Artigos
URI permanente para esta coleçãohttps://locus.ufv.br/handle/123456789/11800
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Item Separation of Cd and Ni from Ni–Cd batteries by an environmentally safe methodology employing aqueous two-phase systems(Journal of Power Sources, 2009-09-05) Lacerda, Vânia Gonçalves; Mageste, Aparecida Barbosa; Santos, Igor José Boggione; Silva, Luis Henrique Mendes da; Silva, Maria do Carmo Hespanhol daThe separation of Cd and Ni from Ni–Cd batteries using an aqueous two-phase system (ATPS) composed of copolymer L35, Li2SO4 and water is investigated. The extraction behavior of these metals from the bottom phase (BP) to the upper phase (UP) of the ATPS is affected by the amount of added extractant (potassium iodide), tie-line length (TLL), mass ratio between the phases of the ATPS, leaching and dilution factor of the battery samples. Maximum extraction of Cd (99.2 ± 3.1)% and Ni (10.6 ± 0.4)% is obtained when the batteries are leached with HCl, under the following conditions: 62.53% (w/w) TLL, concentration of KI equal to 50.00 mmol kg−1, mass ratio of the phases equal to 0.5 and a dilution factor of battery samples of 35. This novel methodology is efficient to separate the metals in question, with the advantage of being environmentally safe, since water is the main constituent of the ATPS, which is prepared with recyclable and biodegradable compounds.Item Aqueous two-phase systems: a new approach for the determination of p-aminophenol(Journal of Hazardous Materials, 2011-08-15) Rodrigues, Guilherme Dias; Lemos, Leandro Rodrigues de; Patrício, Pamela da Rocha; Silva, Luis Henrique Mendes da; Silva, Maria do Carmo Hespanhol daA new method has been developed for the spectrophotometric determination of p-aminophenol (PAP) in water, paracetamol formulations and human urine samples with a recovery rate between 94.9 and 101%. This method exploits an aqueous two-phase system (ATPS) liquid–liquid extraction technique with the reaction of PAP, sodium nitroprusside and hydroxylamine hydrochloride in pH 12.0, which produces the [Fe2(CN)10]^10− anion complex that spontaneously concentrates in the top phase of the ATPS (). The ATPS does not require an organic solvent, which is a safer and cleaner liquid–liquid extraction technique for the determination of PAP. The linear range of detection was from 5.00 to 500 μg kg^−1 (R ≥ 0.9990; n = 8) with a coefficient of variation of 2.11% (n = 5). The method exhibited a detection limit of 2.40 μg kg^−1 and a quantification limit of 8.00 μg kg^−1. The ATPS method showed a recovery that ranged between 96.4 and 103% for the determination of PAP in natural water and wastewater samples, which was in excellent agreement with the results of the standard 4-aminoantipyrine method that was performed on the same samples.Item A green and sensitive method to determine phenols in water and wastewater samples using an aqueous two-phase system(Talanta, 2009-09-04) Rodrigues, Guilherme Dias; Lemos, Leandro Rodrigues de; Silva, Luis Henrique Mendes da; Silva, Maria do Carmo Hespanhol da; Minim, Luis Antonio; Coimbra, Jane Sélia dos ReisA greener and more sensitive spectrophotometric procedure has been developed for the determination of phenol and o-cresol that exploits an aqueous two-phase system (ATPS) using a liquid–liquid extraction technique. An ATPS is formed mostly by water and does not require organic solvent. Other ATPS components used in this study were the polymer, polyethylene oxide, and some salts (i.e., Li2SO4, Na2SO4 or K2HPO4 + KOH). The method is based on the reaction between phenol, sodium nitroprusside (NPS) and hydroxylamine hydrochloride (HL) in an alkaline medium (pH 12.0), producing the complex anion [Fe2(CN)10]^10− that spontaneously concentrates in the top phase of the system. The linear range was 1.50–500 μg kg^−1 (R ≥ 0.9997; n = 8) with coefficients of variation equal to 0.38% for phenol