Synthetic and natural iron oxide characterization through microparticle voltammetry

Se presentan los resultados de un estudio sobre el uso de la Voltametría de Micropartículas (VMP), aplicada a la identificación de óxidos y oxihidróxidos de hierro. Mediante esta técnica, fue posible diferenciar hematita, goethita, magnetita y maghemita, en muestras sintéticas y naturales. La medición de pigmentos sintéticos tratados a diferentes temperaturas, evidenció la existencia de un patrón de comportamiento que permite diferenciarlos. Se constató que la ubicación del pico de corriente (valor de potencial), varía en función de la especie mineral, el tamaño de grano y el grado de cristalinidad, el área, en relación con la concentración de especie electroactiva y el ancho, con la distribución de tamaños de partícula. En muestras con elevadas concentraciones de óxidos y oxihidróxidos de hierro, los picos se definieron a corrientes del orden de los mA (miliamperes) y en muestras de paleosuelos con un contenido de hierro total inferior al 6%, los picos se registraron a corrientes del orden de los µA (microamperes). De esta manera, se constata la posibilidad de aplicación de la técnica en estudios ambientales y paleoambientales que tengan en cuenta a estos minerales. Las principales ventajas de la VMP, respecto a los métodos convencionales, se refieren a la rapidez y simplicidad de aplicación y a la posibilidad de procesar pocos microgramos de muestra, sin limitación de su grado de cristalinidad. A diferencia de los métodos magnéticos, fuertemente condicionados por la presencia de magnetita, la VMP resulta altamente sensible a la detección de especies débilmente magnéticas.We are hereby presenting the results obtained from a study on using Microparticle Voltammetry (MPV) for identifying Iron oxides and oxy–hydroxides. This technique allowed us to distinguish different mineral species, such as hematite, goethite, magnetite and maghemite, in both synthetic and natural samples. By measuring synthetic pigments at different temperatures, evidence was found of an electrochemical behavioral pattern which allowed differenciating them. The current peak location (potential value) proved to vary according to the mineral species, grain size and chrystallinity degree. The area varies in terms of electroactive concentration of the species given. Width varies according to particle size distribution. In high iron oxide and oxy–hydroxide concentration samples, peaks were defined at current values of mA (milliampers) and in paleosol samples having an overall iron content lower than 6%, peaks were recorded at currents of µA (microampers). Therefore, a possibility arises of applying this technique to environmental and palaeo–environmental studies of these minerals. MPVs main advantages compared to conventional methods are speed and simplicity as well as the fact that it allows processing a few sample grains, in spite of its chrystallinity degree. Unlike magnetic methods – strongly influenced by the presence of magnetite– MPV is highly sensitive for detecting weakly magnetic species.Fil: Rico, Yamile. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; ArgentinaFil: Bidegain, Juan Carlos. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; ArgentinaFil: Elsner, Cecilia Ines. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Tecnología de Pinturas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones en Tecnología de Pinturas; Argentin

Paraoxonase gene polymorphisms and haplotype analysis in a stroke population

Peer reviewedPublisher PD

Electronic structure calculations of metal-nanotube contacts with or without oxygen adsorption

The Schottky barrier at the metal-nanotube contact has been a prime issue in the nanoscale devices. Here we use ab initio density-functional calculations to investigate the electronic structure and the Fermi level alignment at the metal-nanotube contacts. Consistent with the common concept of the large (small) work function of gold (aluminum) surfaces, the Fermi level of the gold layer is found to be aligned at the valence band edge, while that of the aluminum sits at the conduction band edge of the semiconducting carbon nanotube. However, upon the oxidation, the work function of aluminum surface becomes as large as that of the clean gold surface, causing the Fermi level to be aligned at the valence band edge of the semiconducting nanotube. This suggests that the carrier type of the nanotube field effect transistor could transform from n-type to p-type upon oxygen adsorption on the electrode surface. The oxidation-induced increase of the tunneling barrier is also investigated.open342

Objective optical classifier for tobacco leaves.

The main objective of the current research was to search the optimum method to segregate the most frequent color commercial quality classes of tobacco leaves (c.v. "Virginia"). These color classes cover the whole continuous color scale, between "Pale Lemon" and "Oxidated Brown". With the usual expert classification there exists a significant level of uncertainty . Within this research, several methods for data discrimination were tested, in order to solve uncertainty. Classification errors below 5% were obtained with this proposed classifier along two different seasons (1994&1995)

Editorial: biodegradable materials

This Special Issue “Biodegradable Materials” features research and review papers concerning recent advances on the development, synthesis, testing and characterisation of biomaterials. These biomaterials, derived from natural and renewable sources, offer a potential alternative to existing non-biodegradable materials with application to the food and biomedical industries amongst many others. In this Special Issue, the work is expanded to include the combined use of fillers that can enhance the properties of biomaterials prepared as films. The future application of these biomaterials could have an impact not only at the economic level, but also for the improvement of the environment

The use HPTLC and Direct Analysis in Real Time-Of-Flight Mass Spectrometry DART-TOF-MS for rapid analysis of degradation by oxidation and sonication of an azo dye

International audienceAdvanced oxidation processes are efficient for the removal of recalcitrant compounds, like azo-dyes. However, the intermediates produced during their degradation can be more toxic than the parent compounds. Improving the knowledge concerning the degradation pathways may be therefore helpful to optimize the process. In this aim, HPTLC and Direct Analysis in Real Time-Of-Flight Mass Spectrometry DART-TOF-MS were considered and applied to analyze the sono-oxidation of an azo dye, methyl red sodium salt (MRSS) as a model compound. Initial and final UV-Vis spectra showed a clear disappearance of the maximum absorption peak, but shows limit since it cannot allow by-products identification. MRSS degradation was confirmed by HPTLC, which also confirmed that MRSS degradation was mainly due to oxidation, while in the considered experimental conditions the sonication effect appeared negligible. Three major peaks were observed by DART-TOF-MS after MRSS oxidation, m/z=139.002, m/z=223.073 and m/z=279.137, Relative abundance of m/z=139.002, which was much higher after oxidation, tends to prove that a large proportion of initial oxydized MRSS was fragmented. The MRSS m/z = 270.078. The coupling of HPTLC and DART-TOF-MS may be subsequently considered to identify the oxidation reaction products