Room temperature ionic liquids (RTILs) represent a recent new class of solvents applied in liquid/liquid extraction based nuclear fuel reprocessing, whereas the related coordination chemistry and detailed extraction processes are still not well understood and remain of deep fundamental interest. The work herein provides a new insight of coordination and extraction of uranium(VI) with N-donating ligands, e.g., N,N′-diethyl-N,N′-ditolyldipicolinamide (EtpTDPA), in commonly used RTILs. Exploration of the extraction mechanism, speciation analyses of the extracted U(VI), and crystallographic studies of the interactions of EtpTDPA with U(VI) were performed, including the first structurally characterized UO2(EtpTDPA)2(NTf2) and UO2(EtpTDPA)2(PF6)2 compounds and a first case of crystallographic differentiation between the extracted U(VI) complexes in RTILs and in molecular solvents. It was found that in RTILs two EtpTDPA molecules coordinate with one U(VI) ion through the carbonyl and pyridine nitrogen moieties, while NTf2– and PF6– act as counterions. The absence of NO3– in the complexes is coincident with a cation-exchange extraction. In contrast, both the extracted species and extraction mechanisms are greatly different in dichloromethane, in which UO22+ coordinates in a neutral complex form with one EtpTDPA molecule and two NO3– cations. In addition, the complex formation in RTILs is independent of the cation exchange since incorporating UO2(NO3)2, EtpTDPA, and LiNTf2 or KPF6 in a solution also produces the same complex as that in RTILs, revealing the important roles of weakly coordinating anions on the coordination chemistry between U(VI) and EtpTDPA. These findings suggest that cation-exchange extraction mode for ILs-based extraction system probably originates from the supply of weakly coordinating anions from RTILs. Thus the coordination of uranium(VI) with extractants as well as the cation-exchange extraction mode may be potentially changed by varying the counterions of uranyl or introducing extra anions.

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 (126)(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.

The incorporation and diffusion behaviors of Xe in uranium mononitride (UN) have been studied using first-principles density functional theory calculations. The incorporation and binding energies of Xe located at different sites are calculated. Because of strain relief related to moving Xe atom from highly strained interstitial site into the large steric vacancy site, a stronger binding energy between the incorporated Xe and the large steric vacancy forms. Using ab initio molecular dynamics simulations and climbing-image nudged elastic band calculations, we found that the activation barrier of interstitial Xe in UN in the “kick-out” diffusion mechanism is lower than that in the direct interstitial mechanism, and the net Xe diffusion occurs with vacancies mediated; that is, once an interstitial Xe atom is trapped in a U vacancy site, it will be immobile without other uranium vacancies mediated.

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.

With the rapid developments of nanotechnology, chances of exposing nanoscale particles to humans (e.g., workers and consumers) also increase correspondingly, which raises serious concerns on their biosafety. Entrance of nanoparticles into diverse biological environment endows them with new and dynamic biological identities as the so-called nanoparticle–protein corona. Therefore, understanding the role of these nanoparticle–protein coronas and resulting biological responses is crucial, as it helps to clarify the biological mechanism and prevent the potential adverse effects of nanoparticles. In this review, we summarize the latest developments relating to the nanoparticle–protein interaction and corresponding biological responses, with an emphasis on the characterization methods, induced biological effects and possible molecular mechanisms. In addition, we overview both the challenges and opportunities (particularly in nanomedicine) raised by this entrance of nanoparticles into the living creatures, especially human beings, with some future perspectives based on our understanding.

The potential industrial application of thorium (Th), as well as the environmental and human healthy problems caused by thorium, promotes the development of reliable methods for the separation and removal of Th(IV) from environmental and geological samples. Herein, the phosphonate-amino bifunctionalized mesoporous silica (PAMS) was fabricated by a one-step self-assembly approach for enhancing Th(IV) uptake from aqueous solution. The synthesized sorbent was found to possess ordered mesoporous structures with uniform pore diameter and large surface area, characterized by SEM, XRD, and N2 sorption/desorption measurements. The enhancement of Th(IV) uptake by PAMS was achieved by coupling of an access mechanism to a complexation mechanism, and the sorption can be optimized by adjusting the coverage of the functional groups in the PAMS sorbent. The systemic study on Th(IV) sorption/desorption by using one coverage of PAMS (PAMS12) shows that the Th(IV) sorption by PAMS is fast with equilibrium time of less than 1 h, and the sorption capacity is more than 160 mg/g at a relatively low pH. The sorption isotherm has been successfully modeled by the Langmuir isotherm and D-R isotherm, which reveals a monolayer homogeneous chemisorption of Th(IV) in PAMS. The Th(IV) sorption by PAMS is pH dependent but ionic strength independent. In addition, the sorbed Th(IV) can be completely desorbed using 0.2 mol/L or more concentrated nitric acid solution. The sorption test performed in the solution containing a range of competing metal ions suggests that the PAMS sorbent has a desirable selectivity for Th(IV) ions.Keywords: amino; bifunctionality; mesoporous silica; phosphonate; sorption; thorium;

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 η2 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 UO22+ 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.

