Adsorção de picloram utilizando biossorventes e biocarvões: explorando o potencial da casca de cacau modificada por solvente eutético profundo

Abstract

The cocoa industry generates large volumes of lignocellulosic residues, especially in Brazil, one of the world's largest producers. For each ton of processed seeds (7% moisture), up to 120 kg of husk is produced, rich in lignin, cellulose, and hemicellulose, with potential for use as environmentally relevant adsorbent precursors. The modification of this biomass using deep eutectic solvents (DES) is a promising strategy for sustainable residue management and mitigation of pollution by persistent pesticides such as picloram. This study evaluated the removal of picloram from aqueous solution using biosorbents and biochars derived from cocoa husk modified with DES based on choline chloride (ChCl) combined with formic, oxalic, or methanesulfonic acid, as well as modification directly with methanesulfonic acid (MSA). The materials modified with MSA and ChCl:MSA exhibited the best performance and were characterized by FTIR, SEM, pHPZC, conductometric titration, XPS, and TGA. XPS analysis confirmed greater surface acidity and the introduction of sulfonated groups. Adsorption studies were conducted for BC-MSA and BC-MSADES, evaluating dosage, pH, ionic strength, kinetics, and isotherms. BC-MSADES achieved removal above 90% within 240 min (~120 mg g⁻¹), with stable performance over a wide pH and salinity range and best fit to the Freundlich model. BC- MSA exhibited higher uptake at elevated equilibrium concentrations, fitting the Sips model. Reusability assays indicated greater desorption reversibility for BC-MSADES. Therefore, modification with MSA or ChCl:MSA followed by pyrolysis proved to be an efficient route for producing high-performance biochars, representing a sustainable alternative for the treatment of herbicide-contaminated waters. Future perspectives include performance evaluation in continuous systems and integration with complementary contaminant degradation processes.