Scientific Publications 2009
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2009. "Spatially Resolved U(VI) Partitioning and Speciation: Implications for Plume Scale Behavior of Contaminant U in the Hanford Vadose Zone." Environmental Science & Technology 43(7):2247-2253. Abstract A saline-alkaline brine containing high concentration of U(VI) was accidentally spilled at the Hanford Site in 1951, introducing 10 tons of U into sediments under storage tank BX-102. U concentrations in the deep vadose zone and groundwater plumes increase with time, yet how the U has been migrating is not fully understood. We simulated the spill event in laboratory soil columns, followed by aging, and obtained spatially resolved U partitioning and speciation along simulated plumes. We found after aging, at apparent steady state, that the pore aqueous phase U concentrations remained surprisingly high (up to 0.022 M), in close agreement with the recently reported high U concentrations (up to 0.027 M) in the vadose zone plume (1). The pH values of aged pore liquids varying from 10 to 7, consistent with the measured pH of the field borehole sediments varying from 9.5 to 7.4 (2), from near the plume source to the plume front. The direct measurements of aged pore liquids together with thermodynamic calculations using a Pitzer approach revealed that UO2(CO3)34- is the dominant aqueousUspecies within the plume body (pH 8-10), whereas Ca2UO2(CO3)3 and CaUO2(CO3)32- are also significant in the plume front vicinity (pH 7-8), consistent with that measured from field borehole pore-waters (3). U solid phase speciation varies at different locations along the plume flow path and even within single sediment grains, because of location dependent pore and micropore solution chemistry. Our results suggest that continuous gravitydriven migration of the highly stable UO2(CO3)34- in the residual carbonate and sodium rich tank waste solution is likely responsible for the detected growing U concentrations in the vadose zone and groundwater.
2009. "Crystal and Electronic Structure of Lithiated Nanosized RutileTiO2 by Electron Diffraction and Electron Energy-loss Spectroscopy." Applied Physics Letters 94(23):Art. No.: 233116. doi:10.1063/1.3152783 Abstract The electronic structure of the nanosized rutile TiO2 before and after mechanical lithiation were studied using TEM and EELS. EELS reveals the Li K-edge at the energy-loss position of ~ 61 eV. After lithiation, the separation of the t2g-eg crystal-field splitting on both Ti L2,3-edge and O K-edge decreases, the O K-edge shifts towards a higher energy-loss position and the separation between the pre-edge peak and main peak on the O K-edge decreases. These results suggest that the lithiation of rutile TiO2 was accompanied by the reduction of Ti ion and a charge transfer from Li to Ti.
2009. "Morphology and Electronic Structure of the Oxide Shell on the Surface of Iron Nanoparticles." Journal of the American Chemical Society 131(25):8824–8832. doi:10.1021/ja900353f Abstract A iron nanoparticle exposed to air at room temperature will be instantly covered by an oxide shell of typical thickness of ~ 3 nm. This native oxide shell in combination with an underlying iron core determines the physical and chemical behavior of this type of core-shell nanoparticles. One of the great challenges for characterizing this type of nanoparticles is determination of the structure of the oxide shell, as it is FeO, Fe3O4, -Fe2O3, -Fe2O3, or anything else. Significant research effort, mostly based on x-ray diffraction and spectroscopy and electron diffraction and transmission electron microscopy imaging, has been made to determine the structure of this thin layer of iron oxide. Most of the experimental results have been framed with one of the known iron oxide structures, although it is not necessarily true that this thin layer of iron oxide consists of a standard iron oxide. In this paper, the structure of the oxide shell on iron nanoparticle is probed using electron energy loss spectroscopy (EELS) at O K-edge with a spatial resolution of several nanometers (individual particle). Two types of representative particles were studied: particles that are fully oxidized and core-shell particle which possesses a Fe core. We found that the O K-edge spectra collected on the oxide shell in the nanoparticles shows distinctive differences as compared with that of the known iron oxide. Based on finger printing and quantum mechanical calculations results, we conclude that the distances between the absorbing oxygen and the next-nearest neighbor oxygens are more widely distributed than that in bulk Fe3O4 for both of these two types of particles. For smaller and fully oxidized particles, there is also a broadened distribution between the absorbing oxygen and the nearest neighbor oxygens. These results clearly demonstrate that the coordination configuration in the oxide shell on Fe nanoparticle is defective as compared with that of their bulk counterpart. Of the two types particles examined in this work, the degree of disorder is larger for the smaller fully oxidized particles.
