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Spectator ions have known and emerging roles in aqueous metal-cation chemistry, respectively directing solubility, speciation, and reactivity. Here, we isolate and structurally characterize the last two metastable members of the alkali uranyl triperoxide series, the Rb+ and Cs+ salts (Cs-U1 and Rb-U1). We document their rapid solution polymerization via small-angle X-ray scattering, which is compared to the more stable Li+, Na+ and K+ analogues. To understand the role of the alkalis, we also quantify alkali-hydroxide promoted peroxide deprotonation and decomposition, which generally exhibits increasing reactivity with increasing alkali size. Cs-U1, the most unstable of the uranyl triperoxide monomers, undergoes ambient direct air capture of CO2 in the solid-state, converting to Cs4[UVIO2(CO3)3], evidenced by single-crystal X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. We have attempted to benchmark the evolution of Cs-U1 to uranyl tricarbonate, which involves a transient, unstable hygroscopic solid that contains predominantly pentavalent uranium, quantified by X-ray photoelectron spectroscopy. Powder X-ray diffraction suggests this intermediate state contains a hydrous derivative of CsUVO3, where the parent phase has been computationally predicted, but not yet synthesized.

The crystal structures of mixed-ligand sulfato-, selenato-, phosphato-, arsenato-, and chromato-fluoride complexes of uranyl and of mixed-ligand carboxylato-fluoride and mixed-ligand fluoride complexes with neutral donor ligands studied by the single-crystal X-ray diffraction method were systematized and discussed. The crystal chemical features of the structures of the mixed-ligand fluoride complexes of uranyl were determined: the coordination polyhedron of the hexavalent uranium atom in the structures of the mixed-ligand fluoride complexes of uranyl (except for three hexagonal-bipyramidal complexes) has a pentagonal-bipyramidal structure: the oxygen atoms of the uranyl group are located on the vertical axis of the pentagonal bipyramid, perpendicular to the equatorial plane in which five atoms are located. In dimeric and polymeric chains of mixed-ligand fluoride complexes of uranyl (with the exception of one compound in which the common bridge in the dimer complex is oxygen atoms), the uranyl units are linked via fluoride bridges. Inorganic and organic ligands, which contained O-donor atoms, combine dimers and polymer chains into layers and three-dimensional formation. [ABSTRACT FROM AUTHOR]

An upconversion fluorescence sensing platform was developed with upconversion nanoparticles (UCNPs) as energy donors and gold nanoparticles (AuNPs) as energy acceptors, based on the FRET principle. They were used for quantitative detection of uranyl ions (UO22+) by amplifying the signal of the hybrid chain reaction (HCR). When UO22+ are introduced, the FRET between AuNPs and UCNPs can be modulated through a HCR in the presence of high concentrations of sodium chloride. This platform provides exceptional sensitivity, with a detection limit as low as 68 pM for UO22+ recognition. We have successfully validated the reliability of this method by analyzing authentic water samples, achieving satisfactory recoveries (89.00%–112.50%) that are comparable to those of ICP-MS. These results indicate that the developed sensing platform has the capability to identify trace UO22+ in complex environmental samples. [ABSTRACT FROM AUTHOR]

AbstractSediments from aquatic environments can be contaminated with uranium from natural and anthropogenic sources; the behavior of U(VI) was investigated in two natural (SPT and DS) and gamma-irradiated (SPT-I) aquifer sediments in batch systems. Sediments were characterized, and quartz, albite, and kaolinite were mainly found in both sediments by X-ray diffraction. The points of zero charge were 5.4, 5.3, and 5.5, and the organic matter percentages were 48.0, 46.0, and 4.7% for SPT, SPT-I, and DS, respectively. Uranyl nitrate solutions were put in contact with each sediment considering different parameters (pH, contact time, initial concentration of uranium, and temperature). DS sediment did not adsorb any quantity of uranium at different pH values; SPT and SPT-I, attained the highest qe values at pH 3.5–4. The results show chemisorption on homogenous materials and endothermic processes. Desorption behavior of U(VI)/SPT showed a hundred percent desorption with nitric acid and humic acid solutions; in the last case, it is due to the high stability constant of the complex of uranium with the humic acids. The results help to understand the contamination and decontamination processes of sediments with uranium, the bioavailability of uranium, the ecological risk of U-contaminated sediments, and remediation. Doses of 1 MGy of Co-60 gamma radiation did not affect the uranyl ions behavior in the aquifer sediment. [ABSTRACT FROM AUTHOR]

The behavior of soluble uranium (VI) on the adsorption/desorption processes in the presence of a natural forest soil (FS) or a gamma-irradiated forest soil (FS-I) provides important knowledge on the fate and mobility of this element in contaminated soils and groundwater. Soil from a forest was irradiated with a dose of 1 MGy 60Co gamma radiation and was compared with natural soil to determine the behavior of U(VI) in these materials. Both natural and gamma irradiated soils were characterized by several physicochemical techniques. Kinetics, isotherms, effects of pH, U(VI) concentration, temperature, and stability of the U(VI)/adsorbents were considered. The equilibrium of adsorption processes ${\rm{UO}}_2^{2 + }$UO22+/FS and ${\rm{UO}}_2^{2 + }$UO22+/FS-I were achieved in 2 h, and the data were well fitted to the pseudo first (FS-I), pseudo second (FS), and Elovich models (FS): qe value was 14 mg g−1 for FS, slightly higher than 12 mg g−1 for FS-I. The isotherm data were well-fitted to the Langmuir and Temkin models for FS and FS-I, respectively. The processes of both materials are independent of the temperature between 30 and 50°C; however, they are sensitive to pH and U(VI) concentration. Furthermore, acidic media and complexing agents were good desorbents for U(VI) from the natural and irradiated soils. [ABSTRACT FROM AUTHOR]

