Sensores eletroquímicos baseados em eletrodos de pasta de carbono modificados pela adição de precursores de silicatos de bário dopados com Európio (III)

Pós-graduação em Química - IBILCE

Luminescência em sistemas coloidais polifosfato-polioxometalatos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Preparação e caracterização de filmes óxidos contendo componentes opticamente ativos

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

Role of the reactive atmosphere during the sol-gel synthesis on the enhancing of the emission quantum yield of urea cross-linked tripodal siloxane-based hybrids

Transparent monoliths and films of urea cross-linked tripodal siloxane-based hybrids (named tri-ureasils) were prepared by the sol-gel process, under controlled atmosphere (inside a glove box) and ambient conditions and their structure and optical features were compared. X-ray diffraction data point out that all the materials are essentially amorphous and Si-29 NMR reveal an increase in the condensation degree (0.97) for the hybrids prepared under controlled atmosphere relatively to that found for those prepared under ambient conditions (0.84-0.91). The tri-ureasils are white light emitters under UV/Visible excitation (from 250 to 453 nm) being observed for the composites prepared inside the glove box a significant enhancement (60-80 %) of the absorption coefficient and higher emission quantum yield values (similar to 0.27 and similar to 0.20 for monoliths and films, respectively) relatively to those synthesized under ambient condition.

Preparação e caracterização de vidros contendo nanopartículas de Ag

This work consists of preparation and characterization of glasses containing transition noble metals and the study of optical properties of such materials. The glasses were prepared by quenching of the glass melt followed by heat treatment and polishing of the monoliths. The structural characterization of glasses was made using differential thermal analysis, X-ray, Raman and infrared spectroscopies, while the optical properties were studied by UV-Vis and M-Lines spectroscopies. Preliminary results have shown that the color of the glasses is dependent on both concentration of silver and the melting temperature of the melt. Controlled heat treatments have been used to induce the crystallization of Ag nanoparticles within the glass. The study of crystallization was accompanied by electron microscopy and UV-Vis spectroscopy. Data from electron diffraction, as well as chemical analysis, EDX, were obtained using a transmission electron microscope. EDX data have shown that the atomic percentage of Ag is higher on the nanoparticle. X-ray diffraction was used in order to characterize the composition of the crystals and cubic AgCl was identified as the main crystallized nanophase obtained after annealing

Propriedades estruturais de géis de sílica preparados com adições de dodecil sulfato de sódio

This work aims to study the structural characteristics of silica gels obtained from the acid hydrolysis of tetraethoxysilane (TEOS) in water solutions with different concentrations of sodium dodecyl sulfate (SDS). The structural characteristics were studied in stages ranging from the wet gel to the dry stages of the gels (aerogels and xerogels). Aerogels were obtained by ambient pressure drying (APD) after silylation process using trimethylchlorosilane (TMCS) as silylating agent. Xerogels were obtained by conventional evaporating the liquid phase from non silylated gels. The samples were characterized by nitrogen adsorption and small angle X-ray scattering (SAXS). The structure of the wet gels and of the aerogels prepared with the surfactant exhibited characteristics of mass-fractal structures with fractal dimension D in the range 2.1-2.2 for the wet gels and 2.3-2.4 for the aerogels. The characteristic size  of the fractal domain reduces while the size a0 of the primary silica particle composing the fractal structure increases with the drying of the gels, in a process in which share of the porosity is eliminated. Aerogels exhibited typical values for the specific surface of 900 m2g-1 and of 3.5 cm3.g-1 for the total pore volume. These values are correspondingly comparable to those of the aerogels prepared by supercritical drying, since the silylation process replaces hydrophilic –OH groups by hydrophobic –Si-R3 ones, inhibiting the porosity elimination on drying. The silica particle size also increases lightly with the silylation because the attachment of the –Si-R3 groups on the silica surface. The pore size distribution curves of the aerogels are similar for all samples exhibiting a maximum in around 40 nm, independent the concentration of surfactant. This suggests that the characteristic size of 40 nm is due to the association of surfactant micelles... (Complete abstract click electronic access below)

Optical filters and resonant cavities based on di-ureasil organic–inorganic hybrids

Sol–gel derived poly(oxyethylene)/siloxane organic–inorganic di-ureasil hybrids containing different amounts (20–60% mol) of methacrylic acid (McOH) modified zirconium oxo-clusters (Zr-OMc) were processed as thin films and transparent and shape controlled monoliths. Laser direct writing was used to create channel waveguides, Bragg gratings, Fabry–Perot cavities and optical filters. The resulting Fabry–Perot optical cavity displays a free spectral range of 16.55 GHz and a fringe intensity contrast of 5.35 dB. Optical rejection values between 6.7 and 10.4 dB were obtained by varying the amount of the Zr-OMc oxo-clusters.

Nanostructured TiO2-based composites for light absorption

Metal oxidenanocomposites were prepared by two different routes: polyol and sol-gel. Characterization by X ray diffraction showed that the first processproducesdirectly a two-phase material, while the sol-gelpowder never showed second phase below 600 degrees C. Light spectroscopy of the treated powders indicated similarities for the processed materials. Although the overall material compositions are about the same, different structural characteristics are found for each processing. With the exception of Ti-Zn materials, all the double metal oxide powders showed higher absorbance than either TiO2 powder.

Aluminas macro-mesoporosas produzidas pelo método sol-gel para aplicação em catálise heterogênea

Pós-graduação em Química - IQ