A series of actinide (An) species of L-An-N compounds [An = Pa–Pu, L = [N(CH2CH2NSiPri3)3]3–, Pri = CH(CH3)2] have been investigated using scalar relativistic density functional theory (DFT) without considering spin–orbit coupling effects. The ground state geometric and electronic structures and natural bond orbital (NBO) analysis of actinide compounds were studied systematically in neutral and anionic forms. It was found that with increasing actinide atomic number, the bond length of terminal multiple An–N1 bond decreases, in accordance with the actinide contraction. The Mayer bond order of An–N1 decreases gradually from An = Pa to Pu, which indicates a decrease in bond strength. The terminal multiple bond for L–An–N compounds contains one σ and two π molecular orbitals, and the contributions of the 6d orbital to covalency are larger in magnitude than the 5f orbital based on NBO analysis and topological analysis of electron density. This work may help in understanding of the bonding nature of An–N multiple bonds and elucidating the trends and electronic structure changes across the actinide series. It can also shed light on the construction of novel An–N multiple bonds.

In this work, we reported a phenanthroline-based tetradentate ligand with hard–soft donors combined in the same molecule, N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen), for the group separation of actinides over lanthanides. The synthesis and solvent extraction as well as complexation behaviors of the ligand with actinides and lanthanides are studied experimentally and theoretically. The ligand exhibits excellent extraction ability and high selectivity toward hexavalent, tetravalent, and trivalent actinides over lanthanides in highly acidic solution. The chemical stoichiometry of Th(IV) and U(VI) complexes with Et-Tol-DAPhen is determined to be 1:1 using X-ray crystallography. The stability constants of some typical actinide and lanthanide complexes of Et-Tol-DAPhen are also determined in methanol by UV–vis spectrometry. Density functional theory (DFT) calculations reveal that the An–N bonds of the Et-Tol-DAPhen complexes have more covalent characters than the corresponding Eu–N bonds, which may in turn lead to the selectivity of Et-Tol-DAPhen toward actinides. This ligand possesses merits of both alkylamide and 2,9-bis-(5,6-dialkyl-1,2,4-triazin-3-yl)-1,10-phenanthroline (R-BTPhen) extractants for efficient actinide extraction and the selectivity toward minor actinides over lanthanides and hence renders huge potential opportunities in high-level liquid waste (HLLW) partitioning.

Spherical UO2 nanoparticles with an average diameter varying from 30 to 250 nm and U3O8 nanocuboids with a width of 400 nm and a length of 1 μm have been successfully synthesized just by a simply additive-free hydrothermal synthesis method. To selectively obtain the phase-pure U3O8 and UO2 nanoparticles, the experimental conditions, such as the solution pH and temperature as well as the concentration of hydrazine, have been established and optimized. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). In order to investigate the growth mechanism of the uranium oxide nanoparticles, XRD, SEM and Fourier transform infrared (FT-IR) spectrum measurements were carried out for the precursors prepared at different pH and hydrothermal time. The crucial factor for tunable fabrication of uranium oxide nanoparticles could come from the different reducing ability of hydrazine at various solution pH.

Graphene oxide (GO) has been receiving increasing research efforts in recent years because of its wide applications in various scientific fields. In this work the sorption of Th(IV) onto graphene oxide (GO) was studied using a batch method under ambient conditions. The sorption kinetics were found to be fast and fitted the pseudo-second-order model very well, with an equilibrium time of about 10 min. The sorption is strongly dependent on the solution pH but independent of the ionic strength of the solution. The maximum sorption capacity of as high as 214.6 mg g−1 can be achieved at pH 2.60 ± 0.05, and Th(IV) can be desorbed readily from the GO with 1.0 M HNO3. The thermodynamic investigations revealed that the sorption of Th(IV) on the GO was an endothermic and spontaneous process. The Scanning Electron Microscopy (SEM) results indicated obvious surface morphology changes of the GO induced by Th(IV) sorption. Furthermore, the interaction mechanism of Th(IV) and the GO was investigated by infrared (IR) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy combined with density functional theory (DFT) calculations. The results of EXAFS indicated that Th(IV) was bonded to ∼8 or 9 oxygen atoms and the average bond length of Th–O was estimated to be ∼2.45 Å in the first coordination shell. The DFT calculations further confirm the rationality of experimental and the EXAFS results. This work demonstrates the tremendous potential opportunities offered by GO in pre-concentration and removal of thorium and other tetravalent actinides for the recovery and remediation of the environment.

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.

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.

