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1.
Inorg Chem ; 2020 Jul 19.
Artigo em Inglês | MEDLINE | ID: mdl-32683862

RESUMO

Keggin-type polyaluminum species (ε-Al13, δ-Al13, Al26, Al30, Al32) can form upon partial hydrolysis of Al3+-bearing solutions and are important species for water purification and contaminant transport. While the structural features for the major Al3+ polyaluminum species have been delineated, much less is known regarding heteroatom substitution and resultant structures other than the previously identified ε-GaAl127+ and ε-GeAl128+ cations. Single-atom substitution within polyaluminum species can change the surface reactivity within water treatment scenarios; thus, it is important to understand heteroatom incorporation within this system. The present work describes the synthesis and characterization of two novel Ga3+-substituted Keggin-type polyaluminum species. Na[GaO4Al12(OH)24(H2O)12](2,6-NDS)4(H2O)20.5 (δ-GaAl12) and [Ga2O8Al28.5Ga0.5(OH)58(H2O)27(SO4)2](SO4)4Cl7(H2O)8.5 (Ga2.5Al28.5) were crystallized from a thermally aged, partially hydrolyzed Ga3+/Al3+ solution. Structural refinement from single-crystal X-ray diffraction indicated fully occupied Ga3+ within tetrahedral site(s) of both isolated species. Partial substitution was observed for octahedral sites for the larger Ga2.5Al28.5 cluster. The chemical compositions of both clusters were confirmed by inductively coupled plasma mass spectrometry (ICP-MS). Density functional theory (DFT) calculations corroborated the structural refinement, with the energetics of Ga3+ substitution suggesting preferential substitution within tetrahedral sites for both species. Additional theoretical work suggests that the rotated trimer in δ-GaAl12 is highly reactive, which can serve as the driving force in the formation of the Ga2.5Al28.5 cluster.

2.
Dalton Trans ; 2020 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-32383725

RESUMO

The neptunyl (Np(v)O2+/Np(vi)O22+) cation is the dominant form of 237Np in acidic aqueous solutions and the stability of the Np(v) and Np(vi) species is driven by the specific chemical constituents present in the system. Hydrogen bonding with the oxo group may impact the stability of these species, but there is limited understanding of how these intermolecular interactions influence the behavior of both solution and solid-state species. In the current study, we systematically evaluate the interactions between the neptunyl tetrachloride species and hydrogen donors in coordination complexes and in the related aqueous solutions. Both Np(v) compounds (N2C4H12)2[Np(v)O2Cl4]Cl (Np(V)pipz) and (NOC4H10)3[Np(v)O2Cl4] (Np(V)morph) exhibit directional hydrogen bonding to the neptunyl oxo group while Np(vi) compounds (NC5H6)2[Np(vi)O2Cl4] (Np(VI)pyr) and (NOC4H10)4[Np(vi)O2Cl4]·2Cl (Np(VI)morph) assemble via halogen interactions. The Raman spectra of the solid-state phases indicate the activation of vibrational bands when there is asymmetry of the neptunyl bond, while these spectral features are not observed within the related solution phase spectra. Density functional theory calculations of the Np(V)pipz system suggest that activation of the ν3 asymmetric stretch and other combination modes lead to additional complexity within the solid-state spectra. Electrochemical analyses of complexes in the solution phases are consistent with the results of the crystallization experiments as the voltammetric potentials of Np(v)/Np(vi) complexes in the presence of protonated heterocycles differ from the potentials of pure Np(v) and may correlate with the hydrogen bonding interactions.

