Adsorption of Eu3+ and Am3+ ion towards hard donor-based diglycolamic acid-functionalised carbon nanotubes: density functional theory guided experimental verification

Abstract

Structure, bonding, energetic and thermodynamic parameters of trivalent Eu3+ and Am3+ with diglycolamic acid-functionalised carbon nanotubes (CNT–DGA) in gas and solvent phases are reported in order to understand their complexation and extraction behaviour. The calculation was performed with generalised gradient approximated BP86 density functional and hybrid B3LYP functional using SVP/TZVP basis set. The free energy of extraction, ΔGext, of Eu3+ and Am3+ was computed using the Born–Haber thermodynamic cycle in conjunction with conductor-like screening model solvation approach. The calculated free energy of extraction was found to be exergonic using an explicit cluster water model for hydrating the ions and it was found to be higher for Eu3+ ion over Am3+ ion. From the estimated distribution constant using synthesised CNT–DGA, it is indisputably established that the Eu3+ ion is preferentially extracted over Am3+ ion and hence confirms the acceptance of the explicit cluster model for ion solvation free energy and thermodynamic cycle for the evaluation of free energy of extraction in solution phase. This is perhaps the first of its kind that a combined theoretical and experimental study has been performed on the free energy of extraction of Eu3+ and Am3+ using CNT–DGA.