Adsorption And Desorption Of Typical Heavy Metal Ions On Carbon Nanotubes

Due to their unique structure and fascinating properties, carbon nanotubes(CNTs) have attracted great interests and have lots of attractive applications in many important ?elds, including energy, electronics and materials. For example, CNTs as adsorbents show very high adsorption capacity for various pollutants, therefore will have widely applications in water treatment in future. In the same time, d ue to the valuable applications and great potentials, the biosafety of CNTs has been seriously concerned. Recently, the synergistic toxicity of CNTs and heavy metals has aroused great interests of some researchers. Several studies reported that CNTs could aggravate the toxicity of heavy metal ions. However, the available studies mainly focused on describing the synergistic effects rather than the underneath mechanism. To fully understand the underneath mechanism, the ?rst step is to investigate the adsorption and desorption of heavy metals on CNTs in biological systems.Herein, we oxidized multi-walled CNTs(MWCNTs) with H2SO4 /HNO3 into oxidized MWCNTs(O-MWCNTs). Then we systematically evaluated the adsorption/desorption behaviors of heavy metal ions on O-MWCNTs in simulated bio?uids. The adsorption isotherms and kinetics of Pb2+, Cu2+, Zn2+ and Cd2+ on CNTs were measured. The competitive adsorption of the four ions on CNTs was evaluated, too. The desorption behaviors of Pb2+, Cu2+, Zn2+ and Cd2+ from CNTs in simulated bio?uids were investigated one-by-one and also in a competitive way.Our results clearly showed that CNTs adsorbed heavy metal ions fast and effectively. O-MWCNTs had meaningful adsorption capacities for Pb2+, Cu2+, Zn2+ and Cd2+, while Pb2+ showed the highest adsorption in the competitive adsorption evaluations. The desorption behaviors of heavy metal ions were completely different in various bio?uids, where the desorption was signi?cantly in?uenced by p H and the presence of proteins/other cations. The desorption was most effective in simulated stomach juice, and much less effective in other simulated bio?uids. Pb2+ showed higher af?nity to CNTs and lower desorption. The competitive desorption of four ions showed quite different behaviors from individua l desorption.The information obtained in this study is very important to the biosafety assessment of CNTs and the mechanism study of the joint effect of CNTs and metal ions.