3.
Inorg Chem ; 2020 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-32437172

RESUMO

Naturally occurring uranium is a widespread contaminant present in the water resources around the abandoned uranium mines in the southwest United States. A novel method for rapid uranium detection has been recently developed that relies on the sequestering of uranium by amidoximated polyacrylonitrile (AO-PAN) polymer mats and uses the Raman-active (ν1) symmetric stretch as the signal. The Raman signals obtained from uranium bearing AO-PAN were challenging to interpret due to an unknown uranyl speciation on the surface of the mats. Herein, we provide the synthesis and structural characterization of six model coordination compounds that contain acetamidoxime/benzamidoxime (AAO/BAO) coordinated to the uranyl cation: [UO2(η1-AAO)(NO3)2(H2O)] (1), [UO2(η1-AAO)2(NO3)2] (2), [UO2(η2-BAO)2(CH3OH)2] (3), [(UO2)3(η2-BAO)3(µ2-NO3)3] (4), [(UO2)4(µ3-O)2(µ2-BAO)4(η1-BAO)4(H2O)2](NO3)4 (5), and [(UO2)4(µ3-O)2(µ2-BAO)4(η1-BAO)6Na(NO3)2](NO3)3 (6). Solid-state Raman spectra of 1-6 showed dramatic differences in the uranyl ν1 symmetric stretch depending on the coordination of the amidoxime functional group. The assignments made from the solid-state Raman spectra were used to deconvolute the solution-state Raman spectra of uranyl-acetamidoxime/benzamidoxime methanol solutions at different metal to ligand molar ratios. At low molar ratios (1 U:1 AAO/BAO and 1 U:2 AAO/BAO) the dominant species is the uranyl coordinated via the η1-oxygen atom of the oxime group, while at high molar ratios (1 U:3 AAO/BAO and 1 U:4 AAO/BAO) the dominant species are a tetrameric uranyl-µ3-O-η1-amidoxime complex similar to compounds 5 and 6 and a uranyl-η2-amidoxime complex similar to compounds 3 and 4. Solid-state Raman spectra showed good agreement with Raman signals obtained from the uranyl-AO-PAN mats, demonstrating that binding motifs between uranyl and amidoxime in compounds 5 and 6 are the most representative of the uranyl species on the surface of the AO-PAN mats.

4.
Angew Chem Int Ed Engl ; 58(51): 18429-18433, 2019 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-31605410

RESUMO

Current synthetic pathways for uranyl peroxide materials introduce high initial concentrations of aqueous H2 O2 that decline over time. Alternatively, in situ generation of organic peroxide would maintain constant concentrations of peroxide over prolonged periods of time and open new pathways to novel uranyl peroxide compounds. Herein, we demonstrate this concept through the synthesis of a nanotube-like uranyl peroxide phosphate (NUPP), Na12 [(UO2 )(µ-O2 )(HPO4 )]6 (H2 O)40 , making use of the inhibited autoxidation of benzaldehyde in benzyl alcohol solutions in the presence of phosphonate ligands. The unique feature of NUPP is the bent dihedral angle U-(µ-O2 )-U (123.9°±0.4° to 124.6°±0.5°), which allows hexameric uranyl peroxide macrocycles to adopt the nanotubular topology and prevents the formation of nanocapsules. Raman spectroscopy of the solution phase confirms our mechanistic understanding of the reaction pathway and confirms that consistent levels of peroxide are generated in situ over an extended period of time.

5.
Chem Commun (Camb) ; 55(63): 9319-9322, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31313772

RESUMO

Crown-ether molecules are used in radiochemical separations due to their high selectivity for a range of metal cations. Previous investigations regarding the interactions of 18-crown-6 (18C6) with 237Np suggested the formation of a Np(v) inclusion complex, but also reported rapid reduction of Np(vi) to Np(v) in the presence of the ether molecule. Herein, we investigate the impact of crown ether functionalization by exploring the Np(v) and Np(vi) dicyclohexano-18-crown-6 (DCH-18C6) systems. Two [X(DCH-18C6)]2[Np(vi)O2Cl4] compounds (X = K (1) and Na (2)) were crystallized and characterized by single crystal X-ray diffraction and Raman spectroscopy. Additional studies of Np(vi), Np(v), and Np(v)/Np(vi) in solution indicated redox stability in the presence of functionalized crowns and preferential crystallization of Np(vi) DCH-18C6 solids. These results indicate that functionalization of the crown can lead to higher resistance to radiolysis and increased stability of the Np(vi) oxidation state in solution.

