2009. "Mineralogical transformations controlling acid mine drainage chemistry." Chemical Geology 262(3-4):169-178. Abstract The role of Fe(III) minerals in controlling acid mine drainage (AMD) chemistry was studied using samples from two AMD sites [Gum Boot (GB) and Fridays-2 (FR)] located in northern Pennsylvania. Chemical extractions, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) were used to identify and characterize Fe(III) phases. The mineralogical analysis revealed that schwertmannite and goethite were the principal Fe(III) phases in the sediments. Schwertmannite transformation occurred at the GB site where poorly-crystallized goethite rich in surface-bound sulfate was initially formed. In contrast, no schwertmannite transformation occurred at the FR site. The goethite in GB sediments had spherical morphology due to preservation of schwertmannite structure by adsorbed sulfate. Results of chemical extractions showed that poorly-crystallized goethite was subject to further crystallization accompanied by sulfate desorption. Changes in sulfate speciation preceded its desorption, with a conversion of bidentate- to monodentate-bound sulfate surface complexes. Laboratory sediment incubation experiments were conducted to evaluate the effect of mineral transformation on water chemistry. Incubation experiments were carried out with schwertmannite-containing sediments and AMD waters with different pH and chemical composition. The pH decreased to 1.9-2.2 in all suspensions and the concentrations of dissolved Fe and S increased significantly. Regardless of differences in the initial water composition, pH, Fe and S were similar in suspensions of the same sediment. XRD measurements revealed that schwertmannite transformed into goethite in GB and FR sediments during laboratory incubation. The incubation experiment demonstrated that schwertmannite transformation controlled AMD water chemistry during “closed system” laboratory contact.
2009. "In situ Studies of Soft- and Reactive Landing of Mass-Selected Ions Using Infrared Reflection Absorption Spectroscopy." Analytical Chemistry 81(17):7302-7308. doi:10.1021/ac901149s Abstract Grazing incidence infrared reflection absorption spectroscopy (IRRAS) for in situ and in real time characterization of substrates modified by soft- and reactive landing (SL and RL) of complex ions was implemented on a mass-selected ion deposition instrument. Ions produced by electrospray ionization were mass-selected using a quadrupole mass filter and deposited onto inert and reactive self-assembled monolayer (SAM) surfaces. Surface composition during and after ion deposition was monitored using IRRAS. Physisorption of a cyclic peptide, Garmicidin S (GS), was studied for 8 hrs during deposition and additional 12 hrs after the end of deposition. The integrated signal of the characteristic amide bands followed a linear increase during the deposition and stayed unchanged after the deposition was finished. Similar linear increase in IRRAS signal was obtained following reactive deposition of the protonated dodecanediamine onto SAMs of dithiobis (succinimidyl undecanoate) (NHS-SAM) and 16-mercaptohexadecanoic acid fluoride (COF-SAM) on gold. IRRAS allowed us to monitor for the first time the formation of the amide bond between reactive SAM surfaces and the projectile molecule.
2009. "Passive Standoff Detection of RDX Residues on Metal Surfaces via Infrared Hyperspectral Imaging." Analytical and Bioanalytical Chemistry 395(2):337-348. doi:10.1007/s00216-009 Abstract Hyperspectral images of galvanized steel plates, each containing a stain of RDX, were recorded using a commercial longwave infrared imaging spectrometer. Demonstrations of passive RDX chemical detection at areal dosages between 16 and 90 µg / cm2 were carried out over practical stand-off ranges between 14 and 50 m. Efforts to develop better chemical anomaly and target detection through chemometric analyses are described.
