Magnetic and optical characterization of Mn-doped PbS nanocrystals supported in oxide glass matrix

The evidence of successful growth of Mn-doped PbS (Pb(1-x)Mn(x)S) nanocrystals (NCs) in SiO(2)-Na(2)CO(3)-Al(2)O(3)-PbO(2)-B(2)O(3) template, using the fusion method, is reported on in this study. The as-grown Pb(1-x)Mn(x)S NC is characterized using optical absorption, electron paramagnetic resonance, and atomic force microscopy. The data are discussed in terms of two distinct scenarios, namely a core-doped and a shell-doped nanostructure. (C) 2008 Elsevier B.V. All rights reserved.

A geochemical and lead isotopic record from a small pond in a remote equatorial island, Fernando de Noronha, Brazil

A 72 cm long core was collected from Lagoa da Viracao (LV), a small poind in the Fernando de Noronha island, northern Brazil. Sediments from the lower section of the core (20-72 cm depth) contain essentially mineral matter, while in the upper section (0-20 cm depth) mineral matter is mixed with organic matter. Lithogenic conservative elements - Si, Al, Fe, Ti, Co, Cr, Cu, Ba, Ga, Hf, Nb, Ni, Y, V, Zn, Zr and REE - exhibit remarkably constant values throughout the core, with concentrations similar to those of the bedrock. The vertical distribution of soluble elements - Ca, Mg, Na, K, P, Mn and Sr - is also homogeneous, but these elements are systematically depleted in relation to the bedrock. LOI, TOC, Br, Se, Hg and Pb, although showing nearly constant values in the lower section of the core, are significantly enriched in the upper section. The concentration profiles of Br and Se suggest that they may be accounted for by natural processes, related to the slight affinity of these elements for organic matter. On the other hand, the elevated levels of Hg and Pb in recent sediments may be explained by their long-range atmospheric transport and deposition. Furthermore, the isotopic composition of Pb clearly indicates that anthropogenic sources contributed to the Pb burden in the uppermost pond sediments.

Water-soluble Cu, Fe, Mn and Zn species in nuts and seeds

An approach was developed to estimate molecular weight distribution of water-soluble Cu, Fe, Mn and Zn species in Brazil nut, cupuassu seed and coconut pulp by size exclusion chromatography (SEC) coupled on-line to ultra-violet (UV) and off-line to graphite furnace atomic absorption spectrometry (GF-AAS) detectors and matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF-MS). SEC-UV analytical signals showed the prevalence of high molecular weight (HMW) species (79-1.7 kDa for Brazil nut, 50-1.7 kDa for coconut pulp, and 34-1.7 kDa for cupuassu seeds). The Brazil nut SEC-UV, GF-AAS and MALDI-TOF mass spectra gave confirmation of the association of the elements with water-soluble compounds. The elemental profiles were associated with fractions of compounds of molecular weight 1.2-16 kDa for Brazil nut, 1.7-13 kDa for coconut pulp, and 1.2-7.6 kDa for cupuassu seeds. (C) 2009 Elsevier Inc. All rights reserved.

Formation of out of plane oxime metallacycles in [Cu(2)] and [Cu(4)] complexes

The reaction Of Cu(ClO(4))(2)center dot 6H(2)O with dimethylglyoxime (H(2)dmg) in a 1:1 mole ratio in aqueous methanol at room temperature affords the dinuclear complex [Cu(2)(mu-Hdmg)(4)] (1). Reaction of 1 with [Cu(bpy)(H(2)O)(2)](ClO(4))(2) (bpy = 2,2`-bipyridine) in a 1:1 mole ratio in aqueous methanol at room temperature yields the tetranuclear complex [Cu(2)(mu-HdMg)(2)(mu-dMg)(2)(bpy)(2)(H(2)O)(2)](ClO(4))(2) (2). The direct reaction of Cu(ClO(4))(2)center dot 6H(2)O with H(2)dmg and bpy in a 2:21 mole ratio in aqueous methanol at room temperature also yields 2 quantitatively. The complexes 1 and 2 were structurally characterized by X-ray crystallography. Unlike the binding in Ni/Co-dmg, two different types of N-O bridging modes during the oxime based metallacycle formation and stacking of square planar units have been identified in these complexes. The neutral dinuclear complex 1 has CuN(4)O coordination spheres and complex 2 consists of a dicationic [Cu(2)(mu-HdMg)(2)(mu-dMg)(2)(bpy)(2)(H(2)O)(2)](2+) unit and two uncoordinated ClO(4)(-) anions having CuN(4)O and CuN(2)O(3) coordination spheres. The two copper(II) ions are at a distance of 3.846(8) angstrom in 1 for the trans out of plane link and at 3.419(10) and 3.684(10) angstrom in 2 for the trans out of plane and cis in plane arrangements, respectively. The average Cu-N(oxime) distances are 1.953 and 1.935 angstrom, respectively. The average basal and apical Cu-N(oxime) distances are 1.945, 2.295 and 2.429 angstrom. The UV-Vis spectra of 2 is similar to the spectrum of the reaction mixture of 1 and [Cu(bpy)(H(2)O)(2)](2+). Variable temperature magnetic properties measurement shows that the interaction between the paramagnetic copper centers in complex I is antiferromagnetic in nature. The EPR spectra of frozen solution of the complexes at 77 K consist of axially symmetric fine-structure transitions (Delta M(S) = 1) and half-field signals (Delta M(S) = 2) at ca. 1600 G, suggesting the presence of appreciable Cu-Cu interactions. (C) 2009 Elsevier Ltd. All rights reserved.

