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Sample records for gas phase photocatalytic

  1. Photocatalytic degradation of 2-phenethyl-2-chloroethyl sulfide in liquid and gas phases.

    PubMed

    Vorontsov, Alexandre V; Panchenko, Alexander A; Savinov, Evgueni N; Lion, Claude; Smirniotis, Panagiotis G

    2002-12-01

    This work explores the ability of photocatalysis to decontaminate water and air from chemical warfare agent mustard using its simulant 2-phenethyl 2-chloroethyl sulfide (PECES). PECES like mustard slowly dissolves in water with hydrolysis, forming 2-phenethyl 2-hydroxyethyl sulfide (PEHES). Irradiation of TiO2 suspension containing PECES with the unfiltered light of a mercury lamp (lambda > or = 254 nm) decomposed all PECES mostly via photolysis. Reaction under filtered light (lambda > 300 nm) proceeds mainly photocatalytically and requires longer time. Sulfur from starting PECES is completely transformed into sulfuric acid at the end of the reaction. Detected volatile, nonvolatile, surface products, and the suggested scheme of degradation are reported. The main volatile products are styrene and benzaldehyde, nonvolatile--hydroxylated PEHES, surface--2-phenethyl disulfide. Photolysis of PECES produced the same set of volatile products as photocatalysis. Photocatalytic degradation of gaseous PECES in air results in its mineralization but is accompanied by TiO2 deactivation. The highest rate of mineralization with minimum deactivation was observed at about room temperature and a water concentration of 27,500 ppm. No gaseous products except CO2 were detected. The main extracted surface product was styrene. It was concluded that PECES photocatalytic degradation proceeds mainly via C-S bond cleavage and further oxidation of the products. Hydrolysis of the C-S bond was detected only in gas-phase photocatalytic degradation. The quantum efficiency of gas-phase degradation (0.28%) was much higher than that of liquid-phase degradation (0.008%). The results demonstrate the ability of photocatalysis to decontaminate an aqueous and especially an air environment

  2. Photocatalytic oxidation of gas-phase BTEX-contaminated waste streams

    SciTech Connect

    Gratson, D A; Nimlos, M R; Wolfrum, E J

    1995-03-01

    Researchers at the National Renewable Energy Laboratory (NREL) have been exploring heterogeneous photocatalytic oxidation (PCO) as a remediation technology for air streams contaminated with benzene, toluene, ethyl-benzene, and xylenes (BTEX). This research is a continuation of work performed on chlorinated organics. The photocatalytic oxidation of BTEX has been studied in the aqueous phase, however, a study by Turchi et al. showed a more economical system would involve stripping organic contaminants from the aqueous phase and treating the resulting gas stream. Another recent study by Turchi et al. indicated that PCO is cost competitive with such remediation technologies as activated carbon adsorption and catalytic incineration for some types of contaminated air streams. In this work we have examined the photocatalytic oxidation of benzene using ozone (0{sub 3}) as an additional oxidant. We varied the residence time in the PCO reactor, the initial concentration of the organic pollutant, and the initial ozone concentration in a single-pass reactor. Because aromatic hydrocarbons represent only a small fraction of the total hydrocarbons present in gasoline and other fuels, we also added octane to the reaction mixture to simulate the composition of air streams produced from soil-vapor-extraction or groundwater-stripping of sites contaminated with gasoline.

  3. Gas-phase photocatalytic oxidation: Cost comparison with other air pollution control technologies

    SciTech Connect

    Turchi, C S; Wolfrum, E J; Miller, R A

    1994-11-01

    Gas-phase photocatalytic oxidation (PCO) appears to be particularly well suited for waste streams with low pollutant concentrations (1000 ppm or less) and low to moderate flow rates (< 20,000 cubic feet per minute, cfm). The PCO technology is modular in nature and thus is well suited to treat dispersed or low flow rate streams. This same attribute minimizes the advantages of scale for PCO and makes the technology comparatively less attractive for high volume waste streams. Key advantages for PCO lie in its low operating cost and ability to completely destroy pollutants at ambient temperature and pressure.

  4. Ultraviolet-gas phase and -photocatalytic synthesis from CO and NH3.

    PubMed

    Hubbard, J S; Voecks, G E; Hobby, G L

    1975-08-05

    The major photoproduct obtained on irradiation of gaseous NH3 and CO mixtures is ammonium cyanate; lesser amounts of urea, biurea, biuret semi-carbazide, formamide and cyanide were observed. The formation of the major gas phase photolysis product may be rationalized by the following reaction sequence: (see article). Urea is probably formed from NH4NCO in a thermal reaction while formamide may result from the disproportionation of NH2CO. Photocatalytic syntheses of 14C-urea, -formamide, and -formadehyde are effected by irradiation of 14CO and NH3 in the presence of Vycor, silica gel, or volcanic ash shale surfaces. These syntheses are catalyzed by ultraviolet wavelengths longer than those absorbed by the gaseous reactants. The syntheses are also effected when the surface material is first irradiated in the presence of CO followed by a dark incubation with NH3. Apparently, the initiating step is a light dependent formation of a reactive form of CO on the surface. A discussion is given on the possible contribution of these reactions to the abiotic synthesis of organic nitrogen compounds on Mars, on the primitive Earth and in interstellar space.

  5. Effect of Precursor Selection on the Photocatalytic Performance of Indium Oxide Nanomaterials for Gas-Phase CO 2 Reduction

    DOE PAGES

    Hoch, Laura B.; He, Le; Qiao, Qiao; ...

    2016-06-01

    Nonstoichiometric indium oxide nanoparticles, In2O3–x(OH)y, have been shown to function as active photocatalysts for gas-phase CO2 reduction under simulated solar irradiation. We demonstrate that the choice of starting material has a strong effect on the photocatalytic activity of indium oxide nanoparticles. We also examine three indium oxide materials prepared via the thermal decomposition of either indium(III) hydroxide or indium(III) nitrate and correlate their stability and photocatalytic activity to the number and type of defect present in the material. Furthermore, we use 13CO2 isotope-tracing experiments to clearly identify the origins of the observed carbon-containing products. Significantly, we find that the oxidizingmore » nature of the precursor anion has a substantial impact on the defect formation within the sample. Our study demonstrates the importance of surface defects in designing an active heterogeneous photocatalyst and provides valuable insight into key parameters for the precursor design, selection, and performance optimization of materials for gas-phase CO2 reduction.« less

  6. The rate of photocatalytic oxidation of aromatic volatile organic compounds in the gas-phase

    NASA Astrophysics Data System (ADS)

    Boulamanti, Aikaterini K.; Korologos, Christos A.; Philippopoulos, Constantine J.

    In the present study, the gas-solid heterogeneous photocatalytic oxidation (PCO) of six aromatic species of volatile organic compounds (VOCs), benzene, toluene, ethylbenzene, m-, o- and p-xylene over illuminated titania was carried out at ambient temperature in a continuous stirring-tank reactor. Initial VOC concentrations were in the low parts per million (ppm) range. Maximum conversions were over 90% for all compounds except from benzene, ethylbenzene and o-xylene, while the residence time varied from 50 to 210 s. Intermediates were detected only in the case of the xylenes, but catalyst deactivation occurred for all six compounds. The PCO kinetics were well fit by a Langmuir-Hinshelwood (L-H) model for monomolecular surface reaction and it was proved that the reaction rate is related to both constants. The rate constants ranged from 0.147 ppm s -1 g cat-1 for benzene to 1.067 ppm s -1 g cat-1 for m-xylene, while the adsorption constants from 0.424 ppm -1 for ethylbenzene to 0.69 ppm -1 for toluene. The molecular structure of the compounds was found to play an important role in the reaction. Finally the efficiency of the procedure in the case of a mixture of these aromatic substances was tested.

  7. Gas-phase photocatalytic degradation of perchloroethylene on glass pellets immobilized with TiO{sub 2}

    SciTech Connect

    Hung, C.H.; Yuan, C.S.

    1998-12-31

    The objective of this research was to study gas-phase photocatalytic degradation of perchloroethylene (PCE) under illumination of four 10-W near-ultraviolet (UV) light lamps. Experiments were performed in a photocatalytic reactor packed with Degussa P-25 TiO{sub 2}-coated glass pellets. Anatase TiO{sub 2} was applied as the photocatalyst in the investigation. The effects of reaction parameters including influent PCE concentrations (10 to 50 ppm), water vapor content (0 to 100 % relative humidity), oxygen concentrations (0.31 to 21%), reactor space times (0.55 to 1.83 seconds), and irradiated light intensity (0.4 to 1.0 mW/cm{sup 2}) were investigated in the study. Experimental results indicated that fast photocatalytic degradation of PCE took place in the presence of TiO2 illuminated with near-UV light. Experimental results also showed that the highest degradation rate and quantum efficiency of PCE were 0.523 m mol/secgm and 5.2 %, respectively. The highest conversion ratio of PCE of 99.8 % was achieved in the study. Greater conversation ratios of PCE were observed for longer reaction time. Increase in the reaction rates of PCE by increasing influent PCE and oxygen concentrations were presented. Higher reaction rates of PCE under stronger illumination light intensity were detected. The degradation rates of PCE were proportional to light intensity with the power order of 1.2. On the other hand, the inhibited degradation of PCE was observed in the presence of water vapor. Lower reaction rates of PCE were detected when water vapor was present in the reaction. A modified Langmuir-Hishelwood kinetic was applied to model photocatalytic degradation of PCE. Two different adsorption sites on irradiated TiO2{sub 2} surfaces for the adsorption of PCE and oxygen molecules respectively were assumed in the model. The assumption of water vapor competing with PCE for reactive sites was considered in the reaction.

  8. Ultraviolet-gas phase and -photocatalytic synthesis from CO and NH3. [photolysis products

    NASA Technical Reports Server (NTRS)

    Hubbard, J. S.; Voecks, G. E.; Hobby, G. L.; Ferris, J. P.; Williams, E. A.; Nicodem, D. E.

    1975-01-01

    Ammonium cyanate is identified as the major product of the photolysis of gaseous NH3-CO mixtures at 206.2 or 184.9 nm. Lesser amounts of urea, biurea, biuret semicarbazide, formamide and cyanide are observed. A series of 18 reactions underlying the formation of photolysis products is presented and discussed. Photocatalytic syntheses of C-14-urea, -formamide, and -formaldehyde are carried out through irradiation of (C-14)O and NH3 in the presence of Vycor, silica gel, or volcanic ash shale surfaces. The possible contributions of the relevant reactions to the abiotic synthesis of organic nitrogen compounds on Mars, the primitive earth, and in interstellar space are examined.

  9. Photocatalytic oxidation of H2S in the gas phase over TiO2-coated glass fiber filter.

    PubMed

    Brancher, Marlon; Franco, Davide; de Melo Lisboa, Henrique

    2016-11-01

    To promote the photocatalytic oxidation (PCO) of hydrogen sulfide (H2S) in the gas phase, TiO2-coated glass fiber filters were packed in an annular photoreactor. Glass fibers coated with TiO2 thin films were characterized structurally and morphologically by field emission gun scanning electron microscopy (FEG-SEM), scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) and X-ray diffractometry (XRD). Flow rate and H2S inlet concentration were evaluated to determine the performance of the reactor. Removal efficiencies up to 99% were achieved for flow rate of 25 L h(-1) (residence time of 121 s) and H2S inlet concentration from 12 to 14 ppmv. The long-term experiment presented H2S removal of 89% for 16 h. After 28 h of continuous use, H2S degradation was observed at 64%, which suggests that the photocatalyst was losing activity due to deactivation. Moreover, the kinetics of the PCO of H2S according to the Langmuir-Hinshelwood (L-H) approach along with the mass balance of a plug-flow reactor was modeled. The reaction constant (k) was calculated at approximately 10.5 μmol m(-3) s(-1) and the adsorption constant (K) of approximately 5263 m(-3) mol with linearity (R2) of 0.98.

  10. Optimization of operating parameters for gas-phase photocatalytic splitting of H2S by novel vermiculate packed tubular reactor.

    PubMed

    Preethi, V; Kanmani, S

    2016-10-01

    Hydrogen production by gas-phase photocatalytic splitting of Hydrogen Sulphide (H2S) was investigated on four semiconductor photocatalysts including CuGa1.6Fe0.4O2, ZnFe2O3, (CdS + ZnS)/Fe2O3 and Ce/TiO2. The CdS and ZnS coated core shell particles (CdS + ZnS)/Fe2O3 shows the highest rate of hydrogen (H2) production under optimized conditions. Packed bed tubular reactor was used to study the performance of prepared photocatalysts. Selection of the best packing material is a key for maximum removal efficiency. Cheap, lightweight and easily adsorbing vermiculate materials were used as a novel packing material and were found to be effective in splitting H2S. Effect of various operating parameters like flow rate, sulphide concentration, catalyst dosage, light irradiation were tested and optimized for maximum H2 conversion of 92% from industrial waste H2S.

  11. ZnS/ZnO@CNT and ZnS@CNT nanocomposites by gas phase conversion of ZnO@CNT. A systematic study of their photocatalytic properties.

    PubMed

    Okeil, Sherif; Krausmann, Jan; Dönges, Inga; Pfleger, Sandra; Engstler, Jörg; Schneider, Jörg J

    2017-04-04

    ZnS nanoparticles have been synthesized on vertically aligned carbon nanotubes by gas-phase conversion of ZnO nanoparticles which have been tethered on vertically aligned carbon nanotubes using atomic layer deposition (ALD). The resulting ZnO@CNT nanocomposite has been converted to ZnS@CNT by reacting it with hydrogen sulfide using thioacetamide as a precursor. The composition of the resulting nanocomposite could be tuned from a mixed ternary ZnS/ZnO@CNT nanocomposite to a pure ZnS@CNT nanocomposite. At the same time, the amount of wurtzite and sphalerite phases varies in the ZnS@CNT nanocomposite. The resulting nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), selected area electron diffraction (SAED), ultraviolet-visible diffuse reflectance spectroscopy (UV-VIS DRS) and photoluminescence spectroscopy (PL). Finally, the different nanocomposites were tested for their photocatalytic activity by the photocatalytic decomposition under visible light using methyl orange (MO). Herein a systematic study of the photocatalytic activity of different compositions of ZnS in the ZnS@CNT nanocomposite was performed for the first time.

  12. Effect of Precursor Selection on the Photocatalytic Performance of Indium Oxide Nanomaterials for Gas-Phase CO 2 Reduction

    SciTech Connect

    Hoch, Laura B.; He, Le; Qiao, Qiao; Liao, Kristine; Reyes, Laura M.; Zhu, Yimei; Ozin, Geoffrey A.

    2016-06-01

    Nonstoichiometric indium oxide nanoparticles, In2O3–x(OH)y, have been shown to function as active photocatalysts for gas-phase CO2 reduction under simulated solar irradiation. We demonstrate that the choice of starting material has a strong effect on the photocatalytic activity of indium oxide nanoparticles. We also examine three indium oxide materials prepared via the thermal decomposition of either indium(III) hydroxide or indium(III) nitrate and correlate their stability and photocatalytic activity to the number and type of defect present in the material. Furthermore, we use 13CO2 isotope-tracing experiments to clearly identify the origins of the observed carbon-containing products. Significantly, we find that the oxidizing nature of the precursor anion has a substantial impact on the defect formation within the sample. Our study demonstrates the importance of surface defects in designing an active heterogeneous photocatalyst and provides valuable insight into key parameters for the precursor design, selection, and performance optimization of materials for gas-phase CO2 reduction.

  13. A high-throughput reaction system to measure the gas-phase photocatalytic oxidation activity of TiO2 nanotubes

    NASA Astrophysics Data System (ADS)

    Grasser, Jordan A.; Muggli, Darrin S.

    2009-07-01

    A sixteen-channel, high-throughput system was designed and built to test the activity of catalysts for gas-phase photocatalytic oxidation of methanol. The system utilizes granular catalyst films to model relevant applications and allow for rapid processing. It is capable of 48 catalyst tests per day using the procedure described herein. Several experiments were performed to minimize both the within-node and between-node variances of the system. Utilizing the high-throughput system, the significance of preparation methods on the photocatalytic activity of TiO2 nanotubes was investigated. A one-half fractional factorial experiment identified the factors that significantly impact catalyst activity as the following: precursor type (Degussa P-25, or nanotubes), platinum loading, the interaction between precursor and dope time, and the interaction between the precursor and calcination temperature. Based on experimental results, catalyst activity is optimized by doping TiO2 nanotubes directly (rather than doping P-25 prior to nanotube formation), a low platinum loading (0.01 wt %), and using a dope time of 30 min followed by calcination at 773 K. The optimum catalyst preparation conditions produced a catalyst that was three times more active than the starting P-25 material.

  14. Solving widespread low-concentration VOC air pollution problems: Gas-phase photocatalytic oxidation answers the needs of many small businesses

    SciTech Connect

    Lyons, C; Turchi, C; Gratson, D

    1995-04-01

    Many small businesses are facing new regulations under the 1990 Amendments to the Clean Air Act. Regulators, as well as the businesses themselves, face new challenges to control small point-source air pollution emissions. An individual business-such as a dry cleaner, auto repair shop, bakery, coffee roaster, photo print shop, or chemical company-may be an insignificant source of air pollution, but collectively, the industry becomes a noticeable source. Often the businesses are not equipped to respond to new regulatory requirements because of limited resources, experience, and expertise. Also, existing control strategies may be inappropriate for these businesses, having been developed for major industries with high volumes, high pollutant concentrations, and substantial corporate resources. Gas-phase photocatalytic oxidation (PCO) is an option for eliminating low-concentration, low-flow-rate emissions of volatile organic compounds (VOCs) from small business point sources. The advantages PCO has over other treatment techniques are presented in this paper. This paper also describes how PCO can be applied to specific air pollution problems. We present our methodology for identifying pollution problems for which PCO is applicable and for reaching the technology`s potential end users. PCO is compared to other gas-phase VOC control technologies.

  15. The effect of water presence on the photocatalytic oxidation of benzene, toluene, ethylbenzene and m-xylene in the gas-phase

    NASA Astrophysics Data System (ADS)

    Korologos, Christos A.; Philippopoulos, Constantine J.; Poulopoulos, Stavros G.

    2011-12-01

    In the present work, the gas-solid heterogeneous photocatalytic oxidation of benzene, toluene, ethylbenzene and m-xylene (BTEX) over UV-irradiated titanium dioxide was studied in an annular reactor operated in the CSTR (continuous stirred-tank reactor) mode. GC-FID and GC-MS were used for analysing reactor inlet and outlet streams. Initial BTEX concentrations were in the low parts per million (ppmv) range, whereas the water concentration was in the range of 0-35,230 ppmv and the residence time varied from 50 to 210 s. The effect of water addition on the photocatalytic process showed strong dependence on the type of the BTEX and the water vapour concentration. The increase in residence time resulted in a considerable increase in the conversion achieved for all compounds and experimental conditions. There was a clear interaction between residence time and water presence regarding the effect on conversions achieved. It was established that conversions over 95% could be achieved by adjusting appropriately the experimental conditions and especially the water concentration in the reactor. In all cases, no by-products were detected above the detection limit and carbon dioxide was the only compound detected. Finally, various Langmuir-Hinshelwood kinetic models have been tested in the analysis of the experimental data obtained. The kinetic data obtained confirmed that water had an active participation in the photocatalytic reactions of benzene, toluene, ethylbenzene and m-xylene since the model involving reaction of BTEX and water adsorbed on different active sites yielded the most successful fitting to the experimental results for the first three compounds, whereas the kinetic model based on the assumption that reaction between VOC and water dissociatively adsorbed on the photocatalyst takes place was the most appropriate in the case of m-xylene.

  16. Gas phase photocatalytic degradation on TiO{sub 2} pellets of volatile chlorinated organic compounds from a soil vapor extraction well

    SciTech Connect

    Yamazaki-Nishida, S.; Read, H.W.; Nagano, J.K.; Anderson, M.A.; Cervera-March, S.; Jarosch, T.R.; Eddy-Dilek, C.A.

    1993-05-20

    The mineralization of trichloroethylene (TCE) and tetrachloroethylene (PCE) in gas stream from a soil vapor extraction (SVE) well was demonstrated with an annular photocatalytic reactor packed with porous TiO{sub 2} pellets in field trials at the Savannah River Site in Aiken, SC. The TiO{sub 2} pellets were prepared using a sol-gel method. The experiments were performed at 55 to 60{degree}C using space times of 10{sup 8} to 10{sup 10} g s/mol for TCE and PCE. Chloroform (CHCl{sub 3}) and carbon tetrachloride (CCl{sub 4}) were detected as minor products from side reactions. On a molar basis, CCl{sub 4} and CHCl{sub 3} produced were about 2% and 0.2 % of the reactants.

  17. Photocatalytic oxidation of selected gas-phase VOCs using UV light, TiO2, and TiO2/Pd.

    PubMed

    Fujimoto, Tânia M; Ponczek, Milena; Rochetto, Ursula L; Landers, Richard; Tomaz, Edson

    2016-03-30

    Heterogeneous photocatalytic oxidation systems using titanium dioxide (TiO2) have been extensively studied for the removal of several volatile organic compounds (VOCs). The addition of noble metals such as palladium on TiO2 may improve photocatalytic activity by increasing charge separation efficiency. In this work, palladium was impregnated on TiO2 and the efficiency of the new catalyst was tested and compared with that of pure TiO2. Pd was impregnated on TiO2 by the reduction method, using NaBH4, and was characterized by XRD, XPS, UV-Vis, and H2 chemisorption. The photocatalytic tests were performed in an annular coated-wall reactor using octane, isooctane, n-hexane, and cyclohexane at inlet concentrations varying from 100 to 120 ppmv. Compared with pure TiO2 film, the photocatalytic activity of TiO2 impregnated with 1 wt% of palladium was improved. All the aforementioned analytical techniques confirmed the presence of Pd incorporated into the structure of TiO2, and the conversion rates were studied in a broad range of residence times, yielding up to 90 % or higher rates in 40 s of residence time, thus underscoring the relevant contribution of the technology.

  18. Gas Phase Nanoparticle Synthesis

    NASA Astrophysics Data System (ADS)

    Granqvist, Claes; Kish, Laszlo; Marlow, William

    This book deals with gas-phase nanoparticle synthesis and is intended for researchers and research students in nanomaterials science and engineering, condensed matter physics and chemistry, and aerosol science. Gas-phase nanoparticle synthesis is instrumental to nanotechnology - a field in current focus that raises hopes for environmentally benign, resource-lean manufacturing. Nanoparticles can be produced by many physical, chemical, and even biological routes. Gas-phase synthesis is particularly interesting since one can achieve accurate manufacturing control and hence industrial viability.

  19. Solar photocatalytic gas-phase degradation of n-decane--a comparative study using cellulose acetate monoliths coated with P25 or sol-gel TiO₂ films.

    PubMed

    Miranda, Sandra M; Lopes, Filipe V S; Rodrigues-Silva, Caio; Martins, Susana D S; Silva, Adrián M T; Faria, Joaquim L; Boaventura, Rui A R; Vilar, Vítor J P

    2015-01-01

    Cellulose acetate monoliths (CAM) were used as the substrate for the deposition of TiO2 films to produce honeycombed photoactive structures to fill a tubular photoreactor equipped with a compound parabolic collector. By using such a setup, an efficient single-pass gas-phase conversion was achieved in the degradation of n-decane, a model volatile organic compound. The CAM three-dimensional, gas-permeable transparent structure with a rugged surface enables a good adhesion of the catalytic coating. It also provides a rigid structure for packing the tubular photoreactor, and maximizing the illuminated catalyst surface. The efficiency of the photocatalytic oxidation (PCO) process on n-decane degradation was evaluated under different operating conditions, such as feeding concentration (73 and 146 ppm), gas stream flow rate (73, 150, and 300 mL min(-1)), relative humidity (3 and 25 %), and UV irradiance (18.9, 29.1, and 38.4 WUV m(-2)). The results show that n-decane degradation by neat photolysis is negligible, but mineralization efficiencies of 86 and 82 % were achieved with P25-CAM and SG-CAM, respectively, for parent pollutant conversions above 95 %, under steady-state conditions. A mass transfer model, considering the mass balance to the plug-flow packed photoreactor, and PCO reaction given by a Langmuir-Hinshelwood bimolecular non-competitive two types of sites equation, was able to predict well the PCO kinetics under steady-state conditions, considering all the operational parameters tested. Overall, the performance of P25-CAM was superior taking into account mineralization efficiency, cost of preparation, surface roughness, and robustness of the deposited film.

  20. Valorization of Flue Gas by Combining Photocatalytic Gas Pretreatment with Microalgae Production.

    PubMed

    Eynde, Erik Van; Lenaerts, Britt; Tytgat, Tom; Blust, Ronny; Lenaerts, Silvia

    2016-03-01

    Utilization of flue gas for algae cultivation seems to be a promising route because flue gas from fossil-fuel combustion processes contains the high amounts of carbon (CO2) and nitrogen (NO) that are required for algae growth. NO is a poor nitrogen source for algae cultivation because of its low reactivity and solublilty in water and its toxicity for algae at high concentrations. Here, we present a novel strategy to valorize NO from flue gas as feedstock for algae production by combining a photocatalytic gas pretreatment unit with a microalgal photobioreactor. The photocatalytic air pretreatment transforms NO gas into NO2 gas and thereby enhances the absorption of NOx in the cultivation broth. The absorbed NOx will form NO2(-) and NO3(-) that can be used as a nitrogen source by algae. The effect of photocatalytic air pretreatment on the growth and biomass productivity of the algae Thalassiosira weissflogii in a semicontinuous system aerated with a model flue gas (1% CO2 and 50 ppm of NO) is investigated during a long-term experiment. The integrated system makes it possible to produce algae with NO from flue gas as the sole nitrogen source and reduces the NOx content in the exhaust gas by 84%.

  1. Chemical absorption process for degradation of VOC gas using heterogeneous gas-liquid photocatalytic oxidation: toluene degradation by photo-Fenton reaction.

    PubMed

    Tokumura, Masahiro; Nakajima, Rina; Znad, Hussein Tawfeek; Kawase, Yoshinori

    2008-10-01

    A novel process for degradation of toluene in the gas-phase using heterogeneous gas-liquid photocatalytic oxidation has been developed. The degradation of toluene gas by photo-Fenton reaction in the liquid-phase has experimentally examined. The photo-Fenton reaction in the liquid-phase could improve the overall toluene absorption rate by increasing the driving force for mass transfer and as a result enhance the removal of toluene in the exhaust gas. The toluene concentrations in the inlet gas were varied in the range from 0.0968 to 8.69 g m(-3) with initial hydrogen peroxide concentration of 400 mg l(-1) and Fe dose of 5.0 mg l(-1). It was found that toluene in the inlet gas was almost completely dissolved into water and degraded in the liquid-phase for the inlet toluene gas concentration of less than 0.42 g m(-3). The dynamic process of toluene gas degradation by the photo-Fenton reaction providing information for reaction kinetics and mass transfer rate was examined. Toluene removal kinetic analysis indicated that photo-Fenton degradation was significantly affected by H(2)O(2) concentration. The experimental results were satisfactorily described by the predictions simulated using the simplified tanks-in-series model combined with toluene removal kinetic analysis. The present results showed that the proposed chemical absorption process using the photo-Fenton heterogeneous gas-liquid photocatalytic oxidation is very effective for degradation of volatile organic gases.

  2. Gas-phase chemical dynamics

    SciTech Connect

    Weston, R.E. Jr.; Sears, T.J.; Preses, J.M.

    1993-12-01

    Research in this program is directed towards the spectroscopy of small free radicals and reactive molecules and the state-to-state dynamics of gas phase collision, energy transfer, and photodissociation phenomena. Work on several systems is summarized here.

  3. Gas phase chemistry in comets

    NASA Technical Reports Server (NTRS)

    Oppenheimer, M.

    1976-01-01

    The significance of gas phase reactions in determining the nuclear structure of comets is discussed. The sublimation of parent molecules such as H2O, CH4, CO2, and NH3 from the surface of the nucleus and their subsequent photodissociation and ionization in forming observed cometary molecular species are elaborated.

  4. Hydrothermal synthesis, phase structure, optical and photocatalytic properties of Zn2SnO4 nanoparticles.

    PubMed

    Ben Ali, Monaam; Barka-Bouaifel, Fatiha; Elhouichet, Habib; Sieber, Brigitte; Addad, Ahmed; Boussekey, Luc; Férid, Mokhtar; Boukherroub, Rabah

    2015-11-01

    Zinc stannate (Zn2SnO4 or ZTO) nanoparticles were synthesized via hydrothermal method using NaOH as a mineralizer. X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) of the synthesized ZTO nanoparticles revealed the formation of highly pure ZTO phase with the spinel-like structure. The nanoparticles have spherical shape with an average size of about 25 nm. The Raman spectrum of the sample was dominated by the A(1g) vibration mode of pure ZTO phase. From UV-Vis measurement, a band gap E(g) of 3.465 eV was determined. The photocatalytic activity of the ZTO nanoparticles was evaluated for the photodegradation of rhodamine B (RhB) under visible light irradiation. The influence of catalyst concentration and irradiation time on the photocatalytic process was investigated. The ZTO catalyst showed the best photocatalytic performance at a concentration of 0.2 g/L, and the photodecomposition of RhB followed first-order kinetics with a rate constant k=0.0249 min(-1). The ZTO-assisted photocatalytic degradation of RhB occurred via two competitive processes: a photocatalytic process and a photosensitized process. The detection of hydroxyl radicals by fluorescence measurements suggests that these species play an important role in the photocatalytic process.

  5. Hydrogen evolution from aqueous-phase photocatalytic reforming of ethylene glycol over Pt/TiO2 catalysts: Role of Pt and product distribution

    NASA Astrophysics Data System (ADS)

    Li, Fuying; Gu, Quan; Niu, Yu; Wang, Renzhang; Tong, Yuecong; Zhu, Shuying; Zhang, Hualei; Zhang, Zizhong; Wang, Xuxu

    2017-01-01

    Pt nanoparticles were loaded on anatase TiO2 by the photodeposition method to investigate their photocatalytic activity for H2 evolution in an aqueous solution containing a certain amount of ethylene glycol (EG) as the sacrificial agent. The surface properties and chemical states of the Pt/TiO2 sample were characterized by X-ray powder diffraction analysis, Brunauer-Emmett-Teller surface area analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance, and electrochemical resistance. The aqueous-phase photocatalytic EG reforming using Pt/TiO2 and anatase TiO2 generated not only H2 and CO2, but also CO, CH4, C2H6, and C2H4. Moreover, the amount of formate and acetate complexes in the solution increased gradually. The EG adsorption and gas-phase intermediates during photocatalytic reaction processes were investigated by the in situ FTIR spectrum. Finally, the photocatalytic EG reforming reaction mechanism was elucidated. This helped to better understand the role of a sacrificial agent in a photocatalytic hydrogen production.

  6. Enhanced photocatalytic performance of porous TiO2 nanobelts with phase junctions

    NASA Astrophysics Data System (ADS)

    Pang, Lai-xue; Wang, Xiao-ying; Tang, Xin-de

    2015-01-01

    Porous TiO2 nanobelts with rutile/anatase phase junctions are successfully prepared through a hydrothermal route and ion exchange process. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were conducted to characterize the products. The photocatalytic performance of the porous nanobelts was evaluated by measuring the degradation of methyl blue under UV light irradiation. The photocatalytic activity of the porous nanobelts is much superior to that of P-25 and pristine non-porous nanobelts. The excellent photocatalytic of porous nanobelts can be attributed to pores which enhanced ability in UV-light harvesting. What's more, the existence of rutile/anatase phase junction is favorable for the formation and separation of the hole-electron pair, resulting in a reduced electron-hole recombination.

  7. Removal of high concentration dimethyl methylphosphonate in the gas phase by repeated-batch reactions using TiO2.

    PubMed

    Mera, Nobuaki; Hirakawa, Tsutomu; Sano, Taizo; Takeuchi, Koji; Seto, Yasuo; Negishi, Nobuaki

    2010-05-15

    The aim of our study is to develop apparatuses that use TiO(2) for effective decontamination of air contaminated by Sarin gas. We performed photocatalytic decomposition of gaseous dimethyl methylphosphonate (DMMP) by TiO(2) and identified the oxidization products. The high activity of TiO(2) (0.01 g) was observed under UV-light irradiation and high concentration DMMP (33.5 microM) was removed rapidly. On the other hand, DMMP was not decreased under UV-light irradiation without TiO(2). This indicates that photocatalytic treatment is very effective for the removal of DMMP. Methanol, formaldehyde, formic acid, methyl formate, CO, CO(2) and H(2)O were detected as the primary products. In the gas phase, no highly poisonous substances were detected. In order to examine the performance of photocatalytic activity during long-term reactions, we performed photocatalytic decomposition by repeated-batch reactions using TiO(2). High photocatalytic activities decreased gradually. Meanwhile, the strong adsorption of TiO(2) against DMMP was observed as photocatalytic activities decreased. During the repeated-batch reactions with the sample scaled up (TiO(2): 0.1g), the total amount of removed DMMP reached 968.5 microM by both photocatalytic decomposition and the strong adsorption of TiO(2). These results suggest the possibility of removing large amounts of DMMP.

  8. High photocatalytic activity of mixed anatase-rutile phases on commercial TiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Ruu Siah, Wai; Lintang, Hendrik O.; Shamsuddin, Mustaffa; Yuliati, Leny

    2016-02-01

    Titanium dioxide (TiO2) is well-known as an active photocatalyst for degradation of various organic pollutants. Over the years, a wide range of TiO2 nanoparticles with different phase compositions, crystallinities, and surface areas have been developed. Due to the different methods and conditions used to synthesize these commercial TiO2 nanoparticles, the properties and photocatalytic performance would also be different from each other. In this study, the photocatalytic removal of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5- trichlorophenoxyacetic acid (2,4,5-T) was investigated on commercial Evonik P25, Evonik P90, Hombikat UV100 and Hombikat N100 TiO2 nanoparticles. Upon photocatalytic tests, it was found that overall, the photocatalytic activities of the P25 and the P90 were higher than the N100 and the UV100 for the removal of both 2,4-D and 2,4,5-T. The high activities of the P25 and the P90 could be attributed to their phase compositions, which are made up of a mixture of anatase and rutile phases of TiO2. Whereas, the UV100 and the N100 are made up of 100% anatase phase of TiO2. The synergistic effect of the anatase/rutile mixture was reported to slow down the recombination rate of photogenerated electron-hole pairs. Consequently, the photocatalytic activity was increased on these TiO2 nanoparticles.

  9. Photocatalytic oxidation of methyl orange in water phase by immobilized TiO2-carbon nanotube nanocomposite photocatalyst

    NASA Astrophysics Data System (ADS)

    Dong, Yinmao; Tang, Dongyan; Li, Chensha

    2014-03-01

    We developed an immobilized carbon nanotube (CNT)-titanium dioxide (TiO2) heterostructure material for the photocatalytic oxidation of methyl orange in aqueous phase. The catalyst material was prepared via sol-gel method using multi-walled CNTs grown on graphite substrate as carriers. The multi-walled CNTs were synthesized from thermal decomposing of hydrocarbon gas directly on thin graphite plate, forming immobilized 3-dimensional network of CNTs. The nanophase TiO2 was synthesized coating on CNTs to form "coral"-shaped nanocomposite 3-dimensional network on graphite substrate, thus bringing effective porous structure and high specific surface area, and possessing the merit of dispersive powder photocatalysts, which is the fully available surface area, while adapting the requirement for clean and convenient manipulation as an immobilized photocatalyst. Moreover, the CNT-TiO2 heterostructure reduced the electron-hole pair recombination rate and enhanced the photoabsorption and the adsorption ability, resulting in elevating the photocatalysis efficiency. These synergistic effects due to the hybrid nature of the materials and interphase interaction greatly improved the catalytic activity, and demonstrated superior photocatalytic performances. Our work can be a significant inspiration for developing hybrid nano-phase materials to realize sophisticated functions, and bear tremendous significance for the development and applications of semiconductor nano-materials.

  10. Rate processes in gas phase

    NASA Technical Reports Server (NTRS)

    Hansen, C. F.

    1983-01-01

    Reaction-rate theory and experiment are given a critical review from the engineers' point of view. Rates of heavy-particle, collision-induced reaction in gas phase are formulated in terms of the cross sections and activation energies for reaction. The effect of cross section function shape and of excited state contributions to reaction both cause the slope of Arrhenius plots to differ from the true activation energy, except at low temperature. The master equations for chemically reacting gases are introduced, and dissociation and ionization reactions are shown to proceed primarily from excited states about kT from the dissociation or ionization limit. Collision-induced vibration, vibration-rotation, and pure rotation transitions are treated, including three-dimensional effects and conservation of energy, which have usually been ignored. The quantum theory of transitions at potential surface crossing is derived, and results are found to be in fair agreement with experiment in spite of some questionable approximations involved.

  11. Photocatalytic Activity of Nanostructured Anatase Coatings Obtained by Cold Gas Spray

    NASA Astrophysics Data System (ADS)

    Gardon, M.; Fernández-Rodríguez, C.; Garzón Sousa, D.; Doña-Rodríguez, J. M.; Dosta, S.; Cano, I. G.; Guilemany, J. M.

    2014-10-01

    This article describes a photocatalytic nanostructured anatase coating deposited by cold gas spray (CGS) supported on titanium sub-oxide (TiO2- x ) coatings obtained by atmospheric plasma spray (APS) onto stainless steel cylinders. The photocatalytic coating was homogeneous and preserved the composition and nanostructure of the starting powder. The inner titanium sub-oxide coating favored the deposition of anatase particles in the solid state. Agglomerated nano-TiO2 particles fragmented when impacting onto the hard surface of the APS TiO2- x bond coat. The rough surface provided by APS provided an ideal scenario for entrapping the nanostructured particles, which may be adhered onto the bond coat due to chemical bonding; a possible bonding mechanism is described. Photocatalytic experiments showed that CGS nano-TiO2 coating was active for photodegrading phenol and formic acid under aqueous conditions. The results were similar to the performance obtained by competitor technologies and materials such as dip-coating P25® photocatalysts. Disparity in the final performance of the photoactive materials may have been caused by differences in grain size and the crystalline composition of titanium dioxide.

  12. Efficient Photocatalytic Activities of TiO2 Hollow Fibers with Mixed Phases and Mesoporous Walls

    PubMed Central

    Hou, Huilin; Shang, Minghui; Wang, Lin; Li, Wenge; Tang, Bin; Yang, Weiyou

    2015-01-01

    Currently, Degussa P25, with the typical mixed phases of anatase and rutile TiO2, is widely applied as the commercial photocatalysts. However, there are still some of obstacles for the P25 nanoparticles with totally high photocatalytic activities, especially for the catalytic stability due to their inevitable aggregation of the nanoparticles when used as the photocatalysts. In the present work, we reported the exploration of a novel TiO2 photocatalyst, which could offer an ideal platform for synergetic combination of the mixed-phase composition, hollow architecture and mesoporous walls for the desired excellent photocatalytic efficiency and robust stability. The mesoporous TiO2 hollow nanofibers were fabricated via a facile single capillary electrospinning technique, in which the foaming agents were used for creating mesopores throughout the walls of the hollow fibers. The obtained hollow fibers exhibit a high purity and possess the mixed phases of 94.6% anatase and 5.4% rutile TiO2. As compared to P25, the as-fabricated mesoporous TiO2 hollow fibers exhibited much higher efficient photocatalytic activities and stabilities toward the hydrogen evolution with a rate of ~499.1 μmol g−1·h−1 and ~99.5% degradation Rhodamine B (RhB) in 60 min, suggesting their promising application in efficient photocatalysts. PMID:26470013

  13. Gas phase kinetics during normal combustion

    NASA Technical Reports Server (NTRS)

    Price, C. F.; Boggs, T. L.; Eisel, J. L.; Atwood, A. I.; Zurn, D. E.

    1980-01-01

    The role of gas phase kinetics during combustion was explored in the steady state modeling efforts and in the analysis of ignition phenomena. In both cases it was shown that the combustion characteristics of some high energy ingredients and propellants are strongly affected, if not dictated, by the gas phase reactions which take place.

  14. Hydrated metal ions in the gas phase.

    PubMed

    Beyer, Martin K

    2007-01-01

    Studying metal ion solvation, especially hydration, in the gas phase has developed into a field that is dominated by a tight interaction between experiment and theory. Since the studied species carry charge, mass spectrometry is an indispensable tool in all experiments. Whereas gas-phase coordination chemistry and reactions of bare metal ions are reasonably well understood, systems containing a larger number of solvent molecules are still difficult to understand. This review focuses on the rich chemistry of hydrated metal ions in the gas phase, covering coordination chemistry, charge separation in multiply charged systems, as well as intracluster and ion-molecule reactions. Key ideas of metal ion solvation in the gas phase are illustrated with rare-gas solvated metal ions.

  15. Photocatalytic abatement of NOx by C-TiO2/polymer composite coatings obtained by low pressure cold gas spraying

    NASA Astrophysics Data System (ADS)

    Robotti, M.; Dosta, S.; Fernández-Rodríguez, C.; Hernández-Rodríguez, M. J.; Cano, I. G.; Melián, E. Pulido; Guilemany, J. M.

    2016-01-01

    In the present work, we study the photocatalytic activity of carbon-modified TiO2 (C-TiO2)/polymer composite coatings obtained by low pressure cold gas spraying (LP-CGS). To produce the novel coatings, C-TiO2 was mixed with a ductile material, the polymer ECTFE, by means of a low energy ball milling (LEBM) process. The LEBM system permits the mechanical anchoring of small TiO2 aggregates around the large ductile polymeric particles. A well-bonded coating with good mechanical coupling was formed between the ball-milled mixture and the substrate. Photocatalytic tests showed that the LP-CGS nano-TiO2 coatings actively photodegraded NO and the by-product, NO2. Compared to commercial paint, the as-prepared coatings presented here enhanced photocatalytic performance.

  16. Photocatalytic Properties of TiO2 Thin Films Modified with Ag and Pt Nanoparticles Deposited by Gas Flow Sputtering.

    PubMed

    Maicu, M; Glöss, D; Frach, Peter; Hecker, D; Gerlach, G; Córdoba, José M

    2015-09-01

    In this work, a gas flow sputtering (GFS) process which allows the production and deposition of metal nanoparticles (NPs) in a vacuum environment is described. Aim of the study is to prove the potential of this technology for the fabrication of new TiO2 films with enhanced photocatalytic properties. For this purpose, Ag and Pt NPs have been produced and deposited on photocatalytic float glass coated with TiO2 thin films by magnetron sputtering. The influence of the process parameters and of the metal amount on the final properties of the particles (quantity, size, size distribution, oxidation state etc.,) was widely investigated. Moreover, the effect of the NPs on the photocatalytic activity of the resulting materials was evaluated for the case of the decomposition of stearic acid (SA) during UV-A irradiation. The reduction of the water contact angle (WCA) during the irradiation period was measured in order to test the photo-induced super-hydrophilicity (PSH).

  17. Phase-Modulation Gas-Correlation Spectroscopy

    NASA Technical Reports Server (NTRS)

    Rider, David M.; Schofield, John T.; Margolis, Jack S.; Mccleese, Daniel J.

    1989-01-01

    Electro-optic phase-modulation gas-correlation spectroscopy demonstrated in laboratory tests promising candidate technique for remote sensing of gases, temperatures, and wind velocities in atmosphere. In technique radiation emitted by sample atmosphere passed through electro-optic phase modulator, and modulated and unmodulated versions of spectrum alternately passed through reference absorption cell containing gas to be detected. Radiation emerging from reference cell band-pass filtered and detected. Correlation signal is difference in intensity between phase-modulated and unmodulated detected signals.

  18. Photocatalytic selective oxidation of hydrocarbons in the aqueous phase

    SciTech Connect

    Gonzalez, M.A.; Howell, S.G.; Sikdar, S.K.

    1999-04-01

    The sustainable transformation of an inert alkane into its corresponding oxygenates has been the subject of intense chemical research. These oxygenates typically produced from processes using stringent conditions and materials offer disadvantages that include decreased selectivities to the partial oxygenates and by-product formation. As environmental concerns and regulations become more rigorous, the need for alternative catalytic oxidation processes that use mild or ambient conditions is increased. In this Note, the authors have investigated the use of photocatalysis as a low-temperature and green alternative for the direct and selective oxidation of alkanes with molecular oxygen. Research has been directed toward the use of a heterogeneous liquid-phase reactor for the partial oxidation of cyclohexane, toluene, methylcyclohexane, ethylbenzene, and cumene to their corresponding oxygenates.

  19. Thermal phases of interstellar and quasar gas

    NASA Technical Reports Server (NTRS)

    Lepp, S.; Mccray, R.; Shull, J. M.; Woods, D. T.; Kallman, T.

    1985-01-01

    Interstellar gas may be in a variety of thermal phases, depending on how it is heated and ionized; here a unified picture of the equation of state of interstellar and quasar gas is presented for a variety of such mechanisms over a broad range of temperatures, densities, and column densities of absorbing matter. It is found that for select ranges of gas pressure, photoionizing flux, and heating, three thermally stable phases are allowed: coronal gas (T above 100,000 K); warm gas (T about 10,000 K); and cold gas (T less than 100 K). With attenuation of ultraviolet and X-ray radiation, the cold phase may undergo a transition to molecules. In quasar broad-line clouds, this transition occurs at column density N(H) = about 10 to the 23rd/sq cm and could result in warm molecular cores and observable emission from H2 and OH. The underlying atomic physics behind each of these phase transitions and their relevance to interstellar matter and quasars are discussed.

  20. Real Gas/Blunt Cone. Phase 2

    NASA Technical Reports Server (NTRS)

    Deiwert, George S.; Eitelberg, Georg

    1998-01-01

    In this chapter recent activity in real-gas database definition and code validation will be summarized. In the Phase I report of the Working Group (WG) 181, aerothermodynamic problems were classified, for purpose of discussion, into seven types: aerodynamic parameters, viscous/shock interaction, boundary-layer transition, forebody-heating/heat-transfer, radiation and ablation, lee and base-region flow, and low-density flow. Several of these problem types were the subject of various chapters of the Phase 1 report describing real-gas effects and ground test facility issues. In this chapter some background and objectives outlined in the real-Gas effects Chapter V of the Phase 1 report will be reviewed. The results of the blunt cone test campaign developed under the auspices of the WG18 activity to study real-gas phenomena will be summarized, including the experimental and computational programs, issues and questions, and recommendations. Further, recent progress in other real-gas areas beyond the blunt cone test campaign will be discussed. Finally, a summary in which the present status of our understanding of real-gas issues will be presented.

