NMR Spectrometer: 500 MHz NB CMX for Liquids (and solids) Publications

2009

O'Hara MJ, SR Burge, and JW Grate. 2009. "Quantification of Technetium-99 in Complex Groundwater Matrixes using a Radiometric Preconcentrating Minicolumn Sensor in an Equilibration-based Sensing Approach." Analytical Chemistry 81(3):1068-1078. Abstract A preconcentrating minicolumn sensor for pertechnetate detection in water consists of a packed bed containing a mixture of anion exchange resin and scintillating plastic beads. The column materials are contained in a transparent plastic flow cell placed between two photomultiplier tubes for radiometric detection. Upon retention of pertechnetate anions, the radioactive decay of Tc-99 results in detectable scintillation pulses that are counted in coincidence. In equilibration-based sensing mode, the sample is pumped through the packed bed until complete chromatographic equilibrium is achieved between the activity concentration in the water sample and the concentration on the anion exchange resin. The analytical signal is the observed steady state count rate at equilibrium. The sensitivity is related to a measurement efficiency parameter that is the product of the retention volume and the absolute radiometric detection efficiency. This sensor can readily detect pertechnetate to levels ten times below the drinking water standard of 0.033 Bq/mL. The potential for other anions in natural groundwater and contaminated groundwater plumes to interfere with pertechnetate detection and quantification have been examined in detail, with reference to the groundwater chemistry at the Hanford Site in Washington State. Individual anions such as nitrate, carbonate, chloride and iodide, at natural or elevated concentrations, do not interfere significantly with pertechnetate uptake on the anion exchange resin. Elevated chromate or sulfate anion concentrations can interfere with pertechnetate uptake by the resin, but only at levels substantially higher than typical concentrations in groundwater or contamination plumes. Nevertheless, elevated anion concentrations may reduce pertechnetate uptake and sensitivity of the sensor when present in combination. Chromate is retained on the anion exchange resin from water at ppb levels, leading to an orange stain that interferes with pertechnetate detection by the absorption of scintillation light pulses (color quench). Radioactivity from radioiodine, tritium, and uranium are not expected to create a significant positive bias in groundwater analyses. A method of automated fluidic standard addition is demonstrated that corrects for matrix interferences leading to accurate analyses over a wide range of groundwater compositions.

2008

Pierce EM, EA Rodriguez, LJ Calligan, WJ Shaw, and BP McGrail. 2008. "An Experimental Study of the Dissolution Rates of Simulated Aluminoborosilicate Waste Glasses as a Function of pH and Temperature under Dilute Conditions." Applied Geochemistry 23(9):2559-2573. doi:10.1016/j.apgeochem.2008.05.006 Abstract Single-pass flow-through tests were conducted to determine the pH (7 - 12) and temperature (23- 90°C) dependence of kinetic rate-law parameters; ko, η, and Ea, for the dissolution of glass in aqueous solution. Experiments were performed with three prototypic nuclear waste glasses that span a wide compositional range, which covers, with high probability, the expected processing composition range for candidate immobilized low-activity waste (ILAW) glasses. Comparison of the B to Na release rates for one glass was incongruent at 23 and 40°C, and pH(23°C) = 7.0 and 8.0, suggesting two distinct mechanisms are responsible for the Na+ release, namely Na+-H+ ion exchange and matrix dissolution. Matrix dissolution became the dominant dissolution mechanism for all glasses at pH values greater than 9.0 as evident by the congruent release of Al, B, Na, and Si to solution. By combining the results collected for each ILAW glass at pH values greater than 9.0, pH and temperature dependent rate law parameters were determined for Al, B, Na, and Si release. A comparison of the pH power-law coefficient for Al, B, Na, and Si at each temperature suggest that η does not depend on temperature within experimental error and suggests the release of these elements into solution is controlled by the same dissolution mechanism at the forward rate of reaction. The activation energy (Ea), based on B release, range from 52 ±4 to 56 ±6 kJ/mol which suggest that dissolution is a surface-controlled reaction mechanism. The data presented in this manuscript suggest that for these three ILAW glasses the chemical durability for each glass is relatively the same under these test conditions. A lack of compositional dependence on the dissolution rate is observed even though there is as much as a 39 kJ/mol difference in the free energy of hydration (ΔGhyd) among the borosilicate waste glasses tested. This similarity in dissolution rate despite the large ΔGhyd difference is almost certainly the result of the structural similarities between these glasses, which suggests that ILAW glasses have similar, if not identical, polymerization states. This is evident from their almost identical 29Si chemical shifts and molar ratio of the alkali elements, Σ(Na+ K + Li), to the network former elements, Σ(AlIV + BIV + Fe + Si), contained in each glass. The polymerization state is an indication of the number of framework SiO4 linkages contained in the glass network. In general, the greater the number of framework SiO4 linkages the more durable the glass. Finally, in agreement with previous work, these results suggest breakage of the Si-O bond is the rate-determining dissolution mechanism under alkaline conditions [pH(23°C) > 9.0] far from saturation with respect to a alteration phase or phases.
