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To better understand the diffusion behaviors of Tc(IV)-L complexes in the water-rock system, the diffusion coefficients (Dw) of VO2+ [as a surrogate to 99Tc(IV)] and their complexes with ligands (Oxalate, NTA and EDTA) in water were studied by a capillary method. The density functional theory was employed to investigate the complexation between VO2+ and ligands. The Dw values of [VO(Ox)2]2−, [VO(NTA)]− and [VO(EDTA)]2− were 18–26% higher than that of VO2+ due to the smaller molecular radii of the complexes.

Effectively adjusting and controlling the valence state of neptunium from the spent fuel reprocessing process is essential to separating neptunium. Hydrazine and its derivatives as free-salt reductants have been experimentally demonstrated to effectively reduce Np(VI) to Np(V). We have theoretically investigated the reduction mechanisms of Np(VI) with hydrazine and three derivatives (HOC2H4N2H3, CH3N2H3, and CHON2H3) in previous works. Herein, we further explored the reduction reaction of Np(VI) with phenylhydrazine (C6H5N2H3) including the free radical ion mechanism and the free radical mechanism. Potential energy profiles (PEPs) indicate that the rate-determining step of both mechanisms is the first stage. Moreover, for the free radical ion mechanism, phenylhydrazine possesses better reduction ability to Np(VI) compared to HOC2H4N2H3, CH3N2H3, and CHON2H3, which falls completely in line with the experimental results. Additionally, the analyses of the quantum theory of atoms in molecules (QTAIM), natural bond orbitals (NBOs), electron localization function (ELF), and localized molecular orbitals (LMOs) have been put forward to elucidate the bonding evolution for the structures of the reaction pathways. This work offers insights into the reduction mechanism of Np(VI) with phenylhydrazine from the theory point of view and contributes to design more high-efficiency reductants for the separation of U/Np and Np/Pu in spent fuel reprocessing.

Recently, the observation of the first axially chiral borospherenes (B39−) enriched the members of the boron cluster family, and opened the door to axially chiral boron cages. Herein, we theoretically predicted a series of chiral borospherenes by actinide metal (An) encapsulation, which are new chiral members of the borospherene family. Theoretical calculations demonstrate that the C2 neutral and charged Ac– and Th–B39 boron clusters (Ac@B39, [Ac@B39]2+, and Th@B39, [Th@B39]3+) are the most stable structures, and each borospherene possesses degenerate enantiomers, in accordance with the chiral borospherenes B39−. In contrast, the global minimum structures of Cf embedded borospherenes have no symmetry (C1). All the chiral actinoborospherenes [An@B39]n+ (An = Ac, n = 0, 2; An = Th, n = 0, 3) possess high formation energies, especially C2 [Th@B39]3+. Bonding analysis shows that each complex of [Ac@B39]n+ and [Th@B39]n+ has the characteristic of σ + π double delocalization, and the Th–B bonds possess relatively higher covalency than the Ac–B bonds, resulting in the higher formation energy of C2 [Th@B39]3+. Therefore, the covalent character of An–B bonding may be essential for the formation of these chiral actinoborospherenes. This work extends the chiral borospherenes to actinide metal-doped chiral borospherenes, and sheds light on the design of chiral metalloborospherenes.

The exploration of metal-doped boron clusters has a great significance in the design of high coordination number (CN) compounds. Actinide-doped boron clusters are probable candidates for achieving high CNs. In this work, we systematically explored a series of actinide metal atom (U, Np, and Pu) doped B20 boron clusters An@B20 (An = U, Np, and Pu) by global minimum structural searches and density functional theory (DFT). Each An@B20 cluster is confirmed to be a twenty-coordinate complex, which is the highest CN obtained in the chemistry of actinide-doped boron clusters so far. The predicted global minima of An@B20 are tubular structures with actinide atoms as centers, which can be considered as boron molecular drums. In An@B20, U@B20 has a relatively high symmetry of C2, while both Np@B20 and Pu@B20 exhibit C1 symmetry. Extensive bonding analysis demonstrates that An@B20 has σ and π delocalized bonding, and the U-B bonds possess a relatively higher covalency than the Np-B and Pu-B bonds, resulting in the higher formation energy of U@B20. Therefore, the covalent character of An-B bonding may be crucial for the formation of these high CN actinide-centered boron clusters. These results deepen our understanding of actinide metal doped boron clusters and provide new clues for developing stable high CN boron-based nanomaterials.

