Experimental and Theoretical Unraveling the Separation of An/Ln: Insights to Phenanthroline Diamide Extractant with Variations of Amide Substituent Moieties

2,9-Diamide-1,10-phenanthroline (DAPhen) extractants constitute a novel class of tetradentate agents due to their high affinity for actinides and their adherence to the CHON principle. In this investigation, we explored the performance in extraction and the capabilities for An/Ln separation of a series of N,N′-diethyl-N,N′-diethyl-2,9-diamide-1,10-phenanthroline (Et-Et-DAPhen), N,N′-dioctyl-N,N′-dioctyl-2,9-diamide-1,10-phenanthroline (Oct-Oct-DAPhen), N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen), and N,N′-dialkyl-N,N′-diphenyl-2,9-diamide-1,10-phenanthroline (R-Ph-DAPhen, R = H, Me, Et, Oct) extractants featuring diverse amide substituents. Combining extraction experiments with theoretical calculations reveals that substituting ethyl with octyl enhances the extraction efficiency. Moreover, phenyl amide substituents exhibit superior extraction properties compared with alkyl counterparts. Augmenting the alkyl carbon chain length of the amide substituent proves beneficial for improving extraction performance. In contrast to alkyl, tolyl substituents demonstrate an enhanced favorability for extraction. By comparing the extraction performance and separation performance before and after irradiation, combined with theoretical calculations, it reveals that appropriately increasing the carbon chain length of the amide substituent can enhance radiation stability. Additionally, the incorporation of phenyl-substituted alkanes contributes to the heightened radiation stability of the extractant. This work promises to contribute to the structural design and performance optimization of novel extractants for An–Ln separation, thereby facilitating advances in extraction and separation methodologies.