Context: The efficient extraction of uranyl from spent nuclear fuel wastewater for subsequent reprocessing and reuse is an essential effort toward minimization of long-lived radioactive waste. N-substituted amides and Schiff base ligands are propitious candidates, where extraction occurs via complexation with the uranyl moiety. In this study, we extensively probed chemical bonding in various uranyl complexes, utilizing the local vibrational modes theory alongside QTAIM and NBO analyses. We focused on (i) the assessment of the equatorial O-U and N-U bonding, including the question of chelation, and (ii) how the strength of the axial U = O bonds of the uranyl moiety changes upon complexation. Our results reveal that the strength of the equatorial uranium-ligand interactions correlates with their covalent character and with charge donation from O and N lone pairs into the vacant uranium orbitals. We also found an inverse relationship between the covalent character of the equatorial ligand bonds and the strength of the axial uranium-oxygen bond. In summary, our study provides valuable data for a strategic modulation of N-substituted amide and Schiff base ligands towards the maximization of uranyl extraction. Method: Quantum chemistry calculations were performed under the PBE0 level of theory, paired with the relativistic NESCau Hamiltonian, currently implemented in Cologne2020 (interfaced with Gaussian16). Wave functions were expanded in the cc-pwCVTZ-X2C basis set for uranium and Dunning's cc-pVTZ for the remaining atoms. For the bonding properties, we utilized the package LModeA in the local modes analyses, AIMALL in the QTAIM calculations, and NBO 7.0 for the NBO analyses. [ABSTRACT FROM AUTHOR]

Harnessing solar energy by photocatalytically converting oxygen and water into high-value-added H2O2 is a promising way of alleviating both environmental and energy issues. It is worth noting that suppressing detrimental side reactions, such as the generation of •O2−, is a critical approach to enhancing H2O2 production. Herein, a 2-fold interpenetrating 3D uranium-organic framework (YTU-W-1) was developed and introduced for photocatalytic H2O2 production. The material demonstrates a different photocatalytic mechanism when employing uranyl as an initiator, as compared with the conventional semiconductor photocatalytic pathway involving photo-generated charge carriers. Benefiting from the strong hydrogen abstraction effect of the U≡O• and the direct one-step oxygen reduction pathway, YTU-W-1 exhibits enhanced photocatalytic performance for H2O2 production with yield efficiency of 221 µmol h−1 g−1. Furthermore, YTU-W-1 displays a high H2O2 selectivity of 68%, confirmed by rotating ring-disk electrode (RRDE) measurement. DFT calculations were used to elucidate the critical role of uranyl in the photocatalytic oxygen reduction reaction for H2O2 production. This research introduces an innovative approach to photo driven H2O2 production, underscoring the potential for heterogeneous catalysts to engage in photocatalytic reactions independently of photo-generated charge carriers. [ABSTRACT FROM AUTHOR]

NaUO2(mia)3 (I) crystals (mia: monoiodacetate ion CH2ICOO−) were synthesized and studied by X-ray diffraction and IR spectroscopic analyses. Uranyl-containing complexes [UO2(mia)3]– in the structure correspond to the crystal chemical formula A(B01)3, where A = UO22+, B01 = mia. Using coordination sequences, we analyzed the features of the 3D framework, which is realized in the structure of crystals of I and contains 8 crystallographically nonequivalent U or Na atoms. A semiempirical calculation and comparison of the calculated and experimental vibration frequencies in the IR spectrum of I were performed. [ABSTRACT FROM AUTHOR]

UCl4, UBr4, UBr5, or UO2Cl2 reacted with excess liquid ammonia – in adventitious presence of moisture and/or air – and formed some peculiar uranium compounds of which we present the crystal structures. [(NH3)7(N3)U(μ‐O)U(NH3)8]Cl5 ⋅ 7NH3 contains a dinuclear μ‐O‐bridged uranium(IV) cation, [{(NH3)4UO2}2(μ‐O)]Cl2 ⋅ 4NH3 features a dinuclear μ‐O‐bridged uranyl(VI) cation, while the compounds [(U(VI)O2)2(U(V)O2)2(μ3‐O)2(NH3)12]Br2 ⋅ 6NH3 and [(U(VI)O2)4(U(V)O2)4(μ3‐O)4(NH3)22]Br4 ⋅ 16NH3 are mixed‐valent containing uranyl(V)‐uranyl(VI) units. For these tetra‐ and octanuclear complex cations we observed that the O atoms of the uranyl(V) units can be μ2‐ and even μ3‐bridging to uranyl(VI) units, while the O atoms of the latter are acting as terminal ligands only. [(NH3)8U(μ‐N)U(NH3)5(μ‐N)UO2(NH3)4]Br6 ⋅ 18NH3 presents the first example of a compound where the isoelectronic species UO22+ and UN2 formed a complex with the NUN unit bridging to the U atom of the uranyl(VI) cation. As it is can be difficult to distinguish between N and O atoms with X‐ray diffraction, quantum‐chemical calculations at the DFT‐PBE0/TZVP level of theory were carried out which unequivocally confirmed the atom assignments in the crystal structures. The chemical bonding in the complex cations was studied using intrinsic bonding orbitals and allowed for an additional discrimination of the U(V) and U(VI) atoms in the mixed‐valent compounds. [ABSTRACT FROM AUTHOR]

In this study, we investigated whether the corm tunic structure, which is the underground part of the Crocus (Iridaceae) plant, can be used for adsorption and recovery/removal of uranium from an aqueous solution. The characterization of this structure, which has not been studied for its interaction with metals before, has been elucidated by point zero charge (PZC), FTIR, and SEM analyses. Extensive investigations were conducted on the adsorption properties of the biomass used and the pH, temperature, time, adsorbent dosage, and uranyl ion concentration variables were optimized. The experimental data were interpreted using theoretical adsorption models. The Langmuir model revealed a maximum adsorption capacity of the material to be 0.286 mol kg−1. Adsorption kinetics were also described using pseudo-first order, pseudo-second order, Elovich, and intra-particular diffusion models. It is shown that the adsorption pH reaches the highest adsorption at the natural pH of the uranium solution. Experimental studies showed that the adsorption was endothermic and spontaneous. It has been shown that this biomaterial can be used as an adsorbent for the removal of uranium as well as a biomarker for determining the environmental uranium concentration. [ABSTRACT FROM AUTHOR]

