Valoração do resíduo do café para a adsorção do corante azul de metileno em efluentes têxteis

Abstract

Although Brazil is one of the largest producers of agro-industrial by-products, a significant portion of these resources is still wasted. This study explored the use of coffee grounds, dried at 100 °C and thermally modified at 600 °C, as bioadsorbents for the removal of methylene blue dye. Characterization was performed using X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, point of zero charge (PCZ), and particle size analysis. The influence of pH was evaluated, and a kinetic study was conducted, fitting the data to pseudo-first and pseudo-second-order kinetic models. Adsorption isotherms were analyzed and fitted to the Langmuir, Freundlich, Temkin, and Redlich-Peterson models. The results showed that thermal activation altered the structure and composition of the coffee grounds, enhancing their adsorbent properties. The samples demonstrated a high capacity for methylene blue removal. For the coffee grounds dried at 100 °C, the pseudo-second-order model provided the best fit, while for the thermally modified grounds at 600 °C, the kinetic data fit best with the pseudo-first-order model. The Redlich-Peterson model was the most accurate in describing the experimental data. In the reuse of coffee grounds, the pseudo-second-order model fit the kinetics best, and the Freundlich model was the most appropriate for the isotherms. These findings underscore the potential of thermally modified coffee grounds as a sustainable and effective alternative for pollutant adsorption.