Removal of heavy metals from aqueous solution by multiwalled carbon nanotubes: equilibrium, isotherms, and kinetics

The adsorption of heavy metal ions (Cu2+, Pb2+, Cd2+, Ni2+, and Cr6+) on as-produced and oxidized multiwalled carbon nanotubes (MWCNTs) was investigated as a function of contact time, pH, and dose used in batch technique. The results indicated that the adsorption capacity of metals onto oxidized MWCNTs was greater than that on as-produced MWCNTs. The adsorption on oxidized MWCNTs increased with pH and increased dose. The affinity order of the studied metals was found to be Pb2+> Cu2+> Cr6+> Cd2+> Ni2+. The adsorption process achieved equilibrium within 2 h, and experimental data fitted well the pseudo-second-order model.