Cu and Co exchanged ZSM-5 zeolites: activity towards no reduction and hydrocarbon oxidation

|Cu x|[Si yAl]-MFI and |Co x|[Si yAl]-MFI catalysts were prepared by ion exchange from |Na|[Si yAl]-MFI zeolites (y = 12, 25 and 45). The activity of the catalysts was evaluated in the reduction of NO to N2 in an oxidative atmosphere using propane or methane as reducing agents. The Cu catalysts were only active with propane and they presented higher activity than the Co-based catalysts, the latter being active with both hydrocarbons. H2-TPR and DRS-UV/Vis data allowed correlation between the activity towards NO reduction and the presence of cationic charge-compensating species in the zeolite. It was also verified that the hydrocarbons are preferentially oxidised by O2, a reaction that occurs simultaneously with their oxidation with NO.

Obtención de láminas delgadas de Y-Ba-Cu-O sobre Si (100)

Se ha utilizado la evaporación secuencial de Cu, Y2O3 y BaF2 para la obtención de láminas delgadas superconductoras de YBa-CuO sobre substratos de Si monocristalino con orientación [100], recubiertos con una lámina barrera de Zr02. Se han estudiado los efectos de la variación de los espesores relativos de las láminas constituyentes y del espesor total de la lámina resultante. Las láminas se han caracterizado mediante medidas de la variación de la resistencia con la temperatura, microscopía electrónoca de barrido, difractometría de rayos X, microson-da electrónica y espectometría de masas de iones secundarios. Las láminas presentan un ligero carácter semiconductor en el estado normal, con temperaturas de inicio de la transición su-perconductora alrededor de 90 K, y resistencia nula, en el mejor de los casos, a 45 K.

Decoloración de alginato de sodio extraído de las algas pardas marinas del género Sargassum con el uso de peróxido de hidrógeno

Hydrogen peroxide bleaching of sodium alginate from seaweeds oh the Sargassum genus was studied. The influence of H2O2 concentration (percentage of H2O2 on a dry weight alginate basis, w/w) and NaOH/H2O2 ratio (% NaOH/% H2O2, both referred to a dry weight alginate basis, w/w) on the molecular weight, color removal and content of Fe3+ ions of bleached alginate samples was investigated by UV and IR spectroscopies, colorimetric determination of Fe3+ ions and vapor pressure osmometry. Higher yield, purity and molecular weight of alginate were obtained using 3% (or less) of hydrogen peroxide and a NaOH/H2O2 ratio of 1.2 for bleaching.

Estudo da labilidade de Cu(II), Cd(II), Mn(II) e Ni(II) em substâncias húmicas aquáticas utilizando-se membranas celulósicas organomodificadas

In this work commercial filters papers were organomodified with tetraethylorthosilicate (TEOS) and 3-aminopropyltriethoxysilane (3-APTS), aiming at the development of a new analytical procedure for in-situ speciation of labile and inert metal species in aquatic systems. Parameters that exert influence on the metal lability such as pH, chelating time, concentration and characteristics of the organic matter were studied in the laboratory using tests for metal recuperation. The results showed slower kinetics for Cu ion than for Ni, Mn and Cd in the absence of aquatic humic substances (AHS). The relative lability observed for complexed metals in aquatic humic substances using organomodified filter papers was Cu>>Cd>Ni>Mn. The pH values, structural characteristics and concentration of AHS exert strong influence on the lability of the metals. The results obtained showed that the utilization of organomodified filter papers can be an interesting and promising alternative for in situ characterization of metal lability in aquatic systems.

Produção de hidrogênio a partir da reforma a vapor de etanol utilizando catalisadores Cu/Ni/gama-Al2o3

Cu/Ni/gamma-Al2O3 catalysts were prepared by an impregnation method with 2.5 or 5% wt of copper and 5 or 15% wt of nickel and applied in ethanol steam reforming. The catalysts were characterized by atomic absorption spectrophotometry, X-ray diffraction, temperature programmed reduction with hydrogen and nitrogen adsorption. The samples showed low crystallinity, with the presence of CuO and NiO, both as crystallites and in dispersed phase, as well as of NiO-Al2O3. The catalytic tests carried out at 400 ºC, with a 3:1 water/ethanol molar ratio, indicated the 5Cu/5Ni/Al2O3 catalyst as the most active for hydrogen production, with a hydrogen yield of 77% and ethanol conversion of 98%.

