Adsorptive removal of 2,4-didichlorophenol and 2,6-didichlorophenol from aqueous solution by beta-cyclodextrin/attapulgite composites: Equilibrium, kinetics and thermodynamics

beta-Cyclodextrin/attapulgite (beta-CD/ATP) composites were prepared for the adsorption of 2,4-didichlorophenol (2,4-DCP) and 2,6-didichlorophenol (2,6-DCP) from aqueous solution. beta-CD/ATP composites mainly possessed mesopores, high surface area and big pore volume which were benefit for the adsorption capacity. The batch mode adsorption experiments with respect to pH, temperature, initial concentration, contact time and binary dichlorophenol solution were investigated. Equilibrium data, at various temperatures, were described by the Langmuir. Freundlich and Dubinin-Radushkevich isotherm models. The Langmuir isotherm model was fitted to the experimental data significantly better than the other models. The kinetic data were well fitted to the intraparticle diffusion equation, which indicated that three steps belonged to the pseudo-second-order adsorption process. Intraparticle diffusion increased with the increase of adsorbate concentrations while film and pore diffusion decreased. The initial adsorption factor, R-i, showed that initial adsorption for 2,4-DCP was intermediate while was strong for 2,6-DCP. The thermodynamics parameters (positive values of Delta H degrees and Delta S degrees, negative values of Delta G degrees) indicated that binding systems between beta-CD/ATP composites and adsorbates (2,4-DCP and 2,6-DCP) were endothermic, entropy gained and spontaneous in nature. (C) 2010 Elsevier B.V. All rights reserved.