Optical characterization of sol-gel glasses derived from Eu3+ complex-forming precursors

Fabrication of new optical devices based upon the incorporation of rare earth ions via sol-gel methods depends on elimination of dopant ion clusters and residual hydroxyl groups from the final material. The optical absorption and/or luminescence properties of luminescent rare earth ions are influenced by the local bonding environment and the distribution of the rare-earth dopants in the matrix. Typically, dopants are incorporated into gel via dissolution of soluble species into the initial precursor sol. In this work, Eu3+ is used as optical probe, to assess changes in the local environment. Results of emission, excitation, fluorescence line narrowing and lifetimes studies of Eu3+-doped gels derived from Si(OCH3)4 and fluorinated/chelate Eu3+ precursors are presented. The precursors used in the sol-gel synthesis were: tris (6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) Eu(III), Eu (III) trifluoromethanesulfonate, Eu(III) acetylacetonate hydrate, Eu (III) trifluoroacetate trihidrate, tris (2,2,6,6-tetramethyl-3,5- heptanedionate) Eu(III) and Eu(NO3)3.6H2O. The results were interpreted in terms of the evolution of the Eu3+ fluorescence in systems varying from solution to the gels densified to 800ºC. The lifetimes studies indicate that the fluorinated precursors are effective at reducing the water content in densified gels.

Connectivity in sol-gel silica glasses

In this work it is carried out a review on structural parameters related to the evaluation of pore connectivity of nanostructures. The work describes parameters and methods of evaluation of geometric parameters. The concepts of connectivity are applied to silica gels and glasses obtained from sol-gel process. The study of pores connectivity was carried out using a combination of geometric modeling and experimental evaluation of specific surface area and pore volume. The permeability of the pore structure is evaluated and a permeability geometric factor, Pg, is proposed.

Dióxido de titânio sol-gel: propriedades e comportamento eletrocrômico

Titanium dioxide was prepared by hydrolysis and polycondensation of titanium tetraisopropoxide. TiO2 films were obtained by spin coating of the precursor solution on ITO substractes (glass covered with indium doped tin oxide). Films were prepared using different temperatures and hydrochloric acid contents. The effect of the drying temperature of the films (100 or 400ºC) was also investigated. TiO2 films were characterized by cyclic voltammetry, chronoamperometry, ultraviolete-visible spectroscopy, scanning electron microscopy and X-ray diffractrometry.

Influência da catálise ácida e básica na preparação da sílica funcionalizada pelo método sol-gel

Some aspects of the chemistry involved in the preparation and characterization of functionalized silicon oxide by sol-gel method are considered in this work. The synthesis was performed with different silicon alcoxide precursors and the influence of the acid and basic catalyst was investigated. Characterization was performed by infrared absorption spectroscopy, elemental analysis and 29Si NMR. Infrared data show Si-C and -CH2- vibrational modes at 1250 to 1280 and 2920 to 2940 cm-1, respectively. The elemental analysis confirmed the presence of organic groups in the inorganic silica network. 29Si NMR results show different hydrolisys depending on the acid or base catalysis.

Caracterização textural e estrutural de V2O5/TiO2 obtidos via sol-gel: comparação entre secagem convencional e supercrítica

This work describes a modified sol-gel method for the preparation of V2O5/TiO2 catalysts. The samples have been characterized by N2 adsorption at 77K, x-ray diffractometry (XRD) and Fourier Transform Infrared (FT-IR). The surface area increases with the vanadia loading from 24 m² g-1, for pure TiO2, to 87 m² g-1 for 9wt.% of V2O5. The rutile form is predominant for pure TiO2 but became enriched with anatase phase when vanadia loading is increased. No crystalline V2O5 phase was observed in the catalysts diffractograms. Two species of surface vanadium observed by FT-IR spectroscopy a monomeric vanadyl and polymeric vanadates, the vanadyl/vanadate ratio remains practically constant.

A utilização de materiais obtidos pelo processo de sol-gel na construção de biossensores

The use of sol-gel materials to develop new biosensors has received great attention due to its characteristics and versatility of sol-gel process. An overview is presented of the state-of-the-art of electrochemical biosensors employing sol-gel materials. Low-temperature, porous sol-gel ceramics represent a new class for the immobilization of biomolecules. The rational design of sol-gel sensing materials, based on the judicious choice of the starting alkoxide, encapsulated reagents, and preparation conditions, allows tailoring of material properties in a wide range, and offers great potential for the development of electrochemical biosensors.

