Different Interaction Mechanisms of Eu(III) and ²⁴³Am(III) with Carbon Nanotubes Studied by Batch, Spectroscopy Technique and Theoretical Calculation

Herein the sorption of Eu­(III) and ²⁴³Am­(III) on multiwalled carbon nanotubes (CNTs) are studied, and the results show that Eu­(III) and ²⁴³Am­(III) could form strong inner-sphere surface complexes on CNT surfaces. However, the sorption of Eu­(III) on CNTs is stronger than that of ²⁴³Am­(III) on CNTs, suggesting the difference in the interaction mechanisms or properties of Eu­(III) and ²⁴³Am­(III) with CNTs, which is quite different from the results of Eu­(III) and ²⁴³Am­(III) interaction on natural clay minerals and oxides. On the basis of the results of density functional theory calculations, the binding energies of Eu­(III) on CNTs are much higher than those of ²⁴³Am­(III) on CNTs, indicating that Eu­(III) could form stronger complexes with the oxygen-containing functional groups of CNTs than ²⁴³Am­(III), which is in good agreement with the experimental results of higher sorption capacity of CNTs for Eu­(III). The oxygen-containing functional groups contribute significantly to the uptake of Eu­(III) and ²⁴³Am­(III), and the binding affinity increases in the order of SOH < SCOOH < SCOO^–. This paper highlights the interaction mechanism of Eu­(III) and ²⁴³Am­(III) with different oxygen-containing functional groups of CNTs, which plays an important role for the potential application of CNTs in the preconcentration, removal, and separation of trivalent lanthanides and actinides in environmental pollution cleanup.