  1. Enhanced photocatalytic activity in electrospun bismuth vanadate nanofibers with phase junction.

    PubMed

    Cheng, Jing; Feng, Jing; Pan, Wei

    2015-05-13

    BiVO4 nanofibers were successfully prepared by electrospinning and precisely controlled heat treatment. The obtained BiVO4 nanofibers showed an enhanced photocatalytic activity in the degradation of rhodamine-B under visible light irradiation. The as-prepared nanofibers were characterized by means of numerous techniques. The enhanced photocatalyst activity is attributed to the formation of a phase junction of tetragonal sheelite (s-t) and monoclinic sheelite (s-m) phases in the electrospun BiVO4 nanofibers. We have also investigated the band structure of BiVO4 using first principle calculation. The main photon transition mechanism of the photocatalyst should be from the O 2p to V 3d state of s-m/t BiVO4 nanofibers.

  2. Laser Studies of Gas Phase Radical Reactions.

    DTIC Science & Technology

    1989-01-01

    Acremonium chrysogenum , was prepared according to the published procedure [6]. This fungal enzyme had a specific activity of 0.023 IUmg1, and was estimated to...Dist-lbitionj Avdielbiity Codes jAvail atidjor Dist 6a A-I . p -1- Laser Studies of Gas Phase Radical Reactions G. Hancock Physical Chemistry...some additional experiments concerning the formation of carbene radicals in liquid phase enzyme cleavage studies are described. Keywords Laser

  3. Synthesis and photocatalytic performance of g-C3N4 nanosheets via liquid phase stripping

    NASA Astrophysics Data System (ADS)

    Miao, Jilin; Xu, Guangqing; Liu, Jiaqin; Lv, Jun; Wu, Yucheng

    2017-02-01

    Well dispersed g-C3N4 nanosheets were prepared by exfoliating the bulk g-C3N4 in concentrated sulfuric acid. Phase structures, morphologies and elemental compositions were characterized by X-ray diffractometer, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectrometer, respectively. Optical absorption and photoluminescence were also used to explain the optical performances of samples. NaI, BQ and IPA were used as the sacrificial agents for studying the surface reactions in the photocatalytic process. By the precipitation of g-C3N4 nanosheets in ethanol with different ratios between concentrated sulfuric acid and ethyl alcohol, well dispersed g-C3N4 nanosheets with high specific surface area can be obtained. The optimized g-C3N4 (1:10) nanosheets achieve the highest photocatalytic activities under UV light illumination, which can degrade 10 mg/L RhB about 98% in 60 min, which is 6 times that of bulk g-C3N4 under UV light.

  4. Continuous-Flow Gas-Phase Bioreactors

    NASA Technical Reports Server (NTRS)

    Wise, Donald L.; Trantolo, Debra J.

    1994-01-01

    Continuous-flow gas-phase bioreactors proposed for biochemical, food-processing, and related industries. Reactor contains one or more selected enzymes dehydrated or otherwise immobilized on solid carrier. Selected reactant gases fed into reactor, wherein chemical reactions catalyzed by enzyme(s) yield product biochemicals. Concept based on discovery that enzymes not necessarily placed in traditional aqueous environments to function as biocatalysts.

  5. EPA GAS PHASE CHEMISTRY CHAMBER STUDIES

    EPA Science Inventory

    Gas-phase smog chamber experiments are being performed at EPA in order to evaluate a number of current chemical mechanisms for inclusion in EPA regulatory and research models. The smog chambers are 9000 L in volume and constructed of 2-mil teflon film. One of the chambers is co...

  6. Gas-Phase Infrared; JCAMP Format

    National Institute of Standards and Technology Data Gateway

    SRD 35 NIST/EPA Gas-Phase Infrared; JCAMP Format (PC database for purchase)   This data collection contains 5,228 infrared spectra in the JCAMP-DX (Joint Committee for Atomic and Molecular Physical Data "Data Exchange") format.

  7. Enzyme-catalyzed, gas-phase reactions.

    PubMed

    Barzana, E; Klibanov, A M; Karel, M

    1987-06-01

    Dehydrated preparations of alcohol oxidase adsorbed on DEAE-cellulose vigorously catalyze a gas-phase oxidation of ethanol vapors with molecular oxygen. The gas-phase reaction is strongly dependent on the water activity of the system. The enzymatic activity is severely inhibited by the product hydrogen peroxide. This inhibition can be alleviated, however, by an addition of catalase or peroxidase to the dry preparation. Such dehydrated, bienzymic catalysts afford a complete and selective conversion of the substrate to acetaldehyde. Dry alcohol oxidase is much more thermostable than in aqueous solution. The results of this work suggest that dehydrated enzymes have potential applications in the analysis of gaseous compounds and in the development of novel gas-solid bioreactors.

  8. High visible light photocatalytic property of Co2+-doped TiO2 nanoparticles with mixed phases

    NASA Astrophysics Data System (ADS)

    Zhao, Cong; Shu, Xin; Zhu, Da-chuan; Wei, Shang-hai; Wang, Yu-xin; Tu, Ming-jing; Gao, Wei

    2015-12-01

    Mixed phases Co2+-doped TiO2 nanoparticles have been prepared by a novel method combined with sol-gel and hydrothermal methods. The section of sol-gel method, sol, provides an unstable colloidal reaction system for the next reaction process. The hydrothermal method is to treat the above reaction system to prepare undoped and doped samples. The as-prepared samples have been characterized by XRD, SEM, TEM, HRTEM and UV-vis spectroscopy. The results show that the as-prepared samples contain three titania polymorphs: brookite, rutile and anatase phases. These titania polymorphs probably form polymorph-junctions that can extend the lifetime of photogenerated electron-hole pairs. The photocatalytic activity has been evaluated by the photocatalytic degradation of Rhodamine B in air under visible-light irradiation. The degradation results indicate that the photocatalytic activity of as-prepared samples is higher than that of Degussa P25, especially the doped sample. This is ascribed to the fact that the phases with smaller band gap can enhance visible-light photocatalytic activity, the polymorph-junctions effectively extend the photoelectron lifetime and the nano size effect and Co-doping induce the shift of the absorption edge into the visible-light region. Furthermore, the XRD, SEM, and TEM data indicate that Co2+-doping results in the decrease of particle size.

  9. Facile synthesis and photocatalytic activity of bi-phase dispersible Cu-ZnO hybrid nanoparticles

    NASA Astrophysics Data System (ADS)

    Liu, Xiao; Liu, HongLing; Zhang, WenXing; Li, XueMei; Fang, Ning; Wang, XianHong; Wu, JunHua

    2015-04-01

    Bi-phase dispersible Cu-ZnO hybrid nanoparticles were synthesized by one-pot non-aqueous nanoemulsion with the use of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEO-PPO-PEO) as the surfactant. The transmission electron microscopy (TEM) and X-ray diffraction (XRD) show high crystallinity of the Cu-ZnO hybrid nanoparticles and an average particle size of ~19.4 nm. The ultraviolet-visible light absorbance spectrometry (UV-vis) and photoluminescence spectrophotometry (PL) demonstrate well dispersibility and excellent optical performance of Cu-ZnO hybrid nanoparticles both in organic and aqueous solvent. The X-ray photoelectron spectroscopy (XPS) confirms Cu1+ and Cu2+ in ZnO. The observation using Sudan red (III) as probe molecule reveals that the Cu-ZnO hybrid nanoparticles possess enhanced photocatalytic activity and stability which are promising for potential applications in photocatalysis.

  10. Facile synthesis and photocatalytic activity of bi-phase dispersible Cu-ZnO hybrid nanoparticles.

    PubMed

    Liu, Xiao; Liu, HongLing; Zhang, WenXing; Li, XueMei; Fang, Ning; Wang, XianHong; Wu, JunHua

    2015-01-01

    Bi-phase dispersible Cu-ZnO hybrid nanoparticles were synthesized by one-pot non-aqueous nanoemulsion with the use of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEO-PPO-PEO) as the surfactant. The transmission electron microscopy (TEM) and X-ray diffraction (XRD) show high crystallinity of the Cu-ZnO hybrid nanoparticles and an average particle size of ~19.4 nm. The ultraviolet-visible light absorbance spectrometry (UV-vis) and photoluminescence spectrophotometry (PL) demonstrate well dispersibility and excellent optical performance of Cu-ZnO hybrid nanoparticles both in organic and aqueous solvent. The X-ray photoelectron spectroscopy (XPS) confirms Cu(1+) and Cu(2+) in ZnO. The observation using Sudan red (III) as probe molecule reveals that the Cu-ZnO hybrid nanoparticles possess enhanced photocatalytic activity and stability which are promising for potential applications in photocatalysis.

  11. Titanium Dioxide Coatings Sprayed by a Water-Stabilized Plasma Gun (WSP) with Argon and Nitrogen as the Powder Feeding Gas: Differences in Structural, Mechanical and Photocatalytic Behavior

    NASA Astrophysics Data System (ADS)

    Ctibor, P.; Pala, Z.; Sedláček, J.; Štengl, V.; Píš, I.; Zahoranová, T.; Nehasil, V.

    2012-06-01

    Titanium dioxide coatings were sprayed by a water-stabilized plasma gun to form robust self-supporting bodies with a photocatalytically active surface. Agglomerated nanometric powder was used as a feedstock. In one case argon was used as a powder-feeding as well as coating-cooling gas whereas in the other case nitrogen was used. Stainless steel was used as a substrate and the coatings were released after the cooling. Over one millimeter thick self-supporting bodies were studied by XRD, HR-TEM, XPS, Raman spectroscopy, UV-VIS spectrophotometry and photocatalytic tests. Selected tests were done at the surface as well as at the bottom side representing the contact surface with the substrate during the spray process. Porosity was studied by image analysis on polished cross sections where also microhardness was measured. The dominant phase present in the sprayed samples was rutile, whereas anatase was only a minor component. The hydrogen content in the nitrogen-assisted coating was higher, but the character of the optical absorption edge remained the same for both samples. Photoelectron spectroscopy revealed differences in the character of the O1s peak between both samples. The photocatalytic activity was tested by decomposition of acetone at UV illumination, whereas also the end products—CO and CO2—were monitored. The nitrogen-assisted coating was revealed as a more efficient photocatalyst. Certain aspects of a thermal post-treatment on the coatings are discussed as well. Color and electrical conductivity are markedly changed at annealing at 760 °C, whereas only very small changes of the as-sprayed coating character correspond to annealing at 500 °C.

  12. Preparation of electrospun Ag/TiO2 nanotubes with enhanced photocatalytic activity based on water/oil phase separation

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Wei, Jinxin; Shi, Huimin; Zhou, Ming; Zhang, Yu; Chen, Qi; Zhang, Zhengmei

    2017-02-01

    Ag/TiO2 composite nanotubes were prepared by electrospinning based on water/oil phase separation effect, their photocatalytic abilities were evaluated under the UV-visible light irradiation. Comparing with bare TiO2 nanofibers, Ag/TiO2 nanotubes exhibited enhanced photocatalytic activities in the decomposition of Rhodamine B (RhB) solution. The enhanced photocatalytic activity of Ag/TiO2 nanotubes stems from the improved separation of photo-generated electron-hole pairs induced by Ag and the high dyes absorption ability of Ag/TiO2 nanotubes; the high specific surface areas of Ag/TiO2 nanotubes with large amounts of active sites, speeding the photocatalytic activity up; the short diffusion path of photo-generated carriers caused by thin thickness of Ag/TiO2 nanotubes. The strategy, fabrication electrospun Ag/TiO2 hybrid nanotubes based on water/oil phase separation effect, is a one step, simple and versatile method, which can be easily expanded to the fabrication of other materials for photocatalysis, water splitting and energy conversion.

  13. Comparison of electrical and optical characteristics in gas-phase and gas-liquid phase discharges

    NASA Astrophysics Data System (ADS)

    Qazi, H. I. A.; Nie, Qiu-Yue; Li, He-Ping; Zhang, Xiao-Fei; Bao, Cheng-Yu

    2015-12-01

    This paper presents an AC-excited argon discharge generated using a gas-liquid (two-phase) hybrid plasma reactor, which mainly consists of a powered needle electrode enclosed in a conical quartz tube and grounded deionized water electrode. The discharges in the gas-phase, as well as in the two-phase, exhibit two discharge modes, i.e., the low current glow-like diffuse mode and the high current streamer-like constrict mode, with a mode transition, which exhibits a negative resistance of the discharges. The optical emission spectral analysis shows that the stronger diffusion of the water vapor into the discharge region in the two-phase discharges boosts up the generation of OH (A-X) radicals, and consequently, leads to a higher rotational temperature in the water-phase plasma plume than that of the gas-phase discharges. Both the increase of the power input and the decrease of the argon flow rate result in the increase of the rotational temperature in the plasma plume of the water-phase discharge. The stable two-phase discharges with a long plasma plume in the water-phase under a low power input and gas flow rate may show a promising prospect for the degradation of organic pollutants, e.g., printing and dyeing wastewater, in the field of environmental protection.

  14. Comparison of electrical and optical characteristics in gas-phase and gas-liquid phase discharges

    SciTech Connect

    Qazi, H. I. A.; Li, He-Ping Zhang, Xiao-Fei; Bao, Cheng-Yu; Nie, Qiu-Yue

    2015-12-15

    This paper presents an AC-excited argon discharge generated using a gas-liquid (two-phase) hybrid plasma reactor, which mainly consists of a powered needle electrode enclosed in a conical quartz tube and grounded deionized water electrode. The discharges in the gas-phase, as well as in the two-phase, exhibit two discharge modes, i.e., the low current glow-like diffuse mode and the high current streamer-like constrict mode, with a mode transition, which exhibits a negative resistance of the discharges. The optical emission spectral analysis shows that the stronger diffusion of the water vapor into the discharge region in the two-phase discharges boosts up the generation of OH (A–X) radicals, and consequently, leads to a higher rotational temperature in the water-phase plasma plume than that of the gas-phase discharges. Both the increase of the power input and the decrease of the argon flow rate result in the increase of the rotational temperature in the plasma plume of the water-phase discharge. The stable two-phase discharges with a long plasma plume in the water-phase under a low power input and gas flow rate may show a promising prospect for the degradation of organic pollutants, e.g., printing and dyeing wastewater, in the field of environmental protection.

  15. Receptors useful for gas phase chemical sensing

    DOEpatents

    Jaworski, Justyn W; Lee, Seung-Wuk; Majumdar, Arunava; Raorane, Digvijay A

    2015-02-17

    The invention provides for a receptor, capable of binding to a target molecule, linked to a hygroscopic polymer or hydrogel; and the use of this receptor in a device for detecting the target molecule in a gaseous and/or liquid phase. The invention also provides for a method for detecting the presence of a target molecule in the gas phase using the device. In particular, the receptor can be a peptide capable of binding a 2,4,6-trinitrotoluene (TNT) or 2,4,-dinitrotoluene (DNT).

  16. Experimental Thermochemistry of Gas Phase Cytosine Tautomers

    NASA Astrophysics Data System (ADS)

    Morrison, A. M.; Douberly, G. E.

    2011-06-01

    Enthalpies of interconversion are measured for the three lowest energy tautomers of isolated cytosine. The equilibrium distribution of tautomers near 600 K is frozen upon the capture of the gas phase species by low temperature helium nanodroplets. The temperature dependence of the gas phase cytosine tautomer populations is determined with infrared laser spectroscopy of the helium solvated species. The interconverison enthalpies obtained from the van't Hoff relation are 1.14 ± 0.21 and 1.63 ± 0.12 for the C31 rightleftharpoons C32 and C31 rightleftharpoons C1 equilibria, respectively. C31 and C32 are rotamers of an enol tautomer, and C1 is a keto tautomer. The interconversion enthalpies are compared to recent CCSD(T) thermochemistry calculations of cytosine tautomers.

  17. Gas-Phase Photoionization Of A Protein

    NASA Astrophysics Data System (ADS)

    Milosavljevic, A. R.; Giuliani, A.; Nicolas, C.; Gil, J.-F.; Lemaire, J.; Refregiers, M.; Nahon, L.

    2010-07-01

    We present preliminary results on gas phase photoionization of electrosprayproduced multiply protonated cytochrome c protein (104 amino acids; ˜12.4 kDa), which has been achieved with a newly developed experimental system for spectroscopy of electrosprayed ions in a linear quadrupole ion trap using a monochromatized vacuum ultraviolet (VUV) synchrotron radiation and tandem mass spectrometry method. The investigation of proteins in the gas phase, where they are free of the influence of counterions and solvent molecules, offer a possibility to understand their intrinsic molecular properties. However, due to limited both ion densities and available number of photons, the use of synchrotron radiation for the trapped ions spectroscopy is a rather challenging task. The feasibility of coupling a Fourier transform ion cyclotron resonance ion trap with soft x-ray synchrotron beamline and the first successful use of synchrotron radiation for spectroscopy of electrosprayed negative ions stored in a three-dimensional quadrupole ion trap have been demonstrated only recently (R. Thissen et al., 2008, Phys. Rev. Lett., 100, 223001; A. Giulliani et al., Proc. 57th ASMS Conf., Philadelphia, 2009). The present results are the first reported on photoionization of kDa species in the gas phase and are valuable regarding both a fundamental interest of accessing physical properties of large biological ions isolated in vacuo and potential development of a new technique for proteomics.

  18. Nonaqueous seeded growth of flower-like mixed-phase titania nanostructures for photocatalytic applications

    SciTech Connect

    Hsu, Y.-C.; Lin, H.-C.; Chen, C.-H.; Liao, Y.-T.; Yang, C.-M.

    2010-09-15

    A nonaqueous seeded-grown synthesis of three-dimensional TiO{sub 2} nanostructures in the benzyl alcohol reaction system was reported. The synthesis was simple, high-yield, and requires no structural directing or capping agents. It could be largely accelerated by applying microwave heating. The TiO{sub 2} nanostructures had a unique flower-like morphology and high surface area. Furthermore, the structural analyses suggested that the nanostructures had a non-uniform distribution of crystalline phases, with the inner part rich in anatase and the outer part rich in rutile. After heat treatments, the mixed-phase TiO{sub 2} nanostructures exhibited high photocatalytic activities for the photodegradation of methylene blue as compared to Degussa P25. The high photoactivities may be associated with the high surface area and the synergistic effect resulting from the anisotropic mixed-phase nanostructures. The results demonstrate the uniqueness of the nonaqueous seeded growth and the potential of the TiO{sub 2} nanostructures for practical applications. - Graphical abstract: Flower-like TiO{sub 2} nanostructures synthesized by a nonaqueous seeded growth without using any structural directing or capping agents.

  19. Nonaqueous seeded growth of flower-like mixed-phase titania nanostructures for photocatalytic applications

    NASA Astrophysics Data System (ADS)

    Hsu, Yu-Chuan; Lin, Huang-Ching; Chen, Chia-Hsiu; Liao, Yi-Ting; Yang, Chia-Min

    2010-09-01

    A nonaqueous seeded-grown synthesis of three-dimensional TiO 2 nanostructures in the benzyl alcohol reaction system was reported. The synthesis was simple, high-yield, and requires no structural directing or capping agents. It could be largely accelerated by applying microwave heating. The TiO 2 nanostructures had a unique flower-like morphology and high surface area. Furthermore, the structural analyses suggested that the nanostructures had a non-uniform distribution of crystalline phases, with the inner part rich in anatase and the outer part rich in rutile. After heat treatments, the mixed-phase TiO 2 nanostructures exhibited high photocatalytic activities for the photodegradation of methylene blue as compared to Degussa P25. The high photoactivities may be associated with the high surface area and the synergistic effect resulting from the anisotropic mixed-phase nanostructures. The results demonstrate the uniqueness of the nonaqueous seeded growth and the potential of the TiO 2 nanostructures for practical applications.

  20. Influence of crystalline phase and defects in the ZrO{sub 2} nanoparticles synthesized by thermal plasma route on its photocatalytic properties

    SciTech Connect

    Nawale, Ashok B.; Kanhe, Nilesh S.; Bhoraskar, S.V.; Mathe, V.L.; Das, A.K.

    2012-11-15

    Graphical abstract: Thermal plasma synthesized nanophase zirconia showing the blue shift in the band gap of monoclinic phase as found from the photoabsorption spectroscopy was found to be the dominant parameter for the enhancement in its photocatalytic activity. The existence of different defect states and their concentration in as synthesized samples also inferred from the photoabsorption measurements were also found to be responsible for the enhanced photocatalytic activity of the samples. Highlights: ► Phase controlled structural formation of nanophase ZrO{sub 2} by thermal plasma route. ► Enhanced photocatalytic degradation rate of methylene blue dye. ► The blue shift in the band gap of monoclinic phase of nanocrystalline ZrO{sub 2}. ► Existence of different defect states in the as synthesized nano phase ZrO{sub 2}. ► Several competing processes which controls the photocatalytic degradation rate. -- Abstract: The photocatalytic activity of pure ZrO{sub 2} samples, prepared by a thermal plasma route, and characterized by X-ray diffraction technique was tested for the degradation of methylene blue, which is known to be a hazardous dye. Although, all these samples synthesized at different operating pressures of the thermal plasma reactor showed the photocatalytic activity; the sample synthesized at 1.33 bar of operating pressure showed the highest photocatalytic activity. The blue shift in the band gap of monoclinic phase, as observed from the photo-absorption spectroscopy, may be attributed to the enhanced photocatalytic activity. The existence of different defect states and their concentration as, inferred from the photo-absorption measurements were also found to be responsible for the enhanced photocatalytic activity of the as synthesized samples.

  1. Mesoporous mixed-phase Ga{sub 2}O{sub 3}: Green synthesis and enhanced photocatalytic activity

    SciTech Connect

    Liu, Jin; Zhang, Gaoke

    2015-08-15

    Highlights: • Mixed-phase Ga{sub 2}O{sub 3} was synthesized by a facile and green method. • Mixed-phase Ga{sub 2}O{sub 3} exhibited good photocatalytic activity and stability. • The reactive species in the photocatalytic process were investigated. - Abstract: Mesoporous mixed-phase Ga{sub 2}O{sub 3} was synthesized by calcining the GaOOH precursor. The composition, crystal phase and microstructures of Ga{sub 2}O{sub 3} were characterized in detail. The phase composition of the as-prepared Ga{sub 2}O{sub 3} depended on the calcination temperature and the mixed-phase Ga{sub 2}O{sub 3} was obtained at 600–700 °C. As compared to the pure-phase α-Ga{sub 2}O{sub 3} and β-Ga{sub 2}O{sub 3}, the mixed-phase Ga{sub 2}O{sub 3} exhibited an enhanced photocatalytic property for the degradation of metronidazole solution. The heterojunction in the mixed-phase Ga{sub 2}O{sub 3} was beneficial to the separation of photogenerated electrons and holes. Moreover, the mixed-phase Ga{sub 2}O{sub 3} possessed mesopore structure, which increased more reaction sites and was in favor of the contact of metronidazole molecules with reaction sites. The recycling experiments show that the mixed-phase Ga{sub 2}O{sub 3} has good stability and can be separated easily from the reaction system.

  2. One-pot solvothermal synthesis of dual-phase titanate/titania Nanoparticles and their adsorption and photocatalytic Performances

    SciTech Connect

    Cheng, Yu Hua; Gong, Dangguo; Tang, Yuxin; Ho, Jeffery Weng Chye; Tay, Yee Yan; Lau, Wei Siew; Wijaya, Olivia; Lim, Jiexiang; Chen, Zhong

    2014-06-01

    Dual phase titanate/titania nanoparticles undergo phase transformation gradually with the increase of solvothermal synthesis temperature from 100 °C to 200 °C, and eventually are fully transformed into anatase TiO{sub 2}. The crystal structure change results in the changes of optical absorption, sensitizer/dopant formation and surface area of the materials which finally affect the overall dye removal ability. Reactions under dark and light have been conducted to distinguish the contributions of surface adsorption from photocatalytic degradation. The sample synthesized at 160 °C (S160) shows the best performances for both adsorption under dark and photocatalytic degradation of methylene blue (MB) under visible light irradiation. The adsorption mechanism for S160 is determined as monolayer adsorption based on the adsorption isotherm test under dark condition, and an impressive adsorption capacity of 162.19 mg/g is achieved. For the photocatalytic application, this sample at 0.1 g/L loading is also able to degrade 20 ppm MB within 6 hours under the visible light (>420 nm) condition. - Graphical abstract: The effect of solvothermal synthesis temperature on the formation and dye removal performance of dual phase titanate/titania nanoparticles was unveiled and optimized. - Highlights: • Low temperature one-pot solvothermal synthesis of dual-phase photocatalysts. • Correlation of the synthesis temperature is made with the phase composition. • Adsorption isotherm, kinetics, photocatalytic degradation were studied. • Synthesis at 160 °C yields the best material for adsorption of MB in dark. • The same sample also shows the best visible light degradation of MB.

  3. Photocatalytical Antibacterial Activity of Mixed-Phase TiO2 Nanocomposite Thin Films against Aggregatibacter actinomycetemcomitans.

    PubMed

    Yeniyol, Sinem; Mutlu, Ilven; He, Zhiming; Yüksel, Behiye; Boylan, Robert Joseph; Ürgen, Mustafa; Karabuda, Zihni Cüneyt; Basegmez, Cansu; Ricci, John Lawrence

    2015-01-01

    Mixed-phase TiO2 nanocomposite thin films consisting of anatase and rutile prepared on commercially pure Ti sheets via the electrochemical anodization and annealing treatments were investigated in terms of their photocatalytic activity for antibacterial use around dental implants. The resulting films were characterized by scanning electron microscopy (SEM), and X-ray diffraction (XRD). The topology was assessed by White Light Optical Profiling (WLOP) in the Vertical Scanning Interferometer (VSI) mode. Representative height descriptive parameters of roughness R a and R z were calculated. The photocatalytic activity of the resulting TiO2 films was evaluated by the photodegradation of Rhodamine B (RhB) dye solution. The antibacterial ability of the photocatalyst was examined by Aggregatibacter actinomycetemcomitans suspensions in a colony-forming assay. XRD showed that anatase/rutile mixed-phase TiO2 thin films were predominantly in anatase and rutile that were 54.6 wt% and 41.9 wt%, respectively. Craters (2-5 µm) and protruding hills (10-50 µm) on Ti substrates were produced after electrochemical anodization with higher R a and R z surface roughness values. Anatase/rutile mixed-phase TiO2 thin films showed 26% photocatalytic decolorization toward RhB dye solution. The number of colonizing bacteria on anatase/rutile mixed-phase TiO2 thin films was decreased significantly in vitro. The photocatalyst was effective against A. actinomycetemcomitans colonization.

  4. Photocatalytical Antibacterial Activity of Mixed-Phase TiO2 Nanocomposite Thin Films against Aggregatibacter actinomycetemcomitans

    PubMed Central

    Yeniyol, Sinem; Mutlu, Ilven; He, Zhiming; Yüksel, Behiye; Boylan, Robert Joseph; Ürgen, Mustafa; Karabuda, Zihni Cüneyt; Basegmez, Cansu; Ricci, John Lawrence

    2015-01-01

    Mixed-phase TiO2 nanocomposite thin films consisting of anatase and rutile prepared on commercially pure Ti sheets via the electrochemical anodization and annealing treatments were investigated in terms of their photocatalytic activity for antibacterial use around dental implants. The resulting films were characterized by scanning electron microscopy (SEM), and X-ray diffraction (XRD). The topology was assessed by White Light Optical Profiling (WLOP) in the Vertical Scanning Interferometer (VSI) mode. Representative height descriptive parameters of roughness Ra and Rz were calculated. The photocatalytic activity of the resulting TiO2 films was evaluated by the photodegradation of Rhodamine B (RhB) dye solution. The antibacterial ability of the photocatalyst was examined by  Aggregatibacter actinomycetemcomitans suspensions in a colony-forming assay. XRD showed that anatase/rutile mixed-phase TiO2 thin films were predominantly in anatase and rutile that were 54.6 wt% and 41.9 wt%, respectively. Craters (2–5 µm) and protruding hills (10–50 µm) on Ti substrates were produced after electrochemical anodization with higher Ra and Rz surface roughness values. Anatase/rutile mixed-phase TiO2 thin films showed 26% photocatalytic decolorization toward RhB dye solution. The number of colonizing bacteria on anatase/rutile mixed-phase TiO2 thin films was decreased significantly in vitro. The photocatalyst was effective against A. actinomycetemcomitans colonization. PMID:26576430

  5. The preparation of Zn2+-doped TiO(2) nanoparticles by sol-gel and solid phase reaction methods respectively and their photocatalytic activities.

    PubMed

    Liu, Guoguang; Zhang, Xuezhi; Xu, Yajie; Niu, Xinshu; Zheng, Liqing; Ding, Xuejun

    2005-06-01

    The photocatalytic oxidation of the organic pollutants with TiO(2) as photocatalyst has been widely studied in the world, and many achievements have been made. The degradation of pollutants is highly related to the photocatalytic activity of TiO(2). It is demonstrated that doping ions to TiO(2) is one way to enhance the photocatalytic activity of TiO(2). In this paper, Zn(2+)-doped TiO(2) nanoparticles were prepared through sol-gel and solid phase reaction methods, characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The photocatalytic activity of the elaborated powders was studied following the degradation of Rhodamine B. The results showed that the photocatalytic activity of Zn(2+)-doped TiO(2) prepared by sol-gel method is close to that of pure TiO(2) particles, however, the photocatalytic activity of Zn(2+)-doped TiO(2) prepared by solid phase reaction method is much higher than that of pure TiO(2) particles. The most efficient degradation of Rhodamine B was found with TiO(2) particles doped with 0.5% Zn(2+) in mole and calcined at 500 degrees C. Also the reason for the enhancement of the photocatalytic activity of TiO(2) by Zn(2+) doping through solid phase reaction method was discussed.

  6. Gas phase thermochemistry of organogermanium compounds

    SciTech Connect

    Engel, J.P.

    1993-12-07

    A variety of silyl- and alkyl-germylene precursors have been synthesized and subsequently pyrolyzed in the gas phase. Arrhenius parameters were obtained employing a pulsed-stirred flow reactor for these unimolecular decompositions. These precursors are divided into two major categories by mechanism of germylene extrusion: {alpha}-elimination precursors and germylacetylenes. The extrusion of germylenes from germylacetylene precursors is of primary interest. A mechanism is proposed employing a germacyclopropene intermediate. Evidence supporting this mechanism is presented. In the process of exploring germylacetylenes as germylene precursors, an apparent dyatropic rearrangement between germanium and silicon was observed. This rearrangement was subsequently explored.

  7. Vaccum Gas Tungsten Arc Welding, phase 1

    NASA Technical Reports Server (NTRS)

    Weeks, J. L.; Krotz, P. D.; Todd, D. T.; Liaw, Y. K.

    1995-01-01

    This two year program will investigate Vacuum Gas Tungsten Arc Welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. VGTAW appears to offer a significant improvement in weldability because of the clean environment and lower heat input needed. The overall objective of the program is to develop the VGTAW technology and implement it into a manufacturing environment that will result in lower cost, better quality and higher reliability aerospace components for the space shuttle and other NASA space systems. Phase 1 of this program was aimed at demonstrating the process's ability to weld normally difficult-to-weld materials. Phase 2 will focus on further evaluation, a hardware demonstration and a plan to implement VGTAW technology into a manufacturing environment. During Phase 1, the following tasks were performed: (1) Task 11000 Facility Modification - an existing vacuum chamber was modified and adapted to a GTAW power supply; (2) Task 12000 Materials Selection - four difficult-to-weld materials typically used in the construction of aerospace hardware were chosen for study; (3) Task 13000 VGTAW Experiments - welding experiments were conducted under vacuum using the hollow tungsten electrode and evaluation. As a result of this effort, two materials, NARloy Z and Incoloy 903, were downselected for further characterization in Phase 2; and (4) Task 13100 Aluminum-Lithium Weld Studies - this task was added to the original work statement to investigate the effects of vacuum welding and weld pool vibration on aluminum-lithium alloys.

  8. Giddings Austin chalk enters deep lean-gas phase

    SciTech Connect

    Moritis, G.

    1995-12-25

    Deep lean gas is the latest phase in the growth of the Giddings field Austin chalk play. The first phase involved drilling vertical oil and gas wells. Next came the horizontal well boom in the shallower Austin chalk area, which is still continuing. And now this third phase places horizontal laterals in the Austen chalk at about 14,000--15,000 ft to produce lean gas. The article describes the producing wells and gas gathering.

  9. A review of engineering development of aqueous phase solar photocatalytic detoxification and disinfection processes

    SciTech Connect

    Goswami, D.Y.

    1997-05-01

    Scientific research on photocatalytic oxidation of hazardous chemicals has been conducted extensively over the last three decades. Use of solar radiation in photocatalytic detoxification and disinfection has only been explored in the last decade. Developments of engineering scale systems, design methodologies, and commercial and industrial applications have occurred even more recently. A number of reactor concepts and designs including concentrating and nonconcentrating types and methods of catalyst deployment have been developed. Some commercial and industrial field tests of solar detoxification systems have been conducted. This paper reviews the engineering developments of the solar photocatalytic detoxification and disinfection processes, including system design methodologies.

  10. Novel nano coordination polymer based synthesis of porous ZnO hexagonal nanodisk for higher gas sorption and photocatalytic activities

    NASA Astrophysics Data System (ADS)

    Rakibuddin, M.; Ananthakrishnan, Rajakumar

    2016-01-01

    Zinc(II)-based nano co-ordination polymers (NCPs) are first prepared at room temperature from three different isomers of dihydroxysalophen (DHS) ligand with Zn(OAc)2·2H2O and 1,4-benzenedicarboxylic acid (BDC) in DMF solvent. Facile calcinations of [Zn (DHS) (BDC)]·nH2O (shortly denoted as Zn(II)-based NCP) at ambient conditions produces porous ZnO hexagonal nanodisks. Moreover, a novel approach has been introduced to observe the effect of ligand of the NCP on the physico-chemical properties of the as-synthesized ZnO. The porous ZnO nanodisks are characterized by FT-IR, PXRD, TEM, FESEM, EDX and BET analysis, and the results exhibit that they possess different sizes, surface areas and porosities. Nitrogen gas sorption capacity and photocatalytic activities of the as-prepared ZnO nanodisks are also checked, and it is noticed that they differ in these physico-chemical properties due to having different porosities and surface areas. A comparative study is also done with commercially available ZnO; interestingly, the commercial ZnO exhibited lower surface area, gas sorption and photocatalytic activity compared to the ZnO nanodisks. Hence, preparation of the ZnO through the NCP route and tuning their physico-chemical properties would offer new directions in synthesis of various nano metal oxides of unique properties.

  11. Carrier dynamics and the role of surface defects: Designing a photocatalyst for gas-phase CO2 reduction

    DOE PAGES

    Hoch, Laura B.; Szymanski, Paul; Ghuman, Kulbir Kaur; ...

    2016-11-28

    In2O3-x(OH)y nanoparticles have been shown to function as an effective gas-phase photocatalyst for the reduction of CO2 to CO via the reverse water–gas shift reaction. Their photocatalytic activity is strongly correlated to the number of oxygen vacancy and hydroxide defects present in the system. To better understand how such defects interact with photogenerated electrons and holes in these materials, we have studied the relaxation dynamics of In2O3-x(OH)y nanoparticles with varying concentration of defects using two different excitation energies corresponding to above-band-gap (318-nm) and near-band-gap (405-nm) excitations. Our results demonstrate that defects play a significant role in the excited-state, charge relaxationmore » pathways. Higher defect concentrations result in longer excited-state lifetimes, which are attributed to improved charge separation. This correlates well with the observed trends in the photocatalytic activity. These results are further supported by density-functional theory calculations, which confirm the positions of oxygen vacancy and hydroxide defect states within the optical band gap of indium oxide. This enhanced understanding of the role these defects play in determining the optoelectronic properties and charge carrier dynamics can provide valuable insight toward the rational development of more efficient photocatalytic materials for CO2 reduction.« less

  12. Influence of anatase and rutile phase in TiO2 upon the photocatalytic degradation of methylene blue under solar irradiation in presence of activated carbon.

    PubMed

    Matos, J; Montaña, R; Rivero, E; Escudero, A; Uzcategui, D

    2014-01-01

    The influence of activated carbon (AC) on the photocatalytic activity of different crystalline TiO2 phases was verified in the photocatalytic degradation of methylene blue under UV and solar irradiation. The results showed a volcano trend with a maximum photoactivity for the crystalline phase ratio of anatase:rutile equal to 80:20 both under UV or solar irradiation. By contrast, in presence of AC the photocatalytic activity of the binary materials of TiO2/AC followed an exponential trend, increasing as a function of the increase in anatase proportion in the TiO2 framework. The increase in the photoactivity of the binary material TiO2/AC relative to neat TiO2 was up to 22 and about 17 times higher under UV and visible irradiation, respectively. The present results suggest that AC interacts more efficiently with anatase phase than with rutile phase.

  13. Phase transition of BiVO4 nanoparticles in molten salt and the enhancement of visible-light photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Li, Chunguang; Pang, Guangsheng; Sun, Shangmei; Feng, Shouhua

    2010-10-01

    BiVO4 nanoparticles are prepared by molten salt method. Tetragonal BiVO4 completely transforms to monoclinic phase after heating in molten LiNO3 at 270 °C for 18 h. The average particle sizes of monoclinic BiVO4 varied from 30 to 52 nm while the initial ratio of BiVO4 to LiNO3 changes from 1:6 to 1:24. The photocatalytic activity is evaluated by measuring decolorization of N, N, N', N'-tetraethylated rhodamine dye solution under visible-light irradiation. Both of the de-ethylation and chromophore cleavage are responsible for the decolorization of RB. The sample with an average particle size of 52 nm and a moderate surface area of 10 m2/g exhibit the highest visible-light photocatalytic activity. The shift of Raman peak position indicates that the symmetry distortions in the local structure of the monoclinic BiVO4. The variations of the local structure result in the modification of the electronic structure, which is responsible for the high visible-light photocatalytic activity.

  14. Fundamentals of gas phase plasmas for treatment of human tissue.

    PubMed

    Kushner, Mark J; Babaeva, Natalia Yu

    2011-01-01

    The use of gas phase plasmas for treating human tissue is at the intersection of two disciplines - plasma physics and engineering, and medicine. In this paper, a primer will be provided for the medical practitioner on the fundamentals of generating gas phase plasmas at atmospheric pressure in air for the treatment of human tissue. The mechanisms for gas phase plasmas interacting with tissue and biological fluids will also be discussed using results from computer modeling.

  15. Photocatalytic Degradation of Two Commercial Reactive Dyes in Aqueous Phase Using Nanophotocatalysts

    NASA Astrophysics Data System (ADS)

    Kansal, Sushil Kumar; Kaur, Navjeet; Singh, Sukhmehar

    2009-07-01

    This study involves the photocatalytic degradation of Reactive Black 5 (RB5) and Reactive Orange 4 (RO4) dyes, employing heterogeneous photocatalytic process. Photocatalytic activity of different semiconductors such as titanium dioxide (TiO2) and zinc oxide (ZnO) has been investigated. An attempt has been made to study the effect of process parameters through amount of catalyst, concentration of dye, and pH on photocatalytic degradation of RB5 and RO4. The experiments were carried out by varying pH (3-11), amount of catalyst (0.25-1.5 g/L), and initial concentration of dye (10-100 mg/L). The optimum catalyst dose was found to be 1.25 and 1 g/L for RB5 and RO4, respectively. In the case of RB5, maximum rate of decolorization was observed in acidic medium at pH 4, whereas the decolorization of RO4 reached maximum in basic region at pH 11. The performance of photocatalytic system employing ZnO/UV light was observed to be better than TiO2/UV system. The complete decolorization of RB5 was observed after 7 min with ZnO, whereas with TiO2, only 75% dye degraded in 7 min. In the case of RO4, 92 and 62% decolorization was noticed in the same duration.

  16. Photocatalytic Degradation of Two Commercial Reactive Dyes in Aqueous Phase Using Nanophotocatalysts

    PubMed Central

    2009-01-01

    This study involves the photocatalytic degradation of Reactive Black 5 (RB5) and Reactive Orange 4 (RO4) dyes, employing heterogeneous photocatalytic process. Photocatalytic activity of different semiconductors such as titanium dioxide (TiO2) and zinc oxide (ZnO) has been investigated. An attempt has been made to study the effect of process parameters through amount of catalyst, concentration of dye, and pH on photocatalytic degradation of RB5 and RO4. The experiments were carried out by varying pH (3–11), amount of catalyst (0.25–1.5 g/L), and initial concentration of dye (10–100 mg/L). The optimum catalyst dose was found to be 1.25 and 1 g/L for RB5 and RO4, respectively. In the case of RB5, maximum rate of decolorization was observed in acidic medium at pH 4, whereas the decolorization of RO4 reached maximum in basic region at pH 11. The performance of photocatalytic system employing ZnO/UV light was observed to be better than TiO2/UV system. The complete decolorization of RB5 was observed after 7 min with ZnO, whereas with TiO2, only 75% dye degraded in 7 min. In the case of RO4, 92 and 62% decolorization was noticed in the same duration. PMID:20596421

  17. Bacteria and fungi inactivation by photocatalysis under UVA irradiation: liquid and gas phase.

    PubMed

    Rodrigues-Silva, Caio; Miranda, Sandra M; Lopes, Filipe V S; Silva, Mário; Dezotti, Márcia; Silva, Adrián M T; Faria, Joaquim L; Boaventura, Rui A R; Vilar, Vítor J P; Pinto, Eugénia

    2016-06-29

    In the last decade, environmental risks associated with wastewater treatment plants (WWTPs) have become a concern in the scientific community due to the absence of specific legislation governing the occupational exposure limits (OEL) for microorganisms present in indoor air. Thus, it is necessary to develop techniques to effectively inactivate microorganisms present in the air of WWTPs facilities. In the present work, ultraviolet light A radiation was used as inactivation tool. The microbial population was not visibly reduced in the bioaerosol by ultraviolet light A (UVA) photolysis. The UVA photocatalytic process for the inactivation of microorganisms (bacteria and fungi, ATCC strains and isolates from indoor air samples of a WWTP) using titanium dioxide (TiO2 P25) and zinc oxide (ZnO) was tested in both liquid-phase and airborne conditions. In the slurry conditions at liquid phase, P25 showed a better performance in inactivation. For this reason, gas-phase assays were performed in a tubular photoreactor packed with cellulose acetate monolithic structures coated with P25. The survival rate of microorganisms under study decreased with the catalyst load and the UVA exposure time. Inactivation of fungi was slower than resistant bacteria, followed by Gram-positive bacteria and Gram-negative bacteria. Graphical abstract Inactivation of fungi and bacteria in gas phase by photocatalitic process performed in a tubular photoreactor packed with cellulose acetate monolith structures coated with TiO2.

  18. A novel phase-mixed MgTiO3-MgTi2O5 heterogeneous nanorod for high efficiency photocatalytic hydrogen production.

    PubMed

    Qu, Yang; Zhou, Wei; Xie, Ying; Jiang, Le; Wang, Jianqiang; Tian, Guohui; Ren, Zhiyu; Tian, Chungui; Fu, Honggang

    2013-10-04

    A phase-mixed MgTiO3-MgTi2O5 heterogeneous nanorod is fabricated via an ethylene glycol-mediated route to promote the photocatalytic hydrogen production activity significantly. The excellent charge separation and fast electron transport are the main reasons for the high efficiency due to the formation of phase-mixed heterogeneous junctions.

  19. Sunlight-induced effective heterogeneous photocatalytic decomposition of aqueous organic pollutants to CO2 assisted by a CO2 sorbent, amine-containing mesoporous silica.

    PubMed

    Ide, Yusuke; Kagawa, Noriko; Sadakane, Masahiro; Sano, Tsuneji

    2012-06-04

    Photocatalytic mineralization of aqueous formic acid and phenol on pure TiO(2) under sunlight irradiation was substantially accelerated to give a reliable photocatalytic efficiency by conducting the reactions in the presence of a CO(2) sorbent, amine-containing SBA-15, placed in the gas phase of the reactor.

  20. Gas phase hydration of organic ions.

    PubMed

    Momoh, Paul O; El-Shall, M Samy

    2008-08-28

    In this work, we study the hydration phenomenon on a molecular level in the gas phase where a selected number of water molecules can interact with the organic ion of interest. The stepwise binding energies (DeltaH degrees (n-1,n)) of 1-7 water molecules to the phenyl acetylene cation are determined by equilibrium measurements using an ion mobility drift cell. The stepwise hydration energies DeltaH degrees (n-1,n) are nearly constant at 39.7 +/- 6.3 kJ mol(-1) from n = 1 to 7. The entropy change is larger in the n = 7 step, suggesting cyclic or cage-like water structures. No water addition is observed on the ionized phenyl acetylene trimer consistent with cyclization of the trimer ion to form triphenyl benzene cations C(24)H(18) (+) which are expected to interact weakly with the water molecules due to steric interactions and the delocalization of the charge on the large organic ion. The work demonstrates that hydration studies of organic ions can provide structural information on the organic ions.

  1. Intramolecular photoelectron diffraction in the gas phase

    NASA Astrophysics Data System (ADS)

    Ueda, K.; Miron, C.; Plésiat, E.; Argenti, L.; Patanen, M.; Kooser, K.; Ayuso, D.; Mondal, S.; Kimura, M.; Sakai, K.; Travnikova, O.; Palacios, A.; Decleva, P.; Kukk, E.; Martín, F.