Síntese de membranas cerâmicas via método sol-gel utilizando TEOS e N,N-dimetilformamida

In this work we obtained microporous and mesoporous silica membranes by sol-gel processing. Tetraethylortosilicate (TEOS) was used as precursor. Nitric acid was used as catalyst. In order to study the affect of N,N-dimethylformamide (NDF) as drying additive, we used a molar ratio TEOS/NDF of 1/3. The performance of N,N-dimethylformamide was evaluated through monolithicity measurements. The structural evolutions occurring during the sol-gel transition and in the interconnected network of the membranes during thermal treatment were monitored by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyses and nitrogen sorption. We noted that in the presence of N,N-dimethylformamide, polymerization goes through a temporary stabilization of oligomers. The Si-O(H) bonds are stronger and belong to a more cross-linked structure for the N,N-dimethylformamide containing sol. The membranes obtained in the presence of N,N-dimethylformamide have larger surface area and its pore structure is in the range of mesoporous. The membranes obtained without additive have pore structure in the range of microporous.

A new experimental procedure to obtain titania powders as anatase phase by a sol-gel process

Titania powders were synthesized by a sol-gel process using titanium tetrabutoxide as precursor. The syntheses were performed in water or in solutions of dimethylformamide (dmf) or dimethylsulfoxide (dmso). It is demonstrated, by X-ray diffraction patterns of the synthesized powders, that the samples obtained in dmf or dmso solutions are crystalline (anatase phase) with some minor amount of brookite phase, whereas the sample synthesized in water is amorphous. The anatase phase can be obtained independently of any previous or further treatment of the synthesized powder, such as hydrothermal or heat treatment, providing a new, simple, quick and inexpensive route to synthesize anatase powders. From the peak broadening of the anatase (101) diffraction, the crystallite sizes were calculated as 6 nm.

La continuidad de una obra medieval: azud, acequias, molinos y pesquera del Bajo Ebro en la época del Renacimiento

La cita que sirve de título a este epígrafe introductorio es del picapedrero aragonés Sebastián Martínez. Forma parte de un informe, redactado en 1556, sobre la construcción de una acequia en el margen izquierdo del Ebro. Y parece ser que pese a la voluntad del maestro muy poca gente, experta o no en el arte del"livell", ha sentido la necesidad de conocer las conclusiones de su estudio, como tampoco se ha sentido apenas la necesidad de estudiar el proceso constructivo del sistema de riego del curso bajo de este río, conocimiento o, más bien, desconocimiento anclado durante muchos años en las teorías que relacionaban su erección con la tecnología de época andalusí.

Alcóxidos como precursores na síntese de novos materiais através do processo sol-gel

An overview about the role of alkoxides in the most recent uses of the sol-gel process in the synthesis of new materials is presented. Special attention is focused on the uses of silicon, aluminum, zirconium and titanium alkoxides. This review shows that the alkoxides enable the synthesis of new matrices with controlled surface area, acidity and porosity, as well as some unusual properties. The property associated with the solubility of metal alkoxides opens enormous possibilities of combining them for the synthesis films of powders with a very large range of metal compositions.

El sol té efectes negatius retardats sobre la pell

PRENDRE EL SOL POT SER UNA ACTIVITAT molt plaent. Tanmateix, la radiació ultraviolada pot esdevenir carcinògena, atesa la seva capacitat d'induir mutacions en l'ADN, motiu pel qual sempre s'ha de prendre amb moderació i utilitzar una crema protectora adequada. Els rajos solars més mutagènics són els ultraviolats de tipus B (UVB), atès que són més energètics. Provoquen mutacions de forma gairebé instantània, de manera que quan deixem de prendre el sol tenim la sensació d'estar protegits. Però un treball publicat a Science demostra que els UVA, que tradicionalment s'han percebut com a menys nocius i per això són els que emeten les làmpades solars per bronzejar-se, també són mutagènics, tot i que actuen de manera diferent dels UVB. La seva capacitat per induir mutacions no és instantània, sinó que perdura fins a tres hores després que hàgim deixat de prendre el sol.

Quimioluminiscencia electrogenerada del luminol usando electrodos de bajo costo

The purpose of the study was to observe eletrogenerated chemiluminescence (ECL) of luminol using different materials as electrodes such as wires, nails, coins, razor blades, etc. Based on the experimental observations and the mechanisms proposed in the literature, students should be capable of analyzing their results in order to understand the phenomena studied. Students could then elaborate a mechanism of action consistent with the experimental results which could rationalize the formation of intermediates in the reaction and the dependence of ECL on solution pH in addition to other points of interest

Guia temàtica Biblioteca ETSAB: Ignasi de Solà-Morales: itineraris intel·lectuals

Postprint (author’s final draft)