[en] We studied geometric and electronic structures as well as thermodynamic properties of complexes [M(CyMe₄–BTBP)₂(NO₃)]²⁺ and [M(CyMe₄–BTBP)₂]³⁺ with M = Am(III), Cm(III) and Ln(III) (La–Lu) theoretically. The actinide–nitrogen bonding is principally ionic with higher covalency in An–N bonds than in the Ln–N analogues. The selectivity towards An(III) over Ln(III) (La, Ce, Pr, Pm, Sm, Eu and Yb) is influenced by formed complexes to different extents by comparison of changes of Gibbs free energy of reaction, ΔΔG_Am/Ln, for formation of [AmL₂]³⁺/[LnL₂]³⁺, [AmL₂(NO₃)]²⁺/[LnL₂(NO₃)]²⁺, and [AmL₂(NO₃)]²⁺/[LnL₂]³⁺. The Am(III) selectivity is enhanced for [AmL₂(NO₃)]²⁺/[LnL₂]³⁺ over [AmL₂]³⁺/[LnL₂]³⁺.

[en] Separation of adjacent actinides (An) americium and curium is a critical and challenging step in advanced nuclear fuel cycles. Herein, we performed a quantum chemical calculation to explore the separation behavior of Am(III) from Cm(III) by two representative amide-type ligands, N,N′-dimethyl-N,N′-dioctyl-2-(2-hexyloxyethyl)malonamide (DMDOHEMA) and N,N,N′,N′,N″,N″-hexaalkyl-nitrilotriacetamide (NTAamide). It was found that the better energy match of Am 5f orbitals and O, N 2p orbitals of the amide-type ligands resulted in the selective ability of these ligands to Am³⁺ over Cm³⁺. Complexation reaction analysis predicted that An(DMDOHEMA)₂(NO₃)₃ and [An(NTAamide)₂]³⁺ were the most probable species in the separation processes.

[en] In this study, the electrochemical behavior of Sm on the binary liquid Al-Ga cathode in the LiCl-KCl molten salt system is investigated. First, the co-reduction process of Sm(Ⅲ)-Al(Ⅲ), Sm(Ⅲ)-Ga(Ⅲ), and Sm(Ⅲ)-Ga(Ⅲ)-Al(Ⅲ) on the W electrode (inert) were studied using cyclic voltammetry (CV), square-wave voltammetry (SWV) and open circuit potential (OCP) methods, respectively. It was identified that Sm(Ⅲ) can be co-reduced with Al(Ⅲ) or Ga(Ⅲ) to form Al_zSm_y or Ga_xSm_y intermetallic compounds. Subsequently, the under-potential deposition of Sm(Ⅲ) at the Al, Ga, and Al-Ga active cathode was performed to confirm the formation of Sm-based intermetallic compounds. The X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analyses indicated that Ga₃Sm and Ga₆Sm intermetallic compounds were formed on the Mo grid electrode (inert) during the potentiostatic electrolysis in LiCl-KCl-SmCl₃-AlCl₃-GaCl₃ melt, while only Ga₆Sm intermetallic compound was generated on the Al-Ga alloy electrode during the galvanostatic electrolysis in LiCl-KCl-SmCl₃ melt. The electrolysis results revealed that the interaction between Sm and Ga was predominant in the Al-Ga alloy electrode, with Al only acting as an additive to lower the melting point

[en] The extraction complexes of Pu(IV) with n-octyl(phenyl)-N,N-diisobutyl-methylcarbamoyl phosphine oxide (CMPO) and diphenyl-N,N-diisobutyl carbamoyl phosphine oxide (Ph₂CMPO) have been studied by using density functional theory (DFT) combined with relativistic small-core pseudopotentials. For most complexes, the CMPO and Ph₂CMPO molecules are coordinated as bidentate chelating ligands through the carbonyl oxygen and phosphoric oxygen atoms. The metal-ligand bonding is mainly ionic for all of these complexes. The neutral PuL(NO₃)₄ and PuL₂(NO₃)₄ complexes are predicted to be the most thermodynamically stable molecules according to the metal-ligand complexation reactions. In addition, hydration energies may also play a significant role in the extractability of CMPO and Ph₂CMPO for the plutonium cations. In most cases, the complexes with CMPO possess qualitatively similar geometries and electron structures to those with Ph₂CMPO, and they also have comparable metal-ligand binding energies. Thus, replacement of alkyl groups by phenyl groups at the phosphorus atom of CMPO seems to have no obvious influence on the extraction of Pu(IV). (orig.)