The study of the structure and properties of extractants is of great significance for developing new extractants. For uranium extraction and recovery requirements in spent fuel reprocessing, three kinds of extractants with different ether-oxygen chains, N,N,N'N'-tetraoctyl-3-oxapentanediamide (TODGA), N,N,N'N'-tetraoctyl-3,6-dioxaoctanediamide (TODOODA) and N,N,N'N'-tetraoctyl-3,6,9-trioxaundecanediamide (TOUDA) were synthesized to study the influence of the ether-oxygen chain skeleton on the extraction of uranium from nitrate media. TODOODA shows a good extraction ability for uranyl ions at high nitric acid concentrations. Equimolar series method, FT–IR spectrum and MALDI–TOF–MS spectra indicated that the extracted structure was formed as [UO2NO3·TODGA]NO3, [UO2NO3·TODOODA]NO3 and [UO2NO3·TOUDA]NO3. [ABSTRACT FROM AUTHOR]

Presented is an infrared-induced sensor constructed of upconversion nanoparticles and DNAzyme for ultra-sensitive, and rapid detection of uranyl ions. The detection method eliminates the use of chemically labeled nucleic acid probes, possesses high selectivity, and a uranyl detection limit of 39 nM. The technique is successfully applied to the detection of uranyl in various water samples as well as human serum, illustrating the excellent sensitivity and specificity of the quantification platform. [ABSTRACT FROM AUTHOR]

A series of bidentate, viz., 1,1'-(1,2-ethylene)-3,3'-dimethyldiimidazoline-2,2'-diylidene (L1), 1-methyl-3-(2-pyridylmethyl)-imidazoline-2-ylidene (L2) and tridentate, viz., 1,3-bis(2-pyridyl)-imidazoline-2-ylidene (L3) ligands have been obtained from their corresponding imidazolium salts through deprotonation reactions. Treatment of UO2Cl2(THF)3 with one equivalent L3 produces air-stable U(VI)-carbene complex 3, characterized by elemental analysis, FTIR, NMR spectroscopy as well as extended X-ray absorption fine structure (EXAFS) analysis. EXAFS result indicates that the ligand is bonded through one C and two N-atoms to the uranium atom. Attempts to synthesize uranyl complexes derived from L1 and L2 were also successful but these complexes are decomposed quickly within one hour at room temperature. 3 produces pure UO2 powder when heated under an argon atmosphere from room temperature to 600 °C with constant heating rate of 5 °C/min. The solid-state UV–Vis spectrum of the compound shows absorption peaks at 332 and 450 nm. The excitation spectrum of 3 (at λem = 520 nm) exhibits two almost symmetrical peaks at 273 and 368 nm. Density functional theory-based quantum mechanical calculations indicate that a partial covalent interaction exists between the carbene C and U while a weak non-covalent interaction exists between carbene N and U atoms. [ABSTRACT FROM AUTHOR]

Copyright of Industrial Minerals & Processing / Huagong Kuangwu yu Jiagong is the property of Industrial Minerals & Processing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A series of compounds of the form [HAr]2[UO2X4] is reported here, wherein Ar is systematically varied between pyridine (1‐X), quinoline (2‐X), acridine (3‐X), 2,5‐dimethylpyrazine (4‐X), quinoxaline (5‐X), and phenazine (6‐X), and X=Cl or Br. With greater conjugation in the organic cation, a larger quenching in uranyl luminescence is observed in the solid state. Supporting our luminescence experiments with computation, we map out the potential energy diagrams for the singlet and triplet states of both the [HAr]+ cations and [UO2Cl4]2− anion in the crystalline state, and of the assembly. The distinct energy transfer pathways in each compound are discussed. [ABSTRACT FROM AUTHOR]

A quantitative understanding of the molecular-scale mechanisms of radionuclide sorption on different clay minerals is crucial for the development and safe implementation of geological nuclear waste disposal technologies. We apply classical molecular dynamics (MD) computer simulations to study the adsorption of uranyl on the external basal surfaces of two typical clay models. In the illite model, negative charge is primarily localized in the tetrahedral sheets, while in the lower-charge smectite model, the isomorphic substitutions are introduced in the octahedral sheet. The comparison of atomic density distributions at the clay surfaces and adsorption-free energies profiles as a function of distance from these surfaces demonstrates that overall U behavior at the basal clay surface is quite similar for illite and smectite. Uranyl is sorbed as a mixture of outer-sphere aqua complexes [UO2(H2O)5]2+ and hydrolyzed aqua complexes [UO2(H2O)4–5OH]+ on both surfaces. The structural and compositional differences between the models do not greatly affect the uranyl's nearest coordination environment and are mainly reflected in the specific localization and orientation of the uranyl ions at both surfaces and in the magnitude of the adsorption-free energies. The observed quantitative characteristics of uranyl interactions with illite and smectite surfaces will help to better understand U behavior during the sorption process on clay minerals for the entire range of mixed-layer illite–smectite structures. A comparison of two versions of the ClayFF force field in the simulations made it possible to more accurately and quantitatively evaluate some subtle features of the uranyl–clay interactions and to obtain a more precise composition of uranyl complex with the modified ClayFF force field (ClayFF-MOH). [ABSTRACT FROM AUTHOR]

