Methylene blue adsorption on activated carbon prepared from Posidonia oceanica (L.) dead leaves: Kinetics and equilibrium studies

Posidonia oceanica (L.) is an endemic species in the Mediterranean Sea, which, like terrestrial plants, loses it leaves seasonally. The dead leaves are accumulated on the beaches in huge quantities as waste material, causing great environmental and economical problems. The dead biomass offers an abundant, renewable and low cost precursor for the production of activated carbon (AC). In that respect ACs were prepared by chemical activation of P. oceanica (L.) dead leaves. The preparation process consisted of zinc chloride impregnation at ratios up to 45%, followed by carbonization in nitrogen atmosphere at temperatures up to 873 K. The prepared P. oceanica (L.) activated carbons (POAC) were studied by SEM and Nitrogen porosimetry and the pore structural characteristics were determined. Concerning the POAC45 sample, a specific surface area of 1483 m2/g and a total pore volume of about 1 cm3/g were achieved, while both microporosity and mesoporosity were obtained. The adsorption potential of POAC for the removal of methylene blue (MB) from aqueous solutions was also investigated under varying conditions of initial concentration, carbon dosage, pH, temperature and the optimum experimental conditions were determined. The samples revealed relatively fast kinetics reaching equilibrium in around 60 min, which follow the second order rate equation, while adsorption was unaffected by the pH of the solution. The Langmuir model provided the best fit to the experimental data and sorption capacity increased with increasing temperature. The results showed that proposed precursor lead to AC with increased sorption capacity for MB reaching a value of 285.7 mg/g at 318 K. In conclusion, P. oceanica (L.) dead leaves can be used as a raw material for preparation of high quality activated carbon.