Biblioteca Digital

The performance of a carbon paste electrode (CPE) modified with SBA-15 nanostructured silica organofunctionalised with 2-benzothiazolethiol in the simultaneous determination of Pb(II), Cu(II) and Hg(II) ions in natural water and sugar cane spirit (cachaca) is described. Pb(II), Cu(II) and Hg(II) were pre-concentrated on the surface of the modified electrode by complexing with 2-benzothiazolethiol and reduced at a negative potential (-0.80 V). Then the reduced products were oxidised by DPASV procedure. The fact that three stripping peaks appeared on the voltammograms at the potentials of -0.48 V (Pb2+), -0.03 V (Cu2+) and +0.36 V (Hg2+) in relation to the SCE, demonstrates the possibility of simultaneous determination of Pb2+, Cu2+ and Hg2+. The best results were obtained under the following optimised conditions: 100 mV pulse amplitude, 3 min accumulation time, 25 mV s(-1) scan rate in phosphate solution pH 3.0. Using such parameters, calibration graphs were linear in the concentration ranges of 3.00-70.0 x 10(-7) mol L-1 (Pb2+), 8.00-100.0 X 10(-7) mol L-1 (Cu2+) and 2.00-10.0 x 10(-6) mol L-1 (Hg2+). Detection limits of 4.0 x 10(-8) mol L-1 (Pb2+), 2.0 x 10(-7) mol L-1 (Cu2+) and 4.0 x 10(-7) mol L-1 (Hg2+) were obtained at the signal noise ratio (SNR) of 3. The results indicate that this electrode is sensitive and effective for simultaneous determination of Pb2+...

Neste trabalho descreve-se o desenvolvimento de metodologias para análise de metais pesados em águas de abastecimento (sistema Guarapiranga) e em água de chuva por métodos voltamétricos, a quantificação de cátions e ânions por eletroforese capilar com detecção condutométrica sem contato (EC-DCC), a construção de eletrodos de prata a partir de CD-Rs e sua aplicação para medidas potenciométricas, amperométricas e voltamétricas, a confecção de microeletrodos de ouro explorando técnicas de micro-fabricação com toner e sua aplicação como detector amperométrico em eletroforese capilar e o uso de máscaras de toner para construção de redes de microeletrodos de ouro, platina e carbono. Para o desenvolvimento de metodologia para monitorar chumbo, cobre e mercúrio em águas de abastecimento e em água de chuva, enfatizou-se a utilização de dispositivos semidescartáveis de ouro construídos a partir de CD-Rs utilizando técnicas eletroanalíticas de redissolução. O limite de detecção para 300 s de pré-concentração foi calculado em 80, 90 e 100 ng L-1 para Pb2+, Cu2+ e Hg2+, respectivamente. O volume mínimo de amostra necessário para esta análise é de 0,5 mL. Para analisar estes metais em amostras de águas coletadas do sistema Guarapiranga...

As cinzas de carvão podem ser convertidas em produtos zeolíticos por tratamento hidrotérmico alcalino. No presente estudo, a capacidade de zeólitas sintetizadas a partir de cinzas de carvão brasileiras (6 amostras da cinza volante do filtro de mangas e 6 amostras da cinza leve do filtro ciclone) na remoção de Zn2+ e Cd2+ de soluções aquosas foi investigada. O tempo de equilíbrio alcançado pela maioria das zeólitas foi de 24 horas. Os dados de equilíbrio obtidos se ajustaram à isoterma de adsorção de Langmuir. As capacidades de troca catiônica máximas estavam entre 25,9 e 39,5 mg g-1 para o Zn2+ e entre 49,5 e 72,3 mg g-1 para o Cd2+. A zeólita sintética (ZM1) apresentou área superficial no valor de 66,38 m2 g-1, baixa relação Si/Al (1,65) e a formação de zeólitas sodalita e faujasita, que contribuíram para seu melhor desempenho. Estudos de adsorção de íons metálicos com a ZM1 indicaram a seguinte seqüência de seletividade: Pb2+ > Cd2+ > Cu2+ > Zn2+ > Ni2+. Para a ZM1, a maior porcentagem de remoção de Zn2+ e Cd2+ foi obtida em pH 5 e a recuperação de metais foi efetivamente realizada com solução de NaCl 2 mol L-1. Comparou-se o desempenho das zeólitas sintetizadas a partir das cinzas de carvão com as zeólitas sintéticas comerciais...

