Adsorption of lead(II) from water by carbon nanotubes: equilibrium, kinetics, and thermodynamics.

Adsorption of lead(II) from water on carbon nanotubes (CNTs) was investigated using a series of batch adsorption experiments. The adsorption rate was studied experimentally at various temperatures, contact times, and initial pH and lead(II) concentrations. It was observed that a considerable amount of lead(II) was adsorbed during the first 5 minutes of contact time. The pH of the solution strongly influenced the amount of adsorption, and the best results were obtained when pH value was approximately 6. For the adsorption isotherm, the experimental data were analyzed by three two-parameter isotherms (Langmuir, Freundlich, and Temkin) and four three-parameter isotherms (Redhich-Peterson, Sips, Toth, and Khan). The three kinetic models used to test the experimental data were Lagergren first-order, second-order, and the Elovich equation. The results obtained from the study of the thermodynamic parameters showed that the adsorption of lead(II) onto CNTs was a spontaneous and endothermic process.