2008. "Reactive Landing of Peptide Ions on Self-Assembled Monolayer Surfaces: A Alternative Approach for Covalent Immobilization of Peptides on Surfaces." Physical Chemistry Chemical Physics. PCCP 10(11):1512-1522. doi:10.1039/b717617a Abstract Soft landing of mass-selected peptide ions onto reactive self-assembled monolayer surfaces (SAMs) was performed using a newly constructed ion deposition apparatus. SAM surfaces before and after soft-landing were characterized ex situ using time of flight-secondary ion mass spectrometry (TOF-SIMS) and infrared reflection absorption spectroscopy (IRRAS). We demonstrate that reactive landing (RL) results in efficient covalent linking of lysine-containing peptides onto the SAM of N-hydroxysuccinimidyl ester terminated alkylthiol on gold (NHS-SAM). Systematic studies of the factors that affect the efficiency of RL revealed that the reaction takes place upon collision and is promoted by the kinetic energy of the ion. The efficiency of RL maximizes at ca. 40 eV collision energy. At high collision energies the RL efficiency decreases because of the competition with scattering of ions off the surface. The reaction yield is independent of the charge state of the projectile ions suggesting that peptide ions undergo efficient neutralization upon collision. Chemical and physical properties of the SAM surface are also important factors that affect the outcome of RL. The presence of chemically reactive functional groups on the SAM surface significantly improves the reaction efficiency. RL of mass- and energy-selected peptide ions on surfaces provides a highly specific approach for covalent immobilization of biological molecules onto SAM surfaces.
2008. "A cryogenic fluorescence spectroscopic study of uranyl carbonate, phosphate, and oxyhydroxide minerals." Radiochimica Acta 96(9-11):591-598. doi:10.1524/ract.2008.1541 Abstract In this work we have applied liquid-helium temperature (LHeT) time-resolved laser-induced fluorescence spectroscopy (TRLIF) to characterize a series of natural and synthetic minerals of uranium carbonate, phosphate and oxyhydroxides including rutherfordine, zellerite, liebigite, phosphuranylite, meta-autunite, meta-torbernite, uranyl phosphate, sodium-uranyl-phosphate, bequerelite, clarkeite, curite, schoepite and compregnacite, and compared their spectral characteristics among these minerals as well as our previously published data on uranyl silicates. For the carbonate minerals, the fluorescence spectra depend on the stoichiometry of the mineral. For the phosphate minerals the fluorescence spectra closely resemble each other despite the differences in their composition and structure. For all uranium oxyhydroxides, the fluorescence spectra are largely red-shifted as compared with those of the uranium carbonates and phosphates and their vibronic bands are broadened and less resolved. The much enhanced spectra resolution at LHeT allows more accurate calculation of the O=U=O symmetrical stretch frequency, ν1, corresponding to the average spacing of the vibronic peaks of the fluorescence spectra and the spectral origin as reflected by the position of the first vibronic band. It was found that both the average ν1 and λ1 values correlate well with the average basicity of the inorganic anion.
2008. "Nanoparticle-Based Electrochemical Immunosensor for the Detection of Phosphorylated Acetylcholinesterase: An Exposure Biomarker of Organophosphate Pesticides and Nerve AgentsOrganophosphate Pesticides and Nerve Agents ." Chemistry - a European Journal 14(32):9951-9959. doi:10.1002/chem.200800412 Abstract A nanoparticle-based electrochemical immunosensor has been developed for the detection of phosphorylated acetylcholinesterase (AChE) adducts, which is a potential exposure biomarker for organophosphate pesticides (OP) and chemical warfare nerve agent exposures. Zirconia nanoparticles (ZrO2 NPs) were used as selective sorbents to capture the phosphorylated AChE adduct, and quantum dots (ZnS@CdS, QDs) were used as tags to label monoclonal anti-AChE antibody to track the immunorecognition events. The sandwich-like immunoreactions were performed among the ZrO2 NPs, which were pre-coated on a screen printed electrode (SPE) by electrodeposition, phosphorylated AChE and QD-anti-AChE. The captured QD tags were determined on the SPE by electrochemical stripping analysis of its metallic component (cadmium) after an acid-dissolution step. Paraoxon was used as a model OP insecticide to prepare the phosphorylated AChE adduct to demonstrate the proof of principle for this sensor technology. The paraoxon-AChE adduct was characterized by Fourier Transform Infrared Spectrum, and the binding affinity of anti-AChE to the paraoxon-AChE was validated with an enzyme-linked immunosorbent assay. The parameters (e.g., amount of ZrO2 NP, QD-anti-AChE concentration,) that govern the electrochemical response of immunosensors were optimized. The voltammetric response of the immunosensor is highly linear over the range of 10 pM to 4 nM paraoxon-AChE, and the limit of detection is estimated to be 8 pM. This new nanoparticle-based electrochemical immunosensor thus provides a sensitive and quantitative tool for biomonitoring exposure to OP pesticides and nerve agents.
