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Characterization of thiol-functionalised silica films deposited on electrode surfaces

CESARINO, Ivana; CAVALHEIRO, Éder Tadeu Gomes
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica
ENG
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Thiol-functionalised silica films were deposited on various electrode surfaces (gold, platinum, glassy carbon) by spin-coating sol-gel mixtures in the presence of a surfactant template. Film formation occurred by evaporation induced self-assembly (EISA) involving the hydrolysis and (co)condensation of silane and organosilane precursors on the electrode surface. The characterization of such material was performed by IR spectroscopy, thermogravimetry (TG), elemental analysis (EA), atomic force microscopy (AFM), scanning electron microscopy (SEM) and cyclic voltammetry (CV).; Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES); FAPESP

Synthesis and structure of cage-like mesoporous silica using different precursors

Fantini, Marcia Carvalho de Abreu; Kanagussuko, Cíntia Fabiana; Zilioti, George José Martins; MARTINS, T. S.
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
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In this work the synthesis of cubic, FDU-1 type, ordered mesoporous silica (OMS) was developed from two types of silicon source, tetraethyl orthosilicate (TEOS) and a less expensive compound, sodium silicate (Na(2)Si(3)O(7)), in the presence of a new triblock copolymer template Vorasurf 504 (EO(38)BO(46)EO(38)). For both silicon precursors the synthesis temperature was evaluated. For TEOS the effect of polymer dissolution in methanol and the acid solution (HCl and HBr) on the material structure was analyzed. For Na(2)Si(3)O(7) the influence of the polymer mass and the hydrothermal treatment time were the explored experimental parameters. The samples were examined by Small Angle X-ray Scattering (SAXS) and Nitrogen Sorption. For both precursors the decrease on the synthesis temperature from ambient, -25 degrees C, to -15 degrees C improved the ordered porous structure. For TEOS, the SAXS results showed that there is an optimum amount of hydrophobic methanol that contributed to dissolve the polymer but did not provoke structural disorder. The less electronegative Br-ions, when compared to Cl-, induced a more ordered porous structure, higher surface areas and larger lattice parameters. For Na(2)Si(3)O(7) the increase on the hydrothermal treatment time as well as the use of an optimized amount of polymer promoted a better ordered porous structure. (C) 2011 Elsevier B.V. All rights reserved.

Influence of pH on the incorporation and growth of Pb(2)CrO(5) crystallites in silica matrix

ARAUJO, Vinicius D.; AVANSI, Waldir; PARIS, Elaine C.; MAIA, Lauro J. Q.; BERNARDI, Maria Inês Basso
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Artigo de Revista Científica
ENG
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Pb(2)CrO(5) nanoparticles were embedded in an amorphous SiO(2) matrix by the sol-gel process. The pH and heat treatment effects were evaluated in terms of structural, microstructural and optical properties from Pb(2)CrO(5)/SiO(2) compounds. X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), energy dispersive spectroscopy (EDS), and diffuse reflectance techniques were employed. Kubelka-Munk theory was used to calculate diffuse reflectance spectra that were compared to the experimental results. Finally, colorimetric coordinates of the Pb(2)CrO(5)/SiO(2) compounds were shown and discussed. In general, an acid pH initially dissolves Pb(2)CrO(5) nanoparticles and following heat treatment at 600 A degrees C crystallized into PbCrO(4) composition with grain size around 6 nm in SiO(2) matrix. No Pb(2)CrO(5) solubilization was observed for basic pH. These nanoparticles were incorporated in silica matrix showing a variety of color ranging from yellow to orange.

Evaluation of a carbon paste electrode modified with organofunctionalised SBA-15 nanostructured silica in the simultaneous determination of divalent lead, copper and mercury ions

CESARINO, Ivana; MARINO, Glimaldo; MATOS, Jivaldo do Rosario; CAVALHEIRO, Eder Tadeu Gomes
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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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+...

