Uranium (U) poses a significant contamination hazard to soils, sediments, and groundwater due to its extensive use for energy production. Despite advances in modeling the risks of this toxic and ...radioactive element, lack of information about the mechanisms controlling U transport hinders further improvements, particularly in reducing environments where UIV predominates. Here we establish that mineral surfaces can stabilize the majority of U as adsorbed UIV species following reduction of UVI. Using X-ray absorption spectroscopy and electron imaging analysis, we find that at low surface loading, UIV forms inner-sphere complexes with two metal oxides, TiO2 (rutile) and Fe3O4 (magnetite) (at <1.3 U nm–2 and <0.037 U nm–2, respectively). The uraninite (UO2) form of UIV predominates only at higher surface loading. UIV–TiO2 complexes remain stable for at least 12 months, and UIV–Fe3O4 complexes remain stable for at least 4 months, under anoxic conditions. Adsorbed UIV results from UVI reduction by FeII or by the reduced electron shuttle AH2QDS, suggesting that both abiotic and biotic reduction pathways can produce stable UIV–mineral complexes in the subsurface. The observed control of high-affinity mineral surface sites on UIV speciation helps explain the presence of nonuraninite UIV in sediments and has important implications for U transport modeling.
Plasmonic/Magnetic Bifunctional Nanoparticles Peng, Sheng; Lei, Changhui; Ren, Yang ...
Angewandte Chemie (International ed.),
March 28, 2011, Letnik:
50, Številka:
14
Journal Article
Recenzirano
Superparafragilistic: An amorphous seed‐mediated strategy has been developed for the synthesis of hybrid nanoparticles (see images) that are composed of silver (yellow) and iron oxide (blue) ...nanodomains and exhibit unique optical properties. These properties originate from both the strong surface plasmon resonance of the silver and the strong superparamagnetic responses of the iron oxide nanodomains.
Green rusts, which are mixed ferrous/ferric hydroxides, are found in many suboxic environments and are believed to play a central role in the biogeochemistry of Fe. Analysis by U LIII-edge X-ray ...absorption near edge spectroscopy of aqueous green rust suspensions spiked with uranyl (UVI) showed that UVI was readily reduced to UIV by green rust. The extended X-ray absorption fine structure (EXAFS) data for uranium reduced by green rust indicate the formation of a UO2 phase. A theoretical model based on the crystal structure of UO2 was generated by using FEFF7 and fitted to the data for the UO2 standard and the uranium in the green rust samples. The model fits indicate that the number of nearest-neighbor uranium atoms decreases from 12 for the UO2 structure to 5.4 for the uranium-green rust sample. With an assumed four near-neighbor uranium atoms per uranium atom on the surface of UO2, the best-fit value for the average number of uranium atoms indicates UO2 particles with an average diameter of 1.7 ± 0.6 nm. The formation of nanometer-scale particles of UO2, suggested by the modeling of the EXAFS data, was confirmed by high-resolution transmission electron microscopy, which showed discrete particles (∼2−9 nm in diameter) of crystalline UO2. Our results clearly indicate that UVI (as soluble uranyl ion) is readily reduced by green rust to UIV in the form of relatively insoluble UO2 nanoparticles, suggesting that the presence of green rusts in the subsurface may have significant effects on the mobility of uranium, particularly under iron-reducing conditions.
We report the photoluminescence (PL) properties of colloidal Si nanocrystals (NCs) up to 800 K and observe PL retention on par with core/shell structures of other compositions. These ...alkane-terminated Si NCs even emit at temperatures well above previously reported melting points for oxide-embedded particles. Using selected area electron diffraction (SAED), powder X-ray diffraction (XRD), liquid drop theory, and molecular dynamics (MD) simulations, we show that melting does not play a role at the temperatures explored experimentally in PL, and we observe a phase change to β-SiC in the presence of an electron beam. Loss of diffraction peaks (melting) with recovery of diamond-phase silicon upon cooling is observed under inert atmosphere by XRD. We further show that surface passivation by covalently bound ligands endures the experimental temperatures. These findings point to covalently bound organic ligands as a route to the development of NCs for use in high temperature applications, including concentrated solar cells and electrical lighting.
