Luminescent multifunctional hybrids obtained by grafting of ruthenium complexes on mesoporous silica

This work evaluates the luminescent properties of new hybrids obtained by covalent grafting of ruthenium complexes on mesoporous silica particles. Spray pyrolysis afforded the mesoporous silica particles in one step; two different types of structure-directing agents were employed. Scanning and transmission electron microscopy (SEM and TEM, respectively) analyses confirmed that the particles had spherical morphology and ordered hexagonal mesoporosity (2 and 5nm), which justified the high surface area up to 1420m2g-1 measured by Brunauer-Emmett-Teller (BET) surface area analysis. Covalent grafting of silylated ruthenium(II) complexes [Ru(bpy)21]Cl2 and [Ru(bpy)22]Cl2 on the mesoporous particles gave monolayered hybrids, characterized by fourier transform infrared spectroscopy (FTIR), TEM, and photoluminescence. Results highlighted the formation of new luminescent platforms containing an estimated 0.11mmol of ruthenium(II) complex per gram of silica, which corresponded to 0.09 ruthenium(II) complex nm−2 of silica

Orange emission in Pr3+-doped fluoroindate glasses

We synthesize and study the properties of praseodymium doped fluoroindate glasses. Glass compositions with praseodymium molar concentrations up to 5% were obtained with good optical quality. Thermal, optical, and luminescence properties are investigated. Judd–Ofelt analysis is used to determine radiative lifetime and emission cross-section of the orange transition originating from the 3P0 level. We find that these glasses are good candidates for the realization of blue diode laser pumped orange lasers for quantum information processing applications

Orange Pectin Mediated Growth and Stability of Aqueous Gold and Silver Nanocolloids

International audienceThe role of orange based pectin in the nucleation and growth of silver and gold nanoparticles is addressed. Pectin is a complex polysaccharide found in fruits such as oranges, lemons, passion fruits or apples. It displays smooth and hairy chain regions contg. hydroxyl-​, ester-​, carboxylate- and eventually amine groups that can act as surface ligands interacting under various pH conditions more or less efficiently with growing nanometals. Here, a high methoxy pectin (>50​% esterified) was used as a stabilizer​/reducing agent in the prepn. of gold, silver and silver-​gold nanoparticles. Com. pectin (CP) and pectin extd. from orange bagasse (OP) were used. Optionally, trisodium citrate or oxalic acid we used to reduce AgNO3 and HAuCl4 in aq. environment. Characterization methods included UV-​vis absorption spectroscopy, transmission electron microscopy, electron diffraction and energy-​dispersive X-​ray spectroscopy. The results show that under different pH conditions, pectin and reducing agents allow producing various nanostructures shapes (triangles, spheres, rods, octahedrons and decahedrons) often with high polydispersity and sizes ranging between 5 nm and 30 nm. In addn., depending on Ag​/Au-​ratio and pH, the surface plasmon bands can be continuously shifted between 410 nm and 600 nm. Finally, pectin seems to be a highly efficient stabilizer of the colloidal systems that show a remarkable stability and unchanged optical spectral response even after five years

A História da Alimentação: balizas historiográficas

Os M. pretenderam traçar um quadro da História da Alimentação, não como um novo ramo epistemológico da disciplina, mas como um campo em desenvolvimento de práticas e atividades especializadas, incluindo pesquisa, formação, publicações, associações, encontros acadêmicos, etc. Um breve relato das condições em que tal campo se assentou faz-se preceder de um panorama dos estudos de alimentação e temas correia tos, em geral, segundo cinco abardagens Ia biológica, a econômica, a social, a cultural e a filosófica!, assim como da identificação das contribuições mais relevantes da Antropologia, Arqueologia, Sociologia e Geografia. A fim de comentar a multiforme e volumosa bibliografia histórica, foi ela organizada segundo critérios morfológicos. A seguir, alguns tópicos importantes mereceram tratamento à parte: a fome, o alimento e o domínio religioso, as descobertas européias e a difusão mundial de alimentos, gosto e gastronomia. O artigo se encerra com um rápido balanço crítico da historiografia brasileira sobre o tema