Preparação de sílica organofuncionalizada à base de zircônia e estudos de adsorção de hidrocarbonetos policíclicos aromáticos e pesticidas organoclorados

Geller, Ana Maria
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
POR
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O trabalho realizado conjuga informações de preparação e caracterização de materiais à base de sílica, com avaliação de possível aplicação potencial na área de química analítica ambiental. As sílicas organofuncionalizadas foram preparadas segundo 2 métodos: grafting e sol-gel. Os 4 sólidos obtidos por grafting diferem essencialmente na natureza da esfera de coordenação em torno do centro metálico (átomo de zircônio), enquanto que os 2 sólidos obtidos pelo processo sol-gel são sólidos híbridos, contendo ligantes indenil, grupos silanóis e etóxidos na superfície, diferindo entre si pela presença de centro metálico. Os teores de metal, determinados por RBS, nas sílicas organofuncionalizadas ficaram em torno de 0,3 % para os sólidos preparados por grafting e 4,5 %,no caso, do sólido preparado por sol-gel. A análise por DRIFTS confirmou a presença dos ligantes orgânicos e, ainda, grupos silanóis residuais nos adsorventes preparados por grafting. A capacidade de adsorção das sílicas organofuncionalizadas foi avaliada frente a duas famílias de compostos: HPAs e pesticidas organoclorados. A identificação e quantificação dos HPAs foi conduzida através de cromatografia gasosa com detector seletivo de massas. Os resultados da capacidade de adsorção para os 16 HPAs prioritários não foram quantitativamente considerados satisfatórios...

Monitoramento morfológico do xerogel híbrido 3-(1,4-fenilenodiamina)propil/silica obtido sob diferentes condições de síntese

Gay, Débora Simone Figueiredo
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
POR
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Neste trabalho, foi obtido o xerogel híbrido 3-(1,4-fenilenodiamina) propil/sílica, usando-se o método sol-gel de síntese, variando-se as condições experimentais de síntese. Foram usados como reagentes precursores o tetraetilortosilicato (TEOS) e o 3-[(1,4-fenilenodiamina)propil]trimetoxisilano (FDAPS) sintetizado em nosso laboratório. As condições experimentais de síntese variadas foram: a concentração de precursor orgânico (FDAPS), a temperatura de gelificação, o tipo de solvente e o pH do meio reacional. O trabalho foi dividido em duas etapas: na primeira, foram obtidas duas séries de materiais onde se variou a temperatura de gelificação (5, 25, 50 e 70 °C), além da quantidade de precursor orgânico (FDAPS), adicionado à síntese (1,5 e 5,0 mmol). Na segunda etapa variou-se o pH do meio reacional (4, 7 e 10) além do tipo de solvente (etanol, butanol e octanol), mantendo-se a quantidade de precursor orgânico adicionado e a temperatura de gelificação constantes em 5,0 mmol e 25 oC, respectivamente. Em ambas etapas utilizou-se HF como catalisador e manteve-se o sistema fechado, porém não vedado, durante a gelificação. Na caracterização dos xerogéis híbridos foram usadas as seguintes técnicas: a) termoanálise no infravermelho...

Tunable visible photoluminescence of powdered silica glass

Pizani, P. S.; Joya, M. R.; Pontes, Fenelon Martinho Lima; Santos, L. P. S.; Godinho, M.; Leite, E. R.; Longo, Elson
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 476-479
ENG
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intense photoluminescence in the visible region was observed at room temperature in standard soda-lime-silica glass powder, mechanically milled in a high-energy attrition mill. The emission band maximum shows an interesting dependence on the exciting wavelength, suggesting the possibility to tune the PL emission. These findings indicate that the photoluminescence may be directly related to unsatisfied chemical bonds correlated with the high surface area. The Raman scattering and ultraviolet-visible optical reflectance measurements corroborate this assertion. Transmission electron microscopy measurements indicate that samples milled more than 10 h present the formation of nanocrystallites with about 10-20 nm. (C) 2007 Elsevier B.V. All rights reserved.

Stripping voltammetry of mercury(II) with a chemically modified carbon paste electrode containing silica gel functionalized with 2,5-dimercapto-1,3,4-thiadiazole

Dias, N. L.; do Carmo, D. R.
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica Formato: 1540-1546
ENG
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The accumulation voltammetry of mercury(II) was investigated at a carbon paste electrode chemically modified with silica gel functionalized with 2,5-dimercapto-1,3,4-thiadiazole (DTTPSG-CPE). The repetitive cyclic voltammogram of mercury(II) solution in the potential range -0.2 to +0.8 V (vs. Ag/AgCl), (0.02 mol L-1 KNO3; nu=20 mV s(-1)) show two peaks one at about 0.0 V and other at 0.31 V. However, the cathodic wave peak, around 0.0 V, is irregular and changes its form in each cycle. This peak at about 0.0 V is the reduction current for mercury(II) accumulated in the DTTPSG-CPE. The anodic wave peak at 0.31 V is well-defined and does not change during the cycles. The resultant material was characterized by cyclic and differential pulse anodic stripping voltammetry performed with the electrode in differents supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, cleaning solution, possible interferences and other variables. The precision for six determinations (n=6) of 0.05 and 0.20 mg (L)-(1) Hg(II) was 2.8 and 2.2% (relative standard deviation), respectively. The method was satisfactory and used to determine the concentration of mercury(II) in natural waters contaminated by this metal.