2008. "Hygroscopic Behavior of Substrate-Deposited Particles Studied by micro-FT-IR Spectroscopy and Complementary Methods of Particle Analysis." Analytical Chemistry 80(3):633-642. doi:10.1021/ac701638r Abstract The application of Microscopic Fourier Transform Infrared (micro-FTIR) spectroscopy combined with complementary methods of particle analysis is demonstrated here for investigations of phase transitions and hygroscopic growth of micron-sized particles. The approach utilizes the exposure of substrate-deposited, isolated particles to humidified nitrogen inside a sample cell followed by micro-FTIR spectroscopy over selected sample area. Phase transitions of NaCl, sea salt, NaNO3 and (NH)4SO4 particles are monitored with this technique to evaluate its utility and applicability for particle hydration studies. The results are found in excellent agreement with literature data in terms of (a) reliable and reproducible detection of deliquescence and efflorescence phase transitions, (b) quantitative measurements of water-to-solute ratios in particles as a function of relative humidity, and (c) changes in the IR spectra resulting from phase transitions and changing relative humidity. Additional methods of particle analysis are employed to complement and assist in the interpretation of particle hygroscopicity data obtained from micro-FTIR measurements. The analytical approach and the experimental setup presented here are relatively simple, inexpensive, readily available, and therefore may be practical for hydration studies of environmental particles collected in both laboratory and field studies.
2008. "Strategies for Detecting Organic Liquids on Soils Using Mid-Infrared Reflection Spectroscopy ." Environmental Science & Technology 42(15):5700-5705. doi:10.1021/es8005404 Abstract Stand-off monitoring for chemical spills can provide timely information for clean-up efforts and mid-infrared reflection-absorption spectroscopy is one approach being investigated. Anomaly and target detection strategies were examined for detection of four different low-volatility organic liquids on two different soil types. Several preprocessing and signal weighting strategies were studied. Anomaly detection for C−H bands was very good using second derivative preprocessing and provided similar performance to target detection approaches such as generalized least squares (GLS) and partial least squares (PLS) with detections at soil loads of approximately 0.6 to 1.5 mg/cm2. Good performance was also found for detection of P=O, O–H and C=O bands but the optimal strategy varied. The simplicity and generality of anomaly detection is attractive, however target detection provides more capability for classification.
2008. "Detection of Low Volatility Organic Analytes on Soils Using Infrared Reflection Spectroscopy." Journal of Near Infrared Spectroscopy 16(3):179-187. doi:10.1255/jnirs.776 Abstract Previous work on detection of low-volatility liquid organic (and organophosphorus) analytes on soil indicated strong signal in FTIR spectra in the 2966–2855 cm-1 range attributed to C–H vibrational stretching modes. This range is the focus of detection strategies examined here as an anticipated prelude to subsequent detection and classification approaches utilizing additional spectral bands. This laboratory study is being used to test detection algorithms that may be useful for rapid standoff detection of organics compounds on soil. Six signal processing methods (designed to minimize irrelevant variability in the recorded soil reflection-absorption spectra while enhancing signal from analyte compounds possibly present on soil) were studied. These included Savitzky-Golay second derivatives, extended multiplicative scatter correction (EMSC), and a novel alternative to piece-wise EMSC. The preprocessed signal was then used for detection. Previous work utilized principal components analysis (PCA) based multivariate statistical process control methodologies for detection. Six alternative anomaly detection statistics were examined here that were based on the preprocessed signal, weighted signal, and generalized weighted signal. The latter statistic can be considered easier than PCA with many of the same benefits. Two tests corresponding to different monitoring strategies were examined: test data ‘local’ and ‘non-local’ to the calibration data. Although the results are expected to be optimistic, the generalized weighted approach worked extremely well for the ‘local’ detection test, but was less successful for ‘non-local’ test. Results suggest that good characterization of analyte-free soil prior to monitoring will lead to the best detection performance. Second derivative preprocessing showed the best results on receiver operator characteristic curves and it’s ease of application is a distinct advantage. However, it may not be universally successful for all bands to be considered in the future. Both EMSC and the novel ‘piece-wise’ EMSC methodology showed promise, but some improvements may be necessary.
