small-angle X-ray scattering (SAXS). The goals of this work were to determine which cation coordinating site of the host matrix (ether oxygen atoms or carbonyl oxygen atoms) is active in each of the materials analyzed, its influence on the nanostructure of the samples and its relation with the photoluminescence properties. The main conclusion derived from this study is that the hydrogen-bonded associations formed throughout the materials play a major role in the hybrids nanostructure and photoluminescence properties.

In situ and simultaneous nanostructural and spectroscopic studies of ZnO nanoparticle and Zn-HDS formations from hydrolysis of ethanolic zinc acetate solutions induced by water

The simultaneous formation of nanometer sized zinc oxide (ZnO), and acetate zinc hydroxide double salt (Zn-HDS) is described. These phases, obtained using the sol-gel synthesis route based on zinc acetate salt in alcoholic media, were identified by direct characterization of the reaction products in solution using complementary techniques: nephelometry, in situ Small-Angle X-ray Scattering (SAXS), UV-Vis spectroscopy and Extended X-ray Absorption Fine Structures (EXAFS). In particular, the hydrolytic pathway of ethanolic zinc acetate precursor solutions promoted by addition of water with the molar ratio N = [H2O]/[Zn2+] = 0.05 was investigated in this paper. The aim was to understand the formation mechanism of ZnO colloidal suspension and to reveal the factors responsible for the formation of Zn-HDS in the final precipitates. The growth mechanism of ZnO nanoparticles is based on primary particle (radius approximate to 1.5 nm) rotation inside the primary aggregate (radius < 3.5 nm) giving rise to an epitaxial attachment of particles and then subsequent coalescence. The growth of second ZnO aggregates is not associated with the Otswald ripening, and could be associated with changes in equilibrium between solute species induced by the superficial etching of Zn-HDS particles at the advanced stage of kinetic.

Distributed feedback multipeak laser emission in Rhodamine 6G doped organic-inorganic hybrids

Organic-inorganic hybrid materials were prepared from an ureasil precursor (ureapropyltriethoxysilane designated as UPTES) and acrylic acid modified zirconium (IV) n-propoxide. Thin films containing rhodamine 6G (Rh6G) were prepared by spin-coating on glass substrates with different Zr:Si molar ratios (Zr:Si = 75:25, 50:50 and 25:75). Refractive index, thickness, number of propagating modes and attenuation coefficient were measured at 543.5, 632.8 and 1550 nm wavelengths by the prism coupling technique. Distributed feedback (DFB) laser effect was observed and studied as a function of films thickness and refractive index.

A study of the hydrolysis pathway in oxalic acid catalyzed reacting TMOS-water mixtures under ultrasound stimulation

The hydrolysis of TMOS in oxalic acid catalyzed reacting TMOS-water mixtures, under ultrasound stimulation, was studied by fitting a simplified dissolution and reaction modeling for samples, the hydrolysis rate of which had been measured in a previous work. The reaction pathway represented in a ternary diagram shows a heterogeneous step for the reaction which gradually progresses until complete homogenization of the system. Besides the water dissolved due to the homogenizing effect of the alcohol, ultrasound maintains a virtual and additional dissolution of water located at the interface between the TMOS and water during the heterogeneous step of the reaction. The mean radius of the heterogeneity represented by water dispersed in TMOS was evaluated as around 150 Angstrom. The oxalic acid concentration accordingly increases the hydrolysis rate constant but its fundamental role on the solubility of water in TMOS could not unequivocally be established.

Multi-scale structural description of siloxane-PPO hybrid ionic conductors doped by sodium salts

Alkaline metal doped organic - inorganic hybrids have potential applications in the field of portable energy sources. Attractive sol - gel derived urea cross-linked polyether, siloxane - PPO ( poly( propylene oxide)) hybrids doped with sodium salts ( NaClO4 and NaBF4) were examined by multi-spectroscopic approach that includes complex impedance, X-ray powder diffraction (XRPD), small angle X-ray scattering (SAXS), Si-29 and Na-23 magic-angle spinning nuclear magnetic resonance (NMR/MAS), Na K-edge X-ray absorption near edge structure (XANES) and Raman spectroscopies. The goals of this work were to determine which cation coordinating site of the host matrix ( ether oxygen atoms or carbonyl oxygen atoms) is active in each of the materials analyzed, its influence on the nanostructure of the samples and its relation with the thermal and electrical properties. The main conclusion derived from this study is that the NaBF4 salt has a much lower solubility in the hybrid matrix than the NaClO4 salt. Furthermore, the addition of a large amount of salt plays a major role in the hybrid nanostructure and electrical properties, modifying the PPO chain conformation, weakening or breaking the hydrogen bond of the polyether - urea associations and changing the polycondensation and aggregation processes involving the siloxane species.