Synthesis, characterization, and application of modified silica in the removal and preconcentration of lead ions from natural river water

Ferreira, Guilherme; Caetano, Laercio; Castro, Renata S. D.; Padilha, Pedro Magalhaes; Castro, Gustavo Rocha
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 397-402
ENG
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Processo FAPESP: 06/54946-9; This paper describes the synthesis, modification, and application of modified silica for the removal of lead ions from aqueous medium. The modification reaction provided a reduction in surface are from 737 to 399 m(2) g(-1), which was attributed to the 4-amine-2-mercaptopyrimidine molecule attachment onto its surface. The characterization through FTIR spectra demonstrated bands at 3347 cm(-1) assigned to N-H stretching vibrations and the absence of thiol bands at 2600 e 2547 cm(-1) at Si-mod spectrum is an indicative that the attachment occurred via SH groups. The linearization of adsorption isotherm data through the modified Langmuir equation resulted in a maximum adsorption capacity of 2.9 mu mol g(-1). The material was applied in a continuous flow system in the preconcentration of water samples from Parana River and the results were in agreement with metal concentration determined directly through atomic absorption spectrometry with graphite furnace. The method validation was performed through analysis of water standard reference material (1643e), which also presented a 7.2-fold enrichment factor.

Copper determination in ethanol fuel by differential pulse anodic stripping voltammetry at a solid paraffin-based carbon paste electrode modified with 2-aminothiazole organofunctionalized silica

Takeuchi, Regina M.; Santos, Andre L.; Padilha, Pedro M.; Stradiotto, Nelson R.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 771-777
ENG
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Solid paraffin-based carbon paste electrodes modified with 2-aminothiazole organofunctionalized silica have been applied to the anodic stripping determination of copper ions in ethanol fuel samples without any sample treatment. The proposed method comprised four steps: (1) copper ions preconcentration at open circuit potential directly in the ethanol fuel sample; (2) exchange of the solution and immediate cathodic reduction of the absorbate at controlled potential; (3) differential pulse anodic stripping voltammetry; (4) electrochemical surface regeneration by applying a positive potential in acid media. Factors affecting the preconcentration, reduction and stripping steps were investigated and the optimum conditions were employed to develop the analytical procedure. Using a preconcentration time of 20 min and reduction time of 120 s at -0.3 V versus Ag/AgCl(sat) a linear range from 7.5 x 10(-8) to 2.5 x 10(-6) mol L(-1) with detection limit of 3.1 x 10(-8) mol L(-1) was obtained. Interference studies have shown a decrease in the interference effect according to the sequence: Ni > Zn > Cd > Pb > Fe. However, the interference effects of these ions have not forbidden the application of the proposed method. Recovery values between 98.8 and 102.3% were obtained for synthetic samples spiked with known amounts of Cu(2+) and interfering metallic ions. The developed electrode was successfully applied to the determination of Cu(2+) in commercial ethanol fuel samples. The results were compared to those obtained by flame atomic absorption spectroscopy by using the F-test and t-test. Neither F-value nor t-value have exceeded the critical values at 95% confidence level...

Determination of Cu, Ni, and Zn in fuel ethanol by FAAS after enrichment in column packed with 2-aminothiazole-modified silica gel

Roldan, P. S.; Alcantara, I. L.; Castro, G. R.; Rocha, J. C.; Padilha, CCF; Padilha, P. M.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 574-577
ENG
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This work describes the synthesis and characterization of 2-aminothiazole-modified silica gel (SiAT), as well as its application for preconcentration (in batch and column technique) of Cu(II), Ni(II) and Zn(II) in ethanol medium. The adsorption capacities of SiAT determined for each metal ion were (mmol g(-1)): Cu(II)=1.20, Ni(II)=1.10 and Zn(II)=0.90. In addition, results obtained in flow experiments, showed a recovery of ca. 100% of the metal ions adsorbed in a column packed with 500 mg of SiAT. The eluent was 2.0 mol L-1 HCl. The sorption-desorption of the studied metal ions made possible the development of a preconcentration method for metal ions at trace level in fuel ethanol using flame AAS for their quantification.