Group 11 (Cu, Ag, Au) promotion of 15%Co/Al(2)O(3) Fischer-Tropsch synthesis catalysts

Co/Al(2)O(3) Fischer-Tropsch synthesis catalysts promoted with different quantities of Group 11 metals (Cu, Ag, Au) were characterized and tested. The presence of relatively small quantities of such metals enhanced Co reducibility and, in the cases of Ag and Au, improved the surface Co metal active site densities. EXAFS experiments with the most loaded catalyst samples show that only Co-Co and Me-Me (Me = Cu, Ag and Au) coordination could be observed. This suggests that the greater fraction of the metals form different phases. However, the reduction promoting effect of the Group 11 metal is severely hampered once the catalyst receives a mild passivation treatment following primary reduction. An explanation in terms of promoter segregation during primary reduction is proposed. At lower promoter levels (0.83%Ag and 1.51%Au) and higher Ag levels (2.76%), significant gains in Co active site densities were achieved resulting in improved CO conversion levels relative to the unpromoted catalyst. Moreover, slight decreases in light product (e.g., CH(4)) selectivity and slight increases in C(5)+ selectivity were achieved. At high Au loading (5.05%), however, too much Au was loaded which, although significantly increasing the fraction of Co reduced, blocked Co surface sites and resulted in decreased Co conversion rates. While Cu facilitated Co reduction, the increased fraction of reduced Co did not translate to improved active site densities. It appears that a fraction of Cu tended to cover the rim of Co clusters, resulting in decreases in CO conversion rates and detrimental increases in light product selectivity. (C) 2009 Elsevier B.V. All rights reserved.

Production of hydrogen via steam reforming of biofuels on Ni/CeO(2)-Al(2)O(3) catalysts promoted by noble metals

The catalytic activity of Ni/CeO(2)-Al(2)O(3) catalysts modified with noble metals (Pt, Ir, Pd and Ru) was investigated for the steam reform of ethanol and glycerol. The catalysts were characterized by the following techniques: Energy-dispersive X-ray, BET, X-ray diffraction, temperature-programmed reduction, UV-vis diffuse reflectance spectroscopy and X-ray absorption near edge structure (XANES). The results showed that the formation of inactive nickel aluminate was prevented by the presence of CeO(2) dispersed on alumina. The promoting effect of noble metals included a decrease in the reduction temperatures of NiO species interacting with the support, due to the hydrogen spillover effect. It was seen that the addition of noble metal stabilized the Ni sites in the reduced state along the reforming reaction, increasing the ethanol and glycerol conversions and decreasing the coke formation. The higher catalytic performance for the ethanol steam reforming at 600 degrees C and glycerol steam reforming was obtained for the NiPd and NiPt catalysts, respectively, which presented an effluent gaseous mixture with the highest H(2) yield with reasonably low amounts of CO. (c) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Effects of adding La and Ce to hydrotalcite-type Ni/Mg/Al catalyst precursors on ethanol steam reforming reactions

Catalyst precursors composed of Ni/Mg/Al oxides with added La and Ce were tested in ethanol steam reforming (ESR) reactions. La and Ce were added by anion-exchange. The oxides were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) analysis. The catalyst precursors consist of a mixture of oxides, with the nickel in the form of NiO strongly interacting with the support Mg/Al. The XPS analysis showed a lanthanum-support interaction, but no interaction of Ce species with the support. The reaction data obtained with the active catalysts showed that the addition of Ce and La resulted in better H(2) production at 550 degrees C. The CeNi catalyst provided the higher ethanol conversion, with lower acetaldehyde production, possibly clue to a favoring of water adsorption on the weakly interacting clusters of CeO(2) on the surface. (C) 2010 Elsevier B.V. All rights reserved.

