Uso de hidrogéis compósitos à base de acrilamida, acrilato e bentonita para remoção do corante catiônico azul de metileno

Abstract

The development of dye chemistry has allowed that environmental problems arise due to discharge of industrial effluents into bodies of water. This affects water organisms directly and it can even reach the local population. Many alternatives have been studied, one of which is adsorption. It has been shown interesting because of its simplicity and efficiency. A lot of materials have been evaluated as adsorbents. The hydrogels could be an option due to their capacity of interacting with dissolved substances. Their properties can be improved by adding clays, which gives rise the composites. Bentonite, alike other clays, can retain dyes through cation exchange. The present work proposes the synthesis of a copolymer made of poly(acrylamide-co-sodium acrylate) with bentonite and evaluate its efficiency of methylene blue (AzMe) removal as well as the likely mechanism involved on this process. A central composite design (DCC) was performed to study the effect of five variables: clay content, hydrogel dosage, cross-linking content, pH, and temperature. The results show that only clay content and hydrogel dosage were significant to removal efficiency. These two variables were taken to a rotational central composite design (DCCR), which allows that response was optimized. In addition, a more predictive model was achieved. The optimal hydrogel, named P(Am-NaAc)/Bent, was characterized with the copolymer P(Am-NaAc) and bentonite. The employed techniques were infrared absorption spectroscopy (FTIR), X-ray diffraction (DRX), scanning electron microscopy (MEV), and adsorption/desorption of N2. All these techniques show evidence of a possible interaction between the clay and the copolymer. The point zero charge (pHPCZ) of those materials was also determined, and the results suggest the surface features of the composite are different from bentonite and the copolymer. Adsorption kinetics and isotherms were also performed to evaluate the effect of time and initial concentration of AzMe onto adsorption capacity and removal efficiency. Therefore, the work presents a promising material to adsorb the methylene blue dye.