Adsorption Kinetics and Structural Arrangements of Cationic Surfactants on Silica Surfaces

Atkin, R; Craig, Vincent; Biggs, Simon
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
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The adsorption of cetyltrimethylammonium bromide (CTAB) to the silica-aqueous interface has been studied using optical reflectometry. The effect of pH, salt, and surface preparation on the surface excess and adsorption kinetics has been studied. The adsorption kinetics have been measured and compared to the theoretical diffusion limited flux of surfactant, the quotient being the `sticking ratio'. Analysis of the sticking ratio as a function of CTAB concentration reveals that the adsorption process is cooperative above the critical micelle concentration (CMC). At the critical surface aggregation concentration (CSAC), adsorption proceeds slowly in the absence of salt and takes hours to reach an equilibrium value. At all other concentrations and even at the CSAC when salt is present, the adsorption is complete within minutes. These results indicate that, above the CMC, micelles adsorb directly to the silica surface, and this is reflected in the structure of the surface layer. At the CSAC the equilibrium surface structure is analogous to adsorbed micelles, but as only monomers are present in solution, the adsorption proceeds to equilibrium slowly.

The Influence of Chain Length and Electrolyte on the Adsorption Kinetics of Cationic Surfactants at the Silica-aqueous Solution Interface

Atkin, R; Craig, Vincent; Wanless, Erica J; Biggs, Simon
Fonte: Academic Press Publicador: Academic Press
Tipo: Artigo de Revista Científica
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The equilibrium and kinetic aspects of the adsorption of alkyltrimethylammonium surfactants at the silica-aqueous solution interface have been investigated using optical reflectometry. The effect of added electrolyte, the length of the hydrocarbon chain,

Deep Dry-etch of Silica in a Helicon Plasma Etcher for Optical Waveguide Fabrication

Li, Wei; Bulla, Douglas; Love, John; Luther-Davies, Barry; Charles, Christine; Boswell, Roderick
Fonte: American Institute of Physics (AIP) Publicador: American Institute of Physics (AIP)
Tipo: Artigo de Revista Científica
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Dry-etch of SiO2 layers using a CF4 plasma in a helicon plasma etcher for optical waveguide fabrication has been studied. Al2O3 thin films, instead of the conventional materials, such as Cr or photoresist, were employed as the masking materials. The Al2O3 mask layer was obtained by periodically oxidizing the surface of an Al mask in an oxygen plasma during the breaks of the SiO2 etching process. A relatively high SiO2/Al2O3 etching selectivity of ∼100:1, compared with a SiO2/Al selectivity of ∼15:1, was achieved under certain plasma condition. Such a high etching selectivity greatly reduced the required Al mask thickness from over 500 nm down to ∼100nm for etching over 5-μm-thick silica, which make it very easy to obtain the mask patterns with near vertical and very smooth sidewalls. Accordingly, silica wavegudies with vertical sidewalls whose roughness was as low as 10 nm were achieved. In addition, the mechanism of the profile transformation from a mask to the etched waveguide was analyzed numerically; and it was found that the slope angle of the sidewalls of the mask patterns only needed to be larger than 50° for achieving vertical sidewalls of the waveguides, if the etching selectivity was increased to 100.

Heavy Ion Elastic Recoil Detection Analysis of Silicon-Rich Silica Films

Dall (previously Weijers), Tessica; Elliman, Robert; Timmers, Heiko
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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Heavy ion elastic recoil detection (ERD) is shown to be a powerful tool for studying the deposition and processing of Si-rich silica films deposited by plasma enhanced chemical vapour deposition (PECVD). Such films are of interest for the fabrication of SiO2 layers containing silicon nanocrystals and are commonly deposited using SiH4 and N2O source gases. Heavy ion ERD reveals that as-deposited films can contain high concentrations of N, potentially reducing the efficacy of nanocrystal formation due to competing reactions between Si and N. This is believed to explain why high excess-Si concentrations are required to produce luminescent nanocrystals in such layers. Analysis of samples following high temperature (1200 °C) annealing also reveal the loss of H from the layers and highlight an experimental artefact associated with such high temperature processing.