Efficient separation of neptunium and plutonium from spent nuclear fuel is essential for advanced nuclear fuel cycles. At present, the development of effective actinide separation ligands has become a top priority. As common adsorbents for extracting uranium from seawater, amidoxime-based adsorbents may also be able to separate actinides from high-level liquid waste (HLLW). In this work, the complexation of Np(IV,V,VI) and Pu(IV) and alkyl chains (R = C13H26) modified with amidoximate (AO−) and carboxyl (Ac−) functional groups was systematically studied by quantum chemical calculations. For all the studied complexing species, the RAc− and RAO− ligands act as monodentate or bidentate ligands. Complexes with AO− groups show higher covalency of the metal–ligand bonding than the analogues with Ac− groups, in line with the binding energy analysis. Bonding analysis verifies that these amidoxime/carboxyl-based adsorbents possess higher coordination affinity toward Pu(IV) than toward Np(IV), and the Np(VI) complexes have stronger covalent interactions than Np(V). According to thermodynamic analysis, these adsorbents have the ability to separate Np(IV,V,VI) and Pu(IV), and also exhibit potential performance for partitioning Pu(IV) from Np(IV) under acidic conditions. This work can help to deeply understand the interaction between transuranium elements and amidoxime-based adsorbents, and provide a theoretical basis for the separation of actinides with amidoxime-based adsorbents.

Separation of trivalent actinides An(III) from lanthanides Ln(III) is a worldwide challenge owing to their very similar chemical behaviors. It is highly desirable to understand the nature of selectivity for the An(III)/Ln(III) separation with various ligands through theoretical calculations because of their radiotoxicity and experimental difficulties. In this work, we have investigated three dithioamide-based ligands and their extraction behaviors with Am(III) and Eu(III) ions using the scalar-relativistic density functional theory. The results show that the dithioamide-based ligands have stronger electron donating ability than do the corresponding diamide-based ones. All analyses including geometry, Mulliken population, QTAIM (quantum theory of atoms in molecules), and NBO (natural bond orbital) suggest that the Am-S/N bonds possess more covalency compared to the Eu-S/N bonds, and the M-S bonds have more covalent character than the M-N bonds. Thermodynamic results reveal that N2,N9-diethyl-N2,N9-di-p-tolyl-1,10-phenanthroline-2,9-bis(carbothioamide) (L1) has a stronger complexing ability with metal ions owing to its rigid structure and that N6,N6'-diethyl-N6,N6'-di-p-tolyl-[2,2'-bipyridine]-6,6'-bis(carbothioamide) (L2) shows a higher selectivity for the Am(III)/Eu(III) separation. In addition, these dithioamide-based ligands possess Am(III)/Eu(III) selectivity higher than those of the corresponding diamide-based ones, although the former have weaker complexing ability with metal ions, probably due to the greater covalency of the M-S bonds. This theoretical evaluation provides valuable insights into the nature of the selectivity for the Am(III)/Eu(III) separation and information on designing of efficient An(III)/Ln(III) separation with dithioamide-based ligands.

The study of metal–metal bonds is one of the important challenges in organometallic chemistry and of great significance in applied and structural chemistry. We built a series of potential complexes...

Actinide nitrides possessing the advantages of high burn-up, superior thermophysical properties and easy reprocessing in nitric acid, are currently considered as promising fuels for advanced nuclear reactors. In this work, a systemic study on the stability, mechanical and thermodynamic properties of (Pu, Zr)N was conducted employing the first-principles density functional theory approaches. We found that the ternary compound (Pu, Zr)N tends to exist in the form of single cubic NaCl-type solid solution, confirmed by incorporation and solution energies of Zr in PuN crystals. The calculated elastic constants of the (Pu, Zr)N crystals satisfy the stability criteria of tetragonal structures, proving their mechanical stability. It is revealed that the elastic constants and mechanical properties such as mechanic moduli and Poisson's ratio monotonically change with the concentration of Zr in (Pu, Zr)N crystals. Additionally, the specific heat also changes monotonically with the concentration of Zr derived from phonon-dispersion spectrums. The obtained results can shed light on the understanding of plutonium nitride materials in the nuclear energy cycles.