    2013-09-01

    We report unambiguous experimental and theoretical evidence of intramolecular photoelectron diffraction in the collective vibrational excitation that accompanies high-energy photoionization of gas-phase CF4, BF3, and CH4 from the 1s orbital of the central atom. We show that the ratios between vibrationally resolved photoionization cross sections (v-ratios) exhibit pronounced oscillations as a function of photon energy, which is the fingerprint of electron diffraction by the surrounding atomic centers. This interpretation is supported by the excellent agreement between first-principles static-exchange and time-dependent density functional theory calculations and high resolution measurements, as well as by qualitative agreement at high energies with a model in which atomic displacements are treated to first order of perturbation theory. The latter model allows us to rationalize the results for all the v-ratios in terms of a generalized v-ratio, which contains information on the structure of the above three molecules and the corresponding molecular cations. A fit of the measured v-ratios to a simple formula based on this model suggests that the method could be used to obtain structural information of both neutral and ionic molecular species.

  2. Intramolecular photoelectron diffraction in the gas phase.

    PubMed

    Ueda, K; Miron, C; Plésiat, E; Argenti, L; Patanen, M; Kooser, K; Ayuso, D; Mondal, S; Kimura, M; Sakai, K; Travnikova, O; Palacios, A; Decleva, P; Kukk, E; Martín, F

    2013-09-28

    We report unambiguous experimental and theoretical evidence of intramolecular photoelectron diffraction in the collective vibrational excitation that accompanies high-energy photoionization of gas-phase CF4, BF3, and CH4 from the 1s orbital of the central atom. We show that the ratios between vibrationally resolved photoionization cross sections (v-ratios) exhibit pronounced oscillations as a function of photon energy, which is the fingerprint of electron diffraction by the surrounding atomic centers. This interpretation is supported by the excellent agreement between first-principles static-exchange and time-dependent density functional theory calculations and high resolution measurements, as well as by qualitative agreement at high energies with a model in which atomic displacements are treated to first order of perturbation theory. The latter model allows us to rationalize the results for all the v-ratios in terms of a generalized v-ratio, which contains information on the structure of the above three molecules and the corresponding molecular cations. A fit of the measured v-ratios to a simple formula based on this model suggests that the method could be used to obtain structural information of both neutral and ionic molecular species.

  3. Instabilities in Lean Gas-Phase Combustion

    NASA Astrophysics Data System (ADS)

    Schneider, K.; Bockhorn, H.; Eigenbrod, Ch.; Emerson, D.; Haldenwang, P.; Hoffmann, F.; Roekaerts, D.; Ronney, P.; Triebel, W.; Tummers, M.

    2005-06-01

    Lean burning is the burning of fuel-air mixtures with less than the chemically- balanced (stoichiometric) mixture. It produces a significant increase in fuel efficiency and reduction in pollution. However, the limits and control of lean burning are still not well understood.This is the motivation behind the study of instabilities in lean gas-phase combustion under microgravity conditions via direct numerical simulations and comparison of the results with experimental data.The goal is to gain fundamental insights in order to identify and understand the intrinsic chemical and fluid dynamical mechanisms responsible for these instabilities.The potential of this microgravity combustion research includes the development of technology that would reduce pollution and fire and explosion hazards, improve hazardous waste incineration and increase efficiency of the conversion of chemical energy to electric power or motive force.The results from this fundamental research will thus benefit chemical engineering and power generation. Its wide range of applications in industry includes lean-burning car engines.

  4. Nitrogen-modified nano-titania: True phase composition, microstructure and visible-light induced photocatalytic NOx abatement

    NASA Astrophysics Data System (ADS)

    Tobaldi, D. M.; Pullar, R. C.; Gualtieri, A. F.; Otero-Irurueta, G.; Singh, M. K.; Seabra, M. P.; Labrincha, J. A.

    2015-11-01

    Titanium dioxide (TiO2) is a popular photocatalyst used for many environmental and anti-pollution applications, but it normally operates under UV light, exploiting ∼5% of the solar spectrum. Nitrification of titania to form N-doped TiO2 has been explored as a way to increase its photocatalytic activity under visible light, and anionic doping is a promising method to enable TiO2 to harvest visible-light by changing its photo-absorption properties. In this paper, we explore the insertion of nitrogen into the TiO2 lattice using our green sol-gel nanosynthesis method, used to create 10 nm TiO2 NPs. Two parallel routes were studied to produce nitrogen-modified TiO2 nanoparticles (NPs), using HNO3+NH3 (acid-precipitated base-peptised) and NH4OH (totally base catalysed) as nitrogen sources. These NPs were thermally treated between 450 and 800 °C. Their true phase composition (crystalline and amorphous phases), as well as their micro-/nanostructure (crystalline domain shape, size and size distribution, edge and screw dislocation density) was fully characterised through advanced X-ray methods (Rietveld-reference intensity ratio, RIR, and whole powder pattern modelling, WPPM). As pollutants, nitrogen oxides (NOx) are of particular concern for human health, so the photocatalytic activity of the NPs was assessed by monitoring NOx abatement, using both solar and white-light (indoor artificial lighting), simulating outdoor and indoor environments, respectively. Results showed that the onset of the anatase-to-rutile phase transformation (ART) occurred at temperatures above 450 °C, and NPs heated to 450 °C possessed excellent photocatalytic activity (PCA) under visible white-light (indoor artificial lighting), with a PCA double than that of the standard P25 TiO2 NPs. However, higher thermal treatment temperatures were found to be detrimental for visible-light photocatalytic activity, due to the effects of four simultaneous occurrences: (i) loss of OH groups and water adsorbed

  5. Hydrocarbon radical thermochemistry: Gas-phase ion chemistry techniques

    SciTech Connect

    Ervin, Kent M.

    2014-03-21

    Final Scientific/Technical Report for the project "Hydrocarbon Radical Thermochemistry: Gas-Phase Ion Chemistry Techniques." The objective of this project is to exploit gas-phase ion chemistry techniques for determination of thermochemical values for neutral hydrocarbon radicals of importance in combustion kinetics.

  6. Pressure Dependence of Gas-Phase Reaction Rates

    ERIC Educational Resources Information Center

    De Persis, Stephanie; Dollet, Alain; Teyssandier, Francis

    2004-01-01

    It is presented that only simple concepts, mainly taken from activated-complex or transition-state theory, are required to explain and analytically describe the influence of pressure on gas-phase reaction kinetics. The simplest kind of elementary gas-phase reaction is a unimolecular decomposition reaction.

  7. Modeling the Phase Composition of Gas Condensate in Pipelines

    NASA Astrophysics Data System (ADS)

    Dudin, S. M.; Zemenkov, Yu D.; Shabarov, A. B.

    2016-10-01

    Gas condensate fields demonstrate a number of thermodynamic characteristics to be considered when they are developed, as well as when gas condensate is transported and processed. A complicated phase behavior of the gas condensate system, as well as the dependence of the extracted raw materials on the phase state of the deposit other conditions being equal, is a key aspect. Therefore, when designing gas condensate lines the crucial task is to select the most appropriate methods of calculating thermophysical properties and phase equilibrium of the transported gas condensate. The paper describes a physical-mathematical model of a gas-liquid flow in the gas condensate line. It was developed based on balance equations of conservation of mass, impulse and energy of the transported medium within the framework of a quasi-1D approach. Constitutive relationships are given separately, and practical recommendations on how to apply the research results are provided as well.

  8. Time Dependent Studies of Reactive Shocks in the Gas Phase

    DTIC Science & Technology

    1978-11-16

    1 LEVEL NRL Memorandum Report 3W tO Time Dependent Studies of Reactive Shocks in the Gas Phase E.S. ORAN, ’T.R. YOUNG and J.P. BORIS Laboratory for...34-• TIME DEPENDENT STUDIES OF REACTIVE SHOCKS IN THE GAS PHASE I. Introduction This paper presents results obtained from a detailed numerical...chemical kinetics, reaction products, and intermediates produced in reactive gas mixtures ignited by the propagation of a shock front. The model is based

  9. Surface modification of mixed-phase hydrogenated TiO2 and corresponding photocatalytic response

    NASA Astrophysics Data System (ADS)

    Samsudin, Emy Marlina; Hamid, Sharifah Bee Abd; Juan, Joon Ching; Basirun, Wan Jefrey; Kandjani, Ahmad Esmaeiljadeh

    2015-12-01

    Preparation of highly photo-activated TiO2 is achievable by hydrogenation at constant temperature and pressure, with controlled hydrogenation duration. The formation of surface disorders and Ti3+ is responsible for the color change from white unhydrogenated TiO2 to bluish-gray hydrogenated TiO2. This color change, together with increased oxygen vacancies and Ti3+ enhanced the solar light absorption from UV to infra-red region. Interestingly, no band gap narrowing is observed. The photocatalytic activity in the UV and visible region is controlled by Ti3+ and oxygen vacancies respectively. Both Ti3+ and oxygen vacancies increases the electron density on the catalyst surface thus facilitates rad OH radicals formation. The lifespan of surface photo-excited electrons and holes are also sustained thus prevents charge carrier recombination. However, excessive amount of oxygen vacancies deteriorates the photocatalytic activity as it serves as charge traps. Hydrogenation of TiO2 also promotes the growth of active {0 0 1} facets and facilitates the photocatalytic activity by higher concentration of surface OH radicals. However, the growth of {0 0 1} facets is small and insignificant toward the overall photo-kinetics. This work also shows that larger role is played by Ti3+ and oxygen vacancies rather than the surface disorders created during the hydrogenation process. It also demonstrates the ability of hydrogenated TiO2 to absorb wider range of photons even though at a similar band gap as unhydrogenated TiO2. In addition, the photocatalytic activity is shown to be decreased for extended hydrogenation duration due to excessive catalyst growth and loss in the total surface area. Thus, a balance in the physico-chemical properties of hydrogenated TiO2 is crucial to enhance the photocatalytic activity by simply controlling the hydrogenation duration.

  10. Gas-phase nitronium ion affinities.

    PubMed Central

    Cacace, F; de Petris, G; Pepi, F; Angelelli, F

    1995-01-01

    Evaluation of nitronium ion-transfer equilibria, L1NO2+ + L2 = L2NO2+ + L1 (where L1 and L2 are ligands 1 and 2, respectively) by Fourier-transform ion cyclotron resonance mass spectrometry and application of the kinetic method, based on the metastable fragmentation of L1(NO2+)L2 nitronium ion-bound dimers led to a scale of relative gas-phase nitronium ion affinities. This scale, calibrated to a recent literature value for the NO2+ affinity of water, led for 18 ligands, including methanol, ammonia, representative ketones, nitriles, and nitroalkanes, to absolute NO2+ affinities, that fit a reasonably linear general correlation when plotted vs. the corresponding proton affinities (PAs). The slope of the plot depends to a certain extent on the specific nature of the ligands and, hence, the correlations between the NO2+ affinities, and the PAs of a given class of compounds display a better linearity than the general correlation and may afford a useful tool for predicting the NO2+ affinity of a molecule based on its PA. The NO2+ binding energies are considerably lower than the corresponding PAs and well below the binding energies of related polyatomic cations, such as NO+, a trend consistent with the available theoretical results on the structure and the stability of simple NO2+ complexes. The present study reports an example of extension of the kinetic method to dimers, such as L1(NO2+)L2, bound by polyatomic ions, which may considerably widen its scope. Finally, measurement of the NO2+ affinity of ammonia allowed evaluation of the otherwise inaccessible PA of the amino group of nitramide and, hence, direct experimental verification of previous theoretical estimates. PMID:11607578

  11. Gas Phase Organophosphate Detection Using Enzymes Encapsulated Within Peptide Nanotubes

    DTIC Science & Technology

    2014-03-27

    as gas and liquid chromatography, although very sensitive and reliable, have disadvantages. The US Air Force currently uses a field portable gas...biosensors to detect OPCs in liquid (Park et al., 2011; Stevens, 2012) and gas (Baker, 2013) phases. Detection is based upon a redox reaction... injecting a known volume of gas saturated at room temperature with malathion (vapor pressure = 25 ppbv), into a 40 ml vial purged with nitrogen at constant

  12. Structural, morphological, gas sensing and photocatalytic characterization of MoO3 and WO3 thin films prepared by the thermal vacuum evaporation technique

    NASA Astrophysics Data System (ADS)

    Arfaoui, A.; Touihri, S.; Mhamdi, A.; Labidi, A.; Manoubi, T.

    2015-12-01

    Thin films of molybdenum trioxide and tungsten trioxide were deposited on glass substrates using a simplified thermal evaporation under vacuum method monitored by heat treatment in flowing oxygen at 500 °C for 1 h. The structural and morphological properties of the films were investigated using X-ray diffraction, Raman spectroscopy, atomic force microscopy and scanning electron microscopy. The X-ray diffraction analysis shows that the films of MoO3 and WO3 were well crystallized in orthorhombic and monoclinic phase respectively with the crystallites preferentially oriented toward (2 0 0) direction parallel a-axis for both samples. In literature, we have shown in previous papers that structural and surface morphology of metal thin films play an important role in the gas detection mechanism. In this article, we have studied the response evolution of MoO3 and WO3 thin films sensors ethanol versus time, working temperature and the concentration of the ethanol. It was found that these films had high sensitivity to ethanol, which made them as a good candidate for the ethanol sensor. Finally, the photocatalytic activity of the samples was evaluated with respect to the degradation reaction of a wastewater containing methylene blue (MB) under UV-visible light irradiation. The molybdenum trioxide exhibits a higher degradation rate than the tungsten trioxide thin films under similar experimental conditions.

  13. Density, phase behavior keys to acid gas injection

    SciTech Connect

    Carroll, J.J.; Lui, D.W.

    1997-06-23

    Acid gas injection requires an understanding of the complexities of gas phase behavior and physical properties. Injected acid gas streams typically come from the top of the regenerator reflux accumulator of an amine unit. Thus, they are composed mainly of hydrogen sulfide (H{sub 2}S) and carbon dioxide (CO{sub 2}) with significant amounts of methane and lesser amounts of other hydrocarbons. The stream is also saturated with water. The stream from the amine plant has a low pressure and must be compressed to a higher pressure for injection into a disposal well. This article summarizes the available research on acid gas phase behavior and density calculations.

  14. Photocatalytic degradation of gaseous 1-propanol using an annular reactor: kinetic modelling and pathways.

    PubMed

    Vincent, G; Marquaire, P M; Zahraa, O

    2009-01-30

    Photocatalytic oxidation of airborne contaminants appears to be a promising process for remediation of air polluted by Volatile Organic Compounds (VOCs). In the present work, the photocatalytic oxidation of gaseous 1-propanol has been investigated by using an annular photoreactor. The annular photocatalytic reactor was modelled by a cascade of heightened elementary continuously stirred tank reactors. The influence of several kinetic parameters such as pollutant concentration, incident light irradiance, contact time and humidity content has been studied. The photocatalytic degradation by-products of 1-propanol has been identified in the gas-phase by GC/MS. Propionaldehyde and acetaldehyde were found to be the main gaseous intermediates. Propionaldehyde and acetaldehyde have been taken into account in a "two-site model" to evaluate the possible competition of adsorption between 1-propanol and its by-products of degradation. A mechanistic pathway is then proposed for the photocatalytic degradation of 1-propanol.

  15. Gas-Liquid Flows and Phase Separation

    NASA Technical Reports Server (NTRS)

    McQuillen, John

    2004-01-01

    Common issues for space system designers include:Ability to Verify Performance in Normal Gravity prior to Deployment; System Stability; Phase Accumulation & Shedding; Phase Separation; Flow Distribution through Tees & Manifolds Boiling Crisis; Heat Transfer Coefficient; and Pressure Drop.The report concludes:Guidance similar to "A design that operates in a single phase is less complex than a design that has two-phase flow" is not always true considering the amount of effort spent on pressurizing, subcooling and phase separators to ensure single phase operation. While there is still much to learn about two-phase flow in reduced gravity, we have a good start. Focus now needs to be directed more towards system level problems .

  16. Morphology-modulation of SnO2 Hierarchical Architectures by Zn Doping for Glycol Gas Sensing and Photocatalytic Applications

    PubMed Central

    Zhao, Qinqin; Ju, Dianxing; Deng, Xiaolong; Huang, Jinzhao; Cao, Bingqiang; Xu, Xijin

    2015-01-01

    The morphology of SnO2 nanospheres was transformed into ultrathin nanosheets assembled architectures after Zn doping by one-step hydrothermal route. The as-prepared samples were characterized in detail by various analytical techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen adsorption-desorption technique. The Zn-doped SnO2 nanostructures proved to be the efficient gas sensing materials for a series of flammable and explosive gases detection, and photocatalysts for the degradation of methyl orange (MO) under UV irradiation. It was observed that both of the undoped and Zn-doped SnO2 after calcination exhibited tremendous gas sensing performance toward glycol. The response (S = Ra/Rg) of Zn-doped SnO2 can reach to 90 when the glycol concentration is 100 ppm, which is about 2 times and 3 times higher than that of undoped SnO2 sensor with and without calcinations, respectively. The result of photocatalytic activities demonstrated that MO dye was almost completely degraded (~92%) by Zn-doped SnO2 in 150 min, which is higher than that of others (MO without photocatalyst was 23%, undoped SnO2 without and with calcination were 55% and 75%, respectively). PMID:25597269

  17. The effect of doping titanium dioxide nanoparticles on phase transformation, photocatalytic activity and anti-bacterial properties

    NASA Astrophysics Data System (ADS)

    Buzby, Scott Edward

    Nanosized titanium dioxide has a variety of important applications in everyday life including a photocatalyst for pollution remediation, photovoltaic devices, sunscreen, etc. This study focuses on the various properties of titanium dioxide nanoparticles doped with various cation and anion species. Samples were produced by various methods including metalorganic chemical vapor deposition (MOCVD), plasma assisted metalorganic chemical vapor deposition (PA-MOCVD) and sol-gel. Numerous techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron microscopy both scanning (SEM) and transmission (TEM) were used for physical characterization. Photocatalytic properties were determined by the oxidation of methylene blue dye and 2-chlorophenol in water as well as gaseous formic acid with results analyzed by high performance liquid chromatography (HPLC), Fourier transform infrared spectroscopy (FTIR) and ultra violet - visible spectroscopy (UV-VIS). For the purpose of enhancement of the photocatalytic activity of titanium dioxide nanoparticles, the effect of anion doping and the anatase-rutile phase ratio were studied. Although anatase, rutile and mixed crystallite phases all show some degree of activity in photocatalytic reactions, these results show that anatase is better suited for the degradation of organic compounds in an aqueous medium any advantage in photocatalytic activity gained through the enhancement in optical response from the smaller band gap by addition of rutile was overcome by the negatives associated with the rutile phase. Furthermore substitutional nitrogen doping showed significant improvement in UV photocatalysis as well as allowing for visible light activation of the catalyst. Further studies on the phase transitions in titanium dioxide nanoparticles were carried out by synthesizing various cation doped samples by sol-gel. Analysis of the phases by XRD showed an inverse relationship between dopant size and rutile percentage

  18. Enhanced Photocatalytic Performance under Visible and Near-Infrared Irradiation of Cu1.8Se/Cu3Se2 Composite via a Phase Junction

    PubMed Central

    Qiao, Li-Na; Wang, Huan-Chun; Shen, Yang; Lin, Yuan-Hua; Nan, Ce-Wen

    2017-01-01

    A novel Cu1.8Se/Cu3Se2 composite photocatalyst was prepared by the simple precipitation method. This composite possesses a wide photoabsorption until the range of near-infrared light, and exhibits significantly enhanced photocatalytic activity for methyl orange degradation under visible and near-infrared light irradiation compared with bare Cu1.8Se and Cu3Se2. The mechanism of this outstanding photocatalytic behavior can be explained by the calculated energy band positions. The efficient charge separation via a phase junction of Cu1.8Se/Cu3Se2 composite would make a great contribution to its much-enhanced photocatalytic efficiency. PMID:28336853

  19. Mixed Stationary Liquid Phases for Gas-Liquid Chromatography.

    ERIC Educational Resources Information Center

    Koury, Albert M.; Parcher, Jon F.

    1979-01-01

    Describes a laboratory technique for use in an undergraduate instrumental analysis course that, using the interpretation of window diagrams, prepares a mixed liquid phase column for gas-liquid chromatography. A detailed procedure is provided. (BT)

  20. Optically-Based Diagnostics for Gas-Phase Laser Development

    DTIC Science & Technology

    2010-08-01

    Phase Laser Development Acknowledgement of Support and Disclaimer This material is based upon work supported by Air Force Office of Scientific...00-2010 4. TITLE AND SUBTITLE Optically-Based Diagnostics for Gas-Phase Laser Development 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM...Sciences Inc. Role of Optical Diagnostics in High Energy Gas Laser Development  Chemically rich, energetic, reacting flow with competing phenomena

  1. Electron spectrometer for gas-phase spectroscopy

    SciTech Connect

    Bozek, J.D.; Schlachter, A.S.

    1997-04-01

    An electron spectrometer for high-resolution spectroscopy of gaseous samples using synchrotron radiation has been designed and constructed. The spectrometer consists of a gas cell, cylindrical electrostatic lens, spherical-sector electron energy analyzer, position-sensitive detector and associated power supplies, electronics and vacuum pumps. Details of the spectrometer design are presented together with some representative spectra.

  2. Solar Photocatalytic Hydrogen Production from Water Using a Dual Bed Photosystem - Phase I Final Report and Phase II Proposal

    SciTech Connect

    Clovis A. Linkous; Darlene K. Slattery

    2000-09-11

    In this work we are attempting to perform the highly efficient storage of solar energy in the form of H{sub 2} via photocatalytic decomposition of water. While it has been demonstrated that H{sub 2} and O{sub 2} can be evolved from a single vessel containing a single suspended photocatalyst (Sayama 1994; 1997), we are attempting to perform net water-splitting by using two photocatalysts immobilized in separate containers, or beds. A schematic showing how the device would work is shown.

  3. Evaluation of phase envelope on natural gas, condensate and gas hydrate

    NASA Astrophysics Data System (ADS)

    Promkotra, S.; Kangsadan, T.

    2015-03-01

    The experimentally gas hydrate are generated by condensate and natural gas. Natural gas and condensate samples are collected from a gas processing plant where is situated in the northeastern part of Thailand. Physical properties of the API gravity and density of condensate are presented in the range of 55-60° and 0.71-0.76 g/cm3. The chemical compositions of petroleum-field water are analyzed to evaluate the genesis of gas hydrate by experimental procedure. The hydrochemical compositions of petroleum-field waters are mostly the Na-Cl facies. This condition can estimate how the hydrate forms. Phase envelope of condensate is found only one phase which is liquid phase. The liquid fraction is 100% at 15°C and 101.327 kPa, with the critical pressure and temperature of 2,326 kPa and 611.5 K. However, natural gas can be separated in three phases which are vapor, liquid and solid phase with the pressure and temperature at 100 kPa and 274.2 K. The hydrate curves explicit both hydrate zone and nonhydrate zone. Phase envelope of gas hydrate from the phase diagram indicates the hydrate formation. The experimental results of hydrate form can correlate to the hydrate curve. Besides, the important factor of hydrate formation depends on impurity in the petroleum system.

  4. High resolution ion mobility measurements for gas phase proteins: correlation between solution phase and gas phase conformations

    NASA Astrophysics Data System (ADS)

    Hudgins, Robert R.; Woenckhaus, Jürgen; Jarrold, Martin F.

    1997-11-01

    Our high resolution ion mobility apparatus has been modified by attaching an electrospray source to perform measurements for biological molecules. While the greater resolving power permits the resolution of more conformations for BPTI and cytochrome c, the resolved features are generally much broader than expected for a single rigid conformation. A major advantage of the new experimental configuration is the much gentler introduction of ions into the drift tube, so that the observed gas phase conformations appear to more closely reflect those present in solution. For example, it is possible to distinguish between the native state of cytochrome c and the methanol-denatured form on the basis of the ion mobility measurements; the mass spectra alone are not sensitive enough to detect this change. Thus this approach may provide a quick and sensitive tool for probing the solution phase conformations of biological molecules.

  5. Photocatalytic degradation of trichloroethylene in aqueous phase using nano-ZNO/Laponite composites.

    PubMed

    Joo, Jin Chul; Ahn, Chang Hyuk; Jang, Dae Gyu; Yoon, Young Han; Kim, Jong Kyu; Campos, Luiza; Ahn, Hosang

    2013-12-15

    The feasibility of nano-ZnO/Laponite composites (NZLc) as a valid alternative to TiO2 to mineralize trichloroethylene (TCE) without difficulties for recovery of photocatalysts was evaluated. Based on the experimental observations, the removal of TCE using NZLc under UV irradiation was multiple reaction processes (i.e., sorption, photolysis, and photocatalysis). Sorption of TCE was thermodynamically favorable due to the hydrophobic partitioning into crosslinked poly vinyl alcohol, and the adsorption onto high-surface-area mineral surfaces of both ZnO and Laponite. The degradation efficiency of TCE can be significantly improved using NZLc under UV irradiation, indicating that ZnO-mediated heterogeneous photocatalytic degradation occurred. However, the degradation efficiency was found to vary with experimental conditions (e.g., initial concentration of TCE, loading amount of NZLc, the intensity of light and initial solution pH). Although the removal of TCE by NZLc was found to be a complex function of sorption, photolysis, and photocatalysis, the photocatalytic degradation of TCE on the surface of ZnO was critical. Consequently, developed NZLc can be applied as a valid alternative to suspended TiO2 powder, and overcome drawbacks (e.g., filtration and recovery of photocatalysts) in degradation of TCE for various water resources.

  6. Adsorption-Driven Catalytic and Photocatalytic Activity of Phase Tuned In2S3 Nanocrystals Synthesized via Ionic Liquids.

    PubMed

    Sharma, Rahul Kumar; Chouryal, Yogendra Nath; Chaudhari, Sushmita; Saravanakumar, Jeganathan; Dey, Suhash Ranjan; Ghosh, Pushpal

    2017-03-14

    Phase tuned quantum confined In2S3 nanocrystals are accessible solvothermally using task-specific ionic liquids (ILs) as structure directing agents. Selective tuning of size, shape, morphology and, most importantly, crystal phase of In2S3 is achieved by changing the alkyl side chain length, the H-bonding and aromatic -stacking ability of the 1-alkyl-3- methylimidazolium bromide ILs, [Cnmim]Br (n=2,4,6,8 and 10). It is observed that crystallite size is significantly less when ILs are used compared to the synthesis without ILs keeping the other reaction parameters same. At 150oC, when no IL is used, pure tetragonal form of -In2S3 appears however in presence of [Cnmim]Br [n=2,4], at the same reaction condition, a pure cubic phase crystallizes. However in case of methylimidazolium bromides with longer pendant alkyl chains such as hexyl (C6), octyl (C8) or decyl (C10), nanoparticles of the tetragonal polymorph form. Likewise, judicious choice of reaction temperature and precursors has a profound effect to obtain phase pure and morphology controlled nanocrystals. Furthermore, the adsorption driven catalytic and photocatalytic activity of as-prepared nanosized indium sulphide is confirmed by studying the degradation of crystal violet (CV) dye in presence of dark and visible light. Maximum 94.8 % catalytic efficiency is obtained for the In2S3 nanocrystals using tetramethylammonium bromide (TMAB) ionic liquid.

  7. Para-Hydrogen-Enhanced Gas-Phase Magnetic Resonance Imaging

    SciTech Connect

    Bouchard, Louis-S.; Kovtunov, Kirill V.; Burt, Scott R.; Anwar,M. Sabieh; Koptyug, Igor V.; Sagdeev, Renad Z.; Pines, Alexander

    2007-02-23

    Herein, we demonstrate magnetic resonance imaging (MRI) inthe gas phase using para-hydrogen (p-H2)-induced polarization. A reactantmixture of H2 enriched in the paraspin state and propylene gas is flowedthrough a reactor cell containing a heterogenized catalyst, Wilkinson'scatalyst immobilized on modified silica gel. The hydrogenation product,propane gas, is transferred to the NMR magnet and is spin-polarized as aresult of the ALTADENA (adiabatic longitudinal transport and dissociationengenders net alignment) effect. A polarization enhancement factor of 300relative to thermally polarized gas was observed in 1D1H NMR spectra.Enhancement was also evident in the magnetic resonance images. This isthe first demonstration of imaging a hyperpolarized gaseous productformed in a hydrogenation reaction catalyzed by a supported catalyst.This result may lead to several important applications, includingflow-through porous materials, gas-phase reaction kinetics and adsorptionstudies, and MRI in low fields, all using catalyst-free polarizedfluids.

  8. Influence of phase stabilization and perovskite vanadate oxygen vacancies of the BINIVOX catalyst on photocatalytic degradation of azo dye under visible light irradiation

    NASA Astrophysics Data System (ADS)

    Al-Areqi, Niyazi A. S.; Al-Kamali, Ahmed S. N.; Ghaleb, Kh. A. S.; Al-Alas, Ahlam; Al-Mureish, Khalid

    2014-02-01

    A layered Aurivillius-perovskite-type BINIVOX system with the general formula ? was developed as a novel photocatalyst for degradation of organic dyes. A series of the BINIVOX.x catalysts in the compositional range 0≤x≤0.20 were successfully synthesized by the standard solid-state reaction and characterized using X-ray powder diffraction, differential thermal analysis, UV-vis diffuse reflectance spectroscopy and Brunauer-Emmett-Teller BET surface area. Then, the photocatalytic activities of prepared catalysts were investigated for the first time through the degradation of a new azo dye named sodium 4-[(E)-(4,5-dimethyl-1H-pyrazolo [3,4-c] pyridazin-3-yl) diazenyl] naphthalen-1-olate and denoted as 4-SPPN in aqueous solution under visible light irradiation. Adsorption efficiency and photocatalytic activity of BINIVOX.x catalysts were correlated well with the variation in phase crystal structures stabilized at room temperature as a function of composition. The stabilized γ‧-BINIVOX phases in the tetragonal crystal system with space group I4/m mm exhibited the best photocatalytic performance which can be attributed to their higher specific surface area, narrower band-gap energy and higher oxygen-vacancy concentration in the perovskite vanadate layers. In addition, the possible photocatalytic degradation mechanism of aqueous 4-SPPN dye was proposed under visible light irradiation.

  9. Photocatalytic characteristics of single phase Fe-doped anatase TiO{sub 2} nanoparticles sensitized with vitamin B{sub 12}

    SciTech Connect

    Gharagozlou, Mehrnaz; Bayati, R.

    2015-01-15

    Highlights: • Anatase TiO{sub 2}/B{sub 12} hybrid nanostructured catalyst was successfully synthesized by sol–gel technique. • The nanoparticle catalyst was doped with iron at several concentrations. • Nanoparticles were characterized in detail by XRD, Raman, TEM, EDS, and spectroscopy techniques. • The formation mechanism and role of point defects on photocatalytic properties were discussed. • A structure-property-processing correlation was established. - Abstract: We report a processing-structure-property correlation in B{sub 12}-anatase titania hybrid catalysts doped with several concentrations of iron. Our results clearly show that low-level iron doping alters structure, defect content, and photocatalytic characteristics of TiO{sub 2}. XRD and Raman studies revealed formation of a single-phase anatase TiO{sub 2} where no iron based segregation in particular iron oxide, was detected. FT-IR spectra clearly confirmed sensitization of TiO{sub 2} nanoparticles with vitamin B{sub 12}. TEM micrographs and diffraction patterns confirmed crystallization of anatase nanoparticles with a radius of 15–20 nm. Both XRD and Raman signals showed a peak shift and a peak broadening which are surmised to originate from creation of point defects, namely oxygen vacancy and titanium interstitial. The doped samples revealed a narrower band gap as compared to undoped samples. Photocatalytic activity of the samples was assessed through measuring the decomposition rate of rhodamine B. It was found that sensitization with vitamin B{sub 12} and Fe-doping significantly enhances the photocatalytic efficiency of the anatase nanoparticles. We also showed that there is an optimum Fe-doping level where the maximum photocatalytic activity is achieved. The boost of photocatalytic activity was qualitatively understood to originate from a more effective use of the light photons, formation of point defects, which enhance the charge separation, higher carrier mobility.

  10. Constant volume gas cell optical phase-shifter

    DOEpatents

    Phillion, Donald W.

    2002-01-01

    A constant volume gas cell optical phase-shifter, particularly applicable for phase-shifting interferometry, contains a sealed volume of atmospheric gas at a pressure somewhat different than atmospheric. An optical window is present at each end of the cell, and as the length of the cell is changed, the optical path length of a laser beam traversing the cell changes. The cell comprises movable coaxial tubes with seals and a volume equalizing opening. Because the cell is constant volume, the pressure, temperature, and density of the contained gas do not change as the cell changes length. This produces an exactly linear relationship between the change in the length of the gas cell and the change in optical phase of the laser beam traversing it. Because the refractive index difference between the gas inside and the atmosphere outside is very much the same, a large motion must be made to change the optical phase by the small fraction of a wavelength that is required by phase-shifting interferometry for its phase step. This motion can be made to great fractional accuracy.

  11. Oscillatory burning of solid propellants including gas phase time lag.

    NASA Technical Reports Server (NTRS)

    T'Ien, J. S.

    1972-01-01

    An analysis has been performed for oscillatory burning of solid propellants including gas phase time lag. The gaseous flame is assumed to be premixed and laminar with a one-step overall chemical reaction. The propellant is assumed to decompose according to the Arrenhius Law, with no condensed phase reaction. With this model, strong gas phase resonance has been found in certain cases at the characteristic gas-phase frequencies, but the peaking of the acoustic admittance is in the direction favoring the damping of pressure waves. At still higher frequencies, moderate wave-amplifying ability was found. The limit of low frequency response obtained previously by Denison and Baum was recovered, and the limitations of the quasi-steady theory were investigated.

  12. Mesoporous TiO2 single crystals: facile shape-, size-, and phase-controlled growth and efficient photocatalytic performance.

    PubMed

    Zheng, Xiaoli; Kuang, Qin; Yan, Keyou; Qiu, Yongcai; Qiu, Jianhang; Yang, Shihe

    2013-11-13

    In this work, we have succeeded in preparing rutile and anatase TiO2 mesoporous single crystals with diverse morphologies in a controllable fashion by a simple silica-templated hydrothermal method. A simple in-template crystal growth process was put forward, which involved heterogeneous crystal nucleation and oriented growth within the template, a sheer spectator, and an excluded volume, i.e., crystal growth by faithful negative replication of the silica template. A series of mesoporous single-crystal structures, including rutile mesoporous TiO2 nanorods with tunable sizes and anatase mesoporous TiO2 nanosheets with dominant {001} facets, have been synthesized to demonstrate the versatility of the strategy. The morphology, size, and phase of the TiO2 mesoporous single crystals can be tuned easily by varying the external conditions such as the hydrohalic acid condition, seed density, and temperature rather than by the silica template, which merely serves for faithful negative replication but without interfering in the crystallization process. To demonstrate the application value of such TiO2 mesoporous single crystals, photocatalytic activity was tested. The resultant TiO2 mesoporous single crystals exhibited remarkable photocatalytic performance on hydrogen evolution and degradation of methyl orange due to their increased surface area, single-crystal nature, and the exposure of reactive crystal facets coupled with the three-dimensionally connected mesoporous architecture. It was found that {110} facets of rutile mesoporous single crystals can be considered essentially as reductive sites with a key role in the photoreduction, while {001} facets of anatase mesoporous single crystals provided oxidation sites in the oxidative process. Such shape- and size-controlled rutile and anatase mesoporous TiO2 single crystals hold great promise for building energy conversion devices, and the simple solution-based hydrothermal method is extendable to the synthesis of other

  13. Gas and particulate phase products from the ozonolysis of acenaphthylene

    NASA Astrophysics Data System (ADS)

    Riva, Matthieu; Healy, Robert M.; Tomaz, Sophie; Flaud, Pierre-Marie; Perraudin, Emilie; Wenger, John C.; Villenave, Eric

    2016-10-01

    Polycyclic aromatic hydrocarbons (PAHs) are recognized as important secondary organic aerosol (SOA) precursors in the urban atmosphere. In this work, the gas-phase ozonolysis of acenaphthylene was investigated in an atmospheric simulation chamber using a proton transfer reaction time-of-flight-mass spectrometer (PTR-TOF-MS) and an aerosol time-of-flight-mass spectrometer (ATOFMS) for on-line characterization of the oxidation products in the gas and particle phases, respectively. SOA samples were also collected on filters and analyzed by ultra performance liquid chromatography/electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (UPLC/ESI-HR-QTOFMS) and gas chromatography/electron impact ionization-mass spectrometry (GC/EI-MS). The major gas-phase products included a range of oxygenated naphthalene derivatives such as 1,8-naphthalic anhydride, naphthalene 1,8-dicarbaldehyde and naphthaldehyde, as well as a secondary ozonide. Possible reaction mechanisms are proposed for the formation of these products and favoured pathways have been suggested. Many of these products were also found in the particle phase along with a range of oligomeric compounds. The same range of gas and particle phase products was observed in the presence and absence of excess cyclohexane, an OH scavenger, indicating that OH radical production from the ozonolysis of acenaphthylene is negligible. SOA yields in the range 23-37% were determined and indicate that acenaphthylene ozonolysis may contribute to part of the SOA observed in urban areas.

  14. Collision-induced gas phase dissociation rates

    NASA Technical Reports Server (NTRS)

    Hansen, C. Frederick

    1990-01-01

    The Landau-Zener theory of reactive cross sections was applied to diatomic molecules dissociating from a ladder of vibrational states. The result predicts a dissociation rate that is quite well duplicated by an Arrhenius function having a preexponential temperature dependence of about T(sub -1/2), at least for inert collision partners. This relation fits experimental data reasonably well. The theory is then used to calculate the effect of vibrational nonequilibrium on dissociation rate. For Morse oscillators, the results are about the same as given by Hammerling, Kivel, and Teare in their analytic approximation for harmonic oscillators, though at very high temperature a correction for the partition function limit is included. The empirical correction for vibration nonequilibrium proposed by Park, which is a convenient algorithm for CFD calculations, is modified to prevent a drastic underestimation of dissociation rates that occurs with this method when vibrational temperature is much smaller than the kinetic temperature of the gas.

  15. Specific and reproducible gas sensors utilizing gas-phase chemical reaction on organic transistors.

    PubMed

    Zang, Yaping; Zhang, Fengjiao; Huang, Dazhen; Di, Chong-an; Meng, Qing; Gao, Xike; Zhu, Daoben

    2014-05-01

    Utilizing a textbook reaction on the surface of an organic active channel, achieves sensitive detection of HCl, NH3 and NO2, with good selectivity, excellent reproducibility, and satisfactory stability. These results reveal gas-phase reaction assisted detection as a unique and promising approach to construct practical applicable gas sensors with typical organic transistors.

  16. Enantiomeric phase separation in a lattice gas model: Guggenheim approximation

    NASA Astrophysics Data System (ADS)

    Huckaby, Dale A.; Shinmi, Masato; Ausloos, Marcel; Clippe, Paulette

    1986-05-01

    We consider a lattice gas in which the two enantiomeric forms of a tetrahedral molecule, consisting of a central carbon atom bonded to four different groups A, B, G, and H, are adsorbed onto a triangular lattice, such that the carbon atom is above a lattice site, the three bonds to A, B, and G point toward neighboring lattice sites, and the bond to H points perpendicular to and away from the plane of the lattice. For a certain choice of intermolecular interactions, such as may exist between the zwitterion forms of an amino acid, the phase diagram was investigated using a Guggenheim approximation with two order parameters. Enantiomeric phase separation into two symmetric condensed phases occurs at low temperatures. These condensed phases become a single racemic condensed phase at a critical line, and they are in equilibrium with a racemic gas phase along a line of triple points. These two lines coincide at a critical endpoint. The racemic condensed and gas phases are in equilibrium along a two phase coexistence line which begins at the critical endpoint and ends at a critical point. No tricritical point was found in the model for the special choice of interactions studied.

  17. A comparative study of optical absorption and photocatalytic properties of nanocrystalline single-phase anatase and rutile TiO{sub 2} doped with transition metal cations

    SciTech Connect

    Kernazhitsky, L.; Shymanovska, V.; Gavrilko, T.; Naumov, V.; Kshnyakin, V.; Khalyavka, T.

    2013-02-15

    The effect of nanocrystalline TiO{sub 2} doping with transition metal cations (Cu{sup 2+}, Fe{sup 3+}, Co{sup 2+}, Cr{sup 3+}) on their optical absorption and photocatalytic properties was investigated. The obtained metal-doped TiO{sub 2} samples were characterized by X-ray diffraction, scanning electron microscopy, and UV-vis absorption spectroscopy. It is shown that doping effect on anatase (A) and rutile (R) properties is quite different, being much stronger and complicated on A than on R. Contrary to doped R, doped A revealed a significant red shift of the absorption edge along with the band gap narrowing. Photocatalytic activity of anatase increases upon doping in the order: Aphotocatalytic activity of rutile samples decreases upon doping in the series R>R/Co>R/Cu>R/Fe>R/Cr, indicating the inhibitory effect of impurity cations. This fact correlates with the decrease in the UV absorption of the doped rutile in the region of the Hg-lamp irradiation at 4.88 eV. - Graphical abstract: A red shift of the absorption edge of nanocrystalline single-phase anatase after doping with transition metal cations. Highlights: Black-Right-Pointing-Pointer Single-phase anatase and rutile powders surface-doped with transition metal cations. Black-Right-Pointing-Pointer Absorption edge and band gap of rutile do not change with surface doping. Black-Right-Pointing-Pointer Band gap of surface-doped anatase reduces being the lowest for A/Fe. Black-Right-Pointing-Pointer The surface-doping improves photocatalytic activity of anatase. Black-Right-Pointing-Pointer The surface-doping inhibits photocatalytic activity of rutile.

  18. Rupture of the cell envelope by induced intracellular gas phase expansion in gas vacuolate bacteria.

    PubMed Central

    Hemmingsen, B B; Hemmingsen, E A

    1980-01-01

    Using a new approach, we estimated the physical strength of the cell envelopes of three species of gram-negative, gas vacuolate bacteria (Microcyclus aquaticus, Prosthecomicrobium pneumaticum, and Meniscus glaucopis). Populations of cells were slowly (0.5 to 2.9 h) saturated with argon, nitrogen, or helium to final pressures up to 100 atm (10, 132 kPa). The gas phases of the vesicles remained intact and, upon rapid (1 to 2 s) decompression to atmospheric pressure, expanded and ruptured the cells; loss of colony-forming units was used as an index of rupture. Because the cell envelope is the cellular component most likely to resist the expanding intracellular gas phase, its strength can be estimated from the minimum gas pressures that produce rupture. The viable counts indicated that these minimum pressures were between 25 and 50 atm; the majority of the cell envelopes were ruptured at pressures between 50 and 100 atm. Cells in which the gas vesicles were collapsed and the gas phases were effectively dissolved by rapid compression tolerated decompression from much higher gas saturations. Cells that do not normally possess gas vesicles (Escherichia coli) or that had been prevented from forming them by addition of L-lysine to the medium (M. aquaticus) were not harmed by decompression from gas saturation pressures up to 300 atm. PMID:7204336

  19. Gas sensitivity and photocatalytic performance of cuprous oxide with novel morphologies

    NASA Astrophysics Data System (ADS)

    Wu, Ling; Wu, Yulin; Jin, Saijia; Zhang, Lun; Xun, Zhipeng

    2016-10-01

    In this work, Cu2O nanoparticles (NPs) with quasi-spherical and bookmark-like morphologies were successfully synthesized via a new facile solution method. The morphologies of products were characterized to show porous surfaces and the size is as small as approximately 20-50 nm. Given the special morphology, Cu2O NPs exhibited superior gas sensitivity to either ethanol or acetone vapors and strong adsorption abilities and high degradation activities for methyl orange under visible-light irradiation. The investigation provided not only a way of synthesizing Cu2O particles with dozens of nanoscale, but also a way of improving its gas sensitivity and catalytic degradation ability.

  20. Gas Phase Chiral Separations By Ion Mobility Spectrometry

    PubMed Central

    Dwivedi, Prabha; Wu, Ching; Hill, Herbert H.

    2013-01-01

    This manuscript introduces the concept of Chiral Ion Mobility Spectrometry (CIMS) and presents examples demonstrating the gas phase separation of enantiomers of a wide range of racemates including pharmaceuticals, amino acids and carbohydrates. CIMS is similar to traditional ion mobility spectrometry (IMS), where gas phase ions, when subjected to a potential gradient are separated at atmospheric pressure due to differences in their shapes and sizes. In addition to size and shape, CIMS separates ions based on their stereospecific interaction with a chiral gas. In order to achieve chiral discrimination by CIMS, an asymmetric environment was provided by doping the drift gas with a volatile chiral reagent. In this study S-(+)-2-butanol was used as a chiral modifier to demonstrate enantiomeric separations of atenolol, serine, methionine, threonine, methyl-α-glucopyranoside, glucose, penicillamine, valinol, phenylalanine, and tryptophan from their respective racemic mixtures. PMID:17165808

  1. Carrier dynamics and the role of surface defects: Designing a photocatalyst for gas-phase CO2 reduction

    SciTech Connect

    Hoch, Laura B.; Szymanski, Paul; Ghuman, Kulbir Kaur; He, Le; Liao, Kristine; Qiao, Qiao; Reyes, Laura M.; Zhu, Yimei; El-Sayed, Mostafa A.; Singh, Chandra Veer; Ozin, Geoffrey A.

    2016-11-28

    In2O3-x(OH)y nanoparticles have been shown to function as an effective gas-phase photocatalyst for the reduction of CO2 to CO via the reverse water–gas shift reaction. Their photocatalytic activity is strongly correlated to the number of oxygen vacancy and hydroxide defects present in the system. To better understand how such defects interact with photogenerated electrons and holes in these materials, we have studied the relaxation dynamics of In2O3-x(OH)y nanoparticles with varying concentration of defects using two different excitation energies corresponding to above-band-gap (318-nm) and near-band-gap (405-nm) excitations. Our results demonstrate that defects play a significant role in the excited-state, charge relaxation pathways. Higher defect concentrations result in longer excited-state lifetimes, which are attributed to improved charge separation. This correlates well with the observed trends in the photocatalytic activity. These results are further supported by density-functional theory calculations, which confirm the positions of oxygen vacancy and hydroxide defect states within the optical band gap of indium oxide. This enhanced understanding of the role these defects play in determining the optoelectronic properties and charge carrier dynamics can provide valuable insight toward the rational development of more efficient photocatalytic materials for CO2 reduction.

