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Dissimilatory metal-reducing bacteria (DMRB) can harvest energy for growth and activities by respiring metals, but it is so far unknown whether DMRB can acquire crystalline-phase actinides. In the present study, we used Shewanella oneidensis MR-1 to investigate microbially-mediated dissolution and reduction of U(VI) in three uranyl(VI) borate and boronate crystals (i.e., UO 2 (CH 3 BO 2 )(H 2 O) (UCBO); UO 2 B 2 O 4 (UBO); and Na[(UO 2 )B 6 O 10 (OH)]·2H 2 O (NaUBO)). Comparison of the dissolved U(VI) concentrations between samples with and without bacteria indicates that MR-1 facilitated dissolution of UCBO and UBO. Based on the assumption that only dissolved U(VI) was reduced, U(VI) reduction was substantially underestimated for UCBO and NaUBO, indicating that MR-1 directly reduced crystalline U(VI) in these two compounds. Laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis implied that interactions occurred between microbial ligands and the residual particles of uranyl compounds. We found that S. oneidensis MR-1 can mediate the dissolution and reduction of crystalline U(VI) through facilitated dissolution and consequent reduction of crystals or direct reduction of U(VI) in crystals. These results help evaluate the environmental fate of solid-phase U(VI), critical for predicting U transport and remediating U-contaminated sites. [ABSTRACT FROM AUTHOR]

Abstract: Novel crystalline actinide materials can be used to immobilize uranium and transuranium elements at radioactive waste disposal sites. However, the stability and dissolution of such phases are still poorly understood. In this study, we investigated the dissolution kinetics of two uranyl borates and one plutonyl borate, UO2B2O4 (UBO), Na[(UO2)B6O10(OH)]·2H2O (NaUBO), and PuO2[B8O11(OH)4] (PuBO), with three different ligands, i.e., bicarbonate, phosphate, and natural humic acid (HA). These actinide borates were chosen because they possess different topologies that may influence dissolution. In the presence of bicarbonate, the apparent steady-state concentration of dissolved U(VI) and surface area-normalized dissolution rates were much higher for UBO compared to NaUBO. Uranyl phosphate, most likely in the form of (UO2)3(PO4)2(H2O)4, was precipitated on the surface of residual particles of UBO and NaUBO with phosphate. The dissolution rate of PuBO in NaNO3 solution was much higher than UBO or NaUBO. This study revealed that actinide borate crystal dissolution was substantially influenced by crystalline structures of actinide borates and aqueous ligands. [Copyright &y& Elsevier]

Two three-dimensional uranyl framework compounds consisting of 1,2,4-benzenetricarboxylic ligands and uranyl units have been synthesized under mild solvothermal conditions. Compound 1 adopts an open framework structure built from uranyl pentamers, which is a rare topology for uranyl structures. Compound 2 is constructed from UO8 and UO7 bipyramids that are connected by the ligand to form a three-dimensional framework. As a consequence, compound 1 exhibits an unusual photoluminescence spectrum of one broad peak at 545 nm with a significant red shift compared to the typical uranyl emissive peaks as shown in the spectra of uranyl nitrate and compound 2. In addition, since compound 1 crystallizes in the noncentrosymmetric space group Cc, its secondary-harmonic generation property was measured under 1064 nm laser radiation, showing a moderate SHG signal response of 0.91 × KDP. [ABSTRACT FROM AUTHOR]

A uranyl phosphonate framework, (UO2)2(1,3-pbp)(H2O)2·2H2O (UPF-1) (1,3-pbp = 1,3-phenylenebis(phosphonic acid)), experiences a thermally induced order–disorder transition, leading to a negative linear correlation between the photoluminescence intensity and temperature, and may find application as a luminescent thermometer. [ABSTRACT FROM AUTHOR]

