Biochars prepared from anaerobic digestion residue, palm bark, and eucalyptus for adsorption of cationic methylene blue dye: Characterization, equilibrium, and kinetic studies

Biochars prepared from anaerobic digestion residue (BC-R), palm bark (BC-PB) and eucalyptus (BC-E) were used as sorbents for removal of cationic methylene blue dye (MB). The FE-SEM images indicated that the biochars have a well-developed pore structure, and the Brunauer–Emmett–Teller surface areas of BC-R, BC-PB, and BC-E were 7.60, 2.46, and 10.35 m2 g−1, respectively. The efficiencies of MB removal in the samples with initial concentrations of 5 mg L−1 at pH 7.0 and 40 °C by BC-R, BC-PB, and BC-E after 2 h were 99.5%, 99.3%, and 86.1%, respectively. Pseudo-second-order kinetics was the most suitable model for describing the adsorption of MB onto the biochars. The experimental data were best described by the Langmuir isotherm model, with a maximum monolayer adsorption capacity of 9.50 mg g−1 at 40 °C for BC-R. The biochars produced from the three types of solid waste showed considerable potential for adsorption.