Remoção de corante têxtil por adsorção em borra de café

Abstract

The textile industry is one of the main sectors responsible for generating colored effluents due to the extensive use of synthetic dyes, which are often resistant to environmental degradation. Among these dyes, methylene blue stands out as a cationic compound with high solubility and difficult removal. A low-cost and sustainable alternative for treating such pollutants is the use of adsorbents derived from agricultural waste, such as spent coffee grounds, which possess a porous structure and functional groups capable of interacting with organic molecules. This study aimed to evaluate the efficiency of spent coffee grounds in the removal of methylene blue from aqueous solutions. Four commercial coffee brands were used, each subjected to washing, drying, and three different chemical pretreatments: neutral, acid, and basic. UV–Vis spectrophotometry was employed to monitor color removal, while adsorption kinetics and isotherm models Langmuir and Freundlich were applied to analyze the process.The results showed that the basic treatment exhibited the highest dye removal efficiency across all samples, and the coffee grounds from brand C treated with NaOH achieved the best performance, with 92% efficiency. The kinetic data followed the pseudo-first-order model, with correlation coefficients above 0.96. Regarding adsorption isotherms, the Langmuir model provided the best fit, indicating monolayer adsorption, with the highest adsorption capacity obtained at 45 °C. Tests using Direct Yellow and Reactive Orange dyes showed no significant adsorption, even under different pH conditions. Overall, the results confirm that spent coffee grounds represent an efficient, low-cost, and environmentally sustainable alternative for the treatment of water contaminated with cationic synthetic dyes, contributing both to solid waste reduction and to the development of cleaner technologies for the textile sector.