Estudo da adsorção de brometo de etídeo em resina XAD-7

The adsorption of ethidium bromide on XAD-7 resin was studied. The Freundlich model was the most representative isotherm model to describe the sorption behavior. A solid-liquid equilibrium model was proposed to explain the resin mass influence on the sorption. The equilibrium constant value estimated was 2.31. The results showed an ethidium bromide ion-pair physical adsorption, with adsorption enthalpy equals to -19.33 kJ/mol. A pK2 value equals to 4.69 ± 0.01 was estimated by two distinct methods. The results will be applied to the ethidium bromide preconcentration aiming its decomposition.

Adsorção de íons fosfato em óxido de nióbio hidratado

The adsorption kinetics of phosphate on Nb2O5.nH2O was investigated at initial phosphate concentrations 0.25, 0.50 and 1.00 mg.L-1. The kinetic process was described by a pseudo-second-order rate model very well. The adsorption thermodynamics was carried out at 298, 308, 318, 328 and 338 K. The positive values of both ΔH and ΔS suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. ΔG values obtained were negative indicating a spontaneous adsorption process. The Langmuir model described the data better than the Freundlich isotherm model. The effective desorption could be achieved using water at pH 12.

Estudo da adsorção de compostos sulfurados empregando zeólitas contendo zinco

This paper deals with an adosrption of sulphur compounds employing zeolites containing zinc. The zeolites employed were commercial NaY and Beta. The zinc was incorporated in three levels: 0.5; 1.0 and 5%. The sulphur compounds studied were benzothiophene and dibenzothiofene. The results showed that both zeolites can be employed for adsorption of benzothiophene and dibenzothiophene. The Zn incorporation (0.5%) promotes an increase in zeolites adsorption ability. The DBT adsorbs more than BT, probably because it strongly interacts with zeolite structure. The BT adsorbs more in NaY than in beta probably because the NaY zeolite has a high intern volume. This is not observed for DBT.

Remoção de compostos orgânicos em água empregando carvão ativado impregnado com óxido de ferro: ação combinada de adsorção e oxidação em presença de H2O2

In this work, composites based on activated carbon/iron oxide (AC/Fe) were prepared in two different proportions (AC/Fe 5/1 and 1/1) and evaluated in the removal of the organic dye methylene blue (MB). Physical-chemical properties of the composites were determined by X-ray diffraction (XRD), adsorption/dessorption of N2 isotherm, temperature programmed reduction (TPR) and scanning electron microscopy (SEM). Results showed that goethite (α- FeOOH), with nanometer particle size, was formed over carbon surface for both composites. These materials showed high efficiency to remove MB from solution by combined adsorption and oxidation process. The AC/Fe 1/1 showed to be more active in (MB) oxidation then AC/Fe 5/1.

Adsorção do corante reativo laranja 16 de soluções aquosas por zeólita sintética

Coal fly ash, a waste generated in a coal-fired electric power plant, was used to synthesize zeolite by hydrothermal treatment with NaOH solution. This zeolite was used as adsorbent to investigate the adsorption kinetics and isotherm parameters of the reactive orange 16 (RO16) dye from aqueous solutions at different concentrations (1.3-15.4 mg L-1). Three kinetic models, the pseudo-first-order, second-order, and intraparticle diffusion were used to predict the adsorption rate constants. The kinetics of adsorption of the RO16 dye followed pseudo-second-order kinetics. The adsorption isotherm data were closely fitted to the Langmuir equation. Keywords: coal fly ash; zeolite; reactive dye adsorption.

Adsorção de Cr(VI) em esferas reticuladas de quitosana: novas correlações cinéticas e termodinâmicas utilizando microcalorimetria isotérmica contínua

The synthesis and characterization of crosslinked chitosan microbeads and their application in the removal of Cr(VI) are described. New kinetic and thermodynamic parameters of Cr(VI) adsorptions processes were found using continuous isothermal calorimetry. All adsorption processes are exothermic in nature. However, a multivariate statistical analysis have pointed out that adsorption enthalpies were affected by important binary interactions of the initial Cr(VI) in solution and temperature. The adsorption energetic data were well fitted to a kinetic exponential model, which have indicated fractionary adsorption kinetic orders.

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.

Aplicação da casca de arroz na adsorção dos íons Cu2+, Al3+, Ni2+ e Zn2+

The potential use of rice husk as biosorbent to remove Cu2+, Al3+, Ni2+ and Zn2+ ions from aqueous solutions was investigated under both noncompetitive and competitive conditions. The biosorbent was used in the form of particles with size smaller than 0.5 μm and in the concentration of 500 mg L-1 (dry weight). The experiments were performed using batch adsorption technique for concentrations of 10, 30 and 70 mg L-1 of metal ions at pH 4.0 and 5.0. The chemical speciation of metals in the experimental conditions used in this work was predicted by the software Visual MINTEQ 2.6.

