The adsorption mechanism of anionic and cationic dyes by Jerusalem artichoke stalk-based mesoporous activated carbon

Jerusalem artichoke stalk based mesoporous activated carbon (MAC) has been studied for its potential adsorption removal of anionic (methyl orange, MO) and cationic dyes (methylene blue, MB). Batch adsorption experiments found that the adsorption data of both dyes were well fitted by Langmuir model and pseudo second- order kinetics. MB and MO adsorbed by MAC were of endothermic and exothermic nature, respectively. Acidic condition promotes the anionic dye molecules moving onto MAC surface by electrostatic attraction, while limits the initial adsorption rate of cationic dye. The intra- particle diffusion was involved in the whole diffusion process, but not the sole rate- controlling step. The calculated film diffusion coefficient (Df) values, in the range of 10 (6) to 10 (8) cm(2)/ s, was two orders of magnitude higher than intra- particle diffusion coefficient (Di) values, indicating the film diffusion controls the whole diffusion rates of the dye moleculesmoving from aqueous solution onto solid surface. Moreover, the D values for both dyes obtained in present study were superior to many reported carbon adsorbents. This higher D values were the result of more developed internal surface of MAC as higher mesoporosity, which promotes the diffusion rate. (C) 2013 Elsevier Ltd. All rights reserved.