Pierce EM, EL Richards, AM Davis, LR Reed, and EA Cordova. 2008. "Aluminoborosilicate Waste Glass Dissolution under Alkaline Conditions at 40°C: Implications for a Chemical Affinity-Based Rate Equation." Environmental Chemistry 5(1):73-85. doi:10.1071/EN07058 Abstract Single-pass flow-through (SPFT) experiments were conducted with aluminoborosilicate waste glasses to evaluate how changes in solution composition affect the dissolution rate (r) at 40°C and pH(23°C) = 9.0. The three prototypic low-activity waste (LAW) glasses; LAWE-1A, -95A, and -290A, used in these experiments span a wide range covering the expected processing composition of candidate immobilized low-activity waste (ILAW) glasses. Results suggest incongruent release of Al, B, Na, and Si at low flow-rate (q) to sample surface area (S) [log10 (q/S) < -8.9 (m s-1)] whereas congruent release was observed at high q/S [log10 (q/S) > -7.9 (m s-1)]. Dissolution rates increase from log10 (q/S) ≈ -9.3 to -8.0 (m s-1) and then become constant at log10 (q/S) > -7.9 (m s-1). Forward (maximum) dissolution rates, based on B release, are the same irrespective of glass composition, evident by the dissolution rates being within the experimental error of one another (r1A = 0.0301 ±0.0153 g m-2 d-1, r95A = 0.0248 ±0.0125 g m-2 d-1, and r290A = 0.0389 ±0.0197 g m-2 d-1). Finally these results support the use of a chemical affinity based rate law to describe glass dissolution as a function of solution composition.
Icenhower JP, BP McGrail, WJ Shaw, EM Pierce, P Nachimuthu, DK Shuh, EA Rodriguez, and JL Steele. 2008. "Experimentally determined dissolution kinetics of Na-rich borosilicate glass at far from equilibrium conditions: Implications for Transition State Theory." Geochimica et Cosmochimica Acta 72(12):2767-2788. doi:10.1016/j.gca.2008.02.026 Abstract Abstract—The dissolution kinetics of five chemically complex and two chemically simple borosilicate glass compositions (Na-B-Si±Al) were determined over a range of solution saturation values by varying the flow-through rates (1 to 100 mL d-1) in a dynamic single-pass flow-through (SPFT) apparatus. The chemically complex borosilicate glasses are representative of prospective hosts for radioactive waste disposal and are characterized by relatively high molar Si/(Si+Al) and Na/(Al+B) ratios (>0.7 and >1.0, respectively). Analysis by x-ray absorption spectroscopy (XAS) indicates that the fraction of ivB to iiiB (N4) varies from 0.66 to 0.70. Despite large differences in bulk chemistry, values of  29Si peak shift determined by MAS-NMR varies only by about 7 ppm (29Si = -94 to -87 ppm), indicating small differences in polymerization state for the glasses. Forward rates of reaction measured in dynamic experiments converge (average log10 rate [40°C, pH 9] = -1.87±0.79 [g/(m2•d)]) at high values of flow-rate (q) to sample surface area (S). Dissolution rates are independent of total Free Energy of Hydration (FEH) and this model appears to overestimate the impact of excess Na on chemical durability. For borosilicate glass compositions in which molar Na > Al + B, further addition of Na appears to stabilize the glass structure with respect to hydrolysis and dissolution. Compared to other borosilicate and aluminosilicate glasses, the glass specimens from this study dissolve at nearly the same rate (0 to ~55×) as the more polymerized glasses, such as vitreous reedmergnerite (NaBSi3O8), albite, and silica. Dissolution of glass follows the order: boroaluminosilicate glass > vitreous reedmergnerite > vitreous albite > silica glass, which is the same order of increasingly negative 29Si chemical shifts. The chemical shift of 29Si is a measure of the extent of bond overlap between Si and O and correlates with the forward rate of reaction. Thus, dissolution appears to be rate-limited by rupture of the Si—O bond, which is consistent with the tenants of Transition State Theory (TST). Therefore, dissolution at far from equilibrium conditions is dependent upon the speed of the rate-controlling elementary reaction and not on the sum of the free energies of hydration of the constituents of boroaluminosilicate glass.