6.
Dalton Trans ; 48(24): 8861-8871, 2019 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-31139781

RESUMO

The interaction of the actinyl (AnO22+) oxo group with low-valent cations influences the chemical and physical properties of hexavalent actinides, but the impact of these intermolecular interactions on the actinyl bond and their occurrence in solution and solid state phases remain unclear. In this study, we explore the coordination of alkali cations (Li+, Na+, K+) with the [NpO2Cl4]2- coordination complexes using single-crystal X-ray diffraction, Raman spectroscopy, and density functional theory (DFT) calculations and compare to the related uranyl system. Three solid-state coordination compounds ([Li(12-crown-4)]2[NpO2Cl4] (LiNp), [Na(18-crown-6)H2O]2[NpO2Cl4] (NaNp), and [K(18-crown-6)]2[NpO2Cl4] (KNp) have been synthesized and characterized using single-crystal X-ray diffraction and Raman spectroscopy. Only Li+ cations interact with the neptunyl oxo in the solid-state compounds and this results in a red-shift of the NpO22+ symmetric stretch (ν1). Raman spectra of Np(vi) solutions containing lower Li+ concentrations display a single peak at ∼854 cm-1 and increasing the amount of Li+ results in the ingrowth of a second band at 807 cm-1. DFT calculations and vibrational analysis indicate the lower frequency vibrational band is the result of interactions between the Li+ cation and the neptunyl oxo. Comparison to the related uranyl system shows similar interactions occur in the solid state, but subtle differences in the actinyl-cation modes in solution phase.

7.
Environ Sci Process Impacts ; 21(2): 242-255, 2019 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-30556566

RESUMO

Public concern is heightened around flowback and produced water (FPW) generated by the hydraulic fracturing process. FPW is a complex mix of organic and inorganic solutes derived from both the injected hydraulic fracturing fluid and interactions with the subsurface lithology. Few studies to date have systematically investigated the composition of FPW or its individual components. Here, we provide the first systematic characterization of the composition of the solids associated with FPW by analyzing samples from three wells drilled into the Duvernay Formation in Alberta, Canada. The FPW initially returned to the surface with high total dissolved solids (greater than 170 000 mg L-1) and enriched with Fe(ii), silica, sulfate, barium, and strontium. The solids form two distinct phases once the FPW reached the surface: (1) silica-enriched Fe(iii) oxyhydroxides, and (2) a barite-celestine solid solution. We hypothesize that the precipitation of the amorphous silica-enriched Fe(iii) oxyhydroxide is a two-step process, where first the silica precipitates as a function of the cooling of the FPW from elevated subsurface temperatures to ambient surface temperatures. Next, the silica acts as a template for the precipitation of Fe(iii) oxyhydroxide as the diffusion of oxygen into the subsurface causes oxidation of aqueous Fe(ii). The barite-celestine solid solution precipitates solely as a function of cooling. Elevated dissolved Fe concentrations in FPW and modeled saturation indices from five North American shale plays (Marcellus, Fayetteville, Barnett, Bakken, and Denver-Julesburg) indicate that solids similar to those found in Duvernay FPW, specifically Fe(iii) oxyhydroxides, barite and quartz, are likely to occur. With the solids known to carry a significant portion of FPW's toxicity and organic contaminant load, the development of new treatment technologies, such as the oxidation of the Fe(ii) in FPW, may increase FPW reuse and reduce the environmental risk posed by FPW.


Assuntos
Fraturamento Hidráulico , Águas Residuárias/toxicidade , Poluentes Químicos da Água/análise , Alberta , Compostos Férricos
8.
Chem Commun (Camb) ; 54(76): 10698-10701, 2018 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-30187044

RESUMO

Oxo group activation with reduction of neptunyl(vi) and plutonyl(vi) to tetravalent hydroxo species by the hydroxypyridinone siderophore derivative 3,4,3-LI-(1,2-HOPO) was investigated in the gas-phase via electrospray ionization mass spectrometry, in solution via Raman spectroscopy, and computationally via density functional theory. Dissociation of the gas-phase tetravalent complexes resulted in actinide-hydroxo bond cleavage.

