Effects of Anions on Adsorption of Trace Levels of Cu(II), Pb(II) and Cr(VI) by Amino-Functionalized Multi-Walled Carbon Nanotubes

Abstract

This work studies the adsorption of heavy metal ions (Cu(II), Pb(II) and Cr(VI)) in aqueous solutions on amino-functionalized multiwalled carbon nanotubes (MWCNTs-NH2) in the ppb concentration range (50-3000 �g/l) as a function of contact time, initial concentration of heavy metal ions and the presence of four inorganic electrolyte anions (Cl-, SO42-, NO3-, PO43-). The adsorption of heavy metals from aqueous solution was studied using different kinetic models. The results showed that the adsorption process is best fitted with the pseudo-second-order model indicating that the process is controlled by chemisorptions through electrostatic attraction and chemical interaction/complexation between the metal ions and the surface functional groups of MWCNTs-NH2. The intra-particle diffusion model showed that diffusion is slow, but did not govern the rate of the overall adsorption process. The effects of Cl-, SO42-, NO3- and PO43- anions on the adsorption of Cu(II), Pb(II) and Cr(VI) are variable (improvement, reduction, no impact).