2008. "Spectroscopic Characterization of Extracellular Polymeric Substances from Escherichia coli and Serratia marcescens: Suppression using Sub-Inhibitory Concentrations of Bismuth Thiols." Biomacromolecules 9(11):3079-3089. doi:10.1021/bm800600p Abstract Free and capsular EPS produced by Escherichia coli and Serratia marcescens were characterized in detail using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). Total EPS production decreased upon treatment with sub-inhibitory concentrations of lipophilic bismuth thiols (bismuth dimercaptopropanol, BisBAL; bismuth ethanedithiol, BisEDT; and bismuth pyrithione, BisPYR), BisBAL being most effective. Bismuth thiols also influenced acetylation and carboxylation of polysaccharides in EPS from S. marcescens. Extensive homology between EPS samples in the presence and absence of bismuth was observed with proteins, polysaccharides, and nucleic acids varying predominantly only in the total amount expressed. Second derivative analysis of the amide I region of FTIR spectra revealed decreases in protein secondary structures in the presence of bismuth thiols. Hence, anti-fouling properties of bismuth thiols appear to originate in their ability to suppress O-acetylation and protein secondary structures in addition to total EPS secretion.
2008. "Bismuth Dimercaptopropanol (BisBAL) Inhibits the Expression of Extracellular Polysaccharides and Proteins by Brevundimonas diminuta: Implications for Membrane Microfiltration." Biotechnology and Bioengineering 99(3):634-643. doi:10.1002/bit.21615 Abstract A 2:1 molar ratio preparation of bismuth with a lipophilic dithiol (3-dimercapto-1-propanol, BAL)significantly reduced extracellular polymeric substances (EPS) expression by Brevundimonas diminuta in suspended cultures at levels just below the minimum inhibitory concentration (MIC). Total polysaccharides and proteins secreted by B. diminuta decreased by approximately 95% over a 5-day period when exposed to the bismuth-BAL chelate (BisBAL) at near MIC (12 μM). Fourier-transform infrared spectroscopy (FTIR) suggested that a possible mechanism of biofilm disruption by BisBAL is the inhibition of carbohydrate Oacetylation. FTIR also revealed extensive homology between EPS samples with and without BisBAL treatment, with proteins, polysaccharides, and peptides varying predominantly only in the amount expressed. EPS secretion decreased following BisBAL treatment as verified by atomic force microscopy and scanning electron microscopy. Without BisBAL treatment, a slime-like EPS matrix secreted by B. diminuta resulted in biofouling and inefficient hydrodynamic backwashing of microfiltration membranes.
