Adsorption of methylene blue on activated carbon produced from flamboyant pods ( Delonix regia): Study of adsorption isotherms and kinetic models

Abstract

The adsorption of methylene blue (MB) onto activated carbon produced from flamboyant pods ( Delonix regia) and obtained under optimized conditions (AC op) was carried out in this work. The experimental equilibrium data were analyzed using the isotherms of Langmuir, Freundlich, Jovanovic, Harkins–Jura, Tempkin, Redlich–Peterson, Toth, Radke–Prausnitz, Sips, Vieth–Sladek, and Brouers–Sotolongo. The adsorption kinetics of pseudo-first order, pseudo-second order, and Avrami were used for the kinetic studies. For the Toth isotherm, the value of maximum adsorption capacity ( Q m = 889.58 mg g −1) was close to the experimental value ( Q m = 890 mg g −1), and the correlation coefficient ( R 2) was 0.9836. The experimental data fitted very well to Avrami kinetic model. The Fourier-transform infrared spectroscopy spectra and the scanning electron microscopy images showed the presence of MB adsorbed onto AC op. Several possible mechanisms of interaction that can occur in the MB–AC op system are discussed. AC op is a fast and effective adsorbent for removing MB from aqueous solutions.