Reduction of NO by CO on Cu/ZrO(2)/Al(2)O(3) catalysts: Characterization and catalytic activities

ZrO(2), gamma-Al(2)O(3) and ZrO(2)/gamma-Al(2)O(3)-supported copper catalysts have been prepared, each with three different copper loads (1, 2 and 5 wt%), by the impregnation method. The catalysts were characterized by nitrogen adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) with H(2), Raman spectroscopy and electronic paramagnetic resonance (EPR). The reduction of NO by CO was studied in a fixed-bed reactor packed with these catalysts and fed with a mixture of 1% CO and 1% NO in helium. The catalyst with 5 wt% copper supported on the ZrO(2)/gamma-Al(2)O(3) matrix achieved 80% reduction of NO. Approximately the same rate of conversion was obtained on the catalyst with 2 wt% copper on ZrO(2). Characterization of these catalysts indicated that the active copper species for the reduction of NO are those in direct contact with the oxygen vacancies found in ZrO(2). (C) 2009 Published by Elsevier Ltd.

Estudo experimental e teórico das propriedades magnéticas e supercondutoras dos compostos borocarbetos da série Y(Ni 1-x Mn x) 2 B2 C com x = 0,0, 0,01, 0,025, 0,05, 0,10 e 0,15

Apresentamos neste trabalho os resultados de um estudo experimental e teórico dos compostos borocarbetos supercondutores da série Y(Ni1-xMnx)2B2C com x = 0; 0,01; 0,025; 0,05; 0,10; 0,15. A principal motivação para este trabalho foi investigar a estrutura eletrônica e a possível formação do momento magnético sobre os átomos de impureza de Mn nos compostos Y(Ni1- xMnx)2B2C. O aparecimento do momento magnético localizado no sítio da impureza possibilitou estudar a influência do Mn sobre o mecanismo de quebra de pares supercondutores e sobre as propriedades magnéticas do composto. Os borocarbetos são compostos de estrutura cristalina tetragonal de corpo centrado e altamente anisotrópicos (c/a~3). São intermetálicos de alta temperatura crítica supercondutora Tc, com forte acoplamento elétron-fonon. Em alguns casos podem apresentar ordem magnética, supercondutividade e também coexistência ou competição energética entre ambos. As medidas de transporte eletrônico, em função da temperatura, foram feitas utilizando-se um detector síncroton baseado na técnica de quatro pontos operando na faixa de 4,2K até 300K. Essas medidas possibilitaram o estudo das propriedades relacionadas ao transporte eletrônico na fase supercondutora. Na fase normal, extraiu-se a dependência em energia da função espectral de fonons α² F (ω) para alguns compostos da série estudada. As medidas magnéticas em função da temperatura e do campo magnético foram feitas utilizando-se um SQUID (Superconducting Quantun Interference Device – Quantun Design Model MPMS XL). Tais medidas permitiram a caracterização das propriedades magnéticas de nossas amostras. Em particular determinou-se o valor, em regime de saturação, do momento magnético associado ao sítio cristalino do Mn. Foram determinadas também as correntes críticas supercondutoras usando o Modelo de estado crítico de Bean e a variação da temperatura crítica supercondutora (Tc) com a mudança do campo externo aplicado. As medidas magnéticas permitiram a obtenção do diagrama que relaciona o campo crítico inferior (HC1) e a temperatura, variando-se a concentração do átomo dopante de manganês. Foi feito um esforço teórico no sentido de interpretar os resultados experimentais. Para isso foram usados três modelos: O modelo de estado crítico de Bean já citado acima e um modelo baseado na fórmula de Ziman usando uma aproximação para a função espectral de fonons para descrever a resistividade no regime de alta temperatura. Além disto, usou-se o modelo de duas sub-redes para a descrição do momento magnético das impurezas de Mn, em função da concentração, na série Y(Ni ) ( 2 ω α F 1-xMnx)2B2C.

Avaliação de metais na água, no sedimento e nos peixes da lagoa Azul, formada por lavra de mineração de carvão a céu aberto, Siderópolis-SC

