Highly efficient Eugenia dysenterica DC seeds biomass as adsorbent for methylene blue removal

This study investigates the adsorption of methylene blue (MB), a model pollutant, using seeds of Eugenia dysenterica DC as a biosorbent. The choice of this material is justified by its natural abundance in ecosystems such as the African savannah and Brazilian cerrado, as well as its rich lignin and hemicellulose content, which enhances adsorption efficiency. Characterization by FT-IR/ATR and thermal analysis confirmed the presence of these key components. Batch adsorption experiments revealed a strong dependency on pH, with a maximum adsorption capacity of 389 mg/g at pH 11 and 66 mg/g at pH 3. The significant increase in adsorption capacity under basic conditions is attributed to the deprotonation of phenolic − O⁻ groups, enhancing electrostatic attraction and π-π stacking interactions. Kinetic studies demonstrated that adsorption follows the Pseudo-First-Order (PFO) model at pH 11 and the Pseudo-Second-Order (PSO) model at pH 3, reflecting a shift from non-specific physisorption to specific chemical interactions, such as hydrogen bonding and n-π interactions, under acidic conditions. Thermodynamic analysis confirmed the adsorption as endothermic, spontaneous, and characterized by increased randomness at the adsorbent-adsorbate interface. These findings underscore the potential of Eugenia dysenterica DC seeds as an abundant, eco-friendly, and highly efficient biosorbent for dye removal, offering a sustainable and scalable alternative for wastewater treatment.