2009. "Self-assembled TiO2-Graphene Hybrid Nanostructures for Enhanced Li-ion Insertion ." ACS Nano 3(4):907-914. Abstract We used anionic sulfate surfactants to assist the stabilization of graphene in aqueous solutions and facilitate the self-assembly of in-situ grown nanocrystalline TiO2, rutile and anatase, with graphene. These nanostructured TiO2-graphene hybrid materials were used for investigation of Li-ion insertion properties. The hybrid materials showed significantly enhanced Li-ion insertion/extraction in TiO2. The specific capacity was more than doubled at high charge rates, as compared with the pure TiO2 phase. The improved capacity at high charge-discharge rate may be attributed to increased electrode conductivity in presence of a percolated graphene network embedded into the metal oxide electrodes.
2009. "EQCM Immunoassay for Phosphorylated Acetylcholinesterase as a Biomarker for Organophosphate Exposures Based on Selective Zirconia Adsorption and Enzyme-Catalytic Precipitation ." Biosensors and Bioelectronics 24(8):2377-2383. Abstract A zirconia (ZrO2) adsorption-based immunoassay by electrochemical quartz crystal microbalance (EQCM) has been initially developed, aiming at the detection of phosphorylated acetylcholinesterase (AChE) as a potential biomarker for bio-monitoring exposures to organophosphate (OP) pesticides and chemical warfare agents. Hydroxyl-derivatized monolayer was preferably chosen to modify the crystal serving as the template for directing the electro-deposition of ZrO2 film with uniform nanostructures. The resulting ZrO2 film was utilized to selectively capture phosphorylated AChE from the sample media. Horseradish peroxidase (HRP)-labeled anti-AChE antibodies were further employed to recognize the captured phosphorylated protein. Enzyme-catalytic oxidation of the benzidine substrate resulted in the accumulation of insoluble product on the functionalized crystal. Ultrasensitive EQCM quantification by mass-amplified frequency responses as well as rapid qualification by visual color changes of product could be thus achieved. Moreover, 4-chloro-1-naphthol (CN) was comparably studied as an ideal chromogenic substrate for the enzyme-catalytic precipitation. Experimental results show that the developed EQCM technique can allow for the detection of phosphorylated AChE in human plasma. Such an EQCM immunosensing format opens a new door towards the development of simple, sensitive, and field-applicable biosensor for biologically monitoring low-level OP exposures.
2009. "Fluorescent Dye Encapsulated ZnO Particles with Cell-specific Toxicity for Potential use in Biomedical Applications." Journal of Materials Science. Materials in Medicine 20(1):11-22. Abstract Fluorescein isothiocyanate (FITC)-encapsulated core-shell particles with a nanoscale ZnO finishing layer have been synthesized for the first time as multifunctional “smart” nanostructures for particle tracking and cell imaging using the visible fluorescence emission of the dye or UV fluorescence emission of ZnO, and anti-cancer/antibacterial treatments using the selective toxicity of the nanoscale ZnO outer surface. The chemical phase composition, morphology, size, and the layered core-shell architecture of the particles were characterized using detailed transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-vis-NIR spectrophotometry. Systematic XPS studies after removing nanometer thick layers confirmed the expected layered structure in the order ZnO-SiO2-APTMS-FITC proceeding from the surface to the core of the ~200 nm sized particles. Detailed investigation of the fluorescence properties of these hydrophilic particles in bio-compatible media using fluorescence spectroscopy, flow cytometry and fluorescence confocal microscopy demonstrated that the silica/ZnO outer layer offers considerable protection to the encapsulated dye molecules from photobleaching and quenching due to reactive species such as oxygen in the solvent. These particles showed promise toward cell imaging, for example when the bacterium Escherichia coli was used as a test system, the green fluorescence of the particles allowed confocal microscopy to image the cells. The FITC encapsulated ZnO (FITC-ZnO) particles demonstrated excellent selectivity in preferentially killing Jurkat cancer cells (18% cell viability) without any significant toxicity to normal primary immune cells (75% cell viability) at 60 g/mL concentrations and inhibited the growth of both gram-positive and gram negative bacteria at concentrations ≥ 250-500 g/mL (for Staphylococcus aureus and Escherichia coli, respectively). These results indicate that the novel FITC encapsulated multifunctional particles with nanoscale ZnO surface layer are smart nanostructures for particle tracking, cell imaging, antibacterial treatments and cancer therapy.