In the present study, anionic hydrogels, acrylamide (AAm) monomer, and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) comonomer were prepared in the presence of two different cross-linkers. Then, super-anionic hydrogels were prepared by converting the amide groups of neutral AAm in anionic hydrogels to hydroxamic acid with hydroxylamine hydrochloride. The hydrogels were characterized by FTIR, SEM, TG, and DSC analyses. Uranyl adsorption in the hydrogels was investigated by spectroscopic, kinetic, and equilibrium studies. It was determined that uranyl adsorption kinetics in hydrogels were compatible with pseudo-second-order and intra-particular diffusion models. It was determined that the uranyl adsorption isotherms on the hydrogels were L-type according to the Giles isotherm classification. Adsorption parameters were calculated by applying Freundlich and Langmuir models to these isotherms. In addition, it was determined that the amount of adsorbed uranyl increased with the increase in adsorbent mass, did not change with temperature, decreased in the range of pH 2–4, and increased at pH 4–7. It was observed that super-anionic hydrogels had the highest adsorption capacity among these new hydrogels. In addition, molecular electrostatic potential (MEP) mapping was performed to predict the reactive regions of the hydrogels. The results showed that the theoretical and experimental data of hydrogels are in agreement with each other. In conclusion, it can be said that the anionic and super-anionic hydrogels prepared in this study are unique hydrogels with fast and effective properties in removing uranyl. [ABSTRACT FROM AUTHOR]

This paper reviews not the largest, but at the same time quite an interesting, group of natural and synthetic uranyl molybdate compounds. Nowadays, nine minerals of U and Mo are known, but the crystal structures have only been reported for five of them. Almost an order of magnitude more (69) synthetic compounds are known. A significant discrepancy in the topological types for natural and synthetic phases is shown, which is most likely due to elevated temperatures of laboratory experiments (up to 1000 °C), while natural phases apparently grow at significantly lower temperatures. At the same time, the prevalence of dense topologies (with edge-sharing interpolyhedral linkage) among natural phases can be noted, which is fully consistent with other recently considered mineral groups. Uranyl molybdates demonstrate several similarities with compounds of other U-bearing groups; however, even topological matches do not lead to the appearance of completely isotypic compounds. Structural complexity calculations confirm, in general, crystal chemical observations. Considering the prevalence of dense structures in which coordination polyhedra of uranium and molybdenum are connected through common edges as well as framework architectures, one can expect a less significant influence of interlayer species on the formation of the crystal structure than the main U-bearing complexes. The more structural complexity of the uranyl molybdate units, the more complex of the entire crystal structure is. In addition, there is a tendency for complexity to increase with increasing density of the complex; the simplest structures are vertex-shared, while the complexity increases with the appearance of common edges. [ABSTRACT FROM AUTHOR]

The chosen of ligands directly affects the self-assembly behaviors of uranyl compounds, and plays a critical role in the structure and function of the compounds. In this work, several ligands were selected to assembled with uranyl ions by hydrothermal method, and three uranyl coordination polymers(CPs) based on viologen functional groups were synthesized. The main skeleton of the CPs is one-dimensional(1D) chain structure. Among them, compounds 1 and 2 exhibit obvious fluorescence properties. In addition, compound 2 exhibit significantly reversible photochromic/thermochromic properties. Ultraviolet-visible spectrum and electron paramagnetic resonance(EPR) spectrum indicate that the reversible color change is due to the generation of viologen radicals from viologen ligands after irradiation. This research has realized the assembly and synthesis of several uranyl CPs based on viologen ligands, and lead to design and development of more functional materials containing depleted uranium.

The nature of the interaction between actinide ions and ligands is of great significance in the application of the separation of actinide groups. Therefore, we have been devoted to this aspect in recent years. In this article, the coordination structure, stability and bonding properties of the complexes formed by uranyl and macrocyclic ligands are reviewed. First of all, our study found that the coordination structure of actinyl macrocyclic complexes depends on the size of the macrocyclic ligands; secondly, in the case of “side-on” coordination, uranyl tends to form a 1∶2 complex, while in the case of “insertion” structure, uranyl tends to form a 1∶1 complex; thirdly, it has been found that the ligands with ring size of 18 have excellent coordination ability when combined with uranyl, and ［CHP］4- has the strongest binding ability; finally, this stability is mainly due to the greater covalence of U-N than that of U-O and U-S. These structural rules and bonding characteristics provide important theoretical guidance for the experimental screening of reasonable and efficient ligands for the separation of actinides.

The very strong complexing capacity of pyridine-2,6-dicarboxylic acid (DPA) with lanthanides/actinides of different oxidation states in aqueous solutions makes it a selective complexing agent or stripping agent in various separation systems. Besides DPA, its derivatives and their coordination chemistry with lanthanides/actinides have received significant attention for the past a few years as well. Amongst, the mono-amide derivative of DPA, N,N-dimethyl-6-amide-pyridine-2-carboxylic acid (DMAPA, HL) as a multidentate ligand is very appealing because it can bond to metal ions in varying modes through oxygen atoms in both amide and carboxyl groups, and the nitrogen atom of the pyridine-ring. In this work, the coordination chemistry of DMAPA and UO2+2 in aqueous solution was studied with fluorescence spectroscopy, potentiometry, Raman spectroscopy in combination with X-ray single crystal diffraction analysis of the solid complex UO2L2. It is found that besides the two previously reported complexes, UO2L+ and UO2L2, formed by the deprotonated DMAPA (L-), a protonated complex UO2(HL)2+ complex is formed by the neutral DMAPA (HL) molecule. Due to the combination between UO2+2 and L- in the UO2L+ and UO2L2 complexes are too strong, the stability constants can’t be directly determined with potentiometric titration. Therefore, by using HEDTA as a competing ligand, the stability constants of UO2L+ and UO2L2 are determined to be 105.45±0.06 and 107.67±0.10 respectively, which are apparently different from previously reported values of 105.65±0.10 and 108.95±0.15. Because the protonated complex UO2(HL)2+ species exist in relatively acidic solutions in which pH electrode can’t work appropriately, potentiometry method is not suitable for determining the stability constant. Therefore, the stability constant of UO2(HL)2+ is determined to be 106.32±0.09 by fluorescence spectral titration. Interestingly, different from the enhanced fluorescence of U(Ⅵ) in the UO2(DPA) complex, the fluorescence intensity of U(Ⅵ) in UO2L+ and UO2(HL)2+ is lowered, but these observations can’t be well explained by a solid mechanism. By comparing the Raman spectra of the complexes in aqueous solutions and in the solid complex UO2L2, the coordination modes of L- and HL in the complexes of UO2L+ and UO2(HL)2+ are found to be same, L- and HL bond to U(Ⅵ) as tridentate. For the UO2(HL)2+ species, the protonation happens in the carboxyl group, which has no obvious effect on the Raman vibration of uranyl, hence the Raman shift of uranyl in UO2(HL)2+ is almost the same with that in UO2L+.

