Computational-Aided Design of Next-Generation Extractants for Trivalent Actinide and Lanthanide Separation

Abstract The chemical similarities between trivalent actinides (An(III)) and lanthanides (Ln(III)) stemming from their analogous ionic radii and physicochemical properties present a significant challenge in differentiating and separating them via solvent extraction, which is a pressing issue in nuclear and radiochemistry. However, the existing approaches suffer from different drawbacks such as inadequate separation factors, limited stripping efficiency, and undesired co-extraction. In this study, a novel unsymmetrical phenanthroline-derived amide-triazine (Et-Tol-CyMe4-ATPhen) extractant was designed with the aid of theoretical calculations and synthesized using an unprecedented de novo construction method. As expected, the Et-Tol-CyMe4-ATPhen extractant exhibited a favorable extraction ability for Am(III) and minimal extraction for Ln(III), thereby achieving an extremely selective An(III)/Ln(III) separation with a separation factor over 280. Furthermore, Am(III) could be effectively stripped from loaded phases using dilute nitric acid. The underlying coordination mechanisms were thoroughly elucidated by using 1H NMR, ESI-MS, UV-Vis absorption spectrum, fluorescence excitation spectrum, and X-ray single-crystal diffraction. This work holds promise for addressing the current challenges in An(III)/Ln(III) separation and represents a pioneering endeavor in developing next-generation extractants from first principles calculation.