G. Ortega-Zarzosa

Structural Effects of Heat-Treated Silica Xerogel Induced by Incorporation of Chlorophyll Species

Composites containing chlorophyll aggregates dispersed in amorphous silica are of interest because of their optical attractive properties. The silica powders added with chlorophyll species, prepared by the sol-gel method, were studied using X-ray diffraction, IR spectroscopy and differential temperature analysis. Silica xerogel samples were prepared using an ethanol/H2O/TEOS molar ratio of 4:11.6:1 and loaded with extracts from frozen spinach leaves. The silica xerogel microstructure of the powders was studied as a function of the annealing temperature. We found in our samples partial crystallization of the glass matrix in form of tridymite and cristobalite phases and quenching centers or nonfluorescing aggregates due to denaturation of photosystem promoted by chlorophyll decomposition after 400∘C.

Formation and characterization of γ-Fe2O3@SiO2@Ag

Fe2O3@SiO2@Ag composites were synthesized, using the coprecipitation method to obtain maghemite nanoparticles coated with SiO2 using the Stöber method to avoid the oxidation, and finally silver nanoparticles were incorporated by a chemical method. The samples were characterized by X-ray diffraction, transmission electron microscopy, IR spectroscopy and vibrating sample magnetometry.

Coesite Formation at Ambient Pressure and Low Temperatures

Partial crystallization of silica xerogel in the form of coesite has been obtained at low-pressure conditions and temperatures of , in samples containing chlorophyll aggregates dispersed in amorphous silica. Silica xerogel samples were prepared by the sol-gel method using an ethanol::TEOS molar ratio of 4:11.6:1 and loaded with extracts from frozen spinach leaves. The silica xerogel microstructure of the powders was studied as a function of annealing temperature. It was found that partial crystallization of the glass matrix in the form of coestite was obtained at lower pressure than those specified by the phase diagram. Chlorophyll aggregates were added to the starting solutions which, upon thermal treatments, form small colloidal particles in the glass matrix. The presence of coesite is corroborated by the Rietveld refinement method.

Infrared Ellipsometry Analysis of Heritage Photographic Prints

ABSTRACT Focusing on the photographic archive of Julian Carrillo (Mexico), we study and characterize the photographic processes of a set of 13 photographs dated between 1884 and 1925. By using infrared spectroscopic ellipsometry, we classified a selected set of photographs according to its kind of binder. Thus, we recognized for each photograph, the presence of proteins, and therefore, the particular photographic process. Furthermore, we have identified the presence of baryta layer, the use of plasticizer, and the eventual coating utilized to protect the photograph, whose composition was based in natural organic components, mainly shellac, beeswax, or camphor.

Thermo-Stability of Natural Products Based on Chlorophyll Species Embedded in Silica Xerogel

This work studied the thermostability and the biostability of chlorophyll species obtained from an extract of spinach leaves embedded in a silica xerogel matrix. The analysis was done by monitoring the photosystem II (PSII) using fluorescence spectroscopy. Samples were prepared using the sol gel method with a molar ratio of ethanol/H2O/TEOS of 4:11.6:1. Then, silica xerogel matrix was loaded with an extract of spinach leaves, obtained in dark conditions. The measurement of the fluorescence spectra was done at selected temperatures to the corresponding non-physiological regimen. Results indicate that the PSII band position remains unchanged when heat treatment temperature increases up 200°C. For temperatures above 100?C, the fluorescence intensity diminishes linearly when the temperature increases. The photosystem II embedded in silica xerogel matrix is decomposed at temperatures above 200°C.

Preparation and Characterization of Nickel Ferrite-SiO2/Ag Core/Shell Nanocomposites

Magnetic composites with silver nanoparticles bonded to their surface were successfully prepared using a simple chemical method. By means of a sol-gel technique, nickel ferrite nanoparticles have been prepared and coated with silica to control and avoid their magnetic agglomeration. The structural and magnetic properties of the nanoparticles were studied in function of the annealing temperature. Then, silver nanoparticles were incorporated by hydrolysis-condensation of tetraethyl orthosilicate, which contains silver nitrate on the surface of the nickel ferrite-SiO2 core/shell. Samples were characterized using X-ray diffraction, IR spectroscopy, SEM, and magnetometry. Results show that the silica covered the nickel ferrite nanoparticles and the silver nanoparticles remain stable in the surface of the composite.