2009. "Experimental and theoretical investigation of three-dimensional nitrogen-doped aluminum clusters AI8N- and AI8N." Journal of Chemical Physics 130(13):134303-1 to 134303-7. doi:10.1063/1.3097761 Abstract The structure and electronic properties of the Al8N− and Al8N clusters were investigated by combined photoelectron spectroscopy and ab initio studies. Congested photoelectron spectra were observed and experimental evidence was obtained for the presence of multiple isomers for Al8N− Global minimum searches revealed several structures for Al8N− with close energies. The calculated vertical detachment energies of the two lowest-lying isomers, which are of C2v and Cs symmetry, respectively, were shown to agree well with the experimental data. Unlike the three-dimensional structures of Al6N− and Al7N−, in which the dopant N atom has a high coordination number of 6,the dopant N atom in the two low-lying isomers of Al8N− has a lower coordination number of 4 and 5, respectively. The competition between the Al–Al and Al–N interactions are shown to determine the global minimum structures of the doped aluminum clusters and results in the structural diversity for both Al8N− and Al8N. © 2009 American Institute of Physics
2009. "Magnetic doping of the golden cage cluster M@Au16 − (M=Fe,Co,Ni)." Physical Review. B, Condensed Matter and Materials Physics 79(3):Article number: 033413. Abstract Structural, electronic, and magnetic properties of the golden cage doped with a transition-metal atom, MAu16(M=Fe,Co,Ni),are investigated using trapped ion electron diffraction, photoelectron spectroscopy, and density-functional theory. The best agreement to experiment is obtained for endohedral M@Au16 structures but with considerable distortions to the parent Au16 cage. Fe@Au16 and Co@Au16 are found to have similar structures with C2 symmetry while a C1 structure is obtained for Ni@Au16. The 4s electrons are observed to transfer to the Au16 cage, whereas atomiclike magnetism due to the unpaired 3d electrons is retained for all the doped clusters.
2009. "Tuning the electronic properties of the golden buckyball by endohedral doping: M@Au16(-) (M=Ag,Zn, In)." Journal of Chemical Physics 130(5):Art. No. 051101. Abstract The golden Au16 cage is doped systematically with an external atom of different valence electrons:Ag, Zn, and In. The electronic and structural properties of the doped clusters, MAu16 (M=Ag,Zn, In), are investigated by photoelectron spectroscopy and theoretical calculations. It is observed that the characteristic spectral features of Au16, reflecting its near tetrahedral (Td) symmetry, are retained in the photoelectron spectra of MAu16, suggesting endohedral structures with little distortion from the parent Au16 cage for the doped clusters. Density functional calculations show that the endohedral structures of M@Au16 with Td symmetry are low-lying structures, which give simulated photoelectron spectra in good agreement with the experiment. It is found that the dopant atom does not significantly perturb the electronic and atomic structures of Au16, but simply donate its valence electrons to the parent Au16 cage, resulting in a closed-shell 18-electron system for Ag@Au16, a 19-electron system for Zn@Au16 with a large energy gap,and a 20-electron system for In@Au16. The current work shows that the electronic properties of the golden buckyball can be systematically tuned through doping.
2009. "Probing Porosity and Pore Interconnectivity in Crystalline Mesoporous TiO2 Using Hyperpolarized Xe-129 NMR." Journal of Physical Chemistry C 113(16):6577-6583. Abstract Hyperpolarized (HP) 129Xe NMR was used to probe the porosity and interconnectivity of pores in crystalline mesoporous TiO2. We have demonstrated that HP 129Xe NMR can be used to differentiate between similar sized pores within different crystalline phases. Pores of 4 nm size resident in mixed anatase and rutile mesoporous TiO2 phases were identified. Complementary to other techniques, HP 129Xe NMR is able to probe the interconnectivity between pores present in these different phases. The cross peaks in 2D exchange (EXSY) NMR spectra between the signals of xenon in two types of pores on millisecond time scale are clearly visible, indicating substantial pore interconnectivity. Information on porosity and interconnectivity is critical for understanding Li ion transport mechanisms in mesoporous TiO2 anode materials.
2009. "Evidence of Significant Covalent Bonding in Au(CN)2-." Journal of the American Chemical Society 131(45):16368-16370. Abstract There have been intense recent interests in the homogeneous catalytic chemistry of Au(I) complexes.1 Among the Au(I) molecules, the Au(CN)2- ion is the most stable and has been widely used in gold extraction back to ancient times. Although AuCN in the condensed phase has been studied, including solution phase vibrational spectroscopy2 and crystal structures,3 the free AuCN molecule has been studied only very recently by microwave spectroscopy.4 The important Au(CN)2- complex has not been observed and studied in the gas phase. Because of the relativistic effects,5 Au-containing molecules exhibit distinctly different properties among the coinage elements. To elucidate the nature of the Au-ligand binding, high-level ab initio calculations are needed due to the complicated electron correlation and relativistic effects.6-8 The structure and bonding of the AuCN molecule were first examined computationally by Frenking and co-workers.7 Recent high-precision calculations by Pyykkö and co-workers suggest multiple-bond characters between Au-C in AuCN because the Au-C bond length is only slightly longer than the sum of the triple bond covalent radii.
