Isolation of Methylene Blue from Aqueous Solution Using a Fraxinus Excelsior L. (Oleaceae) Based Biosorbent: Isotherm, Kinetics, and Thermodynamics

Biosorption was carried out using Fraxinus excelsior L. (Oleaceae) (FEO) as a natural waste to remove methylene blue from aqueous solutions. Based on the results of the study carried out under optimum conditions (pH: 6, initial dye concentration: 5 mg/L, biosorbent dose: 1 g, contact time: 30 min, stirring speed: 150 rpm, and temperature: 298 K), the FEO biosorbent removed 89% of methylene blue from aqueous solutions. In addition, parameters affecting biosorption (pH, initial dye concentration, biosorbent dose, temperature, and stirring speed) were examined, and isotherm, kinetic, and thermodynamic studies were performed. Freundlich, Langmuir, Elovich, Temkin, and Dubinin-Radushkevich isotherms were calculated in the isotherm studies, and the Freundlich isotherm was higher than the others. The correlation coefficient of pseudo-second-order kinetic model was higher than for the pseudo-first-order kinetic model. The Delta G values from the thermodynamic studies showed that the process occurred spontaneously. Consequently, the FEO biosorbent is suitable in removing synthetic dyes from aqueous solutions due to its effectiveness, low cost, and eco-friendly characteristics.