Renewable and biodegradable polysaccharides have attracted interest for their wide applicability, among them their use as sorbents for heavy metal ions. Their high sorption capacity is due mainly to the acidic groups that populate the polysaccharide backbone, for example, carboxylic groups in alginate and sulfate ester groups in the iota and lambda carrageenans. In this study, these three polysaccharides were employed, alone or in different mixtures, to recover different heavy metal ions from aqueous solutions. All three polysaccharides were capable of adsorbing Eu3+, Sm3+, Er3+, or UO22+ and their mixtures, findings that were also confirmed using XPS, TGA, and FTIR analyses. In addition, the highest sorption yields of all the metal ions were obtained using alginate, alone or in mixtures. While the alginate with carboxylic and hydroxyl groups adsorbed different ions with the same selectivity, carrageenans with sulfate ester and hydroxyl groups exhibited higher adsorption selectivity for lanthanides than for uranyl, indicating that the activity of the sulfate ester groups toward trivalent and smaller ions was higher. [ABSTRACT FROM AUTHOR]

Sunlight‐driven photoreduction of the environmentally mobile uranyl (VI) to less soluble tetravalent uranium is of considerable value to environmental sustainability, yet the pursuit for high‐performance semiconductors is plagued by the current disadvantages of inferior charge separation/migration. This study reports that a nickel single atom isolated on a sulfur‐functionalized graphitic carbon nitride/reduced graphene oxide 2D heterostructure enables exceptional uranyl photoreduction. Under only 11 min of visible light irradiation, the single atom anchored semiconductor yields a high removal rate of 99.8% and a record‐high extraction capacity of 4144 mg g−1 in uranyl‐containing wastewater and seawater. Theoretical calculations confirm that the remarkable uranyl photoreduction originates from the synergetic effect of Ni single atoms and intimate heterojunction establishment that can not only promote the separation/migration of photoexcited carriers, but also greatly reduce the energy barrier of uranyl reduction. This study showcases the exciting potential of single atom semiconductors for efficient uranyl removal from uranium‐contaminated aqueous environments. [ABSTRACT FROM AUTHOR]

The transport and retardation of radioactive elements in hyper-alkaline conditions of radioactive waste repositories is a challenging field that is still poorly understood. In this study, the transport and attenuation of uranium in a column experiment was modelled by considering kinetic reactions, advection–dispersion and chemical/physical retardation processes. The modelling was first performed for three alluvium samples from Yucca Mountain in circumneutral pH to moderately alkaline conditions. Sorption of uranyl ( UO 2 2 + (U VI) ) was found to strongly depend on the surface complexation model assumed, with no significant removal of U VI by precipitation or ion exchange process. The surface/edge site reaction of Al-hydroxyl group in kaolinite was shown to have a high affinity for uranyl adsorption, while the hydrous ferric oxide edge on hematite adsorbed most of the uranyl ions. The model was then used to interpret uranium transport in a laboratory column filled with Hollington sandstone under hyper-alkaline (pH 13) conditions. The simulation results show that uranium adsorption on the Al-hydroxyl edge of kaolinite exceeds adsorption by the calcium silicate hydrate phase. This result may reflect the lack of surface complexation parameters for calcium silicate hydrate minerals. Hence, further studies are required in the field of surface complexation reactions for calcium silicate hydrate phases. Article Highlights: Sorption of uranyl ( UO 2 2 + (U VI) ) was found to strongly depend on the surface complexation model, with no significant removal of U_VI by precipitation or ion exchange process. The aluminol surface edges in kaolinite were shown to have a higher affinity for uranyl adsorption, while the hydrous ferric oxide edge on hematite adsorbed most of the uranyl ions. Uranium adsorption on the aluminol edge of kaolinite exceeds adsorption by the C-S-H phase. This result may reflect the lack of surface complexation parameters for C-S-H minerals. [ABSTRACT FROM AUTHOR]

This paper reviews the state of the art in the structural chemistry of organically templated uranyl sulfates and selenates, which are considered as the most representative groups of U-bearing synthetic compounds. In total, there are 194 compounds known for both groups, the crystal structures of which include 84 various organic molecules. Structural studies and topological analysis clearly indicate complex crystal chemical limitations in terms of the isomorphic substitution implementation, since the existence of isotypic phases has to date been confirmed only for 24 compounds out of 194, which is slightly above 12%. The structural architecture of the entire compound depends on the combination of the organic and oxyanion parts, changes in which are sometimes realized even while maintaining the topology of the U-bearing complex. An increase in the size of the hydrocarbon part and number of charge functional groups of the organic cation leads to the formation of rare and more complex topologies. In addition, the crystal structures of two novel uranyl sulfates and one uranyl selenate, templated by isopropylammonium cations, are reported. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) are crystalline materials that have shown great potential for use within the life science, environmental chemistry, and energy fields owing to their light weight, low density, periodic structure, adjustable pore size, large surface area, and chemical stability. As a naturally occurring radioactive element, uranium is widely used as nuclear fuel, nuclear industry and medicine. It can severely harm the human body during its processing and enrichment. This paper reviews the recent progress of COFs with or without fluorescence sensing or photocatalytic ability for use as uranyl ( UO 2 2 + ) adsorbents, and the interaction mechanisms of COFs with UO 2 2 + are summarized. In addition, the application of UO 2 2 + adsorption in seawater is discussed and the future development trends of UO 2 2 + -based COF materials are prospected. [ABSTRACT FROM AUTHOR]