A kinetic study of the effect of ultrasound power on the sonohydrolysis of tetraethyl orthosilicate

A kinetic study of the ultrasound-stimulated and acid-catalyzed sonohydrolysis of tetraethyl orthosilicate (TEOS) in solventless TEOS-water heterogeneous mixtures was carried out by means of a calorimetric method as a function of the ultrasound power. The hydrolysis reaction starts in acidulated heterogeneous water-TEOS mixtures after an induction period under ultrasonic stimulation. The ultrasound power seems to play a role on the dynamical coupling of the system originating a continuum upward shifting of the base line during the induction period of sonication. The rate in which the base line is upward shifted diminishes with the power. The best coupling between the ultrasound and the reactant heterogeneous mixtures for this experimental setup was found to occur at 50 W, for which the gelation time was found to be a minimum. The kinetics of the heterogeneous TEOS sonohydrolysis was studied on the basis of a dissolution and reaction modeling. The heterogeneous reaction pathway as deduced from the kinetic study was drawn in a ternary diagram as a function of the ultrasound power. (C) 2006 Elsevier B.V. All rights reserved.

Electron trapping of laser-induced carriers in Er-doped SnO2 thin films

In order to investigate optically excited electronic transport in Er-doped SnO2, thin films are excited with the fourth harmonic of an Nd:YAG laser (266nm) at low temperature, yielding conductivity decay when the illumination is removed. Inspection of these electrical characteristics aims knowledge for electroluminescent devices operation. Based on a proposed model where trapping defects present thermally activated cross section, the capture barrier is evaluated as 140, 108, 100 and 148 meV for doped SnO2, thin films with 0.0, 0.05, 0. 10 and 4.0 at% of Er, respectively. The undoped film has vacancy levels as dominating, whereas for doped films. there are two distinct trapping centers: Er3+ substitutional at Sn lattice sites and Er3+ located at grain boundary. (C) 2007 Elsevier Ltd. All rights reserved.

Eu3+ doped polyphosphate-aminosilane organic-inorganic hybrids

The preparation and characterization of new Eu3+ doped polyphosphate-aminosilane hybrids xerogels is reported. Eu3+ D-5(0) emission quantum efficiency ranges from 0.41 to 0.54 depending on the SUP ratio. These rather high values are due to the substitution of phosphate and amino groups for water in the Eu3+ coordination shell. Raman and Si-29 and C-13 CP-MAS NMR results suggest that no strong interaction exists between the polyphosphate and the siloxane parts. Not fully condensed siloxane colloidal domains seem to be homogeneously distributed in the polyphosphate network. Good optical quality and favorable Eu3+ spectroscopic characteristics suggest these new hybrids as good hosts for lanthanide ions in optical devices. (C) 2003 Published by Elsevier B.V.

Photoelectrocatalytic oxidation of remazol turquoise blue and toxicological assessment of its oxidation products

The ability of photoelectrocatalytic oxidation to degrade the commercially important copper-plitalocyanine dye, remazol turquoise blue 15 (RTB) was investigated. The best experimental condition was optimized, evaluating the performance of Ti/TiO2 thin-film electrodes prepared by sol-gel method in the decolourization of 32 mg L-1 RTB dye in 0.5 mol L-1 Na2SO4 pH 8 and applied potential of +1.5 V versus SCE under UV irradiation. Spectrophotometric measurements, high performance liquid chromatography, dissolved organic carbon (TOC) evaluation and stripping analysis of yielding solution obtained after 3 h of photoelectrolysis leads to 100% of absorbance removal from wavelength of 250-800 nm, 79.6% of TOC reduction and the releasing of up to 54.6% dye-bound copper (0.85 mg L-1) into the solution. Both, original and oxidized dye solution did not presented mutagenic activity with the strains TA98 and WOO of Salmonella in the presence and absence of S9 mix at the tested doses. Nevertheless, the yielding photoelectrocatalytic oxidized solution showed an increase in the acute toxicity for Vibrio fischeri bacteria, explained by copper liberation during treatment. (c) 2006 Elsevier B.V. All rights reserved.

