Adsorption kinetics, thermodynamics and isotherm of thiacalix[4]arene-loaded resin to heavy metal ions

A thiacalix[4]arene-loaded resin was prepared and characterized. The adsorption capacities of the thiacalix [4]arene-loaded resin toward Cu2+, Pb2+ and Cd2+ ions were investigated by batch adsorption experiments. It was found that the selective adsorption capacities of the thiacalix[4]arene-loaded resin are mainly attributed to the complex of the loaded thiacalix[4]arene with heavy metal ions. Various factors affecting the adsorption capacities such as contact time, temperature, pH and initial concentration of the metal ions were investigated. The adsorption kinetics was evaluated with the pseudo-first-order and pseudo-second-order models. The equilibrium data were analyzed using Langmuir and Freundlich isotherm models by non-linear regression. The adsorption kinetics followed the pseudo-second-order rate law for the three heavy metal ions, indicating chemical sorption as the rate-limiting step of the adsorption mechanism. The adsorption of heavy metal ions onto the thiacalix[4]arene-loaded resin is fitted better to the Langmuir isotherm than to the Freundlich isotherm, and the maximum adsorption capacities were 21.4, 47.9, and 44.9 mg/g for Cu2+, Pb2+ and Cd2+ ions respectively. Thermodynamic studies revealed that the adsorptions of the thiacalix[4]arene-loaded resin to heavy metal ions were spontaneous and exothermic processes with an increase of entropy. (C) 2010 Elsevier B.V. All rights reserved.