Atherosclerosis is an inflammatory disease characterized by plaques that can cause sudden myocardial infarction upon rupture. Such rupture‐prone plaques have thin fibrous caps due to collagenase ...degradation, and a noninvasive diagnostic tool and targeted therapy that can identify and treat vulnerable plaques and may inhibit the onset of acute cardiac events. Toward this goal, monocyte‐binding, collagenase‐inhibiting, and gadolinium‐modified peptide amphiphile micelles (MCG PAMs) are developed. Monocyte chemoattractant protein‐1 (MCP‐1) binds to C‐C chemokine receptor‐2 expressed on pathological cell types present within plaques. Through the peptide binding motif of MCP‐1, MCG PAMs bind to monocytes and vascular smooth muscle cells in vitro. Moreover, using magnetic resonance imaging, MCG PAMs show enhanced targeting and successful detection of plaques in diseased mice in vivo and act as contrast agents for molecular imaging. Through the collagenase‐cleaving peptide sequence of collagen VPMS‐MRGG, MCG PAMs can compete for collagenases that degrade the fibrous cap of plaques, providing therapy. MCG PAM‐treated mice show increased fibrous cap thickness by 61% and 113% histologically compared to nontargeting micelle‐ or PBS‐treated mice (p = 0.0075 and 0.001, respectively). Overall, this novel multimodal nanoparticle offers new theranostic opportunities for noninvasive diagnosis and treatment of atherosclerotic plaques.
Multimodal monocyte‐binding, collagenase‐inhibiting, and gadolinium‐modified peptide amphiphile micelles (MCG PAMs) are theranostic nanoparticles for atherosclerosis. Real‐time magnetic resonance imaging shows that MCG PAMs identify plaques in mice via monocyte and smooth muscle cell targeting. Histological analyses demonstrate that MCG PAM treatment enhances the fibrous cap thickness of plaques, thereby stabilizing atherosclerotic plaques from rupture in diseased mice.
Green rusts are mixed Fe(II)/Fe(III) hydroxides that are found in many suboxic environments where they are believed to play a central role in the biogeochemical cycling of iron. X-ray absorption fine ...structure analysis of hydroxysulfate green rust suspensions spiked with aqueous solutions of AgCH(3)COO, AuCl(n)(OH)(4-n), CuCl(2), or HgCl(2) showed that Ag(I), Au(III), Cu(II), and Hg(II) were readily reduced to Ag(0), Au(0), Cu(0), and Hg(0). Imaging of the resulting solids from the Ag(I)-, Au(III)-, and Cu(II)-amended green rust suspensions by transmission electron microscopy indicated the formation of submicron-sized particles of Ag(0), Au(0), and Cu(0). The facile reduction of Ag(I), Au(III), Cu(II), and Hg(II) to Ag(0), Au(0), Cu(0), and Hg(0), respectively, by green rust suggests that the presence of green rusts in suboxic soils and sediments can have a significant impact on the biogeochemistry of silver, gold, copper, and mercury, particularly with respect to their mobility.
Niobium carbide thin films were synthesized by atomic layer deposition (ALD) using trimethylaluminum (TMA), NbF5, and NbCl5 precursors. In situ quartz crystal microbalance (QCM) measurements ...performed at 200 and 290 °C revealed controlled, linear deposition with a high growth rate of 5.7 and 4.5 Å/cycle, respectively. The chemical composition, growth rate, structure, and electronic properties of the films were studied over the deposition temperature range 125–350 °C. Varying amounts of impurities, including amorphous carbon (a-C), AlF3, NbF x , and NbCl x , were found in all samples. A strong growth temperature dependence of film composition, growth rate, and room temperature DC resistivity was observed. Increasing film density, decreasing total impurity concentration, and decreasing resistivity were observed as a function of increasing deposition temperature for films grown with either NbF5 or NbCl5. Superconducting quantum interference device (SQUID) magnetometry measurements down to 1.2 K revealed a superconducting transition at T c = 1.8 K in a 75 nm thick film grown at 350 °C with TMA and NbF5. The superconducting critical temperature could be increased up to 3.8 K with additional use of NH3 during ALD film growth.
