Antonio Alberto da Silva Alfaya

Use of rice straw as biosorbent for removal of Cu(II), Zn(II), Cd(II) and Hg(II) ions in industrial effluents.

Adsorption experiments were carried out using waste rice straw of several kinds as a biosorbent to adsorb Cu(II), Zn(II), Cd(II) and Hg(II) ions from aqueous solutions at room temperature. To achieve the best adsorption conditions the influence of pH and contact time were investigated. The isotherms of adsorption were fitted to the Freundlich equation. Based on the experimental data and Freundlich model, the adsorption order was Cd(II)>Cu(II)>Zn(II)>Hg(II) on the rice straw. This quick adsorption process reached the equilibrium before 1.5h, with maximum adsorptions at pH 5.0. Thermodynamic aspects of the adsorption process were investigated. The biosorbent material was used in columns for the removal of ions Cu, Zn, Cd and Hg of real samples of industrial effluent and its efficiency was studied.

A utilização de materiais obtidos pelo processo de sol-gel na construção de biossensores

The use of sol-gel materials to develop new biosensors has received great attention due to its characteristics and versatility of sol-gel process. An overview is presented of the state-of-the-art of electrochemical biosensors employing sol-gel materials. Low-temperature, porous sol-gel ceramics represent a new class for the immobilization of biomolecules. The rational design of sol-gel sensing materials, based on the judicious choice of the starting alkoxide, encapsulated reagents, and preparation conditions, allows tailoring of material properties in a wide range, and offers great potential for the development of electrochemical biosensors.

Chemically modified natural cotton fiber: a low-cost biosorbent for the removal of the Cu(II), Zn(II), Cd(II), and Pb(II) from natural water

AbstractIn this work, the removal of Cu(II), Zn(II), Cd(II), and Pb(II) ions from aqueous solution by natural cotton fiber modified with citric acid (NCFCA) is reported, using both batch and continuous systems. Specifically, kinetics and adsorption isotherms have been determined considering the effect of contact time, pH, and heavy metals concentration. Adsorption isotherms show that the experimental maximum adsorption capacity of Cu(II), Zn(II), Cd(II), and Pb(II) were 6.12, 4.53, 8.22, and 21.62 mg g−1, respectively, at 25°C and pH 5. Furthermore, breakthrough curves were obtained for the adsorption of heavy metals using a fixed bed column packed with NCFCA at pH 5, flow rate = 2.5 mL min−1 and 1.0 × 10–4 mol L−1 of metals concentration. The Thomas model has been used for data fitting of adsorption competitions of continuous experiments and for determining the design parameters that are useful to characterize the performance of the packed bed column. The natural water real samples were treated with the ...

Ion selective electrode for potentiometric determination of saccharin using a thin film of silsesquioxane 3-n-propylpyridinium chloride polymer coated-graphite rod.

ABSTRACT A polymer coated graphite rod ion selective electrode for saccharin was constructed and evaluated for the determination of saccharin in artificial table top sweeteners. The polymer consists of a thin film of silsesquioxane 3-n-propylpyridinium chloride. The electrode response was based on the ion pair formed between saccharinate and the 3-n-propylpyridinium cation from the silsequioxane polymer. The electrode exhibits a Nernstian response for saccharin concentrations between 6.9×10-6 and 5.3×10-3 mol L-1 and a detection limit of 5.5×10-6 mol L-1. The electrode response for saccharin was fast (10-20 s) and the potential independent of pH in the range of 3 to 7. The selectivity coefficients K A, B pot for several anions usually present in commercial table top sweeteners were determined following the IUPAC recommendations. The potentiometric method with the ion selective electrode was validated by the HPLC reference method, through t8543226 determination of saccharin in commercial samples of table top sweeteners. The ion selective electrode is proved suitable for the routine quality control of table top sweeteners by potentiometry.

N-propylpyridinium chloride silsesquioxane polymer film on graphite: electrochemical study of a hexacyanoferrate (II) ion immobilized electrode for oxidation of ascorbic acid

A well polished graphite surface was coated with a thin film of N-propylpyridinium chloride silsesquioxane polymer. On to the strongly graphite-adhered polymer film the electroactive species [Fe(CN)6]4- was adsorbed by means of an ion exchange reaction. The resulting electrode (graph/SiPy+)4[Fe(CN)6 ]4- (graph = graphite and SiPy+ represents the N-propilpyridinium silsesquioxane polymer) was chemically very stable and was used to electrocatalytically oxidize ascorbic acid in solution (pH between 4.5-6.5) in 0.1 mol dm-3 KCl. The electrode was used to determine vitamin C in tablets and in processed orange juices. The results were in accord with those obtained by using the standard 2,6-dichlorophenolindophenol titration method.

