The effective capture of radioiodine, produced or released from nuclear-related activities, is of paramount importance for the sustainable development of nuclear energy. Here, a series of zirconium-based metal−organic frameworks (Zr-MOFs), with a Zr 6 (μ 3 -O) 4 (μ 3 -OH) 4 cluster and various carboxylate linkers, were investigated for the capture of volatile iodine. Their adsorption kinetics and recyclability were investigated in dry and humid environments. The structural change of Zr-MOFs during iodine trapping was studied using powder X-ray diffraction and pore structure measurements. Experimental spectra (Raman and X-ray photoelectron spectroscopy) and density functional theory (DFT) calculations for the linkers and Zr clusters were performed to understand the trapping mechanism of the framework. When interacting with iodine molecules, MOF-808, NU-1000, and UiO-66, with highly connected and/or rigid linkers, have better structural stability than UiO-67 and MOF-867, which have flexible linkers with less connectivity. Particularly, MOF-808, with a rigid and tritopic benzenetricarboxylate linker, has the highest iodine adsorption capacity (2.18 g/g, 80 °C), as well as the largest pore volume after iodine elution. In contrast, UiO-67, with long linear ditopic linkers, exhibits the weakest stability and lowest adsorption capacity (0.53 g/g, 80 °C) because of its most serious collapse of pore structures. After incorporating with strong electron-donating imidazole/pyridine ligands, both the stability and adsorption capacity of MOF-808/NU-1000 decrease. DFT calculations verify that the N-heterocycle groups could enhance the affinity toward iodine by strong charge transfer. DFT calculations also suggest that the terminal −OH in MOF-808 has a strong affinity toward iodine (−54 kJ/mol I 2 ) and water (−63 kJ/mol H 2 O) and a weak affinity toward NO 2 (−27 kJ/mol NO 2 ). With high adsorption capacity and excellent stability, MOF-808 shows great potential for the sustainable removal of radioiodine.

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Efficient capture of highly toxic radionuclides with long half-lives such as Americium-241 is crucial to prevent radionuclides from diffusing into the biosphere. To reach this purpose, three different types of mesoporous silicas functionalized with phosphonic acid ligands (SBA-POH, MCM-POH, and BPMO-POH) were synthesized via a facile procedure. The structure, surface chemistry, and micromorphology of the materials were fully characterized by (31)P/(13)C/(29)Si MAS NMR, XPS, and XRD analysis. Efficient adsorption of Am(III) was realized with a fast rate to reach equilibrium (within 10 min). Influences including structural parameters and functionalization degree on the adsorption behavior were investigated. Slope analysis of the equilibrium data suggested that the coordination with Am(III) involved the exchange of three protons. Moreover, extended X-ray absorption fine structure (EXAFS) analysis, in combination with XPS survey, was employed for an in-depth probe into the binding mechanism by using Eu(III) as a simulant due to its similar coordination behavior and benign property. The results showed three phosphonic acid ligands were coordinated to Eu(III) in bidentate fashion, and Eu(P(O)O)3(H2O) species were formed with the Eu-O coordination number of 7. These phosphonic acid-functionalized mesoporous silicas should be promising for the treatment of Am-containing radioactive liquid waste.

The extracted complexes of trivalent lanthanides (Ln(III)) with purified Cyanex 301 (bis(2,4,4-trimethylpentyl)dithiophosphinic acid, denoted as HA) were investigated by extended X-ray absorption fine structure spectroscopy (EXAFS), UV-Vis and fluorescence spectroscopy. In the complexes prepared under the same conditions of solvent extraction, the light Ln(III) ions are mainly coordinated by the sulfur atoms of the ligands, and the middle Ln(III) ions are coordinated by mixed donors, the sulfur atoms of the ligands and the oxygen atoms of the extracted water, while the heavy Ln(III) ions are completely hydrated in the organic phase without any sulfur atoms of the ligands in the coordination shell. As the atomic number increases, the extracted water molecules gradually replace the sulfur atoms of the ligands in the first coordination shell of Ln(III), and simultaneously the ligand anions become counterions just for balancing the positive charge of the fully hydrated heavy Ln(III) ions. The effect of the change in the complex structures on the extraction of Ln(III) ions with HA was evaluated by the co-extraction of other thirteen individual Ln(III) together with Nd(III). In contrast to most ligands bonding more strongly to heavier Ln(III), HA preferentially extracts lighter Ln(III), suggesting that the unusual extraction capability of HA for Ln(III) might originate from the difference in the complex structures with Ln(III) ions.

In the last decades, the separation of actinides was widely and continuously studied in China. A few kinds of salt-free reductants to adjust Pu and Np valences have been investigated. , -dimethylhydroxylamine is a good reductant with high reduction rate constants for the co-reduction of Pu(IV) and Np(VI), and monomethylhydrazine is a simple compound for the individual reduction of Np(VI). Advanced PUREX based on Organic Reductants (APOR) was proposed. Trialkylphosphine oxide (TRPO) with a single functional group was found to possess strong affinity to tri-, tetra-and hexa-valent actinides. TRPO process has been first explored in China for actinides partitioning from high level waste and the good partitioning performance was demonstrated by the hot test. High extraction selectivity for trivalent actinides over lanthanides by dialkyldithiophosphinic acids was originally found in China. A separation process based on purified Cyanex 301 for the separation of Am from lanthanides was presented and successfully tested in a battery of miniature centrifugal contactors.

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Ag clusters and nanoparticles have attracted much attention in the fields of environmental catalysis and pollutant removal. It is a common strategy to fabricate highly dispersed Ag nanoparticles in porous scaffolds via in situ growth. Here, anionic metal−organic frameworks (MOFs) have been employed to provide robust supports for Ag species. Ag nanoparticles with well-defined sizes are observed in MOFs when internal NH 2 Me 2 + is exchanged with extrinsic Ag + ions. The extended X-ray absorption fine structure and X-ray photoelectron spectroscopy spectra confirm that about 20% of Ag + are reduced into Ag 0 , while the rest 80% are still Ag + species. The comparison of Ag loading into anionic and neutral Cu-BTC MOFs suggests that the exchangeable cations facilitate Ag + migration into the interior of MOFs and thus alleviate its aggregation and spontaneous reduction. Besides, the adsorption tests verify that all the Ag species in MOFs are accessible to iodine vapor to form AgI. The charge transfer from frameworks to trapped iodine and the water in the air promote the formation of iodide ions, which react with Ag + to produce AgI. The iodine adsorption performance of MOF beads was also evaluated using the pore diffusion model. This work provides insights into the evolution of Ag species in MOFs and potential Ag-based adsorbents for radioiodine capture.