Calcium content and speciation in alkaline-cooked corn studied bysynchrotron Ca K-edge X-ray absorption spectroscopy.

Using Ca K-edge X-ray absorption spectroscopy the calcium uptake and species in alkaline corn have been studied and compared with corn starch and crystalline cellulose as main compounds in corn endosperm and pericarp. XANES data showed that calcium binds preferably to hemicelluloses in the pericarp. The main calcium species found by EXAFS in cellulose and starch is calcium carbonate although some protein-calcium species could be formed within the starch granules. From X-ray diffraction and microscopy techniques, pericarp dissolution, mainly at the amorphous hemicellulose fraction was inferred. The hemicellulose dissolution during steeping increases the apparent pericarp crystallinity, while the relative calcium content determined by XANES absorption edges reduces. XANES and EXAFS spectroscopies showed to be a valuable tool in order to determine the calcium species and to make a semiquantitative determination of calcium in the different nixtamalized corn fractions. © 2014 Elsevier Ltd

Graphene oxide powders with different oxidation degree, prepared by synthesis variations of the Hummers method

Graphene oxide (GO) powders with different oxidation degree estimated through the relative intensity of the infrared absorption bands related to oxygen containing groups were prepared through variations of the Hummers method. The GO powders were analyzed by Transmission Electron Microscopy, Energy dispersive spectroscopy, X-ray Photoelectron Spectroscopy, Fourier Transform Infrared Spectroscopy, Raman spectroscopy, X-ray Diffraction, UV-VIS spectroscopy and Electrical Resistance measurements. Several square micron GO sheets with low wrinkling were obtained. Oxygen to carbon ratio is around 0.2 in all the samples although a strong variance in the relative intensity of the oxygen related infrared bands is evident. Thus, the oxidation degree was estimated from the FTIR measurements using the quotient between the C-O related bands area to the total area under the spectra. FTIR shows presence of hydroxyl (-OH), epoxy (C-O-C), carboxyl (-COOH) and carbonyl (CO) moieties and evidence of intermolecular interactions between adjacent groups. These interactions influence the exfoliation degree, the absorbance of the GO suspensions, as well as the electrical resistance, while the crystalline domain sizes, estimated from XRD and Raman do not show a noticeable behavior related with the composition and molecular structure. The results indicate that the electrical resistance is influenced mainly by the surface chemistry of the GO powders and not only by the O/C ratio. The control of the surface chemistry of GO powders would allow their use as additives in organic bulk heterojunction solar cells with enhanced photoconversion efficiency. © 2015 Elsevier B.V. All rights reserved

X-RAY DIFFRACTION AND FOURIER TRANSFORM INFRARED SPECTROSCOPY STUDIES OF GRAPHENE OXIDE FABRICATED BY HUMMERS METHOD

Graphene is a very promising material for different applications including catalysis, biomedical research and photovoltaics between other. Graphene can be prepared from chemical modification of graphene oxide that is prepared by the Hummers method, an efficient approach to large-scale production of graphene and graphenoids materials with low cost. To achieve more exfoliated graphene oxide and to modify the functional groups that form upon oxidation, some modifications to the Hummers method have been assessed in this work. The volume of the oxidants NaNO3 and KMnO4, the pre-oxidation and oxidation times, and the washed volume were varied. NaCO3*H2O2 and NaSO3 were introduced as alternative pre-oxidants. X-ray diffraction and Fourier Transform Infrared Spectroscopy were used to evaluate the oxidation process and the quantity of the functional groups. The results show that graphene oxides prepared with NaSO3 present a higher concentration of the carboxyl and carbonyl functional groups. On the other hand, the best exfoliation level was obtained by increasing the heating period of the NaNO3+ KMnO4+ H2SO4+ H2O mixture at 98°C up to 45 minutes

Mg-doped CdS films prepared by chemical bath deposition. Optical and electrical properties

Mg-doped CdS thin films were prepared onto glass substrates by the chemical bath deposition method increasing Mg2+ contents in the chemical bath. Film composition was studied by X-ray photoelectron spectroscopy. The physical properties of the films such as the lattice parameter, crystallite size and crystal structure were studied by X-ray diffraction and the film morphology was examined by atomic force microscopy. XPS results indicate an incorporation of up to 0.27 at. %. X-ray diffraction showed that films occur primarily in the hexagonal phase. The band gap increased with the Mg2+ added to the bath. The film resistance reduced with the Mg doping and an increased photocurrent response was observed under illumination. Using photocurrent sensing atomic force microscopy (PCAFM) in selected samples, an increasing photocurrent response was measured in the grain boundaries. I-V curves in PCAFM indicate n-type doping character. © 2015, National Institute R and D of Materials Physics. All rights reserved

DFT studies on electronic and structure properties of PbSe1-xSx alloys using VCA and EBS

In this study, density functional theory has been used to investigate the structural and electronic properties of lead selenide (PbSe) and lead sulfide (PbS) semiconductors and their alloys PbSe1-xSx using the virtual crystal approximation (VCA) and random structure (RS) generations. The generalized gradient approximation (GGA) has been used to obtain lattice parameters which are compared with theory and experimental results. The generalized gradient approximation (MGGA) of TB09LDA has been used to calculate the electronic bands, for different sulfur compositions (0≤x≤1, ∆x=0.1). It has been observed that the transition from the valence band to the conduction band takes place at the L point, which agrees with previous theoretical investigations. It has been observed that both the bandgap and lattice parameters of the alloys obey Vegard\u27s law. Effective band diagrams obtained from the unfolding of supercell band diagrams, reported for the first time for this system, show that the impacts of alloy disorder are low in the vicinity of the L point, indicating that the alloy composition do not appear to influence the transport phenomena. This work shows the suitability of the VCA approximation and the band unfolding method, to deal and describe the composition-dependent properties of the PbSe1-xSx pseudo binary alloys

Dithiol-capped Cdse nanoparticle Fims prepared by a soft chemistry method.