  2. Surfactant-Tuned Phase Structure and Morphologies of Cu2ZnSnS4 Hierarchical Microstructures and Their Visible-Light Photocatalytic Activities

    NASA Astrophysics Data System (ADS)

    Guo, Yaxin; Wei, Jie; Liu, Yalong; Yang, Tiantian; Xu, Zhuo

    2017-03-01

    Cu2ZnSnS4 (CZTS) hierarchical microstructures were synthesized by using a facile and nontoxic hydrothermal route, which were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Raman spectra, and UV-Vis absorption spectra. The results and analysis show that surfactants used in the hydrothermal process have significant effect on the phase structures, morphologies, and photocatalytic activities of CZTS powders. Especially, the well-crystallized and pure kesterite CZTS hierarchical microstructures were synthesized with the addition of high-concentration tartaric acid (TA) in the hydrothermal process. A nucleation-dissolution-recrystallization mechanism was discussed, and the photocatalytic activities of CZTS hierarchical microstructures for the degradation of rhodamine B (RhB) were also evaluated. We argue that the crystalline structure and particle morphology have played key roles on the photocatalytic properties of CZTS crystals. A considerably high photocatalytic efficiency of 51.66% after 4 h irradiation was obtained in pure kesterite CZTS hierarchical microstructures, which suggests that CZTS would be a promising candidate of photocatalyst.

  3. Surfactant-Tuned Phase Structure and Morphologies of Cu2ZnSnS4 Hierarchical Microstructures and Their Visible-Light Photocatalytic Activities.

    PubMed

    Guo, Yaxin; Wei, Jie; Liu, Yalong; Yang, Tiantian; Xu, Zhuo

    2017-12-01

    Cu2ZnSnS4 (CZTS) hierarchical microstructures were synthesized by using a facile and nontoxic hydrothermal route, which were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Raman spectra, and UV-Vis absorption spectra. The results and analysis show that surfactants used in the hydrothermal process have significant effect on the phase structures, morphologies, and photocatalytic activities of CZTS powders. Especially, the well-crystallized and pure kesterite CZTS hierarchical microstructures were synthesized with the addition of high-concentration tartaric acid (TA) in the hydrothermal process. A nucleation-dissolution-recrystallization mechanism was discussed, and the photocatalytic activities of CZTS hierarchical microstructures for the degradation of rhodamine B (RhB) were also evaluated. We argue that the crystalline structure and particle morphology have played key roles on the photocatalytic properties of CZTS crystals. A considerably high photocatalytic efficiency of 51.66% after 4 h irradiation was obtained in pure kesterite CZTS hierarchical microstructures, which suggests that CZTS would be a promising candidate of photocatalyst.

  4. Conversion of nitrogen oxides on commercial photocatalytic dispersion paints

    NASA Astrophysics Data System (ADS)

    Laufs, S.; Burgeth, G.; Duttlinger, W.; Kurtenbach, R.; Maban, M.; Thomas, C.; Wiesen, P.; Kleffmann, J.

    2010-06-01

    In the present study, photocatalytic reactions of nitrogen oxides (NO x = NO + NO 2) were studied on commercial TiO 2 doped facade paints in a flow tube photoreactor under simulated atmospheric conditions. Fast photocatalytic conversion of NO and NO 2 was observed only for the photocatalytic paints and not for non-catalytic reference paints. Nitrous acid (HONO) was formed in the dark on all paints studied, however, it efficiently decomposes under irradiation only on the photocatalytic samples. Thus, it is concluded that photocatalytic paint surfaces do not represent a daytime source of HONO, in contrast to other recent studies on pure TiO 2 surfaces. As main final product, the formation of adsorbed nitric acid/nitrate anion (HNO 3/NO 3-) was observed with near to unity yield. In addition, traces of H 2O 2 were observed in the gas phase only in the presence of O 2. Formation of the greenhouse gas nitrous oxide (N 2O) could be excluded. The uptake kinetics of NO, NO 2 and HONO was very fast under atmospheric conditions (e.g. γ(NO + TiO 2) > 10 -5). Thus, the uptake on urban surfaces (painted houses, etc.) will be limited by transport. For a hypothetically painted street canyon, an average reduction of nitrogen oxide levels of ca. 5% is estimated. Since the harmful HNO 3/NO 3- is formed on the surface of the photoactive paints, whereas it is formed in the gas phase in the atmosphere, the use of photocatalytic paints may also help to reduce acid deposition, e.g. on plants, or nitric acid related health issues.

  5. A superior photocatalytic performance of a novel Bi2SiO5 flower-like microsphere via a phase junction

    NASA Astrophysics Data System (ADS)

    Liu, Di; Wang, Jun; Zhang, Mo; Liu, Yanfang; Zhu, Yongfa

    2014-11-01

    A phase junction over a Bi2SiO5 photocatalyst with the orthorhombic Bi2SiO5 and the tetragonal Bi2SiO5 structure was successfully synthesized via an ion exchange method using BiOBr solid microspheres as the sacrificial template. In the meantime, the as-prepared Bi2SiO5 phase junction possesses a novel morphology of a flower-like microsphere with nanoparticles evenly embedded in its nano-petals. It was found that the Bi2SiO5 phase junction not only showed a highly enhanced photocatalytic activity and excellent durability under UV or simulated solar irradiation, but also showed a remarkable visible-light activity for photo-degradation of phenol. Experimental results reveal that the tetragonal Bi2SiO5 phase in this phase junction possesses a narrower band gap, thus leading to its extended light absorption. The efficient charge separation via a phase junction would make a great contribution to its highly enhanced photocatalytic activity under UV or simulated solar irradiation. The high efficiency in the degradation of organic pollutants makes the as-prepared photocatalyst a promising candidate for photocatalytic environmental purification.A phase junction over a Bi2SiO5 photocatalyst with the orthorhombic Bi2SiO5 and the tetragonal Bi2SiO5 structure was successfully synthesized via an ion exchange method using BiOBr solid microspheres as the sacrificial template. In the meantime, the as-prepared Bi2SiO5 phase junction possesses a novel morphology of a flower-like microsphere with nanoparticles evenly embedded in its nano-petals. It was found that the Bi2SiO5 phase junction not only showed a highly enhanced photocatalytic activity and excellent durability under UV or simulated solar irradiation, but also showed a remarkable visible-light activity for photo-degradation of phenol. Experimental results reveal that the tetragonal Bi2SiO5 phase in this phase junction possesses a narrower band gap, thus leading to its extended light absorption. The efficient charge separation

  6. Gas phase metal cluster model systems for heterogeneous catalysis.

    PubMed

    Lang, Sandra M; Bernhardt, Thorsten M

    2012-07-14

    Since the advent of intense cluster sources, physical and chemical properties of isolated metal clusters are an active field of research. In particular, gas phase metal clusters represent ideal model systems to gain molecular level insight into the energetics and kinetics of metal-mediated catalytic reactions. Here we summarize experimental reactivity studies as well as investigations of thermal catalytic reaction cycles on small gas phase metal clusters, mostly in relation to the surprising catalytic activity of nanoscale gold particles. A particular emphasis is put on the importance of conceptual insights gained through the study of gas phase model systems. Based on these concepts future perspectives are formulated in terms of variation and optimization of catalytic materials e.g. by utilization of bimetals and metal oxides. Furthermore, the future potential of bio-inspired catalytic material systems are highlighted and technical developments are discussed.

  7. Effect of phase behavior on bypassing in enriched gas floods

    SciTech Connect

    Burger, J.E.; Bhogeswara, R.; Mohanty, K.K. )

    1994-05-01

    Enriched gas floods incorporate a complex interaction of heterogeneity, fingering, multiphase flow, and phase behavior. Experiments and simulations indicate that the optimum solvent enrichment in high-viscosity-ratio secondary gas floods can be below minimum miscibility enrichment (MME). The compositional path and resulting mobility profile in multidimensional multiple-contact miscible (MCM) or immiscible floods are different from their 1D counterparts for high-viscosity-ratio floods in heterogeneous media.

  8. Phase space analysis of some interacting Chaplygin gas models

    NASA Astrophysics Data System (ADS)

    Khurshudyan, M.; Myrzakulov, R.

    2017-02-01

    In this paper we discuss a phase space analysis of various interacting Chaplygin gas models in general relativity. Linear and nonlinear sign changeable interactions are considered. For each case appropriate late time attractors of field equations are found. The Chaplygin gas is one of the dark fluids actively considered in modern cosmology due to the fact that it is a joint model of dark energy and dark matter.

  9. Gas phase chemical detection with an integrated chemical analysis system

    SciTech Connect

    CASALNUOVO,STEPHEN A.; FRYE-MASON,GREGORY CHARLES; KOTTENSTETTE,RICHARD; HELLER,EDWIN J.; MATZKE,CAROLYN M.; LEWIS,PATRICK R.; MANGINELL,RONALD P.; BACA,ALBERT G.; HIETALA,VINCENT M.

    2000-04-12

    Microfabrication technology has been applied to the development of a miniature, multi-channel gas phase chemical laboratory that provides fast response, small size, and enhanced versatility and chemical discrimination. Each analysis channel includes a sample preconcentrator followed by a gas chromatographic separator and a chemically selective surface acoustic wave detector array to achieve high sensitivity and selectivity. The performance of the components, individually and collectively, is described.

  10. Freeze drying for gas chromatography stationary phase deposition

    DOEpatents

    Sylwester, Alan P.

    2007-01-02

    The present disclosure relates to methods for deposition of gas chromatography (GC) stationary phases into chromatography columns, for example gas chromatography columns. A chromatographic medium is dissolved or suspended in a solvent to form a composition. The composition may be inserted into a chromatographic column. Alternatively, portions of the chromatographic column may be exposed or filled with the composition. The composition is permitted to solidify, and at least a portion of the solvent is removed by vacuum sublimation.

  11. Gas-phase azide functionalization of carbon.

    PubMed

    Stenehjem, Eric D; Ziatdinov, Vadim R; Stack, T Daniel P; Chidsey, Christopher E D

    2013-01-23

    Tailoring the surface and interfacial properties of inexpensive and abundant carbon materials plays an increasingly important role for innovative applications including those in electrocatalysis, energy storage, gas separations, and composite materials. Described here is the novel preparation and subsequent use of gaseous iodine azide for the azide modification of carbon surfaces. In-line generation of gaseous iodine azide from iodine monochloride vapor and solid sodium azide is safe and convenient. Immediate treatment of carbon surfaces with this gaseous stream of iodine azide provides a highly reproducible, selective, and scalable azide functionalization that minimizes waste and reduces deleterious side reactions. Among the possible uses of azide-modified surfaces, they serve as versatile substrates for the attachment of additional functionality by coupling with terminal alkynes under the mild copper-catalyzed azide-alkyne cycloaddition (CuAAC) "click" reaction. For instance, coupling ethynylferrocene to azide-modified glassy carbon surfaces achieves ferrocene coverage up to 8 × 10(13) molecules/cm(2) by voltammetric and XPS analyses. The 1,2,3-triazole linker formed during the CuAAC reaction is robust and hydrolytically stable in both aqueous 1 M HClO(4) and 1 M NaOH for at least 12 h at 100 °C.

  12. Capillary gas chromatography with two new moderately high temperature phases.

    NASA Technical Reports Server (NTRS)

    Pollock, G. E.

    1972-01-01

    Gas chromatography test results are presented for two new moderately high-temperature phases of Dexsil 400-GC with free hydroxyl end groups (uncapped) and with end groups covered by trimethyl silyl groups (capped). The two Dexsil 400-GC phases were tested for their ability to resolve N-TFA-DL-(+)-2-butyl esters and n-butyl esters, as well as fatty acid methyl esters and hydrocarbon standards. Generally the more polar uncapped phase was superior to the capped phase in all separation comparisons, except for the hydrocarbons.

  13. Negative ion gas-phase chemistry of arenes.

    PubMed

    Danikiewicz, Witold; Zimnicka, Magdalena

    2016-01-01

    Reactions of aromatic and heteroaromatic compounds involving anions are of great importance in organic synthesis. Some of these reactions have been studied in the gas phase and are occasionally mentioned in reviews devoted to gas-phase negative ion chemistry, but no reviews exist that collect all existing information about these reactions. This work is intended to fill this gap. In the first part of this review, methods for generating arene anions in the gas phase and studying their physicochemical properties and fragmentation reactions are presented. The main topics in this part are as follows: processes in which gas-phase arene anions are formed, measurements and calculations of the proton affinities of arene anions, proton exchange reactions, and fragmentation processes of substituted arene anions, especially phenide ions. The second part is devoted to gas-phase reactions of arene anions. The most important of these are reactions with electrophiles such as carbonyl compounds and α,β-unsaturated carbonyl and related compounds (Michael acceptors). Other reactions including oxidation of arene anions and halogenophilic reactions are also presented. In the last part of the review, reactions of electrophilic arenes with nucleophiles are discussed. The best known of these is the aromatic nucleophilic substitution (SN Ar) reaction; however, other processes that lead to the substitution of a hydrogen atom in the aromatic ring are also very important. Aromatic substrates in these reactions are usually but not always nitroarenes bearing other substituents in the ring. The first step in these reactions is the formation of an anionic σ-adduct, which, depending on the substituents in the aromatic ring and the structure of the attacking nucleophile, is either an intermediate or a transition state in the reaction path. In the present review, we attempted to collect the results of both experimental and computational studies of the aforementioned reactions conducted since the

  14. Understanding Gas-Phase Ammonia Chemistry in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Chambers, Lauren; Oberg, Karin I.; Cleeves, Lauren Ilsedore

    2017-01-01

    Protoplanetary disks are dynamic regions of gas and dust around young stars, the remnants of star formation, that evolve and coagulate over millions of years in order to ultimately form planets. The chemical composition of protoplanetary disks is affected by both the chemical and physical conditions in which they develop, including the initial molecular abundances in the birth cloud, the spectrum and intensity of radiation from the host star and nearby systems, and mixing and turbulence within the disk. A more complete understanding of the chemical evolution of disks enables a more complete understanding of the chemical composition of planets that may form within them, and of their capability to support life. One element known to be essential for life on Earth is nitrogen, which often is present in the form of ammonia (NH3). Recent observations by Salinas et al. (2016) reveal a theoretical discrepancy in the gas-phase and ice-phase ammonia abundances in protoplanetary disks; while observations of comets and protostars estimate the ice-phase NH3/H2O ratio in disks to be 5%, Salinas reports a gas-phase NH3/H2O ratio of ~7-84% in the disk surrounding TW Hydra, a young nearby star. Through computational chemical modeling of the TW Hydra disk using a reaction network of over 5000 chemical reactions, I am investigating the possible sources of excess gas-phase NH3 by determining the primary reaction pathways of NH3 production; the downstream chemical effects of ionization by ultraviolet photons, X-rays, and cosmic rays; and the effects of altering the initial abundances of key molecules such as N and N2. Beyond providing a theoretical explanation for the NH3 ice/gas discrepancy, this new model may lead to fuller understanding of the gas-phase formation processes of all nitrogen hydrides (NHx), and thus fuller understanding of the nitrogen-bearing molecules that are fundamental for life as we know it.

  15. CHEMKIN2. General Gas-Phase Chemical Kinetics

    SciTech Connect

    Rupley, F.M.

    1992-01-24

    CHEMKIN is a high-level tool for chemists to use to describe arbitrary gas-phase chemical reaction mechanisms and systems of governing equations. It remains, however, for the user to select and implement a solution method; this is not provided. It consists of two major components: the Interpreter and the Gas-phase Subroutine Library. The Interpreter reads a symbolic description of an arbitrary, user-specified chemical reaction mechanism. A data file is generated which forms a link to the Gas-phase Subroutine Library, a collection of about 200 modular subroutines which may be called to return thermodynamic properties, chemical production rates, derivatives of thermodynamic properties, derivatives of chemical production rates, or sensitivity parameters. Both single and double precision versions of CHEMKIN are included. Also provided is a set of FORTRAN subroutines for evaluating gas-phase transport properties such as thermal conductivities, viscosities, and diffusion coefficients. These properties are an important part of any computational simulation of a chemically reacting flow. The transport properties subroutines are designed to be used in conjunction with the CHEMKIN Subroutine Library. The transport properties depend on the state of the gas and on certain molecular parameters. The parameters considered are the Lennard-Jones potential well depth and collision diameter, the dipole moment, the polarizability, and the rotational relaxation collision number.

  16. Gas purification in the dense phase at the CATS terminal

    SciTech Connect

    Openshaw, P.J.; Carnell, P.J.H.; Rhodes, E.F.

    1999-07-01

    The purification and transportation of natural gas at very high pressures can help to minimize the capital cost of pipelines and processing equipment. However, complex mixtures of hydrocarbons undergo unusual phase changes, such as retrograde condensation, as the temperature and pressure are altered. The Central Area Transmission System (CATS) is a joint venture of Amoci, BG, Amerada Hess, Phillips, Agip and Fina operated by Amoco on behalf of the owners. The design of the CATS terminal has provided an interesting processing challenge. The terminal receives a total of 1.6 Bscf/d of rich gas from a number of offshore fields. All are relatively sweet but the small amounts of H{sub 2}S and Hg are removed. Fixed bed technology was selected as the most economic purification process, while minimizing hydrocarbon loss and operator involvement. Conventionally, the raw gas would be split into the different hydrocarbon fractions and each would be processed separately. This would require the installation of a large number of reactors. A more elegant solution is to treat the gas on arrival at the terminal in the dense phase. This option raised questions around whether a fixed bed would be prone to fouling, could the pressure drop be kept low enough to avoid phase separation and would inadvertent wetting by condensation cause problems. Details are given of the test work carried out to prove the viability of using fixed bed technology for dense phase gas processing, the eventual design adopted and the performance over the first year of service.

  17. Enhancement of gas phase heat transfer by acoustic field application.

    PubMed

    Komarov, Sergey; Hirasawa, Masahiro

    2003-06-01

    This study discusses a possibility for enhancement of heat transfer between solids and ambient gas by application of powerful acoustic fields. Experiments are carried out by using preheated Pt wires (length 0.1-0.15 m, diameter 50 and 100 micro m) positioned at the velocity antinode of a standing wave (frequency range 216-1031 Hz) or in the path of a travelling wave (frequency range 6.9-17.2 kHz). A number of experiments were conducted under conditions of gas flowing across the wire surface. Effects of sound frequency, sound strength, gas flow velocity and wire preheating temperature on the Nusselt number are examined with and without sound application. The gas phase heat transfer rate is enhanced with acoustic field strength. Higher temperatures result in a vigorous radiation from the wire surface and attenuate the effect of sound. The larger the gas flow velocity, the smaller is the effect of sound wave on heat transfer enhancement.

  18. Gas Phase Hydration of Methyl Glyoxal to Form the Gemdiol

    NASA Astrophysics Data System (ADS)

    Kroll, Jay A.; Axson, Jessica L.; Vaida, Veronica

    2016-06-01

    Methylglyoxal is a known oxidation product of volatile organic compounds (VOCs) in Earth's atmosphere. While the gas phase chemistry of methylglyoxal is fairly well understood, its modeled concentration and role in the formation of secondary organic aerosol (SOA) continues to be controversial. The gas phase hydration of methylglyoxal to form a gemdiol has not been widely considered for water-restricted environments such as the atmosphere. However, this process may have important consequences for the atmospheric processing of VOCs. We will report on spectroscopic work done in the Vaida laboratory studying the hydration of methylglyoxal and discuss the implications for understanding the atmospheric processing and fate of methylglyoxal and similar molecules.

  19. Fischer Indole Synthesis in the Gas Phase, the Solution Phase, and at the Electrospray Droplet Interface

    NASA Astrophysics Data System (ADS)

    Bain, Ryan M.; Ayrton, Stephen T.; Cooks, R. Graham

    2017-02-01

    Previous reports have shown that reactions occurring in the microdroplets formed during electrospray ionization can, under the right conditions, exhibit significantly greater rates than the corresponding bulk solution-phase reactions. The observed acceleration under electrospray ionization could result from a solution-phase, a gas-phase, or an interfacial reaction. This study shows that a gas-phase ion/molecule (or ion/ion) reaction is not responsible for the observed rate enhancement in the particular case of the Fischer indole synthesis. The results show that the accelerated reaction proceeds in the microdroplets, and evidence is provided that an interfacial process is involved.

  20. UV and visible light photocatalytic activity of Au/TiO2 nanoforests with Anatase/Rutile phase junctions and controlled Au locations

    PubMed Central

    Yu, Yang; Wen, Wei; Qian, Xin-Yue; Liu, Jia-Bin; Wu, Jin-Ming

    2017-01-01

    To magnify anatase/rutile phase junction effects through appropriate Au decorations, a facile solution-based approach was developed to synthesize Au/TiO2 nanoforests with controlled Au locations. The nanoforests cons®isted of anatase nanowires surrounded by radially grown rutile branches, on which Au nanoparticles were deposited with preferred locations controlled by simply altering the order of the fabrication step. The Au-decoration increased the photocatalytic activity under the illumination of either UV or visible light, because of the beneficial effects of either electron trapping or localized surface plasmon resonance (LSPR). Gold nanoparticles located preferably at the interface of anatase/rutile led to a further enhanced photocatalytic activity. The appropriate distributions of Au nanoparticles magnify the beneficial effects arising from the anatase/rutile phase junctions when illuminated by UV light. Under the visible light illumination, the LSPR effect followed by the consecutive electron transfer explains the enhanced photocatalysis. This study provides a facile route to control locations of gold nanoparticles in one-dimensional nanostructured arrays of multiple-phases semiconductors for achieving a further increased photocatalytic activity. PMID:28117448

  1. UV and visible light photocatalytic activity of Au/TiO2 nanoforests with Anatase/Rutile phase junctions and controlled Au locations

    NASA Astrophysics Data System (ADS)

    Yu, Yang; Wen, Wei; Qian, Xin-Yue; Liu, Jia-Bin; Wu, Jin-Ming

    2017-01-01

    To magnify anatase/rutile phase junction effects through appropriate Au decorations, a facile solution-based approach was developed to synthesize Au/TiO2 nanoforests with controlled Au locations. The nanoforests cons®isted of anatase nanowires surrounded by radially grown rutile branches, on which Au nanoparticles were deposited with preferred locations controlled by simply altering the order of the fabrication step. The Au-decoration increased the photocatalytic activity under the illumination of either UV or visible light, because of the beneficial effects of either electron trapping or localized surface plasmon resonance (LSPR). Gold nanoparticles located preferably at the interface of anatase/rutile led to a further enhanced photocatalytic activity. The appropriate distributions of Au nanoparticles magnify the beneficial effects arising from the anatase/rutile phase junctions when illuminated by UV light. Under the visible light illumination, the LSPR effect followed by the consecutive electron transfer explains the enhanced photocatalysis. This study provides a facile route to control locations of gold nanoparticles in one-dimensional nanostructured arrays of multiple-phases semiconductors for achieving a further increased photocatalytic activity.

  2. UV and visible light photocatalytic activity of Au/TiO2 nanoforests with Anatase/Rutile phase junctions and controlled Au locations.

    PubMed

    Yu, Yang; Wen, Wei; Qian, Xin-Yue; Liu, Jia-Bin; Wu, Jin-Ming

    2017-01-24

    To magnify anatase/rutile phase junction effects through appropriate Au decorations, a facile solution-based approach was developed to synthesize Au/TiO2 nanoforests with controlled Au locations. The nanoforests cons®isted of anatase nanowires surrounded by radially grown rutile branches, on which Au nanoparticles were deposited with preferred locations controlled by simply altering the order of the fabrication step. The Au-decoration increased the photocatalytic activity under the illumination of either UV or visible light, because of the beneficial effects of either electron trapping or localized surface plasmon resonance (LSPR). Gold nanoparticles located preferably at the interface of anatase/rutile led to a further enhanced photocatalytic activity. The appropriate distributions of Au nanoparticles magnify the beneficial effects arising from the anatase/rutile phase junctions when illuminated by UV light. Under the visible light illumination, the LSPR effect followed by the consecutive electron transfer explains the enhanced photocatalysis. This study provides a facile route to control locations of gold nanoparticles in one-dimensional nanostructured arrays of multiple-phases semiconductors for achieving a further increased photocatalytic activity.

  3. Solid state synthesis of tin-doped ZnO at room temperature: characterization and its enhanced gas sensing and photocatalytic properties.

    PubMed

    Jia, Xiaohua; Fan, Huiqing; Afzaal, Mohammad; Wu, Xiangyang; O'Brien, Paul

    2011-10-15

    A room temperature solid-state reaction has been used to prepare crystalline tin-doped ZnO. Zinc nitrate hexahydrate, cetyltrimethyl ammonium bromide, stannic chloride pentahydrate and sodium hydroxide with proper ratios were ground together. As-synthesized samples were characterized by inductively coupled plasma analysis (ICP), scanning electron microscopy (SEM) and X-ray powder diffraction (XRD); The products were of different morphologies, well dispersed and exhibited good crystallinity, it is also found that the growth direction and morphology of ZnO depend on the amount of Sn doped, which is mainly caused by the difference in sizes between Zn and Sn atoms as well as the change of pH value. Moreover, gas sensing and photocatalytic properties of the obtained products were studied. The materials showed a high gas response to ethanol vapor, and the gas response can reach a maximum of R(a)/R(g) = 124. In addition, tin-doped ZnO materials exhibited improved photocatalytic performance toward methyl orange (MO) solution under a current density of 0.03 mg L(-1) comparison with undoped ZnO.

  4. Anion-exchange engineering of cookie-like Bi2S3/Bi2MoO6 heterostructure for enhanced photocatalytic activities and gas-sensing properties.

    PubMed

    Pei, Yu; Li, Xiaoguang; Chu, Hang; Ge, Yuancai; Dong, Pei; Baines, Robert; Pei, Liyuan; Ye, Mingxin; Shen, Jianfeng

    2017-04-01

    Developing efficient visible-light-driven photocatalysts will advance alternative energy technologies, ultimately curbing the environmental pollution associated with fossil fuels. In this work, Bi2S3/Bi2MoO6 photocatalysts with a heterogeneous cookie-like structure were prepared for the first time by in-situ anion exchange at relatively low temperatures. The catalysts exhibited enhanced photocatalytic activity, which we attributed to the photocurrent response, a diminished recombination rate of photogenerated electron-hole pairs, and the existence of a large heterojunction interface. These governing factors were discerned by photoelectrochemical measurements, calculated energy band positions and photoluminescence spectra. Bi2S3/Bi2MoO6 nanocomposites also exhibit better performance in response to gas than bare Bi2MoO6 according to gas sensing tests. Our work, in relaying a feasible method to synthesize Bi2S3/Bi2MoO6-based heterojunction superstructures, and documents a universal preparation method of synthetic heterogeneous complexes, and provides necessary groundwork for the development of next generation semiconductor photocatalytic technology and gas sensor.

  5. Ion-Molecule Reactions in Gas Phase Radiation Chemistry.

    ERIC Educational Resources Information Center

    Willis, Clive

    1981-01-01

    Discusses some aspects of the radiation chemistry of gases, focusing on the ion-molecule and charge neutralization reactions which set study of the gas phase apart. Uses three examples that illustrate radiolysis, describing the radiolysis of (1) oxygen, (2) carbon dioxide, and (3) acetylene. (CS)

  6. The Dipeptide Ala-Gly in the Gas Phase

    NASA Astrophysics Data System (ADS)

    Bermúdez, Celina; Varela, Marcelino; Cabezas, Carlos; Peña, Isabel; Alonso, José L.

    2014-06-01

    The dipeptide Ala-Gly has been examined in gas phase by laser ablation molecular beam Fourier transform microwave (LA-MB-FTMW) spectroscopy in the frequency region 3-12 GHz. Three rotamers have been detected in the supersonic expansion. The quadrupole hyperfine structure of two 14N (I=1) nuclei has been totally resolved allowing the conclusive identification of one conformer.

  7. INVESTIGATION OF GAS-PHASE OZONE AS A POTENTIAL BIOCIDE

    EPA Science Inventory

    The paper presents data on the effect of ozone on both vegetative and spore-forming fungi as well as on spore-forming bacteria. (NOTE: Despite the wide use of ozone generators in indoor air cleaning, there is little research data on ozone's biocidal activity in the gas phase.) Dr...

  8. Gas-phase chemistry of ruthenium and rhodium carbonyl complexes.

    PubMed

    Cao, Shiwei; Wang, Yang; Qin, Zhi; Fan, Fangli; Haba, Hiromitsu; Komori, Yukiko; Wu, Xiaolei; Tan, Cunmin; Zhang, Xin

    2016-01-07

    Short-lived ruthenium and rhodium isotopes were produced from a (252)Cf spontaneous fission (SF) source. Their volatile carbonyl complexes were formed in gas-phase reactions in situ with the carbon-monoxide containing gas. A gas-jet system was employed to transport the volatile carbonyls from the recoil chamber to the chemical separation apparatus. The gas-phase chemical behaviors of these carbonyl complexes were studied using an online low temperature isothermal chromatography (IC) technique. Long IC columns made up of FEP Teflon were used to obtain the chemical information of the high-volatile Ru and Rh carbonyls. By excluding the influence of precursor effects, short-lived isotopes of (109-110)Ru and (111-112)Rh were used to represent the chemical behaviours of Ru and Rh carbonyls. Relative chemical yields of about 75% and 20% were measured for Ru(CO)5 and Rh(CO)4, respectively, relative to the yields of KCl aerosols transported in Ar gas. The adsorption enthalpies of ruthenium and rhodium carbonyl complexes on a Teflon surface were determined to be around ΔHads = -33(+1)(-2) kJ mol(-1) and -36(+2)(-1) kJ mol(-1), respectively, by fitting the breakthrough curves of the corresponding carbonyl complexes with a Monte Carlo simulation program. Different from Mo and Tc carbonyls, a small amount of oxygen gas was found to be not effective for the chemical yields of ruthenium and rhodium carbonyl complexes. The general chemical behaviors of short-lived carbonyl complexes of group VI-IX elements were discussed, which can be used in the future study on the gas-phase chemistry of superheavy elements - Bh, Hs, and Mt carbonyls.

  9. Flavin Adenine Dinucleotide Structural Motifs: From Solution to Gas Phase

    PubMed Central

    2015-01-01

    Flavin adenine dinucleotide (FAD) is involved in important metabolic reactions where the biological function is intrinsically related to changes in conformation. In the present work, FAD conformational changes were studied in solution and in gas phase by measuring the fluorescence decay time and ion-neutral collision cross sections (CCS, in a trapped ion mobility spectrometer, TIMS) as a function of the solvent conditions (i.e., organic content) and gas-phase collisional partner (i.e., N2 doped with organic molecules). Changes in the fluorescence decay suggest that FAD can exist in four conformations in solution, where the abundance of the extended conformations increases with the organic content. TIMS-MS experiments showed that FAD can exist in the gas phase as deprotonated (M = C27H31N9O15P2) and protonated forms (M = C27H33N9O15P2) and that multiple conformations (up to 12) can be observed as a function of the starting solution for the [M + H]+ and [M + Na]+molecular ions. In addition, changes in the relative abundances of the gas-phase structures were observed from a “stack” to a “close” conformation when organic molecules were introduced in the TIMS cell as collision partners. Candidate structures optimized at the DFT/B3LYP/6-31G(d,p) were proposed for each IMS band, and results showed that the most abundant IMS band corresponds to the most stable candidate structure. Solution and gas-phase experiments suggest that the driving force that stabilizes the different conformations is based on the interaction of the adenine and isoalloxazine rings that can be tailored by the “solvation” effect created with the organic molecules. PMID:25222439

  10. Novel stationary phases based on asphaltenes for gas chromatography.

    PubMed

    Boczkaj, Grzegorz; Momotko, Malwina; Chruszczyk, Dorota; Przyjazny, Andrzej; Kamiński, Marian

    2016-07-01

    We present the results of investigations on the possibility of the application of the asphaltene fraction isolated from the oxidized residue from vacuum distillation of crude oil as a stationary phase for gas chromatography. The results of the investigation revealed that the asphaltene stationary phases can find use for the separation of a wide range of volatile organic compounds. The experimental values of Rohrschneider/McReynolds constants characterize the asphaltenes as stationary phases of medium polarity and selectivity similar to commercially available phases based on alkyl phthalates. Isolation of asphaltenes from the material obtained under controlled process conditions allows the production of a stationary phase having reproducible sorption properties and chromatographic columns having the same selectivity. Unique selectivity and high thermal stability make asphaltenes attractive as a material for stationary phases for gas chromatography. A low production cost from a readily available raw material (oxidized petroleum bitumens) is an important economic factor in case of application of the asphaltene stationary phases for preparative and process separations.

  11. Gas-Phase Studies of Formamidopyrimidine Glycosylase (Fpg) Substrates.

    PubMed

    Kiruba, G S M; Xu, Jiahui; Zelikson, Victoria; Lee, Jeehiun K

    2016-03-07

    Gas-phase thermochemical properties (tautomerism, acidity, and proton affinity) have been measured and calculated for a series of nucleobase derivatives that have not heretofore been examined under vacuum. The studied species are substrates for the enzyme formamidopyrimidine glycosylase (Fpg), which cleaves damaged nucleobases from DNA. The gas-phase results are compared and contrasted to solution-phase data, to afford insight into the Fpg mechanism. Calculations are also used to probe the energetics of various possible mechanisms and to predict isotope effects that could potentially allow for discrimination between different mechanisms. Specifically, (18) O substitution at the ribose O4' is predicted to result in a normal kinetic isotope effect (KIE) for a ring-opening "endocyclic" mechanism and an inverse KIE for a direct base excision "exocyclic" pathway.

  12. The physical chemistry of Criegee intermediates in the gas phase

    DOE PAGES

    Osborn, David L.; Taatjes, Craig A.

    2015-07-24

    Here, carbonyl oxides, also known as Criegee intermediates, are key intermediates in both gas phase ozonolysis of unsaturated hydrocarbons in the troposphere and solution phase organic synthesis via ozonolysis. Although the study of Criegee intermediates in both arenas has a long history, direct studies in the gas phase have only recently become possible through new methods of generating stabilised Criegee intermediates in sufficient quantities. This advance has catalysed a large number of new experimental and theoretical investigations of Criegee intermediate chemistry. In this article we review the physical chemistry of Criegee intermediates, focusing on their molecular structure, spectroscopy, unimolecular andmore » bimolecular reactions. These recent results have overturned conclusions from some previous studies, while confirming others, and have clarified areas of investigation that will be critical targets for future studies. In addition to expanding our fundamental understanding of Criegee intermediates, the rapidly expanding knowledge base will support increasingly predictive models of their impacts on society.« less

  13. The physical chemistry of Criegee intermediates in the gas phase

    SciTech Connect

    Osborn, David L.; Taatjes, Craig A.

    2015-07-24

    Here, carbonyl oxides, also known as Criegee intermediates, are key intermediates in both gas phase ozonolysis of unsaturated hydrocarbons in the troposphere and solution phase organic synthesis via ozonolysis. Although the study of Criegee intermediates in both arenas has a long history, direct studies in the gas phase have only recently become possible through new methods of generating stabilised Criegee intermediates in sufficient quantities. This advance has catalysed a large number of new experimental and theoretical investigations of Criegee intermediate chemistry. In this article we review the physical chemistry of Criegee intermediates, focusing on their molecular structure, spectroscopy, unimolecular and bimolecular reactions. These recent results have overturned conclusions from some previous studies, while confirming others, and have clarified areas of investigation that will be critical targets for future studies. In addition to expanding our fundamental understanding of Criegee intermediates, the rapidly expanding knowledge base will support increasingly predictive models of their impacts on society.

  14. Hydration of Gas-Phase Ions Formed by Electrospray Ionization

    PubMed Central

    Rodriguez-Cruz, Sandra E.; Klassen, John S.; Williams, Evan R.

    2005-01-01

    The hydration of gas-phase ions produced by electrospray ionization was investigated. Evidence that the hydrated ions are formed by two mechanisms is presented. First, solvent condensation during the expansion inside the electrospray source clearly occurs. Second, some solvent evaporation from more extensively solvated ions or droplets is apparent. To the extent that these highly solvated ions have solution-phase structures, then the final isolated gas-phase structure of the ion will be determined by the solvent evaporation process. This process was investigated for hydrated gramicidin S in a Fourier-transform mass spectrometer. Unimolecular dissociation rate constants of isolated gramicidin S ions with between 2 and 14 associated water molecules were measured. These rate constants increased from 16 to 230 s−1 with increasing hydration, with smaller values corresponding to magic numbers. PMID:10497808

  15. Gas Phase Reactivity of Carboxylates with N-Hydroxysuccinimide Esters

    PubMed Central

    Peng, Zhou; McGee, William M.; Bu, Jiexun; Barefoot, Nathan Z.; McLuckey, Scott A.

    2015-01-01

    N-hydroxysuccinimide (NHS) esters have been used for gas phase conjugation reactions with peptides at nucleophilic sites, such as primary amines (N-terminus, ε-amine of lysine) or guanidines, by forming amide bonds through a nucleophilic attack on the carbonyl carbon. The carboxylate has recently been found to also be a reactive nucleophile capable of initiating a similar nucleophilic attack to form a labile anhydride bond. The fragile bond is easily cleaved, resulting in an oxygen transfer from the carboxylate-containing species to the reagent, nominally observed as a water transfer. This reactivity is shown for both peptides and non-peptidic species. Reagents isotopically labeled with O18 were used to confirm reactivity. This constitutes an example of distinct differences in reactivity of carboxylates between the gas-phase, where they are shown to be reactive, and the solution-phase, where they are not regarded as reactive with NHS esters. PMID:25338221

  16. Gas Phase Reactivity of Carboxylates with N-Hydroxysuccinimide Esters

    NASA Astrophysics Data System (ADS)

    Peng, Zhou; McGee, William M.; Bu, Jiexun; Barefoot, Nathan Z.; McLuckey, Scott A.

    2015-01-01

    N-hydroxysuccinimide (NHS) esters have been used for gas-phase conjugation reactions with peptides at nucleophilic sites, such as primary amines (N-terminus, ɛ-amine of lysine) or guanidines, by forming amide bonds through a nucleophilic attack on the carbonyl carbon. The carboxylate has recently been found to also be a reactive nucleophile capable of initiating a similar nucleophilic attack to form a labile anhydride bond. The fragile bond is easily cleaved, resulting in an oxygen transfer from the carboxylate-containing species to the reagent, nominally observed as a water transfer. This reactivity is shown for both peptides and non-peptidic species. Reagents isotopically labeled with O18 were used to confirm reactivity. This constitutes an example of distinct differences in reactivity of carboxylates between the gas phase, where they are shown to be reactive, and the solution phase, where they are not regarded as reactive with NHS esters.

  17. Influences of TiO2 phase structures on the structures and photocatalytic hydrogen production of CuOx/TiO2 photocatalysts

    NASA Astrophysics Data System (ADS)

    Liu, Yuanxu; Wang, Zhonglei; Huang, Weixin

    2016-12-01

    CuOx/TiO2 photocatalysts employing TiO2 with different phase structures as well as P25 as supports were prepared, and their structures and activity for photocatalytic H2 production in methanol/water solution under simulated solar light were comparatively studied. Structural characterization results demonstrated that the TiO2 phase structure strongly affects the CuOx-TiO2 interaction and copper species in various CuOx/TiO2 photocatalysts. The Cu2O-rutile TiO2 interaction is much stronger than the Cu2O-anatase TiO2 interaction, facilitates the interfacial charge transfer process within the Cu2O-rutile TiO2 heterojunction but disables supported Cu2O to catalyze the hole-participated methanol oxidation. The Cu2O-anatase TiO2 heterojunction with the appropriate Cu2O-anatase TiO2 interaction and thus the balancing efficiencies between the interfacial charge transfer process and hole-participated methanol oxidation is most photocatalytic active, and CuOx/P25 with the largest population of Cu2O-anatase TiO2 heterojunction exhibits the highest photocatalytic H2 production. These results provide novel insights in the applied surface science of CuOx/TiO2 photocatalysts.

  18. Phase transformations during HLnTiO{sub 4} (Ln=La, Nd) thermolysis and photocatalytic activity of obtained compounds

    SciTech Connect

    Silyukov, Oleg I. Abdulaeva, Liliia D.; Burovikhina, Alena A.; Rodionov, Ivan A.; Zvereva, Irina A.

    2015-03-15

    Layered HLnTiO{sub 4} (Ln=La, Nd) compounds belonging to Ruddlesden–Popper phases were found to form partially hydrated compounds Ln{sub 2}Ti{sub 2}O{sub 7}·xH{sub 2}O during thermal dehydration as well as defect oxides Ln{sub 2}□Ti{sub 2}O{sub 7} as final products. Further heating of metastable defect Ln{sub 2}□Ti{sub 2}O{sub 7} substances leads to the formation of pyrochlore-type oxides Ln{sub 2}Ti{sub 2}O{sub 7} {sub (p)}, with subsequent transformation under higher temperatures to stable layered 110-type perovskites Ln{sub 2}Ti{sub 2}O{sub 7}. The occurring structure transformations lead to an increase of photocatalytic activity in the order of HLnTiO{sub 4}photocatalytic activity in the order of HLnTiO{sub 4}photocatalytic activity of all obtained compounds. The hydrogen evolution rate increased in the course of the structure changes during thermolysis.

  19. Preconceptual design of the gas-phase decontamination demonstration cart

    SciTech Connect

    Munday, E.B.

    1993-12-01

    Removal of uranium deposits from the interior surfaces of gaseous diffusion equipment will be a major portion of the overall multibillion dollar effort to decontaminate and decommission the gaseous diffusion plants. Long-term low-temperature (LTLT) gas-phase decontamination is being developed at the K-25 Site as an in situ decontamination process that is expected to significantly lower the decontamination costs, reduce worker exposure to radioactive materials, and reduce safeguard concerns. This report documents the preconceptual design of the process equipment that is necessary to conduct a full-scale demonstration of the LTLT method in accordance with the process steps listed above. The process equipment and method proposed in this report are not intended to represent a full-scale production campaign design and operation, since the gas evacuation, gas charging, and off-gas handling systems that would be cost effective in a production campaign are not cost effective for a first-time demonstration. However, the design presented here is expected to be applicable to special decontamination projects beyond the demonstration, which could include the Deposit Recovery Program. The equipment will therefore be sized to a 200 ft size 1 converter (plus a substantial conservative design margin), which is the largest item of interest for gas phase decontamination in the Deposit Recovery Program. The decontamination equipment will allow recovery of the UF{sub 6}, which is generated from the reaction of ClF{sub 3} with the uranium deposits, by use of NaF traps.

  20. Gas Phase Chemical Detection with an Integrated Chemical Analysis System

    SciTech Connect

    Baca, Albert G.; Casalnuovo, Stephen A.; Frye-Mason, Gregory C.; Heller, Edwin J.; Hietala, Susan L.; Hietala, Vincent M.; Kottenstette, Richard J.; Lewis, Patrick R.; Manginell, Ronald P.; Matzke, Carloyn M.; Reno, John L.; Sasaki, Darryl Y.; Schubert, W. Kent

    1999-07-08

    Microfabrication technology has been applied to the development of a miniature, multi-channel gas phase chemical laboratory that provides fast response, small size, and enhanced versatility and chemical discrimination. Each analysis channel includes a sample concentrator followed by a gas chromatographic separator and a chemically selective surface acoustic wave detector array to achieve high sensitivity and selectivity. The performance of the components, individually and collectively, is described. The design and performance of novel micromachined acoustic wave devices, with the potential for improved chemical sensitivity, are also described.

  1. Collaborative Advanced Gas Turbine Program: Phase 1. Final report

    SciTech Connect

    Hollenbacher, R.; Kesser, K.; Beishon, D.

    1994-12-01

    The Collaborative Advanced Gas Turbine (CAGT) Program is an advanced gas turbine research and development program whose goal is to accelerate the commercial availability, to within the turn of the century, of high efficiency aeroderivative gas turbines for electric power generating applications. In the first project phase, research was conducted to prove or disprove the research hypothesis that advanced aeroderivative gas turbine systems can provide a promising technology alternative, offering high efficiency and good environmental performance characteristics in modular sizes, for utility applications. This $5 million, Phase 1 research effort reflects the collaborative efforts of a broad and international coalition of industries and organizations, both public and private, that have pooled their resources to assist in this research. Included in this coalition are: electric and gas utilities, the Electric Power Research Institute, the Gas Research Institute and the principal aircraft engine manufacturers. Additionally, the US Department of Energy (DOE) and the California Energy Commission have interacted with the CAGT on both technical and executive levels as observers and sources of funding. The three aircraft engine manufacturer-led research teams participating in this research include: Rolls-Royce, Inc., and Bechtel; the Turbo Power and Marine Division of United Technologies and Fluor Daniel; and General Electric Power Generation, Stewart and Stevenson, and Bechtel. Each team has investigated advanced electric power generating systems based on their high-thrust (60,000 to 100,000 pounds) aircraft engines. The ultimate goal of the CAGT program is that the community of stakeholders in the growing market for natural-gas-fueled, electric power generation can collectively provide the right combination of market-pull and technology-push to substantially accelerate the commercialization of advanced, high efficiency aeroderivative technologies.