The present study sheds some light on the long‐standing debate concerning the coordination properties between uranyl ions and the amidoxime ligand, which is a key ingredient for achieving efficient extraction of uranium. Using X‐ray absorption fine structure combined with theoretical simulation methods, the binding mode and bonding nature of a uranyl–amidoxime complex in aqueous solution were determined for the first time. The results show that in a highly concentrated amidoxime solution the preferred binding mode between UO22+ and the amidoxime ligand is η2 coordination with tris‐amidoximate species. In such a uranyl–amidoximate complex with η2 binding motif, strong covalent interaction and orbital hybridization between U 5f/6d and (N, O) 2p should be responsible for the excellent binding ability of the amidoximate ligand to uranyl. The study was performed directly in aqueous solution to avoid the possible binding mode differences caused by crystallization of a single‐crystal sample. This work also is an example of the simultaneous study of local structure and electronic structure in solution systems using combined diagnostic tools. [ABSTRACT FROM AUTHOR]

We present a depleted uranium-based metal organic framework, UO2(C8H3O6N)·DMF, that exhibits highly sensitive and selective detection towards Fe3+ ions in aqueous media with an extremely low detection limit of 6.3 ppb. This work offers insight into exploring the potential applications of actinide-based metal organic frameworks in the area of chemical sensing with intrinsic advantages of high selectivity and sensitivity. [ABSTRACT FROM AUTHOR]

Precise detection of low-dose X- and γ-radiations remains a challenge and is particularly important for studying biological effects under low-dose ionizing radiation, safety control in medical radiation treatment, survey of environmental radiation background, and monitoring cosmic radiations. We report here a photoluminescent uranium organic framework, whose photoluminescence intensity can be accurately correlated with the exposure dose of X- or γ-radiations. This allows for precise and instant detection of ionizing radiations down to the level of 10−4 Gy, representing a significant improvement on the detection limit of approximately two orders of magnitude, compared to other chemical dosimeters reported up to now. The electron paramagnetic resonance analysis suggests that with the exposure to radiations, the carbonyl double bonds break affording oxo-radicals that can be stabilized within the conjugated uranium oxalate-carboxylate sheet. This gives rise to a substantially enhanced equatorial bonding of the uranyl(VI) ions as elucidated by the single-crystal structure of the γ-ray irradiated material, and subsequently leads to a very effective photoluminescence quenching through phonon-assisted relaxation. The quenched sample can be easily recovered by heating, enabling recycled detection for multiple runs. [ABSTRACT FROM AUTHOR]

Precise detection of low-dose X- and γ-radiations remains a challenge and is particularly important for studying biological effects under low-dose ionizing radiation, safety control in medical radiation treatment, survey of environmental radiation background, and monitoring cosmic radiations. We report here a photoluminescent uranium organic framework, whose photoluminescence intensity can be accurately correlated with the exposure dose of X- or γ-radiations. This allows for precise and instant detection of ionizing radiations down to the level of 10−4 Gy, representing a significant improvement on the detection limit of approximately two orders of magnitude, compared to other chemical dosimeters reported up to now. The electron paramagnetic resonance analysis suggests that with the exposure to radiations, the carbonyl double bonds break affording oxo-radicals that can be stabilized within the conjugated uranium oxalate-carboxylate sheet. This gives rise to a substantially enhanced equatorial bonding of the uranyl(VI) ions as elucidated by the single-crystal structure of the γ-ray irradiated material, and subsequently leads to a very effective photoluminescence quenching through phonon-assisted relaxation. The quenched sample can be easily recovered by heating, enabling recycled detection for multiple runs. [ABSTRACT FROM AUTHOR]

The equatorial coordination nature of the uranyl unit has resulted in only three uranyl borate 3D framework compounds reported so far formed from boric acid flux reactions conducted at 190 °C while all others are 2D layers. Here in this work, by increasing the reaction temperature to 250 °C, a new potassium uranyl borate K[(UO2)B6O10(OH)] (KUBO-4) framework compound is synthesized that shares the same layer topology with the previously reported 2D layered KUBO-1. The 3D structure of KUBO-4 is achieved by interlayer hydroborate condensation. The KUBO-4 was further characterized with single crystal XRD, SHG and fluorescence spectra, and TG/DSC measurements. A deep understanding regarding the dissolution behaviours of uranyl borate is achieved via solubility studies of the KUBO-1 and KUBO-4 performed using a combination of ICP-MS, powder XRD, and fluorescence spectroscopy techniques. The results confirm the lack of stability of borates in aqueous solutions with the presence of coordinating ligands in the environment regardless of the structure types. [ABSTRACT FROM AUTHOR]

