An unmet challenge in the thorium-uranium fuel cycle is the efficient separation of uranium from thorium. Herein, two new tetradentate N,O-hybrid ligands, N,N′-diethyl-N,N′-di-p-tolyl-2,2′-bipyridine-6,6′-dicarboxamide (Et-Tol-BPDA) and N,N′-diethyl-N,N′-di-p-tolyl-2,2′-bipyrimidine-4,4′-dicarboxamide (Et-Tol-BPymDA), comprising a bipyridine or bipyrimidine core and amide moieties were designed and synthesized for selectively complexing and separating U(VI) from Th(IV). The high U(VI)/ Th(IV) extraction selectivity was achieved by Et-Tol-BPDA (SF U/Th = 33 at 3 M HNO 3 ) and Et-Tol-BPymDA (SF U/Th = 73 at 3 M HNO 3 ) in nitric acid solutions. The extraction process for U(VI) or Th(IV) with these two ligands primarily proceeded through the solvation mechanism, as evidenced by slope analyses. Thermodynamic studies for the extraction of U(VI) and Th(IV) revealed a spontaneous process. Results from UV−vis spectroscopic titration and slope analyses demonstrated that U(VI) and Th(IV) each form a 1:1 complex with the two ligands both in the monophasic organic solution and the biphasic extraction system. The stability constants of the 1:1 complexes of Et-Tol-BPDA or Et-Tol-BPymDA with U(VI) were found to be larger than those with Th(IV), which coincide well with the high U(VI)/Th(IV) extraction selectivity. The solid-state structures of Et-Tol-BPDA, Et-Tol-BPymDA, and 1:1 complexes of the two ligands with U(VI) or Th(IV) were analyzed by X-ray diffraction technique. The results from this work implicate the potential of bipyridine-and bipyrimidinederived diamide ligands for uranium/thorium separation.

No abstract

The capture of palladium from spent nuclear fuel is crucial for the sustainable development of nuclear energy and resource recovery. One of the most challenging issues in this direction is the survival of adsorbents under extreme reprocessing conditions such as strongly acidic media and high radiation fields while still maintaining high extraction ability and selectivity. Herein, an approach to addressing this issue is reported by incorporating macrocycle into nitrogen‐rich covalent organic polymers (COPs). Dramatically outperforming current adsorbing materials, pillar[5]arene‐based COPs with pyridyl and triazolyl functionalities display record adsorption capacity for Pd(II) at 3 M HNO3 (403 mg g−1), extraordinary stability under 500 kGy gamma irradiation, and ultra‐high selectivity toward Pd(II) over both 17 coexisting cations and six anions. In particular, the material P5COP‐m‐BPT with the best performance also shows remarkable dynamic adsorption efficiency for Pd(II). This study not only provides a strategy to enhance all‐sided adsorption performance in palladium separation with nitrogen‐rich COPs materials but also demonstrates the superiority of customizing advanced materials with macrocycles.