Singlewalled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) were oxidized by NaClO solutions and were employed as sorbents to study their sorption kinetics and thermodynamics of Ni2+ from aqueous solutions. The amount of Ni2+ sorbed onto SWCNTs and MWCNTs increased with a rise in temperature. The sorption kinetics follows the pseudo-second-order rate law while the sorption thermodynamics indicates the endothermic and spontaneous nature. Under the same conditions, the SWCNTs and MWCNTs possess better performance of Ni2+ sorption than the commercially available granular activated carbon, reflecting that both CNTs are efficient Ni2+ sorbents in water and wastewater treatment. The competitive sorption of Ni2+ and Zn2+ onto SWCNTs and MWCNTs was also conducted and revealed that the sorption capacities of Ni2+ and Zn2+ Without competition are much greater than those with competition. The competition which Zn2+ exerts on the sorption of Ni2+ is stronger than the competition exerted by Ni2+ on the sorption of Zn2+. (C) 2009 Elsevier B.V. All rights reserved.