  2. A Uranyl Peroxide Dimer in the Gas Phase.

    PubMed

    Dau, Phuong D; Dau, Phuong V; Rao, Linfeng; Kovács, Attila; Gibson, John K

    2017-04-03

    The gas-phase uranyl peroxide dimer, [(UO2)2(O2)(L)2](2+) where L = 2,2'-trifluoroethylazanediyl)bis(N,N'-dimethylacetamide), was synthesized by electrospray ionization of a solution of UO2(2+) and L. Collision-induced dissociation of this dimer resulted in endothermic O atom elimination to give [(UO2)2(O)(L)2](2+), which was found to spontaneously react with water via exothermic hydrolytic chemisorption to yield [(UO2)2(OH)2(L)2](2+). Density functional theory computations of the energies for the gas-phase reactions are in accord with observations. The structures of the observed uranyl dimer were computed, with that of the peroxide of particular interest, as a basis to evaluate the formation of condensed phase uranyl peroxides with bent structures. The computed dihedral angle in [(UO2)2(O2)(L)2](2+) is 145°, indicating a substantial deviation from the planar structure with a dihedral angle of 180°. Energies needed to induce bending in the most elementary gas-phase uranyl peroxide complex, [(UO2)2(O2)](2+), were computed. It was found that bending from the lowest-energy planar structure to dihedral angles up to 140° required energies of <10 kJ/mol. The gas-phase results demonstrate the inherent stability of the uranyl peroxide moiety and support the notion that the uranyl-peroxide-uranyl structural unit is intrinsically planar, with only minor energy perturbations needed to form the bent structures found in studtite and uranyl peroxide nanostructures.

  3. Carbon Dioxide Separation from Flue Gas by Phase Enhanced Absorption

    SciTech Connect

    Liang Hu

    2006-06-30

    A new process, phase enhanced absorption, was invented. The method is carried out in an absorber, where a liquid carrier (aqueous solution), an organic mixture (or organic compound), and a gas mixture containing a gas to be absorbed are introduced from an inlet. Since the organic mixture is immiscible or at least partially immiscible with the liquid carrier, the organic mixture forms a layer or small parcels between the liquid carrier and the gas mixture. The organic mixture in the absorber improves mass transfer efficiency of the system and increases the absorption rate of the gas. The organic mixture serves as a transportation media. The gas is finally accumulated in the liquid carrier as in a conventional gas-liquid absorption system. The presence of the organic layer does not hinder the regeneration of the liquid carrier or recovery of the gas because the organic layer is removed by a settler after the absorption process is completed. In another aspect, the system exhibited increased gas-liquid separation efficiency, thereby reducing the costs of operation and maintenance. Our study focused on the search of the organic layer or transportation layer to enhance the absorption rate of carbon dioxide. The following systems were studied, (1) CO{sub 2}-water system and CO{sub 2}-water-organic layer system; (2) CO{sub 2}-Potassium Carbonate aqueous solution system and CO{sub 2}-Potassium Carbonate aqueous solution-organic layer system. CO{sub 2}-water and CO{sub 2}-Potassium Carbonate systems are the traditional gas-liquid absorption processes. The CO{sub 2}-water-organic layer and CO{sub 2}-Potassium Carbonate-organic layer systems are the novel absorption processes, phase enhanced absorption. As we mentioned early, organic layer (transportation layer phase) is used for the increase of absorption rate. Our study showed that the absorption rate can be increased by adding the organic layer. However, the enhanced factor is highly depended on the liquid mass transfer

  4. Spectroscopic studies of cold, gas-phase biomolecular ions

    NASA Astrophysics Data System (ADS)

    Rizzo, Thomas R.; Stearns, Jaime A.; Boyarkin, Oleg V.

    While the marriage of mass spectrometry and laser spectroscopy is not new, developments over the last few years in this relationship have opened up new horizons for the spectroscopic study of biological molecules. The combination of electrospray ionisation for producing large biological molecules in the gas phase together with cooled ion traps and multiple-resonance laser schemes are allowing spectroscopic investigation of individual conformations of peptides with more than a dozen amino acids. Highly resolved infrared spectra of single conformations of such species provide important benchmarks for testing the accuracy of theoretical calculations. This review presents a number of techniques employed in our laboratory and in others for measuring the spectroscopy of cold, gas-phase protonated peptides. We show examples that demonstrate the power of these techniques and evaluate their extension to still larger biological molecules.

  5. Substituent effects on the gas-phase acidity of silane

    SciTech Connect

    Gordon, M.S.; Volk, D.E. ); Gano, D.R. )

    1989-12-20

    In a previous paper, the gas-phase acidities of XH{sub n} compounds (X = C, N, O, F, Si, P, S, Cl) were predicted with ab initio wave functions. At the MP4{sup 2} level of theory with extended basis sets acidities for these species were determined to be within 2 kcal/mol of experimental value. In the present work, with 6-31G(d) geometries and full MP4/MC-311++G{sup 6}(3df,2pd) energies, the effects of CH{sub 3}, NH{sub 2}, OH, F, SiH{sub 3}, PH{sub 2}, SH, and Cl on the gas-phase acidity of silane are examined. Only a few related calculations have been carried out. All calculations were performed with Gaussian86, and all structures were verified as minima by diagonalizing the analytically determined hessians. Only the valence electrons were correlated in the perturbation theory calculations.

  6. The nucleoside uridine isolated in the gas phase.

    PubMed

    Peña, Isabel; Cabezas, Carlos; Alonso, José L

    2015-03-02

    Herein we present the first experimental observation of the isolated nucleoside uridine, placed in the gas phase by laser ablation and characterized by Fourier transform (FT) microwave techniques. Free from the bulk effects of their native environments, anti/C2'-endo-g+ conformation has been revealed as the most stable form of uridine. Intramolecular hydrogen bonds involving uracil and ribose moieties have been found to play an important role in the stabilization of the nucleoside.

  7. Gas phase fractionation method using porous ceramic membrane

    DOEpatents

    Peterson, Reid A.; Hill, Jr., Charles G.; Anderson, Marc A.

    1996-01-01

    Flaw-free porous ceramic membranes fabricated from metal sols and coated onto a porous support are advantageously used in gas phase fractionation methods. Mean pore diameters of less than 40 .ANG., preferably 5-20 .ANG. and most preferably about 15 .ANG., are permeable at lower pressures than existing membranes. Condensation of gases in small pores and non-Knudsen membrane transport mechanisms are employed to facilitate and increase membrane permeability and permselectivity.

  8. Research on Sources of Gas Phase Metastable Atoms and Molecules

    DTIC Science & Technology

    1982-05-01

    PAGI(Whi DeE# WA..teod) -systems of interest to such diverse areas as gas discharge physics, chemical physics, flame chemistry and plasma physics. "A...second task involved a literature review of prior basic research meta- stable sources followed by the development and experimental testing of appro...appropriate for this phase of the program. The operation of this type of metastable source wab investigated and tested for the production of metastable argon

  9. The Nucleoside Uridine Isolated in the Gas Phase**

    PubMed Central

    Peña, Isabel; Cabezas, Carlos; Alonso, José L.

    2016-01-01

    Herein we present the first experimental observation of the isolated nucleoside uridine, placed in the gas phase by laser ablation and characterized by Fourier transform microwave techniques. Free from the bulk effects of their native environments, anti/C2’-endo-g+ conformation has been revealed as the most stable form of uridine. Intramolecular hydrogen bonds involving uracil and ribose moieties have been found to play an important role in the stabilization of the nucleoside. PMID:25683559

  10. A varying polytropic gas universe and phase space analysis

    NASA Astrophysics Data System (ADS)

    Khurshudyan, M.

    2016-05-01

    In this paper, we will consider a phenomenological model of a dark fluid that is able to explain an accelerated expansion of our low redshift universe and the phase transition to this accelerated expanding universe. Recent developments in modern cosmology towards understanding of the accelerated expansion of the large scale universe involve various scenarios and approaches. Among these approaches, one of well-known and accepted practice is modeling of the content of our universe via dark fluid. There are various models of dark energy fluid actively studied in recent literature and polytropic gas is among them. In this work, we will consider a varying polytropic gas which is a phenomenological modification of polytropic gas. Our model of varying polytropic dark fluid has been constructed to analogue to a varying Chaplygin gas actively discussed in the literature. We will consider interacting models, where dark matter is a pressureless fluid, to have a comprehensive picture. Phase space analysis is an elegant mathematical tool to earn general understanding of large scale universe and easily see an existence of a solution to cosmological coincidence problem. Imposing some constraints on parameters of the models, we found late time attractors for each case analytically. Cosmological consequences for the obtained late time attractors are discussed.

  11. Photocatalytic transformations of organic sulfur compounds and H2S

    NASA Astrophysics Data System (ADS)

    Vorontsov, A. V.

    2008-10-01

    Modern views on the products, pathways and kinetic features of liquid- and gas-phase photocatalytic reactions of sulfur compounds in the presence of heterogeneous and homogeneous photocatalysts are generalised. Attention is focussed on the aliphatic and aromatic reduced sulfur compounds and pesticides. The reaction rate in the liquid and gas phases are analysed as function of solution pH, temperature, catalyst content, substrate concentration, solvent type, air moisture and added oxidants. Photocatalyst deactivation and the ways for recovery of its activity are considered.

  12. Carbon Dioxide Separation from Flue Gas by Phase Enhanced Absorption

    SciTech Connect

    Tim Fout

    2007-06-30

    A new process, phase enhanced absorption, was invented. The method is carried out in an absorber, where a liquid carrier (aqueous solution), an organic mixture (or organic compound), and a gas mixture containing a gas to be absorbed are introduced from an inlet. Since the organic mixture is immiscible or at least partially immiscible with the liquid carrier, the organic mixture forms a layer or small parcels between the liquid carrier and the gas mixture. The organic mixture in the absorber improves mass transfer efficiency of the system and increases the absorption rate of the gas. The organic mixture serves as a transportation media. The gas is finally accumulated in the liquid carrier as in a conventional gas-liquid absorption system. The presence of the organic layer does not hinder the regeneration of the liquid carrier or recovery of the gas because the organic layer is removed by a settler after the absorption process is completed. In another aspect, the system exhibited increased gas-liquid separation efficiency, thereby reducing the costs of operation and maintenance. Our study focused on the search of the organic layer or transportation layer to enhance the absorption rate of carbon dioxide. The following systems were studied, (1) CO{sub 2}-water system and CO{sub 2}-water-organic layer system; (2) CO{sub 2}-Potassium Carbonate aqueous solution system and CO{sub 2}-Potassium Carbonate aqueous solution-organic layer system. CO{sub 2}-water and CO{sub 2}-Potassium Carbonate systems are the traditional gas-liquid absorption processes. The CO{sub 2}-water-organic layer and CO{sub 2}-Potassium Carbonate-organic layer systems are the novel absorption processes, phase enhanced absorption. As we mentioned early, organic layer is used for the increase of absorption rate, and plays the role of transportation of CO{sub 2}. Our study showed that the absorption rate can be increased by adding the organic layer. However, the enhanced factor is highly depended on the

  13. The organic matter of Comet Halley as inferred by joint gas phase and solid phase analyses

    NASA Astrophysics Data System (ADS)

    Krueger, F. R.; Korth, A.; Kissel, J.

    1991-04-01

    During encounters with Comet Halley, the experiment PICCA onboard Giotto measured the gas-phase organic ion composition of the coma, and the experiment PUMA onboard Vega-1 measured the dust composition. Joining both results gives a consistent picture of the parent organic matter from which dust and gas is produced: a complex unsaturated polycondensate, which splits during coma formation into the more refractory C=C,C-N-containing dust part and the more volatile C=C,C-O-containing gas part. The responsible exothermal chemical reactions, which are triggered by sunlight, may play a major role in the dynamics of coma formation.

  14. Gas Phase Model of Surface Reactions for N{2} Afterglows

    NASA Astrophysics Data System (ADS)

    Marković, V. Lj.; Petrović, Z. Lj.; Pejović, M. M.

    1996-07-01

    The adequacy of the homogeneous gas phase model as a representation of the surface losses of diffusing active particles in gas phase is studied. As an example the recent data obtained for the surface recombination coefficients are reanalyzed. The data were obtained by the application of the breakdown delay times which consists of the measurements of the breakdown delay times t_d as a function of the afterglow period tau. It was found that for the conditions of our experiment, the diffusion should not be neglected as the final results are significantly different when obtained by approximate gas phase representation and by exact numerical solution to the diffusion equation. While application of the gas phase effective coefficients to represent surface losses gives an error in the value of the recombination coefficient, it reproduces correctly other characteristics such as order of the process which can be obtained from simple fits to the experimental data. Dans cet article, nous étudions la validité du modèle approximatif représentant les pertes superficielles des particules actives qui diffusent de la phase gazeuse comme pertes dans la phase homogène du gaz. Les données actuelles du coefficient de recombination en surface sont utilisées par cette vérification . Les données experimentales sont obtenues en utilisant la technique qui consiste en la mesure du temps de retard du début de la décharge en fonction de la période de relaxation. Nous avons trouvé que, pour nos conditions expérimentales, la diffusion ne peut être négligée. Aussi, les résultats finals sont considérablement différents quand ils sont obtenus en utilisant le modèle approximatif par comparaison aves les résultats obtenus par la solution numérique exacte de l'équation de la diffusion. L'application des coefficients effectifs dans la phase gaseuse pour la présentation des pertes superficielles donne, pour les coefficients de la recombinaison, des valeurs qui diffèrent en

  15. Gas-phase chemistry of technetium carbonyl complexes.

    PubMed

    Wang, Yang; Qin, Zhi; Fan, Fang-Li; Haba, Hiromitsu; Komori, Yukiko; Cao, Shi-Wei; Wu, Xiao-Lei; Tan, Cun-Min

    2015-05-28

    Gas-phase chemical behaviors of short-lived technetium carbonyl complexes were studied using a low temperature isothermal chromatograph (IC) coupled with a (252)Cf spontaneous fission (SF) source. Fission products recoiled from the (252)Cf SF source were thermalized in a mixed gas containing CO, and then technetium carbonyl complexes were formed from reactions between CO gas and various technetium isotopes. A gas-jet system was employed to transport the volatile carbonyl complexes from a recoil chamber to the IC. Short IC columns made of Fluorinated Ethylene Propylene (FEP) Teflon and quartz were used to obtain chemical information about the technetium carbonyl complexes. The results for the (104)Tc-(106)Tc carbonyl complexes were found to be strongly influenced by the precursors, and showed the chemical behaviors of (104)Mo-(106)Mo carbonyl complexes, respectively. However, (107)Tc and (108)Tc could represent the chemical information of the element technetium due to their high independent yields and the very short half-lives of their precursors (107)Mo and (108)Mo. An adsorption enthalpy of about ΔHads = -43 kJ mol(-1) was determined for the Tc carbonyl complexes on both the Teflon and quartz surfaces by fitting the breakthrough curves of the (107)Tc and (108)Tc carbonyl complexes with a Monte Carlo simulation program. Chemical yields of around 25% were measured for the Tc carbonyl complexes relative to the transport yields obtained with the gas-jet transport of KCl aerosol particles with Ar carrier gas. Furthermore, the influence of a small amount of O2 gas on the yields of the Mo and Tc carbonyl complexes was studied.

  16. Theory of Gas Injection: Interaction of Phase Behavior and Flow

    NASA Astrophysics Data System (ADS)

    Dindoruk, B.

    2015-12-01

    The theory of gas injection processes is a central element required to understand how components move and partition in the reservoir as one fluid is displacing another (i.e., gas is displacing oil). There is significant amount of work done in the area of interaction of phase-behavior and flow in multiphase flow conditions. We would like to present how the theory of gas injection is used in the industry to understand/design reservoir processes in various ways. The tools that are developed for the theory of gas injection originates from the fractional flow theory, as the first solution proposed by Buckley-Leveret in 1940's, for water displacing oil in porous media. After 1960's more and more complex/coupled equations were solved using the initial concept(s) developed by Buckley-Leverett, and then Welge et al. and others. However, the systematic use of the fractional flow theory for coupled set of equations that involves phase relationships (EOS) and phase appearance and disappearance was mainly due to the theory developed by Helfferich in early 80's (in petroleum literature) using method of characteristics primarily for gas injection process and later on by the systematic work done by Orr and his co-researchers during the last two decades. In this talk, we will present various cases that use and extend the theory developed by Helfferich and others (Orr et al., Lake et al. etc.). The review of various injection systems reveals that displacement in porous media has commonalities that can be represented with a unified theory for a class of problems originating from the theory of gas injection (which is in a way generalized Buckley-Leverett problem). The outcome of these solutions can be used for (and are not limited to): 1) Benchmark solutions for reservoir simulators (to quantify numerical dispersion, test numerical algorithms) 2) Streamline simulators 3) Design of laboratory experiments and their use (to invert the results) 4) Conceptual learning and to investigate

  17. Enhanced photocatalytic activity of TiO2 nanobarbed fibers treated with atmospheric pressure plasma using O2 gas

    NASA Astrophysics Data System (ADS)

    Lee, Hyun-Uk; Ahn, Kyun; Jeong, Se-Young; Cho, Chae-Ryong; Kim, Jong-Pil; Bae, Jong-Seong; Kim, Hyun-Gyu; Kwon, Se-Hun; Lee, Hyung Woo

    2010-11-01

    TiO2 nanobarbed fibers (NBFs) were prepared by growing rutile TiO2 nanorods on anatase TiO2 nanofibers via electrospinning and hydrothermal reaction processes. There was a large increase in the photocatalytic activity of O2-plasma-treated (OP)-TiO2 NBFs relative to that of the TiO2 NBFs; this is due to the hydroxylation of the surface of the TiO2 NBFs by OP treatment. The repeatability of the photocatalytic activity of the OP-TiO2 NBFs was found to be high and the decolorization rate after ten cycles was 88.3% of the initial value. These results indicate that OP-TiO2 NBFs have great potential for use as a photocatalyst.

  18. Star formation and gas phase history of the cosmic web

    NASA Astrophysics Data System (ADS)

    Snedden, Ali; Coughlin, Jared; Phillips, Lara Arielle; Mathews, Grant; Suh, In-Saeng

    2016-01-01

    We present a new method of tracking and characterizing the environment in which galaxies and their associated circumgalactic medium evolve. We have developed a structure finding algorithm that uses the rate of change of the density gradient to self-consistently parse and follow the evolution of groups/clusters, filaments and voids in large-scale structure simulations. We use this to trace the complete evolution of the baryons in the gas phase and the star formation history within each structure in our simulated volume. We vary the structure measure threshold to probe the complex inner structure of star-forming regions in poor clusters, filaments and voids. We find that the majority of star formation occurs in cold, condensed gas in filaments at intermediate redshifts (z ˜ 3). We also show that much of the star formation above a redshift z = 3 occurs in low-contrast regions of filaments, but as the density contrast increases at lower redshift, star formation switches to the high-contrast regions, or inner parts, of filaments. Since filaments bridge the void and cluster regions, it suggests that the majority of star formation occurs in galaxies in intermediate density regions prior to the accretion on to groups/clusters. We find that both filaments and poor clusters are multiphase environments distinguishing themselves by different distributions of gas phases.

  19. Gas phase oxidation downstream of a catalytic combustor

    NASA Technical Reports Server (NTRS)

    Tien, J. S.; Anderson, D. N.

    1979-01-01

    Effect of the length available for gas-phase reactions downstream of the catalytic reactor on the emission of CO and unburned hydrocarbons was investigated. A premixed, prevaporized propane/air feed to a 12/cm/diameter catalytic/reactor test section was used. The catalytic reactor was made of four 2.5 cm long monolithic catalyst elements. Four water cooled gas sampling probes were located at positions between 0 and 22 cm downstream of the catalytic reactor. Measurements of unburned hydrocarbon, CO, and CO2 were made. Tests were performed with an inlet air temperature of 800 K, a reference velocity of 10 m/s, pressures of 3 and 600,000 Pa, and fuel air equivalence ratios of 0.14 to 0.24. For very lean mixtures, hydrocarbon emissions were high and CO continued to be formed downstream of the catalytic reactor. At the highest equivalence ratios tested, hydrocarbon levels were much lower and CO was oxidized to CO2 in the gas phase downstream. To achieve acceptable emissions, a downstream region several times longer than the catalytic reactor could be required.

  20. Phase-locked measurements of gas-liquid horizontal flows

    NASA Astrophysics Data System (ADS)

    Zadrazil, Ivan; Matar, Omar; Markides, Christos

    2014-11-01

    A flow of gas and liquid in a horizontal pipe can be described in terms of various flow regimes, e.g. wavy stratified, annular or slug flow. These flow regimes appear at characteristic gas and liquid Reynolds numbers and feature unique wave phenomena. Wavy stratified flow is populated by low amplitude waves whereas annular flow contains high amplitude and long lived waves, so called disturbance waves, that play a key role in a liquid entrainment into the gas phase (droplets). In a slug flow regime, liquid-continuous regions travel at high speeds through a pipe separated by regions of stratified flow. We use a refractive index matched dynamic shadowgraphy technique using a high-speed camera mounted on a moving robotic linear rail to track the formation and development of features characteristic for the aforementioned flow regimes. We show that the wave dynamics become progressively more complex with increasing liquid and gas Reynolds numbers. Based on the shadowgraphy measurements we present, over a range of conditions: (i) phenomenological observations of the formation, and (ii) statistical data on the downstream velocity distribution of different classes of waves. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.

  1. Computational phase diagrams of noble gas hydrates under pressure

    SciTech Connect

    Teeratchanan, Pattanasak Hermann, Andreas

    2015-10-21

    We present results from a first-principles study on the stability of noble gas-water compounds in the pressure range 0-100 kbar. Filled-ice structures based on the host water networks ice-I{sub h}, ice-I{sub c}, ice-II, and C{sub 0} interacting with guest species He, Ne, and Ar are investigated, using density functional theory (DFT) with four different exchange-correlation functionals that include dispersion effects to various degrees: the non-local density-based optPBE-van der Waals (vdW) and rPW86-vdW2 functionals, the semi-empirical D2 atom pair correction, and the semi-local PBE functional. In the He-water system, the sequence of stable phases closely matches that seen in the hydrogen hydrates, a guest species of comparable size. In the Ne-water system, we predict a novel hydrate structure based on the C{sub 0} water network to be stable or at least competitive at relatively low pressure. In the Ar-water system, as expected, no filled-ice phases are stable; however, a partially occupied Ar-C{sub 0} hydrate structure is metastable with respect to the constituents. The ability of the different DFT functionals to describe the weak host-guest interactions is analysed and compared to coupled cluster results on gas phase systems.

  2. Computational phase diagrams of noble gas hydrates under pressure

    NASA Astrophysics Data System (ADS)

    Teeratchanan, Pattanasak; Hermann, Andreas

    2015-10-01

    We present results from a first-principles study on the stability of noble gas-water compounds in the pressure range 0-100 kbar. Filled-ice structures based on the host water networks ice-Ih, ice-Ic, ice-II, and C0 interacting with guest species He, Ne, and Ar are investigated, using density functional theory (DFT) with four different exchange-correlation functionals that include dispersion effects to various degrees: the non-local density-based optPBE-van der Waals (vdW) and rPW86-vdW2 functionals, the semi-empirical D2 atom pair correction, and the semi-local PBE functional. In the He-water system, the sequence of stable phases closely matches that seen in the hydrogen hydrates, a guest species of comparable size. In the Ne-water system, we predict a novel hydrate structure based on the C0 water network to be stable or at least competitive at relatively low pressure. In the Ar-water system, as expected, no filled-ice phases are stable; however, a partially occupied Ar-C0 hydrate structure is metastable with respect to the constituents. The ability of the different DFT functionals to describe the weak host-guest interactions is analysed and compared to coupled cluster results on gas phase systems.

  3. Femtosecond gas phase electron diffraction with MeV electrons.

    PubMed

    Yang, Jie; Guehr, Markus; Vecchione, Theodore; Robinson, Matthew S; Li, Renkai; Hartmann, Nick; Shen, Xiaozhe; Coffee, Ryan; Corbett, Jeff; Fry, Alan; Gaffney, Kelly; Gorkhover, Tais; Hast, Carsten; Jobe, Keith; Makasyuk, Igor; Reid, Alexander; Robinson, Joseph; Vetter, Sharon; Wang, Fenglin; Weathersby, Stephen; Yoneda, Charles; Wang, Xijie; Centurion, Martin

    2016-12-16

    We present results on ultrafast gas electron diffraction (UGED) experiments with femtosecond resolution using the MeV electron gun at SLAC National Accelerator Laboratory. UGED is a promising method to investigate molecular dynamics in the gas phase because electron pulses can probe the structure with a high spatial resolution. Until recently, however, it was not possible for UGED to reach the relevant timescale for the motion of the nuclei during a molecular reaction. Using MeV electron pulses has allowed us to overcome the main challenges in reaching femtosecond resolution, namely delivering short electron pulses on a gas target, overcoming the effect of velocity mismatch between pump laser pulses and the probe electron pulses, and maintaining a low timing jitter. At electron kinetic energies above 3 MeV, the velocity mismatch between laser and electron pulses becomes negligible. The relativistic electrons are also less susceptible to temporal broadening due to the Coulomb force. One of the challenges of diffraction with relativistic electrons is that the small de Broglie wavelength results in very small diffraction angles. In this paper we describe the new setup and its characterization, including capturing static diffraction patterns of molecules in the gas phase, finding time-zero with sub-picosecond accuracy and first time-resolved diffraction experiments. The new device can achieve a temporal resolution of 100 fs root-mean-square, and sub-angstrom spatial resolution. The collimation of the beam is sufficient to measure the diffraction pattern, and the transverse coherence is on the order of 2 nm. Currently, the temporal resolution is limited both by the pulse duration of the electron pulse on target and by the timing jitter, while the spatial resolution is limited by the average electron beam current and the signal-to-noise ratio of the detection system. We also discuss plans for improving both the temporal resolution and the spatial resolution.

  4. Fluorescence Spectroscopy of Gas-phase Polycyclic Aromatic Hydrocarbons

    NASA Technical Reports Server (NTRS)

    Thomas, J. D.; Witt, A. N.

    2006-01-01

    The purpose of this investigation was to produce fluorescence spectra of polycyclic aromatic hydrocarbon (PAH) molecules in the gas-phase for comparison with blue luminescence (BL) emission observed in astrophysical sources Vijh et al. (2004, 2005a,b). The BL occurs roughly from 350 to 450 nm, with a sharp peak near 380 nm. PAHs with three to four rings, e.g. anthracene and pyrene, were found to produce luminescence in the appropriate spectral region, based on existing studies. Relatively few studies of the gas-phase fluorescence of PAHs exist; those that do exist have dealt primarily with the same samples commonly available for purchase such as pyrene and anthracene. In an attempt to understand the chemistry of the nebular environment we also obtained several nitrogen substituted PAHs from our colleagues at NASA Ames. In order to simulate the astrophysical environment we also took spectra by heating the PAHs in a flame. The flame environment counteracts the formation of eximers and permits the spectroscopy of free-flying neutral molecules. Experiments with coal tar demonstrate that fluorescence spectroscopy reveals primarily the presence of the smallest molecules, which are most abundant and which possess the highest fluorescence efficiencies. One gas-phase PAH that seems to fit the BL spectrum most closely is phenanthridine. In view of the results from the spectroscopy of coal tar, a compound containing a mixture of PAHs ranging from small to very large PAH molecules, we can not preclude the presence of larger PAHs in interstellar sources exhibiting BL.

  5. Neurotransmitters in the Gas Phase: La-Mb Studies

    NASA Astrophysics Data System (ADS)

    Cabezas, C.; Mata, S.; López, J. C.; Alonso, J. L.

    2011-06-01

    LA-MB-FTMW spectroscopy combines laser ablation with Fourier transform microwave spectroscopy in supersonic jets overcoming the problems of thermal decomposition associated with conventional heating methods. We present here the results on LA-MB-FTMW studies of some neurotransmitters. Six conformers of dopamine, four of adrenaline, five of noradrenaline and three conformers of serotonin have been characterized in the gas phase. The rotational and nuclear quadrupole coupling constants extracted from the analysis of the rotational spectrum are directly compared with those predicted by ab initio methods to achieve the conclusive identification of different conformers and the experimental characterization of the intramolecular forces at play which control conformational preferences.

  6. Multiscale Aspects of Modeling Gas-Phase Nanoparticle Synthesis

    PubMed Central

    Buesser, B.; Gröhn, A.J.

    2013-01-01

    Aerosol reactors are utilized to manufacture nanoparticles in industrially relevant quantities. The development, understanding and scale-up of aerosol reactors can be facilitated with models and computer simulations. This review aims to provide an overview of recent developments of models and simulations and discuss their interconnection in a multiscale approach. A short introduction of the various aerosol reactor types and gas-phase particle dynamics is presented as a background for the later discussion of the models and simulations. Models are presented with decreasing time and length scales in sections on continuum, mesoscale, molecular dynamics and quantum mechanics models. PMID:23729992

  7. Theoretical calculations of EPR parameters of gas phase hydracrylonitrile radical

    NASA Astrophysics Data System (ADS)

    Sarikaya, Ebru Karakaş; Dereli, Ömer

    2017-02-01

    As a result of detailed conformational search of the hydracrylonitrile, four different conformers of molecule have been obtained. For these conformations, eleven possible radicals were modelled by using density functional theory (DFT) computations with respect to molecular structure. Electron Paramagnetic Resonance parameters of these model radicals were calculated and then they were compared with the experimental ones. Geometry optimizations of the molecule and modeled radicals were calculated by B3LYP method using 6-311++G(d,p) basis sets in gas phase.

  8. Seven Conformers of Pipecolic Acid Identified in the Gas Phase

    NASA Astrophysics Data System (ADS)

    Cabezas, Carlos; Simao, Alcides; Alonso, José L.

    2016-06-01

    The multiconformational landscape of the non-proteinogenic cyclic amino acid pipecolic acid has been explored in the gas phase. Solid pipecolic acid (m.p. 280°C) was vaporized by laser ablation (LA) and expanded in a supersonic jet where the rotational spectra of seven conformers were obtained by broadband microwave spectroscopy (CP-FTMW). All conformers were conclusively identified by comparison of the experimental spectroscopic constants with those predicted theoretically. The relative stability of the conformers rests on a delicate balance of the different intramolecular hydrogen bonds established between the carboxylic and the amino groups.

  9. Femtosecond analysis of free molecular rotation in the gas phase

    NASA Astrophysics Data System (ADS)

    Borisevich, N. A.; Khoroshilov, E. V.; Kryukov, I. V.; Kryukov, P. G.; Sharkov, A. V.; Blokhin, A. P.; Tolstorozhev, G. B.

    1992-04-01

    The time-resolved S 1→S *n absorption anisotropy decay resulting from rotation of free gas phase POPOP molecules at 593 K and PPO molecules at 483 K was studied after S 0→S *1 excitation by femtosecond linearly polarized pulses at 308 nm. The time evolution of the anisotropy measured through a few picoseconds after excitation is in agreement with the results of calculations made for POPOP and PPO using orientational correlation functions developed for rigid asymmetric top molecules.

  10. The solar system/interstellar medium connection - Gas phase abundances

    NASA Technical Reports Server (NTRS)

    Lutz, Barry L.

    1987-01-01

    Gas-phase abundances in the outer solar system are presented as diagnostics of the interstellar medium at the time of the solar system formation, some 4.55 billion years ago. Possible influences of the thermal and chemical histories of the primitive solar nebula and of the processes which led to the formation and evolution of the outer planets and comets on the elemental and molecular composition of the primordial matter are outlined. The major components of the atmospheres of the outer planets and of the comae of comets are identified, and the cosmogonical and cosmological implications are discussed.

  11. Gas-phase energetics of thorium fluorides and their ions.

    PubMed

    Irikura, Karl K

    2013-02-14

    Gas-phase thermochemistry for neutral ThF(n) and cations ThF(n)(+) (n = 1-4) is obtained from large-basis CCSD(T) calculations, with a small-core pseudopotential on thorium. Electronic partition functions are computed with the help of relativistic MRCI calculations. Geometries, vibrational spectra, electronic fine structure, and ion appearance energies are tabulated. These results support the experimental results by Lau, Brittain, and Hildenbrand for the neutral species, except for ThF. The ion thermochemistry is presented here for the first time.

  12. Trapping a Metastable Ferroelectric Phase by Size Reduction in Semiconducting Ferroelectric BiFeO3-PbTiO3 and Its Implications for Photocatalytic Response

    NASA Astrophysics Data System (ADS)

    Narayan, Bastola; Adhikari, Sangeeta; Madras, Giridhar; Ranjan, Rajeev

    2017-02-01

    We show that the large elastostatic and electrostatic energies associated with the supertetragonal spontaneous strain and polarization of a semiconducting ferroelectric (1 -x )BiFe O3-(x )PbTiO3 forces the ground state to switch to the rhombohedral (R ) ferroelectric phase on reduction of crystallite size. The continuity of the pinned tetragonal domain walls, however, prevents a direct tetragonal-to-rhombohedral transformation as the size is gradually reduced by physical means at room temperature. The trapped metastable tetragonal phase in the small crystallites is found to show significantly enhanced photocatalytic activity as compared to its stable tetragonal- or rhombohedral-phase counterparts. Our study suggests that the size effect in multidomain ferroelectrics can be exploited as an effective strategy for the manipulation of functional properties.

  13. Nitrogen-modified nano-titania: True phase composition, microstructure and visible-light induced photocatalytic NO{sub x} abatement

    SciTech Connect

    Tobaldi, D.M.; Otero-Irurueta, G.; Singh, M.K.; Seabra, M.P.; Labrincha, J.A.

    2015-11-15

    Titanium dioxide (TiO{sub 2}) is a popular photocatalyst used for many environmental and anti-pollution applications, but it normally operates under UV light, exploiting ∼5% of the solar spectrum. Nitrification of titania to form N-doped TiO{sub 2} has been explored as a way to increase its photocatalytic activity under visible light, and anionic doping is a promising method to enable TiO{sub 2} to harvest visible-light by changing its photo-absorption properties. In this paper, we explore the insertion of nitrogen into the TiO{sub 2} lattice using our green sol–gel nanosynthesis method, used to create 10 nm TiO{sub 2} NPs. Two parallel routes were studied to produce nitrogen-modified TiO{sub 2} nanoparticles (NPs), using HNO{sub 3}+NH{sub 3} (acid-precipitated base-peptised) and NH{sub 4}OH (totally base catalysed) as nitrogen sources. These NPs were thermally treated between 450 and 800 °C. Their true phase composition (crystalline and amorphous phases), as well as their micro-/nanostructure (crystalline domain shape, size and size distribution, edge and screw dislocation density) was fully characterised through advanced X-ray methods (Rietveld-reference intensity ratio, RIR, and whole powder pattern modelling, WPPM). As pollutants, nitrogen oxides (NO{sub x}) are of particular concern for human health, so the photocatalytic activity of the NPs was assessed by monitoring NO{sub x} abatement, using both solar and white-light (indoor artificial lighting), simulating outdoor and indoor environments, respectively. Results showed that the onset of the anatase-to-rutile phase transformation (ART) occurred at temperatures above 450 °C, and NPs heated to 450 °C possessed excellent photocatalytic activity (PCA) under visible white-light (indoor artificial lighting), with a PCA double than that of the standard P25 TiO{sub 2} NPs. However, higher thermal treatment temperatures were found to be detrimental for visible-light photocatalytic activity, due to the effects

  14. Photocatalytic reactor

    DOEpatents

    Bischoff, B.L.; Fain, D.E.; Stockdale, J.A.D.

    1999-01-19

    A photocatalytic reactor is described for processing selected reactants from a fluid medium comprising at least one permeable photocatalytic membrane having a photocatalytic material. The material forms an area of chemically active sites when illuminated by light at selected wavelengths. When the fluid medium is passed through the illuminated membrane, the reactants are processed at these sites separating the processed fluid from the unprocessed fluid. A light source is provided and a light transmitting means, including an optical fiber, for transmitting light from the light source to the membrane. 4 figs.

  15. The partitioning of ketones between the gas and aqueous phases

    NASA Astrophysics Data System (ADS)

    Betterton, Eric A.

    Most ketones are not significantly hydrated; they therefore retain their chromophore and they could be photolytically degraded in solution yielding a variety of products including carboxylic acids, aldehydes and radicals. It is difficult to accurately model the partitioning of ketones between the gas phase and aqueous phase because of the lack suitable estimates of the Henry's Law constants; consequently the fate and environmental effects of ketones cannot be confidently predicted. Here we report the experimental determination of the Henry's Law constants of a series of ketones that has yielded a simple straight line equation to predict the Henry's Law constants of simple aliphatic ketones: log H ∗ =0.23Σσ ∗ + 1.51; where H ∗ is the effective Henry's Law constant (M atm -1, and Σσ ∗ is the Taft polar substituents constants. The results for 25°C are (M atm -1) CH 3COCH 3, 32; C 6H 5COCH 3, 110; CH 2ClCOCH 3, 59; CH 3COCOCH 3, 74; CF 3COCH 3, 138. Acetophenone appears to have an abnormally high H ∗. Most low molecular weight aliphatic ketones are predicted to characterized by H ∗⩾30 M atm -1 and therefore they are expected to be found in the aqueous phase at concentrations of ⩾5 - 0.5 μM (given a typical gas-phase concentration range of 1-10 ppbv). The expected rate of decomposition of ketones due to photolysis in hydrometers is briefly discussed.

  16. Carbon and Noble Gas Isotope Banks in Two-Phase Flow: Changes in Gas Composition During Migration

    NASA Astrophysics Data System (ADS)

    Sathaye, K.; Larson, T.; Hesse, M. A.

    2015-12-01

    In conjunction with the rise of unconventional oil and gas production, there has been a recent rise in interest in noble gas and carbon isotope changes that can occur during the migration of natural gas. Natural gas geochemistry studies use bulk hydrocarbon composition, carbon isotopes, and noble gas isotopes to determine the migration history of gases from source to reservoir, and to trace fugitive gas leaks from reservoirs to shallow groundwater. We present theoretical and experimental work, which helps to explain trends observed in gas composition in various migration scenarios. Noble gases are used as tracers for subsurface fluid flow due to distinct initial compositions in air-saturated water and natural gases. Numerous field studies have observed enrichments and depletions of noble gases after gas-water interaction. A theoretical two-phase gas displacement model shows that differences in noble gas solubility will cause volatile gas components will become enriched at the front of gas plumes, leaving the surrounding residual water stripped of dissolved gases. Changes in hydrocarbon gas composition are controlled by gas solubility in both formation water and residual oil. In addition to model results, we present results from a series of two-phase flow experiments. These results demonstrate the formation of a noble gas isotope banks ahead of a main CO2 gas plume. Additionally, we show that migrating hydrocarbon gas plumes can sweep biogenic methane from groundwater, significantly altering the isotope ratio of the gas itself. Results from multicomponent, two-phase flow experiments qualitatively agree with the theoretical model, and previous field studies. These experimentally verified models for gas composition changes can be used to aid source identification of subsurface gases.

  17. Project ARGO: Gas phase formation in simulated microgravity

    NASA Technical Reports Server (NTRS)

    Powell, Michael R.; Waligora, James M.; Norfleet, William T.; Kumar, K. Vasantha

    1993-01-01

    The ARGO study investigated the reduced incidence of joint pain decompression sickness (DCS) encountered in microgravity as compared with an expected incidence of joint pain DCS experienced by test subjects in Earth-based laboratories (unit gravity) with similar protocols. Individuals who are decompressed from saturated conditions usually acquire joint pain DCS in the lower extremities. Our hypothesis is that the incidence of joint pain DCS can be limited by a significant reduction in the tissue gas micronuclei formed by stress-assisted nucleation. Reductions in dynamic and kinetic stresses in vivo are linked to hypokinetic and adynamic conditions of individuals in zero g. We employed the Doppler ultrasound bubble detection technique in simulated microgravity studies to determine quantitatively the degree of gas phase formation in the upper and lower extremities of test subjects during decompression. We found no evidence of right-to-left shunting through pulmonary vasculature. The volume of gas bubble following decompression was examined and compared with the number following saline contrast injection. From this, we predict a reduced incidence of DCS on orbit, although the incidence of predicted mild DCS still remains larger than that encountered on orbit.

  18. Gas-Phase Fragmentation Analysis of Nitro-Fatty Acids

    PubMed Central

    Bonacci, Gustavo; Asciutto, Eliana K.; Woodcock, Steven R.; Salvatore, Sonia R.; Freeman, Bruce A.; Schopfer, Francisco J.

    2012-01-01

    Nitro-fatty acids are electrophilic signaling mediators formed in increased amounts during inflammation by nitric oxide and nitrite-dependent redox reactions. A more rigorous characterization of endogenously-generated species requires additional understanding of their gas-phase induced fragmentation. Thus, collision induced dissociation (CID) of nitroalkane and nitroalkene groups in fatty acids were studied in the negative ion mode to provide mass spectrometric tools for their structural characterization. Fragmentation of nitroalkanes occurred mainly through loss of the NO2− anion or neutral loss of HNO2. The CID of nitroalkenes proceeds via a more complex cyclization, followed by fragmentation to nitrile and aldehyde products. Gas-phase fragmentation of nitroalkene functional groups with additional γ or δ unsaturation occurred through a multiple step cyclization reaction process, leading to 5 and 6 member ring heterocyclic products and carbon chain fragmentation. Cyclization products were not obtained during nitroalkane fragmentation, highlighting the role of double bond π electrons during NO2− rearrangements, stabilization and heterocycle formation. The proposed structures, mechanisms and products of fragmentation are supported by analysis of 13C and 15N labeled parent molecules, 6 different nitroalkene positional isomers, 6 nitroalkane positional isomers, accurate mass determinations at high resolution and quantum mechanics calculations. Multiple key diagnostic ion fragments were obtained through this analysis, allowing for the precise placement of double bonds and sites of fatty acid nitration, thus supporting an ability to predict nitro positions in biological samples. PMID:21953257

  19. High resolution dissociative electron attachment to gas phase adenine

    SciTech Connect

    Huber, D.; Beikircher, M.; Denifl, S.; Zappa, F.; Matejcik, S.; Bacher, A.; Grill, V.; Maerk, T. D.; Scheier, P.

    2006-08-28

    The dissociative electron attachment to the gas phase nucleobase adenine is studied using two different experiments. A double focusing sector field mass spectrometer is utilized for measurements requiring high mass resolution, high sensitivity, and relative ion yields for all the fragment anions and a hemispherical electron monochromator instrument for high electron energy resolution. The negative ion mass spectra are discussed at two different electron energies of 2 and 6 eV. In contrast to previous gas phase studies a number of new negative ions are discovered in the mass spectra. The ion efficiency curves for the negative ions of adenine are measured for the electron energy range from about 0 to 15 eV with an electron energy resolution of about 100 meV. The total anion yield derived via the summation of all measured fragment anions is compared with the total cross section for negative ion formation measured recently without mass spectrometry. For adenine the shape of the two cross section curves agrees well, taking into account the different electron energy resolutions; however, for thymine some peculiar differences are observed.

  20. Gas-phase Dissociation of homo-DNA Oligonucleotides

    NASA Astrophysics Data System (ADS)

    Stucki, Silvan R.; Désiron, Camille; Nyakas, Adrien; Marti, Simon; Leumann, Christian J.; Schürch, Stefan

    2013-12-01

    Synthetic modified oligonucleotides are of interest for diagnostic and therapeutic applications, as their biological stability, pairing selectivity, and binding strength can be considerably increased by the incorporation of unnatural structural elements. Homo-DNA is an oligonucleotide homologue based on dideoxy-hexopyranosyl sugar moieties, which follows the Watson-Crick A-T and G-C base pairing system, but does not hybridize with complementary natural DNA and RNA. Homo-DNA has found application as a bioorthogonal element in templated chemistry applications. The gas-phase dissociation of homo-DNA has been investigated by ESI-MS/MS and MALDI-MS/MS, and mechanistic aspects of its gas-phase dissociation are discussed. Experiments revealed a charge state dependent preference for the loss of nucleobases, which are released either as neutrals or as anions. In contrast to DNA, nucleobase loss from homo-DNA was found to be decoupled from backbone cleavage, thus resulting in stable products. This renders an additional stage of ion activation necessary in order to generate sequence-defining fragment ions. Upon MS3 of the primary base-loss ion, homo-DNA was found to exhibit unspecific backbone dissociation resulting in a balanced distribution of all fragment ion series.

  1. Nahoon: Time-dependent gas-phase chemical model

    NASA Astrophysics Data System (ADS)

    Wakelam, V.

    2014-09-01

    Nahoon is a gas-phase chemical model that computes the chemical evolution in a 1D temperature and density structure. It uses chemical networks downloaded from the KInetic Database for Astrochemistry (KIDA) but the model can be adapted to any network. The program is written in Fortran 90 and uses the DLSODES (double precision) solver from the ODEPACK package to solve the coupled stiff differential equations. The solver computes the chemical evolution of gas-phase species at a fixed temperature and density and can be used in one dimension (1D) if a grid of temperature, density, and visual extinction is provided. Grains, both neutral and negatively charged, and electrons are considered as chemical species and their concentrations are computed at the same time as those of the other species. Nahoon contains a test to check the temperature range of the validity of the rate coefficients and avoid extrapolations outside this range. A test is also included to check for duplication of chemical reactions, defined over complementary ranges of temperature.

  2. Highly efficient and stable Au/Bi2MoO6/Bi2WO6 heterostructure with enhanced photocatalytic activity for NO gas removal under visible light irradiation

    NASA Astrophysics Data System (ADS)

    Jia, Jia; Du, Xiao; Liu, Enzhou; Wan, Jun; Pan, Chao; Ma, Yongning; Hu, Xiaoyun; Fan, Jun

    2017-04-01

    The ternary composite photocatalyst Au/Bi2MoO6/Bi2WO6 has been successfully synthesized by a facile hydrothermal process and microwave-assisted chemical reduction method for the first time. A series of characterization results reveal that Au nanoparticles are uniformly dispersed on the surface of Bi2MoO6/Bi2WO6 microspheres. The unique photocatalytic performance of the novel composite material is evaluated by the photocatalytic removal of NO gas at ppb levels under visible light irradiation. The photocatalytic removal rate of NO gas in the presence of Au/Bi2MoO6/Bi2WO6 sample is the highest, which directly attributes to the effective separation of photoinduced charge carriers through the formation of the heterojunction and the Schottky junction at the interface between Au nanoparticles and Bi2MoO6 or Bi2WO6. Additionally, it is indicated that the h + and \\centerdot \\text{O}2- play indispensable role in photocatalytic process by free radicals trapping experiments and the oxidation products of NO gas on the surface of the catalysts are nitrate by drawing the standard curve of total N content in nitrate. Meanwhile, a possible mechanism for the photocatalytic activity enhancement of the Au/Bi2MoO6/Bi2WO6 composites is proposed. These results demonstrate that the Au/Bi2MoO6/Bi2WO6 photocatalyst is a promising candidate for indoor air purification under solar light irradiation.