Adsorção e propriedades de volume de misturas binárias água álcool: um experimento didático com base em medidas de tensão superficial

An undergraduate physical chemistry experiment based on the drop counting method for surface tension measurements is proposed to demonstrate adsorption isotherms of binary aqueous solutions of ethanol, n-propanol, and n-butanol. Excess surface is obtained by the derivative of surface tension taken with respect to alcohol activity, after this activity calculation using van Laar equation. Laboratory class contents are surface tension, excess surface, percolation of hydrogen bonds, micelle, activity, and ideal solution.

Adsorção de chumbo, cádmio e prata em óxido de nióbio (V) hidratado preparado pelo método da precipitação em solução homogênea

This paper describes the adsorption of heavy metals ions from aqueous solution by hydrous niobium oxide. Three heavy metals were selected for this study: cadmium, lead and silver. Adsorption isotherms were well fitted by Langmuir model. Maximum adsorption capacity (Q0) for Pb2 +, Ag+ and Cd2 + was found to be 452.5, 188.68 and 8.85 mg g-1, respectively.

Adsorção de arsênio(V) pelo compósito magnético hidrotalcita: óxido de ferro

In this work, hydrotalcite, a layered double hydroxide, had its adsorption and ion exchange properties combined with the magnetic properties of iron oxide to produce a magnetic adsorbent, HT-Fe. The removal of As(V) by a HT-Fe adsorbent was evaluated under various conditions. The Kinetic process was well described by a pseudo-second order rate model. The maximum adsorption capacity, calculated with the Langmuir model showed to be dependent on pH, reaching values of 24.09, 10.19 and 7.44 mg g-1, respectively, for pH values of 4.0, 7.0 and 9.0. The inhibition by competition of anions is dependent on the type of ionic species.

Adsorção do corante azul de metileno em partículas de argilominerais: análise dos tamanhos das partículas

Interactions of cationic dye methylene blue (MB) with clay particles in aqueous suspension have been extensively studied. As already known, the number of natural negative charges on the clay modifies significantly the particle sizes dispersed in water and therefore the nature of the interaction with the dye. This work evaluated with UV-Vis spectroscopy method how the clay particle sizes weighted on the adsorption and rearrangement of the dye molecules in aqueous system. The results obtained from light-scattering measurements confirmed that larger particles are found in suspensions containing the high-charged clays as the visible absorption band related to the MB aggregates (570 nm) on these suspensions prevailed.

Adsorção do corante vermelho congo por derivados da o-carboximetilquitosana hidrofobicamente modificados

Hydrophobically modified O-carboxymethylchitosan derivatives were synthesized through a reaction with lauroyl chloride and applied for adsorption of congo red dye. The Langmuir-Freundlich isotherm model was found to be the most suitable one for the VC adsorption and maximum adsorption capacity obtained was 281.97 mg g-1 at a pH value of 7.0 for HL 1.0. The adsorption process follows the pseudo-second-order kinetics and the corresponding rate constants were obtained. The thermodynamic parameters showed that adsorption process is spontaneous (positive ∆Hº) and favorable (negative ∆Gº). The hydrophobic derivatives are able to adsorb the dye even in high pH values.

Avaliação da porosidade de microcápsulas contendo proteína bioativa por porosimetria de mercúrio e adsorção de nitrogênio

Microcapsules containing lactoferrin were produced by spray drying using dextrin:octenylsuccinate starch, as wall materials. Porosity characteristics of spray-dried microcapsules were investigated by mercury intrusion porosimetry and nitrogen adsorption. The outer and inner structures of microcapsules were studied by Scanning Electron Microscopy and sizes were determined by Laser Diffraction. Results indicate that all microcapsules presents adsorption isotherm of type II and that micropores on the microcapsules surface will be very few or none. Our results show that microstructure, surface area and size of microcapsules are affected by dextrin: octenylsuccinate starch proportion. Pore characteristics for various microcapsules are found to be different.

Determinação dos parâmetros cinéticos e termodinâmicos da adsorção de L-cisteína em ouro por meio da técnica de microbalança a cristal de quartzo

This article discusses the adsorption kinetics of a L-cysteine monolayer onto a gold surface by means of information obtained through the QCM technique. The results indicate that the adsorption process is rapid and follows the Langmuir isotherm, in which adsorption and desorption are considered. From these measurements the following parameter values were obtained: k d = (4.2 ± 0.4) x 10-3 s-1, k a = 75 ± 6 M-1 s-1, Keq=(1.8 ± 0.3) x 10(4) M-1 and ΔGads = - (5.8 ± 0.2) kcal mol-1.