2009. "Microsolvation of the acetate anion [CH3CO-2(H2O)n,n=1-3]: A photoelectron spectroscopy and ab initio computational sutdy." Chemical Physics Letters 477(1-3):41-44. Abstract A combined photoelectron spectroscopy and ab initio theoretical study was carried out to study the microsolvation of the acetate anion. Photoelectron spectra of cold solvated clusters CH3CO-2 ðH2OÞn (n = 1-3) at 12 K were obtained and compared with theoretical calculations. The first water is shown to bind to the -CO -2 group in a bidentate fashion, whereas both water-water and water-CO-2 interactions are shown for n = 2 and 3. Significant rearrangement of the solvation structures is observed upon electron detachment, and water-CH3 interactions are present for all the neutral clusters, CH3CO2(H2O)n (n = 1-3).
2009. "Observation of a remarkable temperature effect in the hydrogen bonding structure and dynamics of the CN-(H2O) cluster." Journal of Physical Chemistry A 113(35):9579-9584. Abstract The CN-(H2O) cluster represents a model diatomic monohydrate with multiple solvation sites. We report joint experimental and theoretical studies of its structure and dynamics using temperature-controlled photoelectron spectroscopy (PES) and ab-initio electronic structure calculations. The observed PES spectra of CN-(H2O) display a remarkable temperature effect, namely that the T=12 K spectrum shows an unexpectedly large blue shift of 0.25 eV in the electron binding energy relative to the Room Temperature (RT) spectrum. Extensive theoretical analysis of the potential energy function (PEF) of the cluster at the CCSD(T) level of theory reveal the existence of two nearly isoenergetic isomers corresponding to H2O forming a H-bond with either the C or the N atom, respectively. This results in four topologically distinct minima, i.e., CN-(HaOHb), CN-(HbOHa), NC-(HaOHb) and NC-(HbOHa). There are two main pathways connecting these minima: (i) CN- tumbling relative to water and (ii) water rocking relative to CN-. The relative magnitude of the barriers associated with these two motions reverses between low [pathway (i) is preferred] and high [pathway (ii) is preferred] temperatures. As a result, at T=12 K the cluster adopts a structure that is close to the minimum energy CN-(H2O) configuration, while at RT it can effectively access regions of the PEF close to the transition state for pathway (ii), explaining the surprisingly large spectral shift between the 12 K and RT PES spectra. This work was supported by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences, US Department of Energy. Battelle operates Pacific Northwest National Laboratory for the US Department of Energy.
2009. "Photoelectron Spectroscopy of Cold Hydrated Sulfate Clusters, SO42−(H2O)N ((N = 4−7): Temperature-Dependent Isomer Populations." Journal of Physical Chemistry A 113(19):5567-5576. Abstract Sulfate is an important inorganic anion and its interactions with water are essential to understand its chemistry in aqueous solution. Studies of sulfate with well-controlled solvent numbers provide molecular-level information about the solute-solvent interactions and critical data to test theoretical methods for weakly bounded species. Here we report a low-temperature photoelectron spectroscopy study of hydrated sulfate clusters SO42-(H2O)n (n ) 4-7) at 12 K and ab initio studies to understand the structures and dynamics of these unique solvated systems. A significant increase of electron binding energies was observed for the 12 K spectra relative to those at room temperature, suggesting different structural isomers were populated as a function of temperature. Theoretical calculations revealed a competition between isomers with optimal water-solute and water-water interactions. The global minimum isomers all possess higher electron binding energies due to their optimal water-solute interactions, giving rise to the binding energy shift in the 12 K spectra, whereas many additional low-lying isomers with less optimal solvent-solute interactions were populated at room temperature, resulting in a shift to lower electron binding energies in the observed spectra. The current work demonstrates and confirms the complexity of the water-sulfate potential energy landscape and the importance of temperature control in studying the solvent-solute systems and in comparing calculations with experiment.