Metz TO, JS Page, ES Baker, K Tang, J Ding, Y Shen, and RD Smith. 2008. "High Resolution Separations and Improved Ion Production and Transmission in Metabolomics." Trends in Analytical Chemistry. TrAC 27(3):205-214. doi:10.1016/j.trac.2007.11.003 Abstract The goal of metabolomics experiments is the detection and quantitation of as many sample components as reasonably possible in order to identify “features” that can be used to characterize the samples under study. When utilizing electrospray ionization to produce ions for analysis by mass spectrometry (MS), it is imperative that metabolome sample constituents be efficiently separated prior to ion production, in order to minimize the phenomenon of ionization suppression. Similarly, optimization of the MS inlet can lead to increased measurement sensitivity. This review will focus on the role of high resolution liquid chromatography (LC) separations in conjunction with improved ion production and transmission for LC-MS-based metabolomics.
Verrier CLM, JH Kwak, DH Kim, CHF Peden, and J Szanyi. 2008. "NOx uptake on alkaline earth oxides (BaO, MgO, CaO and SrO) supported on γ-Al2O3." Catalysis Today 136(1-2):121-127. doi:doi:10.1016/j.cattod.2007.12.138 Abstract NOx uptake experiments were performed on a series of alkaline earth oxide (AEO) (MgO, CaO, SrO, BaO) on γ-alumina materials. Temperature Programmed Desorption (TPD) conducted on He flow revealed the presence of two kinds of nitrate species: i.e. bulk and surface nitrates. The ratio of these two types of nitrate species strongly depends on the nature of the alkaline earth oxide. The amount of bulk nitrate species increases with the basicity of the alkaline earth oxide. This conclusion was supported by the results of infrared and 15N solid state NMR studies of NO2 adsorption. Due to the low melting point of the precursor used for the preparation of MgO/Al2O3 material (Mg(NO3)2), a significant amount of Mg was lost during sample activation (high temperature annealing) resulting in a material with properties were very similar to that of the γ-Al2O3 support. The effect of water on the NOx species formed in the exposure of the AEO-s to NO2 was also investigated. In agreement with our previous findings for the BaO/γ-Al2O3 system, an increase of the bulk nitrate species and the simultaneous decrease of the surface nitrate phase were observed for all of these materials.
Kim DH, JH Kwak, X Wang, J Szanyi, and CHF Peden. 2008. "Sequential high temperature reduction, low temperature hydrolysis for the regeneration of sulfated NOx trap catalysts." Catalysis Today 136(1-2):183-187. doi:doi:10.1016/j.cattod.2007.12.134 Abstract We describe a new method that minimizes irreversible Pt sintering during the desulfation of sulfated Pt/BaO/Al2O3 lean NOx trap (LNT) catalysts. While it is known that the addition of H2O to H2 promotes desulfation, we find that the significant and irreversible Pt sintering arising from the presence of water is unavoidable. Control of precious metal sintering is considered to be one of the critical issues in the development of durable LNT catalysts. The new method described here is a sequential desulfation process: the first step is to reduce the sulfates with hydrogen only at higher temperatures to form BaS, followed by a treatment of the thus reduced sample with water at low to moderate temperatures to convert BaS to BaO and H2S. The data showed that Pt sintering was significantly inhibited due to the absence of H2O during the desulfation at high temperatures, and also demonstrates the similar NOx uptake with the desulfated sample cooperatively with H2 and H2O. Therefore, the sequential desulfation process may find applications in realistic systems to inhibit the irreversible sintering of the Pt in the lean NOx trap catalyst, leading to a longer catalyst life.