In the process of spent fuel reprocessing, it is highly difficult to extract transplutonium elements from adjacent actinides. A deep understanding of the electronic structure of transplutonium complexes is essential for development of steady ligands for in-group separation of transplutonium actinides. In this work, we have systematically explored the potential in-group separation ability of transplutonium elements of typical quadridentate N-donor ligands (phenanthroline-derived bis-triazine, BTPhen derivatives) through quasi-relativistic density functional theory (DFT). Our calculations demonstrate that ligands with electron-donating groups have stronger coordination abilities, and the substitutions of Br and phenol at the 4-position of the 1,10-phenanthroline have a higher effect on the ligand than those at the 5-position. Bonding analysis indicates that the covalent interaction of An3+ complexes becomes stronger from Am to Cf apart from Cm, which is because the energy of the 5f orbital gradually decreases and becomes energy-degenerate with the 2p orbitals of ligands. The most negative values of binding energies indicate the higher stability of Cf3+ complexes, in line with the larger covalency in the Cf-L bonds compared with An-L (An = Am, Cm, Bk). In addition, electron-donating group phenol can enhance the covalent interaction between ligands and heavy actinides. Consequently, the extraction ability of ligands with electron-donating substituents for heavy actinides is generally stronger than other ligands. Nevertheless, these ligands exhibit diverse separation abilities to in-group actinide recovery. Therefore, the enhancement of covalency does not necessarily lead to the improvement of separation ability, which may be caused by different extraction abilities. Compared with the tetradentate N, O-donor ligands (2,9-diamide-1,10-phenanthrolinel, DAPhen derivatives), species with BTPhen ligands display stronger covalent interaction and higher extraction capacity. In terms of in-group separation ability, the BTPhen ligands seem to have advantages in separation of californium from curium, while the DAPhen ligands possess stronger abilities to separate americium from curium. These results may afford some afflatus for the development of effective agents for in-group separation of transplutonium elements.

The key to effective separation of neptunium from the spent fuel reprocessing process is to adjust and control its valence state. Hydrazine and its derivatives have been experimentally confirmed to be effective salt-free reductants for reducing Np(VI) to Np(V). We theoretically studied the reduction reactions of Np(VI) with three hydrazine derivatives (2-hydroxyethyl hydrazine (HOC

On the basis of the first structurally authenticated LArU–FeCp(CO)2 (LAr = deprotonated p-terphenyl bis(aniline) ligand) complex bearing an unsupported U–Fe bond, we expanded the structures of comp...

Separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) is one of the most important steps in spent nuclear fuel reprocessing. However, it is very difficult and challenging to separate them due to their similar chemical properties. Recently the pyridylpyrazole ligand (PypzH) has been identified to show good separation ability toward Am(III) over Eu(III). In this work, to explore the Am(III)/Eu(III) separation mechanism of PypzH at the molecular level, the geometrical structures, bonding nature, and thermodynamic behaviors of the Am(III) and Eu(III) complexes with PypzH ligands modified by alkyl chains (Cn-PypzH, n = 2, 4, 8) have been systematically investigated using scalar relativistic density functional theory (DFT). According to the NBO (natural bonding orbital) and QTAIM (quantum theory of atoms in molecules) analyses, the M-N bonds exhibit a certain degree of covalent character, and more covalency appears in Am-N bonds compared to Eu-N bonds. Thermodynamic analyses suggest that the 1:1 extraction reaction, [M(NO

s The composition of electrolytes is one of the key factors that determine the electrochemical properties of elements in an electrochemical process. In this work, the influence of LiF introduction into LiCl-KCl molten salt on the electrochemical behavior and coordination properties of uranium was studied by combining electrochemical and spectroscopic techniques as well as ab initio molecular dynamic simulations. The results showed that, compared to coordination with U(III), F− ion readily coordinates with U(IV), which has a smaller ion radius and larger charge density. The involvement of F− ion in coordination makes U(IV) complex more stable, and the equilibrium potential of U(IV)/U(III) shifts to the negative direction, closer to that of U(III)/U(0). In the presence of a large amount of Cl− ions, F− ions cannot completely replace the role of Cl− ions, so U(IV) and U(III) prefer to form UCl3F32− and UCl5F3− complexes, respectively. Anyway, the involvement of F− ion in coordination may lead to smaller volume of uranium complexes in melt, resulting in slight increase of the diffusion coefficient of U(IV). In addition, the effect of substitution of Cl− by F− ions on the crystal field splitting energy of U(III) complex was observed. The in-depth understanding of the relationship between the coordination structure and electrochemical properties of uranium in melt will be of much significance for the design and control of more efficient electrochemical process for actinide separation.