The example of phase transformation from a centrosymmetric space group at low temperature (LT) to a chiral space group at high temperature (HT) is reported, which was clearly resolved in a single-crystal-to-single-crystal manner in a 3D uranyl(vi) phosphonate compound [TMA][(UO2)2(1,3-pbpH)(1,3-pbpH2)] (1) (TMA+ = tetramethylammonium cation; 1,3-pbpH4 = 1,3-phenylenebis(phosphonic acid)). [ABSTRACT FROM AUTHOR]

The ionothermal reactions of uranyl nitrate and 1,3-pbpH4 (1,3-pbpH4 = 1,3-phenylenebis(phosphonic acid) ligand in ionic liquids of [C4mim][Dbp], [C4mpyr][Br], and [Etpy][Br], respectively, afforded three new uranyl phosphonates, namely [C4mim][(UO2)2(1,3-pbpH)(1,3-pbpH)·Hmim] (1), [UO2(1,3-pbpH2)H2O·mpr] (2), and [Etpy][UO2(1,3-pbpH2)F] (3). Compound 1 exhibits a rare example of a chiral uranyl phosphonate 3D framework structure built from achiral building units of tetragonal bipyramidal uranium polyhedra and 1,3-pbp ligands. The structure adopts a network with channels extending along the b axis, which are filled with C4mim+ and protonated 1-methylimidazole. In sharp contrast, compounds 2 & 3 both show pillared topology composed of uranyl pentagonal bipyramid polyhedra and phosphonate ligands. The layers are neutral in compound 2 with N-methylpyrrole molecules in the interlayer space, while compound 3 adopts anionic layer, and the charge is compensated with N-ethyl-pyridinium cations between the layers. Although compounds 1, 2, and 3 were synthesized under identical conditions with sole variation of the ionic liquid species, the resulting structures show a rich diversity in the local coordination environment of uranyl ions, the protonation of the phosphonate ligand, the conformation of ionic liquid ions, and the overall arrangement of the structure. All compounds were characterized by absorption, temperature dependent fluorescence, as well as infrared and Raman spectroscopies. [ABSTRACT FROM AUTHOR]

Uranyl ion exists at trace levels in the environment and can cause severe adverse effects to human health. Therefore, it is desirable to develop analytical methods that can determine the trace uranyl ion in aqueous medium. We report here a new method using a thermo–responsive polymeric fluorescent sensor. Specifically, 5,10,15,20–tetrakis(4–carboxyphenyl)–porphyrin terminated poly( N –isopropylacrylamide) (TCPP–PNIPAM) was synthesized by controlled free radical polymerization for the detection of uranyl ion. The maximum fluorescence intensity at ~658 nm of TCPP–PNIPAM increases with molecular weights and is also closely related to the temperature. The polymeric sensor is sensitive to pH (1.0~5.0) with a fast responsive time (~3 min). Under optimized experimental conditions, the sensor exhibits a stable response for uranyl ion with high selectivity over a concentration range from 1.0×10 –3 to 1.0×10 –7 mol/L. For the trace uranyl ion (such as 1.0×10 –8 or 10 –9 mol/L), the determination could be successfully achieved after concentrating 100 times by centrifugation above 32 °C. The properties enable the polymeric sensor to have great potential for environmental application. [ABSTRACT FROM AUTHOR]

α-Ba2[UO2(PO4)2] (I) and β-Ba2[UO2(PO4)2] (II) are prepared by H3BO3/B2O3 flux reactions using stoichiometric amounts of BaCO3, BPO4, and UO2(NO3)2 (Pt crucible, 1. [ABSTRACT FROM AUTHOR]