  3. Surfactants from the gas phase may promote cloud droplet formation.

    PubMed

    Sareen, Neha; Schwier, Allison N; Lathem, Terry L; Nenes, Athanasios; McNeill, V Faye

    2013-02-19

    Clouds, a key component of the climate system, form when water vapor condenses upon atmospheric particulates termed cloud condensation nuclei (CCN). Variations in CCN concentrations can profoundly impact cloud properties, with important effects on local and global climate. Organic matter constitutes a significant fraction of tropospheric aerosol mass, and can influence CCN activity by depressing surface tension, contributing solute, and influencing droplet activation kinetics by forming a barrier to water uptake. We present direct evidence that two ubiquitous atmospheric trace gases, methylglyoxal (MG) and acetaldehyde, known to be surface-active, can enhance aerosol CCN activity upon uptake. This effect is demonstrated by exposing acidified ammonium sulfate particles to 250 parts per billion (ppb) or 8 ppb gas-phase MG and/or acetaldehyde in an aerosol reaction chamber for up to 5 h. For the more atmospherically relevant experiments, i.e., the 8-ppb organic precursor concentrations, significant enhancements in CCN activity, up to 7.5% reduction in critical dry diameter for activation, are observed over a timescale of hours, without any detectable limitation in activation kinetics. This reduction in critical diameter enhances the apparent particle hygroscopicity up to 26%, which for ambient aerosol would lead to cloud droplet number concentration increases of 8-10% on average. The observed enhancements exceed what would be expected based on Köhler theory and bulk properties. Therefore, the effect may be attributed to the adsorption of MG and acetaldehyde to the gas-aerosol interface, leading to surface tension depression of the aerosol. We conclude that gas-phase surfactants may enhance CCN activity in the atmosphere.

  4. The Diamagnetic Phase Transition of Dense Electron Gas: Astrophysical Applications

    NASA Astrophysics Data System (ADS)

    Wang, Zhaojun; Lü, Guoliang; Zhu, Chunhua; Wu, Baoshan

    2016-10-01

    Neutron stars are ideal astrophysical laboratories for testing theories of the de Haas-van Alphen effect and diamagnetic phase transition which is associated with magnetic domain formation. The “magnetic interaction” between delocalized magnetic moments of electrons (the Shoenberg effect), can result in an effect of the diamagnetic phase transition into domains of alternating magnetization (Condon's domains). Associated with the domain formation are prominent magnetic field oscillation and anisotropic magnetic stress which may be large enough to fracture the crust of magnetar with a super-strong field. Even if the fracture is impossible as in “low-field” magnetar, the depinning phase transition of domain wall (DW) motion driven by low field rate (mainly due to the Hall effect) in the randomly perturbed crust can result in a catastrophically variation of magnetic field. This intermittent motion, similar to the avalanche process, makes the Hall effect be dissipative. These qualitative consequences about magnetized electron gas are consistent with observations of magnetar emission, and especially the threshold critical dynamics of driven DW can partially overcome the difficulties of “low-field” magnetar bursts and the heating mechanism of transient, or “outbursting” magnetar.

  5. Synthesis and photocatalytic activity of N-doped TiO2 produced in a solid phase reaction

    NASA Astrophysics Data System (ADS)

    Xin, Gang; Pan, Hongfei; Chen, Dan; Zhang, Zhihua; Wen, Bin

    2013-02-01

    N-doped TiO2 was synthesized by calcining a mixture of titanic acid and graphitic carbon nitride (g-C3N4) at temperatures above 500 °C. The final samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and UV-vis diffuse reflectance spectra. The photocatalytic activity of N-doped TiO2 was studied by assessing the degradation of methylene blue in an aqueous solution, under visible light and UV light irradiation. It was found that the N-doped TiO2 displayed higher photocatalytic activity than pure TiO2, under both visible and UV light.

  6. Gas-phase reactions of halogen species of atmospheric importance

    NASA Astrophysics Data System (ADS)

    Heard, Anne C.

    A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen-containing molecules and between NO3 radicals and the iodine species I2 and I. These experiments have shown that: (1) the reaction of methyl iodide with OH accounts for approximately 2 percent of the removal of CH3I from the troposphere as compared with photolysis; (2) abstraction of I-atoms from a C-I bond by OH is probable in the gas-phase; (3) the halogen-containing anaesthetic substances halothane CF3CClBrH, enflurane CF2HOCF2CFClH, isoflurane CF2HOCClHCF3 and sevoflurane (CF3)2CHOCFH2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross-sections of the compounds in the spectral region 800-1200 cm(exp -1) were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl3 for each compound. The study of the reactions between OH and CF3CFBrH and CF2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of reaction, the rate constant of which was found to be (1.5 +/- 0.5) x 10(exp -12)/cu cm

  7. Catalytic role of TiO(2) terminal oxygen atoms in liquid-phase photocatalytic reactions: oxidation of aromatic compounds in anhydrous acetonitrile.

    PubMed

    Montoya, Juan F; Bahnemann, Detlef W; Peral, José; Salvador, Pedro

    2014-08-04

    On the basis of experiments carried out with controlled amounts of residual oxygen and water, or by using oxygen-isotope-labeled Ti(18) O2 as the photocatalyst, we demonstrate that (18) Os atoms behave as real catalytic species in the photo-oxidation of acetonitrile-dissolved aromatic compounds such as benzene, phenol, and benzaldehyde with TiO2 . The experimental evidence allows a terminal-oxygen indirect electron-transfer (TOIET) mechanism to be proposed, which is a new pathway that involves the trapping of free photogenerated valence-band holes at Os species and their incorporation into the reaction products, with simultaneous generation of oxygen vacancies at the TiO2 surface and their subsequent healing with oxygen atoms from either O2 or H2 O molecules that are dissolved in the liquid phase. According to the TOIET mechanism, the TiO2 surface is not considered to remain stable, but is continuously changing in the course of the photocatalytic reaction, challenging earlier interpretations of TiO2 photocatalytic phenomena.

  8. Gas-phase folding and unfolding of cytochrome c cations.

    PubMed Central

    Wood, T D; Chorush, R A; Wampler, F M; Little, D P; O'Connor, P B; McLafferty, F W

    1995-01-01

    Water is thought to play a dominant role in protein folding, yet gaseous multiply protonated proteins from which the water has been completely removed show hydrogen/deuterium (H/D) exchange behavior similar to that used to identify conformations in solution. Indicative of the gas-phase accessibility to D2O, multiply-charged (6+ to 17+) cytochrome c cations exchange at six (or more) distinct levels of 64 to 173 out of 198 exchangeable H atoms, with the 132 H level found at charge values 8+ to 17+. Infrared laser heating and fast collisions can apparently induce ions to unfold to exchange at a higher distinct level, while charge-stripping ions to lower charge values yields apparent folding as well as unfolding. PMID:7708663

  9. Regenerable Air Purification System for Gas-Phase Contaminant Control

    NASA Technical Reports Server (NTRS)

    Constantinescu, Ileana C.; Finn, John E.; LeVan, M. Douglas; Lung, Bernadette (Technical Monitor)

    2000-01-01

    Tests of a pre-prototype regenerable air purification system (RAPS) that uses water vapor to displace adsorbed contaminants from an adsorbent column have been performed at NASA Ames Research Center. A unit based on this design can be used for removing trace gas-phase contaminants from spacecraft cabin air or from polluted process streams including incinerator exhaust. During the normal operation mode, contaminants are removed from the air on the column. Regeneration of the column is performed on-line. During regeneration, contaminants are displaced and destroyed inside the closed oxidation loop. In this presentation we discuss initial experimental results for the performance of RAPS in the removal and treatment of several important spacecraft contaminant species from air.

  10. Regenerable Air Purification System for Gas-Phase Contaminant Control

    NASA Technical Reports Server (NTRS)

    Constantinescu, Ileana C.; Qi, Nan; LeVan, M. Douglas; Finn, Cory K.; Finn, John E.; Luna, Bernadette (Technical Monitor)

    2000-01-01

    A regenerable air purification system (RAPS) that uses water vapor to displace adsorbed contaminants from an. adsorbent column into a closed oxidation loop is under development through cooperative R&D between Vanderbilt University and NASA Ames Research Center. A unit based on this design can be used for removing trace gas-phase contaminants from spacecraft cabin air or from polluted process streams including incinerator exhaust. Recent work has focused on fabrication and operation of a RAPS breadboard at NASA Ames, and on measurement of adsorption isotherm data for several important organic compounds at Vanderbilt. These activities support the use and validation of RAPS modeling software also under development at Vanderbilt, which will in turn be used to construct a prototype system later in the project.

  11. The intrinsic (gas-phase) acidities of bridgehead alcohols

    NASA Astrophysics Data System (ADS)

    Herrero, Rebeca; Dávalos, Juan Z.; Abboud, José-Luis M.; Alkorta, I.; Koppel, I.; Koppel, I. A.; Sonoda, T.; Mishima, M.

    2007-11-01

    The gas-phase acidities of 1-adamantanol and perfluoro1-adamantanol were determined by means of Fourier transform ion cyclotron resonance spectrometry (FT-ICR). The acidity of perfluoro1-adamantanol seems to be the highest ever reported for an alcohol. A computational study of these species and their anions at both the MP2/6-311 + G(d,p) and B3LYP/6-311 + G(d,p) levels was performed. Also studied were the tertiary alcohols (including their perfluorinated forms) derived from norbornane, bicyclo[2.2E2]octane and cubane. It was found that: (i) the intrinsic acidity of non-fluorinated bridgehead alcohols increases with the strain of the hydrocarbon framework and, (ii) perfluorination of these compounds strongly increases their acidity and, likely, significantly modifies their internal strain.

  12. Gas-phase synthesis of magnetic metal/polymer nanocomposites.

    PubMed

    Starsich, Fabian H L; Hirt, Ann M; Stark, Wendelin J; Grass, Robert N

    2014-12-19

    Highly magnetic metal Co nanoparticles were produced via reducing flame spray pyrolysis, and directly coated with an epoxy polymer in flight. The polymer content in the samples varied between 14 and 56 wt% of nominal content. A homogenous dispersion of Co nanoparticles in the resulting nanocomposites was visualized by electron microscopy. The size and crystallinity of the metallic fillers was not affected by the polymer, as shown by XRD and magnetic hysteresis measurements. The good control of the polymer content in the product nanocomposite was shown by elemental analysis. Further, the successful polymerization in the gas phase was demonstrated by electron microscopy and size measurements. The presented effective, dry and scalable one-step synthesis method for highly magnetic metal nanoparticle/polymer composites presented here may drastically decrease production costs and increase industrial yields.

  13. Gas-phase synthesis of magnetic metal/polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Starsich, Fabian H. L.; Hirt, Ann M.; Stark, Wendelin J.; Grass, Robert N.

    2014-12-01

    Highly magnetic metal Co nanoparticles were produced via reducing flame spray pyrolysis, and directly coated with an epoxy polymer in flight. The polymer content in the samples varied between 14 and 56 wt% of nominal content. A homogenous dispersion of Co nanoparticles in the resulting nanocomposites was visualized by electron microscopy. The size and crystallinity of the metallic fillers was not affected by the polymer, as shown by XRD and magnetic hysteresis measurements. The good control of the polymer content in the product nanocomposite was shown by elemental analysis. Further, the successful polymerization in the gas phase was demonstrated by electron microscopy and size measurements. The presented effective, dry and scalable one-step synthesis method for highly magnetic metal nanoparticle/polymer composites presented here may drastically decrease production costs and increase industrial yields.

  14. Uv Spectroscopy on Gas Phase Cu(I)-BIPYRIDYL Complexes

    NASA Astrophysics Data System (ADS)

    Xu, Shuang; Christopher, Casey; Weber, J. Mathias

    2015-06-01

    Transition metal complexes with bipyridine ligands are of great interest in metal-organic chemistry, since they are prototypes for many applications in photochemistry and homogeneous catalysis. Under-coordinated bipyridyl complexes are elusive species in the condensed phase, and the ligand-induced changes in electronic structure are of fundamental interest. We present UV photodissociation spectra of mass-selected monocationic copper(I)-bipyridyl complexes [bpy-Cu-L]+ with different ligands (L = H2O, D2, N2, MeOH, Cl). Complexes were prepared via electrospray ionization of copper/bipyridine solutions followed by accumulation and buffer gas cooling in a cryogenic Paul trap. In addition, we show spectra of similar species based on copper oxide, [bpy-CuO-L]+.

  15. Dissociative attachment reactions of electrons with gas phase superacids

    SciTech Connect

    Liu, X.

    1992-01-01

    Using the flowing afterglow Langmuir probe (FALP) technique, dissociative attachment coefficients [beta] for reactions of electrons with gas phase superacids HCo(PF[sub 3])[sub 4], HRh(PF[sub 3])[sub 4] and carbonyl hydride complexes HMn(CO)[sub 5], HRe(CO)[sub 5] have been determined under thermal conditions over the approximate temperature range 300[approximately]550 K. The superacids react relatively slowly (<1/20 of [beta][sub max]) with free electrons in a thermal plasma, and the values of [beta] obtained this far do not show a correlation between acidity and [beta]. The pioneer researchers in this field had speculated that any superacid would be a rapid attacher of electrons; it was found that this speculation is not true in general. The product distribution of electron attachment reaction to HCo(PF[sub 3])[sub 4] was found to be independent of temperature even though the [beta][HCo(PF[sub 3])[sub 4

  16. Gas and liquid phase acidity of natural antioxidants.

    PubMed

    Leopoldini, Monica; Russo, Nino; Toscano, Marirosa

    2006-04-19

    The gas phase and in solution absolute and relative acidities of nine natural systems contained in red and white wines were determined through theoretical B3LYP/6-311++G** calculations. The aim was to correlate these thermodynamic quantities to the ability that some of these compounds show in chelating metals ions to carry out an antioxidant action following a mechanism recently reported in the literature. Results indicated that both absolute and relative values are affected by molecular features such as electronic delocalization and conjugation and intramolecular hydrogen bonds. Polyphenols characterized by the ortho-dihydroxy functionality were found to be good candidates to act as metal cation chelating ligands. Some differences in absolute acidities values were encountered in going from vacuum to water solution.

  17. Silicon Nanowire-Based Devices for Gas-Phase Sensing

    PubMed Central

    Cao, Anping; Sudhölter, Ernst J.R.; de Smet, Louis C.P.M.

    2014-01-01

    Since their introduction in 2001, SiNW-based sensor devices have attracted considerable interest as a general platform for ultra-sensitive, electrical detection of biological and chemical species. Most studies focus on detecting, sensing and monitoring analytes in aqueous solution, but the number of studies on sensing gases and vapors using SiNW-based devices is increasing. This review gives an overview of selected research papers related to the application of electrical SiNW-based devices in the gas phase that have been reported over the past 10 years. Special attention is given to surface modification strategies and the sensing principles involved. In addition, future steps and technological challenges in this field are addressed. PMID:24368699

  18. Infrared photodissociation spectroscopy of protonated neurotransmitters in the gas phase

    NASA Astrophysics Data System (ADS)

    MacLeod, N. A.; Simons, J. P.

    2007-03-01

    Protonated neurotransmitters have been produced in the gas phase via a novel photochemical scheme: complexes of the species of interest, 1-phenylethylamine, 2-amino-1-phenylethanol and the diastereo-isomers, ephedrine and pseudoephedrine, with a suitable proton donor, phenol (or indole), are produced in a supersonic expansion and ionized by resonant two photon ionization of the donor. Efficient proton transfer generates the protonated neurotransmitters, complexed to a phenoxy radical. Absorption of infrared radiation, and subsequent evaporation of the phenoxy tag, coupled with time of flight mass spectrometry, provides vibrational spectra of the protonated (and also hydrated) complexes for comparison with the results of quantum chemical computation. Comparison with the conformational structures of the neutral neurotransmitters (established previously) reveals the effect of protonation on their structure. The photochemical proton transfer strategy allows spectra to be recorded from individual laser shots and their quality compares favourably with that obtained using electro-spray or matrix assisted laser desorption ion sources.

  19. Synthesis and Gas Phase Thermochemistry of Germanium-Containing Compounds

    SciTech Connect

    Classen, Nathan Robert

    2002-01-01

    The driving force behind much of the work in this dissertation was to gain further understanding of the unique olefin to carbene isomerization observed in the thermolysis of 1,1-dimethyl-2-methylenesilacyclobutane by finding new examples of it in other silicon and germanium compounds. This lead to the examination of a novel phenylmethylenesilacyclobut-2-ene, which did not undergo olefin to carbene rearrangement. A synthetic route to methylenegermacyclobutanes was developed, but the methylenegermacyclobutane system exhibited kinetic instability, making the study of the system difficult. In any case the germanium system decomposed through a complex mechanism which may not include olefin to carbene isomerization. However, this work lead to the study of the gas phase thermochemistry of a series of dialkylgermylene precursors in order to better understand the mechanism of the thermal decomposition of dialkylgermylenes. The resulting dialkylgermylenes were found to undergo a reversible intramolecular β C-H insertion mechanism.

  20. Ceramic microreactors for heterogeneously catalysed gas-phase reactions.

    PubMed

    Knitter, Regina; Liauw, Marcel A

    2004-08-01

    The high surface to volume ratio of microchannel components offers many advantages in micro chemical engineering. It is obvious, however, that the reactor material and corrosion phenomena play an important role when applying these components. For chemical reactions at very high temperatures or/and with corrosive reactants involved, microchannel components made of metals or polymers are not suited. Hence, a modular microreactor system made of alumina was developed and fabricated using a rapid prototyping process chain. With exchangeable inserts the system can be adapted to the requirements of various reactions. Two heterogeneously catalysed gas-phase reactions (oxidative coupling of methane, isoprene selective oxidation to citraconic anhydride) were investigated to check the suitability of the system at temperatures of up to 1000 degrees C. Apart from the high thermal and chemical resistance, the lack of any blind activity was found to be another advantage of ceramic components.

  1. Surfactants from the gas phase may promote cloud droplet formation

    PubMed Central

    Sareen, Neha; Schwier, Allison N.; Lathem, Terry L.; Nenes, Athanasios; McNeill, V. Faye

    2013-01-01

    Clouds, a key component of the climate system, form when water vapor condenses upon atmospheric particulates termed cloud condensation nuclei (CCN). Variations in CCN concentrations can profoundly impact cloud properties, with important effects on local and global climate. Organic matter constitutes a significant fraction of tropospheric aerosol mass, and can influence CCN activity by depressing surface tension, contributing solute, and influencing droplet activation kinetics by forming a barrier to water uptake. We present direct evidence that two ubiquitous atmospheric trace gases, methylglyoxal (MG) and acetaldehyde, known to be surface-active, can enhance aerosol CCN activity upon uptake. This effect is demonstrated by exposing acidified ammonium sulfate particles to 250 parts per billion (ppb) or 8 ppb gas-phase MG and/or acetaldehyde in an aerosol reaction chamber for up to 5 h. For the more atmospherically relevant experiments, i.e., the 8-ppb organic precursor concentrations, significant enhancements in CCN activity, up to 7.5% reduction in critical dry diameter for activation, are observed over a timescale of hours, without any detectable limitation in activation kinetics. This reduction in critical diameter enhances the apparent particle hygroscopicity up to 26%, which for ambient aerosol would lead to cloud droplet number concentration increases of 8–10% on average. The observed enhancements exceed what would be expected based on Köhler theory and bulk properties. Therefore, the effect may be attributed to the adsorption of MG and acetaldehyde to the gas–aerosol interface, leading to surface tension depression of the aerosol. We conclude that gas-phase surfactants may enhance CCN activity in the atmosphere. PMID:23382211

  2. Gas phase plasma impact on phenolic compounds in pomegranate juice.

    PubMed

    Herceg, Zoran; Kovačević, Danijela Bursać; Kljusurić, Jasenka Gajdoš; Jambrak, Anet Režek; Zorić, Zoran; Dragović-Uzelac, Verica

    2016-01-01

    The aim of the study was to evaluate the effect of gas phase plasma on phenolic compounds in pomegranate juice. The potential of near infrared reflectance spectroscopy combined with partial least squares for monitoring the stability of phenolic compounds during plasma treatment was explored, too. Experiments are designed to investigate the effect of plasma operating conditions (treatment time 3, 5, 7 min; sample volume 3, 4, 5 cm(3); gas flow 0.75, 1, 1.25 dm(3) min(-1)) on phenolic compounds and compared to pasteurized and untreated pomegranate juice. Pasteurization and plasma treatment resulted in total phenolic content increasing by 29.55% and 33.03%, respectively. Principal component analysis and sensitivity analysis outputted the optimal treatment design with plasma that could match the pasteurized sample concerning the phenolic stability (5 min/4 cm(3)/0.75 dm(3) min(-1)). Obtained results demonstrate the potential of near infrared reflectance spectroscopy that can be successfully used to evaluate the quality of pomegranate juice upon plasma treatment considering the phenolic compounds.

  3. Estimation of gas phase mixing in packed beds

    SciTech Connect

    Frigerio, S.; Thunman, H.; Leckner, B.; Hermansson, S.

    2008-04-15

    An improved model is presented for estimation of the mixing of gaseous species in a packed bed for fuel conversion. In particular, this work clarifies the main characteristics of mixing of volatiles and oxidizers in a burning bed of high-volatile solid fuel. Expressions are introduced to represent the active role of degradation of the solid particles in the mixing within the gas phase. During drying and devolatilization the solids modify the behavior of the gas flow: the volatiles released from the surface of the particles increase the turbulence in the system, and hence the rates of the homogeneous reactions under mixing-limited conditions. Numerical experiments are carried out to test the validity of this conclusion regarding mixing in different geometries. The flow of volatiles leaving the fuel particles is shown to contribute significantly to mixing, especially at low air flows through a bed. However, the fraction of the particle surface where volatiles are released and its orientation in the bed should be better determined in order to increase the accuracy of the estimates of turbulent mixing. (author)

  4. Gas phase structures of peroxides: experiments and computational problems.

    PubMed

    Oberhammer, Heinz

    2015-02-02

    Gas-phase structures of several organic and inorganic peroxides X-O-O-X and X-O-O-X', which have been determined experimentally by gas electron diffraction and/or microwave spectroscopy, are discussed. The OO bond length in these peroxides varies from 1.481(8) Å in Me3 SiOOSiMe3 to 1.214(2) Å in FOOF and the dihedral angle ϕ(XO-OX) between 0° in HC(O)O-OH and near 180° in Bu(t) O-OBu(t) . Some of the peroxides cause problems for quantum chemistry, since several computational methods fail to reproduce the experimental structures. Extreme examples are MeO-OMe and FO-OF. In the case of MeO-OMe only about half of the more than 100 computational methods reported in the literature reproduce the experimentally determined double-minimum shape of the torsional potential around the OO bond correctly. For FO-OF only a small number of close to 200 computational methods reproduce the OO and OF bond lengths better than ±0.02 Å.

  5. Gas phase hydrogen permeation in alpha titanium and carbon steels

    NASA Technical Reports Server (NTRS)

    Johnson, D. L.; Shah, K. K.; Reeves, B. H.; Gadgeel, V. L.

    1980-01-01

    Commercially pure titanium and heats of Armco ingot iron and steels containing from 0.008-1.23 w/oC were annealed or normalized and machined into hollow cylinders. Coefficients of diffusion for alpha-Ti and alpha-Fe were determined by the lag-time technique. Steady state permeation experiments yield first power pressure dependence for alpha-Ti and Sievert's law square root dependence for Armco iron and carbon steels. As in the case of diffusion, permeation data confirm that alpha-titanium is subject to at least partial phase boundary reaction control while the steels are purely diffusion controlled. The permeation rate in steels also decreases as the carbon content increases. As a consequence of Sievert's law, the computed hydrogen solubility decreases as the carbon content increases. This decreases in explained in terms of hydrogen trapping at carbide interfaces. Oxidizing and nitriding the surfaces of alpha-titanium membranes result in a decrease in the permeation rate for such treatment on the gas inlet surfaces but resulted in a slight increase in the rate for such treatment on the gas outlet surfaces. This is explained in terms of a discontinuous TiH2 layer.

  6. Tm-doped TiO2 and Tm2Ti2O7 pyrochlore nanoparticles: enhancing the photocatalytic activity of rutile with a pyrochlore phase

    PubMed Central

    De los Santos, Desiré M; Aguilar, Teresa; Sánchez-Coronilla, Antonio; Fernández-Lorenzo, Concha; Alcántara, Rodrigo; Piñero, Jose Carlos; Blanco, Ginesa; Martín-Calleja, Joaquín

    2015-01-01

    Summary Tm-doped TiO2 nanoparticles were synthesized using a water-controlled hydrolysis reaction. Analysis was performed in order to determine the influence of the dopant concentration and annealing temperature on the phase, crystallinity, and electronic and optical properties of the resulting material. Various characterization techniques were utilized such as X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and UV–vis spectroscopy. For the samples annealed at 773 and 973 K, anatase phase TiO2 was obtained, predominantly internally doped with Tm3+. ICP–AES showed that a doping concentration of up to 5.8 atom % was obtained without reducing the crystallinity of the samples. The presence of Tm3+ was confirmed by X-ray photoelectron spectroscopy and UV–vis spectroscopy: the incorporation of Tm3+ was confirmed by the generation of new absorption bands that could be assigned to Tm3+ transitions. Furthermore, when the samples were annealed at 1173 K, a pyrochlore phase (Tm2Ti2O7) mixed with TiO2 was obtained with a predominant rutile phase. The photodegradation of methylene blue showed that this pyrochlore phase enhanced the photocatalytic activity of the rutile phase. PMID:25821701

  7. Phase separation in a polarized Fermi gas with spin-orbit coupling

    SciTech Connect

    Yi, W.; Guo, G.-C.

    2011-09-15

    We study the phase separation of a spin-polarized Fermi gas with spin-orbit coupling near a wide Feshbach resonance. As a result of the competition between spin-orbit coupling and population imbalance, the phase diagram for a uniform gas develops a rich structure of phase separation involving topologically nontrivial gapless superfluid states. We then demonstrate the phase separation induced by an external trapping potential and discuss the optimal parameter region for the experimental observation of the gapless superfluid phases.

  8. Synthesis of nanocrystalline anatase TiO2 by one-pot two-phase separated hydrolysis-solvothermal processes and its high activity for photocatalytic degradation of rhodamine B.

    PubMed

    Xie, Mingzheng; Jing, Liqiang; Zhou, Jia; Lin, Jingsheng; Fu, Honggang

    2010-04-15

    Si-doped and un-doped nanocrystalline TiO(2) samples have been synthesized by simple one-pot water-organic two-phase separated hydrolysis-solvothermal (HST) processes, and characterized by XRD, BET, TEM, FT-IR, DRS and surface photovoltage techniques. The effects of the solvothermal temperature and Si doping on the anatase thermal stability, and on the photocatalytic activity for degrading rhodamine B were investigated in detail. The results show that, as the solvothermal temperature rises, the crystallinity and thermal stability of the resulting nano-sized anatase TiO(2) gradually increase. Noticeably, the as-prepared TiO(2) obtained at appropriate solvothermal temperature (160 degrees C) exhibits high photocatalytic activity. Moreover, although Si doping does not improve the photocatalytic activity of the as-prepared anatase TiO(2), it greatly enhances the anatase thermal stability and inhibits crystallite growth during the process of post-thermal treatment. Interestingly, the Si-doped TiO(2) post-treated at high temperature displays much higher photocatalytic activity than commercial P25 TiO(2). It is clearly demonstrated that the joint effects of high anatase crystallinity and large surface area lead to high photocatalytic activity. This work provides a simple and effective strategy for the synthesis of high-performance TiO(2)-based functional nanomaterials.

  9. Full field gas phase velocity measurements in microgravity

    NASA Technical Reports Server (NTRS)

    Griffin, Devon W.; Yanis, William

    1995-01-01

    Measurement of full-field velocities via Particle Imaging Velocimetry (PIV) is common in research efforts involving fluid motion. While such measurements have been successfully performed in the liquid phase in a microgravity environment, gas-phase measurements have been beset by difficulties with seeding and laser strength. A synthesis of techniques developed at NASA LeRC exhibits promise in overcoming these difficulties. Typical implementation of PIV involves forming the light from a pulsed laser into a sheet that is some fraction of a millimeter thick and 50 or more millimeters wide. When a particle enters this sheet during a pulse, light scattered from the particle is recorded by a detector, which may be a film plane or a CCD array. Assuming that the particle remains within the boundaries of the sheet for the second pulse and can be distinguished from neighboring particles, comparison of the two images produces an average velocity vector for the time between the pulses. If the concentration of particles in the sampling volume is sufficiently large but the particles remain discrete, a full field map may be generated.

  10. The gas-phase ozonolysis of α-humulene.

    PubMed

    Beck, M; Winterhalter, R; Herrmann, F; Moortgat, G K

    2011-06-21

    α-Humulene contains three double bonds (DB), and after ozonolysis of the first DB the first-generation products are still reactive towards O(3) and produce second- and third-generation products. The primary aim of this study consisted of identifying the products of the three generations, focusing on the carboxylic acids, which are known to have a high aerosol formation potential. The experiments were performed in a 570 litre spherical glass reactor at 295 K and 730 Torr. Initial mixing ratios were 260-2090 ppb for O(3) and 250-600 ppb for α-humulene in synthetic air. Reactants and gas-phase products were measured by in situ FTIR spectroscopy. Particulate products were sampled on Teflon filters, extracted with methanol and analyzed by LC-MS/MS-TOF. Using cyclohexane (10-100 ppm) as an OH-radical scavenger and by monitoring the yield of cyclohexanone by PTR-MS, an OH-yield of (10.5 ± 0.7)% was determined for the ozonolysis of the first DB, and (12.9 ± 0.7)% of the first-generation products. The rate constant of the reaction of O(3) with α-humulene is known as k(0) = 1.17 × 10(-14) cm(3) molecule(-1) s(-1) [Y. Shu and R. Atkinson, Int. J. Chem. Kinet., 1994, 26, 1193-1205]. The reaction rate constants of O(3) with the first-generation products and the second-generation products were, respectively, determined as k(1) = (3.6 ± 0.9) × 10(-16) and k(2) = (3.0 ± 0.7) × 10(-17) cm(3) molecule(-1) s(-1) by Facsimile-simulation of the observed ozone decay by FTIR. A total of 37 compounds in the aerosol phase and 5 products in the gas phase were tentatively identified: 25 compounds of the first-generation products contained C13-C15 species, 9 compounds of the second-generation products contained C8-C11 species, whereas 8 compounds of the third-generation products contained C4-C6 species. The products of all three generations consisted of a variety of dicarboxylic-, hydroxy-oxocarboxylic- and oxo-carboxylic acids. The formation mechanisms of some of the products are

  11. Photo-catalytic activity of Plasmonic Ag@AgCl nanoparticles (synthesized via a green route) for the effective degradation of Victoria Blue B from aqueous phase.

    PubMed

    Devi, Th Babita; Begum, Shamima; Ahmaruzzaman, M

    2016-07-01

    This study reports a green process for the fabrication of Ag@AgCl (silver@silver chloride) nanoparticles by using Aquilaria agallocha (AA) leaves juice without using any external reagents. The effect of various reaction parameters, such as reaction temperature, reaction time and concentration of Aquilaria agallocha leaves juice in the formation of nanoparticles have also been investigated. From the FTIR spectra of leaves juice and phytochemicals test, it was found that flavonoids present in the leaves are responsible for the reduction of Ag(+) ions to Ag(0) species and leads to the formation of Ag@AgCl NPs. The synthesized Ag@AgCl NPs were utilized for the removal of toxic and hazardous dyes, such as Victoria Blue B from aqueous phase. Approximately, 99.46% degradation of Victoria Blue B dye were observed with Ag@AgCl NPs. Furthermore, the photocatalytic activity of the Ag@AgCl nanoparticles was unchanged after 5cycles of operation.

  12. Gas-phase synthesis of semiconductor nanocrystals and its applications

    NASA Astrophysics Data System (ADS)

    Mandal, Rajib

    Luminescent nanomaterials is a newly emerging field that provides challenges not only to fundamental research but also to innovative technology in several areas such as electronics, photonics, nanotechnology, display, lighting, biomedical engineering and environmental control. These nanomaterials come in various forms, shapes and comprises of semiconductors, metals, oxides, and inorganic and organic polymers. Most importantly, these luminescent nanomaterials can have different properties owing to their size as compared to their bulk counterparts. Here we describe the use of plasmas in synthesis, modification, and deposition of semiconductor nanomaterials for luminescence applications. Nanocrystalline silicon is widely known as an efficient and tunable optical emitter and is attracting great interest for applications in several areas. To date, however, luminescent silicon nanocrystals (NCs) have been used exclusively in traditional rigid devices. For the field to advance towards new and versatile applications for nanocrystal-based devices, there is a need to investigate whether these NCs can be used in flexible and stretchable devices. We show how the optical and structural/morphological properties of plasma-synthesized silicon nanocrystals (Si NCs) change when they are deposited on stretchable substrates made of polydimethylsiloxane (PDMS). Synthesis of these NCs was performed in a nonthermal, low-pressure gas phase plasma reactor. To our knowledge, this is the first demonstration of direct deposition of NCs onto stretchable substrates. Additionally, in order to prevent oxidation and enhance the luminescence properties, a silicon nitride shell was grown around Si NCs. We have demonstrated surface nitridation of Si NCs in a single step process using non?thermal plasma in several schemes including a novel dual-plasma synthesis/shell growth process. These coated NCs exhibit SiNx shells with composition depending on process parameters. While measurements including

  13. Gas-Phase Reactions of Halogen Species of Atmospheric Importance.

    NASA Astrophysics Data System (ADS)

    Heard, Anne C.

    Available from UMI in association with The British Library. Requires signed TDF. A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen -containing molecules and between NO_3 radicals and the iodine species I_2 and I. These experiments have shown that: (i) the reaction of methyl iodide with OH accounts for approximately 2% of the removal of CH_3I from the troposphere as compared with photolysis; (ii) abstraction of I-atoms from a C-I bond by OH is probable in the gas -phase; (iii) the halogen-containing anaesthetic substances halothane CF_3CCl BrH, enflurane CF_2HOCF _2CFClH, isoflurane CF_2HOCClHCF _3 and sevoflurane (CF_3) _2CHOCFH_2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross -sections of the compounds in the spectral region 800-1200 cm^{-1} were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl_3 for each compound. The study of the reactions between OH and CF_3CFBrH and CF _2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of

  14. Various types of semiconductor photocatalysts modified by CdTe QDs and Pt NPs for toluene photooxidation in the gas phase under visible light

    NASA Astrophysics Data System (ADS)

    Marchelek, M.; Grabowska, E.; Klimczuk, T.; Lisowski, W.; Zaleska-Medynska, A.

    2017-01-01

    A novel synthesis process was used to prepare TiO2 microspheres, TiO2 P-25, SrTiO3 and KTaO3 decorated by CdTe QDs and/or Pt NPs. The effect of semiconductor matrix, presence of CdTe QDs and/or Pt NPs on the semiconductor surface as well as deposition technique of Pt NPs (photodeposition or radiolysis) on the photocatalytic activity were investigated. The as-prepared samples were characterized by X-ray powder diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) with energy-dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM), photoluminescence spectrometry (PL), Fourier transform infrared (FT-IR) and Raman spectra, diffuse reflectance spectroscopy (DRS) and BET surface area analysis. The photocatalytic decomposition of toluene in gas phase, activated by light-emitting diodes (LEDs), with the CdTe/Pt nanoparticles-modified TiO2 microspheres, P25, SrTiO3 and KTaO3 semiconductors was investigated under UV-vis and visible irradiation.The results showed that the photoactivity depends on semiconductor matrix. The highest photoactivity under Vis light was observed for KTaO3/CdTe-Pt(R) sample (56% of toluene was decompose after 30 min of irradiation). The efficiency of the most active sample was 3 times higher than result for P25 and two times higher than for unmodified KTaO3.

  15. Measurement of Gas-phase Acids in Diesel Exhaust

    NASA Astrophysics Data System (ADS)

    Wentzell, J. J.; Liggio, J.; Li, S.; Vlasenko, A. L.; Staebler, R. M.; Brook, J.; Lu, G.; Poitras, M.; Chan, T.

    2012-12-01

    Gas-phase acids were measured using chemical ionization mass spectrometry (CIMS) as part of the Diesel Engine Emission Research Experiment (DEERE). The CIMS technique, utilizing acetate ion (CH3COO-) as a reagent ion, proved to be a rapid (measurements on the order of seconds) and sensitive (several counts/pptv) method of quantifying the acid emissions. Diluted diesel exhaust measurements were made from a Constant Volume Sampling dilution tunnel using a light duty (1.9L turbocharged Volkswagen Jetta TDI) diesel engine equipped with an OEM diesel oxidation catalyst and exhaust gas recirculation, mounted on an engine dynamometer. Acids measured included isocyanic, nitrous, nitric, propionic and sum of lactic and oxalic, as well as other unidentified compounds. Complimentary measurements of CO, CO2, Total Hydrocarbon (THC), and NOx, were also performed. Several engine modes (different engine rpm and torque outputs) at steady state were examined to determine their effect on acid emissions. Emission rates with respect to NOx and fuel based emission factors were determined. Measurements of HONO fuel emission factors agree well with real-world measurements within a traffic tunnel.1 The first estimate of isocyanic acid emission factors from a diesel engine is reported, and suggests that the emission of this highly toxic compound in diesel exhaust should not be ignored. 1. Kurtenbach, R., Becker, K. H., Gomes, J. A. G., Kleffmann, J.,Lorzer, J. C., Spittler, M., Wiesen, P., Ackermann, R., Geyer, A.,and Platt, U.: Investigations of emissions and heterogeneous formation of HONO in a road traffic tunnel, Atmos. Environ., 35, 3385-3394, doi:10.1016/S1352-2310(01)00138-8, 2001.

  16. Ozone Cross-Section Measurement by Gas Phase Titration.

    PubMed

    Viallon, Joële; Moussay, Philippe; Flores, Edgar; Wielgosz, Robert I

    2016-11-01

    Elevated values of ground-level ozone damage health, vegetation, and building materials and are the subject of air quality regulations. Levels are monitored by networks using mostly ultraviolet (UV) absorption instruments, with traceability to standard reference photometers, relying on the UV absorption of ozone at the 253.65 nm line of mercury. We have redetermined the ozone cross-section at this wavelength based on gas phase titration (GPT) measurements. This is a well-known chemical method using the reaction of ozone (O3) with nitrogen monoxide (NO) resulting in nitrogen dioxide (NO2) and oxygen (O2). The BIPM GPT facility uses state-of-the-art flow measurement, chemiluminescence for NO concentration measurements, a cavity phase shift analyzer (CAPS) for NO2 measurements, and a UV ozone analyzer. The titration experiment is performed over the concentration range 100-500 nmol/mol, with NO and NO2 reactants/calibrants diluted down from standards with nominal mole fractions of 50 μmol/mol. Accurate measurements of NO, NO2, and O3 mole fractions allow the calculation of ozone absorption cross section values at 253.65 nm, and we report a value of 11.24 × 10(-18) cm(2) molecule(-1) with a relative expanded uncertainty of 1.8% (coverage factor k = 2) based on nitrogen monoxide titration values and a value of 11.22 × 10(-18) cm(2) molecule(-1) with a relative expanded uncertainty of 1.4% (coverage factor k = 2) based on nitrogen dioxide titration values. The excellent agreement between these values and recently published absorption cross-section measurements directly on pure ozone provide strong evidence for revising the conventionally accepted value of ozone cross section at 253.65 nm.

  17. Uridine Nucleoside Thiation: Gas-Phase Structures and Energetics

    NASA Astrophysics Data System (ADS)

    Hamlow, Lucas; Lee, Justin; Rodgers, M. T.; Berden, Giel; Oomens, Jos

    2016-06-01

    The naturally occurring thiated uridine nucleosides, 4-thiouridine (s4Urd) and 2-thiouridine (s2Urd), play important roles in the function and analysis of a variety of RNAs. 2-Thiouridine and its C5 modified analogues are commonly found in tRNAs and are believed to play an important role in codon recognition possibly due to their different structure, which has been shown by NMR to be predominantly C3'-endo. 2-Thiouridine may also play an important role in facilitating nonenzymatic RNA replication and transcription. 4-Thiouridine is a commonly used photoactivatable crosslinker that is often used to study RNA-RNA and RNA-protein cross-linking behavior. Differences in the base pairing between uracil and 4-thiouracil with adenine and guanine are an important factor in their role as a cross linker. The photoactivity of s4Urd may also aid in preventing near-UV lethality in cells. An understanding of their intrinsic structure in the gas-phase may help further elucidate the roles these modified nucleosides play in the regulation of RNAs. In this work, infrared multiple photon dissociation (IRMPD) action spectra of the protonated forms of s2Urd and s4Urd were collected in the IR fingerprint region. Structural information is determined by comparison with theoretical linear IR spectra generated from density functional theory calculations using molecular modeling to generate low-energy candidate structures. Present results are compared with analogous results for the protonated forms of uridine and 2'-deoxyuridine as well as solution phase NMR data and crystal structures.

  18. Concurrence of aqueous and gas phase contamination of groundwater in the Wattenberg oil and gas field of northern Colorado.

    PubMed

    Li, Huishu; Son, Ji-Hee; Carlson, Kenneth H

    2016-01-01

    The potential impact of rapid development of unconventional oil and natural gas resources using hydraulic fracturing and horizontal drilling on regional groundwater quality has received significant attention. Major concerns are methane or oil/gas related hydrocarbon (such as TPHs, BTEX including benzene, toluene, ethybenzene and xylene) leaks into the aquifer due to the failure of casing and/or stray gas migration. Previously, we investigated the relationship between oil and gas activity and dissolved methane concentration in a drinking water aquifer with the major finding being the presence of thermogenic methane contamination, but did not find detectable concentrations of TPHs or BTEX. To understand if aqueous and gas phases from the producing formation were transported concurrently to drinking water aquifers without the presence of oil/gas related hydrocarbons, the ionic composition of three water groups was studied: (1) uncontaminated deep confined aquifer, (2) suspected contaminated groundwater - deep confined aquifer containing thermogenic methane, and (3) produced water from nearby oil and gas wells that would represent aqueous phase contaminants. On the basis of quantitative and spatial analysis, we identified that the "thermogenic methane contaminated" groundwater did not have similarities to produced water in terms of ionic character (e.g. Cl/TDS ratio), but rather to the "uncontaminated" groundwater. The analysis indicates that aquifer wells with demonstrated gas phase contamination have not been contacted by an aqueous phase from oil and gas operations according to the methodology we use in this study and the current groundwater quality data from COGCC. However, the research does not prove conclusively that this the case. The results may provide insight on contamination mechanisms since improperly sealed well casing may result in stray gas but not aqueous phase transport.

  19. Parameters Influencing the Photocatalytic Activity of Suspension-Sprayed TiO2 Coatings

    NASA Astrophysics Data System (ADS)

    Toma, Filofteia-Laura; Berger, Lutz-Michael; Shakhverdova, Irina; Leupolt, Beate; Potthoff, Annegret; Oelschlägel, Kathrin; Meissner, Tobias; Gomez, José Antonio Ibáñez; de Miguel, Yolanda

    2014-10-01

    Photocatalytic properties of titania have been studied very intensively for a variety of applications, including air and water purification. In order to clarify the influence of the phase composition and other parameters, thermal spraying with suspensions was applied to produce photocatalytically active titania coatings starting from two commercially available anatase and rutile submicron powders. Aqueous suspensions containing 40% solids by weight were sprayed with an HVOF process using ethylene as the fuel gas. The spray parameters were chosen in order to produce mechanically stable coatings and to preserve a high content of the initial crystalline phases of the powders. The coating microstructures, phase compositions, and surface properties were characterized. The photocatalytic performance was evaluated by degradation of the pink dye Rhodamine B (RB) using two techniques: degradation of an aqueous solution of RB and discoloration of impregnated RB. All the coatings exhibited photocatalytic activity to varying degrees, depending on the phase composition as well as other factors, namely, the coating microstructure, surface morphology, surface hydroxylation, light absorption, and interaction with the pollutant.

  20. Experimental Determination of Gas Phase Thermodynamic Properties of Bimolecular Complexes

    NASA Astrophysics Data System (ADS)

    Hansen, Anne S.; Maroun, Zeina; Mackeprang, Kasper; Kjaergaard, Henrik G.

    2016-06-01

    Accurate determination of the atmospheric abundance of hydrogen bound bimolecular complexes is necessary, as hydrogen bonds are partly responsible for the formation and growth of aerosol particles. The abundance of a complex is related to the Gibbs free energy of complex formation (Δ G), which is often obtained from quantum chemical calculations that rely on calculated values of the enthalpy (Δ H) and entropy (Δ S) of complex formation. However, calculations of Δ H and in particular Δ S are associated with large uncertainties, and accurate experimental values are therefore crucial for theoretical benchmarking studies. Infrared measurements of gas phase hydrogen bound complexes were performed in the 300 to 373 K range, and lead to a purely experimental determination of Δ H using the van't Hoff equation. Equilibrium constants were determined by combining an experimental and calculated OH-stretching intensity, from which values of Δ G and hence Δ S could be determined. Thus we can determine Δ G, Δ H and Δ S for a bimolecular complex. We find that in the 300 to 373 K temperature range the determined Δ H and Δ S values are independent of temperature.