2009. "Probing the electronic stablility of multiply charged anions:sulfonated pyrene tri- and tetraanions." Journal of the American Chemical Society 131(28):9836-9842. Abstract The strong intramolecular Coulomb repulsion in multiply charged anions (MCAs) creates a potential barrier that provides dynamic stability to MCAs and allows electronically metastable species to be observed. The 1-hydroxy-3,6,8-pyrene-trisulfonate {[Py(OH)(SO3)3]3- or HPTS3-} was recently observed as a long-lived metastable MCA with a large negative electron binding energy of -0.66 eV. Here we use Penning trap mass spectrometry to monitor the spontaneous decay of HPTS3- f HPTS•2- + e- and have determined the half-life of HPTS3- to be 0.1 s. To explore the limit of electronic metastability, we tried to make the related quadruply charged pyrene-1,3,6,8-tetrasulfonate {[Py(SO3)4]4-}. However, only its decay product, the triply charged radical anion [Py(SO3)4]•3-, as well as the triply charged ion-pairs [Py(SO3)4H]3- and [Py(SO3)4Na]3-, was observed, suggesting that the tremendous intramolecular Coulomb repulsion makes the [Py(SO3)4]4- anion extremely short-lived. Photoelectron spectroscopy data showed that [Py(SO3)4]•3- is an electronically stable species with electron binding energies of +0.5 eV, whereas [Py(SO3)4H]3- and [Py(SO3)4Na]3- possess electron binding energies of 0.0 and -0.1 eV, respectively. Ab initio calculations confirmed the stability of these triply charged species and further predicted a large negative electron binding energy (-2.78 eV) for [Py(SO3)4]4-, consistent with its short lifetime
2009. "Microstructure and ionic-conductivity of alternating-multilayer structured Gd-doped ceria and zirconia thin films." Journal of Materials Science 44(8):2021-2026. Abstract Multilayer thin-film of consisting of alternating Gd-doped ceria and zirconia have been grown by sputter-deposition on -Al2O3 (0001) substrates. The films were characterized using x-ray diffraction (XRD), atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The Gd-doped ceria and zirconia layers had the fluorite structure and are highly textured such that the (111) plane of the films parallel to the (0001) plane of the -Al2O3. The epitaxial relationship can be written as (111)ZrO2/CeO2//(0001)Al2O3 and [11-2]ZrO2/CeO2//[-2110]Al2O3.. The absence of Ce3+ features in the XPS spectra indicates that the Gd-doped ceria films are completely oxidized. The ionic conductivity of this structure shows great improvement as compared with that of the bulk crystalline material. This research provides insight on designing of material for low-temperature electrolyte applications.
2009. "Structure and electronic properties of saturated and unsaturated gallium nitride nanotubes." Journal of Physical Chemistry C 113(44):19281-19285. doi:10.1021/jp907657z Abstract The atomic and electronic structures of saturated and unsaturated GaN nanotubes along the [001] direction with (100) lateral facets are studied using first-principles calculations. Atomic relaxation of nanotubes shows that appreciable distortion occurs in the unsaturated nanotubes. All the nanotubes considered, including saturated and unsaturated ones, exhibit semiconducting, with a direct band gap. Surface states arisen from the threefold-coordinated N and Ga atoms at the lateral facets exist inside the bulk-like band gap. When the nanotubes saturated with hydrogen, these dangling bond bands are removed from the band gap, but the band gap decreases with increasing the wall thickness of the nanotubes.
2009. "A Flow-Through Ultrasonic Lysis System for the Disruption of Bacterial Spores." JALA. Journal of the Association for Laboratory Automation 14(5):277-284. Abstract An automated, flow-through spore lysis instrument that is capable of rapidly disrupting bacterial spores is described. The system utilizes a flow-through chamber that allows for direct injection of the sample without the need for a chemical or enzymatic pre-treatment step to soften the spore coat prior to lysis. Lysis of Bacillus subtilis spores, a benign simulant of Bacillus anthracis, is achieved by flowing the sample through a tube whose axis is parallel to the faces of two transducers that deliver 10 W cm-2 to the surface of the tube at 1.4 MHz frequency. Increases in amplifiable DNA were assessed by real-time PCR analysis, which showed at least a 25-fold increase in amplifiable DNA following ultrasonic treatment, and dilution-to-extinction PCR, which suggests up to a 100-1000-fold increase. The modular design of the ultrasonic system and integrated fluidics allow it to be incorporated into multi-step sample treatment and detection systems.
