Filme fino de ZrO2 enxertado sobre a superfície de sílica gel: preparação e propriedade de adsorção de Cr(VI)

The present experiment describes an easy procedure for obtaining SiO2/ZrO2 by reacting ZrOCl2 with SiO2 with the following characteristics: S BET = 500 m² g-1 and an average pore diameter of 6 nm. The material obtained presented 1.3 wt% ZrO2 content corresponding to 140 mumol g-1. The average density of ZrO2 onto SiO2/ZrO2 matrix is 2.8x10-11 mol cm-2. The adsorption isotherm for Cr(VI) showed a maximum of adsorption value (200 mumol g-1) at pH 2. The adsorption can be described by the reaction: =Zr(OH)2 + 2HCrO4- + 2H+ [(=Zr(OH2+)2) (HCrO4-)2]. Above the zero point of charge, i.e. pH > 5.5 due to the surface charge inversion, desorption of Cr(VI) occurs according to the reaction: [(=Zr(OH2+)2) (HCrO4-)2] + 6OH- (=ZrO2)2- + 6H2O + 2CrO4(2-).

Determinação de Mn, Cu e Zn em matrizes salinas após separação e pré-concentração usando Amberlite XAD-7 impregnada com Vermelho de Alizarina S

The aim of this work was to explore the possibility of the application of a non-ionic resin obtained by impregnation of Alizarin Red S (VAS) in Amberlite XAD-7 for manganese, copper and zinc separation and preconcentration in saline matrices. For these system, the metals were quantitatively retained, in the pH range 8.5-10.0, by using 0.50 g of solid phase, stirring time of five minutes and a total mass up to 200 mug of each cation. The sorbed elements were subsequently eluted and a fifty-fold, ten-fold and ten-fold preconcentration factor for to Zn, Cu and Mn were obtained, respectively.

Caracterização de amostras comerciais de vermicomposto de esterco bovino e avaliação da influência do pH e do tempo na adsorção de Co(II), Zn(II) and Cu(II)

Some commercial samples of vermicompost from bovine manure (humus) were characterized by thermogravimetry with respect to humidity, organic matter and ash contents, the percentages of which range from 6.55 to 5.35%, 53.01 to 69.96% and 46.44 to 66,14%, respectively. The capacity of adsorption of Cu2+, Zn2+ and Co2+ ions by these samples has been evaluated as a function of pH and time. The contents of several metal ions in the original vermicompost samples have been determined by flame atomic absorption spectrometry after digestion in a microwave oven. The high nitrogen content suggests that the earthworms used in the maturation procedure lead to an efficient degradation of organic matter. The metal retention was affected by both pH and adsorption time. The results also show that adsorption follows the order Cu2+ > Zn2+ > Co2+.

Decomposição do NO sobre Cu suportado em zeólitas

Direct decomposition of NO on copper supported on zeolite catalysts such as MCM-22 and Beta was compared with that on the thoroughly studied Cu-ZSM-5. The catalysts were prepared by ion-exchange in basic media. They were characterized by atomic absorption, surface area, nitrogen adsorption at 77K, X-ray diffraction and temperature programmed reduction. The products of the reaction were analyzed by Fourier transform infrared spectroscopy using a gas cell. Catalytic activity tests indicated that zeolite catalysts, like Beta and MCM-22, lead to NO conversion values comparable to ZSM-5.

Remoção de Cu+2 de soluções aquosas em zeólita NaX: efeito da granulometria

The present study consists in evaluating the NaX zeolite efficiency in removing Cu2+ from aqueous solutions, for future use of NaX in removing metals from wastewaters. The experiments were performed in batch systems (with shaking and continous stirring) and for different time intervals (1 to 24 h). Three particle sizes were employed: < 850 µm, 850 µm - 1 mm and 3 mm. It has been concluded that it is possible to employ the NaX zeolite for metal removal and the particle size plays an important role in the adsorption process. Specifically, NaX zeolites of smaller particle size achieved the maximum adsorption capacity of 152.36 mg of Cu2+/g of zeolite at pH = 4.5.

Adsorção de As, Cu, Pb e Cr na avaliação da capacidade de fixação de metais por resíduo de mineradoras de ferro

Two samples of residues from iron mining plants have been investigated for their retention capacity of As, Cu, Cr, and Pb. The sample with the higher content of iron oxides showed the highest capacity to retain metals. The adsorption affinity series changes from Pb>Cu>Cr~As to As>Pb>Cu>Cr or As>Cu>Cr>Pb, depending on the material and the concentration of the initial solution. In the competitive environment, the Pb adsorption decreases and the As, Cu and Cr adsorption increases. Sequential extraction procedures, carried out after adsorption batch experiments, showed that the most important adsorption process occurs in the oxide fraction and that the major part of the absorbed metal is remobilized from exchangeable and oxide fractions.

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%.