Two crystalline phases, which are analogues of common secondary uranyl minerals, namely, becquerelite (Ca[(UO2)6O4 (OH)6]·8H2O) and phurcalite (Ca2[(UO2)3O2 (PO4)2]·7H2O) were identified on the surface of a Chernobyl corium-containing sample affected by hydrothermal alteration in distilled water at 150 °C for one year. Phases were characterized using Single-Crystal X-ray Diffraction Analysis (SCXRD) as well as optical and scanning electron microscopy. Features of the structural architecture of novel phases, which come from the specific chemical composition of the initial fragment of Chernobyl sample, are reported and discussed. Precise identification of these phases is important for modelling of severe nuclear accidents and their long-term consequences, including expected corium–water interaction processes at three damaged Units of the Nuclear Power Plant Fukushima Daiichi. [ABSTRACT FROM AUTHOR]

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In this study, polyacrylamide-pollen (P@PAA) composite adsorbent was synthesized by in situ polymerization method using polyacrylamide hydrogel and pollen. The adsorptive properties of the P@PAA hybrid polymer composite adsorbent were investigated for the removal of UO22+ ions. The findings obtained as a result of the structural characterizations showed that the P@PAA composite adsorbent has various functional group variations. The max adsorption capacity of UO22+ ions was 0.695 mol kg−1. The thermodynamic parameters of the adsorption of UO22+ ions onto P@PAA hybrid polymer composite were determined and it was clarified that the adsorption was spontaneous. [ABSTRACT FROM AUTHOR]

The results of combined single-crystal X-ray diffraction, electron probe microanalysis, Fourier microspectroscopy, and photoluminescence spectroscopy study of crystals of turkestanite from the Dara-i-Pioz deposit, Tien-Shan Mountains, Tajikistan are reported. It is a single-layer sheet silicate belonging to the ekanite group with a steacyite structural type. Averaged major-element analysis provided (wt.%): K2O 4.13(6), CaO 8.1(1), Na2O 2.3(1), ThO2 25.8(4), UO2 3.6(4) and SiO2 55.9(1). The averaged crystal-chemical formula for the studied turkestanite is (Th0.84U0.12)Σ0.96(Ca1.24Na0.65)Σ1.89(K0.75☐0.25)Σ1.00Si8O19.72(OH)0.28. Single-crystal structural refinement of turkestanite gave tetragonal, space group P 4/ mcc , a = 7.5708(3) Å, c = 14.7300(11) Å, V = 844.27(6) Å3 and Z = 2. Luminescence of the uranyl ion (UO2)2+ is observed in turkestanite. In the excitation spectrum, the bands corresponding to a charge transfer transition from the 2p states of the ligand to the 5f state of uranium were found. [ABSTRACT FROM AUTHOR]

Uranyl coordination polymers have caught more and more attention due to their rich topological structures and potential practical applications in nuclear waste processing and management. In this work, four novel uranyl coordination polymers have been successfully synthesized by the utilization of a semirigid ligand and uranyl nitrate under hydrothermal reactions through the introducing of different kinds of auxiliary ligands (NaCl, oxalate acid, succinic acid). Therein, the powder X-ray diffraction, Infrared spectroscopy and luminescence properties of compounds 3 and 4 are investigated. [ABSTRACT FROM AUTHOR]

Magnetic hydroxyapatite nanoparticles (Fe3O4/HAP) are prepared in the present work to remove uranyl ions via copercipitation method for the first time. The sorbent was prepared with the weight ratio of magnetic nanoparticles to hydroxyapatite (Fe3O4/HAP) as (1:1), (1:2), (1:3), and (1:5). After finding physical, chemical, and magnetic features, their ability to absorb uranyl ions was examined via UV-Vis method, measuring the absorbance of element complex with arsenazo (III). The effects of parameters such as temperature, pH, contact time, rate of the adsorbent, the concentration of uranyl, and the effects of interference of other ions on the removal of uranyl were analyzed. Also, the experiments showed that the highest rate of uranyl was absorbed by using 0.015 g Fe3O4/HAP (1:5) during 150 min at pH equal to 7. The prepared nanoparticles in 17±2 nm could absorb uranyl in the concentration range of 0.2-100 ppm, eliminating over 96% of uranyl. The absorbing capability of 99.82 mg/g was obtained at 25°C. The results indicate the high potential of the prepared nano-particles in absorbing and eliminating uranyl and show its capability in the waste water containing uranyl.

We report the synthesis and characterization of a novel strippable polymeric matrix of polyvinyl alcohol (PVA) aqueous solutions embedded with 2-thenoyl trifluoroacetone (TTA) organic ligand for decontamination of heavy metal ions. The TTA-containing polymeric matrix was applied to several contaminated surfaces comprising various concentrations of UO22+, Cu2+, Fe3+ and Cs+ contaminants. Except for Cs+, the contaminants were found to interact with the ligand contained in the polymeric matrix, accompanied by a consequent indicative strong color change, specific to the metal contaminant. The dried coating is easily exfoliated leaving the surface decontaminated. ATR-IR and Raman spectroscopies were also applied, showing a clear spectroscopic signature of each metal contaminant, in particular when contained in a mixed ion solution. All in all, the utilization of vibrational spectroscopies is shown to provide important complementary detection signatures that are otherwise vague when surfaces comprising trace amounts of contaminants, lacking color responsive behavior, are involved.