2009. "Quantum dot immunoassays in renewable surface column and 96-well plate formats for the fluorescence detection of Botulinum neurotoxin using high-affinity antibodies." Biosensors and Bioelectronics 25(1):179-184. Abstract A fluorescence sandwich immunoassay using high affinity antibodies and quantum dot (QD) reporters has been developed for detection of botulinum toxin serotype A (BoNT/A). For the development of the assay, a nontoxic recombinant fragment of the holotoxin (BoNT/A-HC-fragment) has been used as a structurally valid simulant for the full toxin molecule. The antibodies used, AR4 and RAZ1, bind to nonoverlapping epitopes present on both the full toxin and on the recombinant fragment. In one format, the immunoassay is carried out in a 96-well plate with detection in a standard plate reader. Detection down to 31 pM of the BoNT/Hc-fragment was demonstrated with a total incubation time of 3 hours, using AR4 as the capture antibody and QD-coupled RAZ1 as the reporter. In a second format, the AR4 capture antibody was coupled to Sepharose beads, and the immunochemical reactions were carried out in microcentrifuge tubes with an incubation time of 1 hour. These beads were subsequently captured and concentrated in a rotating rod “renewable surface” flow cell as part of a sequential injection fluidic system. This flow cell was equipped with a fiber optic system for fluorescence measurements. In PBS buffer solution matrix, the BoNT/A-HC-fragment was detected to concentrations as low as 5 pM using the fluidic measurement approach.
2009. "Reduction of Hg(II) to Hg(0) by Magnetite." Environmental Science & Technology 43(14):5307-5313. doi:10.1021/es9003608 Abstract Mercury (Hg) is a highly toxic element, and its contamination of groundwater presents a significant threat to terrestrial ecosystems. Understanding the geochemical processes that mediate mercury transformations in the subsurface is necessary to predict its fate and transport. In this study, we investigated the redox transformation of mercuric Hg (Hg[II]) in the presence of the Fe(II)/Fe(III) mixed valence iron oxide mineral magnetite. Kinetic and spectroscopic experiments were performed to elucidate reaction rates and mechanisms. The experimental data demonstrated that reaction of Hg(II) with magnetite results in the loss of Hg(II) and the formation of volatile elemental Hg (Hg[0]). Kinetic experiments showed that Hg(II) reduction occurred within minutes, with reaction rates increasing with increasing magnetite suspension density (0.05 to 0.2 g/L) and solution pH (4.8 to 6.7), and decreasing with increasing chloride concentration (10-6 to 10-2 mol/L). Mössbauer spectroscopic analysis of reacted magnetite samples revealed a decrease in Fe(II) content, corresponding the oxidation of Fe(II) to Fe(III) in the magnetite structure. X-ray photoelectron spectroscopy detected the presence of Hg(II) on magnetite surfaces, suggesting that adsorption is involved in the electron transfer process. These results suggest that Hg(II) reaction with solid-phase Fe(II) is a kinetically favorable pathway for Hg(II) reduction in magnetite-bearing environmental systems.
2009. "An automated tool for three types of saturated hydraulic conductivity laboratory measurements." Soil Science Society of America Journal 73(2):466-470. Abstract Acquisition of porous medium hydraulic conductivity in the laboratory is usually time-consuming and costly because of the manual labor associated with the currently available techniques. Lately, there has been increased interest in automating hydraulic conductivity laboratory techniques to reduce analysis time and improve data consistency. A new apparatus is presented that is able to determine hydraulic conductivity values with the falling head, constant head, and constant flux methods in an automated fashion. In addition, the columns are designed forcing water to flow in a nominally one-dimensional manner throughout the porous medium. In this paper, hydraulic conductivity data for standard laboratory sands are presented and compared to results obtained using a standard Tempe cell configuration. Hydraulic conductivity values obtained with the new tool for the laboratory sands are consistent with literature data. For highly permeable sands, the newly obtained hydraulic conductivity values are considerable larger then values acquired using a Tempe cell configuration. The lower conductivity values for the Tempe Cell configuration are primarily the result of insufficient spreading of water in the inlet and outlet reservoirs.