Elaboration of boehmite nano-powders by spray-pyrolysis

Boehmite (gamma-AlOOH) synthesis have been investigated using a spray pyrolysis (SP) device starting from a stable sol of Al-tri-sec-butoxide peptized by nitric acid. Free spherical particles from 100 to 500 nm have been elaborated. Particles sub-structure is made of nano-crystalline boehmite with very small average crystallite size (one crystal cell along the b axis). The nano-crystalline boehmite synthesized by SP at low temperature (200 degrees C) is spontaneously dispersible in water without any surface treatment. Boehmite powder may be transformed to transition gamma-alumina by heat post-treatment. Powders of sub-micrometric and spherical gamma-alumina particles may also be synthesized by SP at 700 degrees C. (C) 2008 Elsevier B.V. All rights reserved.

Development and Evaluation of a Nanoporous Iron (Hydr)oxide Electrode for Phosphate Sensing

Nanoporous iron (hydr) oxide electrodes are evaluated as phosphate sensors using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The intensity of the reduction peak current (I-cp) of the ferrihydrite working electrode is tied to phosphate concentration at low pH; however, a hematite electrode combined with the use of EIS provided reliable sensing data at multiple pH values. Nanoporous hematite working electrodes produced an impedance phase component (theta) that shifts with increasing phosphate, and, at chosen frequencies, theta values were fitted for the range 1 nM to 0.1 mM phosphate at pH 4 and pH 7 in 5 mM NaClO4.

Synthesis, ferroelectric and optical properties of (Pb,Ca)TiO3 thin films by soft solution processing

Calcium modified lead titanate sol was synthesized using a soft solution processing, the so-called polymeric precursor method. In soft chemistry method, soluble precursors such as lead acetate trihydrate, calcium carbonate and titanium isopropoxide, as starting materials, were mixed in aqueous solution. Pb0.7Ca0.3TiO3 thin films were deposited on platinum-coated silicon and quartz substrates by means of the spinning technique. The surface morphology and crystal structure, dielectric and optical properties of the thin films were investigated. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) capacitors. The typical measured small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 299 and 0.065, respectively, for a thin film with 230 nm thickness annealed at 600degreesC for 2 h. The remanent polarization (2P(r)) and coercive field (E-c) were 32 muC/cm(2) and 100 kV/cm, respectively. Transmission spectra were recorded and from them, refractive index, extinction coefficient, and band gap energy were calculated. Thin films exhibited good optical transmissivity, and had optical direct transitions. The present study confirms the validity of the DiDomenico model for the interband transition, with a single electronic oscillator at 6.858 eV. The optical dispersion behavior of PCT thin film was found to fit well the Sellmeir dispersion equation. The band gap energy of the thin film, annealed at 600degreesC, was 3.56 eV. The results confirmed that soft solution processing provides an inexpensive and environmentally friendly route for the preparation of PCT thin films.

Tin oxide nanoparticle formation using a surface modifying agent

This work presents results concerning the preparation of redispersible tin oxide nanoparticles achieved by using Tiron molecule ((OH)(2)C(6)H(2) (SO(3)Na)(2)) as surface modifying agent. The adsorption isotherm measurements show that an amount of 10 wt.% of Tiron is need to recover the SnO(2) nanoparticles surface with a monolayer. These nanoparticles can be easily redispersed in tetramethyl ammonium hydroxide at pH greater than or equal to11 until a powder concentration of 12 vol.% of tin. Under these conditions, hydrodynamic particle size is about 7 nm and increases until 52 nm at pH 6 due to the aggregation phenomenon. The time evolution of the viscoelastic properties indicates that the suspensions at pH 12.5, containing 12 vol.% tin oxide and 10 wt.% of surface modifier are kinetically stable. After thermal treatment at different temperature the powder characterisation evidences that the presence of Tiron monolayer at the nanoparticles surface increases the thermal stability of the porous texture and prevent the micropore size growth. This set of results contributes to satisfy the demand for more controlled synthesis of nanoparticles with high thermal stability as required for fabrication of ultrafiltration ceramic membranes. (C) 2004 Elsevier Ltd. All rights reserved.