Kim DH, JH Kwak, J Szanyi, SJ Cho, and CHF Peden. 2008. "Roles of Pt and BaO in the Sulfation of Pt/BaO/Al2O3 Lean NOx Trap Materials: Sulfur K-edge XANES and Pt LIII XAFS Studies." Journal of Physical Chemistry C 112(8):2981-2987. doi:10.1021/jp077563i Abstract The roles of barium oxide and platinum during the sulfation of Pt-BaO/Al2O3 lean NOx trap catalysts were investigated by S K edge XANES (X-ray absorption near-edge spectroscopy) and Pt LIII XAFS (X-ray absorption fine structure). All of the samples studied (Al2O3, BaO/Al2O3, Pt/Al2O3 and Pt-BaO/Al2O3) were pre-sulfated prior to the X-ray absorption measurements. It was found that barium oxide itself has the ability to directly form barium sulfate even in the absence of Pt and gas phase oxygen. In the platinum-containing samples, the presence of Pt-O species plays an important role in the formation of sulfate species. Even if barium and aluminum sites are available for SO2 to form sulfate, for the case of the BaO(8)/Al2O3 sample, where the barium coverage is about 0.26 ML, S XANES spectroscopy results show that barium sulfates are preferentially produced over aluminum sulfates . When oxygen is absent from the gas phase, the sulfation route that involves Pt-O is eliminated after the initially present Pt-O species are completely consumed. In this case, formation of sulfates is suppressed unless barium oxide is also present. Pt LIII XAFS results show that the first coordination sphere around the Pt atoms in the Pt particles is dependent upon the redox nature of the gas mixture used during the sulfation process. Sulfation under reducing environments (e.g. SO2+H2) leads to formation of Pt-S bonds, while oxidizing conditions (e.g. SO2+O2) continue to show the presence of Pt-O bonds. In addition, the former condition was found to give rise to a higher degree of Pt sintering than the latter one. This result explains why samples sulfated under reducing conditions had lower NOx uptakes than those sulfated under oxidizing conditions. Therefore, our results provide needed information for the development of optimum practical operation conditions (e.g. sulfation or desulfation) for lean NOx trap catalysts that minimize deactivation by sulfur.
Kwak JH, DH Kim, J Szanyi, and CHF Peden. 2008. "Excellent Sulfur Resistance of Pt/BaO/CeO2 Lean NOx Trap Catalysts." Applied Catalysis. B, Environmental 84(3-4):545-551. doi:10.1016/j.apcatb.2008.05.009 Abstract In this work, we investigated the NOx storage behavior of Pt-BaO/CeO2 catalysts, especially in the presence of SO2. High surface area CeO2 (~ 110 m2/g) with a rod like morphology was synthesized and used as a support. The Pt-BaO/CeO2 sample demonstrated slightly higher NOx conversion in the entire temperature range studied compared with Pt-BaO/γ-Al2O3. More importantly, this ceria-based catalyst showed higher sulfur tolerance than the alumina-based one. The time of complete NOx uptake was maintained even after exposing the sample to ~3 g/L of SO2. The same sulfur exposure, on the other hand, eliminated the complete NOx uptake time on the alumina-based NOx storage catalysts. TEM images show no evidence of either Pt sintering or BaS phase formation during reductive de-sulfation up to 600°C on the ceria based catalyst, while the same process over the alumina-based catalyst resulted in both a significant increase in the average Pt cluster size and the agglomeration of a newly-formed BaS phase into large crystallites. XPS results revealed the presence of about 5 times more residual sulfur after reductive de-sulfation at 600°C on the alumina based catalysts in comparison with the ceria-based ones. All of these results strongly support that, besides their superior intrinsic NOx uptake properties, ceria based catalysts have a) much higher sulfur tolerance and b) excellent resistance against Pt sintering when they are compared to the widely used alumina based catalysts.
Kim DH, YH Chin, JH Kwak, and CHF Peden. 2008. "Promotional Effects of H2O Treatment on NOx Storage over Fresh and Thermally Aged Pt-BaO/Al2O3 Lean NOx Trap Catalysts ." Catalysis Letters 124(1-2):39-45. doi:10.1007/s10562-008-9505-6 Abstract A simple liquid water treatment applied to fresh and thermally aged Pt(2wt%)-BaO(20wt%)/Al2O3 lean NOx trap catalysts at room temperature induces morphological and structural changes in the barium species as followed by XRD and TEM analysis. During the water treatment, liquid water sufficient to fill the catalyst pore volume is brought into contact with the samples. It was found that irrespective of the original barium chemical state (highly dispersed BaO or crystalline BaAl2O4), exposing the sample to this liquid water treatment promotes the formation of BaCO3 crystallites (about 15 – 25 nm of its size) without changing the Pt particle size. Such transformations of the barium species are found to significantly promote NOx uptake from 250 °C to 450 °C. The increase in the NOx uptake for the water-treated samples can be attributed to an enhanced Pt-Ba interaction through the redistribution of barium species. These results provide useful information for the regeneration of aged lean NOx trap catalysts since water is plentiful in the exhaust of diesel or lean-burn engines.

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