Evaluation of the mobility behaviour of radionuclides under highly saline and alkaline conditions is a major concern for the performance assessment of radioactive waste disposal. The aim of this study was to determine the effect of up to 2.8 mol/kgsolution content of NaNO3, on the solubility and the retention of U(VI) at 22 °C onto a hardened cement paste (HCP) prepared from ordinary Portland cement (CEM I). To avoid the interference of the high salt concentration and ionic strength, and because of the expected low solubility of uranium under such alkaline conditions, time-resolved laser fluorescence spectroscopy (TRLFS) was selected to accurately measure U(VI) concentration in solution using the standard addition method in 85% H3PO4. This allows both limiting the dilution and matrix effects and determining the resulting [U(VI)] in solution with acceptable precision for the distribution factor (Rd) in both sorption and desorption experiments. The operational solubility limit measured at high ionic strength lowered by a factor of three compared to the reference cementitious condition, and its Rd values decreased by a factor ca. four. The sorption of U(VI) appears to be reversible under these conditions. [ABSTRACT FROM AUTHOR]

The crystal structures of uranyl fluoride complexes with alkali metal cations and ammonium, with protonated cations of organic bases, with divalent transition metal cations, and with mixed monovalent and divalent transition metal cations studied by the single-crystal X-ray diffraction method have been systematized and discussed. The crystal chemical features of the structures of the uranyl fluoride complexes were determined: the coordination polyhedron of the hexavalent uranium atom in the structures of the uranyl fluoride complexes has a pentagonal-bipyramidal structure; the oxygen atoms of the uranyl group are located on the vertical axis of the bipyramid, perpendicular to the equatorial plane in which five atoms of the coordinated ligands are located. With the exception of UO2F2 (uranium center CN 6), a pentagonal-bipyramidal configuration of the central atom polyhedron is realized in all the studied structures of the fluoride complexes of uranyl. Based on the performed studies on the structural chemistry of uranyl fluoride complexes, the regularity in the formation of this class of compounds was established. The dependence of the frequency of the asymmetric stretching vibration of the uranyl ion on the structure of the complex anion and on the formation of hydrogen bonds in the structures of the investigated uranyl fluoride complexes has been established. [ABSTRACT FROM AUTHOR]

As a class of typical metal-organic framework materials(MOFs), actinide-based MOFs feature their unique actinide-ligand bonds. However, how these coordination interactions participate in and affect the lattice assembly process of organic ligands remains less studied. In this work, the coordination assembly of carbazole tricarboxylic acid organic ligands and uranyl ions was taken as a showcase study, and the regulation of uranyl coordination on the assembly process of carbazole tricarboxylic acid in lattice by controlling the synthesis conditions was studied in detail. Single-crystal analyses show that with the introduction of uranyl metal nodes, the assembly of carbazole tricarboxylic acid has realized a gradual evolution from a hydrogen bond-organic framework structure to a metal-organic network. In this regulation process, the connection of hydrogen bonds between different carbazole tricarboxylic acids is gradually replaced by uranyl coordination. The two-dimensional network structure also changes from sextuple intercatenated non-planar network through planar supramolecular network to final coordination network. The related transformation process is mainly manifested in gradual participation of the carboxyl groups in the coordination of uranyl center, which has also been confirmed by infrared spectroscopy. This work reveals the molecular mechanism of the synthesis of inorganic-organic porous materials through uranyl-ligand coordination and the detailed process of material structure evolution.

[Display omitted] • Phosphate promotes the immobilization of uranyl arsenate under acidic conditions. • Phosphate can induce the transformation of crystalline phases of uranyl arsenate-bearing compounds. • Phosphate improved the chemical stability of the formed uranyl arsenate-bearing compounds. • The formation of Fe(UO 2) 2 (AsO 4) 2 ·H 2 O is relatively thermodynamically favorable in the presence of phosphate. Understanding the formation of uranyl-arsenate compounds (M(UO 2) 2 (AsO 4) 2 ·nH 2 O, M represents divalent metallic cations) is of great importance in controlling the mobility and fate of uranium (U) and arsenic (As) in the natural environment. Phosphate is a ubiquitous coexisting ion with properties similar to arsenate and can complex with uranyl to form uranyl phosphate compounds, thus potentially affecting the formation of uranyl-arsenate compounds. Herein, the effect of phosphate, on the immobilization of uranyl, arsenate and divalent metallic cations (e.g., Fe2+, Mg2+, Ni2+, Cu2+) was explored. Surprisingly, the presence of phosphate promoted the immobilization of uranyl arsenate with the divalent metallic cations under acidic conditions. For example, at pH 3.0, the immobilization efficiency of uranyl and arsenate in the uranyl-arsenate-Fe2+ system increased from 20.6 % and 18.6 % to 82.6 % and 52.2 %, respectively. Moreover, the chemical stability of the formed uranyl arsenate-bearing compounds in the presence of phosphate is significantly improved, and the TCLP leachability of As and U decreased by 81 % and 97 %, respectively. The experimental results illustrated that with PO 4 3- served as a proton acceptor, uranyl and arsenate species were changed and more metallic cations participate in immobilization. Gibbs free energy and Gibbs free energies change also illustrated that the formation of Fe(UO 2) 2 (AsO 4) 2 ·5H 2 O was relatively thermodynamically favorable in the presence of phosphate. The results of thermodynamic calculations could account for the enhancement effects of phosphate on immobilization of uranyl arsenate. The findings have important implications for the mobility and fate of U and As and the solution of their co-contamination, especially in acidic environments. [ABSTRACT FROM AUTHOR]