2007. "Mixed-Valent Fe Films ('Schwimmeisen') on the Surface of Reduced Ephemeral Pools." Clays and Clay Minerals 55(6):635-643. doi:10.1346/CCMN.2007.0550610 Abstract Floating, mixed-valent Fe films have been observed worldwide in wetlands, ferrous iron rich seeps, and in seasonally reduced soils, but are usually misidentified as oil or biofilms. Little characterization or explanation to their formation has taken place. Along the Oregon coast such films were found on ephemeral pools where Fe(II) rich groundwater (~ 100 μM Fe) discharged at the base of Pleistocene sand dunes. Fe(II) oxidized to Fe(III) at the air-water interface to form ~ 100 to 300nm thick films. Analyses indicated that the films contained both Fe(III) and Fe(II) in a ratio of 3:1. Si was the other main cation, OH was the main anion and some C was identified as well. The film morphology was flat, under optical and electron microscopy with some attached floccules having a stringlike morphology. Energy filtered electron diffraction patterns (EFED) showed three diffraction rings at 4.5, 2.6, and 1.4 Å in some places and 2 rings (2.6 and 1.4 Å) in others. Upon further oxidation the films became 2-line ferrihydrite. We are proposing the name „Schwimmeisen“ for the floating, mixed-valent Fe film.
2006. "Quantification of Volatile Organics in Soil Aging Experiments Using Fourier Transform Infrared Spectroscopy." Applied Spectroscopy 60(8):914-919. doi:10.1366/000370206778062156 Abstract Soil aging may have a significant influence on the success of environmental remediation strategies and the accuracy of numerical models that estimate contaminant transport. The focus of this study was to define the ability of online Fourier transform infrared (FT-IR) spectroscopy to monitor the concentration of halogenated volatile organic compounds in a process that simulates long-term slow accumulation of contaminants in soils.
2006. "Multivariate Curve Resolution Applied to Infrared Reflection Measurements of Soil Contaminated with an Organophosphorus Analyte." Applied Spectroscopy 60(7):713-722. doi:10.1366/000370206777887026 Abstract Multivariate curve resolution (MCR) is a powerful technique for extracting chemical information from measured spectra on complex mixtures. The difficulty with applying MCR to soil reflectance measurements is that light scattering artifacts can contribute much more variance to the measurements than the analyte(s) of interest. Two methods were integrated into a MCR decomposition to account for light scattering effects. Firstly, an extended mixture model using pure analyte spectra augmented with scattering ‘spectra’ was used for the measured spectra. And secondly, second derivative preprocessed spectra, which have higher selectivity than the unprocessed spectra, were included in a second block as a part of the decomposition. The conventional alternating least squares (ALS) algorithm was modified to simultaneously decompose the measured and second derivative spectra in a two-block decomposition. Equality constraints were also included to incorporate information about sampling conditions. The result was an MCR decomposition that provided interpretable spectra from soil reflectance measurements.
2005. "Fluorescence Spectroscopy of U(VI)-Silicates and U(VI)-Contaminated Hanford Sediment." Geochimica et Cosmochimica Acta 69(6):1391-1403. doi:10.1016/j.gca.2004.08.028 Abstract Time-resolved U(VI) laser fluorescence spectra (TRLFS) were recorded for a series of natural uranium-silicate minerals including boltwoodite, uranophane, soddyite, kasolite, sklodowskite, cuprosklodowskite, haiweeite, and weeksite, a synthetic boltwoodite, and four U(VI)-contaminated Hanford vadose zone sediments. Lowering the sample temperature from RT to ~ 5.5 K significantly enhanced the fluorescence intensity and spectral resolution of both the minerals and sediments, offering improved possibilities for identifying uranyl species in environmental samples. At 5.5 K, all of the uranyl silicates showed unique, well-resolved fluorescence spectra. The symmetric O=U=O stretching frequency, as determined from the peak spacing of the vibronic bands in the emission spectra, were between 705 to 823 cm-1 for the uranyl silicates. These were lower than those reported for uranyl phosphate, carbonate, or oxy-hydroxides. The fluorescence emission spectra of all four sediment samples were similar to each other. Their spectra shifted minimally at different time delays or upon contact with basic Na/Ca-carbonate electrolyte solutions that dissolved up to 60 % of the precipitated U(VI) pool. The well-resolved vibronic peaks in the fluorescence spectra of the sediments indicated that the major fluorescence species was a crystalline uranyl mineral phase, while the peak spacing of the vibronic bands pointed to the likely presence of uranyl silicate. Although, an exact match was not found between the U(VI) fluorescence spectra of the sediments with that of any individual uranyl silicates, the major spectral characteristics indicated that the sediment U(VI) was a uranophane-type solid (uranophane, boltwoodite) or soddyite, as was concluded from microprobe, EXAFS, and solubility analyses.
