Ligand structure optimization leads to efficient acid-resist Am(III)/Eu(III) separation in n-octanol

Liquid-liquid extraction is the most wildly adopted industrial Lns/Ans separation approach which takes advantages of the subtle atomic size differences for Lns and Ans. Preorganized ligand architecture with coordination configuration locking strategy has been proven to be very efficient to enhance the separation factors by size exclusive effect from the preset ligand cavity while drawbacks such as sophisticated ligand synthesis, unbalanced extraction/stripping performances and limited solubility in environmental benign solvents prevent the economic practicability. In the current contribution, calculation-guided ligand structure optimization was utilized to optimize the hard/soft tetradentate phenanthroline diamide ligands. Reducing the number of alkyl chains around the binding sites from amide to imide led to less rotation energy barriers, eventually boosted both metal distributions and separation factors. Additionally, the formation of hydrogen bonds in the imine ligands enhanced their solubility in industrial-friendly solvent, such as n-octanol, leading to superior extraction performances. Finally, balanced extraction, stripping and recycling of the reported ligands were demonstrated to unravel the potential to be integrated into current industrial plants. The ligand design philosophy as discussed in this work could inspire the searching for new environment-friendly high-performance lipophilic ligand to close the current nuclear fuel cycle.