Este trabalho teve como objetivo avaliar a bioadsorção dos íons Cd2+, Cu2+, Pb2+, Ni2+ e Zn2+ pela macrófita aquática Limnobium spongia em sistema estático. Diagramas de especiação em função do pH, foram simulados usando o software HYDRA, de modo a se conhecer as diferentes espécies em meio aquoso, nas condições estudadas. Observa-se que em pH<5,0 não ocorre precipitação para todos os íons estudados. A técnica de Espectroscopia na Região do Infravermelho (FTIR) foi utilizada para identificação dos grupos funcionais presentes no bioadsorvente, que poderiam estar envolvidos no processo de bioadsorção. Observou-se que os grupos aminos, amidas e ácidos carboxílicos participam do processo de bioadsorção dos íons metálicos estudados. Para análise da superfície do bioadsorvente nas diferentes condições estudadas foi utilizada a Microscopia Eletrônica de Varredura (MEV). A técnica de EDX (Espectroscopia de Raios X por Energia Dispersiva) acoplada a MEV foi utilizada para caracterizar as espécies naturalmente presentes na macrófita e fazer um mapeamento da distribuição das diferentes espécies metálicas bioadsorvidas. Verificou-se grande quantidade de íons Mg2+, Na2+, Al3+, e Ca2+, naturalmente presentes na macrófita e redução destes íons após a bioadsorção dos íons metálicos estudados...

Dissertação (mestrado)—Universidade de Brasília, Instituto de Química, 2007.; A catalase é uma enzima responsável pela redução de peróxido de hidrogênio (H O ) a água (H O) e oxigênio (O ), que apresenta alguns sítios de 2 2 2 2 ligação para íons metálicos (Cys, His). A ligação entre a enzima e os íons metálicos pode causar mudanças conformacionais ou estabilizar a estrutura da enzima, resultando na sua inibição ou ativação. A inibição da CAT, que ocorre com excesso de metal, contribui para o aumento da geração de espécies reativas de oxigênio, levando ao estresse oxidativo. Neste trabalho, foi estudado separadamente a 2+ 2+ 2+ 2+ interação dos íons metálicos Zn , Cu , Cd e Pb com a catalase, em meio semelhante ao fisiológico, por voltametria de redissolução anódica de pulso diferencial (DPASV), voltametria cíclica (CV) e voltametria de pulso diferencial (DPV). Os objetivos principais deste trabalho foram verificar a existência de interações entre os íons metálicos e a CAT, determinar os parâmetros quantitativos do sistema (estequiometria, constante de dissociação (K ) e potencial padrão de d 0´ redução do complexo (E )) e identificar por meio de estudo teórico os possíveis 2+ 2+ 2+ 2+ sítios de ligação dos íons Zn ...

In this work two distinct (flocculent and non-flocculent) yeast wastes from Portuguese breweries were used for the selective removal of Cu2+, Cd2+ and Pb2+ from aqueous solutions. One of the goals was to establish both the pH profiles for the removal of each metal ion (1.0 mM) and the effect on the biomass biosorption capacity of pH adjustment during the process. The effect of the presence of multiple metal ions, in the 0.1-1.0 mM range, on metal removal efficiency was also studied. The results showed that, in the absence of pH adjustment, the optimum initial pH for the removal of three cations was in the 4.5-5.5 range for both types of biomass. However, a gradual pH increase was observed during the removal process, up to a final equilibrium value of 7.0-8.0. Regarding the biomass efficiency for metal removal in multi-cation systems, it was verified that only Cu2+ was significantly affected by the presence of the other metals in solution and only when the non-flocculent yeast biomass was used as biosorbent. Cd2+ was only slightly affected by the presence of both Cu2+ and Pb2+, and Pb2+ removal was not affected by the presence of any or both of the interferent metals for the two biosorbents used in this work. The highest and lowest metal removal yields were obtained for Pb2+ and Cu2+...

