Herein, we present new hydrophilic tridentate ligands, bistriazolyl pyrazines. Their design was inspired by structurally similar and promising bis-triazolyl-pyridines (PyTri) ligands as well as theoretically derived criteria for the design of tridentate ligands for An/Ln separations suggested by theoretical studies. These ligands have been synthesised, characterised and tested as possible extractants for An/Ln nuclear separations. In addition, UV and fluorescence studies, pKa determination, and crystallographic and theoretical studies have been performed to explain their observed behaviour. Although the results of the solvent extraction studies have shown that these ligands do not possess sufficient selectivity for the extraction of Am vs Eu in i-SANEX conditions, this study presents a valuable test of the criteria for the design of tridentate heterocyclic N-donor ligands for advanced nuclear separation as postulated by theoretical studies a decade ago. Our experimental observations and theoretical studies have found that these criteria might not be the best guidance for designing novel hydrophilic ligands for An/Ln separations in i-SANEX conditions.

90 Sr, as a long-lived and high -energy beta -emitting radioactive isotope of the fission product of 235 U and 239 Pu, has been widely concerned owing to its high fission yield and unique potential distinctive applications in thermal sources and medicine. In this study, the silicon- and vanadium-doped Sb 2 O 5 (designated as SiSb-x or VSb-x, where x represents the molar ratios of Si or V to Sb), SiSb and VSb were synthesized and utilized as adsorbents for the selectively removing of Sr(II) ions from HLLW with high acidity and multiple competing ions. Batch experiments revealed that SiSb-0.5 and VSb-0.5 exhibited exceptional adsorption capacities for Sr(II) in a 3 mol/ L HNO 3 solution. The adsorption processes followed a pseudo-second-order kinetic equation, and the adsorption isotherms were well-described by the Freundlich model. Specifically, SiSb-0.5 and VSb-0.5 demonstrated adsorption capacities of 44.30 mg/g and 38.93 mg/g for Sr(II) in 3 mol/L HNO 3 , respectively. Thermodynamic analysis indicates that the adsorption of Sr(II) was endothermic. Furthermore, both SiSb-0.5 and VSb-0.5 exhibited relatively good stability against gamma -irradiation. Density functional theory (DFT) calculations suggested that the adsorption mechanism involved ion exchange between Sr(II) and H + at Sb - OH sites, along with the interaction between Sr and O atoms.

In order to realize the effective separation of palladium from high-level liquid waste (HLLW), a ligand-supported adsorbent (NTAamide(C8)/SiO2-P) was prepared by the impregnation method in a vacuum. The SiO2-P carrier was synthesized by in situ polymerization of divinylbenzene and styrene monomers on a macroporous silica skeleton. The NTAamide(C8)/SiO2-P adsorbent was fabricated by impregnating an NTAamide(C8) ligand into the pore of a SiO2-P carrier under a vacuum condition. The adsorption performance of NTAamide(C8)/SiO2-P in nitric acid medium has been systematically studied. In a solution of 0.2 M HNO3, the distribution coefficient of Pd on NTAamide(C8)/SiO2-P was 1848 mL/g with an adsorption percentage of 90.24%. With the concentration of nitric acid increasing, the adsorption capacity of NTAamide(C8)/SiO2-P decreases. Compared to the other 10 potential interfering ions in fission products, NTAamide(C8)/SiO2-P exhibited excellent adsorption selectivity for Pd(II). The separation factor (SFPd/other metals > 77.8) is significantly higher than that of similar materials. The interference of NaNO3 had a negligible effect on the adsorption performance of NTAamide(C8)/SiO2-P, which maintained above 90%. The adsorption kinetics of Pd(II) adsorption on NTAamide(C8)/SiO2-P fits well with the pseudo-second order model. The Sips model is more suitable than the Langmuir and Freundlich model for describing the adsorption behavior. Thermodynamic analysis showed that the adsorption of Pd(II) on NTAamide(C8)/SiO2-P was a spontaneous, endothermic, and rapid process. NTAamide(C8)/SiO2-P also demonstrated good reusability and economic feasibility.

The effective separation of palladium isotopes from high-level radioactive waste offers significant advantages, not only in ensuring the safe management and disposal of radioactive materials but also in addressing the scarcity of noble metals. In this study, a covalent organic framework (COF-SSH) modified with thiol and thioether groups is synthesized for the purpose of palladium separation. The experimental results demonstrate that the adsorption of Pd(II) occurs rapidly, reaching equilibrium within just 10 min. The adsorption isotherm for Pd(II) aligns well with the Langmuir model, revealing a maximum adsorption capacity of 420.2 mg/g at 3 M HNO 3 . Through Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Photoelectron Spectroscopy (XPS), and Density Functional Theory (DFT) analyses, the interaction between Pd and S atoms as being crucial for the adsorption process is identified. Moreover, COF-SSH exhibits exceptional selectivity for Pd(II) in simulated nuclear wastewater and maintains its performance throughout six consecutive adsorption and regeneration cycles. These results suggest that COF-SSH is a promising adsorbent for palladium separation, offering both acid resistance and high selectivity, making it a valuable candidate to the field of radioactive waste management and noble metal recovery.

