Theoretical Insights into the Separation of Am(III)/Eu(III) by Hydrophilic Sulfonated Ligands.

In this work, we focused on the separation of Am(III)/Eu(III) with four hydrophilic sulfonated ligands (L) based on the framework of phenanthroline and bipyridine through scalar relativistic density functional theory. We studied the electronic structures of [ML(NO3)3] (M = Am, Eu) complexes and the bonding nature between metal and ligands as well as evaluated the separation selectivity of Am(III)/Eu(III). The tetrasulfonated ligand L2 with a bipyridine framework has the strongest complexing ability for metal ions probably because of the better solubility and flexible skeleton. The disulfonated ligand L1 has the highest Am(III)/Eu(III) selectivity, which is attributed to the covalent difference between the Am-N and Eu-N bonds based on the quantum theory of atoms in the molecule analysis. Thermodynamic analysis shows that the four hydrophilic sulfonated ligands are more selective toward Am(III) over Eu(III). In addition, these hydrophilic sulfonated ligands show better complexing ability and Am(III)/Eu(III) selectivity compared to the corresponding hydrophobic nonsulfonated ones. This work provides theoretical support for the separation of Am(III)/Eu(III) using hydrophilic sulfonated ligands.