Crystallization of ZrF4-LaF3-AlF3 glasses

0.7125ZrF4-0.2375(1 - xLaF3 • xLnF3)-0.05AIF3 with x = 0.01, 0.02 and 0.03 for Ln = Er and x = 0.03 for Ln = Pr, Nd glasses were studied by differential thermal analysis (DTA), X-ray diffraction and optical spectroscopy. Avrami parameters (Ec and n) were obtained from DTA curves. With La3+ substitution a decrease in the stability against crystallization was observed. This decrease follows the order Er3+ > Nd3+ ≈ Pr3+ for 3% molar substitution. n values suggest an interface controlled growth mechanism with grain edge nucleation abler saturation. Two crystalline polymorphs of the LaZr3F15 phase were identified. With the substitution of 3 mol% of Pr3+, Nd3+ or Er3+ for La3+ only the crystallization of the rhombohedral α-LnZr3F15 phase was observed. An increase in Ω6 Judd's intensity parameter occurs with crystallization and also an increase in the 1.04 μm peak emission cross-section for Nd3+ 4I3/2 state suggesting the potential application of these glass ceramics in optical amplification devices. © 1997 Elsevier Science B.V

Viscosity of fluoroindate glasses

The viscosity of two fluoroindate glasses was measured as a function of temperature in the range of 310 °C - 362 °C. In such interval, the viscosity values were found to be similar to those reported for fluorozirconate glasses. The log η - 1/T plots had an unexpected behavior: two viscosity regions that seem to obey Arrhenius equation were identified and the activation energy for viscous flow (EA) for the region near Tg is smaller than the value found above the transition range. This behavior is probably due to structural changes occurred around Tg. The low values of the activation energy for viscous flow obtained for the indium fluoride-based glasses studied, suggest a good resistance against the devitrification process, what can make them suitable for fiber preparation

Optical properties of ZrO2, SiO2 and TiO2-SiO2 xerogels and coatings doped with Eu3+ and Eu2+

Eu3+ doped bulk monoliths and thin films were obtained by sol-gel methods in the ZrO2, SiO2 and SiO2-TiO2 systems. Eu3+ 5D0 <FONT FACE="Symbol">®</font> 7FJ emission and decay time characteristics were measured during the entire experimental preparation route from the initial sol to the final xerogels. The crystalline phases identified were tetragonal ZrO2 and mixtures of rutile and anatase TiO2 at high temperature treatments in bulk samples. Good quality thin films were obtained for all systems by dip-coating optical glasses (Schott BK270). The same spectroscopic features were observed either for the bulk monoliths or the films. By appropriate heat treatments under H2 atmosphere Eu2+ containing samples could be obtained in the SiO2-TiO2 system

Bacterial cellulose from glucanacetobacter xylinus: Preparation, properties and applications

This chapter deals with the cellulose produced by the Glucanacetobacter xylinus strain, called bacterial cellulose, which is a remarkably versatile biomaterial usable in wide variety of domains, such as papermaking, optics, electronics, acoustics, and biomedical devices. Its unique structure shows entangled ultrafine fibers, which provide excellent mechanical strength, besides biodegradability, biocompatibility, high water-holding capacity, and high crystallinity. Some of its applications are described, such as complementary nutrition (. nata de coco), artificial temporary skin for wounds and burns, dental aid, artificial blood vessels and micronerve surgery, DNA separation, composite reinforcement, electronic paper, light emitting diodes, and fuel cell membranes. © 2007 Elsevier Ltd. All rights reserved

SnO2:Eu nanocrystallites in SnO2 monolithic xerogels

By simple room temperature broad band time-resolved spectroscopy it was possible to discriminate different Eu3+ spectra in SnO2 monolithic gels obtained by a sol-gel synthetic route. Nanocrystalline domains of the cassiterite-like SnO2:Eu could be easily identified in the transparent medium. From X-ray diffraction profiles a mean particle radius of 2.2 nm was estimated. © 1992

Zirconium-methacrylate oxoclusters as new hybrid materials for the modification of epoxy systems

International audienceOxozirconium clusters bearing methacrylate moiety (ZrMe) were synthesized by sol-gel process and used in epoxy networks to develop epoxy-based nanocomposites with potential application as encapsulant for light-emitting diode. Diglycidyl ether of bisphenol A-based epoxy resin was previously functionalized with acrylic acid to introduce some vinyl groups in the matrix and improve its interaction with the oxocluster. The ZrMe particles were previously dispersed in the epoxy matrix or in the 4-methyl-tetrahydrophthalic anhydride used as hardener, and the systems were cured with anhydride or with a combination of anhydride and benzoyl peroxide. The last compound promotes the covalent bond between the epoxy matrix and the ZrMe through free radical reactions between the vinyl groups. The dispersion of ZrMe into the epoxy matrix resulted in a significant increase in viscosity, mainly for systems dispersed with a combination of high shear mechanical mixing and ultrasonification. The dispersion of ZrMe into the anhydride resulted in nanocomposites with higher transparency, better dispersion of the oxocluster into the matrix bulk, as observed by transmission electron microscopy, and higher thermal conductivity, mainly for systems cured with anhydride and peroxide. The use of anhydride in combination with BPO also resulted in significant increase in glass transition temperature