RESUMO
In this work, a hybrid silica/chitosan was synthesized and characterized by nitrogen elemental analysis and thermal analysis (TG, DTG, DTA, and DSC) and BET surface area. The hybrid was used in adsorption studies of two anionic dyes from aqueous solutions. A rise of temperature accelerates mass transfer of dyes into the hybrid. However, the maximum adsorption capacities reach similar values from 25 to 55 degrees C. The kinetic data were first evaluated in relation to the decrease of the time-related residual concentration of the dyes in solution, where the second-order model has presented the best fitting. The solid-phase interaction of dye data presents a rough fitting to the traditional first-order Lagergren kinetic model. However, a modified Avrami kinetic equation was successfully fitted to the kinetic quantities, where from five to seven kinetic regions were found. A pore-diffusion model has also demonstrated that the diffusion is the rate-controlling interaction mechanism. However, the experimental-calculated comparative values are the best way to evaluate a specific aqueous- or solid-phase kinetic model.
Assuntos
Quitosana/química , Corantes/química , Modelos Químicos , Dióxido de Silício/química , Adsorção , Ânions/química , Cinética , Estrutura Molecular , Soluções/química , Temperatura , Água/químicaRESUMO
Sílica-dithizone (Sil-dtz) was synthesized and used to adsorb Hg(II) in solution at pH 6.0. Increasing the temperature accelerates the mass transfer of Hg(II) to the silica surface. The kinetic data were evaluated using the traditional pseudo-first-order Lagergren equation and an alternative Avrami kinetic equation. From the latter equation, two regions presenting distinct kinetic parameters were found, at 25 and 35 degrees C, and the use of the parameter n was also related to the determination of distinct kinetic orders. Variations of the adsorption kinetic rate in relation to the time and the temperature were also calculated and are discussed. The adsorption isotherms data were well fitted to the Freundlich model. Interestingly, good adsorption data correlation of the Langmuir model and experimental values was observed only at 45 and 50 degrees C, suggesting, for this temperature range, the formation of complexes with the proportion Hg:dithizone 1:1 on the silica surface.
Assuntos
Ditizona/química , Mercúrio/química , Dióxido de Silício/química , Adsorção , Ditizona/síntese química , Cinética , Estrutura Molecular , Dióxido de Silício/síntese química , Propriedades de Superfície , Temperatura , Fatores de TempoRESUMO
In this work, thin chitosan membranes were utilized as an adsorbent for the removal of Hg(II) from aqueous solutions. A rise of temperature accelerates the mass transfer of Hg(II) to the membranes, surfaces. The kinetic data did not present a good fitting to the traditional Lagergren adsorption kinetic equations. An alternative Avrami kinetic equation was employed and successfully fitted to the kinetic adsorption quantities. From this new equation, two regions presenting distinct kinectic parameters were found, and the use of the parameter n was also relationed to the determination of the kinetic order. Variations of the adsorption kinetic rate in relation to the time, the initial Hg(II) concentration, and the temperature were also calculated and are discussed.