A simple and fast approach for solid phase extraction is herein described, and used to determine trace amounts of Pb2+ and Cu2+ metal ions. The solid phase support is sodium dodecyl sulfate (SDS)-coated γ-alumina modified with bis(2-hydroxy acetophenone)-1,6-hexanediimine (BHAH) ligand. The adsorbed ions were stripped from the solid phase by 6 mL of 4 M nitric acid as eluent. The eluting solution was analyzed by flame atomic absorption spectrometry (FAAS). The sorption recovery of metal ions was investigated with regard to the effects of pH, amount of ligand, γ-alumina and surfactant and the amount and type of eluent. Complexation of BHAH with Pb2+ or Cu2+ ions was examined via spectrophotometry using the HypSpec program. The detection limit for Cu2+ was 7.9 µg L-1 with a relative standard deviation of 1.67%, while that for Pb2+ was 6.4 µg L-1 with a relative standard deviation of 1.64%. A preconcentration factor of 100 was achieved for these ions. The method was successfully applied to determine analyte concentrations in samples of liver, parsley, cabbage, and water.

This paper studies the bioadsorption of Pb2+, Cu2+, Cd2+ and Zn2+ ions by marine alga Sargassum filipendula and by the alginate biopolymer extracted from this alga. The objective is to evaluate the importance of this biopolymer in removing different metallic ions by the marine alga S. filipendula. In the equilibrium study, the same affinity order was observed for both bioadsorbents: Pb2+ > Cu2+ > Zn2+ > Cd2+. For Pb2+ and Cu2+ ions when the alginate is isolated and acting as bioadsorbents, adsorption capacities greater than those found for the alga were observed, indicating that it is the main component responsible for the removal of metallic ions. For Zn2+ and Cd2+ ions, greater bioadsorption capacities were observed for the alga, indicating that other functional groups of the alga, such as sulfates and amino, are also important in the bioadsorption of these ions.

The acute effects of aqueous solutions of As, Cd, Cu, Pb, F, and Zn ions at concentrations from 0.01 to 100 micrograms per milliliter and solutions adjusted to pH 2 to 6 with nitric or sulfuric acid were studied with respect to acetylene reduction, net photosynthesis, respiration rate, and chlorophyll content in Vernal alfalfa (Medicago sativa L. cv. Vernal). The effects of the various treatments on acetylene reduction varied from no demonstrable effect by any concentration of F− and 42% inhibition by 100 micrograms Pb2+ per milliliter, to 100% inhibition by 10 micrograms Cd2+ per milliliter and 100 micrograms per milliliter As, Cu2+, and Zn2+ ions. Zn2+ showed statistically significant inhibition of activity at 0.1 micrograms per milliliter. Acid treatments were not inhibitory above pH 2, at which pH nitric acid inhibited acetylene reduction activity more than did sulfuric acid. The inhibition of acetylene reduction by these ions was Zn2+ > Cd2+ > Cu2+ > AsO3− > Pb2+ > F−. The sensitivity of acetylene reduction to the ions was roughly equal to the sensitivity of photosynthesis, respiration, and chlorophyll content when Pb2+ was applied, but was 1,000 times more sensitive to Zn2+. The relationship of the data to field conditions and industrial pollution is discussed.