2009. "Long-Range Electron Transfer Across Cytochrome-Hematite (a-Fe2O3) Interfaces." Journal of Physical Chemistry C 113(6):2096-2103. Abstract Electrochemical scanning tunneling microscopy (EC-STM) was used to assess the distance dependence of electron tunneling facilitated by a bacterial multiheme cytochrome to a single crystal iron oxide surface. We measured tunneling current-distance (I-s) profiles across the nanoscale space between insulated Au STM tips and the basal (001) surface of a hematite (-Fe2O3) crystal, and compared them to the case in which an intervening small tetraheme cytochrome (STC) from Shewanella oneidensis covalently linked to the Au tip surface. Tunneling profiles were collected at constant surface potentials in solutions having a range of ionic strengths. At short tip-sample separation, the distance dependece of the tunneling current shows a quasi-linear behavior. At longer distances it shows an exponential decay. The different regions are discussed in terms of ordering of interfacial water and ion layers in the electrical double layer associated with the hematite surface. The effective tunneling range and its rate of decay are substantially increased when STC is present in the tunneling junction, suggesting that cytochrome molecules provide enhanced tunneling pathways and stronger electronic coupling to the hematite surface. Based on these results, cytochrome-mediated electron transfer during bacterial metal reduction may be possible at distances further than originally thought. Also, as multiheme cytochromes and other similar molecules gain attention for their promising role in fuel cells and molecular electronics, we show that the solution conditions and surface properties of the substrate must be carefully considered.
2009. "Geophysical Monitoring of Coupled Microbial and Geochemical Processes During Stimulated Subsurface Bioremediation." Environmental Science & Technology 43(17):6717–6723. Abstract Understanding how microorganisms alter their physical and chemical environment during bioremediation is hindered by our inability to resolve subsurface microbial activity with high spatial resolution. Here we demonstrate the use of a minimally invasive geophysical technique to monitor stimulated microbial activity during acetate amendment in an aquifer near Rifle, Colorado. During electrical induced polarization (IP) measurements, spatiotemporal variations in the phase response between imposed electric current and the resultant electric field correlated with changes in groundwater geochemistry accompanying stimulated iron and sulfate reduction and sulfide mineral precipitation. The magnitude of the phase response varied with measurement frequency (0.125 and 1 Hz) andwasdependent upon the dominant metabolic process. The spectral effect was corroborated using a biostimulated column experiment containing Rifle sediments and groundwater. Fluids and sediments recovered from regions exhibiting an anomalous phase response were enriched in Fe(II), dissolved sulfide, and cell-associated FeS nanoparticles. The accumulation of mineral precipitates and electroactive ions altered the ability of pore fluids to conduct electrical charge, accounting for the anomalous IP response and revealing the usefulness of multifrequency IP measurements for monitoring mineralogical and geochemical changes accompanying stimulated subsurface bioremediation.
2009. "Accelerated Testing of HT-9 with Zirconia Coatings Containing Gallium using Raman Spectroscopy and XPS." Journal of Nuclear Materials 395(1-3):23-29. doi:10.1016/j.jnucmat.2009.09.011 Abstract Laser Raman spectroscopy and x-ray photoelectron spectroscopy were used to study the evolution of composition of oxide films in the presence of zirconia coatings on miniature HT-9 alloy specimens subjected to elevated temperature in air. The experiments expanded on previous efforts to develop a quick-screening technique for candidate alloys for cladding materials (HT-9) and actinide-based mixed oxide fuel mixtures (represented by the zirconia coating) by investigating the effect of both coating composition and alloy pretreatment conditions on the high temperature reactions. In particular, the presence of the element Ga (a potential impurity in mixed oxide fuel) in the initial zirconia coating was found to accelerate the rate of oxide growth relative to that of yttria-stabilized zirconia studied previously. In addition, HT-9 samples that were subjected to different thermal pretreatments gave different results. The results suggest that the presence of Ga in a mixed oxide fuel will enhance the corrosion of HT-9 cladding under the conditions of this study, although the extent of enhancement is influenced by thermal pretreatment of the cladding material. The results also demonstrate the need to combine Raman spectroscopy with other techniques, particularly photoelectron spectroscopy, for optimizing composition and/or fabrication conditions of both cladding and oxide fuels for advanced nuclear reactors.
2009. "Raman and XPS characterization of fuel-cladding interactions using miniature specimens." Journal of Nuclear Materials 383(3):237-243. Abstract Laser Raman spectroscopy was evaluated as a tool for studying fuel-cladding chemical interactions at elevated temperatures. Materials and conditions were selected to simulate the interface of oxide fuels and fission products with high-temperature cladding materials for TRU-MOX fueled reactors. Both ex-situ and in-situ spectroscopy measurements were performed using polished HT-9 disks, uncoated and coated with yttria-stabilized zirconia, that were exposed to air oxidation at temperatures between 873-973K. Ex-situ measurements (under ambient conditions) were conducted to identify oxide phases, determine oxidation mechanisms and approximate film growth rates with an optimal signal-to-noise for the equipment used. Subsequently performed in-situ measurements were used to evaluate the sensitivity of the technique for measurements at elevated temperature in a hot-stage. Raman spectra were supported with x-ray photoelectron spectroscopy depth profiling. The results, which are for non-fueled materials in this study, illustrated a method for fast screening of candidate alloys with actinide-based MOX fuel mixtures.
