Resumo O objetivo deste trabalho foi avaliar a degradação do corante rodamina B em solução aquosa por reação foto-Fenton sob irradiação visível utilizando uma bentonita rica em ferro como catalisador. O material foi tratado termicamente a baixa temperatura (200 ºC) e caracterizado por DRX, isotermas de adsorção-dessorção de N2, FTIR, MEV-EDS e FRX. A lixiviação do ferro na solução aquosa após a reação foto-Fenton foi avaliada por espectroscopia de absorção atômica. O material exibiu uma estrutura mesoporosa, apresentando uma área de superfície específica de 99 m2.g-1. Os resultados catalíticos mostraram alta eficiência na degradação do corante, atingindo 95% de descoloração e 72% de mineralização em 300 min de reação. O catalisador apresentou alta estabilidade química em quatro ciclos de reação. Portanto, esta bentonita rica em Fe tratada termicamente pode ser considerada como um promissor catalisador na reação foto-Fenton heterogênea para a degradação da rodamina B em solução aquosa.

Abstract The objective of this work was to evaluate the degradation of rhodamine B dye from aqueous solution by photo-Fenton reaction under visible irradiation using a Fe-rich bentonite as a catalyst. The material was thermally treated at a low temperature (200 °C) and characterized by XRD, N2 adsorption-desorption isotherms, FTIR, SEM-EDS and XRF. Iron leaching in aqueous solution after the photo-Fenton reaction was evaluated by atomic absorption spectroscopy. The material exhibited a mesoporous structure, containing a specific surface area of 99 m2.g-1. The catalytic results showed significant dye degradation, reaching 95% of decolorization and 72% of mineralization at 300 min of reaction. The catalyst showed high chemical stability in four reaction cycles. Therefore, this thermally treated Fe-rich bentonite can be considered as a promising catalyst in the heterogeneous photo-Fenton reaction for the degradation of rhodamine B from aqueous solution.

Resumo Neste trabalho, zeólita ZSM-5 mesoestruturada foi preparada usando quitina como um novo auxiliar de síntese para produzir mesoporosidade. Foram utilizadas diferentes quantidades de quitina para a síntese de ZSM-5, a fim de verificar a sua influência na formação de mesoporos. Todas as amostras foram preparadas por processo hidrotérmico convencional. Para fins de comparação, a zeólita ZSM-5 também foi sintetizada sem a presença de quitina. As amostras foram caracterizadas por difração de raios X, microscopia eletrônica de varredura e isotermas de adsorção-dessorção de N2. Os resultados experimentais mostraram que o volume de mesoporos das amostras obtidas aumentou com a quantidade crescente de quitina na mistura reacional. Portanto, a quitina mostrou ser um auxiliar de síntese promissor para a obtenção da ZSM-5 com propriedade mesoporosa.

Abstract In this work, mesostructured ZSM-5 zeolite was prepared using chitin as a new template to produce mesoporosity. Different amounts of chitin were used for the synthesis of ZSM-5 in order to verify its influence on the formation of mesopores. All samples were prepared by conventional hydrothermal process. For comparison purposes, ZSM-5 zeolite has also been synthesized without a presence of chitin. The samples were characterized by X-ray diffraction, scanning electron microscopy and N2 adsorption techniques. Experimental results showed that the mesopores volume of the obtained samples increased with increasing amount of chitin in the reaction mixture. Therefore, chitin showed to be a promising template for obtaining the ZSM-5 with mesoporous property.

In this work, ZnAl2O4 spinel was used as photocatalyst for dye degradation in aqueous solutions under UV irradiation. This material was prepared by a route with chitosan as template. The effects of process variables, such as, initial dye concentration and photocatalyst concentration were investigated. Kinetic parameters were obtained and the reaction order was determined. The results revealed that both studied variables presented strong influence on the dye degradation efficiency, which attained 100% in some cases. It was found that the dye photocatalytic degradation under UV irradiation followed a first order kinetic behavior. The results indicated that ZnAl2O4 spinel can be used to treat dye containing effluents

The equilibrium and thermodynamics of azo dye (tartrazine and allura red) biosorption onto Spirulina platensis biomass were investigated. The equilibrium curves were obtained at 298, 308, 318 and 328 K, and four isotherm models were fitted the experimental data. Biosorption thermodynamic parameters (ΔG, ΔH and ΔS) were estimated. The results showed that the biosorption was favored by a temperature decrease. For both dyes, the Sips model was the best to represent the equilibrium experimental data (R²>0.99 and ARE<5.0%) and the maximum biosorption capacities were 363.2 and 468.7 mg g-1 for tartrazine and allura red, respectively, obtained at 298 K. The negative values of ΔG and ΔH showed that the biosorption of both dyes was spontaneous, favorable and exothermic. The positive values of ΔS suggested that the system disorder increases during the biosorption process.

Chitosan is a natural polymer that has been employed in dye adsorption. In this work, adsorption and thermodynamic data for the interaction of FD&C Red n° 40 food dye with chitosan in aqueous solutions were investigated. The equilibrium adsorption isotherms were determined by the batch method, from 298 to 338 K. Adsorption data were adjusted to five isotherm models: Langmuir, Freundlich, Redlich-Peterson, Temkin and Dubinin-Radushkevich, in order to determine which presented the best adjustment to the experimental data. Error analysis showed that the Langmuir isotherm model was the most appropriate for fitting the experimental data, with a maximum monolayer adsorption of 3065.8 µmol g-1 at 308 K. Negative enthalpy (-112.7 kJ mol-1), entropy (-0.338 kJ mol-1 K-1) and Gibbs free energy (-15.6 to 1.0 kJ mol-1) values demonstrated that the adsorption process is exothermic, spontaneous, favorable, and that randomness of the system decreases during the adsorption process.