Platinum nanoclusters in silica: Photoluminescent properties and their application for enhancing the emission of silicon nanocrystals in an integrated configuration

"We studied photoluminescence of ion implanted platinum nanoclusters embedded in silica. Pt ions were implanted at 2 MeV and the Pt nanoclusters were then nucleated by thermal treatment under either argon, air, or a reducing atmosphere of hydrogen and nitrogen. The nanoclusters showed broad photoluminescence spectra (400 to 600 nm) with a maximum intensity at 530 nm. The photoluminescence intensity of the Pt nanoclusters was sensitive to the ion fluence used during the ion implantation, and luminescence quenching was observed in samples fabricated at high Pt-ion fluence. A hybrid system composed of silicon nanocrystals and platinum nanoclusters embedded in a silica matrix was also made. The photoluminescence of the hybrid system spanned the entire visible spectrum, and emission from the silicon nanocrystals was enhanced.

Identification of diagenetic calcium arsenates using synchrotron-based micro X-ray diffraction

"In this work, we identify the type of calcium arsenates found in sediment samples from an aquifer located in Matehuala, San Luis Potosí, México. Sediments in contact with levels up to 158 mg/L of arsenic in neutral pH water were studied by X-ray diffraction, scanning electron microscopy coupled to energy dispersive X-ray analyses (SEM-EDS), and synchrotron based X-ray diffraction. Identification of these calcium arsenates by X-ray analysis has proved to be very difficult to achieve because the precipitates of interest are on the microscale and immerse in a matrix of calcite, gypsum, and quartz comprising nearly 100 % of the samples. Needle-like specimens composed of calcium, arsenic, and oxygen were, however, commonly observed in sediment samples during SEM-EDS analyses in backscattered mode. Synchrotron based X-ray analyses revealed some peaks that were compared with published data for guerinite, haindingerite, and pharmacolite suggesting that these were the calcium arsenates present in sediments, the calcium arsenates that control the solubility of arsenic in the contaminated aquifer in Matehuala, and the calcium arsenates that prevail in the long-term in the environment after cycles of dissolution and precipitation. The identification of these calcium arsenates is consistent with the environmental conditions prevailing at the study area and the SEM-EDS observations. However, its identification is not unequivocal as the comparison of experimental data collected in single crystal specimens against X-ray diffraction references collected in powders prevents a strictly proper identification of the specimens analyzed. In this way, scorodite was also identified by synchrotron based X-ray analyses however its presence is inconsistent with the environmental conditions and the calcium arsenate associations found in this study. Scorodite identification was therefore considered tentative. A thorough examination, with additional and/or improved analytical techniques, should be undertaken to find an environmentally sound explanation for the diffraction peaks assigned to scorodite, which might be from a clay a mineral, probably with no arsenic.""En este trabajo identificamos el tipo de arseniatos de calcio que se encuentran en muestras de sedimento de un acuífero altamente contaminado con arsénico ubicado en Matehuala, San Luis Potosí, México. Los sedimentos en contacto con hasta 158 mg/L de arsénico en agua a pH neutro se estudiaron por difracción convencional de rayos X, microscopía electrónica de barrido acoplado a análisis de dispersión de energía de rayos X (SEM- EDS) y micro difracción de rayos X en sincrotrón. La identificación de arseniatos de calcio por análisis convencionales de difracción de rayos X no fue posible debido a que los especímenes de interés son de tamaño microscópico y se encuentran en una matriz de calcita, yeso y cuarzo que comprende casi el 100 % de las muestras, lo que imposibilita separar la señal de los arseniatos de la señal de la matriz y/o el ruido. No obstante, especímenes aciculares compuestos de calcio, arsénico y oxígeno se observaron comúnmente en las muestras de sedimento durante los analices SEM-EDS utilizando un detector de electrones retrodispersados. En contraste, los análisis de rayos X en sincrotrón permitieron revelar algunos picos característicos de guerinita, haidingerita y farmacolita, lo que sugiere que estos son los arseniatos de calcio presentes en los sedimentos, los arseniatos de calcio que controlan la solubilidad del arsénico en el acuífero contaminado en Matehuala y los arseniatos de calcio que prevalecen a largo plazo en el ambiente después de ciclos de disolución y precipitación. La identificación de estos arseniatos es consistente con las condiciones ambientales del sitio de estudio y las observaciones SEM-EDS, sin embargo, dicha identificación no es inequívoca debido a la comparación de patrones experimentales de difracción de rayos X tomados en monocristales contra tarjetas de difracción de polvos, lo que previene la identificación estrictamente apropiada de los especímenes analizados. En este sentido, también se identificó escorodita pero su presencia es cuestionable a pH 7 y en presencia de guerinita, haidingerita y farmacolita por lo que este último resultado debe tomarse con reserva y un estudio más profundo, con técnicas analíticas adicionales y/o mejoradas, debe llevarse a cabo para encontrarle una explicación ambientalmente consistente a los picos de difracción de rayos X asignados a la escorodita, mismos que podrían corresponder a algún mineral arcilloso que podría no contener arsénico.

