Lead ions removal from aqueous solution using modified carbon nanotubes

Surface-modified carbon nanotubes (CNTs) were prepared in order to remove lead ions (Pb2+) from aqueous solution. The modification of CNTs was conducted by oxidation, using a mixture of nitric acid (HNO3) and sulphuric acid (H2SO4). The adsorption behaviour was well fitted to the Langmuir model and the maximum adsorption capacity of Pb2+ was found to be 100 mg g(-1). The adsorption of Pb2+ reached equilibrium in 80 min. The experimental data were well fitted to a pseudo-second-order rate model rather than a pseudo-first-order model. The activation energy and activation enthalpy of the adsorption calculated from Arrhenius and Eyring equations were, respectively, 21.08 and 18.56 kJ mol(-1), which reflect the outside surface adsorption and ion exchange mechanism. The thermodynamical studies showed that the adsorption of Pb2+ was a spontaneous and endothermic process. The ion exchange mechanism of Pb2+ removal was confirmed by the pH and electrical conductivity data in solution before and after adsorption.