This paper reviews not the largest, but at the same time quite an interesting, group of natural and synthetic uranyl molybdate compounds. Nowadays, nine minerals of U and Mo are known, but the crystal structures have only been reported for five of them. Almost an order of magnitude more (69) synthetic compounds are known. A significant discrepancy in the topological types for natural and synthetic phases is shown, which is most likely due to elevated temperatures of laboratory experiments (up to 1000 °C), while natural phases apparently grow at significantly lower temperatures. At the same time, the prevalence of dense topologies (with edge-sharing interpolyhedral linkage) among natural phases can be noted, which is fully consistent with other recently considered mineral groups. Uranyl molybdates demonstrate several similarities with compounds of other U-bearing groups; however, even topological matches do not lead to the appearance of completely isotypic compounds. Structural complexity calculations confirm, in general, crystal chemical observations. Considering the prevalence of dense structures in which coordination polyhedra of uranium and molybdenum are connected through common edges as well as framework architectures, one can expect a less significant influence of interlayer species on the formation of the crystal structure than the main U-bearing complexes. The more structural complexity of the uranyl molybdate units, the more complex of the entire crystal structure is. In addition, there is a tendency for complexity to increase with increasing density of the complex; the simplest structures are vertex-shared, while the complexity increases with the appearance of common edges.

Four new hybrid organic‐inorganic uranyl phosphate compounds were structurally characterized after single crystals were grown via ionothermal synthesis using the ionic liquids 1‐ethyl‐3‐methylimidazolium dimethyl phosphate and 1‐ethyl‐3‐methylimidazolium dibutyl phosphate. Three of the new crystal structures presented here incorporate dimethyl or monomethyl phosphate ligands into the structural unit to form one chain‐based compound and two sheet‐based compounds. One of the structures utilizes dibutyl phosphate to form a previously reported uranyl compound, a structural polymorph that crystallized in space group P21/c in contrast to the previously reported P‐1 structure. The structural and topological relationships are compared to those of uranyl phosphate minerals as well as previously reported organophosphate compounds. The roles of the organics on the phosphate anions in impacting uranyl coordination and stabilizing the crystal structures are discussed. [ABSTRACT FROM AUTHOR]

Crystals UO2(mac)2⋅L, where mac is the methacrylate ion C3H5COO– and L is diethylacetamide (DEA) or dimethylformamide (DMF), are synthesized and studied via IR spectroscopy and X-ray diffraction. It is established that the crystal structure of the resulting adducts has the same structure and contains dimers [UO2(mac)2⋅L]2 belonging to the crystal chemical group AВ2B01М1 (А = , B2 and B01 = mac–, М1 = DEA or DMF) of uranyl complexes. The effect the nature of amides has on the composition and structure of adducts that form in the UO2(mac)2/L/H2O systems is discussed. [ABSTRACT FROM AUTHOR]

Mg-Al layered double hydroxides (LDH) (F-MgAl-LDHs and O-MgAl-LDHs) and Mg-Al layered double oxides (LDO) (F-MgAl-LDO and O-MgAl-LDO) nanosheets were prepared using a modified co-precipitation and oven/freeze dry route for adsorption of uranium. The freeze dry could evidently promote the adsorption ability. It's resulted from larger specific surface (F-MgAl-LDO > F-MgAl-LDHs > O-MgAl-LDO > O-MgAl-LDHs) and pore size, as well as sufficient expose of vacant sites in the inner struture of F-MgAl-LDHs and F-MgAl-LDO. The pH, shaking time, initial uranium concentation and temperature influenced the adsorption capacity of F-MgAl-LDHs, O-MgAl-LDHs, F-MgAl-LDO and O-MgAl-LDO, while ionic strength exerted slightly little influence. Na2CO3 highlighted the best desorption effectivity, with desorption efficiency of 97.84% for F-MgAl-LDHs and 98.52% for F-MgAl-LDO, respectively. It is noteworthy that maximum adsorption capacity of F-MgAl-LDO reached 1099.93 mg/g, locating the top rank in the uranium-specific adsorbents. The adsorption conformed to the pseudo-second-order model, indicating chemical adsorption in nature. The thermodynamic was also investigated. The adsorption mechanism was determined that M-O and C-O bonds participated the complex process in the uranium adsorption. The study proposed the freeze dry as an efficient method to promote adsorbent performance. [ABSTRACT FROM AUTHOR]

To design an effective Uranium decorporation agent for chelation therapy, it is crucial to understand coordination chemistry properties of decorporation agent and the complex. In this paper, a new containing-silicon hydroxypyridinone ligand with two different configurations Si-5LIO-1-Cm-3,2-HOPO(A) and Si-5LIO-1-Cm-3,2-HOPO(B) was designed for capturing Uranium using Carbon/Silicon exchange method and the complexation mechanisms of them with uranyl were systematically investigated by DFT calculations and wave function analysis methods. It was found that the complexes' structures were greatly changed after "Carbon/Silicon exchange", the uranyl chelation selectivity coefficients toward Si-5LIO-1-Cm-3,2-HOPO(A)/Si-5LIO-1-Cm-3,2-HOPO(B) in different solvents were all over than 99%. The chelation ability of Si-5LIO-1-Cm-3,2-HOPO(A) to uranyl was much stronger than those of Si-5LIO-1-Cm-3,2-HOPO(B) and 5LIO-1-Cm-3,2-HOPO. The complex UO2-Si-5LIO-1-Cm-3,2-HOPO(A) with NH...O = C intramolecular hydrogen bond showed higher binding energy of the ligand with uranyl than the others. The figures that π electrons transfer from pyridine to oxygen donors to chelate with U(VI) were revealed graphically and quantitatively. This study represents a lot of valuable information of actinides coordination chemistry and provide a guidance for the design of Uranium capturing agent. [ABSTRACT FROM AUTHOR]