9.
Chem Commun (Camb) ; 54(77): 10828-10831, 2018 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-30137085

RESUMO

Physical properties of actinyl materials are influenced by the presence of oxo functional groups. Herein, we report large thermal expansion coefficients for a uranyl metal organic nanotube that switch from positive to negative upon dehydration. Different behaviour is observed in the neptunyl system due to variations in the oxo interactions.

10.
Inorg Chem ; 57(10): 6016-6028, 2018 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-29732879

RESUMO

Intermolecular interactions between the oxo group of an actinyl cation and other metal cations (i.e., cation-cation interactions) are dependent on the strength of the actinyl bond. These cation-cation interactions are prominently observed for the neptunyl cation [Np(V)O2]+ and are sufficiently stable enough to explore using a variety of chemical techniques. Herein, we investigate these intermolecular interactions in the neptunyl 18-crown-6 system, because this macrocyclic ligand provides both stable coordination and the proper sterics to engage the oxo group in bonding with both low-valent metal cations and neighboring neptunyl units. We report the structural and spectroscopic characterization of five neptunyl, [Np(V,VI)O2]+,2+, compounds: Np1a ([NpO2(18-crown-6)]ClO4), Np1b ([NpO2(18-crown-6)]AuCl4), Na-Np ([Np(V)O2(18-crown-6)(Na(H2O)(18-crown-6)][Np(VI)O2Cl4], Np-Np ([NpO2(18-crown-6)](NpO2Cl2NO3)], and Np-Cl (NpO2Cl(H2O)1.75). Each of these compounds were prepared from the ambient reactions of Np(V) in HX (where X = Cl, NO3) with the 18-crown-6 ether molecule. Structural information obtained from single-crystal X-ray diffraction data was paired with solid-state and solution Raman spectroscopy to provide information on the interaction of the neptunyl oxo atom with neighboring cations. Neptunyl (Np═O) bond lengths are not perturbed upon interaction with the Na+ cation (Na-Np), but elongation is observed upon formation of a neptunyl-neptunyl interaction (Np-Np). This is also the first structurally characterized isolated, molecular complex that contains a simple T-shaped neptunyl-neptunyl interaction. Raman spectroscopy indicates little perturbation to the neptunyl bond until the formation of the neptunyl-neptunyl motif, which also results in activation of the ν3 asymmetric stretch. Additional spectroscopic studies indicated that the neptunyl 18-crown-6 inclusion complexes form in solution and persist in the presence of other low-valence cations.

11.
Anal Chem ; 90(11): 6766-6772, 2018 06 05.
Artigo em Inglês | MEDLINE | ID: mdl-29741873

RESUMO

Reproducible detection of uranyl, an important biological and environmental contaminant, from complex matrixes by surface-enhanced Raman scattering (SERS) is successfully achieved using amidoximated-polyacrylonitrile (AO-PAN) mats and carboxylated gold (Au) nanostars. SERS detection of small molecules from a sample mixture is traditionally limited by nonspecific adsorption of nontarget species to the metal nanostructures and subsequent variations in both the vibrational frequencies and intensities. Herein, this challenge is overcome using AO-PAN mats to extract uranyl from matrixes ranging in complexity including HEPES buffer, Ca(NO3)2 and NaHCO3 solutions, and synthetic urine. Subsequently, Au nanostars functionalized with carboxyl-terminated alkanethiols are used to enhance the uranyl signal. The detected SERS signals scale with uranyl uptake as confirmed using liquid scintillation counting. SERS vibrational frequencies of uranyl on both hydrated and lyophilized polymer mats are largely independent of sample matrix, indicating less complexity in the uranyl species bound to the surface of the mats vs in solution. These results suggest that matrix effects, which commonly limit the use of SERS for complex sample analysis, are minimized for uranyl detection. The presented synergistic approach for isolating uranyl from complex sample matrixes and enhancing the signal using SERS is promising for real-world sample detection and eliminates the need of radioactive tracers and extensive sample pretreatment steps.