Heterogeneous reduction of U(VI) by structural Fe2+ and S2− is a key process influencing its fate and transport in subsurface environment. In this study, the adsorption of U(VI) on nanomagnetite was primarily conducted and then, it was desorbed by adding S2−. The desorption of absorbed U(VI) significantly increased with the increase in S2−, whereas S2− consumption was higher than the desorbed amount of U(VI) due to the volatilization (H2S) and sulfidization (FeS) at low and high pH, respectively. The XRD analysis demonstrated that the main components of corrosion products for nanomagnetite after adding S2− at pH 3.0 and 7.0 are lepidocrocite and mackinawite, respectively, after a reaction time of 128 days. According to analyses of ITFA and XANES spectra, the main speciation of uranium at pH 3.0 and 7.0 were U(V) and U(IV) species, respectively. The required energy of U(V) desorbed from lepidocrocite (−12.78 kcal mol−1) at pH 3.0 after 128 days was higher than that of U(IV) (−26.16 kcal mol−1) by theoretical calculations, indicating that U(V) can be stably incorporated into the secondary phase. These findings are crucial for understanding the speciation of uranium at low pH and reducing conditions.

The adsorption and dissociation behaviors of water on the UN (110) surface have been investigated by using DFT + U method in combination with ab initio atomistic thermodynamic simulations. The most stable adsorption site for H, O, and OH adsorption is the uranium bridge site. For a water monomer, the adsorption energies are −0.90, −3.23, and −4.46 eV for the most stable molecular, partially dissociative, and completely dissociative adsorption, respectively. The dissociation of water from H2O to OH and H has a very small energy barrier, while from OH to O and H has a high energy barrier of 1.63 eV. The coverage dependence for molecular adsorption is not obvious, while for partially dissociative and completely dissociative adsorption, the coverage dependence is quite obvious. Besides, we have investigated the adsorption of water under different temperature and pressure conditions by using the “ab initio atomistic thermodynamic” method.

Although metal-organic frameworks (MOFs) have been reported as important porous materials for the potential utility in metal ion separation, coordinating the functionality, structure, and component of MOFs remains a great challenge. Herein, a series of anionic rare earth MOFs (RE-MOFs) were synthesized via a solvothermal template reaction and for the first time explored for uranium(VI) capture from an acidic medium. The unusually high extraction capacity of UO22+ (e.g., 538 mg U per g of Y-MOF) was achieved through ion-exchange with the concomitant release of Me2NH2+, during which the uranium(VI) extraction in the series of isostructural RE-MOFs was found to be highly sensitive to the ionic radii of the metal nodes. That is, the uranium(VI) adsorption capacities continuously increased as the ionic radii decreased. In-depth mechanism insight was obtained from molecular dynamics simulations, suggesting that both the accessible pore volume of the MOFs and hydrogen-bonding interactions contribute to the strong periodic tendency of uranium(VI) extraction.

Recently, the carbon nanobelt (CNB) comprising a closed loop of fully fused edge-sharing benzene rings has been reported in an experiment. To explore its potential molecular properties and applications, we performed scalar relativistic density functional theory investigations on the interaction mechanisms of the CNB with a series of actinide atoms (An = Th-Am). Computations indicate that doping of actinide (An) atoms onto the surface of the CNB can result in the formation of stable actinide endohedral An@CNB compounds, along with the formation of C-An-C rings as well as a drastic structural transformation of the CNB. Compared to transuranium actinides, Th, Pa, and U exhibit a stronger adsorption affinity to the CNB in terms of the calculated binding energies. The adaptive natural density partitioning analysis shows that there form five 3c-2e bonds and two 5c-2e bonds in An@CNB for An = Th, Pa, and U, with fewer multicenter bonds for An = Np, Pu, and Am. These theoretical results provide a new strategy for chemical modification and functionalization of the CNB by actinide doping in the future.