2009. "Computational Nanoscience with NWChem." Journal of Computational and Theoretical Nanoscience 6(6 SP ISS):1297-1304. Abstract The NWChem software as been used to examine many nanoscale systems and their properties over the years. In this paper, an overiew of the general capabilities of NWChem is given as well as more specific details on the planewave and Gaussian based density functional codes usually used for nanoscale investigations. Examples are given of the scientific literature using NWChem, as well as two case studies: 1) Band gaps in oxides using exact-exchange based exchange-correlation functionals with the planewave DFT module, 2) Optical properties of chromophores using the Gaussian based DFT module.
2009. "Glucose Biosensor Based on Immobilization of Glucose Oxidase in Platinum Nanoparticles/Graphene/Chitosan Nanocomposite Film." Talanta 80(1):403-406. doi:10.1016/j.talanta.2009.06.054 Abstract The bionanocomposite film consisting of glucose oxidase/Pt/functional graphene sheets/chitosan (GOD/Pt/FGS/chitosan) for glucose sensing was described. With the electrocatalytic synergy of FGS and Pt nanoparticles to hydrogen peroxide, a sensitive biosensor with detection limit of 0.6 µM glucose was achieved. The biosensor also had good reproducibility, long term stability and negligible interfering signals from ascorbic acid and uric acid comparing to the response to glucose. The large surface area and good conductivity of graphene suggests that graphene is a potential candidate for sensor material. The hybrid nanocomposite glucose sensor provides new opportunity for clinical diagnosis and point-of-care applications.
2009. "An integrated top-down and bottom-up strategy for broadly characterizing protein isoforms and modifications." Journal of Proteome Research 8(3):1347-1357. Abstract We present an integrated top-down and bottom-up approach facilitated by concurrent liquid chromatography-mass spectrometry (LC-MS) analysis and fraction collection for comprehensive high-throughput intact protein profiling. The approach employs high resolution reversed phase (RP) LC separations coupled on-line with a 12T Fourier transform ion cyclotron resonance (FTICR) spectrometer to profile and tentatively identify modified proteins, using detected intact protein masses in conjunction with bare protein identifications from the bottom-up analysis of the same fraction. Selected identifications are incorporated into a target ion list for subsequent offline gas phase fragmentation that uses only an aliquot of the original fraction used for bottom-up analysis.
2009. "An integrated workflow for characterizing intact phosphoproteins from complex mixtures." Analytical Chemistry 81(11):4210-4219. doi:10.1021/ac802487q Abstract The phosphorylation of any site on a given protein can affect its activity, degradation rate, ability to dock with other proteins or bind divalent cations, and/or its localization. These effects can operate within the same protein; in fact, multisite phosphorylation is a key mechanism for achieving signal integration in cells. Hence, knowing the overall phosphorylation signature of a protein is essential for understanding the "state" of a cell. However, current technologies to monitor the phosphorylation status of proteins are inefficient at determining the relative stoichiometries of phosphorylation at multiple sites. Here we report a new capability for comprehensive liquid chromatography-mass spectrometry (LC-MS) analysis of intact phosphoproteins. The technology platform built upon integrated bottom-up and top-down approach that is facilitated by intact protein reversed-phase (RP)LC concurrently coupled with Fourier transform ion cyclotron resonance (FTICR) MS and fraction collection.
2009. "The basic function scheme of polynomial type." Applied Mathematics and Mechanics 30(9):1091-1103. doi:10.1007/s10483-009-0903-y Abstract A new numerical method---Basic Function Method is proposed. This method can directly discrete differential operator on unstructured grids. By using the expansion of basic function to approach the exact function, the central and upwind schemes of derivative are constructed. By using the second-order polynomial as basic function and applying the technique of flux splitting method and the combination of central and upwind schemes to suppress the non-physical fluctuation near the shock wave, the second-order basic function scheme of polynomial type for solving inviscid compressible flow numerically is constructed in this paper. Several numerical results of many typical examples for two dimensional inviscid compressible transonic and supersonic steady flow illustrate that it is a new scheme with high accuracy and high resolution for shock wave. Especially, combining with the adaptive remeshing technique, the satisfactory results can be obtained by these schemes.