Plasmonic Sensing of Aqueous-Divalent Metal Ions by Biogenic Gold Nanoparticles

Research Article Plasmonic Sensing of Aqueous-Divalent Metal Ions by Biogenic Gold NanoparticlesThe chemical interaction between biogenic gold nanoparticles (AuNPs) and several metal (II) ions can be regarded as a practical, twofold, colorimetric, and plasmon resonance sensing method for the recognition of some divalent metal ions in aqueous solutions. The green synthesized AuNPs, using Camellia sinensis as a reducing agent, were characterized by a surface plasmon resonance (SPR) using UV-Vis spectroscopy, infrared spectroscopy, and transmission electron microscopy. The AuNP colloidal solutions obtained have a pink-reddish color with SPRs centered between 529 and 536 nm. AuNPs with spherical, triangular, and hexagonal shapes were found by TEM analyses. Despite their divergent morphologies, these AuNPs can be employed as colorimetric and plasmon resonance sensors for detection of Ca2+, Sr2+, Cu2+, and Zn2+, primarily, in aqueous solutions. Sensibility studies based on molar concentrations were also performed for these metal ions. Furthermore, solid biogenic AuNPs/cellulosic biocomposites were prepared with the aim of developing portable, fast, and dependable colorimetric sensors; nevertheless, these biocomposites resulted to be good adsorbent materials of metal ions

Morphology and Solubility Products of Calcium Arsenates Found in Arsenic Contaminated Soils in an Abandoned Smelter

"The dissolution of calcium arsenates in residues released on the premises of an inactive smelter has caused high levels of arsenic pollution in the adjacent down-gradient 6 km of a perched aquifer, reaching up to 158 mg/L of dissolved arsenic, and releasing a total of 7.5 tons of arsenic in a year. We characterized the morphology of the calcium arsenates responsible of this pollution and determined their thermodynamic solubility products by (1) following the dissolution of arsenic from soil samples in batch reactors until equilibrium was reached and (2) modeling dissolution data using the geochemical code PHREEQC. Solubility product calculations took into account soil solution chemistry. Our results provide critical thermodynamic data to better understand interactions between water and arsenic containing minerals in the environment.

Obtención y caracterización de nanopartículas de plata soportadas en fibra de algodón

"En este trabajo se prepararon biocompositos de nanopartículas de plata utilizando fibra de algodón como soporte y Camellia sinensis como agente reductor. Para la preparación de los biocompositos primero se llevó a cabo la inmersión de fibras de algodón cargadas aniónicamente en una solución de iones de plata. Posteriormente se hizo una segunda inmersión de las fibras en una solución de Camellia sinensis. Los biocompositos obtenidos se caracterizaron por espectroscopia infrarroja para determinar cambios estructurales en la celulosa. Las fibras fueron observadas por las técnicas Microscopía Electrónica de Barrido de Emisión de Campo (FE-SEM) y Microscopia Electrónica de Transmisión de Emisión de Campo (FE-TEM) para determinar la impregnación de la superficie con las nanopartículas de plata y la distribución de tamaño de las mismas, obteniendo tamaños promedio de 5 y 11nm para dos diferentes muestras. Finalmente se determinaron las energías de enlace de la plata reducida por la técnica de Espectroscopia Fotoelectrónica de Rayos X (XPS), la cual mostro que se encontraban presentes en la fibra plata metálica (Ag0) y un complejo formado por plata y oxigeno (Ag-O).""In this work, silver nanoparticles biocomposite by using cotton fiber as support and Camellia sinensis as reducing agent were prepared. For biocomposite preparation, anionically charged cotton fibers were first immersed in a silver ions solution. Later, a second immersion of the fibers in a Camellia sinensis solution was done. The biocomposites were characterized by infrared spectroscopy in order to identify structural changes of cellulose. The fibers were observed in Field Emission Scanning Electron Microscopy (FE-SEM) and Field Emission Transmission Electron Microscopy (FETEM) in order to determine the surface impregnation of the fibers with Ag nanoparticles and the grain size distribution respectively, finding average sizes of 5 y 11 nm for two different probes. Finally, the binding energies of the reduced silver as measured by X-ray photoelectron spectroscopy (XPS) show that metallic silver (Ag0) and a complex of silver and oxygen (Ag-O) were presented on the fibers.

