Caesalpinia ferrea Fruits as a Biosorbent for the Removal of Methylene Blue Dye from an Aqueous Medium

In the present work, a biosorbent was produced through the alkaline washing of Brazilian ironwood fruits. Infrared and thermogravimetric analyses showed changes in the obtained biosorbent with the removal of extractives, whose micrograph presents a more fibrous structure for the treated material. The biosorption behavior of the methylene blue dye shows efficiency at pH above five, and at alkaline pH, it reaches removal efficiency of up to 90% for five successive cycles. Adsorption kinetics is fast and fits the pseudo-second-order model, which, with the best fit of the Langmuir isotherm model, indicates a chemical adsorption mechanism. The thermodynamic trials express the spontaneity of biosorption and enthalpy and entropy variations of − 10.47 kJ mol⁻¹ and 51.84 J mol⁻¹ K⁻¹, respectively. The maximum biosorption capacity is of 125.2 mg g⁻¹ for the temperature of 25 °C, consisting in a low-cost alternative for the removal of this type of contaminant from an aqueous medium.