Adsorption of methylene blue onto activated carbon developed from biomass waste by H2SO4 activation: kinetic, equilibrium and thermodynamic studies

Sulphuric acid (H2SO4) was utilized as an activator for the preparation of activated carbon from a biomass solid waste, coconut leaves. The sulphuric acid-treated activated carbon (SAC) was used as low-cost adsorbent for the removal of methylene blue (MB) cationic dye from aqueous solution. Adsorption of MB using SAC from aqueous solution under equilibrium and kinetic conditions in batch mode was evaluated by varying adsorbent dose (0.2-2.5g/L), solution pH (3-11), initial dye concentration (30-400mg/L), contact time (0-180min) and temperature (303-323K). The Langmuir isotherm model showed better fit to the equilibrium data than the Freundlich model. The adsorption capacity (q(m)) of SAC increased with temperature where q(m) varied as follows: 126.9 (303K), 137.0 (313K) and 149.3mg/g (323K). The kinetic uptake results were well described by the pseudo-second-order (PSO) kinetic for each temperatures. The thermodynamic adsorption parameters (G degrees, H degrees and S degrees) were driven by favourable entropic factors, in accordance with the low activation energy (29.70kJ/mol) of the system. This study reveals that SAC is an effective and low-cost adsorbent for the removal of MB from aqueous solution.