The acidity constants for (N3)H of the uridine-type ligands (U) 5-fluorouridine, 5-chloro-2′-deoxyuridine, uridine, and thymidine (2′-deoxy-5-methyluridine) and the stability constants of the M(U–H)+ complexes for M2+ = Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+ were measured (potentiometric pH titrations; aqueous solution; 25°C; I = 0.1 M, NaNO3). Plots of documentclass[12pt]{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} setlength{oddsidemargin}{-69pt} egin{document} egin{equation*}{mathrm{log}}K_{{mathrm{M}}({mathrm{U}}-{mathrm{H}})}^{{mathrm{M}}}end{equation*}end{document} vs. documentclass[12pt]{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} setlength{oddsidemargin}{-69pt} egin{document} egin{equation*}{mathrm{p}}K_{{mathrm{U}}}^{{mathrm{H}}}end{equation*}end{document} result in straight lines that are compared with previous plots for simple pyridine-type and o-amino(methyl)pyridine-type ligands as well as with the stabilities of the corresponding M(cytidine)2+ complexes. The results indicate monodentate coordination to (N3)– in M(U–H)+ for Co2+ and Ni2+. For the M(U–H)+ species of Cd2+...

A Nafion-Graphene (Nafion-G) nanocomposite solution in combination with an in situ plated mercury film electrode was used as a highly sensitive electrochemical platform for the determination of Zn2+, Cd2+, Pb2+ and Cu2+ in 0.1 M acetate buffer (pH 4.6) by square-wave anodic stripping voltammetry (SWASV). Various operational parameters such as deposition potential, deposition time and electrode rotation speed were optimized. The Nafion-G nanocomposite sensing platform exhibited improved sensitivity for metal ion detection, in addition to well defined, reproducible and sharp stripping signals. The linear calibration curves ranged from 1 μg L−1 to 7 μg L−1 for individual analysis. The detection limits (3σ blank/slope) obtained were 0.07 μg L−1 for Pb2+, Zn2+ and Cu2+ and 0.08 μg L−1 for Cd2+ at a deposition time of 120 s. For practical applications recovery studies was done by spiking test samples with known concentrations and comparing the results with inductively coupled plasma mass spectrometry (ICP-MS) analyses. This was followed by real sample analysis.

The present study aims to evaluate the competitive biosorption of lead, cadmium, copper, and arsenic ions by using native algae. A series of experiments were carried out in a batch reactor to obtain equilibrium data for adsorption of single, binary, ternary, and quaternary metal solutions. The biosorption of these metals is based on ion exchange mechanism accompanied by the release of light metals such as calcium, magnesium, and sodium. Experimental parameters such as pH, initial metal concentrations, and temperature were studied. The optimum pH found for removal were 5 for Cd2+ and As3+ and 3 and 4 for Pb2+ and Cu2+, respectively. Fourier transformation infrared spectroscopy analysis was used to find the effects of functional groups of algae in biosorption process. The results showed that Pb2+ made a greater change in the functional groups of algal biomass due to high affinity to this metal. An ion exchange model was found suitable for describing the biosorption process. The affinity constants sequence calculated for single system was KPb > KCu > KCd > KAs; these values reduced in binary, ternary, and quaternary systems. In addition, the experimental data showed that the biosorption of the four metals fitted well the pseudo-second-order kinetics model.

Protease widely exists in the digestive tract of animals and humans, playing a very important role in protein digestion and absorption. In this study, a high protease-producing strain Planomicrobium sp. L-2 was isolated and identified from the digestive tract of Octopus variabilis. The strain was identified by physiological and biochemical experiments and 16S rDNA sequences analysis. A protease was obtained from the strain Planomicrobium sp. L-2 through ammonium sulfate precipitation, dialysis and enrichment, DEAE-Sephadex A50 anion-exchange chromatography, and Sephadex G-100 gel chromatography. The molecular weight and properties of the protease were characterized, including optimum temperature and pH, thermal stability, protease inhibitions and metal ions. According to our results, the protease from Planomicrobium sp. L-2 strain designated as F1-1 was obtained by three-step separation and purification from crude enzyme. The molecular weight of the protease was 61.4 kDa and its optimum temperature was 40°C. The protease F1-1 showed a broad pH profile for casein hydrolysis between 5.0~11.0. No residual activity was observed after incubation for 40 min at 60°C and 60 min at 50°C. F1-1 protease was inhibited by Mn2+, Hg2+, Pb2+, Zn2+...