Two thorium organic frameworks, Th(BDC)2 and Th(OH)(BCPBA) have been hydrothermally synthesized using 1,4-benzenedicarboxylic acid (H2BDC) and 3,5-bi(4-carboxyphenoxy)benzoic acid (H3BCPBA), respectively. The obtained two compounds were determined by single-crystal XRD, and they exhibited two new topologies. Th(BDC)2 shows a 3-dimensional (4,4,8)-connected framework with the Schläfli symbol of (414·612·82)(42·63·8)(44·62), and it is a mononuclear thorium(IV) complex. Th(OH)(BCPBA) possesses a (4,6)-connected topology with the Schläfli symbol of (415)2(46)3, and it has a dinuclear thorium(IV) asymmetric unit with the shortest Th–Th distances. Viewing along suitable directions, channels with different shapes can be found in the obtained two frameworks. Based on calculation with PLATON, the amount of void space is 21.9% and 13.5% in Th(BDC)2 and Th(OH)(BCPBA), respectively. Density functional theory (DFT) studies revealed that the metal-ligand interactions were mainly of ionic character in both compounds and the hydroxyl ions might play an important role in the stability of dinuclear thorium(IV) of Th(OH)(BCPBA).

Although the first organoactinide chloride Cp3UCl (Cp=η5-C5H5) was synthesized more than 50 years ago, binuclear uranium halides remain very rare in organoactinide chemistry. Herein, a series of binuclear trivalent and tetravalent uranium halides and cyanides with cyclooctatetraene ligands, (COT)2U2X n (COT=η8-C8H8; X=F, Cl, CN; n=2, 4), have been systematically studied using scalar-relativistic density functional theory (DFT). The structures with bridging halide or cyanide ligands were predicted to be the most stable complexes of (COT)2U2X n , and all the complexes show weak antiferromagnetic interactions between the uranium centers. However, for each species, there is no significant uranium-uranium bonding interaction. The bonding between the metal and the ligands shows some degree of covalent character, especially between the metal and terminal halide or cyanide ligands. The U-5f and 6d orbitals are predominantly involved in the metal-ligand bonding. All the (COT)2U2X n species were predicted to be more stable compared to the mononuclear half-sandwich complexes at room temperature in the gas phase such that (COT)2U2X4 might be accessible through the known (COT)2U complex. The tetravalent derivatives (COT)2U2X4 are more energetically favorable than the trivalent (COT)2U2X2 analogs, which may be attributed to the greater number of strong metal-ligand bonds in the former complexes.

Valence state control and adjustment of neptunium in spent fuel reprocessing is very important for improving the separation efficiency of U/Np and Np/Pu. Hydrazine and its derivatives have been experimentally demonstrated to be effective in the reduction of NpVI to NpV. In this work, hydrazine was used as a representative reductant and the reduction mechanisms of NpVI induced by hydrazine were investigated using density functional theory (DFT) calculations. Three reaction pathways were taken into account and characterized by gradually transferring a hydrogen atom from N2H4 to the “yl”-oxygen of [NpVIO2(H2O)5]2+ followed by the valence state adjustment from NpVI to NpV. The calculated results of the potential energy profiles (PEPs) revealed that Pathway I should be the most likely to occur as the process of forming ˙N2H3 is considered to be the rate-determining step with the highest energy barrier of 32.02 kcal mol−1, which is in favor of the experimental results. Pathway II hardly occurs and Pathway III probably occurs. The bonding evolution, along with the reaction pathways, was explored through natural bond orbitals (NBOs), quantum theory of atoms-in-molecules (QTAIM) and electron localization function (ELF) analyses. This work can shed light on the understanding of redox mechanisms of NpVI with N2H4 and its derivatives and help further attempts to design more efficient reductants for the separation of U/Np and Np/Pu in spent nuclear fuel reprocessing in the near future.

The in-pile performance of ceramic fuels is significantly affected by the fission products. In this work, we have performed first-principles density functional theoretical calculations to study the interaction between metallic fission products (barium and zirconium) and the uranium dinitride UN2 matrix. The thermodynamic properties and bonding nature of Ba and Zr atoms in different incorporation configurations indicate that Zr is more soluble in UN2 matrix than Ba. With increasing the concentration of the impurity atoms, Zr-doped UN2 exhibits a slight tendency to contract, while Ba-doped UN2 tends to swell. Based on the competition between steric effect and chemical interaction, various incorporation trends for Ba and Zr in UN2 as well as in UN have been understood.