Bulk heterojunction solar cells require adequuate concentrations of the nanoparticulated n-type semiconductor within the polymeric matrix, but also a good interfacial interaction between the. Thiol and dithiol molecules have been devised as good candidates to provide interaction betwen the components as well as electrical conduction by tunnel effect, with the advantage of polar heads that would increase nanoparticle-nanoparticles structuring in a tridimensional net

EXPERIMENTAL AND THEORETICAL STUDY OF CdS DEPOSITION BY CHEMICAL BATH

In this work experimental data from a chemical bath deposition process for CdS growth were compared against simulated data of the evolution of the concentration curves of Cd2+, S2-, and cadmium complexes (CdnOHm, Cdn(NH4)m2+, CdClm), obtained with HySS speciation software. We considered equilibrium reactions of complexes from atmospheric CO2 hydrolysis like HCO3- and CO32- on CdS formation mechanism. Series of CdS thin films were prepared in a bath containing 0.02M CdCl2, 0.5M KOH, 1.5M NH4NO3, 0.2M SC(NH2)2 at 65 ºC, compared with another growth with only CdCl2 + KOH + NH4NO3 to compare CdCO3 formation non related with thiourea hydrolysis. The model was initially feed with experimental data from the chemical bath, i.e. [NO3-] was determined by Raman spectroscopy, pH, pCd2+ and pS2- from potentiometric data. The pH evolution was reproduced almost exactly with the proposed model. Films were characterized by XRD and UV-Vis spectroscopy, Film thickness was calculated by using SCOUT software from transmittance data. CdCO3 was identified by XRD confirming the influence of atmospheric CO2 and also the data indicate an important role of the nitrate complexes in the film growth kinetics

SONOCHEMICAL-ASSISTED CuInSe2 ELECTRODEPOSITION AND ELECTROCHEMICAL POST-SELENIZATION TREATMENTS

CuInSe2 films have been prepared onto Cu substrates by an electrochemical, ultrasonic-assisted method, using a home-made potentiostat and deposition cell. Films were prepared by sweeping the potential at 5 mVs-1from 0 to -1500 mV vs SSC and left there during 15 min with ultrasonic agitation. The electrolytic bath composition was varied in order to study its effect on the phases present in the films. The precursor solutions were mixed in Cu:In:Se ratios of 1:1:1, 1:2:1 and 1:2.5:1, while the precursor concentration was varied from 1.5 mM to 4 mM, with respect to Cu. A 1 M NaCl solution was used as supporting electrolyte when needed. An electrochemical selenization procedure was done after film deposition, by immersing the films in a 1.5 mM Se electrolyte and sweeping the potential from -200 to -800 mV vs SSC and left there during 5 min. The effect of thermal annealing in N2-flux on the film structure was also assessed. Films were characterized by X-ray diffraction, Raman spectroscopy and atomic force microscopy. Ultrasonic agitation leads to compact, uniform films. Raman spectra of the as-grown films indicate the presence of In-Se and CIS in the tetragonal and cubic forms. In-rich films were obtained at the higher In ratios and precursor concentrations. The selenization treatment showed to affect the phase composition, while thermal treatment increased the crystallinity

Una caja para el Sol, hecha de casi nada: nanomateriales estructurales para fusión nuclear

Uno de los problemas más apremiantes de este siglo es el suministro sustentable de energía, pues actualmente más del 85% de la producción de energía primaria en el mundo se origina a partir de combustibles fósiles. Sin embargo, el número de candidatos no fósiles concebibles que los podrían reemplazar es muy limitado: energías renovables, fisión y fusión nuclear. En particular, el desarrollo de la tecnología de fusión nuclear, proceso mediante el cual el Sol y las estrellas generan su energía, se está desarrollando para producir energía eléctrica de manera controlada y sostenible en la Tierra. La fusión será segura al no producir desechos radiactivos, ecológicamente atractiva y su combustible, el deuterio, existe en cantidad suficiente en el agua ordinaria como para satisfacer las necesidades de energía eléctrica del mundo a la tasa actual de consumo durante millones de años. Sin embargo, los retos científicos y tecnológicos para construir y poner en operación un reactor de fusión nuclear son complejos, y su desarrollo lleva más de siete décadas de esfuerzo a nivel internacional. Tal como dijo el laureado con el premio Nobel de Física, Pierre-Gilles de Gennes, sobre la fusión nuclear: Decimos que pondremos el Sol en una caja. La idea es hermosa, el problema está en que no sabemos cómo, ni de qué hacer la caja. En este trabajo se revisan los conceptos fundamentales y los desafíos actuales alrededor de la fusión nuclear, y a continuación se describen algunos de los nuevos materiales avanzados propuestos para la construcción de reactores de fusión, en especial los que se usarían cerca de la cámara de combustible, que permitirán en principio contener el poder energético del Sol en una caja