Síntesis de arseniatos de calcio (Guerinita, haidingerita y farmacolita) morfológicamente similares a los encontrados en suelos contaminados

"En el acuífero somero de Matehuala y Cerrito Blanco, en el estado de San Luis Potosí, México, se han reportado concentraciones de hasta 158 mg/L de arsénico cuya movilidad ha podido ser representada por la disolución de Ca5H2(AsO4)4·n H2O, según modelaciones hidrogeoquímicas. Con la finalidad de probar la posible precipitación de este arseniato de calcio, en este estudio se llevaron a cabo experimentos de laboratorio de precipitación de arseniatos de calcio a pH y relación molar Ca/As similares a las encontradas en el acuífero somero de Matehuala y Cerrito Blanco. Los experimentos de precipitación de arseniatos de calcio se llevaron a cabo en dos síntesis. Para la síntesis 1, se mezclaron soluciones 85.9 mM de Na2HAsO4·7H2O con suspensiones 0.93 % (m/v) de Ca(OH)2. Para la síntesis 2 se mezclaron soluciones 114.4 mM de Na2HAsO4·7H2O con suspensiones 0.97 % (m/v) de Ca(OH)2. En total, se prepararon 6 reactores que se almacenaron a temperatura ambiente por 500 h. La temperatura, las concentraciones de arsénico, calcio y pH fueron medidos a lo largo del tiempo, mientras que los precipitados obtenidos fueron identificados por análisis de difracción de rayos X (DRX) y observados por microscopía electrónica de barrido (MEB). Los resultados de DRX muestran la precipitación de un arseniato de calcio [guerinita, Ca5H2(AsO4)4·9H2O] con una estequiometría similar a la obtenida por modelación hidrogeoquímica [Ca5H2(AsO4)4·nH2O]. Adicionalmente, se obtuvieron otros dos arseniatos de calcio llamados haidingerita (CaHAsO4·H2O) y farmacolita (CaHAsO4·2H2O). La observación de los precipitados obtenidos por MEB permitió la identificación de hábitos laminares, laminares aplanados y aciculares que se asociaron a haidingerita, guerinita y farmacolita, respectivamente. La morfología de los arseniatos de calcio precipitados en este estudio coincide con la observada en arseniatos de calcio encontrados en suelos contaminados en Matehuala. Los resultados de este estudio aportan al reconocimiento morfológico de arseniatos de calcio presentes en el ambiente.""Total dissolved arsenic concentrations up to 158 mg/L have been reported in the Matehuala and Cerrito Blanco aquifer in San Luis Potosi, Mexico from the dissolution of Ca5H2(AsO4)4·n H2O, as determined by hydrogeochemical modelling. In order to test the precipitation of this calcium arsenate, in this study, calcium arsenates were synthesized at similar pH and Ca/As aquifer conditions. Precipitation experiments were carried out in two synthesis. For synthesis 1, calcium arsenates were prepared by mixing 85.9 mM Na2HAsO4·7H2O solutions with slurries of 0.93 % (w/v) Ca(OH)2. For synthesis 2, calcium arsenates were prepared by mixing 114.4 mM Na2HAsO4·7H2O solutions with slurries of 0.97 % (w/v) Ca(OH)2. A total of six reactors were prepared, they were stored at room temperature for 500 h. Temperature, arsenic, calcium concentrations and pH were measured over time while the precipitates were identified by X-ray diffraction analyses and observed by scanning electron microscopy. According to X-ray diffraction results and the experimental conditions, a calcium arsenate, namely guerinite [Ca5H2(AsO4)4·9H2O] with the predicted stoichiometry, precipitated. Additionally, other two calcium arsenate mineral phases, namely haidingerite (CaHAsO4·H2O) and pharmacolite (CaHAsO4·2H2O) precipitated. The observation of the calcium arsenates precipitates allowed the identification of laminar, platty, and acicular habits associated to haidingerite, guerinite and pharmacolite, respectively. The morphology of the calcium arsenates precipitates in this study agrees with the morphology observed in calcium arsenates found in contaminated soils in Matehuala. Results from this study contribute to the morphological identification of calcium arsenates in the environment.

