Adsorção do corante azul de metileno em nanotubos de titanato de hidrogênio

Abstract

Textile effluents are considered one of the most polluting in terms of volume and composition. In these, the dyes stand out because they cause significant environmental impacts, mainly due to their structures of difficult degradation. Several processes have been studied for the purpose of finding an efficient and viable treatment to remove the dye of the textile effluents, and the adsorption is one of them. The aim of the present work was to evaluate the ability to remove the methylene blue dye from aqueous solutions by the adsorption technique using hydrogen titanate nanotubes as an adsorbent. For the characterization of the adsorbent material, the zero charge point (pHPCZ), indicating that the surface of the hydrogen titanate nanotubes is anionic when in the dye solution. The kinetic test was performed with the mass of adsorbent equivalent to 5 mg and with the concentration of dye equal to 5 mg L-1. The results obtained were adjusted to the pseudo-first kinetic models and pseudo-second order in which the last one was that best described the adsorption process. Batch isothermal tests were performed in triplicate by varying the adsorbent mass and at different temperatures (25, 35 and 45 °C) with the constant concentration of 5 mg L-1 of the dye solution. The experimental isotherms were tested in Langmuir models and Freundlich and Freundlich's was the most adequate, indicating a multiple layer adsorption. From the results obtained at the different temperatures, the thermodynamic study was developed, whereby the adsorption of the methylene blue dye in hydrogen titanate nanotubes was determined as an endothermic process. The values for the Gibbs energy obtained were negative for the temperatures studied, and positive values for the entropy, indicating that the adsorption process is spontaneous and that the adsorbent has good affinity with the adsorbate. Thus, from this work, it was possible to conclude that the hydrogen titanate nanotubes can be considered a promising adsorbent material for the color removal of the aqueous solution of methylene blue dye.