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 dissociation of the first hydrogen atom and its combination with a neighboring surface hydrogen atom. The above two formation pathways possess the energy barriers of 0.56 and 0.53 eV, corresponding to the large reaction energies of −2.62 and −2.64 eV, respectively.

MOF-76 exhibits not only high sensitivity for the detection of U(VI), but also high adsorption capacity of 298 mg g−1 at a low pH value of ∼3.0. Furthermore, the high selectivity for uranium adsorption over a series of competing metal ions is also illustrated.

A series of extraction complexes of Eu(III) and Am(III) with CMPO (n-octyl(phenyl)-N,N-diisobutyl-methylcarbamoyl phosphine oxide) and its derivative Ph2CMPO (diphenyl-N,N-diisobutyl carbamoyl phosphine oxide) have been studied using density functional theory (DFT). It has been found that for the neutral complexes of 2:1 and 3:1 (ligand/metal) stoichiometry, CMPO and Ph2CMPO predominantly coordinate with metal cations through the phosphoric oxygen atoms. Eu(III) and Am(III) prefer to form the neutral 2:1 and 3:1 type complexes in nitrate-rich acid solutions, and in the extraction process the reactions of [M(NO3)(H2O)7]2+ + 2NO3– + nL → MLn(NO3)3 + 7H2O (M = Eu, Am; n = 2, 3) are the dominant complexation reactions. In addition, CMPO and Ph2CMPO show similar extractability properties. Taking into account the solvation effects, the metal–ligand binding energies are obviously decreased, i.e., the presence of solvent may have an significant effect on the extraction behavior of Eu(III) and Am(III) with CMPOs. Moreover, these CMPOs reagents have comparable extractability for Eu(III) and Am(III), confirming that these extractants have little lanthanide/actinide selectivity in acidic media.

Two new layered 3D uranyl fluoride complexes: Na3(UO2)2F3(OH)4(H2O)2 (1) and Cs(UO2)2F5 (2) have been prepared using the hydrothermal method and characterized via single crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic space group C2/c [a = 15.125(3) Å, b = 6.941(1) Å, c = 11.257(2) Å, and β = 94.76(3)°] and compound 2 in the orthorhombic space group Cmcm [a = 12.149(2) Å, b = 11.862(2) Å, c = 12.366(2) Å], respectively. Both of them possess extended 3D structures. Furthermore, UVIO–alkalis (Na, Cs) interactions were observed in two compounds, which is relatively rare in U(VI) complexes. By introducing alkali ions, the layered structures can be further assembled into three-dimensional ones. Density functional theory (DFT) studies confirmed that the interactions between the alkalis and the oxygens of uranyl mainly ionic with small proportion of covalency, which results in the formation of these uranyl fluoride complexes with 3D structures.

•Uranium removal by ZVI-nps: independent of pH, the presence of CO32−, humic acid, or mimic groundwater constituents.•Rapid removal kinetics and sorption capacity of ZVI-nps is 8173 mg U/g.•Two reaction mechanisms: sufficient Fe0 → reductive precipitation as U3O7; insufficient Fe0 → hydrolysis precipitation of U(VI).•Fe/graphene composites: improved kinetics and higher U(VI) reduction ratio.Zero-valent iron nanoparticle (ZVI-np) and its graphene composites were prepared and applied in the removal of uranium under anoxic conditions. It was found that solutions containing 24 ppm U(VI) could be completely cleaned up by ZVI-nps, regardless of the presence of NaHCO3, humic acid, mimic groundwater constituents or the change of solution pH from 5 to 9, manifesting the promising potential of this reactive material in permeable reactive barrier (PRB) to remediate uranium-contaminated groundwater. In the measurement of maximum sorption capacity, removal efficiency of uranium kept at 100% until C0(U) = 643 ppm, and the saturation sorption of 8173 mg U/g ZVI-nps was achieved at C0(U) = 714 ppm. In addition, reaction mechanisms were clarified based on the results of SEM, XRD, XANES, and chemical leaching in (NH4)2CO3 solution. Partially reductive precipitation of U(VI) as U3O7 was prevalent when sufficient iron was available; nevertheless, hydrolysis precipitation of U(VI) on surface would be predominant as iron got insufficient, characterized by releases of Fe2+ ions. The dissolution of Fe0 cores was assigned to be the driving force of continuous formation of U(VI) (hydr)oxide. The incorporation of graphene supporting matrix was found to facilitate faster removal rate and higher U(VI) reduction ratio, thus benefitting the long-term immobilization of uranium in geochemical environment.Download full-size image

MOF-76 exhibits not only high sensitivity for the detection of U(VI), but also high adsorption capacity of 298 mg g−1 at a low pH value of ∼3.0. Furthermore, the high selectivity for uranium adsorption over a series of competing metal ions is also illustrated.