Ionic-liquid-regulated interfacial coordination reconstruction of uranyl(VI) species during tributyl phosphate...

The extraction and separation of uranyl species from nitric acid media are critical processes in nuclear fuel reprocessing, while the molecular-level coordination mechanism remains insufficiently understood. Herein, the extraction behavior and mechanism of U(VI) in the tributyl phosphate (TBP)/tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide ([P₁₄₄₄][NTf₂]) ionic liquid system were systematically investigated by combining experiments with molecular simulations. The results demonstrate efficient U(VI) extraction, rapid kinetics, and good temperature adaptability. Slope analysis and ion competition experiments reveal that extraction involves TBP-assisted coordination coupled with cation-exchange contributions, indicating dynamic solvation and coordination reconstruction during phase transfer. Electrostatic potential and dipole moment analyses indicate that the ionic-liquid environment modifies the electronic distribution of TBP and increases its polarization, particularly around the phosphoryl (PO) group, potentially influencing its interactions with uranyl species. Molecular dynamics simulations reveal a sequential extraction process involving interfacial enrichment, coordination reconstruction, and phase transfer. At the aqueous-organic interface, U(VI)-containing species undergo partial dehydration and accumulate at the interface. TBP progressively enters the first coordination sphere of U(VI), replacing some coordinated water molecules, while some nitrate ligands remain in the first coordination sphere. Upon transfer into the ionic liquid phase, TBP becomes the dominant coordinating ligand and stabilizes TBP-rich uranium complexes. Overall, this work demonstrates that U(VI) extraction in the TBP/[P₁₄₄₄][NTf₂] system is governed by an ionic-liquid-regulated interfacial coordination reconstruction process, where electronic modulation and dynamic ligand exchange collectively promote efficient uranium transfer.