Planejamento estatístico de experimentos como uma ferramenta para otimização das condições de biossorção de Cu(II) em batelada utilizando-se casca de nozes pecã como biossorvente

In order to reduce the total number of experiments for achieving the highest amount of adsorbed Cu2+ (qmax) using pecan nutshells (Carya illinoensis) as biosorbent, a full 2(4) factorial design with two central points was carried out (mass of biosorbent- m, pH, initial metallic ion concentration- C0, time of contact- t). In order to continue the optimization of the system, a central composite surface analysis design with two factors and five central points was carried out. The maximum amount of Cu2+ taken up by the pecan nutshells was 20 mg g-1. These results were confirmed by determining a Cu2+ isotherm using the best conditions attained by the statistical design of experiments.

Avaliação da concentração de alguns íons metálicos em diferentes espécies de líquens do cerrado Sul-Mato-Grossense

Concentrations of Fe, Mn, Co, Cr, Zn and Cu were determinated using flame atomic absorption spectrometry in nine lichen species of the Sul-Mato-Grossense cerrado. The average metal ion concentrations varied in the following ranges: Fe, 248.41-1568.01; Mn, 98.50-397.33; Co, 10.08-24.81; Cr, 18.24-44.26; Zn, 14.62-34.79 and Cu, 3.23-7.57 mg kg-1. Statistical analysis (Pearson and Cluster) applied to the metal ion concentrations indicated that the accumulation of these ions can be due to several anthropogenic sources including agricultural activities, mineral exploration, biomass burning, soil mineral composition and leather tanning processes by chromium.

Adsorção de íons cobre(II) pela quitosana usando coluna em sistema sob fluxo hidrodinâmico

The adsorption of Cu(II) ions from aqueous solution by chitosan using a column in a closed hydrodynamic flow system is described. The adsorption capacities as a function of contact time of copper(II) ions and chitosan were determined by varying the ionic strength, temperature and the flow of the metal solution. The Langmuir model reproduced the adsorption isothermal data better than the Freundlich model. The experimental kinetic data correlate properly with the second-order kinetic reaction for the whole set of experimental adsorption conditions. The rate constants exercise great influence on the time taken for equilibrium to be established by complexation or electrostatic interaction between the amino groups of chitosan and the metal.

Uso da casca de coco verde como adsorbente na remoção de metais tóxicos

Green coconut shells were treated with acid, base and hydrogen peroxide solutions for 3, 6, 12 and 24 h for removing toxic metals from synthetic wastewater. The removal of ions by the adsorbent treated with 0.1 mol L-1 NaOH/ 3h was 99.5% for Pb2+ and 97.9% for Cu2+. The removal of Cd2+, Ni2+, Zn2+, using adsorbent treated with 1.0 mol L-1 NaOH/3 h, was 98.5, 90.3 and 95.4%, respectively. Particle size, adsorbent concentration and adsorption kinetics were also studied. An adsorbent size of 60-99 mesh and a concentration of 30-40 g/L for 5 min exposure were satisfactory for maximum uptake of Pb2+, Ni2+, Cd2+, Zn2+ and Cu2+ and can be considered as promising parameters for treatment the aqueous effluents contaminated with toxic metals.

Estudo do equilíbrio e cinética da biossorção do pb2+ por saccharomyces cerevisiae

The biosorption, based on the use of biomass for removal of ions is distinguished as an innovative and promising technology when compared with the traditional methods. In this context, the aim of the present work is to use Saccharomyces cerevisiae as biosorbent for the retention of Pb2+ metal ions. Factorial design was used for evaluation of the process. The observed equilibrium data were well described by Langmuir and Freundlich adsorption isotherms. The maximum adsorption capacity was 1486.88 mg/g. The results indicated that Saccharomyces cerevisiae is suitable for biosorption of Pb2+ metal ions.

