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Lanthanide/actinide separation is a worldwide challenge for atomic energy and nuclear waste treatment. Separation of americium (Am), a critical actinide element in the nuclear fuel cycle, from lanthanides (Ln) is highly desirable for minimizing the long-term radiotoxicity of nuclear waste, yet it is extremely challenging given the chemical similarity between trivalent Am­(III) and Ln­(III). Selective oxidation of Am­(III) to a higher oxidation state (OS) could facilitate this separation, but so far, it is far from satisfactory for practical application as a result of the unstable nature of Am in a high OS. Herein, we find a novel strategy to generate stable pentavalent Am (Am­(V)) through coordination of Am­(III) with a diglycolamide ligand and oxidation with Bi­(V) species in the presence of an organic solvent. This strategy leads to efficient stabilization of Am­(V) and an extraordinarily high separation factor (>104) of Am from Ln through one single contact in solvent extraction, thereby opening a new avenue to study the high-OS chemistry of Am and fulfill the crucial task of Ln/Am separation in the nuclear fuel cycle. The synergistic coordination and oxidation process is found to occur in the organic solvent, and the mechanism has been well elucidated by quantum-theoretical modeling.

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The selective separation of trivalent americium from lanthanides in a nitric acid medium by a tetradentate ligand, N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen), in an ionic liquid (IL), C 4 mimNTf 2 , was studied by batch solvent extraction and spectroscopic approaches. The effect of various parameters such as the contact time, temperature, extractant concentration, and acidity on the extraction of Am 3+ and Eu 3+ have been evaluated. A significant enhancement in the extraction ability of Et-Tol-DAPhen dissolved in IL was observed as compared to that in molecular diluents under low-acid conditions. The chemical stoichiometry of Am 3+ and Eu 3+ complexes during extraction was determined to be 1:2 (metal/ ligand) by slope analysis of the extraction data. The extraction mechanism of Am 3+ and Eu 3+ by Et-Tol-DAPhen in IL was determined to be cation exchange on the basis of the effect of nitrate, NTf 2 − , and C 4 mim + ions on extraction. The coordination chemistry of Ln 3+ with the ligand in C 4 mimNTf 2 was studied by spectroscopic titrations, which helped to further identify and confirm the extracted species as well as the extraction mechanism. Results from the present study emphasize the unique role of IL in altering the extraction behavior and suggest that the Et-Tol-DAPhen/IL system has potential applications in trivalent actinide/ lanthanide separation under low-acid conditions.

In the present study C/PLA composites with different fiber surface conditions (untreated and with nitric acid oxidation for 4 h and 8 h) were prepared to determine the influence of surface treatment on the interfacial adhesion strength and mechanical properties of the composites. A chemical reaction at the fiber–matrix interfaces was confirmed by XPS studies. Nitric acid treatment was found to improve the amount of oxygen‐containing functional groups (particularly the carboxylic group, —COOH) on carbon fiber surfaces and to increase the surface roughness because of the formation of longitudinal crevices. The treated composites exhibited stronger interface adhesion and better mechanical properties in comparison to their untreated counterparts. There was a greater percentage of improvement in interfacial adhesion strength than in the mechanical properties. The strengthened interfaces and improved mechanical performance have been mainly attributed to the greater extent of the chemical reaction between the PLA matrix and the carbon fibers. The increased surface roughness also has had a slight contribution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 367–376, 2001