Assuntos
Resinas Acrílicas/química , Ouro/química , Nanopartículas Metálicas/química , Urânio/análise , Análise Espectral Raman , Propriedades de Superfície
12.
Coord Chem Rev ; 374: 314-344, 2018 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-30713345

RESUMO

The purpose of this review is to provide an overview of uranium speciation using vibrational spectroscopy methods including Raman and IR. Uranium is a naturally occurring, radioactive element that is utilized in the nuclear energy and national security sectors. Fundamental uranium chemistry is also an active area of investigation due to ongoing questions regarding the participation of 5f orbitals in bonding, variation in oxidation states and coordination environments, and unique chemical and physical properties. Importantly, uranium speciation affects fate and transportation in the environment, influences bioavailability and toxicity to human health, controls separation processes for nuclear waste, and impacts isotopic partitioning and geochronological dating. This review article provides a thorough discussion of the vibrational modes for U(IV), U(V), and U(VI) and applications of infrared absorption and Raman scattering spectroscopies in the identification and detection of both naturally occurring and synthetic uranium species in solid and solution states. The vibrational frequencies of the uranyl moiety, including both symmetric and asymmetric stretches are sensitive to the coordinating ligands and used to identify individual species in water, organic solvents, and ionic liquids or on the surface of materials. Additionally, vibrational spectroscopy allows for the in situ detection and real-time monitoring of chemical reactions involving uranium. Finally, techniques to enhance uranium species signals with vibrational modes are discussed to expand the application of vibrational spectroscopy to biological, environmental, inorganic, and materials scientists and engineers.

13.
Inorg Chem ; 56(21): 13014-13028, 2017 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-29048881

RESUMO

The interactions between aqueous aluminum (Al) nanoclusters and ions in solution influence the reactivity of nanomaterials in natural waters and are crucial to the targeted syntheses of aluminum oxides. To contribute to the fundamental understanding of how both anion and Al-nanocluster properties affect the interactions, we carry out systematic modeling studies that employ density functional theory calculations embedded in a continuum solvent model. Energetic and electronic structure analysis is applied toward delineating the interactions of a range of probe adsorbate anions with Al nanoclusters to elucidate how small molecules may react with naturally occurring nanomaterials. The study spans seven small molecules on three model Al nanoclusters. Using this ion set, we correlate the size, shape, and formal charge of the adsorbate to the trends in adsorption energies. A key finding is that the collective effects of exposed oxygen functional groups, i.e., the distribution of functional groups, dictates the electrostatic potential of the nanocluster surface, which, in turn, controls trends in anion adsorption. The computed adsorption and deprotonation trends are correlated to known synthetic routes of Al-nanocluster formation and subsequent crystallization to give insight into the potential optimization of synthetic conditions.

14.
Angew Chem Int Ed Engl ; 56(34): 10161-10164, 2017 08 14.
Artigo em Inglês | MEDLINE | ID: mdl-28508441

RESUMO

Multimeric oxo-hydroxo Al clusters function as models for common mineral structures and reactions. Cluster research, however, is often slowed by a lack of methods to prepare clusters in pure form and in large amounts. Herein, we report a facile synthesis of the little known cluster Al8 (OH)14 (H2 O)18 (SO4 )5 (Al8 ) through a simple dissolution method. We confirm its structure by single-crystal X-ray diffraction and show by 27 Al NMR spectroscopy, electrospray-ionization mass spectrometry, and small- and wide-angle X-ray scattering that it also exists in solution. We speculate that Al8 may form in natural water systems through the dissolution of aluminum-containing minerals in acidic sulfate solutions, such as those that could result from acid rain or mine drainage. Additionally, the dissolution method produces a discrete Al cluster on a scale suitable for studies and applications in materials science.