Determinação voltamétrica por redissolução anódica de Cu(II) em águas residuárias empregando um eletrodo de pasta de carbono modificado com quitosana

The electrochemical applications of a CPE modified with chitosan for the determination of Cu(II) in wastewater samples using anodic stripping voltammetry are described. The best voltammetric response was observed for a paste containing 25% m/m of chitosan. A 0.10 mol L-1 NaNO3 solution (pH 6.5) as supporting electrolyte, a pre-concentration potential of -0.20 V, pre-concentration time of 270 s and a scan rate of 25 mV s-1 were selected. The calibration graph was linear in the Cu(II) concentration range from 2.0 x 10-7 to 7.4 x 10-6 mol L-1, with a detection limit of 8.3 x 10-8 mol L-1.

Pré-tratamentos de melaço de cana-de-açúcar e água de maceração de milho para a bioprodução de carotenóides

This work studied the pretreatment of sugarcane molasses (CM) and corn steep liquor (CS) for the production of carotenoids by Sporidiobolus salmonicolor (CBS 2636). The acid pretreatment removed less micronutrients than that with activated carbon and led to high removals of Cu and Mn. Reduction in optical density of the prepared medium and removal of glucose from it were 22% and 7% for CM and 95% and 38% for CS, respectively. Total carotenoids obtained with substrates pretreated with acids (541 mg/L) were higher than the results obtained when the medium was treated with activated carbon (208 mg/L).

Cloud point extraction for the determination of copper in environmental samples by flame atomic absorption spectrometry

A simple cloud point extraction procedure is presented for the preconcentration of copper in various samples. After complexation by 4-hydroxy-2-mercapto-6-propylpyrimidine (PTU), copper ions are quantitatively extracted into the phase rich in Triton X-114 after centrifugation. Methanol acidified with 0.5 mol L-1 HNO3 was added to the surfactant-rich phase prior to its analysis by flame atomic absorption spectrometry (FAAS). Analytical parameters including concentrations for PTU, Triton X-114 and HNO3, bath temperature, centrifugation rate and time were optimized. The influences of the matrix ions on the recoveries of copper ions were investigated. The detection limits (3SDb/m, n=4) of 1.6 ng mL-1 along with enrichment factors of 30 for Cu were achieved. The proposed procedure was applied to the analysis of environmental samples.

Laüe back-reflection method for crystallographic orientation of a martensitic Cu-Zn-Al single crystal of the monoclinic system

A martensitic single crystal Cu-23.95Zn-3.62(wt.%)Al alloy was obtained melting pure Cu, Zn and Al using Bridgman's method. The martensitic phase (monoclinic) can present up to 24 variants, and orienting the surface according to a certain plane is a very hard task. The single crystal was submitted to 8 tons of tension (stress) along the longitudinal direction to reduce the number of variants and facilitate the surface orientation according to the desired plane. This single crystal was oriented using the Laüe back-reflection method to give surfaces with the following oriented crystallographic planes: (010), (120) and (130). It was observed that the tension stress was applied along the [010] direction.

Titulações potenciométricas de cátions metálicos tendo como eletrodo indicador o sistema Cu/Cu(II)-EDTA

In potentiometric titrations of metal cations with EDTA the Hg/HgY2- system is usually used to detect the end point. However, the use of mercury has been discouraged in analytical procedures due to its toxicity. In this work the Cu/CuY2- system was used as indicator electrode for potentiometric titrations of some metal cations with EDTA. The solutions of Cu2+, Cd2+, Mn2+, Co2+ and Zn2+ were titrated with Na2EDTA solution in the presence of a small concentration of the CuY2- complex using a copper wire as indicator electrode. The potentiometric titrations with the Cu/CuY2- system showed good correlation when compared with an Hg/HgY2- system.