Molecular and dissociative adsorption behavior of H2O along with the accompanying H2 formation mechanism on the UO2 (111) and (110) surfaces have been investigated by using DFT+U calculations. According to our calculations, the higher stability of the (111) surface leads to higher oxygen vacancy formation energy compared to the (110) surface. On the stoichiometric (111) and (110) surfaces, the first hydrogen atom of water molecule can dissociate readily with very small or no energy barrier. On the contrary, dissociation of the second one becomes the rate-determining step, and water-catalysis leads to the decrease of energy barrier from 0.92 to 0.70 eV and from 2.36 to 1.21 eV on the stoichiometric (111) and (110) surfaces, respectively. H2 formation resulting from water dissociation may undergo two pathways in the presence of surface oxygen vacancy on the reduced UO2 (111) surface. One is characterized by direct combination of two hydrogen atoms of one water molecule, and the other is characterized by dis...

Recovery of uranium from seawater is extremely challenging but important for the persistent development of nuclear energy, and thus exploring the coordination structures and bonding nature of uranyl complexes becomes essential for designing highly efficient uranium adsorbents. In this work, the interactions of uranium and a series of adsorbents with various well-known functional groups including amidoximate (AO(-)), carboxyl (Ac(-)), glutarimidedioximate (HA(-)), and bifunctional AO(-)/Ac(-), HA(-)/Ac(-) on different alkyl chains (R'═CH3, R″═C13H26) were systematically studied by quantum chemical calculations. For all the uranyl complexes, the monodentate and η(2) coordination are the main binding modes for the AO(-) groups, while Ac(-) groups act as monodentate and bidentate ligands. Amidoximes can also form cyclic imide dioximes (H2A), which coordinate to UO2(2+) as tridentate ligands. Kinetic analysis of the model displacement reaction confirms the rate-determining step in the extraction process, that is, the complexing of uranyl by amidoxime group coupled with the dissociation of the carbonate group from the uranyl tricarbonate complex [UO2(CO3)3](4-). Complexing species with AO(-) groups show higher binding energies than the analogues with Ac(-) groups. However, the obtained uranyl complexes with Ac(-) seem to be more favorable according to reactions with [UO2(CO3)3](4-) as reactant, which may be due to the higher stability of HAO compared to HAc. This is also the reason that species with mixed functional group AO(-)/Ac(-) are more stable than those with monoligand. Thus, as reported in the literature, the adsorbability of uranium can be improved by the synergistic effects of amidoxime and carboxyl groups.

Barium and zirconium solution behaviors in antiferromagnetic uranium mononitride (UN) have been studied based on first-principles density functional theory. By calculating the incorporation and solution energies in UN, it is found that the most favorable solution sites are U vacancies for both Ba and Zr, and Zr is more soluble than Ba. The volume of the Ba-doped system keeps expanding with increasing Ba doping concentration, whereas that of the Zr-doped system changes from swelling to contraction with increasing Zr doping concentration. This phenomenon may result from the difference of these two elements in atom radius and coordination mechanism. Furthermore, the solution energies of metallic and nitride phases of Ba and Zr indicate that both phases of Ba are insoluble in the UN matrix, whereas the metallic phase of Zr is insoluble, and its nitride ZrN is soluble in the UN matrix.

Studying the bonding nature of uranyl ion and graphene oxide (GO) is very important for understanding the mechanism of the removal of uranium from radioactive wastewater with GO-based materials. We have optimized 22 complexes between uranyl ion and GO applying density functional theory (DFT) combined with quasi-relativistic small-core pseudopotentials. The studied oxygen-containing functional groups include hydroxyl, carboxyl, amido, and dimethylformamide. It is observed that the distances between uranium atoms and oxygen atoms of GO (U-OG) are shorter in the anionic GO complexes (uranyl/GO(-/2-)) compared to the neutral GO ones (uranyl/GO). The formation of hydrogen bonds in the uranyl/GO(-/2-) complexes can enhance the binding ability of anionic GO toward uranyl ions. Furthermore, the thermodynamic calculations show that the changes of the Gibbs free energies in solution are relatively more negative for complexation reactions concerning the hydroxyl and carboxyl functionalized anionic GO complexes. Therefore, both the geometries and thermodynamic energies indicate that the binding abilities of uranyl ions toward GO modified by hydroxyl and carboxyl groups are much stronger compared to those by amido and dimethylformamide groups. This study can provide insights for designing new nanomaterials that can efficiently remove radionuclides from radioactive wastewater.