Alcaligenes sp. MTCC 10674 has a bienzymatic system for the hydrolysis of nitriles. The nitrile hydratase and amidase have been purified simultaneously to homogeneity using a combination of (NH)4SO4 precipitation, ion exchange chromatography and gel permeation chromatography. Nitrile hydratase and amidase have molecular weight of 47 and 114 kDa, respectively and exist as heterodimer. Optimum temperatures for maximum activity of nitrile hydratase and amidase were 15 °C (2.4 U/mg protein) and 45 °C (2.3 U/mg protein), respectively. Nitrile hydratase showed maximum 7.8 U/mg protein at 50 mM acrylonitrile and amidase has 9.2 U/mg protein at 25 mM propionamide. Nitrile hydratase has Vmax 10 μmol/min/mg and Km 40 mM, while amidase has Vmax 12.5 μmol/min/mg and Km 45.5 mM, respectively. Heavy metal ions Hg2+, Ag+, Pb2+ and Cu2+ were strong inhibitors of nitrile hydratase and amidase activity.

1. Distribution of trace elements between biotite and hydrous granitic melt. The synthetic system haplogranite-anorthite-biotite-H2O, doped with a suite of trace elements (V, Cr, Co, Ni, Cu, Zn, Rb, Cs, Sr, Ba, Mo, W, Nb, Ta, REE, Pb and Zr) was experimentally investigated over the temperature interval of 700-800°C at 200 MPa (H2O) to study the distribution of trace elements between biotite and coexisting hydrous melt. The starting materials were a series of volatile-free synthetic glasses obtained by heating a mixture of appropriate reagent grade chemicals (oxides, carbonates or hydroxides) corresponding to ~76 wt% haplogranite (35 wt% SiO2, 40 wt% NaAlSi3O8 and 25 wt% KAlSi3O8), ~8 wt% anorthite, ~15 wt% biotite (with a 1:1 molar ratio of Mg/Fe) and ~1 wt% total trace elements, so selected as to avoid peak interference during microprobe analysis. Experiments were carried out under water-saturated conditions in cold-seal autoclaves with run durations of between 35 and 45 days. The oxygen fugacity was close to the Ni-NiO buffer. Run products were analysed by electron microprobe. Besides biotite, run products contained other phases including amphibole (hornblende), clino-pyroxene, plagioclase, magnetite, allanite and glass. Measured partition coefficients indicate that most alkalis...

Pesquisas no campo da tecnologia têm buscado avaliar técnicas e/ou processos econômicos e eficientes para o tratamento de efluentes que contenham metal pesado. Atualmente a bioadsorção vem se apresentando como uma boa alternativa às tecnologias existentes. Este trabalho teve como objetivo a investigação da macrófita Azolla pinnata como bioadsorvente de cinco íons metálicos: Cd2+, Cu2+, Ni2+, Pb2+ e Zn2+ em soluções sintéticas. A caracterização do biomaterial foi realizada utilizando-se técnicas como Microscopia Eletrônica de Varredura (MEV) para análise da superfície do material; análise de Espectroscopia de Energia Dispersiva de Raios-X (EDX), que mostrou que qualitativamente a diminuição de íons de competição (Ca, Na e K) após o processo de adsorção, evidenciando que a troca iônica pode ser um dos mecanismos do processo; e análise de Infravermelho por Transformada de Fourier (FTIR), em que se pôde constatar que alguns grupos funcionais como carboxilas e grupos sulfonados são fundamentais no processo. A cinética de adsorção foi ajustada pelos modelos de pseudoprimeira e pseudossegunda ordem, sendo que o melhor ajuste variou de acordo com o íon estudado. O modelo de difusão intrapartícula mostrou que muitos mecanismos podem ser limitantes na taxa com a qual ocorre o processo. Os dados de equilíbrio foi ajustado pelos modelos de isoterma de Langmuir e de Freundlich em duas temperaturas...