[en] Two highly symmetrical (3,4)-connected uranyl-organic frameworks (UOFs) were synthesized by a judicious combination of D${}_{3h}$-symmetrical triangular $[$UO${}_2$(COO)${}_3$$]$${}^{-<!--\; ???\; -->}$ and T${}_d$ symmetrical tetrahedral tetrakis(4-carboxyphenyl)methane (H${}_4$MTB). These two as-synthesized UOFs possess similar structural units and coordination modes but totally different topological structures, namely ctn net and bor net. Solvent-induced interpenetration and a morphology change are observed. The two compounds exhibit crystal transformation via a dissolution-crystallization process. Adsorption experiments in CH${}_3$OH solution indicate that both of them can selectively remove positively charged dyes over negatively charged and neutral dyes. Moreover, the electronic structural and bonding properties of the two compounds were systematically explored by density functional theory (DFT) calculations. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

[en] Room-temperature ionic liquids (RTILs) have recently received increasing attention as solvent alternatives for possible application in spent fuel reprocessing, particularly in the extraction of metal ions from high-level radioactive aqueous waste, due to their unique physical and chemical properties. Herein, the solvent extraction of the uranyl ions (UO₂²⁺) was performed using N,N'-diethyl-N,N'-di(para)tolyl-dipicolinamide (Et_(p)TDPA) as the extractant in a commonly used ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim][PF₆]). The effects of vortexing time, phase ratio and the concentration dependence of Et_(p)TDPA, nitric acid and sodium nitrate on the extraction were studied in detail. The extraction mechanism was deduced based on the slope analysis and UV-vis measurement. The distribution ratio of U from 3 mol/L nitric acid by 0.3 mol/L EtTDPA/C₄mimPF₆ is found to be almost 100. Conventional log-log plot analysis of the extraction equilibrium data suggests that the ions are extracted as a complex in 2:3 ratio of UO₂²⁺ to extractant, and the extraction most likely occurs by a cation-exchange mode since the concentration of C₄mim⁺ in the aqueous phase increases linearly with the percent extraction of UO₂²⁺ evidenced by UV-vis measurement. This work promises to provide new efficient media based on RTILs for separation of uranium from the radioactive aqueous waste. (orig.)

[en] Actinide nanomaterials have great potential for application in the fabrication of nuclear fuels and spent fuel reprocessing in advanced nuclear energy systems. In this work, we used track-etched nanoporous membranes as hard templates to synthesize uranium-based nanomaterials with new structures by electrodeposition. Through electrochemical behavior investigations and subsequent product characterization, the chemical compositions of the deposition product has been confirmed to be uranyl hydroxide. More importantly, accurate control of the morphologies of the deposition product (i.e., nanowires and nanotubes) could be achieved by carefully adjusting the growth parameters such as deposition time and current density. The preferred morphology of the electrodeposition product was nanowires when a low current density was applied, whereas nanotubes could be formed only when a high current density and a short deposition time were both applied. The formation of nanotubes is attributed to the hydrogen bubbles generated by water electrolysis under the overpotential electroreduction conditions. Additionally, we transformed the main chemical composition of the deposition products from uranyl hydroxide to triuranium octoxide by calcination, and SEM results showed that the morphologies of the nanowires and nanotubes were very well maintained after the calcination. Our work provides a useful protocol for the synthesis of one-dimensional uranium-based nanomaterials. (Copyright copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] We theoretically investigated the selective back-extraction towards Am(III) over Eu(III) and Cm(III) with two water-soluble 2,9-bis-triazolyl-1,10-phenanthroline derivatives BTrzPhen1 (with two ethanol side chains) and BTrz-Phen2 (with two 1,2-butanediol side chains) by density functional theory (DFT). The molecular geometries and formation reactions of the metal-ligand complexes were modeled by using M(BTrzPhen)(NO${}_3$)${}_3$ and [M(BTrzPhen)${}_2$(NO${}_3$)]${}^{2+}$. Am(III) selectivity over Eu(III) and Cm(III) with BTrzPhen2 was successfully reproduced by back-extraction reaction free energy analysis. Moreover, bonding properties between the metal cations and coordinated ligands (model complexes) were studied in terms of Mayer bond order and quantum theory of atoms in molecule (QTAIM). The difference in covalency between An–N and Eu–N bonds were found to be the key factors for Am(III)/Eu(III) separation, while the Am(III) selectivity over Cm(III) of BTrzPhen2 might be attributed to the competition of donor atoms for cation binding preference toward Am(III) and Cm(III).