Complex behaviours of americium(III) and europium(III) with nitrate anions have been studied using density functional theory and small-core quasi-relativistic effective core potential. The structural parameters of a series of hydrated and nitrate complexes of Am(III) and Em(III) are probed and compared to available EXAFS studies. The thermodynamic stability of these species is calculated by simulating related complexation reactions both in the gas phase and aqueous solution. For taking into account the solvent effect, both the solvation model density (SMD) implicit solvent model and the conductor-like screening model (COSMO) are adopted for comparison. From our calculations, the octa–aqua and non-aqua species of Am(III) and Eu(III), [M(H2O)8,9]3+ (M = Am, Eu), form square antiprism and trigonal prism structures, respectively. In the presence of rich-enough nitrate ions, at most three nitrate anions can chelate to Am(III)/Eu(III) ions in a bidentate fashion in the first coordination shell, owing to the str...

The interfacial interaction of uranium mononitride (UN) with water from the environment unavoidably leads to corrosion of nuclear fuels, which affects a lot of processes in the nuclear fuel cycle. In this work, the microscopic adsorption behaviors of water on the UN(001) surface as well as water dissociation and accompanying H2 formation mechanisms have been investigated on the basis of DFT+U calculations and ab initio atomistic thermodynamics. For adsorption of one H2O monomer, the predicted adsorption energies are −0.88, −2.07, and −2.07 eV for the most stable molecular, partially dissociative, and completely dissociative adsorption, respectively. According to our calculations, a water molecule dissociates into OH and H species via three pathways with small energy barriers of 0.78, 0.72, and 0.85 eV, respectively. With the aid of the neighboring H atom, H2 formation through the reaction of H* + OH* can easily occur via two pathways with energy barriers of 0.61 and 0.36 eV, respectively. The molecular adsorption of water shows a slight coverage dependence on the surface while this dependence becomes obvious for partially dissociative adsorption as the water coverage increases from 1/4 to 1 ML. In addition, based on the “ab initio atomistic thermodynamic” simulations, increasing H2O partial pressure will enhance the stability of the adsorbed system and water coverage, while increasing temperature will decrease the H2O coverage. We found that the UN(001) surface reacts easily with H2O at room temperature, leading to dissolution and corrosion of the UN fuel materials.

A new 3-fold interpenetrated uranyl organic framework, UO2(bdc)(dmpi), was hydrothermally synthesized using 1,4-benzenedicarboxylic acid (H2bdc) and 1-(4-(1H-imidazol-1-yl)-2,5-dimethylphenyl)-1H-imidazole (dmpi). This framework, which was determined by synchrotron radiation X-ray, exhibited a new 3-fold interpenetrated (2,4)-connected topology with the Schläfli symbol of (12(6))(12)2. Additionally, large incurvation happened to the bond angle of [O=U=O](2+), which was always arranged in a rigorous line. Computational results based on density functional theory (DFT) indicated that the bent geometry of uranyl in UO2(bdc)(dmpi) was mainly due to the higher charge populations in the valence 6d shells of uranium, rendered by the electronegative imidazoles.

Due to the vast application potential of graphene oxide (GO)-based materials in nuclear waste processing, it is of pivotal importance to investigate the interaction mechanisms between actinide cations such as Np(V) and Pu(IV, VI) ions and GO. In this work, we have considered four types of GOs modified by hydroxyl, carboxyl, and carbonyl groups at the edge and epoxy group on the surface, respectively. The structures, bonding nature, and binding energies of Np(V) and Pu(IV, VI) complexes with GOs have been investigated systematically using scalar-relativistic density functional theory (DFT). Geometries and harmonic frequencies suggest that Pu(IV) ions coordinate more easily with GOs compared to Np(V) and Pu(VI) ions. NBO and electron density analyses reveal that the coordination bond between Pu(IV) ions and GO possesses more covalency, whereas for Np(V) and Pu(VI) ions electrostatic interaction dominates the An-OG bond. The binding energies in aqueous solution reveal that the adsorption abilities of all GOs for actinide ions follow the order of Pu(IV)Pu(VI)Np(V), which is in excellent agreement with experimental observations. It is expected that this study can provide useful information for developing more efficient GO-based materials for radioactive wastewater treatment.