and 0.30% for o-cresol (n = 5). The method yielded limits of detection (LODs) of 1.27 and 1.88 μg kg^−1 and limits of quantification (LOQs) of 4.22 and 6.28 μg kg^−1 for phenol and o-cresol, respectively. Recoveries between 95.7% and 107% were obtained for the determination of phenol in natural water and wastewater samples. In addition, excellent agreement was observed between this new ATPS method and the standard 4-aminoantipyrine (4-AAP) method.Item Aqueous two-phase systems: An efficient, environmentally safe and economically viable method for purification of natural dye carmine(Tecnologia de Alimentos, 2009-11-09) Mageste, Aparecida Barbosa; Lemos, Leandro Rodrigues de; Ferreira, Guilherme Max Dias; Silva, Maria do Carmo Hespanhol da; Silva, Luis Henrique Mendes da; Bonomo, Renata Cristina Ferreira; Minim, Luis AntonioPartition of the natural dye carmine has been studied in aqueous two-phase systems prepared by mixing aqueous solutions of polymer or copolymer with aqueous salt solutions (Na2SO4 and Li2SO4). The carmine dye partition coefficient was investigated as a function of system pH, polymer molar mass, hydrophobicity, system tie-line length and nature of the electrolyte. It has been observed that the carmine partition coefficient is highly dependent on the electrolyte nature and pH of the system, reaching values as high as 300, indicating the high potential of the two-phase extraction with ATPS in the purification of carmine dye. The partition relative order was Li2SO4 ≫ Na2SO4. Carmine molecules were concentrated in the polymer-rich phase, indicating an enthalpic specific interaction between carmine and the pseudopolycation, which is formed by cation adsorption along the macromolecule chain. When the enthalpic carmine–pseudopolycation interaction decreases, entropic forces dominate the natural dye-transfer process, and the carmine partitioning coefficient decreases. The optimization of the extraction process was obtained by a central composite face-centered (CCF) design. The CCF design was used to evaluate the influence of Li2SO4 and PEO 1500 concentration and of the pH on the partition coefficient of carmine. The conditions that maximize the partition of carmine into the top phase were determined to be high concentrations of PEO and Li2SO4 and low pH values within the ranges studied.Item Microcalorimetric and SAXS determination of PEO−SDS interactions: The effect of cosolutes formed by ions(The Journal of Physical Chemistry B, 2010-09-23) Barbosa, Aparecida Mageste; Santos, Igor José Boggione; Ferreira, Guilherme Max Dias; Silva, Maria do Carmo Hespanhol da; Teixeira, Alvaro Vianna Novaes de Carvalho; Silva, Luis Henrique Mendes daThe effect of different ionic cosolutes (NaCl, Na2SO4, Li2SO4, NaSCN, Na2[Fe(CN)5NO], and Na3[Co(NO)6]) on the interaction between sodium dodecyl sulfate (SDS) and poly(ethylene oxide) (PEO) was examined by small-angle X-ray scattering (SAXS) and isothermal titration calorimetric techniques. The critical aggregation concentration values (cac), the saturation concentration (C2), the integral enthalpy change for aggregate formation (ΔHagg(int)) and the standard free energy change of micelle adsorption on the macromolecule chain (ΔΔGagg) were derived from the calorimetric titration curves. In the presence of 1.00 mmol L−1 cosolute, no changes in the parameters were observed when compared with those obtained for SDS−PEO interactions in pure water. For NaCl, Na2SO4, Li2SO4, and NaSCN at 10.0 and 100 mmol L−1, the cosolute presence lowered cac, increased C2, and the PEO−SDS aggregate became more stable. In the presence of Na2[Fe(CN)5NO], the calorimetric titration curves changed drastically, showing a possible reduction in the PEO−SDS degree of interaction, possibility disrupting the formed nanostructure; however, the SAXS data confirmed, independent of the small energy observed, the presence of aggregates adsorbed on the polymer chain.