Sorption kinetics, thermodynamics and competition of Ni2+ from aqueous solutions onto surface oxidized carbon nanotubes

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+.