The present work purposes the preparation of a silica gel sorbent organically modified with 2-aminoethyl-3-aminobutylmethyldimethoxysilane (AAMDMS) and imprinted with Cu2+ ions by means surface imprinting technique and its use for selective on-line sorbent preconcentration of Cu2+ ions with further UV-VIS spectrophotometric determination by flow injection analysis. The Cu2+-imprinted silica gel, when compared with non imprinted silica gel and silica gel, showed from the binary mixture of Cu2+/Ni2+ relative selectivity coefficient (k') of 6.84 and 5.43 and 6.64 and 19.83 for the mixture Cu2+/Pb2+, thus demonstrating higher selectivity of Cu2+-imprinted silica gel towards Cu2+ ions. Under optimized condition, the on-line preconcentration method provided detection limit of 3.4 μg L-1 and linear range ranging from 30.0 up to 300.0 μg L-1 (r = 0.995). The accuracy of method was successfully assessed by analyzing different kind of spiked water samples with recovery values ranging from 92.2 up to 103.0%.

A study is made of the removal of metals present in aqueous effluents using a residue of the steelmaking industry denominated rolling mill scale. Mill scale can be considered a cheap material for the removal of toxic metals due to its high content in iron oxides and metallic iron. A study of the removal of Cd2+, Zn2+, Pb2+ y Cu2+ ions from aqueous solutions was made, studying several variables that affect the process. The removal of cadmium, zinc and lead corresponding to a superficial adsorption process, was evaluated using the theories of Langmuir and Freundlich. The removal of copper occurs through a process of oxidationreduction or cementation (Cu2+/Fe). The possibilities of desorption were studied too.; Se estudia la eliminación de metales presentes en efluentes acuosos empleando un residuo de la industria del acero denominado cascarilla de laminación. La cascarilla se puede considerar como un material barato para la eliminación de metales tóxicos por su alto contenido en óxidos de hierro y hierro metálico. Se ha realizado un estudio de la eliminación de los iones Cd2+, Zn2+, Pb2+ y Cu2+ contenidos en soluciones acuosas, estudiándose diversas variables que afectan al proceso. La eliminación de cadmio, cinc y plomo correspondiente a un proceso de adsorción superficial...

The adsorption capacity of hebba clay and activated carbon towards (Fe3+, Cu2+, Zn2+, Pb2+, Cr3+, Cd2+) metal ions was studied. The adsorption capacity was investigated by batch experiment. The effect of weight of hebba was studied and the results showed that the removal percentages increased as the weight of sorbent increased. The effect of contact time was also studied and the results showed that the removal percentages increased as the contact time increased. The effect of pH of the solution was also studied and the removal percentages for (Cu2+, Zn2+ and Cd2+) were affected slightly by changing the pH value, but for (Fe3+, Pb2+ and Cr3+) the effect was higher. Also, the effect of initial concentration of metal ions was studied at four different concentrations (5, 10, 30, 50 mg/L); in case of metal ions (Cu2+, Zn2+ and Cd2+), the removal percentages increased by increasing initial concentration. But for the other metal ions it decreased. The order of increasing removal percentages of metal ions at pH=4.86, concentration of metal ions 30 mg/L, and after four hours of shaking, was (Pb2+ < Cu2+ < Cd2+ < Cr3+ < Zn2+ < Fe3+). But in the case of activated carbon, the order was Cd2+ < Zn2+ < Cu2+ < Pb2+ < Cr6+ < Fe3+.

The chemically modified guar gum sulphonic acid (GSA) resin was used for removal and pre-concentration of Zn2+, Cd2+, Fe2+, Pb2+ and Cu2+ ions in aqueous solutions and steel industry effluent from Jodhpur, India. This type of ion exchange resin represents a new class of hybrid ion exchangers with higher stability, reproducibility and selectivity for toxic metal ions. The characterisation of the resin was carried out by determining the ion exchange capacity, elemental analysis, FT-IR spectra and thermal analysis (TGA). The distribution coefficients (Kd) of toxic metal ions were determined for different pH values. The adsorption of different metal ions on GSA resin follows the order: Cu2+ > Fe2+ > Zn2+ > Cd2+ > Pb2+. The adsorbency of different metal ions on the GSA resin was studied for up to 10 cycles.