  1. Gas phase production and loss of isoprene epoxydiols.

    PubMed

    Bates, Kelvin H; Crounse, John D; St Clair, Jason M; Bennett, Nathan B; Nguyen, Tran B; Seinfeld, John H; Stoltz, Brian M; Wennberg, Paul O

    2014-02-20

    Isoprene epoxydiols (IEPOX) form in high yields from the OH-initiated oxidation of isoprene under low-NO conditions. These compounds contribute significantly to secondary organic aerosol formation. Their gas-phase chemistry has, however, remained largely unexplored. In this study, we characterize the formation of IEPOX isomers from the oxidation of isoprene by OH. We find that cis-β- and trans-β-IEPOX are the dominant isomers produced, and that they are created in an approximate ratio of 1:2 from the low-NO oxidation of isoprene. Three isomers of IEPOX, including cis-β- and trans-β, were synthesized and oxidized by OH in environmental chambers under high- and low-NO conditions. We find that IEPOX reacts with OH at 299 K with rate coefficients of (0.84 ± 0.07) × 10(-11), (1.52 ± 0.07) × 10(-11), and (0.98 ± 0.05) × 10(-11) cm(3) molecule(-1) s(-1) for the δ1, cis-β, and trans-β isomers. Finally, yields of the first-generation products of IEPOX + OH oxidation were measured, and a new mechanism of IEPOX oxidation is proposed here to account for the observed products. The substantial yield of glyoxal and methylglyoxal from IEPOX oxidation may help explain elevated levels of those compounds observed in low-NO environments with high isoprene emissions.

  2. Gas-phase Electronic Spectra of Coronene and Corannulene Cations

    NASA Astrophysics Data System (ADS)

    Hardy, F.-X.; Rice, Corey A.; Maier, John P.

    2017-02-01

    Gas-phase electronic spectra of the coronene ({{{C}}}24{{{{H}}}12}+) and corannulene ({{{C}}}20{{{{H}}}10}+) cations complexed with helium have been recorded in a quadrupole ion trap at 5 K by photodissociation. The electronic spectrum of {{{C}}}20{{{{H}}}10}+ with two helium atoms was also measured to estimate the perturbation. This method is sufficient for an astronomical comparison because the shift due to the weakly bound helium is on the order of 0.2 Å. {{{C}}}24{{{{H}}}12}+{--}{He} has the origin band of the {{{A}}}2{{{E}}}1g≤ftarrow X{}2{{{E}}}2u transition at 9438.3 Å and that to a much higher state {{{D}}}3≤ftarrow X{}2{{{E}}}2u at 4570 Å. The corannulene cation is subject to a Jahn–Teller distortion in the electronic ground state, leading to the {3}2{{A}}\\prime ≤ftarrow {{X}}{}2{{A}}\\prime \\prime and {3}2{{A}}\\prime \\prime ≤ftarrow {{X}}{}2{{A}}\\prime transitions with origin band maxima when complexed with helium at 5996.1 and 5882.6 Å. These absorptions lie in a region where there is a congestion of diffuse interstellar bands (DIBs). However, the recorded features have no match with astronomical observations, removing coronene and corannulene cations and probably other aromatic hydrocarbons of this size as possible carriers of the DIBs.

  3. Microwave spectrum and the gas phase structure of phthalimide

    NASA Astrophysics Data System (ADS)

    Pejlovas, Aaron M.; Lin, Wei; Oncer, Onur; Kukolich, Stephen G.

    2015-11-01

    The microwave spectrum of phthalimide (PhI) was measured in the 4.8-9.5 GHz range using a Flygare-Balle type, pulsed-beam Fourier transform microwave spectrometer. Rotational transitions were measured for the parent and all unique single 13C substituted isotopologues. The rotational (MHz), centrifugal distortion (kHz), and quadrupole coupling constants (MHz) were determined for the parent to be A = 1745.6655(10), B = 1199.3309(6), C = 711.0864(3), DJ = 0.012(7), DJK = -0.05(9), 1.5χaa = 2.719(11), and 0.25(χbb - χcc) = 1.236(3). Using the measured rotational constants of the isotopologues, a nonlinear least squares fit was performed to obtain the best fit gas phase structure. The inertial defect is Δ = -0.175 amu Å2, indicating a planar structure for PhI. Calculations using B3LYP/aug-cc-pVQZ provided rotational constants which are much closer to the experimental values compared to the MP2/6-311++G∗∗ calculated values.

  4. Microwave spectrum and gas phase structure of maleimide

    NASA Astrophysics Data System (ADS)

    Pejlovas, Aaron M.; Oncer, Onur; Kang, Lu; Kukolich, Stephen G.

    2016-01-01

    The rotational spectrum of maleimide was measured in the 5-12 GHz range using a Flygare-Balle type, pulsed-beam Fourier transform microwave spectrometer. Rotational transitions were measured for the parent, all unique singly substituted 13C isotopologues, and an sbnd ND, deuterium substituted isotopologue. The parent (or normal isotopologue) rotational constants, centrifugal distortion constants, and quadrupole coupling constants are A = 6815.3251(12) MHz, B = 2361.85011(64) MHz, C = 1754.32750(64) MHz, DJ = 0.232(24) kHz, DJK = 0.546(54) kHz, 1.5χaa = 2.4227(53) MHz, and 0.25(χbb-χcc) = 1.3679(15) MHz. A best fit gas phase structure was determined using the experimental rotational constants of the isotopologues and some parameters from calculations. The inertial defect is Δ = -0.054 amu Å2, indicating a planar structure for maleimide, with no large amplitude motions observed on the sbnd NH hydrogen atom. Calculations using B3LYP/aug-cc-pVTZ provided rotational constants which are much closer (within 1-2%) to the experimental values compared to the MP2/aug-cc-pVTZ calculated values.

  5. Surface plasmon sensing of gas phase contaminants using optical fiber.

    SciTech Connect

    Thornberg, Steven Michael; White, Michael I.; Rumpf, Arthur Norman; Pfeifer, Kent Bryant

    2009-10-01

    Fiber-optic gas phase surface plasmon resonance (SPR) detection of several contaminant gases of interest to state-of-health monitoring in high-consequence sealed systems has been demonstrated. These contaminant gases include H{sub 2}, H{sub 2}S, and moisture using a single-ended optical fiber mode. Data demonstrate that results can be obtained and sensitivity is adequate in a dosimetric mode that allows periodic monitoring of system atmospheres. Modeling studies were performed to direct the design of the sensor probe for optimized dimensions and to allow simultaneous monitoring of several constituents with a single sensor fiber. Testing of the system demonstrates the ability to detect 70mTorr partial pressures of H{sub 2} using this technique and <280 {micro}Torr partial pressures of H{sub 2}S. In addition, a multiple sensor fiber has been demonstrated that allows a single fiber to measure H{sub 2}, H{sub 2}S, and H{sub 2}O without changing the fiber or the analytical system.

  6. GAS PHASE SELECTIVE PHOTOXIDATION OF ALCOHOLS USING LIGHT-ACTIVATED TITANIUM DIOXIDE AND MOLECULAR OXYGEN

    EPA Science Inventory

    Gas Phase Selective Oxidation of Alcohols Using Light-Activated Titanium Dioxide and Molecular Oxygen

    Gas phase selective oxidations of various primary and secondary alcohols are studied in an indigenously built stainless steel up-flow photochemical reactor using ultravi...

  7. DEMONSTRATION OF FUEL CELLS TO RECOVER ENERGY FROM LANDFILL GAS: PHASE II. PRETREATMENT SYSTEM PERFORMANCE MEASUREMENT

    EPA Science Inventory

    The report describes Phase II of a demonstration of the utilization of commercial phosphoric acid fuel cells to recover energy from landfill gas. This phase consisted primarily of the construction and testing of a Gas Pretreatment Unit (GPU) whose function is to remove those impu...

  8. Study on measures to improve gas-liquid phase mixing in a multiphase pump impeller under high gas void fraction

    NASA Astrophysics Data System (ADS)

    Zhang, J. Y.; Zhu, H. W.; Ding, K.; Qiang, R.

    2012-11-01

    Rotodynamic multiphase pump can transport crude gas-liquid mixture produced from oil well, and is regarded as the good choice of oil-gas multiphase transportation in offshore product system, for its advantages that compact structure, large flow rate, not sensitive to solid particles in the fluid. However, it is prone to bring about gas-liquid separation within the impeller under high gas void fraction. To solve the problem, this paper presents several measures to break gas packet and inhibit gas-liquid separation, such as, depositing the short blades, opening holes at the blades where gas packets gather, using T-shaped blades, etc. Then, CFD software was used to simulate the flow fields which were added measures to inhibit gas-liquid separation. The results show that streamlines in three new impellers distribute more evenly than in original impeller, the gas-liquid two phases mixed degree was improved, and the gas-liquid separation was inhibited to some extent. However, adding the short blades and using T-blade impeller failed to improve the differential pressure of impellers. So the placement and the geometrical parameters of the measures inhibiting gas-liquid separation should be further optimized.

  9. Controllable synthesis of recyclable core-shell γ-Fe2O3@SnO2 hollow nanoparticles with enhanced photocatalytic and gas sensing properties.

    PubMed

    Zhang, Shaofeng; Ren, Feng; Wu, Wei; Zhou, Juan; Xiao, Xiangheng; Sun, Lingling; Liu, Ying; Jiang, Changzhong

    2013-06-07

    Composite materials containing different components with well-defined structures may cooperatively enhance their performance and extend their applications. In this work, core-shell γ-Fe2O3@SnO2 hollow nanoparticles (NPs) were synthesized by a low-cost and environmentally friendly seed-mediated hydrothermal method. Firstly, the γ-Fe2O3 hollow NPs were synthesized by a template-free method. Then they were used as the cores for the growth of SnO2 shells. The thickness of the shell can be simply tailored by controlling the reaction time. Various techniques, including SEM, XRD, TEM and HRTEM, were employed to investigate the morphology, structure and formation process of the special core-shell hollow structures. The combination of magnetic semiconductor (γ-Fe2O3) and wide band-gap semiconductor (SnO2) endowed them with great potential to be used as recyclable photocatalysts. Experiments on photo-degradation of Rhodamin B (RhB) dye in the presence of the samples showed that the hybrid structures possessed higher photocatalytic activities than the monomer structures of SnO2 and γ-Fe2O3 materials indicating a strong coupling enhancement effect between the wide and narrow band-gap semiconductors. Moreover, the gas sensing tests of the γ-Fe2O3@SnO2 hollow NPs revealed that the samples exhibited fast response and recovery rates, which enable them to be promising materials for gas sensors.

  10. Triplet-state energies and substituent effects of excited aroyl compounds in the gas phase.

    PubMed

    Lin, Z P; Aue, W A

    2000-01-01

    Triplet-state energy values obtained from the gas phase are still scarce. In this study, the triplet-state energies of 58 aroyl compounds, introduced as gas chromatographic peaks at atmospheric pressure and typically 473 K, have been determined from the 0-0 bands of their n --> pi* type phosphorescence spectra in excited nitrogen. Correlations of those gas-phase triplet-state energies with Hammett constants could be observed for substituted acetophenones, benzaldehydes and benzophenones.

  11. Harvesting hydrogen gas from air pollutants with an un-biased gas phase photo-electrochemical cell.

    PubMed

    Verbruggen, Sammy W; Van Hal, Myrthe; Bosserez, Tom; Rongé, Jan; Hauchecorne, Birger; Martens, Johan A; Lenaerts, Silvia

    2017-02-08

    The concept of an all-gas-phase photo-electrochemical cell (PEC) producing hydrogen gas from volatile organic contaminated gas and light is presented. Without applying any external bias, organic contaminants are degraded and hydrogen gas is produced in separate electrode compartments. The system works most efficiently with organic pollutants in inert carrier gas. In the presence of oxygen gas, the cell performs less efficiently but still significant photocurrents are generated, showing the cell can be run on organic contaminated air. The purpose of this study is to demonstrate new application opportunities of PEC technology and to encourage further advancement toward photo-electrochemical remediation of air pollution with the attractive feature of simultaneous energy recovery and pollution abatement.

  12. Electron attachment to ? and ? in the gas phase

    NASA Astrophysics Data System (ADS)

    Smith, David; Spanel, Patrik

    1996-11-01

    The fullerene molecule 0953-4075/29/21/030/img3 is known to attach several electrons in the solid phase, but only recently has it been recognized that it can also attach electrons in the gas phase. The first electron - molecular beam results showed that 0953-4075/29/21/030/img3 and 0953-4075/29/21/030/img5 molecules non-dissociatively attached a single electron over the unusually wide electron energy range from near thermal to about 10 eV, but these studies were not able to provide either the magnitude of the cross sections or describe the low-energy attachment behaviour. But using our flowing afterglow - Langmuir probe (FALP) apparatus we have been able to determine the absolute attachment rate coefficients for both 0953-4075/29/21/030/img3 and 0953-4075/29/21/030/img5 over the electron temperature range 300 - 4500 K. These FALP experiments have shown that attachment to 0953-4075/29/21/030/img3 at low electron energies (<1 eV) proceeds predominantly by p-wave electron capture, and that a centrifugal barrier of 0.26 eV is evident which was corroborated by subsequent theory. A similar situation is observed for attachment to 0953-4075/29/21/030/img5 except that for this fullerene molecule there is evidence that at very low electron energies (< 0.05 eV) inefficient s-wave capture may also occur. These FALP data further indicate that at energies above about 0.3 eV extraordinarily efficient electron attachment occurs to both 0953-4075/29/21/030/img3 and 0953-4075/29/21/030/img5, and when the mean thermal cross sections derived from these FALP data are used to normalize the crossed electron - molecular beam data at the common low energies accessible in both experiments, it is clear that electron attachment to these fullerene molecules is very efficient over a wide electron energy range from about 0.3 - 10 eV above which electron thermionic emission occurs from the hot 0953-4075/29/21/030/img12 and 0953-4075/29/21/030/img13 nascent negative ions.

  13. Detection of Gas-Phase Ammonia Using Photothermal Interferometry.

    NASA Astrophysics Data System (ADS)

    Owens, Melody Avery

    1995-01-01

    Ammonia in the atmosphere plays an important chemical role in diverse ecological and physical systems. It is challenging to measure because it adheres to many commonly used sampling materials, is soluble in water, and forms particles. A new instrument has been built to detect gas -phase ammonia in ambient air by photothermal interferometry. Ammonia molecules in sampled air are excited to upper vibrational rotational states of the nu_2 band of ammonia by absorption of 9.22 mu m light from the 9R30 line of a carbon dioxide laser. Excited ammonia molecules transfer this energy as heat to the air by collisions. The temperature and consequent refractive index change is measured as a phase shift in one arm of a sensitive homodyne interferometer. The CO_2 laser output is modulated at 1.2 kHz, and the AC signal from the interferometer is measured with a lock -in amplifier. The +/-2sigma detection limit of the interferometer at this frequency is 1.2 times 10^{ -7} radians, only a factor of four above the quantum noise limit. The ammonia detector is calibrated by dynamic dilution of two permeation tube outputs and by standard addition. Permeation rates are verified by NH _3 conversion to nitric oxide on hot platinum foil followed by chemiluminescent NO detection, and are monitored by mass loss history. The sample cell, inlet and calibration plumbing is glass to minimize NH _3 sample loss by wall adsorption. Sample flow is 2 l/min, with residence time less than one second. The detector is zeroed by sampling through tubing filled with H_3PO_4-coated Teflon. A Stark signal shift of 7.9 mV was measured for 507 ppb of NH_3 with 925 V/mm of applied field density as an alternative zeroing method. The linear dynamic range of the detector is broad, (greater than 5 orders of magnitude), and the detector is sensitive, with a 31 ppt 4sigma lower detection limit measured in 100 s. Signal gain is insensitive to water vapor and CO_2. The instrument response is fast, with a 1 s e

  14. Gas-phase spin relaxation of Xe129

    NASA Astrophysics Data System (ADS)

    Anger, B. C.; Schrank, G.; Schoeck, A.; Butler, K. A.; Solum, M. S.; Pugmire, R. J.; Saam, B.

    2008-10-01

    We have completed an extensive study of Xe129 longitudinal spin relaxation in the gas phase, involving both intrinsic and extrinsic mechanisms. The dominant intrinsic relaxation is mediated by the formation of persistent Xe2 van der Waals dimers. The dependence of this relaxation on applied magnetic field yields the relative contributions of the spin-rotation and chemical-shift-anisotropy interactions; the former dominates at magnetic fields below a few tesla. This relaxation also shows an inverse quadratic dependence on temperature T ; the maximum low-field intrinsic relaxation for pure xenon at room temperature (measured here to be 4.6h , in agreement with previous work) increases by ≈60% for T=100°C . The dominant extrinsic relaxation is mediated by collisions with the walls of the glass container. Wall relaxation was studied in silicone-coated alkali-metal-free cells, which showed long (many hours or more) and robust relaxation times, even at the low magnetic fields typical for spin-exchange optical pumping (≈3mT) . The further suppression of wall relaxation for magnetic fields above a few tesla is consistent with the interaction of Xe129 with paramagnetic spins on or inside the surface coating. At 14.1T and sufficiently low xenon density, we measured a relaxation time T1=99h , with an inferred wall-relaxation time of 174h . A prototype large storage cell ( 12cm diameter) was constructed to take advantage of the apparent increase in wall-relaxation time for cells with a smaller surface-to-volume ratio. The measured relaxation time in this cell at 3mT and 100°C was 5.75h . Such a cell (or one even larger) could be used to store many liters of hyperpolarized Xe129 produced by a flow-through polarizer and accumulator for up to three times longer than currently implemented schemes involving freezing xenon in liquid nitrogen.

  15. Gas-Phase Combustion Synthesis of Nonoxide Nanoparticles in Microgravity

    NASA Technical Reports Server (NTRS)

    Axelbaum, R. L.; Kumfer, B. M.; Sun, Z.; Chao, B. H.

    2001-01-01

    Gas-phase combustion synthesis is a promising process for creating nanoparticles for the growing nanostructure materials industry. The challenges that must be addressed are controlling particle size, preventing hard agglomerates, maintaining purity, and, if nonoxides are synthesized, protecting the particles from oxidation and/or hydrolysis during post-processing. Sodium-halide Flame Encapsulation (SFE) is a unique methodology for producing nonoxide nanoparticles that addresses these challenges. This flame synthesis process incorporates sodium and metal-halide chemistry, resulting in nanoparticles that are encapsulated in salt during the early stages of their growth in the flame. Salt encapsulation has been shown to allow control of particle size and morphology, while serving as an effective protective coating for preserving the purity of the core particles. Metals and compounds that have been produced using this technology include Al, W, Ti, TiB2, AlN, and composites of W-Ti and Al-AlN. Oxygen content in SFE synthesized nano- AlN has been measured by neutron activation analysis to be as low as 0.54wt.%, as compared to over 5wt.% for unprotected AlN of comparable size. The overall objective of this work is to study the SFE process and nano-encapsulation so that they can be used to produce novel and superior materials. SFE experiments in microgravity allow the study of flame and particle dynamics without the influence of buoyancy forces. Spherical sodium-halide flames are produced in microgravity by ejecting the halide from a spherical porous burner into a quiescent atmosphere of sodium vapor and argon. Experiments are performed in the 2.2 sec Drop Tower at the NASA-Glenn Research Center. Numerical models of the flame and particle dynamics were developed and are compared with the experimental results.

  16. Gas-phase interactions of organotin compounds with cysteine.

    PubMed

    Latrous, Latifa; Salpin, Jean-Yves; Haldys, Violette; Léon, Emmanuelle; Correia, Catarina; Lamsabhi, Al Mokhtar

    2016-11-01

    The gas-phase interactions of cysteine with di-organotin and tri-organotin compounds have been studied by mass spectrometry experiments and quantum calculations. Positive-ion electrospray spectra show that the interaction of di- and tri-organotins with cysteine results in the formation of [(R)2 Sn(Cys-H)](+) and [(R)3 Sn(Cys)](+) ions, respectively. MS/MS spectra of [(R)2 Sn(Cys-H)](+) complexes are characterized by numerous fragmentation processes, notably associated with elimination of NH3 and (C,H2 ,O2 ). Several dissociation routes are characteristic of each given organic species. Upon collision, both the [(R)3 Sn(Gly)](+) and [(R)3 Sn(Cys)](+) complexes are associated with elimination of the intact amino acid, leading to the formation of [(R)3 Sn](+) cation. But for the latter complex, two additional fragmentation processes are observed, associated with the elimination of NH3 and C3 H4 O2 S. Calculations indicate that the interaction between organotins and cysteine is predominantly electrostatic but also exhibits a considerable covalent character, which is slightly more pronounced in tri-organotin complexes. A preferred bidentate interaction of the type -η(2) -S-NH2 , with sulfur and the amino group, is observed. As for the [(R)3 Sn(Cys)](+) complexes, their stability is due to the combination of the hydrogen bond taking place between the amino group and the sulfur lone pair and the interaction between the carboxylic oxygen atom and the metal. Copyright © 2016 John Wiley & Sons, Ltd.

  17. IV-VI semiconductor lasers for gas phase biomarker detection

    NASA Astrophysics Data System (ADS)

    McCann, Patrick; Namjou, Khosrow; Roller, Chad; McMillen, Gina; Kamat, Pratyuma

    2007-09-01

    A promising absorption spectroscopy application for mid-IR lasers is exhaled breath analysis where sensitive, selective, and speedy measurement of small gas phase biomarker molecules can be used to diagnose disease and monitor therapies. Many molecules such as nitric oxide, ethane, formaldehyde, acetaldehyde, acetone, carbonyl sulfide, and carbon disulfide have been connected to diseases or conditions such as asthma, oxidative stress, breast cancer, lung cancer, diabetes, organ transplant rejection, and schizophrenia. Measuring these and other, yet to be discovered, biomarker molecules in exhaled breath with mid-IR lasers offers great potential for improving health care since such tests are non-invasive, real-time, and do not require expensive consumables or chemical reagents. Motivated by these potential benefits, mid-IR laser spectrometers equipped with presently available cryogenically-cooled IV-VI lasers mounted in compact Stirling coolers have been developed for clinical research applications. This paper will begin with a description of the development of mid-IR laser instruments and their use in the largest known exhaled breath clinical study ever performed. It will then shift to a description of recent work on the development of new IV-VI semiconductor quantum well materials and laser fabrication methods that offer the promise of low power consumption (i.e. efficient) continuous wave emission at room temperature. Taken together, the demonstration of compelling clinical applications with large market opportunities and the clear identification of a viable pathway to develop low cost mid-IR laser instrumentation can create a renewed focus for future research and development efforts within the mid-IR materials and devices area.

  18. Dissociative electron attachment to the gas-phase nucleobase hypoxanthine

    SciTech Connect

    Dawley, M. Michele; Tanzer, Katrin; Denifl, Stephan E-mail: Sylwia.Ptasinska.1@nd.edu; Carmichael, Ian; Ptasińska, Sylwia E-mail: Sylwia.Ptasinska.1@nd.edu

    2015-06-07

    We present high-resolution measurements of the dissociative electron attachment (DEA) to isolated gas-phase hypoxanthine (C{sub 5}H{sub 4}N{sub 4}O, Hyp), a tRNA purine base. The anion mass spectra and individual ion efficiency curves from Hyp were measured as a function of electron energy below 9 eV. The mass spectra at 1 and 6 eV exhibit the highest anion yields, indicating possible common precursor ions that decay into the detectable anionic fragments. The (Hyp − H) anion (C{sub 5}H{sub 3}N{sub 4}O{sup −}) exhibits a sharp resonant peak at 1 eV, which we tentatively assign to a dipole-bound state of the keto-N1H,N9H tautomer in which dehydrogenation occurs at either the N1 or N9 position based upon our quantum chemical computations (B3LYP/6-311+G(d,p) and U(MP2-aug-cc-pVDZ+)) and prior studies with adenine. This closed-shell dehydrogenated anion is the dominant fragment formed upon electron attachment, as with other nucleobases. Seven other anions were also observed including (Hyp − NH){sup −}, C{sub 4}H{sub 3}N{sub 4}{sup −}/C{sub 4}HN{sub 3}O{sup −}, C{sub 4}H{sub 2}N{sub 3}{sup −}, C{sub 3}NO{sup −}/HC(HCN)CN{sup −}, OCN{sup −}, CN{sup −}, and O{sup −}. Most of these anions exhibit broad but weak resonances between 4 and 8 eV similar to many analogous anions from adenine. The DEA to Hyp involves significant fragmentation, which is relevant to understanding radiation damage of biomolecules.

  19. Gas phase depletion and flow dynamics in horizontal MOCVD reactors

    NASA Astrophysics Data System (ADS)

    Van de Ven, J.; Rutten, G. M. J.; Raaijmakers, M. J.; Giling, L. J.

    1986-08-01

    Growth rates of GaAs in the MOCVD process have been studied as a function of both lateral and axial position in horizontal reactor cells with rectangular cross-sections. A model to describe growth rates in laminar flow systems on the basis of concentration profiles under diffusion controlled conditions has been developed. The derivation of the growth rate equations includes the definition of an entrance length for the concentration profile to developed. In this region, growth rates appear to decrease with the 1/3 power of the axial position. Beyond this region, an exponential decrease is found. For low Rayleigh number conditions, the present experimental results show a very satisfactory agreement with the model without parameter fitting for both rectangular and tapered cells, and with both H 2 and N 2 as carrier gases. Theory also predicts that uniform deposition can be obtained over large areas in the flow direction for tapered cells, which has indeed been achieved experimentally. The influence of top-cooling in the present MOCVD system has been considered in more detail. From the experimental results, conclusions could be drawn concerning the flow characteristics. For low Rayleigh numbers (present study ≲ 700) it follows that growth rate distributions correspond with forced laminar flow characteristics. For relatively high Rayleigh numbers (present work 1700-2800), free convective effects with vortex formation are important. These conclusions are not specific for the present system, but apply to horizontal cold-wall reactors in general. On the basis of the present observations, recommendations for a cell design to obtain large area homogeneous deposition have been formulated. In addition, this work supports the conclusion that the final decomposition of trimethylgallium in the MOCVD process mainly takes place at the hot substrate and susceptor and not in the gas phase.

  20. Gas-Phase Combustion Synthesis of Aluminum Nitride Powder

    NASA Technical Reports Server (NTRS)

    Axelbaum, R. L.; Lottes, C. R.; Huertas, J. I.; Rosen, L. J.

    1996-01-01

    Due to its combined properties of high electrical resistivity and high thermal conductivity aluminum nitride (AlN) is a highly desirable material for electronics applications. Methods are being sought for synthesis of unagglomerated, nanometer-sized powders of this material, prepared in such a way that they can be consolidated into solid compacts having minimal oxygen content. A procedure for synthesizing these powders through gas-phase combustion is described. This novel approach involves reacting AlCl3, NH3, and Na vapors. Equilibrium thermodynamic calculations show that 100% yields can be obtained for these reactants with the products being AlN, NaCl, and H2. The NaCl by-product is used to coat the AlN particles in situ. The coating allows for control of AlN agglomeration and protects the powders from hydrolysis during post-flame handling. On the basis of thermodynamic and kinetic considerations, two different approaches were employed to produce the powder, in co-flow diffusion flame configurations. In the first approach, the three reactants were supplied in separate streams. In the second, the AlCl3 and NH3 were premixed with HCl and then reacted with Na vapor. X-ray diffraction (XRD) spectra of as-produced powders show only NaCl for the first case and NaCl and AlN for the second. After annealing at 775 C tinder dynamic vacuum, the salt was removed and XRD spectra of powders from both approaches show only AlN. Aluminum metal was also produced in the co-flow flame by reacting AlCl3 with Na. XRD spectra of as-produced powders show the products to be only NaCl and elemental aluminum.

  1. CHAOS III: Gas-phase Abundances in NGC 5457

    NASA Astrophysics Data System (ADS)

    Croxall, Kevin V.; Pogge, Richard W.; Berg, Danielle A.; Skillman, Evan D.; Moustakas, John

    2016-10-01

    We present Large Binocular Telescope observations of 109 H ii regions in NGC 5457 (M101) obtained with the Multi-Object Double Spectrograph. We have robust measurements of one or more temperature-sensitive auroral emission lines for 74 H ii regions, permitting the measurement of “direct” gas-phase abundances. Comparing the temperatures derived from the different ionic species, we find: (1) strong correlations of T[N ii] with T[S iii] and T[O iii], consistent with little or no intrinsic scatter; (2) a correlation of T[S iii] with T[O iii], but with significant intrinsic dispersion; (3) overall agreement between T[N ii], T[S ii], and T[O ii], as expected, but with significant outliers; (4) the correlations of T[N ii] with T[S iii] and T[O iii] match the predictions of photoionization modeling while the correlation of T[S iii] with T[O iii] is offset from the prediction of photoionization modeling. Based on these observations, which include significantly more observations of lower excitation H ii regions, missing in many analyses, we inspect the commonly used ionization correction factors (ICFs) for unobserved ionic species and propose new empirical ICFs for S and Ar. We have discovered an unexpected population of H ii regions with a significant offset to low values in Ne/O, which defies explanation. We derive radial gradients in O/H and N/O which agree with previous studies. Our large observational database allows us to examine the dispersion in abundances, and we find intrinsic dispersions of 0.074 ± 0.009 in O/H and 0.095 ± 0.009 in N/O (at a given radius). We stress that this measurement of the intrinsic dispersion comes exclusively from direct abundance measurements of H ii regions in NGC 5457.

  2. On the method of indirectly measuring gas and particulate phase velocities in shock induced dusty-gas flows

    NASA Astrophysics Data System (ADS)

    Lock, G. D.

    A method of indirectly measuring the temporally varying velocities of the gas and particulate phases in the nonequilibrium region of a shock wave moving at constant speed in a dusty-gas flow is described, and this method is assessed by using experimental data from shock-induced air flows containing 40-micron-diameter glass beads in a dusty-gas shock-tube facility featuring a large horizontal channel (19.7-cm by 7.6-cm in cross section). Simultaneous measurements of the shock-front speed with time-of-arrival gauges, particle concentration by light extinctiometry, and gas-particle mixture density by beta-ray absorption are used in conjunction with two mass conservation laws to obtain the indirect velocity measurements of both phases. A second indirect measurement of the gas-phase velocity is obtained when the gas pressure is simultaneously recorded along with the particle concentration and shock-front speed when used in conjunction with the conservation of mixture momentum. Direct measurements of the particulate-phase velocity by laser-Doppler velocimetry are also presented as a means of assessing the indirect velocity measurement method.

  3. The Noble Gas Record of Gas-Water Phase Interaction in the Tight-Gas-Sand Reservoirs of the Rocky Mountains

    NASA Astrophysics Data System (ADS)

    Ballentine, C. J.; Zhou, Z.; Harris, N. B.

    2015-12-01

    The mass of hydrocarbons that have migrated through tight-gas-sandstone systems before the permeability reduces to trap the hydrocarbon gases provides critical information in the hydrocarbon potential analysis of a basin. The noble gas content (Ne, Ar, Kr, Xe) of the groundwater has a unique isotopic and elemental composition. As gas migrates through the water column, the groundwater-derived noble gases partition into the hydrocarbon phase. Determination of the noble gases in the produced hydrocarbon phase then provides a record of the type of interaction (simple phase equilibrium or open system Rayleigh fractionation). The tight-gas-sand reservoirs of the Rocky Mountains represent one of the most significant gas resources in the United States. The producing reservoirs are generally developed in low permeability (averaging <0.1mD) Upper Cretaceous fluvial to marginal marine sandstones and commonly form isolated overpressured reservoir bodies encased in even lower permeability muddy sediments. We present noble gas data from producing fields in the Greater Green River Basin, Wyoming; the the Piceance Basin, Colorado; and in the Uinta Basin, Utah. The data is consistent from all three basins. We show how in each basin the noble gases record open system gas migration through a water column at maximum basin burial. The data within an open system model indicates that the gas now in-place represents the last ~10% of hydrocarbon gas to have passed through the water column, most likely prior to permeability closedown.

  4. Capillary effects on gas hydrate three-phase stability in marine sediments

    NASA Astrophysics Data System (ADS)

    Liu, X.; Flemings, P. B.

    2013-12-01

    We study the three-phase (Liquid + Gas + Hydrate) stability of the methane hydrate system in marine sediments by considering the capillary effects on both hydrate and free gas phases. The aqueous CH4 solubilities required for forming hydrate (L+H) and free gas (L+G) in different pore sizes can be met in a three-phase zone. The top of the three-phase zone shifts upward in sediments as the water depth increases and the mean pore size decreases. The thickness of the three-phase zone increases as the pore size distribution widens. The top of the three-phase zone can either overlie the three-phase stability depth at deepwater Blake Ridge or underlie the three-phase stability depth at Hydrate Ridge in shallow water. Our model prediction is compatible with worldwide observations that the bottom-simulating reflector is systematically shifted upward relative to the bulk equilibrium depth as water depth (pressure) is increased. The gas hydrate and free gas saturations of the three-phase zone at Blake Ridge Comparison of the globally compiled BSR temperatures with the three-phase equilibrium curves for the systems of pure CH4 + 3.5 wt.% seawater (solid line) and pure CH4 + 2.0 wt.% seawater (dotted line). The discrepancies between the observed BSR temperature and the calculated three-phase temperature are systematically larger in deep water than in shallow water.

  5. CO2 Capture from Flue Gas by Phase Transitional Absorption

    SciTech Connect

    Liang Hu

    2009-06-30

    A novel absorption process called Phase Transitional Absorption was invented. What is the Phase Transitional Absorption? Phase Transitional Absorption is a two or multi phase absorption system, CO{sub 2} rich phase and CO{sub 2} lean phase. During Absorption, CO{sub 2} is accumulated in CO{sub 2} rich phase. After separating the two phases, CO{sub 2} rich phase is forward to regeneration. After regeneration, the regenerated CO{sub 2} rich phase combines CO{sub 2} lean phase to form absorbent again to complete the cycle. The advantage for Phase Transitional Absorption is obvious, significantly saving on regeneration energy. Because CO{sub 2} lean phase was separated before regeneration, only CO{sub 2} rich phase was forward to regeneration. The absorption system we developed has the features of high absorption rate, high loading and working capacity, low corrosion, low regeneration heat, no toxic to environment, etc. The process evaluation shows that our process is able to save 80% energy cost by comparing with MEA process.

  6. Laboratory Investigations of Titan Haze Formation: Characterization of Gas Phase and Particle Phase Nitrogen

    NASA Astrophysics Data System (ADS)

    Horst, Sarah; Yoon, Heidi; Li, Rui; deGouw, Joost; Tolbert, Margaret

    2014-11-01

    Prior to the arrival of the Cassini-Huygens spacecraft, aerosol production in Titan’s atmosphere was believed to begin in the stratosphere where chemical processes are predominantly initiated by far ultraviolet (FUV) radiation. However, the discovery of very heavy ions, coupled with Cassini Ultraviolet Imaging Spectrograph (UVIS) occultation measurements that show haze absorption up to 1000 km altitude (Liang et al., 2007), indicates that haze formation initiates in the thermosphere. The energy environment of the thermosphere is significantly different from the stratosphere; in particular there is a greater flux of extreme ultraviolet (EUV) photons and energetic particles available to initiate chemical reactions, including the destruction of N2, in the upper atmosphere. The discovery of previously unpredicted nitrogen species in measurements of Titan’s atmosphere by the Cassini Ion and Neutral Mass Spectrometer (INMS) indicates that nitrogen participates in the chemistry to a much greater extent than was appreciated before Cassini (Vuitton et al., 2007). Additionally, measurements obtained by the Aerosol Collector Pyrolyzer (ACP) carried by Huygens to Titan’s surface may indicate that Titan’s aerosols contain significant amounts of nitrogen (Israël et al., 2005, 2006). The degree of nitrogen incorporation in the haze particles is important for understanding the diversity of molecules that may be present in Titan’s atmosphere and on its surface. We have conducted a series of Titan atmosphere simulation experiments using either spark discharge (tesla coil) or FUV photons (deuterium lamp) to initiate chemistry in CH4/N2 gas mixtures ranging from 0.01% CH4/99.99% N2 to 10% CH4/90% N2. We obtained in situ measurements using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) to measure the particle composition as a function of particle size and a proton-transfer ion-trap mass spectrometer (PIT-MS) to measure the composition of gas phase

  7. A new method for measurement of gas-phase ammonia and amines in air

    NASA Astrophysics Data System (ADS)

    Dawson, M. L.; Gomez, A.; Arquero, K. D.; Perraud, V. M.; Finlayson-Pitts, B. J.

    2013-12-01

    Accurately predicting particle formation and growth from gas phase precursors is an essential component of modeling the impact of particulate matter on human health, visibility and climate. While the reactions of ammonia with nitric and sulfuric acids to form particulate nitrate and sulfate particles is well known, it has been recently recognized that gas-phase amines, even at low ppb levels, significantly enhance particle formation from common atmospheric acids. As a result, accurate data on the sources, sinks and typical background concentrations of gas-phase amines, are crucial to predicting new particle formation in the atmosphere. However, gas-phase amines are notoriously difficult to measure, as they have a tendency to stick to surfaces, including sampling lines and inlets. In addition, background amine concentrations in the atmosphere are typically a few ppb or lower, requiring low detection limits for ambient sampling techniques. Here we report the development of a simple, reliable method for detection of gas-phase amines at atmospherically relevant concentrations using collection on a cation exchange sorbent followed by in-line extraction and ion chromatography. Gas-phase standards of several amines and ammonia are used to characterize the technique and results from ambient samples in an agricultural area are presented. The application of this technique to field measurements as well as to laboratory measurements of new particle formation from gas-phase ammonia and amines are discussed.

  8. Condensed-phase versus gas-phase ozonolysis of catechol: A combined experimental and theoretical study

    NASA Astrophysics Data System (ADS)

    Barnum, Timothy J.; Medeiros, Nicholas; Hinrichs, Ryan Z.

    2012-08-01

    Anthropogenic emissions of volatile aromatic compounds contribute to the formation of secondary organic aerosols (SOA), especially in urban environments. Aromatic SOA precursors typically require oxidation by hydroxyl radicals, although recent work suggests that ozonolysis of 1,2-benzenediols produces SOA in high yields. We employed attenuated total reflectance and transmission infrared spectroscopy to investigate the heterogeneous ozonolysis of catechol thin films. Formation of the dominant condensed-phase product muconic acid was highly dependent on relative humidity (RH) with few products detected below 40% RH and a maximum reactive uptake coefficient of γ = (5.6 ± 0.5) × 10-5 measured at 81.2% RH. We also performed quantum chemical calculations mapping out several reaction pathways for the homogeneous ozonolysis of gaseous catechol. 1,3-cycloaddition transition states were rate limiting with the most favorable activation energies at 45.4 and 47.1 kJ mol-1 [CCSD(T)/6-311++G(d,p)] corresponding to addition across and adjacent to the diol Cdbnd C, respectively. Gas-phase rate constants, calculated using transition state theory, were six orders of magnitude slower than experimental values. In contrast, a calculated activation energy was lower for the ozonolysis of a catechol•H2O complex, which serves as a first-approximation for modeling the ozonolysis of condensed-phase catechol. These combined results suggests that homogeneous ozonolysis of catechol may not be important for the formation of secondary organic aerosols but that ozonolysis of surface-adsorbed catechol may contribute to SOA growth.

  9. Gas phase dispersion in compost as a function of different water contents and air flow rates.

    PubMed

    Sharma, Prabhakar; Poulsen, Tjalfe G

    2009-07-21

    Gas phase dispersion in a natural porous medium (yard waste compost) was investigated as a function of gas flow velocity and compost volumetric water content using oxygen and nitrogen as tracer gases. The compost was chosen because it has a very wide water content range and because it represents a wide range of porous media, including soils and biofilter media. Column breakthrough curves for oxygen and nitrogen were measured at relatively low pore gas velocities, corresponding to those observed in for instance soil vapor extraction systems or biofilters for air cleaning at biogas plants or composting facilities. Total gas mechanical dispersion-molecular diffusion coefficients were fitted from the breakthrough curves using a one-dimensional numerical solution to the advection-dispersion equation and used to determine gas dispersivities at different volumetric gas contents. The results showed that gas mechanical dispersion dominated over molecular diffusion with mechanical dispersion for all water contents and pore gas velocities investigated. Importance of mechanical dispersion increased with increasing pore gas velocity and compost water content. The results further showed that gas dispersivity was relatively constant at high values of compost gas-filled porosity but increased with decreasing gas-filled porosity at lower values of gas-filled porosity. Results finally showed that measurement uncertainty in gas dispersivity is generally highest at low values of pore gas velocity.

  10. Peptide bond formation via glycine condensation in the gas phase.

    PubMed

    Van Dornshuld, Eric; Vergenz, Robert A; Tschumper, Gregory S

    2014-07-24

    Four unique gas phase mechanisms for peptide bond formation between two glycine molecules have been mapped out with quantum mechanical electronic structure methods. Both concerted and stepwise mechanisms, each leading to a cis and trans glycylglycine product (four mechanisms total), were examined with the B3LYP and MP2 methods and Gaussian atomic orbital basis sets as large as aug-cc-pVTZ. Electronic energies of the stationary points along the reaction pathways were also computed with explicitly correlated MP2-F12 and CCSD(T)-F12 methods. The CCSD(T)-F12 computations indicate that the electronic barriers to peptide bond formation are similar for all four mechanisms (ca. 32-39 kcal mol(-1) relative to two isolated glycine fragments). The smallest barrier (32 kcal mol(-1)) is associated with the lone transition state for the concerted mechanism leading to the formation of a trans peptide bond, whereas the largest barrier (39 kcal mol(-1)) was encountered along the concerted pathway leading to the cis configuration of the glycylglycine dipeptide. Two significant barriers are encountered for the stepwise mechanisms. For both the cis and trans pathways, the early electronic barrier is 36 kcal mol(-1) and the subsequent barrier is approximately 1 kcal mol(-1) lower. A host of intermediates and transition states lie between these two barriers, but they all have very small relative electronic energies (ca. ± 4 kcal mol(-1)). The isolated cis products (glycylglycine + H2O) are virtually isoenergetic with the isolated reactants (within -1 kcal mol(-1)), whereas the trans products are about 5 kcal mol(-1) lower in energy. In both products, however, the water can hydrogen bond to the dipeptide and lower the energy by roughly 5-9 kcal mol(-1). This study indicates that the concerted process leading to a trans configuration about the peptide bond is marginally favored both thermodynamically (exothermic by ca. 5 kcal mol(-1)) and kinetically (barrier height ≈ 32 kcal mol(-1

  11. Gas-phase interactions of organotin compounds with glycine.

    PubMed

    Latrous, Latifa; Tortajada, Jeanine; Haldys, Violette; Léon, Emmanuelle; Correia, Catarina; Salpin, Jean-Yves

    2013-07-01

    Gas-phase interactions of organotins with glycine have been studied by combining mass spectrometry experiments and quantum calculations. Positive-ion electrospray spectra show that the interaction of di- and tri-organotins with glycine results in the formation of [(R)2Sn(Gly)-H](+) and [(R)3Sn(Gly)](+) ions, respectively. Di-organotin complexes appear much more reactive than those involving tri-organotins. (MS/MS) spectra of the [(R)3Sn(Gly)](+) ions are indeed simple and only show elimination of intact glycine, generating the [(R)3Sn](+) carbocation. On the other hand, MS/MS spectra of [(R)2Sn(Gly)-H](+) complexes are characterized by numerous fragmentation processes. Six of them, associated with elimination of H2O, CO, H2O + CO and formation of [(R)2SnOH](+) (-57 u),[(R)2SnNH2](+) (-58 u) and [(R)2SnH](+) (-73 u), are systematically observed. Use of labeled glycines notably concludes that the hydrogen atoms eliminated in water and H2O + CO are labile hydrogens. A similar conclusion can be made for hydrogens of [(R2)SnOH](+) and [(R2)SnNH2](+) ions. Interestingly, formation [(R)2SnH](+) ions is characterized by a migration of one the α hydrogen of glycine onto the metallic center. Finally, several dissociation routes are observed and are characteristic of a given organic substituent. Calculations indicated that the interaction between organotins and glycine is mostly electrostatic. For [(R)2Sn(Gly)-H](+) complexes, a preferable bidentate interaction of the type η(2)-O,NH2 is observed, similar to that encountered for other metal ions. [(R)3Sn](+) ions strongly stabilize the zwitterionic form of glycine, which is practically degenerate with respect to neutral glycine. In addition, the interconversion between both forms is almost barrierless. Suitable mechanisms are proposed in order to account for the most relevant fragmentation processes.

  12. Gas-phase mercury reduction to measure total mercury in the flue gas of a coal-fired boiler.

    PubMed

    Meischen, Sandra J; Van Pelt, Vincent J; Zarate, Eugene A; Stephens, Edward A

    2004-01-01

    Gaseous elemental and total (elemental + oxidized) mercury (Hg) in the flue gas from a coal-fired boiler was measured by a modified ultraviolet (UV) spectrometer. Challenges to Hg measurement were the spectral interferences from other flue gas components and that UV measures only elemental Hg. To eliminate interference from flue gas components, a cartridge filled with gold-coated sand removed elemental Hg from a flue gas sample. The Hg-free flue gas was the reference gas, eliminating the spectral interferences. To measure total Hg by UV, oxidized Hg underwent a gas-phase, thermal-reduction in a quartz cell heated to 750 degrees C. Simultaneously, hydrogen was added to flash react with the oxygen present forming water vapor and preventing Hg re-oxidation as it exits the cell. Hg concentration results are in parts per billion by volume Hg at the flue gas oxygen concentration. The modified Hg analyzer and the Ontario Hydro method concurrently measured Hg at a field test site. Measurements were made at a 700-MW steam turbine plant with scrubber units and selective catalytic reduction. The flue gas sampled downstream of the selective catalytic reduction contained 2100 ppm SO2 and 75 ppm NOx. Total Hg measured by the Hg analyzer was within 20% of the Ontario Hydro results.

  13. Spectroscopy of PAH species in the gas phase

    NASA Astrophysics Data System (ADS)

    Robinson, Michael S.; Beegle, Luther W.; Wdowiak, Thomas J.

