Microesferas magnéticas de quitosana para remoção do corante violeta de metila 2B em meio aquoso

Abstract

The increasing use of dyes in the industry generates great quantities of waste. When disposed improperly, they become a source of pollution of aquatic systems which are essential to life and to maintain the equilibrium of natural ecosystems. For this reason, it is important to develop effective treatment methods for the removal of dyes. In this context, this work aimed to evaluate the adsorption capacity of magnetic chitosan microspheres for the removal of methyl violet 2B (MV 2B) dye in aqueous media. Initially, magnetite (Fe3O4) was prepared by chemical precipitation of iron salts (II) and (III). Then, chitosan microspheres were prepared by the suspension crosslinking technique. Finally, Fe3O4 was added to chitosan in order to achieve magnetic properties. These materials were characterized by their morphology and chemical characteristics. The experimental parameters of the adsorption process were optimized by varying the mass of adsorbent, the stirring rate, and the initial pH of the medium. The adsorbent capacity of magnetic chitosan microspheres was evaluated in a batch system at 25 °C. After the adsorption process in an aqueous medium, the remaining concentration of MV 2B solution was determined by molecular absorption spectroscopy in the visible region. The results showed that the magnetic chitosan microspheres present a high potential for the purpose, with a high capacity for removing MV 2B (~86%). The adsorption process followed pseudo-second-order rate kinetics, and the adsorption equilibrium was better described by the Freundlich isotherm (R2 higher than 0.98). The thermodynamic data revealed a spontaneous ( G° = -3.96 kJ mol-1), exothermic ( H° = -1.70 kJ mol-1), and S° = -3.73 J mol-1 K-1, which suggests a small variation in the randomness at the solidsolution interface.