Ammonium ion sensor based on SiO2/ZrO2/phosphate-NH4+ composite for quantification of ammonium ions in natural waters

Ion selective-electrode was constructed and evaluated for determination of ammonium ions in natural waters. The electrode consists of paste carbon with the composite SiO2/ZrO2/phosphate-NH4+ obtained through sol-gel process. The electrode exhibits a sub-Nernstian response for ammonium concentrations between 7.7´10-7 and 4.0´10-2 mol L-1 and a detection limit of 1.58´10-7 mol L-1 (8.5´10-3 ppm). The electrode response for ammonium was fast (1 minute). The selectivity coefficients KpotA,B for several ions usually present in natural waters were determined applying the matched potential method. The potentiometric method with the ion selective electrode was validated by the Berthelot method (standard method), through the determination of ammonium ions in natural waters. The ion selective-electrode proved suitable for routine quality control of natural waters by potentiometry.

Silsesquioxane 3-n-Propylpyridinium chloride: a new polymer for the potentiometric analysis of Cr(VI) in electroplating and leather industry wastes

A new polymer, silsesquioxane 3-n-propylpyridinium chloride (SiPy+Cl-), was used in the preparation of an electrode. The polymer coated graphite rod ion selective electrode for Cr(VI) was constructed and evaluated for the determination of Cr(VI) in samples of electroplating and leather industry wastes. This electrode exhibited a Nernstian response for Cr(VI) concentrations between 3.1´10-6 and 1.8´10-2 mol L-1 and a detection limit of 2.8´10-6 mol L-1 (0.15 ppm). The response of the electrode for Cr(VI) was fast (15 s) and the independent potential of pH in the range of 3.0 to 7.0. The selectivity coefficients for several anions showed that the electrode presents excellent performance. The sensor exhibits a shelf-life of 6 months with good reproducibility. Determination of Cr(VI) in electroplating and leather wastes using the sensor was successfully achieved.

Mexerica mandarin (Citrus nobilis) peel as a new biosorbent to remove Cu(II), Cd(II), and Pb(II) from industrial effluent

Abstract Adsorption experiments were carried out using waste Mexerica mandarin “Citrus nobilis” peel as a new biosorbent to adsorb Cu(II), Cd(II), and Pb(II) ions from aqueous solutions at room temperature. To achieve the best adsorption conditions, the influences of pH and contact time were investigated. The isotherms of adsorption were fitted to the Langmuir and Freundlich equations. Based on the experimental data the adsorption order was Pb(II)>Cd(II)>Cu(II) (in mg g−1) on the new biosorbent. This quick adsorption process reached the equilibrium before 20 min, with maximum adsorptions at pH 5.0. Kinetic studies were carried out using the pseudo-first-order and pseudo-second-order models. Thermodynamic aspects of the adsorption process were investigated. The new biosorbent was used in columns for the removal of Cu, Cd, and Pb ions of the samples of industrial effluent and its efficiency and regeneration potential were studied.

Analytical performance of new mixed oxide (SiO2/TiO2/ZnO)-based sorbent for development of a reliable mechanized enrichment system for copper determination in water and food samples

No presente estudo, um novo material composito (SiO2/TiO2/ZnO) foi avaliado para pre-concentracao de cobre em amostras de agua e alimentos. O sorvente foi caracterizado por microscopia eletronica de varredura (SEM), infravermelho com transformada de Fourier (FT-IR), analise de dados texturais, fluorescencia de raios X por energia dispersiva (EDXRF) e difratometria de raios X (XRD). A pre-concentracao em linha e determinacao espectrofotometrica na regiao visivel foi baseada na pre-concentracao de 20,0 mL de amostra em pH 7,0 atraves de 50 mg do sorvente, numa vazao de 6,4 mL min-1. Um volume fixo de 0,3 mL de HNO3 0,5 mol L-1 elui os ions cobre que reagem com dietilditiocarbamato (DDTC) 0,3% (m/m) cujo complexo formado (Cu(DDTC)2) e monitorado a 452 nm. A seletividade do sorvente foi examinada avaliando o efeito de ions interferentes. O metodo proposto forneceu linearidade variando de 20,0 a 230,0 mg L-1 (r = 0,998), fator de pre-concentracao de 35,9 e limite de deteccao de 5,6 mg L-1. Amostras de agua e alimentos foram analisadas com sucesso pelo metodo proposto e a exatidao foi checada por meio de analises de materiais certificados de referencia de proteina e figado de peixe.

Incorporação de CuSO 4 residual em argamassa, como método de disposição final

Residual CuSO4 was incorporated into the mass utilized for cement preparation. To a cement mass with 1:0.5:5 of cement, lime and sand to 0.25, 0.50, 0.75 and 1.00% of residual CuSO4 were added. The sulfate was mixed separately with lime and water to induce metal precipitation. The hardened test bodies were submerged in Milli-Q water for three months. No Cu was detected in the water by Atomic Absorption Spectrometry. The best proportion for mechanical resistance and porosity is 0.50%. The cement is adequate for non-structural objects.