Is sulfur the responsible for color of yellow Chiapas Amber?

Amber is a fossilized natural resin found in specific areas of the world; its geographical origin is associated to a characteristic color. Amber all over the world share basic characteristics due to a common polymeric matrix; however, its color is associated to the environment where it was formed. In this work, based on a compositional analysis, it is proposed that yellow color of Mexican amber is originated from the sulfur physical and chemical interaction within its polymeric matrix. The effect of sulfur present in yellow Mexican amber is studied by employing X-ray photoelectron and UV-Vis spectroscopies. Results show that sulfur is incorporated inside the polymer matrix with two different chemical environments; one related with sulfur-carbon bonds and the other with sulfur-sulfur bonds. The optical transmission spectrum simulated considering amber as a composite material reproduce the scattering contribution observed experimentally.

Estudio espectroscópico de nanopartículas de plata pasivadas con el polímero conjugado PEDOT:PSS

Se sintetizaron nanopartículas de plata AgNPs a partir de nitrato de plata, empleando borohidruro de sodio como agente reductor y poli(etilendioxitiofeno):poli(estiren sulfonato de sodio), PEDOT:PSS, como estabilizador. Se variaron los siguientes parámetros de síntesis: 1) contenido relativo entre PEDOT y PSS, utilizando tres formulaciones comerciales; y 2) relación molar entre sal de plata y agente reductor. Por espectroscopia UV-Vis, se corroboró la formación de las AgNPs mediante la banda plasmónica a ~ 400 nm, además se observaron cambios espectrales para el PEDOT cuando se utilizan las formulaciones con mayor contenido de PEDOT, y relación sal/agente reductor de ~1, lo cual de acuerdo con los espectros Raman se asocia con un cambio conformacional del PEDOT hacia una estructura más benzenoide. En las demás condiciones, las propiedades espectroscópicas son similares a las de nanopartículas preparadas con puro PSS. Con base en los resultados, se plantea que las AgNPs se estabilizan con el PSS en exceso, afuera de los dominios PEDOT:PSS, cuando la formulación tiene más contenido de PSS o empleando bajas cantidades de NaBH4. Al incrementar el contenido de NaBH4, las AgNPs se forman también adentro de los dominios. El mecanismo de estabilización permite así modular las propiedades ópticas y eléctricas de las NPs.

In memoriam. Orlando Zelaya-Angel’s contributions in Superficies y Vacío

Professor Orlando Zelaya Angel was an outstanding member of the research community on Solid State Physics. He served as President to the Sociedad Mexicana de Ciencia de Superficies y Vacío (SMCSyV; currently Sociedad Mexicana de Ciencia y Tecnología de Superficies y Materiales – SMCTSM), for the period 1995-1996. Professor Zelaya formed many researchers in Mexico, who continue developing research, either in Mexico, in their countries of origin, or abroad. Throughout the evolution of Superficies y Vacío, Professor Zelaya, contributed with sixteen articles on subjects ranging from thin films for optoelectronic applications, through hard coatings and studies on the process for production of Tortillas; covering most of his research areas of interest. Here is a subject-chronological compilation of the abstracts to his articles in Superficies y Vacío, after a year of his departure.

Influence of Te layer on CdTe thin films and their performance on CdS/CdTe solar cells

CdTe semiconductor is an absorbent material used in “tandem” photovoltaic solar cells. This material is commonly deposited by thermal evaporation presenting electrical resistivity values about of 105 W·cm to 109 W·cm. CdTe is applied in thin solar cells as p-type layer which is in contact with metal back electrode in solar cells. In the CdTe/metal junction a Schottky barrier exits; and small number of charge carriers have enough energy to get over the barrier and cross to the metal back contact. To solve part of this problem, nanostructured Te thin films were used as intermediate layers between CdTe and metal contact. Te layers whit different physical properties were deposited on CdS/CdTe structure by thermal evaporation employing different growth parameters. The electrical parameters of CdTe solar cells were influenced by p+ Te regions. p+ Te regions used as intermediate layer with large deposition time increases the FF and VOC values from 30% to 60% and 560 mV to 730 mV respectively. Also, the electrical resistivity is reduced from 106 W·cm to 103 W·cm. In this sense, Te region implemented as nanostructure allows to reduce the series resistance from 99 W to 20 W and increases the shunt resistance from 1445 W to 4424 W; Te region as thin films demonstrated not be adequate.

Application of XPS and PA techniques in the study of lime used in the Talavera House from the historical center of Mexico City

X-ray Photoelectron Spectroscopy (XPS) and Photoacoustic (PA) techniques are useful to identify the structure and optical properties of chemical compounds used in archaeology, among others. In the present study XPS and PA techniques were used to analyze seven samples obtained from the Talavera House, during the conservation and restoration works carried out in the 2012-2013 period. Talavera House is located between the República del Salvador, Talavera and Roldán streets, in the historic center of Mexico City. The objective of this study was to identify the chemical compounds added to the lime when burned in the furnace and its use in the tanneries during the 18th century, both elements located in the second yard, as well as in the construction of the corridor in the 20th century located in the first courtyard. The samples were collected at these points and analyzed by XPS and Photoacoustic (PA) techniques, comparing these results with other excavated sites.

