Synthesis and Study of the Photophysical Properties of a New Eu3+ Complex with 3-Hydroxypicolinamide

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effect of variations in annealing temperature and metallic cations on nanostructured molybdate thin films

Crystalline molybdate thin films were prepared by the complex polymerization method. The AMoO(4) (A = Ca, Sr, Ba) films were deposited onto Si wafers by the spinning technique. The Mo-O bond in the AMoO(4) structure was confirmed by FTIR spectra. X-ray diffraction revealed the presence of crystalline scheelite-type phase. The mass, size, and basicity of A(2+) cations was found to be dependent on the intrinsic characteristics of the materials. The grain size increased in the following order: CaMoO4 < SrMoO4 < BaMoO4. The emission band wavelength was detected at around 576 nm. Our findings suggest that the material's morphology and photoluminescence were both affected by the variations in cations (Ca, Sr, or Ba) and in the thermal treatment.

Thermal evaporation furnace with improved configuration for growing nanostructured inorganic materials

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Fabrication of coaxial TiO2/Sb2S3 nanowire hybrids for efficient nanostructured organic- inorganic thin film photovoltaics

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Electrochemical Determination of Inorganic Contaminants in Automotive Fuels

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Waveguides and gratings fabrication in zirconium-based organic/inorganic hybrids

Sol-gel derived poly(oxyethylene)/siloxane organic/inorganic di-ureasil hybrids containing different amounts of methacrylic acid (McOH, CH(2)=C(CH(3))COOH)) modified zirconium oxo-clusters (Zr-OMc) were processed as thin films deposited in glassy substrates via spin coating and as transparent and shape controlled monoliths. Channel monomode waveguides and diffraction gratings were UV patterned using the Talbot interferometer and the Lloyd mirror interferometer experimental setups. The time dependence of the diffraction gratings efficiency was studied for hybrids containing different amounts of Zr-OMc. Finally, the number of propagating modes and the refractive index gradient within the waveguide region, determined as a Gaussian section located below the patterned channel, was evaluated and modeled, a maximum index contrast of 2.43 X 10(-5) being estimated.

Low optical loss planar waveguides prepared in an organic-inorganic hybrid system

HfO2-(3-glycidoxipropil)trimethoxisilane (GPTS) planar waveguides were prepared by a sol-gel route. A stable sol of Hafnia nanocrystals was prepared and characterized by photon correlation spectroscopy and high resolution transmission electron microscopy. The suspension was incorporated in GPTS host and the resulting sol was deposited on borosilicate substrates by the spin coating technique. Optical properties such as refractive index, thickness, number of propagating modes, and attenuation coefficient were measured at 632.8, 543.5, and 1550 nm by the prism coupling technique as a function of the HfO2 content. (C) 2000 American Institute of Physics. [S0003-6951(00)03348-9].

Planar and UV written channel optical waveguides prepared with siloxane poly(oxyethylene)-zirconia organic-inorganic hybrids. Structure and optical properties

Organic-inorganic hybrids were prepared using ureapropyltriethoxysilane, methacryloxypropyltrimethoxysilane and acrylic acid modified zirconium(IV) n-propoxide precursors and were characterized by small angle X-ray scattering, X-ray diffraction and photoluminescence spectroscopy. The results indicate an effective interaction between the zirconium-based nanoparticles and the siliceous nanodomains that induces changes in the hybrids' emission features. Planar waveguides were obtained by spin-coating of the prepared sols on sodalime and silica substrates. Refractive index, thickness, number of propagating modes, and attenuation coefficient were measured at 543.5, 632.8 and 1550 nm by the prism coupling technique. The synergism between the two hybrid precursors resulted in monomode planar waveguides with low losses in the infrared ( from 0.6-1.1 dB cm(-1)) which also support a number of propagating modes in the visible ( losses from 0.4-1.5 dB cm(-1)). Channel waveguides were also obtained by UV photopatterning using amplitude or phase masks and propagating modes were observed at 1550 nm.

