Competitive adsorption of heavy metal ions on carbon nanotubes and the desorption in simulated biofluids.

Carbon nanotubes (CNTs) had meaningful adsorption capacities for Pb(2+), Cu(2+), Zn(2+) and Cd(2+), while Pb(2+) showed the highest adsorption in the competitive adsorption evaluations. The desorption behaviors of heavy metal ions were completely different in various biofluids, where the desorption was significantly influenced by pH and the presence of proteins/other cations. The desorption was most effective in simulated stomach juice, and much less effective in other simulated biofluids. More Pb(2+) stuck to CNTs than others, resulting in less desorption. Interestingly, the competitive desorption behaviors of four ions were largely changed comparing to the individual desorption behaviors. The implications to the biosafety evaluations and synergistic effects of CNT are discussed.