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Cologgi D.L.,Michigan State University | Cologgi D.L.,University of Alberta | Speers A.M.,Michigan State University | Bullard B.A.,Michigan State University | And 2 more authors.
Applied and Environmental Microbiology | Year: 2014

Biofilms formed by dissimilatory metal reducers are of interest to develop permeable biobarriers for the immobilization of soluble contaminants such as uranium. Here we show that biofilms of the model uranium-reducing bacterium Geobacter sulfurreducens immobilized substantially more U(VI) than planktonic cells and did so for longer periods of time, reductively precipitating it to a mononuclear U(IV) phase involving carbon ligands. The biofilms also tolerated high and otherwise toxic concentrations (up to 5 mM) of uranium, consistent with a respiratory strategy that also protected the cells from uranium toxicity. The enhanced ability of the biofilms to immobilize uranium correlated only partially with the biofilm biomass and thickness and depended greatly on the area of the biofilm exposed to the soluble contaminant. In contrast, uranium reduction depended on the expression of Geobacter conductive pili and, to a lesser extent, on the presence of the c cytochrome OmcZ in the biofilm matrix. The results support a model in which the electroactive biofilm matrix immobilizes and reduces the uranium in the top stratum. This mechanism prevents the permeation and mineralization of uranium in the cell envelope, thereby preserving essential cellular functions and enhancing the catalytic capacity of Geobacter cells to reduce uranium. Hence, the biofilms provide cells with a physically and chemically protected environment for the sustained immobilization and reduction of uranium that is of interest for the development of improved strategies for the in situ bioremediation of environments impacted by uranium contamination. © 2014, American Society for Microbiology.

Ravel B.,U.S. National Institute of Standards and Technology | Scorzato C.,Brazilian Synchrotron Light Laboratory (LNLS) | Siddons D.P.,Brookhaven National Laboratory | Kelly S.D.,EXAFS Analysis | Bare S.R.,UOP LLC
Journal of Synchrotron Radiation | Year: 2010

A four-channel ionization chamber has been designed, constructed and tested. This ionization chamber allows X-ray absorption spectra to be collected in transmission from up to four samples simultaneously. This results in spectra that are free of systematic uncertainty in relative energy alignment introduced by scan-to-scan stability of the monochromator or of numerical uncertainty associated with a post-processing alignment algorithm, allowing, in a single shot, an absolute measure of edge shift between four samples of different valence. As four samples can be measured in parallel, the time expended over the course of an experiment to cycle the measurement environment between its rest state and the measurement condition is substantially reduced. The ionization chamber is simple in design and could be implemented at virtually any XAFS beamline with a horizontal fan of radiation such as that provided by a bend magnet or wiggler. © 2010 International Union of Crystallography. Printed in Singapore-all rights reserved.

Scholz S.,TU Munich | Bare S.R.,UOP LLC | Kelly S.D.,EXAFS Analysis | Lercher J.A.,TU Munich
Microporous and Mesoporous Materials | Year: 2011

Novel hierarchically structured macroscopic silica spheres have been synthesized using a biphasic oil-in-water system. The spheres are prepared in a one-step process by injection of the precursor solution into water. This leads to controlled hydrolysis and condensation of the silanes. The precursor solution contained three different silanes, a block copolymer acting as surfactant and a solvent. The spheres have a hierarchically layered morphology, high mechanical stability, specific surface areas up to 700 m2/g with mesopores in the range of 9-27 nm. The synthesis of such materials with a simultaneous control of the macroscopic and microscopic structure allows facile implementation in separation and catalysis. © 2011 Elsevier Inc. All rights reserved.

Kropf A.J.,Argonne National Laboratory | Katsoudas J.,MRCAT | Katsoudas J.,Illinois Institute of Technology | Chattopadhyay S.,MRCAT | And 17 more authors.
AIP Conference Proceedings | Year: 2010

The Materials Research Collaborative Access Team (MRCAT) has completed construction of its bending magnet beamline at the Advanced Photon Source, with commissioning ongoing since October 2008. Full operations including General User access will begin in January 2010. The beamline is designed to operate in two distinct modes: pink beam for lithography, photochemistry and tomography; and monochromatic beam for x-ray absorption spectroscopy and tomography. Pink beam is obtained by means of a 880 mm water cooled Pt mirror combined with filters, while monochromatic beam is selected using a water-cooled double-crystal Si(111) monochromator, providing an energy range from below 4 keV to greater than 33 keV. Switching between modes is accomplished in under one hour. © 2010 American Institute of Physics.

Chattopadhyay S.,Argonne National Laboratory | Chattopadhyay S.,Elgin Community College | Kelly S.D.,EXAFS Analysis | Shibata T.,Argonne National Laboratory | And 6 more authors.
Journal of Chemical Physics | Year: 2016

We report a detailed study of the local composition and structure of a model, bi-phasic nanoglass with nominal stoichiometry Cu55Nb45. Three dimensional atom probe data suggest a nanoscale-phase-separated glassy structure having well defined Cu-rich and Nb-rich regions with a characteristic length scale of ≈3 nm. However, extended x-ray absorption fine structure analysis indicates subtle differences in the local environments of Cu and Nb. While the Cu atoms displayed a strong tendency to cluster and negligible structural order beyond the first coordination shell, the Nb atoms had a larger fraction of unlike neighbors (higher chemical order) and a distinctly better-ordered structural environment (higher topological order). This provides the first experimental indication that metallic glass formation may occur due to frustration arising from the competition between chemical ordering and clustering. These observations are complemented by classical as well as ab initio molecular dynamics simulations. Our study indicates that these nanoscale phase-separated glasses are quite distinct from the single phase nanoglasses (studied by Gleiter and others) in the following three respects: (i) they contain at least two structurally and compositionally distinct, nanodispersed, glassy phases, (ii) these phases are separated by comparatively sharp inter-phase boundaries, and (iii) thermally induced crystallization occurs via a complex, multi-step mechanism. Such materials, therefore, appear to constitute a new class of disordered systems that may be called a composite nanoglass. © 2016 AIP Publishing LLC.

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