One of the oldest visual illusions consists of observers' tendency to estimate vertical lines as longer than equal horizontal lines. This Horizontal-Vertical Illusion has been studied widely; ...however, most studies may not generalize to natural contexts because they have not addressed the low-level processes that occur rapidly and in response to context-free lines vs the possibility for high-level processes that arise over time in response to context. These issues were investigated via a novel design: rapid time-sequencing embedded within the context of natural images. Participants saw different levels of context and the Horizontal-Vertical Illusion was measured. In traditional Horizontal-Vertical Illusion displays without natural context, there was a robust invariance of the illusion to stimulus duration. Within context, however, there was strong modulation: the magnitude of the illusion decreased by over 50% or increased over 30%, depending upon placement within context. Knowledge of object properties such as size or line length did not account for this effect. It appears that previous domain-general investigations of the Horizontal-Vertical Illusion did not address the specific higher-order processes that produce the illusion in natural contexts.
Newborn screening (NBS) provides early diagnosis of sickle hemoglobinopathies. After Hb S β6(A3)Glu→Val, GAG>GTG, Hb C β6(A3)Glu→Lys, GAG>AAG is the most common hemoglobin (Hb) abnormality identified ...in the United States (1,2). Published data regarding children with Hb C disease are limited. This study was conducted to summarize a single institution's clinical and laboratory data for patients with Hb C disease, specifically homozygous Hb CC and its variants over a 10-year period. Forty-seven patients, whose mean age at diagnosis was 2.9 years (range 0.04 to 23 years), were identified. Twenty-nine had Hb CC and the remainder had compound heterozygous variants 10 Hb C/β+-thalassemia (β+-thal), four Hb C/β0-thal, and one each with Hb C/Hb Hope or β136(H14)Gly→Asp (GGT>GAT), Hb C/Hb Lepore (a hybrid δβ-globin gene), Hb C/HPFH (hereditary persistence of fetal Hb) probably a Gγ HPFH-2 (the Ghanaian type), and Hb C/Osu-Christiansborg or β52(D3)Asp→Asn (GAT>AAT). All patients had mild microcytic anemia with reticulocytosis and frequent target cells on peripheral smear. Splenomegaly or cholelithiasis occurred in 2.6% of patients <8 years of age, however, these symptoms were more common (71.0%) in patients >8 years of age. No patient had serious infections or painful events resembling vasoocclusion. Accurate diagnosis and understanding of Hb C-related disorders helped to avoid confusion with sickle hemoglobinopathies and aided in proper clinical management.
We report a facile one-step approach which involves no flammable gas, no catalyst, and no in situ polymerization for the preparation of well-aligned carbon nanotube array. A polymer precursor is ...placed on top of an anodized aluminum oxide (AAO) membrane containing regular nanopore arrays, and slow heating under Ar flow allows the molten polymer to wet the template through adhesive force. The polymer spread into the nanopores of the template to form polymer nanotubes. Upon carbonization the resulting multi-walled carbon nanotubes duplicate the nanopores morphology precisely. The process is demonstrated for 230, 50, and 20 nm pore membranes. The synthesized carbon nanotubes are characterized with scanning/transmission electron microscopies, Raman spectroscopy, and resistive measurements. Convenient functionalization of the nanotubes with this method is demonstrated through premixing CoPt nanoparticles in the polymer precursors.
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