15.
Analyst ; 141(17): 5137-43, 2016 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-27326897

RESUMO

The radius of curvature of gold (Au) nanostar tips but not the overall particle dimensions can be used for understanding the large and quantitative surface-enhanced Raman scattering (SERS) signal of the uranyl (UO2)(2+) moiety. The engineered roughness of the Au nanostar architecture and the distance between the gold surface and uranyl cations are promoted using carboxylic acid terminated alkanethiols containing 2, 5, and 10 methylene groups. By systematically varying the self-assembled monolayer (SAM) thickness with these molecules, the localized surface plasmon resonance (LSPR) spectral properties are used to quantify the SAM layer thickness and to promote uranyl coordination to the Au nanostars in neutral aqueous solutions. Successful uranyl detection is demonstrated for all three functionalized Au nanostar samples as indicated by enhanced signals and red-shifts in the symmetric U(vi)-O stretch. Quantitative uranyl detection is achieved by evaluating the integrated area of these bands in the uranyl fingerprint window. By varying the concentration of uranyl, similar free energies of adsorption are observed for the three carboxylic acid terminated functionalized Au nanostar samples indicating similar coordination to uranyl, but the SERS signals scale inversely with the alkanethiol layer thickness. This distance dependence follows previously established models assuming that roughness features associated with the radius of curvature of the tips are considered. These results indicate that SERS signals using functionalized Au nanostar substrates can provide quantitative detection of small molecules and that the tip architecture plays an important role in understanding the resulting SERS intensities.

16.
Environ Sci Process Impacts ; 18(4): 456-63, 2016 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-26952871

RESUMO

Naturally-occurring radioactive materials (NORM) associated with unconventional drilling produced fluids from the Marcellus Shale have raised environmental concerns. However, few investigations into the fundamental chemistry of NORM in Marcellus Shale produced fluids have been performed. Thus, we performed radiochemical experiments with Marcellus Shale produced fluids to understand the partitioning behavior of major radioelements of environmental health concern (uranium (U), thorium (Th), radium (Ra), lead (Pb), and polonium (Po)). We applied a novel radiotracer, (203)Pb, to understand the behavior of trace-levels of (210)Pb in these fluids. Ultrafiltration experiments indicated U, Th, and Po are particle reactive in Marcellus Shale produced fluids and Ra and Pb are soluble. Sediment partitioning experiments revealed that >99% of Ra does not adsorb to sediments in the presence of Marcellus Shale produced fluids. Further experiments indicated that although Ra adsorption is related to ionic strength, the concentrations of heavier alkaline earth metals (Ba, Sr) are stronger predictors of Ra solubility.


Assuntos
Fraturamento Hidráulico , Polônio/análise , Radioisótopos/análise , Rádio (Elemento)/análise , Tório/análise , Urânio/análise , Poluentes Radioativos da Água/análise , Monitoramento Ambiental , Resíduos Industriais/análise , Águas Residuárias/química , West Virginia
17.
Anal Chem ; 88(1): 773-80, 2016 Jan 05.
Artigo em Inglês | MEDLINE | ID: mdl-26607279

RESUMO

Raman spectroscopy is emerging as a powerful tool for identifying hexavalent uranium speciation in situ; however, there is no straightforward protocol for identifying uranyl species in solution. Herein, uranyl samples are evaluated using Raman spectroscopy, and speciation is monitored at various solution pH values and anion compositions. Spectral quality is evaluated using two Raman excitation wavelengths (532 and 785 nm) as these are critical for maximizing signal-to-noise and minimizing background from fluorescent uranyl species. The Raman vibrational frequency of uranyl shifts according to the identity of the coordinating ions within the equatorial plane and/or solution pH; therefore, spectral barcode analysis and rigorous peak fitting methods are developed that allow accurate and routine uranium species identification. All in all, this user's guide is expected to provide a user-friendly, straightforward approach for uranium species identification using Raman spectroscopy.