Nonlinear Optical Response of Ge Nanocrystals in a Silica Matrix

Dowd, A; Elliman, Robert; Samoc, Marek; Luther-Davies, Barry
Fonte: American Institute of Physics (AIP) Publicador: American Institute of Physics (AIP)
Tipo: Artigo de Revista Científica
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Time-resolved degenerate-four-wave-mixing measurements were used to study the nonlinear optical response (intensity-dependent refractive index) of Ge nanocrystallites embedded in a silica matrix. Nanocrystals were fabricated by ion-implanting silica with

Nonlinear Optical Properties of Semiconducting Nanocrystal in Fused Silica

Dowd, A; Samoc, Marek; Luther-Davies, Barry; Elliman, Robert
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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Degenerate four-wave mixing (DFWM) is used to examine the nonlinear optical response of Ge nanocrystals in a silica matrix. The nanocrystals are formed by implanting 1.0 MeV Ge ions into silica to a dose of 3.0×1017 Ge cm-2 and annealing at 1100°C. The

EFFECT OF SILICA FUME ADDITION ON THE CHLORIDE-RELATED TRANSPORT PROPERTIES OF HIGH-PERFORMANCE CONCRETE

LIZARAZO-MARRIAGA,JUAN; LÓPEZ YÉPEZ,LUCIO GUILLERMO
Fonte: DYNA Publicador: DYNA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2012 EN
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Being the corrosion of steel reinforcement due to chloride penetration the major cause of durability problems in concrete, this paper summarizes the results of an experimental research carried out in order to investigate the influence of the silica fume (SF) content on some chloride-related transport properties. To achieve this, the compressive strength, the self-diffusion chloride penetration, the charge passed in a non-steady chloride migration test (ASTM C1202), and the AC resistivity were measured on concrete mixes of high-performance concrete. Four concrete mixes were cast incorporating 5, 10, and 15% of SF as an addition to ordinary Portland cement. The results showed that the silica fume in concrete causes an increase in strength and a reduction in chloride ion permeability; however, clear differences were found between the results of long diffusion and rapid electrical tests.

Reduction of microbial biofilm formation using hydrophobic nano-silica coating on cooling tower fill material

Türetgen,Irfan
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2015 EN
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A cooling tower is a heat removal device, which extracts waste heat to the atmosphere through the cooling of a water stream to a lower temperature. Cooling towers are frequently associated with biofilm problems and Legionnaires disease outbreaks. Where biofilms can cause clogging and corrosion, reduction of biofilms is important for operational reasons and public health. Therefore, effective anti-biofilm strategies are needed in practice. The aim of the present study was to reduce biofilm formation using a nano-hydrophobic coating on cooling tower fill materials - polypropylene cooling tower fill material was coated with nano-silica. The effectiveness of the hydrophobic coating was investigated for a 6-month test period in a model cooling tower system, by monthly counting of the surface-associated bacteria using an epifluorescence microscope. A significant reduction (up to 4 log) in surface-associated bacteria was observed on coated test samples in comparison to uncoated control coupons. This study is the first report regarding the use of nano-silica coatings on cooling tower fills. The coating can be easily fabricated and the range of possible applications can be expanded to include a variety of conditions.

The effect of silica concentration on the biosorption of Cu2+ and Co2+ from aqueous solutions mediated by strains of Bacillus

Dlamini,NP; Mamba,BB; Mulaba-Bafubiandi,AF
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/07/2010 EN
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Bacillus strains were isolated from a mine tailings dump in Nigel town, south-east of Johannesburg. These were then grown at 37(±0.5)ºC in a trace element-agitated liquid media. The effects of pH, contact time, initial ion concentration and the presence of co-cations were studied to ascertain the optimal conditions for biosorption to take place. Test solutions contained 0.002 M, 0.07 M and 0.2 M of either copper or cobalt ions. The Bacillus strains removed the copper and cobalt more efficiently from solutions of low concentration (0.002 M and 0.07 M) than from solutions of high concentration (0.2 M) over a 48 h period. Maximum biosorption was obtained at pH 6.5 and 5.5 for copper and cobalt solutions, respectively. The presence of silica led to an initial increase in both copper and cobalt biosorption, though higher concentrations of silica resulted in a decrease in metal uptake by Bacillus strains.