Misturas de solvente eutético profundo e cloreto de ferro como agentes de modificação pré-pirólise para o desenvolvimento de adsorventes aplicados à remoção de cromo

Abstract

The contamination of water bodies by potentially toxic elements (EPTs), especially chromium in the hexavalent form (Cr(VI)), is a serious environmental and public health problem, and is mostly associated with the inappropriate discharge of industrial effluents. Among the technologies for the treatment of these effluents, adsorption stands out for its high efficiency, operational simplicity and economic viability. In this context, this study aimed to develop and evaluate sugarcane bagasse (BCA) biochars, chemically modified with deep eutectic solvents (DES) based on methanesulfonic acid and choline chloride, as well as with iron(III) chloride, aiming at the removal of Cr(VI) from aqueous solutions. BCA was submitted to pre-pyrolysis treatments using methanesulfonic acid, choline chloride and ferric chloride, alone and in different combinations, followed by pyrolysis at 400 and 600 °C. The materials obtained were characterized by infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray excited photoelectron spectroscopy (XPS) and determination of the zero-charge point (pHPCZ), to elucidate the structural, chemical and morphological changes promoted by the treatments. The adsorption assays showed that the pH of the medium exerts a significant influence on the process, with higher removal efficiencies under acidic conditions, associated with the predominance of dichromate ion and the positively charged surface of the biochars. The CADES4 and CADESF4 materials showed removals greater than 94% at the optimal dose of 2.0 g L⁻¹. The kinetic studies indicated that equilibrium was reached in approximately 720 minutes, and the Elovich model was the one that best described the experimental data, suggesting that adsorption occurs predominantly in energetically heterogeneous active sites. The adsorption isotherms were classified as L-type, with better fit to the Sips model, showing heterogeneous surfaces and maximum adsorption capacities close to 74 mg g⁻¹. In addition, the biochars showed good stability and potential for reuse over four successive cycles, the material removed 74% of chromium (IV) in solution. Thus, the materials developed are promising, sustainable and lowcost alternatives for the remediation of Cr(VI)-contaminated waters.