Entre maio de 2001 e janeiro de 2002, foram realizadas coletas sazonais na lagoa Azul, Siderópolis, SC. Esta lagoa formou-se por lavra de mineração de carvão a céu aberto desativada. Foram avaliadas as concentrações de Cr, Mn, Ni, Zn e Fe na água e no sedimento. Estes metais, exceto o Fe, foram também analisados no músculo e no fígado das espécies dos peixes Oreochromis niloticus (tilápia) e Geophagus brasiliensis (acará). O objetivo foi avaliar a qualidade da lagoa, bem como, das espécies de peixes predominantes, devido a preocupação quanto ao consumo potencial das mesmas pela população do entorno. As análises do sedimento, quando comparada a locais não contaminados, indicam concentração elevada para Fe, Mn, Cr e Zn. No compartimento água as concentrações de Fe, Mn e Ni estão acima do estabelecido para a classe 2 da Resolução CONAMA 20/86. Conforme análise estatística, em ambos os compartimentos abióticos ocorrem diferenças significativas entre os 4 pontos amostrados, porém diferença sazonal ocorre somente para o compartimento água. O conteúdo de metais em peixes não apresenta diferença significativa entre as espécies analisadas, todavia entre os diferentes tecidos analisados, o fígado apresentou a maior concentração em ambas as espécies. Através das análises do músculo (parte comestível), foi possível avaliar o risco à saúde humana. Segundo a estimativa da ingestão diária, os peixes analisados não propiciam risco aparente de contaminação à população do entorno, conforme os critérios adotados para o teor dos metais avaliados.

Análise numérica e experimental da solidificação das ligas Al 3,5% Cu e AA36

A formação interna da estrutura de uma peça fundida deve determinar as características mecânicas dessa peça, quando em serviço. Dessa forma, torna-se fundamental conhecer e parametrizar os elementos que influem na formação da estrutura do componente sólido, para o desenvolvimento adequado de sistemas de solidificação que permitam conduzir a melhoria da qualidade de uma peça no processo de solidificação. Modelos numéricos podem ser empregados para a determinação da formação estrutural, entretanto estes devem ser aferidos adequadamente para garantir sua aplicabilidade. No trabalho em questão, desenvolveu-se uma metodologia que permitiu a aferição de um modelo numérico para a previsão das condições de resfriamento de ligas de alumínio. Elaborou-se um conjunto de coquilhas e moldes que permitiram o acoplamento e verificação da estrutura formada na solidificação em diferentes situações de resfriamento, observando principalmente a direção de extração de calor e a taxa de resfriamento associada. O modelo numérico aplicado respondeu coerentemente aos resultados obtidos permitindo a previsão da estrutura solidificada pela observação dos resultados de evolução das isotermas solidus e liquidus no interior dos sistemas.

Avaliação do potencial genotóxico e citotóxico associado a queima artesanal da castanha de caju no Município de João Câmara

The Brazil is the third largest producer of cashew nuts in the world. Despite the social and economic importance of the cashew nut, its production is still carried out artisanally. One of the main problems encountered in the cashew production chain are the conditions under which the roasting of the nut occurs to obtain the kernel from the shell. In the present study was conducted a biomonitoring of the genotoxic and cytotoxicity effects associated with the elements from the cashew nut roasting in João Câmara - RN, semi-arid region of Brazil. To assess the genotoxic was used the bioassay of micronucleus (MN) in Tradescantia pallida. In addition, it was performed a comparative between the Tradescantia pallida and KU-20 and other biomarkers of DNA damage, such as the nucleoplasmic bridges (NBP) and nuclear fragments (NF) were quantified. The levels of particulate matter (PM1.0, PM2.5, PM10) and black carbon (BC) were also measured and the inorganic chemical composition of the PM2.5 collected was determined using X-ray fluorescence spectrometry analysis and the assessment of the cytotoxicity by MTT assay and exclusion method by trypan blue. . For this purpose, were chosen: the Amarelão community where the roasting occurs and the Santa Luzia farm an area without influence of this process. The mean value of PM2.5 (Jan 2124.2 μg/m3; May 1022.2 μg/m3; Sep 1291.9 μg/m3) and BC (Jan 363.6 μg/m3; May 70.0 μg/m3; Sep 69.4 μg/m3) as well as the concentration of the elements Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Se, Br and Pb obtained at Amarelão was significantly higher than at Santa Luzia farm. The genotoxicity tests with T. pallida indicated a significant increase in the number of MN, NBP and NF and it was found a negative correlation between the frequency of these biomarkers and the rainfall. The concentrations of 200 μg/mL and 400 μg/mL of PM2.5 were cytotoxic to MRC-5 cells. All together, the results indicated genotoxicity and citotoxicity for the community of Amarelão, and the high rates of PM2.5 considered a potential contributor to this effect, mainly by the high presence of transition metals, especially Fe, Ni, Cu, Cr and Zn, these elements have the potential to cause DNA damage. Other nuclear alterations, such as the NPBs and NFs may be used as effective biomarkers of DNA damage in tetrads of Tradescantia pallida. The results of this study enabled the identification of a serious occupational problem. Accordingly, preventative measures and better practices should be adopted to improve both the activity and the quality of life of the population. These measures are of fundamental importance for the sustainable development of this activity.