Lead ions removal from aqueous solution using modified carbon nanotubes

Abstract

Surface-modified carbon nanotubes (CNTs) were prepared in order to remove lead ions (\(\hbox {Pb}^{2+}\)) from aqueous solution. The modification of CNTs was conducted by oxidation, using a mixture of nitric acid (\(\hbox {HNO}_{3}\)) and sulphuric acid (\(\hbox {H}_{2}\hbox {SO}_{4}\)). The adsorption behaviour was well fitted to the Langmuir model and the maximum adsorption capacity of \(\hbox {Pb}^{2+}\) was found to be \(100\,\hbox {mg} \,\hbox {g}^{-1}\). The adsorption of \(\hbox {Pb}^{2+}\) 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 \(18.56\,\hbox {kJ} \,\hbox {mol}^{-1}\), which reflect the outside surface adsorption and ion exchange mechanism. The thermodynamical studies showed that the adsorption of \(\hbox {Pb}^{2+}\) was a spontaneous and endothermic process. The ion exchange mechanism of \(\hbox {Pb}^{2+}\) removal was confirmed by the pH and electrical conductivity data in solution before and after adsorption.