2005. "Kinetic Desorption and Sorption of U(VI) During Reactive Transport in a Contaminated Hanford Sediment." Environmental Science and Technology 39(9):3157-3165. doi:10.1021/es048462q Abstract Column experiments were conducted to investigate U(VI) desorption and sorption kinetics in a sand-textured, contaminated (22.7 µmol kg-1) capillary fringe sediment that had experienced long-term exposure to U(VI). The clay fraction mineralogy of the sediment was dominated by montmorillonite, muscovite, vermiculite, and chlorite. Saturated column experiments were performed under mildly alkaline/calcareous conditions representative of the Hanford site where uranyl–carbonate and calcium–uranyl–carbonate complexes dominate aqueous speciation. A U(VI) free solution was used to study U(VI) desorption in columns where different flow rates were applied. Uranium(VI) sorption was studied after the desorption of labile contaminant U(VI) using different U(VI) concentrations in the leaching solution. Strong kinetic behavior was observed for both U(VI) desorption and sorption. Although U(VI) is semi–mobile in mildly alkaline, calcareous subsurface environments, our results showed substantial U(VI) sorption, significant retardation during transport, and atypical breakthrough curves with extended tailing. A distributed rate model was applied to describe the effluent data and to allow comparisons between the desorption rate of contaminant U(VI) with the rate of short-term U(VI) sorption. Desorption was the slower process. Our results suggest that U(VI) release and transport in the vadose zone and aquifer system from which the sediment was obtained are kinetically controlled.
2005. "Application of Extended Inverse Scatter Correction to Mid-Infrared Reflectance Spectra of Soil." Journal of Chemometrics 19(5-7):271-281. doi:10.1002/cem.929 Abstract Scattering artifacts adversely affect infrared reflectance measurements of powders and soils, and extended inverse scatter correction (EISC) is a flexible method useful for correcting for these artifacts. EISC was used to correct mid-infrared reflectance spectra of two different soils coated with dibutyl phosphate and the results were examined using regression analysis. To determine the correction, EISC fits a measured spectrum to a reference spectrum. However, if measured spectra contain features not included in the reference spectrum the fit can be biased resulting in poor correction. Weighted and robust least squares were used to account for these potential biases. Additionally, the present work demonstrates how analyte-free samples can be used to determine basis functions for an extended mixture model used in the correction. Corrected spectra resulted in partial least squares models that performed at least as well as 2nd derivative spectra and were more interpretable.
2005. "Impact of Highly Basic Solutions on Sorption of Cs+ to Subsurface Sediments from the Hanford Site, USA." Geochimica et Cosmochimica Acta 69(20):4787-4800. Abstract The effect of caustic NaNO3 solutions on the sorption of 137Cs to the Hanford site micaceous subsurface sediment was investigated as a function of time, temperature (10oC or 50oC), and NaOH concentration. At 100C and 0.1 M NaOH, the slow evolution of [Al]aq was in stack contrast to the rapid increase and subsequent loss of [Al]aq observed at 50oC (regardless of base concentration). At 50oC, dissolution of phyllosilicate minerals increased with [OH], at 1 and 3 M NaOH solutions, almost complete dissolution of clay-sized phyllosilicates occurred. At 0.1 M NaOH, a zeolite (tetranatrolite) precipitated after about 7 days, while an unnamed mineral phase (Na2Al2Si3O10•2H2O) precipitated after 4 and 2 days of exposure to 1 M and 3 M NaOH solutions. At 100C there was no conclusive evidence of secondary mineral precipitation. The effect of base dissolution on Cs+ sorption by the Hanford sediment was investigated via i) Cs+ sorption over a large concentration range (10-9 – 10-2 mol/L) to sediment after exposure to 0.1 M NaOH for 56, 112, and 168 days, ii) Cs+ sorption to sediment in the presence of NaOH (0.1 M, 1 M, and 3 M NaOH) at Cs+ concentrations selected to probe high affinity, transition, and low affinity cation exchange sites, and iii) the application of a two-site numeric ion exchange model (Zachara et al. 2002a). No effect on Cs+ sorption to the Hanford sediment was observed during the 168 days sediment was exposed to 0.1 M NaOH, at 10oC; Cs+ sorption in the presence of base was well described by the ion exchange model when enthalpy effects were considered. In contrast, at 50oC, there was a trend toward slightly lower (log ~ 0.25) conditional equilibrium exchange constants over the entire range of surface coverage, and a slight loss of high affinity sites (15%) after 168 days of exposure to 0.1 M base solution. However, model simulations of Cs+ sorption to the sediment in the presence of 0.1 M base for 112 days were good at the lower Cs+ surface densities. At the higher surface densities, model simulations under predicted sorption by 57%. This under prediction was surmised to be the result of tetranatrolite precipitation, and subsequent slow Na → Cs exchange. At higher OH concentrations, Cs+ sorption in the presence of base for 112 days was unexpectedly equal to, or slightly greater than that expected for a pristine sediment. The presence of neoforms, coupled with the fairly unique mica distribution and quantity across all size-fractions in the Hanford sediment, appears to mitigate the impact of base dissolution on Cs+ sorption.
2004. "Biogeochemical Transformation of Fe Minerals in a Petroleum-Contaminated Aquifer." Geochimica et Cosmochimica Acta 68(8):1791-1805. Abstract Biogeochemical Transformation of Fe Minerals in a Petroleum-Contaminated Aquifer
2004. "Cryogenic Laser Induced Fluorescence Characterization of U(VI) in Hanford Vadose Zone Pore Waters." Environmental Science and Technology 38:5591-5597. Abstract Ambient and liquid helium temperature laser-induced time-resolved uranyl fluorescence spectroscopy was applied to study the speciation of aqueous uranyl solutions containing carbonate and phosphate and two porewater samples obtained by ultra-centrifugation of U(VI)-contaminated sediments. The significantly enhanced fluorescence signal intensity and spectral resolution found at liquid helium temperature allowed, for the first time, direct fluorescence spectroscopic observation of the higher aqueous uranyl complexes with carbonate: UO2(CO3)22-, UO2(CO3)34- and (UO2)2(OH)3CO3-. The porewater samples were non-fluorescent at room temperature. However, at liquid helium temperature, both porewater samples displayed strong, well-resolved fluorescence spectra. Comparisons of the spectroscopic characteristics of the porewaters with those of the standard uranyl-carbonate complexes confirmed that U(VI) in the porewaters existed primarily as UO2(CO3)34-. A small amount of the dicalcium-urano-tricarbonate complex, Ca2UO2(CO3)3, was also observed that was consistent with thermodynamic calculation. The U(VI)-carbonate complex is apparently the mobile species responsible for the subsurface migration of U(VI), even though the majority of the in-ground U(VI) inventory at the site from which the samples were obtained exists as intragrain U(VI)-silicate precipitates.