[en] At present, amidoxime-based adsorbents are considered to be the most promising materials for extraction of uranium from seawater. However, the high concentrations of transition metals especially vanadium strongly compete with uranium in the sequestration process, which is extremely limited the commercial use of amidoxime-based adsorbents. In this work, the coordination modes, bonding nature, and stabilities of possible vanadium(IV) (VO"2"+) and (V) (VO_2"+, VO"3"+, V"5"+) complexes with amidoximate (AO"-), carboxyl (Ac"-), glutarimidedioximate (HA"-) and deprotonated glutarimidedioximate (A"2"-) on single and double alkyl chains (R=C_1_3H_2_6) are systematically explored by quantum chemical calculations. Different from the uranyl (UO_2"2"+) complexes, the AO"- groups of the vanadium(IV) and (V) complexes prefer to coordinate as monodentate and chelate ligands, while few species with AO"- groups in η"2-binding mode have been observed in the vanadium complexes. Besides, the vanadium complexes are predicted to have obvious covalent metal-ligand bonds. According to thermodynamic stability analysis, all the vanadium complexes with AO"-, Ac"-, HA"- and A"2"- ligands on double alkyl chains are found to be more stable than corresponding complexes with ligands on a single chain. The synergistic effect of the amidoxime and carboxyl groups can be observed in most of VO_2"+ and VO"3"+ complexes with mixed ligands (AO"-/Ac"-). The vanadium(IV) and (V) complexes are more stable than the corresponding uranyl complexes, and the adsorption capability of the amidoxime-based adsorbents toward vanadium(V) ions decrease in the order of VO_2"+>VO"3"+> V"5"+. The dioxovanadium cation VO_2"+ is predicted to form multinuclear vanadium complex in the sequestration process, possibly resulting in higher stable VO_2"+ complexes. Therefore, the higher complexation ability of the amidoxime-based adsorbents toward vanadium over uranium is probably due to the differences in the coordination modes and bonding nature. The current results might provide important clues for rational design of efficient ligands in sequestration of uranium from seawater.

[en] Ordered mesoporous UO_2 with 3-D structure (for UO_2-KIT-6) and nanowire bundles (for UO_2-SBA-15) was synthesized for the first time by a nanocasting route using different ordered mesoporous silica (KIT-6 and SBA-15, respectively) as templates and uranyl nitrate hexahydrate as the metal precursor. The uranyl nitrate was impregnated into the mesopore of the silica template and was converted to U_3O_8 after the first step. The synthesis of ordered UO_2 mesostructure was achieved by reducing the mesoporous U_3O_8 with silica composites under 5% H_2/Ar atmosphere at 700 C, followed by a template removal process. The as-prepared UO_2-KIT-6 had a particle size of several millimeters, and was constructed with uncoupled subframework mesostructure and crystalline walls, while UO_2-SBA-15 possessed a rope-like morphology and consisted of nanowire arrays. The surface area and pore volume of ordered UO_2 mesostructure are 47.2 m"2 g"-"1 and 0.23 cm"3 g"-"1 for the UO_2-KIT-6, and 54.4 m"2 g"-"1 and 0.28 cm"3 g"-"1 for the UO_2-SBA-15, respectively.