Novel unsymmetric phenanthroline-derived amide triazine (ATPhen) extractant for efficient extraction and separation of Am(III) over Ln(III)

A key step in nuclear fuel reprocessing is using solvent extraction to separate trivalent lanthanides/actinides with similar chemical properties from high-level radioactive liquid waste. Developing extractants with high extraction and selectivity capacity is crucial to solving this challenge. Based on an unsymmetric design strategy, we have developed a tetradental chelating phenanthroline-derived extractant featuring amide and triazine side chains: 2-N-ethyl-N-(tolyl)carboxamide-9-(5,6-diphenyl-diphenyl-1,2,4-triazin-3-yl)-1,10-phenanthroline (Et-Tol-Ph-2-ATPhen). Its strong extraction ability for Am(III) under highly acidic conditions and excellent separation performance for Eu(III) and other Ln(III) ions have been demonstrated (D-Am(III) > 40, SFAm(III)/Ln(III) >= 200, 2 M HNO3). Because the introduction of electron-donating phenyl groups onto the triazine side chain enhanced the affinity of Et-Tol-Ph-2-ATPhen for Am(III), the dilute nitric acid successfully scrubbed the majority of the extracted Eu(III) while Am(III) remained in the organic phase, which will further improve the separation performance between Am(III) and Eu(III) (S-Eu(III) > 75 %, S-Am(III) < 6 %, 0.1-0.001 M HNO3). H-1 NMR titration and high-resolution ESI-MS revealed the stoichiometric ratio of the complexes formed by Et-Tol-Ph-2-ATPhen and Ln(III), whose stability constants were fitted by UV-Vis and fluorescence spectroscopic titrations. X-ray single-crystal diffraction directly confirmed the structures of [Eu(L)(NO3)(3)], [Eu(L)(2)(ClO4)](2+), and [Eu(L)(2)(H2O)](3+). DFT calculation explains the extraction and separation mechanism of Et-Tol-Ph-2-ATPhen from the theoretical level. The novel unsymmetric phenanthroline-derived extractant has application potential and provides a valuable reference for the development of separation processes for Am(III) and Ln(III) under high acidity.