18.
Inorg Chem ; 54(17): 8367-74, 2015 Sep 08.
Artigo em Inglês | MEDLINE | ID: mdl-26252808

RESUMO

Keggin-type aluminum oxyhydroxide species such as the Al30 (Al30O8(OH)56(H2O)26(18+)) polycation can readily sequester inorganic and organic forms of P(V) and As(V), but there is a limited chemical understanding of the adsorption process. Herein, we present experimental and theoretical structural and chemical characterization of [(TBP)2Al2(µ4-O8)(Al28(µ2-OH)56(H2O)22)](14+) (TBP = t-butylphosphonate), denoted as (TBP)2Al30-S. We go on to consider the structure as a model for studying the reactivity of oxyanions to aluminum hydroxide surfaces. Density functional theory (DFT) calculations comparing the experimental structure to model configurations with P(V) adsorption at varying sites support preferential binding of phosphate in the Al30 beltway region. Furthermore, DFT calculations of R-substituted phosphates and their arsenate analogues consistently predict the beltway region of Al30 to be most reactive. The experimental structure and calculations suggest a shape-reactivity relationship in Al30, which counters predictions based on oxygen functional group identity.

19.
Environ Health Perspect ; 123(7): 689-96, 2015 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-25831257

RESUMO

BACKGROUND: The economic value of unconventional natural gas resources has stimulated rapid globalization of horizontal drilling and hydraulic fracturing. However, natural radioactivity found in the large volumes of "produced fluids" generated by these technologies is emerging as an international environmental health concern. Current assessments of the radioactivity concentration in liquid wastes focus on a single element-radium. However, the use of radium alone to predict radioactivity concentrations can greatly underestimate total levels. OBJECTIVE: We investigated the contribution to radioactivity concentrations from naturally occurring radioactive materials (NORM), including uranium, thorium, actinium, radium, lead, bismuth, and polonium isotopes, to the total radioactivity of hydraulic fracturing wastes. METHODS: For this study we used established methods and developed new methods designed to quantitate NORM of public health concern that may be enriched in complex brines from hydraulic fracturing wastes. Specifically, we examined the use of high-purity germanium gamma spectrometry and isotope dilution alpha spectrometry to quantitate NORM. RESULTS: We observed that radium decay products were initially absent from produced fluids due to differences in solubility. However, in systems closed to the release of gaseous radon, our model predicted that decay products will begin to ingrow immediately and (under these closed-system conditions) can contribute to an increase in the total radioactivity for more than 100 years. CONCLUSIONS: Accurate predictions of radioactivity concentrations are critical for estimating doses to potentially exposed individuals and the surrounding environment. These predictions must include an understanding of the geochemistry, decay properties, and ingrowth kinetics of radium and its decay product radionuclides.


Assuntos
Elementos Radioativos/análise , Monitoramento Ambiental/métodos , Fraturamento Hidráulico , Resíduos Industriais/análise , Radioisótopos/análise , Águas Residuárias/química , Poluentes Radioativos da Água/análise , Pennsylvania
20.
Inorg Chem ; 54(4): 1395-404, 2015 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-25587792

RESUMO

Th(IV) readily undergoes hydrolysis and condensation in aqueous solutions to form polynuclear molecular species and the system becomes increasingly complicated when organic chelators or other metals are present in solution, leading to the formation of complexes with vastly different structural topologies. Five compounds containing binary and ternary Th(IV) complexes have been synthesized and structurally characterized using single-crystal X-ray diffraction, including Na4[Th6O2(C10O7N2H14)6]·20.5H2O (Th6hedta), [Th(C9O6NH12)(H2O)(NO3)]·1.5H2O (Th(ntp)), [Th2Al8(OH)14(H2O)12(C6O5NH8)4](NO3)6·17.5H2O (Th2Al8heidi), (C4N2H12) [Th2Fe2(OH)2(H2O)2(C6O7H4)2(C6O7H5)2]·6H2O (Th2Fe2cit), (C4N2H12) [ThFe2O(H2O)3(C11O9N2H13)2]·6H2O (ThFe2dhpta). Additional chemical characterization by infrared spectroscopy and thermogravimetric analysis provides information on the chelation by the organic ligands and thermal stability. These molecular complexes can be utilized to understand aqueous speciation in mixed-metal solutions and also provide information regarding contaminant adsorption on iron(III) and aluminum(III) oxide surfaces.

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