The separation of actinides has a vital place in nuclear fuel reprocessing, recovery of radionuclides and remediation of environmental contamination. Here we propose a new paradigm of nanocluster-based actinide separation, namely nano-extraction, that can achieve efficient sequestration of uranium in an unprecedented form of giant coordination nanocages using a cone-shaped macrocyclic pyrogallol [4]arene as the extractant. The U 24 -based hexameric pyrogallol[4]arene nanocages with distinctive [U 2 PG 2 ] binuclear units (PG = pyrogallol), that rapidly assembled in situ in monophasic solvent, were identified by single-crystal XRD, MALDI-TOF-MS, NMR, and SAXS/SANS. Comprehensive biphasic extraction studies show that this novel separation strategy has enticing advantages such as fast kinetics, high efficiency, and good selectivity over lanthanides, and thus demonstrate its potential for efficient separation of actinide ions.

Phenanthroline-diamide ligands have been reported in the selective separation of actinides over Eu(III); on the contrary, relevant basic coordination chemistry studies are still limited, and extraction under actual application conditions is rarely involved. In this work, N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline [Et-Tol-DAPhen (L)] was applied to explore the coordination performance of lanthanides in simulative high-level liquid waste. For the first time, cascade countercurrent extraction was conducted with Et-Tol-DAPhen as the extractant, which reveals the periodic tendency of the extraction efficiency of lanthanides to decrease gradually as the atomic number increases. Comparison of elements with similar radii verifies the hypothesis that the increase in the atomic number leads to a decrease in the ionic radius, thus reducing the coordination and extraction capacity of ligands. Slope analysis, electrospray ionization mass spectrometry, and ultraviolet−visible titration results show that the ligand forms 1:1 and 1:2 complexes with lanthanides and the coordination ability follows the tendency of extraction efficiency, and the first crystal structures of Lns(III) with a phenanthroline-diamide ligand, i.e., [LaL(NO 3 ) 3 (H 2 O)] and [LaL 2 (NO 3 ) 2 ][(NO 3 )], were obtained, which confirms the conclusions described above. This work promises to enhance our comprehension of the chemical properties of Lns(III) and offer new clues for the design and synthesis of novel separation ligands.

Monitoring and quantification of the photoresponsive behavior of metal–organic frameworks that respond to a light stimulus are crucial to establish a clear structure–activity relationship related to light regulation. Herein, we report the first azobenzene-modified photoresponsive thorium–organic framework (Th-Azo-MOF) with the formula [Th6O4(OH)4(H2O)6 L 6] (H2 L = (E)-2′-p-tolyldiazenyl-1,1′:4′,4′-terphenyl-4,4″-dicarboxylic acid), in which the utilization of a thorium cluster as a metal node leads to one of the largest pore sizes among all the azobenzene-containing metal–organic frameworks (MOFs). The phototriggered transformation of the trans isomer to the cis isomer is monitored and characterized quantitatively by comprehensive analyses of NMR and UV spectroscopy, which reveals that the maximum isomerization ratio of cis Th-Azo-MOF in the solid state is 19.7% after irradiation for 120 min, and this isomerization is reversible and can be repeated several times without apparent performance changes. Moreover, the isomerization-related difference in the adsorption of the Rhodamine B guest is also illustrated and a possible photoregulated mechanism is proposed. This work will shed light on new explorations for constructing functionalized actinide porous materials by the elegant combination of actinide nodes with tailored organic ligands and furthermore will provide a comprehensive understanding of photoisomerization processes in MOF solids and insight into the mechanism on photoregulated cargo adsorption and release by photoactive MOFs.