Structural modelling of Eu3+-based siloxane-poly( oxyethylene) nanohybrids

The modelling of the local structure of sol-gel derived Eu3+-based organic/inorganic hybrids is reported, based on Small-Angle X-ray Scattering (SAXS), photoluminescence and mid-infrared spectroscopy. The hybrid matrix of these organically modified silicates, classed as di-ureasils and termed U(2000) and U(600), is formed by poly( oxyethylene) (POE) chains of variable length grafted to siloxane domains by means of urea cross-linkages. Europium triflate, Eu(CF3SO3)(3), was incorporated in the two di-ureasil matrices with compositions 400 greater than or equal ton greater than or equal to 10, n is the molar ratio of ether oxygens per Eu3+. The SAXS data for undoped hybrids (n=infinity) show the presence of a well-defined peak attributed to the existence of a liquid-like spatial correlation of siloxane rich domains embedded in the polymer matrix and located at the ends of the organic segments. The obtained siloxane particle gyration radius Rg(1) is around 5 Angstrom (error within 10%), whereas the interparticle distance d is 25 +/-2 Angstrom and 40 +/-2 Angstrom, for U(600) and U(2000), respectively. For the Eu3+-based nanocomposites the formation of a two-level hierarchical local structure is discerned. The primary level is constituted by strongly spatially correlated siloxane particles of gyration radius Rg(1) (4-6 and 3-8 Angstrom, errors within 5%, for U(600())n Eu(CF3SO3)(3), 200 greater than or equal ton greater than or equal to 40, and U(2000)(n)Eu(CF3SO3)(3), 400 greater than or equal ton greater than or equal to 40, respectively) forming large clusters of gyration radius Rg(2) (approximate to 75 +/- 10 Angstrom). The local coordination of Eu3+ in both di-ureasil series is described combining the SAXS, photoluminescence and mid-infrared results. In the di-ureasils containing long polymer chains, U(2000)(n)Eu(CF3SO3)(3), the cations interact exclusively with the carbonyl oxygens atoms of the urea bridges at the siloxane-POE interface. In the hybrids containing shorter chains, U(600)(n)Eu(CF3SO3)(3) with n ranging from 200 to 60, the Eu3+ ions interact solely with the ether-type oxygens of the polymer chains. Nevertheless, in this latter family of hybrids a distinct Eu3+ local site environment involving the urea cross-linkages is detected when the europium content is increased up to n=40.

EXAFS, SAXS and Eu3+ luminescence spectroscopy of sol-gel derived siloxane-polyethyleneoxide hybrids

Hybrid Eu3+-doped silica-poliethyleneoxide (PEO) nanocomposites with covalent bonds between the inorganic (siloxane) and organic (PEO) phases have been obtained by sol-gel process. These materials are transparent, flexible and present high Eu3+ luminescence output. Their luminescence properties, local environment around europium ions and structure have been investigated as a function of europium content. EXAFS measurements indicate that the increase in Eu-doping induces a decrease in Eu3+ coordination number. An increase in symmetry degree around the metal ion is also observed for increasing Eu3+ concentration, while non radiative decay paths from the D-5(0) excited state become more important. SAXS results suggest the preferential interaction of europium ions with ether-type oxygens of the polymer chains. However, the existence of interactions between the cations and the carbonyl groups from urea bridges located at the siloxane-PEO interface can not be excluded.

Environmental coordination chemistry: Binary systems comprising some bivalent cations and monocarboxylates in aqueous solution. Ionic medium effects on equilibrium constants

The molar single activity coefficients associated with propionate ion (Pr) have been determined at 25 degrees C and ionic strengths comprised between 0.300 and 3.00 M, adjusted with NaClO4, as background electrolyte. The investigation was carried out potentiometrically by using a second class Hg/Hg2Pr2 electrode. It was found that the dependence of propionate activity coefficients as a function of ionic strength (I) can be assessed through the following empirical equation: log y(Pr) = -0.185 I-3/2 + 0.104 I-2. Next, simple equations relating stoichiometric protonation constants of several monocarboxylates and formation constants associated with 1:1 complexes involving some bivalent cations and selected monocarboxylates, in aqueous solution, at 25 degrees C, as a function of ionic strength were derived, allowing the interconversion of parameters from one ionic strength to another, up to I = 3.00 M. In addition, thermodynamic formation constants as well as parameters associated with activity coefficients of the complex species in the equilibria are estimated. The body of results shows that the proposed calculation procedure is very consistent with critically selected experimental data.

Study of an organically modified clay: Selective adsorption of heavy metal ions and voltammetric determination of mercury(II)

In this work, a hydrophilic clay, Na-montmorillonite from Wyoming, USA, was rendered organophilic by exchanging the inorganic interlayer cations for hexaclecyltrimethylammonium ions (HDTA), with the formulae of [(CH3)(3)N(C16H33)](+) ion. Based on fact that organo-clay has high affinities for non-ionic organic molecules, 1,3,4-thiadiazole-2,5-dithiol was loaded oil the HDTA-montmorillonite surface, resulting in the 1,3,4-thiadiazole-2,5-dithiol-HDTA-montmorillonite complex (TDD-organo-clay).The following properties of TDD-organo-clay are discussed: selective adsorption of heavy metal ions measured by batch and chromatographic column techniques, and utilization as preconcentration agent in a chemically modified carbon paste electrode (CMCPE) for determination of mercury(II).The main point of this paper is the construction of a selective sensor, a carbon paste electrode modified with TDD-organo-clay, its properties and its application to the determination of mercury(II) ions, as this element belongs to the most toxic metals. The chemical selectivity of this functional group and the selectivity of voltammetry were combined for preconcentration and determination. (c) 2005 Elsevier B.V. All rights reserved.