Enhanced refrigerant capacity in two-phase nanocrystalline/amorphous NdPrFe17 melt-spun ribbons

"he magnetocaloric properties of NdPrFe17 melt-spun ribbons composed of nanocrystallites surrounded by an intergranular amorphous phase have been studied. The nanocomposite shows two successive second-order magnetic phase transitions (303 and 332 K), thus giving rise to a remarkable broadening (approximate to 84 K) of the full-width at the half-maximum of the magnetic entropy change curve, Delta S-M(T), with a consequent enhancement of the refrigerant capacity RC. For a magnetic field change of 2 T, vertical bar Delta S-M(peak)vertical bar = 2.1 J kg(-1) K-1 and RC = 175 J kg(-1). Therefore, the reversible magnetocaloric response together with the one-step preparation process makes these nanostructured Fe-rich alloy ribbons particularly attractive for room temperature magnetic refrigeration.

High-Pressure Synthesis of β-Ir4B5 and Determination of the Compressibility of Various Iridium Borides

"A new iridium boride, beta-Ir4B5, was synthesized under high-pressure/high-temperature conditions of 10.5 GPa and 1500 degrees C in a multianvil press with a Walker-type module. The new modification beta-Ir4B5 crystallizes in a new structure type in the orthorhombic space group Pnma (no. 62) with the lattice parameters a = 10.772(2) angstrom, b = 2.844(1) angstrom, and c = 6.052(2) angstrom with R1 = 0.0286, wR2 = 0.0642 (all data), and Z = 2. The structure was determined by single-crystal X-ray and neutron powder diffraction on samples enriched in B-11. The compound is built up by an alternating stacking of boron and iridium layers with the sequence ABA'B'. Additionally, microcalorimetry, hardness, and compressibility measurements of the binary iridium borides alpha-Ir4B5, beta-Ir4B5, Ir5B4, hexagonal Ir4B3-x and orthorhombic Ir4B3-x were carried out and theoretical investigations based on density function theory (DFT) were employed to complement a comprehensive evaluation of structure-property relations. The incorporation of boron into the structures does not enhance the compressibility but leads to a significant reduction of the bulk moduli and elastic constants in comparison to elemental iridium.

Father's occupational exposure to carcinogenic agents and childhood acute leukemia: a new method to assess exposure (a case-control study)

<p>Abstract</p> <p>Background</p> <p>Medical research has not been able to establish whether a father's occupational exposures are associated with the development of acute leukemia (AL) in their offspring. The studies conducted have weaknesses that have generated a misclassification of such exposure. Occupations and exposures to substances associated with childhood cancer are not very frequently encountered in the general population; thus, the reported risks are both inconsistent and inaccurate. In this study, to assess exposure we used a new method, an exposure index, which took into consideration the industrial branch, specific position, use of protective equipment, substances at work, degree of contact with such substances, and time of exposure. This index allowed us to obtain a grade, which permitted the identification of individuals according to their level of exposure to known or potentially carcinogenic agents that are not necessarily specifically identified as risk factors for leukemia. The aim of this study was to determine the association between a father's occupational exposure to carcinogenic agents and the presence of AL in their offspring.</p> <p>Methods</p> <p>From 1999 to 2000, a case-control study was performed with 193 children who reside in Mexico City and had been diagnosed with AL. The initial sample-size calculation was 150 children per group, assessed with an expected odds ratio (OR) of three and a minimum exposure frequency of 15.8%. These children were matched by age, sex, and institution with 193 pediatric surgical patients at secondary-care hospitals. A questionnaire was used to determine each child's background and the characteristics of the father's occupation(s). In order to determine the level of exposure to carcinogenic agents, a previously validated exposure index (occupational exposure index, OEI) was used. The consistency and validity of the index were assessed by a questionnaire comparison, the sensory recognition of the work area, and an expert's opinion.</p> <p>Results</p> <p>The adjusted ORs and 95% confidence intervals (CI) were 1.69 (0.98, 2.92) during the preconception period; 1.98 (1.13, 3.45) during the index pregnancy; 2.11 (1.17, 3.78) during breastfeeding period; 2.17 (1.28, 3.66) after birth; and 2.06 (1.24, 3.42) for global exposure.</p> <p>Conclusion</p> <p>This is the first study in which an OEI was used to assess a father's occupational exposure to carcinogenic agents as a risk factor for the development of childhood AL in his offspring. From our results, we conclude that children whose fathers have been exposed to a high level of carcinogenic agents seem to have a greater risk of developing acute leukemia. However, confounding factors cannot be disregarded due to an incomplete control for confounding.</p