Although a variety of tetradentate ligands, 6,6'-bis(5,6-dialkyl-1,2,4-triazin-3-yl)-2,2'-bipyridines (BTBPs), have been proved as effective ligands for selective extraction of Am(III) over Eu(III) experimentally, the origin of their selectivity is still an open question. To elucidate this question, the geometric and electronic structures of the actinide and lanthanide complexes with the BTBPs have been investigated systematically by using relativistic quantum chemistry calculations. We show herein that in 1:1 (metal:ligand) type complexes substitution of electron-donating groups to the BTBP molecule can enhance its coordination ability and thus the energetic stability of the formed Am(III) and Eu(III) complexes in the gas phase. According to our results, Eu(III) can coordinate to the BTBPs with higher stability in energy than Am(III), no matter whether there are nitrate ions in the inner-sphere complexes. The presence of nitrate ions leads to formation of the probable Am(III) and Eu(III) complexes, M(NO(3))(3)(H(2)O)(n) (M = Am, Eu), in nitric acid solutions. It has been found that the changes of Gibbs free energy play an important role for Am(III)/Eu(III) separation. In fact, the weaker complexing ability of Am(III) with nitrate ions and water molecules makes the decomposition of Am(NO(3))(3)(H(2)O)(4) more favorable in energy, which may thus increase the possibility of formation of Am(BTBPs)(NO(3))(3). Our work may shed light on the design of novel extractants for Am(III)/Eu(III) separation.

A series of point defects in uranium mononitride (UN) have been studied by first-principles DFT+U calculations. The influence of intrinsic defects on the properties of UN was explored by considering the anti-ferromagnetic (AFM) order along the [001] direction. Our results show that all the point defects lead to obvious volume swelling of UN crystal. Energetically, the interstitial nitrogen defect is the most favorable one among single-point defects in UN crystal with the formation energy of 4.539 eV, while the N-Frenkel pair becomes the most preferable one among double-point defects. The AFM order induces obvious electron spin polarization of uranium towards neighboring uranium atoms with opposite spin orientations in UN crystal.

We modeled the solution behavior of zirconium in uranium dioxide (UO2) by using density functional theory. The Coulomb repulsion of uranium 5f elections was characterized by a spherically averaged Hubbard parameter. Our results indicate that zirconium prefers to locate at U vacancies in UO2 and presents a slight tendency to accumulate in thermodynamics. The solution energies for hcp Zr metal and monoclinic ZrO2 indicates that these two precipitates are insoluble in UO2. In perfect UO2, the band-gap opening is governed by U 5f peaks around the Fermi energy, whereas the solution of zirconium further leads to the band gap splitting owing to the introduction of zirconium 4d peaks especially at high defect concentrations.

Due to the rapid development of the nuclear power industry, and consequently, the nuclear accident in Fukushima, much attention has been paid to novel materials for the efficient and rapid separation, removal and recovery of nuclear fuel associated radionuclides from aqueous solutions. Herein, a novel mesoporous material, dihydroimidazole functionalized SBA-15 (DIMS), was synthesized via a post-grafting method and used as an efficient sorbent for the extraction of U(VI) from aqueous solution. The synthesized material was found to possess highly ordered mesoporous structures with a large surface area and a uniform pore diameter. The sorption tests under various conditions demonstrated that the sorption of U(VI) by DIMS was fast, with an equilibrium time of less than 10 min. Additionally, the maximum sorption capacity reached 268 mg g−1 at pH 5.0 ± 0.1. Changes in the solid-to-liquid ratio (msorbent/Vsolution) did not have any remarkable effect on the U(VI) sorption. Besides, the sorbed U(VI) can be easily desorbed by 0.01 mol L−1 or more concentrated HNO3 solution, resulting in a U(VI) solution with a concentration factor of 300 at a solid–liquid ratio as low as 0.013 g L−1. The reclaimed sorbent can be reused with no obvious decrease in the sorption capacity. The selectivity of the DIMS sorbent for U(VI) ions was found to be fairly desirable by the sorption tests with the solutions containing a range of competing metal ions.