Polysubstituted guanidine-based receptors for the selective extraction of pertechnetate anion from high-level waste

Abstract

In this work, we report the design and synthesis of a novel series of guanidine-based extractants tailored for the selective and efficient extraction of the pertechnetate anion (TcO 4 -). A library of 24 structurally diverse ligands was prepared and systematically evaluated for the extraction of technetium from nitric acid solutions and high-level waste (HLW) simulants. Several compounds exhibited outstanding performance, with distribution ratios (D Tc ) exceeding 2000 and selectivity factors up to 400 over competing anions. The extraction mechanism was investigated via backextraction experiments, revealing the influence of nitric acid concentration, temperature, and alkaline stripping agents. The composition of the extracted species was confirmed by single-crystal X-ray diffraction (SC-XRD) and X-ray absorption spectroscopy (XAS), supporting the formation of discrete ion pairs between the guanidinium cation and pertechnetate anion. These results highlight the potential of guanidine-based receptors for targeted separation of Tc(VII) from complex nuclear waste matrices.