Physico-chemical and mechanical thermo-rheological characterization of three varieties of triticale starches

Nowadays, starch is an excellent biodegradable option instead of synthetic polymers, to avoid contamination. In this work, triticale starch from three varieties (Faraón, Peteroa and Aguacero) was isolated and the physico-chemical and thermo-rheological properties were evaluated. Also, mechanical properties of thermoplastic films using this starch were assessed. From the physico-chemical analysis it was found that the moisture, protein and lipids contents were slightly different among starches. Amylose value was similar. Thermo-rheological behavior measured by Mixolab® revealed that initial water uptake was higher for Faraón variety due to the grain morphology observed by Scanning Electron Microscopy (SEM). Values for gelatinization temperature obtained were 82.2 °C for Faraón starch, followed by Peteroa (72.0 °C) and finally Aguacero (65.6 °C). From the mechanical properties, Faraón thermoplastic starch (TPS) films showed the highest value of Young’s modulus (1.90 ± 1.09 MPa) for the composition 50/25/25 (starch/glycerol/water). The highest elongation at break (64.77 ± 14.14 %) was obtained for Peteroa composition 50/35/15 (starch/glycerol/water). Then, triticale mainly used to feed animals more than for human consumption, could be good alternative for preparing biodegradable films with potential applications in agriculture and food packaging.

Physico-chemical and mechanical thermo-rheological characterization of three varieties of triticale starches

Nowadays, starch is an excellent biodegradable option instead of synthetic polymers, to avoid contamination. In this work, triticale starch from three varieties (Faraón, Peteroa and Aguacero) was isolated and the physico-chemical and thermo-rheological properties were evaluated. Also, mechanical properties of thermoplastic films using this starch were assessed. From the physico-chemical analysis it was found that the moisture, protein and lipids contents were slightly different among starches. Amylose value was similar. Thermo-rheological behavior measured by Mixolab® revealed that initial water uptake was higher for Faraón variety due to the grain morphology observed by Scanning Electron Microscopy (SEM). Values for gelatinization temperature obtained were 82.2 °C for Faraón starch, followed by Peteroa (72.0 °C) and finally Aguacero (65.6 °C). From the mechanical properties, Faraón thermoplastic starch (TPS) films showed the highest value of Young’s modulus (1.90 ± 1.09 MPa) for the composition 50/25/25 (starch/glycerol/water). The highest elongation at break (64.77 ± 14.14 %) was obtained for Peteroa composition 50/35/15 (starch/glycerol/water). Then, triticale mainly used to feed animals more than for human consumption, could be good alternative for preparing biodegradable films with potential applications in agriculture and food packaging.

Desarrollo de un sustrato flexible y activo para SERS basado en nanoestructuras de metales nobles (Au y Ag)/poliestireno

La necesidad de contar con sistemas de detección altamente sensibles de moléculas orgánicas, que sean rápidos y asequibles para su uso en campo, ha empujado el desarrollo de dispositivos basados en el efecto SERS (por sus siglas en inglés: Surface-Enhanced Raman Spectroscopy). En el presente estudio se reporta la síntesis verde de nanopartículas de Au con Cymbopogon citratus y Citrus paradisi, con forma de estrella y triangulares respectivamente; así como la síntesis química de nanopartículas cúbicas de Ag. Las nanoestructuras fueron caracterizadas por medio de espectroscopia UV-vis y Microscopia Electrónica de Transmisión. Las nanoestructuras de Ag y Au fueron depositadas sobre una superficie de poliestireno acanalado, para evaluar estos sistemas como sustratos activos para SERS utilizando el azul de metileno como molécula objetivo. En todos los casos se consigue una mejora en las señales Raman características del azul de metileno, especialmente cuando se emplean las nanoestructuras con morfología tipo estrella de Au.

Pt/Ga-SBA-15 composites synthesis and characterization

Pt (0.5, 1 and 1.5 wt%) was impregnated by incipient wetness on SBA-15 and corresponding Ga-modified (3, 5, 10 and 20 wt%) composites. Gallium nitrate was incorporated directly during the mesoporous siliceous network synthesis. Materials were characterized by N2 physisorption, X-ray diffraction, Fourier transformed infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. SBA-15 had surface area greater than 800 m²/g that decreased by Ga incorporation in binary materials. It seemed that tetrahedral gallium was well-incorporated into mesoporous silica walls. Pt dispersion slightly diminished (as to that on SBA-15) by augmenting Ga concentration in composites. Corresponding pore size maxima shifted to lower diameters (as to that of non-impregnated supports) after platinum loading suggesting Pt crystals inside pores of SBA-15 and Ga-modified carriers. Large cubic platinum crystals were observed over all prepared materials probably due to sintering (during calcining at 500 °C) of metallic particles weakly interacting with the carriers surface. After materials annealing (500 °C under static air) metallic platinum was evidenced (by XRD) pointing out to noble metal reduction that could be facilitated by decomposition of organic remains from Si alkoxide used during supports synthesis which presence was ascertained by FTIR.

Insecticide activity of bifenthrin nanoparticles synthesized by laser ablation of solids in liquids

Organic nanoparticles of bifenthrin (agricultural insecticide) were successfully synthesized by the laser ablation of solids in liquids (LASL) technique, using as liquid medium a solution of a polymeric surfactant at 0.1 %. The results showed that the use of the surfactant improves the stability of the organic nanoparticles 18 times as compared to those synthesized in water. The characterization by UV-Vis spectroscopy allowed evaluating the stability of colloids, as well as determining the concentration of nanoparticles in the medium. In the characterization by TEM and HRTEM was possible to observe nanoparticles with the most probable size of 5 nm and interplanar distances which correspond to the crystalline structure of the starting material. Mass coupled gas chromatography technique was used to corroborate the chemical composition of nanoparticles. Results of biological tests using Drosophila Melanogaster fly, showed that the use of the nanostructured compound is effective in lower doses than those used in agriculture in the form of bulk material.