Three phenylpyridine diamide ligands displayed high selectivity for Pu( iv ) over other metals in a HNO 3 medium. They also demonstrated good stripping ability and reusability, with reasonable radiolytic stability up to an absorbed dose of 100 kGy.

In this work, two cyclohexyl o-oxydiamides ligands: 2,2 '-(cyclohexane-1,2-diylbis(oxy))bis(N,N-dio-ctylacetamide)(L1: Octy-CDA) and 2,2 '-(cyclohexane-1,2-diylbis(oxy))bis(N,N-bis(2-ethylhexyl)acetamide) (L2: 2-ethylhexyl-CDA) have been synthesized to study the extraction and coordination behaviors with trivalent lanthanides in HNO3 media. The extractability of ligands increases with the atomic number of lanthanides increasing. The straight alkyl chain demonstrated better extraction ability than the branched chain, which was also most likely caused by the impact of steric hindrance effects. Coordination chemistry studies were evaluated through slope analysis, ultraviolet-visible spectroscopy, nuclear magnetic resonance spectroscopy, electrospray ionization mass spectrometry, Fourier transform infrared spectroscopy and fluorescence, and all the results indicating that lanthanides with the above ligands can form both 1:1 and 1:2 metal/ligand complexes during extraction, and two ligands are tetradentate ligands. Density functional theory (DFT) calculations shed light that the interaction between the carbonyl oxygen atom and Eu(III) in the ligand is much stronger than that of the ether-bonded oxygen atom, and the analysis of the bond-forming properties shows that the stability of the 1:2 complex is stronger than that of the 1:1 complex. This work enriched the coordination study of diamide with lanthanides, which is expected to improve our understanding of the chemical properties of lanthanides during coordination and provide new insight into the design and synthesis of novel ligands.

In this work, the solvent extraction and complexation behaviors of U(VI) by two novel asymmetrical tetra-alkylcarbamides, N,N'-butyl-N,N'-hexylurea (L1: SBHU) and N,N'-butyl-N,N'-pentylurea (L2: SBPU) in HNO3 media were systematically investigated. Both two ligands extract U(VI) more effectively than other metals such as Pu(IV), Np(IV), and Th(IV) in a wide range of acidity. Under 5 mol/L HNO3, DU reached 5.25, while DPu = 1.08, DNp = 0.11, DTh = 0.13.. Additionally, no third-phase was present by the extraction of highly uranium concentration solution with SBHU even under 7 mol/L HNO3 after four cycles demonstrating good acid resistance and resistance to the formation of the third phase. Slope analyses and FT-IR indicate that the U(VI) complexes are a form of UO2(NO3)2.2L for the two ligands during the extraction. Additionally, based on the DFT calculations, the NBO analysis, and topological analysis were analyzed in detail. The results demonstrate that the interactions between ligands and U(VI) are shown mainly as ionic characteristics, and the ligand-to-metal charge transfer was also observed. This study enriches the coordination chemistry of actinides: Th(IV), U(VI), Np(IV), Am(III), and Pu(IV) by tetra-alkylcarbamides, which may shed light on the design and synthesis of novel U(VI) selective ligands. (c) 2022 Elsevier B.V. All rights reserved.

The use of tetra-alkylcarbamides as novel ligands: N,N-butyl-N’,N’-hexylurea (L1: ABHU), and N,N-butyl-N’,N’-pentylurea (L2: ABPU), for the solvent extraction and complexation behaviors of uranium(VI) was synthesized and investigated in this study. The effects of HNO3 and NO3− concentrations in the aqueous phase on the distribution ratio of U(VI) were examined. Under 5 mol/L HNO3 concentration, DU reached 5.02 and 4.94 respectively without third-phase formation. During the extraction, slope measurements and IR spectral analysis revealed that the U(VI) complexes are a form of UO2(NO3)2·2L for both ligands. In addition, thermodynamic studies showed that the uranium extraction reaction was a spontaneous exothermic reaction. The deep structural analysis of the complexes was realized with DFT calculation. The bond length, bond properties, and topology of the complexes were discussed in detail to analyze the extraction behavior. This study enriches the coordination chemistry of U(VI) by tetra-alkylcarbamides, which may offer new clues for the design and synthesis of novel ligands for the separation, enrichment, and recovery of uranium in the nuclear fuel cycle.

Effective and selective separation of technetium from acidic nuclear liquid waste is highly desirable for partitioning and transmutation but is of significant challenge. Highly efficient extraction of pertechnetate can be achieved by taking H-bonding and electrostatic interaction combined strategy. Base on this strategy, an amine-amide ligand NTAamide(n-Oct) was employed to extract TcO4- in HNO3 solution. Using n-dodecane as a diluent, NTAamide(n-Oct) demonstrated excellent extractability and good selectivity toward TcO4- with a rapid extraction equilibrium that could be reached in less than 1 min. Its maximal loading capacity for TcO4- was almost 100 times as much as that of traditional amine extractant Aliquat-336 nitrate. Meanwhile, TcO4- could be efficiently stripped from the loaded organic phase by (NH4)2CO3 solution. Slope analysis indicated the formation of a 1:1 complex of NTAamide(n-Oct) with TcO4-. The extraction conformed to the anion exchange extraction model, as confirmed by analyses of single-crystal X-ray diffraction, 1H NMR titration, FTIR, and ESI-MS.