2003. "The Formation of Sr Silicates at Low Temperature and the Solubility Product of Tobermorite-like Sr5Si6O16(OH)2 5H20." American Mineralogist 88(1):73-79. Abstract The Formation of Strontium Silicates at Low Temperature and the Solubility Product of Tobermorite like Sr5Si6O16(OH)2 5H20
2003. "3-D Structural Modeling of Humic Acids through Experimental Characterization, Computer Assisted Structure Elucidation and Atomistic Simulations. 1. Chelsea Soil Humic Acid." Environmental Science and Technology 37(9):1783-1793. Abstract This paper describes an integrated experimental and computational framework for developing 3-D structural models for humic acids (HAs). This approach combines experimental characterization, computer assisted structure elucidation (CASE), and atomistic simulations to generate all 3-D structural models or a representative sample of these models consistent with the analytical data and bulk thermodynamic/structural properties of HAs. To illustrate this methodology, structural data derived from elemental analysis, diffuse reflectance FT-IR spectroscopy, 1-D/2-D | 1H and 13C solution NMR spectroscopy, and electrospray ionization quadrupole time-of-flight mass spectrometry (ESI QqTOF MS) are employed as input to the CASE program SIGNATURE to generate all 3-D structural models for Chelsea soil humic acid (HA). These models are subsequently used as starting 3-D structures to carry out constant temperature-constant pressure molecular dynamics simulations to estimate their bulk densities and Hildebrand solubility parameters. Surprisingly, only a few model isomers are found to exhibit molecular compositions and bulk thermodynamic properties consistent with the experimental data. The simulated 13C NMR spectrum of * Corresponding author phone: (626)395-2730; fax: (626)585-0918; e-mail: diallo@wag.caltech.edu and mdiallo@howard.edu. Present address: Materials and Process Simulation Center,BeckmanInstitute 139-74, California Institute of Technology, Pasadena, CA 91125. † California Institute of Technology. ‡ Howard University. § University of Toronto. Pacific Northwest National Laboratory. ^ Sandia National Laboratories. # The Ohio State University. ã xxxx American Chemical Society PAGE EST: 11 10.1021/es0259638 CCC: $25.00 Published on Web 00/00/0000 an equimolar mixture of these model isomers compares favorably with the measured spectrum of Chelsea soil HA.
2002. "Sorption of Cs+ to Micaceous Subsurface Sediments from the Hanford Site, USA." Geochimica et Cosmochimica Acta 66(2):193-211. Abstract Sorption of Cs+ to Micaceous Subsurface Sediments from the Hanford Site, USA
2002. "Spectroscopic Investigations of the Structural Phase Transition in Gd2(Ti1-yZry)(2)O-7 Pyrochlores ." Journal of Physical Chemistry B 106(18):4663-4677. Abstract The Gd2(Ti1-yZry)2O7 pyrochlore series undergoes a structural phase transition from pyrochlore (Fd?3m) to defect fluorite (Fm?3m) that can be driven compositionally by increasing the Zr content or thermally by sintering Zr-rich compositions at temperatures above 1550 ?C. Our results demonstrate that ion-beam irradiation can also drive the structural phase transition for Zr-rich compositions. In an effort to understand the effects of composition and ion-beam irradiation on this phase transition, powder X-ray diffraction, polarized Raman, reflection infrared, and X-ray absorption spectroscopy experiments were conducted on Gd2(Ti1-yZry)2O7 pyrochlores prior to and following irradiation with 2 MeV Au2+ ions to a fluence of 5 ions/nm2. Analysis of the vibrational and X-ray absorption data suggests that the structural integrity of the pyrochlore structure is based on distorted corner-shared TiO6 or ZrO6 octahedra. The vibrational spectra indicate that both anion and cation disorder precede the compositionally-driven phase transition, while cation disorder appears to dominate the irradiation-driven transition. Analyses of the extended X-ray absorption fine structure of the Ti and Zr K-edges and the Gd LIII-edges reveal a significant change in the Gd local environment upon irradiation and with increasing Zr content. The Ti and Zr local environments are less affected by irradiation or compositional change, but show evidence of increasing disorder that can be attributed to rotations about shared polyhedral edges and corners.
2001. "Solubilization of Fe(III) Oxide-Bound Trace Metals by a Dissimilatory Fe(III) Reducing Bacterium." Geochimica et Cosmochimica Acta 65(1):75-93.
2000. "Kinetics and Mechanism of Surface Reaction of Salicylate on Alumina in Colloidal Aqueous Suspension ." Geochimica et Cosmochimica Acta 64(7):1159-1172. Abstract N/A
1998. "Bacterial Reduction of Crystalline Fe3+ Oxides in Single Phase Suspensions and Subsurface Materials." American Mineralogist 83(11-12):1426-1443. Abstract There is no abstract currently available for this item