Decomposição térmica de espumas de poliuretano para fabricação de vitrocerâmica celular de Li2O-ZrO2-SiO2-Al2O3 (LZSA)

Characterization of the thermal decomposition of polyurethane (PUR) foams was performed by Fourier-transformed infrared (FT-IR) spectroscopy and thermogravimetric analysis (TGA). Three main weight loss paths were observed by TGA, the residue being lower than 3 wt.% for 3 different PUR foams analyzed. FT-IR spectra indicated CO2, CO, NH3 and isocyanides as main decomposition products. PUR foams of different cell sizes were immersed in a slurry of the parent glass ceramic of composition Li2O-ZrO2-SiO2-Al 2O3 (LZSA) and submitted to heat treatment. The LZSA cellular glass ceramics obtained after sintering and crystallization resembled the original morphology of the PUR foams.

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.

Estudo das interações entre o complexo polieletrolítico trimetilquitosana/carboximetilcelulose e Cu+2, ácido húmico e atrazina em solução aquosa

The polyelectrolyte complex (PEC) resulting from the reaction of sodium carboxymethylcellulose (CMC) and N,N,N-trimethylchitosan hydrochloride (TMQ) was prepared and then characterized by infrared spectroscopy and energy dispersive X rays analysis. The interactions involving the PEC and Cu2+ ions, humic acid and atrazine in aqueous medium were studied. From the adsorption isotherms the maximum amount adsorbed (Xmax) was determined as 61 mg Cu2+/g PEC, 171 mg humic acid/g PEC and 5 mg atrazine/g PEC. The results show that the CMC/TMQ complex has a high affinity for the studied species, indicating its potential application to remove them from aqueous media.

Desenvolvimento e aplicação de sistema passivo de coleta de poluentes atmosféricos para monitoramento de Cd, Cr, Pb, Cu, Fe, Mn, Zn e particulados totais

The objective of this study was to assess a new monitoring technique of particulate and trace metals in the atmosphere via the use of a passive sampler of air pollutants in the city of Goiânia. The average particulate weight and average concentrations of metals Fe, Cr, Zn, Pb, Cu, Mn, and Cd were 0.1104 g and 257.5; 23.4; 17.8; 6.7; 1.9; 0.8; 0.2 μg/m²/day, respectively. Higher Pb and Cr concentrations were obtained in areas with intense traffic. This study revealed that it is possible to monitor trace metals with passive sampling, developed at a low cost and operational facility.

Preparação de membranas de acetato de celulose organomodificadas para adsorção dos íons Cu(II), Cd(II), Mn(II) e Ni(II)

Cellulose acetate polymeric membranes had been prepared by a procedure of two steps, combining the method of phase inversion and the technique of hydrolysis-deposition. The first step was the preparation of the membrane, and together was organomodified with tetraethylortosilicate and 3-aminopropyltrietoxysilane. Parameters that exert influence in the complexation of the metallic ion, as pH, time of complexation, metal concentration, had been studied in laboratory using tests of metal removal. The membranes had presented resistance mechanics and reactivity to cations, being able to be an alternative for the removal, daily pay-concentration or in the study of the lability of metals complexed.

Diesel/biodiesel soot oxidation with ceo2 and ceo2-zro2-modified cordierites: a facile way of accounting for their catalytic ability in fuel combustion processes

CeO2 and mixed CeO2-ZrO2 nanopowders were synthesized and efficiently deposited onto cordierite substrates, with the evaluation of their morphologic and structural properties through XRD, SEM, and FTIR. The modified substrates were employed as outer heterogeneous catalysts for reducing the soot originated from the diesel and diesel/biodiesel blends incomplete combustion. Their activity was evaluated in a diesel stationary motor, and a comparative analysis of the soot emission was carried out through diffuse reflectance spectroscopy. The analyses have shown that the catalyst-impregnated cordierite samples are very efficient for soot oxidation, being capable of reducing the soot emission in more than 60%.

Methanol steam reforming over Cu/CeO2 catalysts: influence of zinc addition

Methanol steam reforming reaction was studied over Cu(5 wt.%)/CeO2 with and without the presence of Zn. The Zn addition decreased the Cu+2 reducibility and increased the oxygen mobility of ceria. The main products were CO2 and H2 with small amount of CO. Selectivity to CO decreased with the Zn addition and it was lower at lower reaction temperatures and lower space velocities. At 230 ºC and W/F MeOH = 648 g min mol-1 selectivities to H2 and to CO2 were 100% on Zn/Cu/Ce. The catalytic results indicated that CO was mainly a secondary product formed from reverse water gas shift reaction.

Influência do eletrólito na eletrodeposição de nanopartículas de Cu sobre eletrodo de diamante dopado com boro

This paper presents the electrolyte influence on deposition and dissolution processes of Cu nanoparticles on boron doped diamond electrodes (BDD). Morphological, structural and electrochemical analysis showed BDD films with good reproducibility, quality and reversible in a specific redox system. Electrodeposition of Cu nanoparticles on DDB electrodes in three different solutions was influenced by pH and ionic strength of the electrolytic medium. Analyzing the process as function of the scan rate, it was verified a better efficiency in 0,5 mol L-1 Na2SO4 solution. Under the influence of the pH and ionic strength, Cu nanoparticles on DDB may be obtained with different morphologies and it was important for defining the desired properties.