Effects of Cu(II) and Ni(II) ions on adsorption of tetracycline to functionalized carbon nanotubes

The environmental applications and implications of functionalized carbon nanotubes (CNTs) have received much attention. In this study, the adsorption interactions of graphitized multi-walled carbon nanotubes (G-MWCNTs) and functionalized MWCNTs, including hydroxylated MWCNTs (OH-MWCNTs), carboxylated MWCNTs (COOH-MWCNTs), and aminated MWCNTs (NH2-MWCNTs), for tetracycline in the aqueous solution were systemically investigated, and the effects of Cu(II) and Ni(II) (two metal ions commonly present in aquatic environments) on MWCNTs-tetracycline interactions were examined. Results showed that the adsorption affinities followed an order of G-MWCNTs > OH-MWCNTs > COOH-MWCNTs > NH2-MWCNTs, indicating that the adsorptive interactions between MWCNTs and tetracycline can be largely affected by the types and abundance of functionalities on the MWCNTs surfaces. Both Cu(II) and Ni(II) had a negligible effect on the adsorption of tetracycline to G-MWCNTs, but varied effects of the metal ions were observed for the three functionalized MWCNTs. In general, Cu(II) exhibited a more pronounced effect for the adsorption of tetracycline than Ni(II), due to the degree of complexing capability.