    1995-02-01

    At elevated temperatures, the structured CH stretch absorption occurring at room temperature of polycyclic aromatic hydrocarbon (PAH) molecules encapsulated in KBr coalesces to a single peak whose wavelength is a very close match for that of the observed 3.3 μm unidentified infrared band (UIR) emission feature (Flickinger and Wdowiak. Astrophys. J.362, L71-L74. 1990). The temperature of approximately 800 K is significant because a PAH molecule in the interstellar radiation field, upon absorption of an ultraviolet photon, is expected to be excited to an energy equivalent to temperatures of this order (Sellgren, Astrophys. J.277, 623 1984). Our previous study of PAH molecules in the vapor phase at 600-800 K showed that the C-H stretch PAH feature near 3.3 μm is at a shorter wavelength than in the condensed state (Flickinger et al., Astrophys. J.380, L43-L46, 1991). Recent work by Joblin et al. ( 1st Symp. on the Infrared Cirrus and Diffuse Interstellar Clouds. 1994) in a short path length diamond cell indicates the gas phase wavelength of the 3.3 μm region C-H stretch feature of naphthalene is directly proportional to temperature over a large temperature range. Laser-excited IR fluorescence studies have also suggested that the wavelength is sensitive to laser photon energy in a direct relationship (Williams and Leone, The Diffuse Interstellar Bands Conf., 1994). Comprehensive studies of PAHs thermally excited up to the decomposition temperature are therefore important to carry out. We have utilized a long-path-length optical heat pipe to confirm that the wavelength of the peak of the C-H stretch band of naphthalene vapor obeys a direct relationship with temperature as reported by Joblin, and to demonstrate that this feature undergoes a strengthening with respect to the longer wavelength band due to an out-of-plane deformation (782 cm -1) as temperature increases. The shift from 3067.6 to 3063.7 cm -1 over the temperature range of 316-996 K seems to be linear

  14. Recycling of excavated asphalt from gas-pipeline installations to Gas Research Institute. Final report - Phase 1

    SciTech Connect

    Lucido, J.; Tobin, A.

    1988-12-01

    Recent estimates indicate that over 11,500 miles of gas distribution piping is installed under existing asphalt pavement annually. This estimate includes 25% of all new installations and 60% of all replacement work. As gas distribution systems grow to meet demands, more projects will involve restoration of asphalt pavements. Because gas distribution piping installed and/or replaced under asphalt pavement can be significantly more expensive than an installation in unpaved soil--it is cause for major concern to the gas industry. The Phase I study addressed the concept of on-site recycling of excavated asphalt for gas utility trenching applications. Commercialization of this concept will eliminate the need for disposal of existing asphalt concrete and the importing of new asphalt concrete, creating potentially significant advantages to the industry.

  15. Mm/submm Study of Gas-Phase Photoproducts from Methanol Interstellar Ice Analogues

    NASA Astrophysics Data System (ADS)

    Mesko, AJ; Smith, Houston Hartwell; Milam, Stefanie N.; Widicus Weaver, Susanna L.

    2016-06-01

    Icy grain reactions have gained quite the popularity in the astrochemistry community to explain the formation of complex organic molecules. Through temperature programmed desorption and photolysis experiments we use rotational spectroscopy to measure the gas-phase products of icy grain reactions. Previous results include testing detection limits of the system by temperature programmed desorption of methanol and water ices, photochemistry of gas-phase methanol, and detection of photodesorbed water from a pure water ice surface. Current work that will be discussed focuses on the detection of gas-phase CO and other photoproducts from an ice surface.

  16. Two-stage coal liquefaction without gas-phase hydrogen

    DOEpatents

    Stephens, H.P.

    1986-06-05

    A process is provided for the production of a hydrogen-donor solvent useful in the liquefaction of coal, wherein the water-gas shift reaction is used to produce hydrogen while simultaneously hydrogenating a donor solvent. A process for the liquefaction of coal using said solvent is also provided. The process enables avoiding the use of a separate water-gas shift reactor as well as high pressure equipment for liquefaction. 3 tabs.

  17. The gas-phase metallicity of central and satellite galaxies in the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Pasquali, Anna; Gallazzi, Anna; van den Bosch, Frank C.

    2012-09-01

    We exploit the galaxy groups catalogue of Yang et al. and the galaxy properties measured in the Sloan Digital Sky Survey Data Releases 4 and 7 to study how the gas-phase metallicities of star-forming galaxies depend on environment. We find that satellite and central galaxies follow a qualitatively similar stellar mass (M★)-gas-phase metallicity relation, whereby their gas-phase metallicity increases with M★. Satellites, though, have higher gas-phase metallicities than equally massive centrals, and this difference increases with decreasing stellar mass. We find a maximum offset of 0.06 dex at log(M★/h-2 M⊙) ≃ 8.25. At fixed halo mass, centrals are more metal rich than satellites by ˜0.5 dex on average. This is simply due to the fact that, by definition, centrals are the most massive galaxies in their groups, and the fact that gas-phase metallicity increases with stellar mass. More interestingly, we also find that the gas-phase metallicity of satellites increases with halo mass (Mh) at fixed stellar mass. This increment is more pronounced for less massive galaxies, and, at M★ ≃ 109 h-2 M⊙, corresponds to ˜0.15 dex across the range 11 < log (Mh/h-1 M⊙) < 14. We also show that low-mass satellite galaxies have higher gas-phase metallicities than central galaxies of the same stellar metallicity. This difference becomes negligible for more massive galaxies of roughly solar metallicity. We demonstrate that the observed differences in gas-phase metallicity between centrals and satellites at fixed M★ are not a consequence of stellar mass stripping (advocated by Pasquali et al. in order to explain similar differences but in stellar metallicity), nor to the past star formation history of these galaxies as quantified by their surface mass density or gas mass fraction. Rather, we argue that these trends probably originate from a combination of three environmental effects: (i) strangulation, which prevents satellite galaxies from accreting new, low

  18. Industrial fuel gas plant project. Phase II. Memphis industrial fuel gas plant. Final report. [U-GAS process

    SciTech Connect

    Not Available

    1983-01-01

    The Industrial Fuel Gas Plant produces a nominal 50 billion Btu/day of product gas. The entire IFG production will be sold to MLGW. Under normal conditions, 20% of the output of the plant will be sold by MLGW to the local MAPCO refinery and exchanged for pipeline quality refinery gas. The MAPCO refinery gas will be inserted into the Memphis Natural Gas Distribution System. A portion (normally 10%) of the IFG output of the plant will be diverted to a Credit Generation Unit, owned by MLGW, where the IFG will be upgraded to pipeline quality (950 Btu/SCF). This gas will be inserted into MLGW's Natural Gas Distribution System. The remaining output of the IFG plant (gas with a gross heating value of 300 Btu/SCF) will be sold by MLGW as Industrial Fuel Gas. During periods when the IFG plant is partially or totally off-stream, natural gas from the Memphis Natural Gas Distribution System will be sent to an air mixing unit where the gas will be diluted to a medium Btu content and distributed to the IFG customers. Drawing 2200-1-50-00104 is the plant block flow diagram showing the process sequence and process related support facilities of this industrial plant. Each process unit as well as each process-related support facility is described briefly.

  19. An investigation into the flow behavior of a single phase gas system and a two phase gas/liquid system in normal gravity with nonuniform heating from above

    NASA Technical Reports Server (NTRS)

    Disimile, Peter J.; Heist, Timothy J.

    1990-01-01

    The fluid behavior in normal gravity of a single phase gas system and a two phase gas/liquid system in an enclosed circular cylinder heated suddenly and nonuniformly from above was investigated. Flow visualization was used to obtain qualitative data on both systems. The use of thermochromatic liquid crystal particles as liquid phase flow tracers was evaluated as a possible means of simultaneously gathering both flow pattern and temperature gradient data for the two phase system. The results of the flow visualization experiments performed on both systems can be used to gain a better understanding of the behavior of such systems in a reduced gravity environment and aid in the verification of a numerical model of the system.

  20. Gas Phase UTE MRI of Propane and Propene

    PubMed Central

    Kovtunov, Kirill V.; Romanov, Alexey S.; Salnikov, Oleg G.; Barskiy, Danila A.; Chekmenev, Eduard Y.; Koptyug, Igor V.

    2016-01-01

    1H MRI of gases can potentially enable functional lung imaging to probe gas ventilation and other functions. In this work, 1H MR images of hyperpolarized and thermally polarized propane gas were obtained using UTE (ultrashort echo time) pulse sequence. A 2D image of thermally polarized propane gas with ~0.9×0.9 mm2 spatial resolution was obtained in less than 2 seconds, demonstrating that even non-hyperpolarized hydrocarbon gases can be successfully utilized for conventional proton MRI. The experiments were also performed with hyperpolarized propane gas and demonstrated acquisition of high-resolution multi-slice FLASH 2D images in ca. 510 s and non slice-selective 2D UTE MRI images in ca. 2 s. The UTE approach adopted in this study can be potentially used for medical lung imaging. Furthermore, the possibility to combine UTE with selective suppression of 1H signals from one of the two gases in a mixture is demonstrated in this MRI study. The latter can be useful for visualizing industrially important processes where several gases may be present, e.g., gas-solid catalytic reactions. PMID:27478870

  1. Resonance Energy Transfer Relates the Gas-Phase Structure and Pharmacological Activity of Opioid Peptides.

    PubMed

    Kopysov, Vladimir; Boyarkin, Oleg V

    2016-01-11

    Enkephalins are efficient pain-relief drugs that bind to transmembrane opioid receptors. One key structural parameter that governs the pharmacological activity of these opioid peptides and is typically determined from condensed-phase structures is the distance between the aromatic rings of their Tyr and Phe residues. We use resonance energy transfer, detected by a combination of cold ion spectroscopy and mass spectrometry, to estimate the Tyr-Phe spacing for enkephalins in the gas phase. In contrast to the condensed-phase structures, these distances appear to differ substantially in enkephalins with different pharmacological efficiencies, suggesting that gas-phase structures might be a better pharmacophoric metric for ligand peptides.

  2. Titanium defect structure change after gas-phase hydrogenation at different temperatures and cooling rates

    NASA Astrophysics Data System (ADS)

    Mikhaylov, Andrey A.; Laptev, Roman S.; Kudiiarov, Viktor N.; Volokitina, Tatiana L.

    2016-11-01

    Influence of gas-phase hydrogenation temperature and cooling rate on defect structure of commercially pure titanium alloy was experimentally studied by means of positron annihilation spectroscopy. The change of temperature in the process of gas-phase hydrogenation was in the range of 500-700°C, while the change of cooling rate was in the range of 0.4-10.4°C/min. With increasing of gas-phase hydrogenation temperature, significant increase of hydrogen sorption rate was found. High temperature gas-phase hydrogenation of commercially pure titanium alloy lead to the formation of vacancy and hydrogen-vacancy complexes. For the same concentration of hydrogen, temperature variation or variation of cooling rate had no effect on the type of defect. However, this variation provides significant changes in defect concentration.

  3. FACTORS INFLUENCING THE DEPOSITION OF A COMPOUND THAT PARTITIONS BETWEEN GAS AND PARTICULATE PHASES

    EPA Science Inventory

    How will atmospheric deposition behave for a compound when it reversibly sorbs between gas and atmospheric particulate phases? Two factors influence the answer. What physical mechanisms occur in the sorption process? What are the concentration and composition of atmospheric par...

  4. DETERMINATION OF CHLOROETHENES IN ENVIRONMENTAL BIOLOGICAL SAMPLES USING GAS CHROMATOGRAPHY COUPLED WITH SOLID PHASE MICRO EXTRACTION

    EPA Science Inventory

    An analytical method has been developed to determine the chloroethene series, tetrachloroethene (PCE), trichloroethene (TCE),cisdichloroethene (cis-DCE) andtransdichloroethene (trans-DCE) in environmental biotreatment studies using gas chromatography coupled with a solid phase mi...

  5. Investigation into adsorption and photocatalytic degradation of gaseous benzene in an annular fluidized bed photocatalytic reactor.

    PubMed

    Geng, Qijin; Tang, Shankang; Wang, Lintong; Zhang, Yunchen

    2015-01-01

    The adsorption and photocatalytic degradation of gaseous benzene were investigated considering the operating variables and kinetic mechanism using nano-titania agglomerates in an annular fluidized bed photocatalytic reactor (AFBPR) designed. The special adsorption equilibrium constant, adsorption active sites, and apparent reaction rate coefficient of benzene were determined by linear regression analysis at various gas velocities and relative humidities (RH). Based on a series of photocatalytic degradation kinetic equations, the influences of operating variables on degradation efficiency, apparent reaction rate coefficient and half-life were explored. The findings indicated that the operating variables have obviously influenced the adsorption/photocatalytic degradation and corresponding kinetic parameters. In the photocatalytic degradation process, the relationship between photocatalytic degradation efficiency and RH indicated that water molecules have a dual-function which was related to the structure characteristics of benzene. The optimal operating conditions for photocatalytic degradation of gaseous benzene in AFBPR were determined as the fluidization number at 1.9 and RH required related to benzene concentration. This investigation highlights the importance of controlling RH and benzene concentration in order to obtain the desired synergy effect in photocatalytic degradation processes.

  6. Processes forming Gas, Tar, and Coke in Cellulose Gasification from Gas-Phase Reactions of Levoglucosan as Intermediate.

    PubMed

    Fukutome, Asuka; Kawamoto, Haruo; Saka, Shiro

    2015-07-08

    The gas-phase pyrolysis of levoglucosan (LG), the major intermediate species during cellulose gasification, was studied experimentally over the temperature range of 400-900 °C. Gaseous LG did not produce any dehydration products, which include coke, furans, and aromatic substances, although these are characteristic products of the pyrolysis of molten LG. Alternatively, at >500 °C, gaseous LG produced only fragmentation products, such as noncondensable gases and condensable C1 -C3 fragments, as intermediates during noncondensable gas formation. Therefore, it was determined that secondary reactions of gaseous LG can result in the clean (tar- and coke-free) gasification of cellulose. Cooling of the remaining LG in the gas phase caused coke formation by the transition of the LG to the molten state. The molecular mechanisms that govern the gas- and molten-phase reactions of LG are discussed in terms of the acid catalyst effect of intermolecular hydrogen bonding to promote the molten-phase dehydration reactions.

  7. Formation mechanism of gas bubble superlattice in UMo metal fuels: Phase-field modeling investigation

    NASA Astrophysics Data System (ADS)

    Hu, Shenyang; Burkes, Douglas E.; Lavender, Curt A.; Senor, David J.; Setyawan, Wahyu; Xu, Zhijie

    2016-10-01

    Nano-gas bubble superlattices are often observed in irradiated UMo nuclear fuels. However, the formation mechanism of gas bubble superlattices is not well understood. A number of physical processes may affect the gas bubble nucleation and growth; hence, the morphology of gas bubble microstructures including size and spatial distributions. In this work, a phase-field model integrating a first-passage Monte Carlo method to investigate the formation mechanism of gas bubble superlattices was developed. Six physical processes are taken into account in the model: 1) heterogeneous generation of gas atoms, vacancies, and interstitials informed from atomistic simulations; 2) one-dimensional (1-D) migration of interstitials; 3) irradiation-induced dissolution of gas atoms; 4) recombination between vacancies and interstitials; 5) elastic interaction; and 6) heterogeneous nucleation of gas bubbles. We found that the elastic interaction doesn't cause the gas bubble alignment, and fast 1-D migration of interstitials along <110> directions in the body-centered cubic U matrix causes the gas bubble alignment along <110> directions. It implies that 1-D interstitial migration along [110] direction should be the primary mechanism of a fcc gas bubble superlattice which is observed in bcc UMo alloys. Simulations also show that fission rates, saturated gas concentration, and elastic interaction all affect the morphology of gas bubble microstructures.

  8. Formation mechanism of gas bubble superlattice in UMo metal fuels: Phase-field modeling investigation

    SciTech Connect

    Hu, Shenyang; Burkes, Douglas E.; Lavender, Curt A.; Senor, David J.; Setyawan, Wahyu; Xu, Zhijie

    2016-07-08

    Nano-gas bubble superlattices are often observed in irradiated UMo nuclear fuels. However, the for- mation mechanism of gas bubble superlattices is not well understood. A number of physical processes may affect the gas bubble nucleation and growth; hence, the morphology of gas bubble microstructures including size and spatial distributions. In this work, a phase-field model integrating a first-passage Monte Carlo method to investigate the formation mechanism of gas bubble superlattices was devel- oped. Six physical processes are taken into account in the model: 1) heterogeneous generation of gas atoms, vacancies, and interstitials informed from atomistic simulations; 2) one-dimensional (1-D) migration of interstitials; 3) irradiation-induced dissolution of gas atoms; 4) recombination between vacancies and interstitials; 5) elastic interaction; and 6) heterogeneous nucleation of gas bubbles. We found that the elastic interaction doesn’t cause the gas bubble alignment, and fast 1-D migration of interstitials along $\\langle$110$\\rangle$ directions in the body-centered cubic U matrix causes the gas bubble alignment along $\\langle$110$\\rangle$ directions. It implies that 1-D interstitial migration along [110] direction should be the primary mechanism of a fcc gas bubble superlattice which is observed in bcc UMo alloys. Simulations also show that fission rates, saturated gas concentration, and elastic interaction all affect the morphology of gas bubble microstructures.

  9. Detection Of Gas-Phase Polymerization in SiH4 And GeH4

    NASA Technical Reports Server (NTRS)

    Shing, Yuh-Han; Perry, Joseph W.; Allevato, Camillo E.

    1990-01-01

    Inelastic scattering of laser light found to indicate onset of gas-phase polymerization in plasma-enhanced chemical-vapor deposition (PECVD) of photoconductive amorphous hydrogenated silicon/germanium alloy (a-SiGe:H) film. In PECVD process, film deposited from radio-frequency glow-discharge plasma of silane (SiH4) and germane (GeH4) diluted with hydrogen. Gas-phase polymerization undesirable because it causes formation of particulates and defective films.

  10. An atmospheric pressure flow reactor: Gas phase kinetics and mechanism in tropospheric conditions without wall effects

    NASA Technical Reports Server (NTRS)

    Koontz, Steven L.; Davis, Dennis D.; Hansen, Merrill

    1988-01-01

    A new type of gas phase flow reactor, designed to permit the study of gas phase reactions near 1 atm of pressure, is described. A general solution to the flow/diffusion/reaction equations describing reactor performance under pseudo-first-order kinetic conditions is presented along with a discussion of critical reactor parameters and reactor limitations. The results of numerical simulations of the reactions of ozone with monomethylhydrazine and hydrazine are discussed, and performance data from a prototype flow reactor are presented.

  11. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    SciTech Connect

    Hall,G.E.; Sears, T.J.

    2009-04-03

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. High-resolution spectroscopy, augmented by theoretical and computational methods, is used to investigate the structure and collision dynamics of chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry. Applications and methods development are equally important experimental components of this work.

  12. Double phase (liquid/gas) xenon scintillation detector for WIMPs direct search

    NASA Astrophysics Data System (ADS)

    Yamashita, M.; Doke, T.; Kikuchi, J.; Suzuki, S.

    2003-10-01

    A double phase (liquid/gas) xenon prototype detector of a 0.3 l active volume for WIMPs direct search has been constructed and tested. Proportional scintillation signals are observed by a multi-wire anode mounted in gas phase after ionization electrons drifted successfully long distance in liquid xenon. Both direct and proportional scintillation were used to discriminate electron recoil from nuclear recoil. Basic performances of the detector and the rejection efficiency of background gamma rays were demonstrated.

  13. Theory and Computing of Gas Phase Chemical Reactions: From Exact Quantum to Approximates Dynamical Treatments

    DTIC Science & Technology

    2006-02-08

    Phys. 110, 5526 (1999); Chem. Phys. 242, 341(1999). [51] R. M. Dreizler and E. K. U. Gross, Density Functional Theory (Springer Verlag, Berlin, 1990...the right hand side member of expression 3 can be derived from the square modulus of the S matrix Theory and Computing of Gas Phase Chemical...deal at the same time with different terms of the electronic functions manifolds (15). In these approaches the Theory and Computing of Gas Phase

  14. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    SciTech Connect

    Hall, G.E.

    2011-05-31

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

  15. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    SciTech Connect

    Hall G. E.; Goncharov, V.

    2012-05-29

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

  16. On the role of ethenol in equilibrium gas-phase ethanal

    NASA Astrophysics Data System (ADS)

    Slanina, Zdeněk

    1984-03-01

    The ethenol content in gas-phase ethanal has been evaluated under equilibrium conditions within a broad temperature interval, and it has been shown that the content thresholds of 1% and 1% can be crossed at about 650 and 1000 K, respectively. At moderate and higher temperatures the presence of ethenol is manifested by contributions to thermodynamic functions of the equilibrium gas-phase ethanal which can be even higher than the usual anharmonicity and non-rigidity corrections.

  17. Template-free preparation of volvox-like Cd(x)Zn(1-x)S nanospheres with cubic phase for efficient photocatalytic hydrogen production.

    PubMed

    Zhou, Hangyue; Liu, Qingyun; Liu, Weimin; Ge, Jiechao; Lan, Minhuan; Wang, Chao; Geng, Jianxin; Wang, Pengfei

    2014-03-01

    Volvox-like Cdx Zn1-x S solid solutions with a cubic zinc blend structure were synthesized through a template-free ethylene glycol process. Cd(Ac)2 ⋅2 H2 O, Zn(Ac)2 ⋅2 H2 O, and thiourea are used as the starting materials and dissolved in ethylene glycol. These reaction precursors and solvent not only contributed to control over the formation of the volvox-like spherical geometry, but also exerted vigorous domination for existence of cubic-phase Cdx Zn1-x S nanostructures. As-prepared volvox-like Cdx Zn1-x S nanospheres have a diameter of around 100 nm with extensional shells. These samples show excellent photocatalytic H2 evolution activity from water splitting under visible-light irradiation without any cocatalyst or scaffolding, owing to their tunable band gap, cubic zinc blend structure, and unique hierarchical porous structure with a high surface area (as high as 95.2 m(2)  g(-1) ).

  18. Constraining the Multi-Phase Gas Content of Galaxies in the Local Cosmic Web

    NASA Astrophysics Data System (ADS)

    Stark, David; Kannappan, S. J.; Wei, L. H.; Baker, A. J.; Haynes, M. P.; Giovanelli, R.; Heitsch, F.; RESOLVE Team; ALFALFA Team

    2010-01-01

    The RESOLVE (REsolved Spectroscopy Of a Local VolumE) Survey is a census of gas, stars, and dark matter in 1500 galaxies down to dwarf-scale baryonic masses of 109 Msun, occupying a range of cluster, group, and filament environments in the local cosmic web. We discuss strategies to estimate the gas mass in HI, H2, and warmer phases. RESOLVE falls largely within the footprint of the ongoing ALFALFA survey, allowing us to acquire accurate HI data for much of the sample. Any missing HI masses will be estimated from color and environment data, based on trends calibrated using the ALFALFA data set. Initially, our constraints on the molecular gas component will be largely indirect, based on either AKARI FIR data or a new technique presented here that links CO-derived H2/HI ratios to stellar-mass normalized color gradients. We discuss additional strategies under development to better measure molecular gas and constrain the mass in warmer phases. In particular, we describe observational constraints on the nature of additional gas that is detected dynamically in a sample of very blue, gas-dominated galaxies, possibly representing a warm-hot phase or a low-metallicity molecular component. Obtaining a full gas census for the RESOLVE survey will allow us to model gas phase transitions and star formation, specifically examining how baryonic mass component ratios and conversion timescales depend on galaxy mass and environment.

  19. DEMONSTRATION BULLETIN: GAS-PHASE CHEMICAL REDUCTION - ECO LOGIC INTERNATIONAL, INC.

    EPA Science Inventory

    The patented Eco Logic Process employs a gas-phase reduction reaction of hydrogen with organic and chlorinated organic compounds at elevated temperatures to convert aqueous and oily hazardous contaminants into a hydrocarbon-rich gas product. After passing through a scrubber, the ...

  20. Formation of complex organic molecules in cold objects: the role of gas-phase reactions

    NASA Astrophysics Data System (ADS)

    Balucani, Nadia; Ceccarelli, Cecilia; Taquet, Vianney

    2015-04-01

    While astrochemical models are successful in reproducing many of the observed interstellar species, they have been struggling to explain the observed abundances of complex organic molecules. Current models tend to privilege grain surface over gas-phase chemistry in their formation. One key assumption of those models is that radicals trapped in the grain mantles gain mobility and react on lukewarm ( ≳ 30 K) dust grains. Thus, the recent detections of methyl formate (MF) and dimethyl ether (DME) in cold objects represent a challenge and may clarify the respective role of grain-surface and gas-phase chemistry. We propose here a new model to form DME and MF with gas-phase reactions in cold environments, where DME is the precursor of MF via an efficient reaction overlooked by previous models. Furthermore, methoxy, a precursor of DME, is also synthesized in the gas phase from methanol, which is desorbed by a non-thermal process from the ices. Our new model reproduces fairly well the observations towards L1544. It also explains, in a natural way, the observed correlation between DME and MF. We conclude that gas-phase reactions are major actors in the formation of MF, DME and methoxy in cold gas. This challenges the exclusive role of grain-surface chemistry and favours a combined grain-gas chemistry.

  1. Enhanced photocatalytic activity for degrading pollutants of g-C3N4 by promoting oxygen adsorption after H3BO3 modification

    NASA Astrophysics Data System (ADS)

    Li, Chengming; Raziq, Fazal; Liu, Chong; Li, Zhijun; Sun, Liqun; Jing, Liqiang

    2015-12-01

    The g-C3N4 has been modified by a hydrothermal post treatment with orthoboric acid. It is shown that the surface modification with an appropriate amount of orthoboric acid obviously enhances the surface photovoltage responses of g-C3N4, clearly indicating that the separation of photogenerated charges is greatly improved. This is well responsible for the enhanced photocatalytic activities for degrading representative gas-phase acetaldehyde, and liquid-phase phenol. Moreover, it is demonstrated that the amount of O2 adsorbed on the surfaces of g-C3N4 is greatly increased after H3BO3 modification based on the O2 temperature-programmed desorption curves. It is suggested that the orthoboric acid modification favors O2 adsorption to promote the photogenerated electrons captured for improved photocatalytic activities. This work would provide feasible routes to further improve the photocatalytic performance of semiconductors for degrading pollutants.

  2. Photocatalytic Coatings for Exploration and Spaceport Design

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This project developed self-cleaning photocatalytic coatings that remove contamination without human intervention. The coatings chemically remove organic contaminants and leave no residue. The photocatalyst will not negatively affect other coating properties, especially corrosion resistance. Titanium dioxide, TiO2, is an extremely popular photocatalyst because of its chemical stability, nontoxicity, and low cost. TiO2 is commonly used in the photocatalytic oxidation of organic matter or pollutants in the gas and liquid phases. However, TiO2 does have some drawbacks. It has limited light absorption because of its large band-gap and suffers from a photonic efficiency of less than 10 percent for organic degradation. Dopants can lower the band-gap and improve efficiency. Since the photocatalytically active form of TiO2 is a nanocrystalline powder, it can be difficult to make a robust coating with enough catalyst loading to be effective. Photocatalysts become active when certain light energy is absorbed. When photons with an energy greater than the band-gap, Eg, (wavelengths shorter than 400 nm) impinge upon the surface of the TiO2, an electron-hole pair is formed. The electron-hole pair oxidizes adsorbed substances either directly or via reactive intermediates that form on the surface, such as hydroxyl radicals (OH) or superoxide ions (O2-). Several factors can influence the band-gap energy of TiO2, two of which are crystal structure and impurities. TiO2 exists as three crystal structures brookite, anatase, and rutile that can be controlled via heat treatment. Anatase is the most photocatalytically active crystal form of TiO2. Doping TiO2 with impurities can alter its band-gap energy, as well as its effectiveness as a catalyst. Depending on their size, dopant atoms can occupy either the substitutional or interstitial lattice positions. Atoms that are relatively large will assume the interstitial positions and create a much greater energy disturbance in the crystal than

  3. Ceramic stationary gas turbine development. Final report, Phase 1

    SciTech Connect

    1994-09-01

    This report summarizes work performed by Solar Turbines Inc. and its subcontractors during the period September 25, 1992 through April 30, 1993. The objective of the work is to improve the performance of stationary gas turbines in cogeneration through implementation of selected ceramic components.

  4. Photocatalytic, highly hydrophilic porcelain stoneware slabs

    NASA Astrophysics Data System (ADS)

    Raimondo, M.; Guarini, G.; Zanelli, C.; Marani, F.; Fossa, L.; Dondi, M.

    2011-10-01

    Photocatalytic, highly hydrophilic industrial porcelain stoneware large slabs were realized by deposition of nanostructured TiO2 coatings. Different surface finishing and experimental conditions were considered in order to assess the industrial feasibility. Photocatalytic and wetting behaviour of functionalized slabs mainly depends on surface phase composition in terms of anatase/rutile ratio, this involving - as a key issue - the deposition of TiO2 on industrially sintered products with an additional annealing step to strengthen coatings' performances and durability.

  5. Selective transport of amino acids into the gas phase: driving forces for amino acid solubilization in gas-phase reverse micelles.

    PubMed

    Fang, Yigang; Bennett, Andrew; Liu, Jianbo

    2011-01-28

    We report a study on encapsulation of various amino acids into gas-phase sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) reverse micelles, using electrospray ionization guided-ion-beam tandem mass spectrometry. Collision-induced dissociation of mass-selected reverse micellar ions with Xe was performed to probe structures of gas-phase micellar assemblies, identify solute-surfactant interactions, and determine preferential incorporation sites of amino acids. Integration into gas-phase reverse micelles depends upon amino acid hydrophobicity and charge state. For examples, glycine and protonated amino acids (such as protonated tryptophan) are encapsulated within the micellar core via electrostatic interactions; while neutral tryptophan is adsorbed in the surfactant layer. As verified using model polar hydrophobic compounds, the hydrophobic effect and solute-interface hydrogen-bonding do not provide sufficient driving force needed for interfacial solubilization of neutral tryptophan. Neutral tryptophan, with a zwitterionic structure, is intercalated at the micellar interface between surfactant molecules through complementary effects of electrostatic interactions between tryptophan backbone and AOT polar heads, and hydrophobic interactions between tryptophan side chain and AOT alkyl tails. Protonation of tryptophan could significantly improve its incorporation capacity into gas-phase reverse micelles, and displace its incorporation site from the micellar interfacial zone to the core; protonation of glycine, on the other hand, has little effect on its encapsulation capacity. Another interesting observation is that amino acids of different isoelectric points could be selectively encapsulated into, and transported by, reverse micelles from solution to the gas phase, based upon their competition for protonation and subsequent encapsulation within the micellar core.

  6. Photocatalytic activity of nanostructured TiO2 films produced by supersonic cluster beam deposition

    NASA Astrophysics Data System (ADS)

    Della Foglia, Flavio; Losco, Tonia; Piseri, Paolo; Milani, Paolo; Selli, Elena

    2009-08-01

    The photocatalytic activity of thin, nanostructured films of titanium dioxide, synthesized by supersonic cluster beam deposition (SCBD) from the gas phase, has been investigated employing the photodegradation of salicylic acid as test reaction. Because of the low deposition energy, the so-deposited highly porous TiO2 films are composed of nanoparticles maintaining their original properties in the film, which can be fully controlled by tuning the deposition and post-deposition treatment conditions. A systematic investigation on the evolution of light absorption properties and photoactivity of the films in relation to their morphology, determined by AFM analysis, and phase composition, determined by Raman spectroscopy, has been performed. The absorption and photocatalytic activity of the nanostructured films in the visible region could be enhanced either through post-deposition annealing treatment in ammonia containing atmosphere or employing mild oxidation conditions, followed by annealing in N2 at 600 °C.

  7. Improved thermodynamic analysis of gas reactions for compound semiconductor growth by vapor-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Inatomi, Yuya; Kangawa, Yoshihiro; Kakimoto, Koichi; Koukitu, Akinori

    2017-03-01

    An improved thermodynamic analysis method for vapor-phase epitaxy is proposed. In the conventional method, the mass-balance constraint equations are expressed in terms of variations in partial pressure. Although the conventional method is appropriate for gas–solid reactions occurring near the growth surface, it is not suitable for gas reactions that involve changes in the number of gas molecules. We reconsider the constraint equations in order to predict the effect of gas reactions on semiconductor growth processes. To demonstrate the feasibility of the improved method, the growth process of group-III nitrides by metalorganic vapor-phase epitaxy has been investigated.

  8. An in-situ synthesis of Ag/AgCl/TiO2/hierarchical porous magnesian material and its photocatalytic performance

    PubMed Central

    Yang, Lu; Wang, Fazhou; Shu, Chang; Liu, Peng; Zhang, Wenqin; Hu, Shuguang

    2016-01-01

    The absorption ability and photocatalytic activity of photocatalytic materials play important roles in improving the pollutants removal effects. Herein, we reported a new kind of photocatalytic material, which was synthesized by simultaneously designing hierarchical porous magnesian (PM) substrate and TiO2 catalyst modification. Particularly, PM substrate could be facilely prepared by controlling its crystal phase (Phase 5, Mg3Cl(OH)5·4H2O), while Ag/AgCl particles modification of TiO2 could be achieved by in situ ion exchange between Ag+ and above crystal Phase. Physiochemical analysis shows that Ag/AgCl/TiO2/PM material has higher visible and ultraviolet light absorption response, and excellent gas absorption performance compared to other controls. These suggested that Ag/AgCl/TiO2/PM material could produce more efficient photocatalytic effects. Its photocatalytic reaction rate was 5.21 and 30.57 times higher than that of TiO2/PM and TiO2/imporous magnesian substrate, respectively. Thus, this material and its intergration synthesis method could provide a novel strategy for high-efficiency application and modification of TiO2 photocatalyst in engineering filed. PMID:26883972

  9. Nonequilibrium Features of the Nuclear Liquid-Gas Phase Transition

    NASA Astrophysics Data System (ADS)

    Zwieglinski, B.; Odeh, T.; Gross, C.; Schwarz, C.; Bassini, R.; Begemann-Blaich, M.; Blaich, T.; Emling, H.; Ferrero, A.; Fritz, S.; Gaff, S. J.; Imme, G.; Iori, I.; Kleinevoss, U.; Kunde, G. J.; Kunze, W. D.; Lindenstruth, V.; Lynen, U.; Mahi, M.; Moroni, A.; Moehlenkamp, T.; Mueller, W. F. J.; Ocker, B.; Pochodzalla, J.; Raciti, G.; Rubehn, Th.; Sann, H.; Schnittker, M.; Schuettauf, A.; Seidel, W.; Serfling, V.; Stroth, J.; Trautmann, W.; Trzcinski, A.; Verde, G.; Woerner, A.; Xi, H.; Zude, E.

    1999-03-01

    Energy spectra of protons emitted by the target residue in Au + Au collisions at 1 GeV/u were measured for different excitation energy bins. They reveal two components with different slopes attributed to preequilibrium and equilibrium emission. The relative contribution of the latter decreases rapidly with excitation energy, so that its presence becomes not apparent for the highest energy bins. It is argued therefore, that equilibrium may not be reached on the gas branch of the caloric curve.

  10. Gas distribution equipment in hydrogen service - Phase II

    NASA Technical Reports Server (NTRS)

    Jasionowski, W. J.; Huang, H. D.

    1980-01-01

    The hydrogen permeability of three different types of commercially available natural gas polyethylene pipes was determined. Ring tensile tests were conducted on permeability-exposed and as-received samples. Hydrogen-methane leakage experiments were also performed. The results show no selective leakage of hydrogen via Poiseuille, turbulent, or orifice flow (through leaks) on the distribution of blends of hydrogen and methane. The data collected show that the polyethylene pipe is 4 to 6 times more permeable to hydrogen than to methane.

  11. An indirect method of measuring gas- and particulate-phase velocities of shock-induced dusty-gas flows

    NASA Astrophysics Data System (ADS)

    Gottlieb, James J.

    1992-03-01

    A method of indirectly measuring the temporally varying velocities of both the particulate and gas phases in the nonequilibrium region of a shock wave moving at constant speed in a dusty-gas mixture is described. This method is implemented by using experimental data from shock-induced air flows containing glass beads 40 microns in diameter in a dusty-gas shock-tube facility featuring a large horizontal channel 197 mm high by 76 mm wide with a special dust-injection device. Simultaneous measurements of the shock-front speed with time-of-arrival gauges, particulate concentration by light extinctiometry, and combined particulate concentration and gas density by beta-ray absorption are used in conjunction with two mass conservation laws to provide these indirect two-phase velocity measurements. Direct measurements of the particulate-phase velocity by laser-Doppler velocimetry are also presented for comparison, and the capability of the indirect velocity-measurement method is assessed.

  12. ANALYSIS OF A GAS-PHASE PARTITIONING TRACER TEST CONDUCTED THROUGH FRACTURED MEDIA

    EPA Science Inventory

    The gas-phase partitioning tracer method was used to estimate non-aqueous phase liquid (NAPL), water, and air saturations in the vadose zone at a chlorinated-solvent contaminated field site in Tucson, AZ. The tracer test was conducted in a fractured clay system that is the confin...

  13. Two parametric flow measurement in gas-liquid two-phase flow

    NASA Astrophysics Data System (ADS)

    Chen, Z.; Chen, C.; Xu, Y.; Zhao, Z.

    The importance and current development of two parametric measurement during two-phase flow are briefly reviewed in this paper. Gas-liquid two-phase two parametric metering experiments were conducted by using an oval gear meter and a sharp edged orifice mounted in series in a horizontal pipe. Compressed air and water were used as gas and liquid phases respectively. The correlations, which can be used to predict the total flow rate and volumetric quality of two-phase flow or volumetric flow rate of each phase, have also been proposed in this paper. Comparison of the calculated values of flow rate of each phase from the correlations with the test data showed that the root mean square fractional deviation for gas flow rate is 2.9 percent and for liquid flow rate 4.4 percent. The method proposed in this paper can be used to measure the gas and liquid flow rate in two-phase flow region without having to separate the phases.

  14. Molecular recognition properties of tartrates and metal-tartrates in solution and gas phase.

    PubMed

    Wijeratne, Aruna B; Schug, Kevin A

    2009-05-01

    Solution phase and gas phase chiral molecular recognition properties of tartrates (salts or esters of tartaric acid) and metal tartrates (binuclear tartrato(4-)-metal-bridged complexes) are reviewed in conjunction with their applications in enantiomeric separation science and their mass spectrometric chiral discrimination properties.

  15. Gas-liquid phase separation in oppositely charged colloids: stability and interfacial tension.

    PubMed

    Fortini, Andrea; Hynninen, Antti-Pekka; Dijkstra, Marjolein

    2006-09-07

    We study the phase behavior and the interfacial tension of the screened Coulomb (Yukawa) restricted primitive model (YRPM) of oppositely charged hard spheres with diameter sigma using Monte Carlo simulations. We determine the gas-liquid and gas-solid phase transitions using free energy calculations and grand-canonical Monte Carlo simulations for varying inverse Debye screening length kappa. We find that the gas-liquid phase separation is stable for kappasigmagas-liquid interfacial tension using grand-canonical Monte Carlo simulations. The interfacial tension decreases upon increasing the range of the interaction. In particular, we find that simple scaling can be used to relate the interfacial tension of the YRPM to that of the restricted primitive model, where particles interact with bare Coulomb interactions.

  16. Influence of gas phase equilibria on the chemical vapor deposition of graphene.

    PubMed

    Lewis, Amanda M; Derby, Brian; Kinloch, Ian A

    2013-04-23

    We have investigated the influence of gas phase chemistry on the chemical vapor deposition of graphene in a hot wall reactor. A new extended parameter space for graphene growth was defined through literature review and experimentation at low pressures (≥0.001 mbar). The deposited films were characterized by scanning electron microscopy, Raman spectroscopy, and dark field optical microscopy, with the latter showing promise as a rapid and nondestructive characterization technique for graphene films. The equilibrium gas compositions have been calculated across this parameter space. Correlations between the graphene films grown and prevalent species in the equilibrium gas phase revealed that deposition conditions associated with a high acetylene equilibrium concentration lead to good quality graphene deposition, and conditions that stabilize large hydrocarbon molecules in the gas phase result in films with multiple defects. The transition between lobed and hexagonal graphene islands was found to be linked to the concentration of the monatomic hydrogen radical, with low concentrations associated with hexagonal islands.

  17. Analysis of volatile phase transport in soils using natural radon gas as a tracer

    SciTech Connect

    Chen, C.; Thomas, D.M.

    1992-12-31

    We have conducted a field study of soil gas transport processes using radon gas as a naturally occurring tracer. The .experiment monitored soil gas radon activity, soil moisture, and soil temperature at three depths in the shallow soil column; barometric pressure, rainfall and wind speed were monitored at the soil surface. Linear and multiple regression analysis of the data sets has shown that the gas phase radon activities under natural environmental conditions are influenced by soil moisture content, barometric pressure variations, soil temperature and soil structure. The effect of wind speed on subsurface radon activities under our field conditions has not been demonstrated.

  18. Analysis of volatile phase transport in soils using natural radon gas as a tracer

    SciTech Connect

    Chen, C.; Thomas, D.M.

    1992-01-01

    We have conducted a field study of soil gas transport processes using radon gas as a naturally occurring tracer. The .experiment monitored soil gas radon activity, soil moisture, and soil temperature at three depths in the shallow soil column; barometric pressure, rainfall and wind speed were monitored at the soil surface. Linear and multiple regression analysis of the data sets has shown that the gas phase radon activities under natural environmental conditions are influenced by soil moisture content, barometric pressure variations, soil temperature and soil structure. The effect of wind speed on subsurface radon activities under our field conditions has not been demonstrated.

  19. Evolution of natural gas composition: Predictive multi-phase reaction-transport modeling

    SciTech Connect

    Ortoleva, P.J.; Chang, K.A.; Maxwell, J.M.

    1995-12-31

    A computational modeling approach is used to investigate reaction and transport processes affecting natural gas composition over geological time. Three basic stages are integrated -- gas generation from organic solids or liquids, interactions during source rock expulsion to the reservoir and reactions within the reservoir. Multi-phase dynamics is handled by solving the fully coupled problem of phase-to-phase transfer, intra-phase organic and inorganic reactions and redox and other reactions between fluid phase molecules and minerals. Effects of capillarity and relative permeability are accounted for. Correlations will be determined between gas composition, temperature history, the mineralogy of rocks with which the gas was in contact and the composition of source organic phases. Questions of H{sub 2}S scavenging by oxidizing minerals and the production or removal of CO{sub 2} are focused upon. Our three spatial dimensional, reaction-transport simulation approach has great promise for testing general concepts and as a practical tool for the exploration and production of natural gas.

  20. Liquid-gas phase transitions in a multicomponent nuclear system with Coulomb and surface effects

    SciTech Connect

    Lee, S. J.; Mekjian, A. Z.

    2001-04-01

    The liquid-gas phase transition is studied in a multicomponent nuclear system using a local Skyrme interaction with Coulomb and surface effects. Some features are qualitatively the same as the results of Mu''ller and Serot where a relativistic mean field was used without Coulomb and surface effects. Surface tension brings the coexistence binodal surface to lower pressure. The Coulomb interaction makes the binodal surface smaller and causes another pair of binodal points at low pressure and large proton fraction with fewer protons in the liquid phase and more protons in the gas phase.

  1. Gas phase condensation of superparamagnetic iron oxide-silica nanoparticles - control of the intraparticle phase distribution

    NASA Astrophysics Data System (ADS)

    Stötzel, C.; Kurland, H.-D.; Grabow, J.; Müller, F. A.

    2015-04-01

    Spherical, softly agglomerated and superparamagnetic nanoparticles (NPs) consisting of maghemite (γ-Fe2O3) and amorphous silica (SiO2) were prepared by CO2 laser co-vaporization (CoLAVA) of hematite powder (α-Fe2O3) and quartz sand (SiO2). The α-Fe2O3 portion of the homogeneous starting mixtures was gradually increased (15 mass%-95 mass%). It was found that (i) with increasing iron oxide content the NPs' morphology changes from a nanoscale SiO2 matrix with multiple γ-Fe2O3 inclusions to Janus NPs consisting of a γ-Fe2O3 and a SiO2 hemisphere to γ-Fe2O3 NPs each carrying one small SiO2 lens on its surface, (ii) the multiple γ-Fe2O3 inclusions accumulate at the NPs' inner surfaces, and (iii) all composite NPs are covered by a thin layer of amorphous SiO2. These morphological characteristics are attributed to (i) the phase segregation of iron oxide and silica within the condensed Fe2O3-SiO2 droplets, (ii) the temperature gradient within these droplets which arises during rapid cooling in the CoLAVA process, and (iii) the significantly lower surface energy of silica when compared to iron oxide. The proposed growth mechanism of these Fe2O3-SiO2 composite NPs during gas phase condensation can be transferred to other systems comprising a glass-network former and another component that is insoluble in the regarding glass. Thus, our model will facilitate the development of novel functional composite NPs for applications in biomedicine, optics, electronics, or catalysis.Spherical, softly agglomerated and superparamagnetic nanoparticles (NPs) consisting of maghemite (γ-Fe2O3) and amorphous silica (SiO2) were prepared by CO2 laser co-vaporization (CoLAVA) of hematite powder (α-Fe2O3) and quartz sand (SiO2). The α-Fe2O3 portion of the homogeneous starting mixtures was gradually increased (15 mass%-95 mass%). It was found that (i) with increasing iron oxide content the NPs' morphology changes from a nanoscale SiO2 matrix with multiple γ-Fe2O3 inclusions to Janus NPs

  2. Surface phase of TiO{sub 2} modified with La{sub 2}O{sub 3} and its effect on the photocatalytic H{sub 2} evolution

    SciTech Connect

    Zhang, Yangyang; Zhang, Jing; Xu, Qian; Yan, Song; Zhao, Shanlin; Luo, Genxiang; Li, Can

    2014-05-01

    Graphical abstract: The La{sub 2}O{sub 3}/TiO{sub 2}-900 °C (or La{sub 2}O{sub 3}/Ti(OH){sub 4}-900 °C), with surface anatase phase, show the similar photocatalytic activity. The presence of the surface anatase phase is important for high photocatalytic activity of TiO{sub 2} modified with La{sub 2}O{sub 3} (La{sub 2}O{sub 3}/Ti(OH){sub 4}-900 °C or La{sub 2}O{sub 3}/Ti(OH){sub 4}-900 °C){sub .} - Highlights: • Loading La{sub 2}O{sub 3} on anatase TiO{sub 2} is an effective method for stabilizing the anatase phases both in the surface and in the bulk region. • The high crystallinity of the surface anatase phase is important for high photocatalytic activity of TiO{sub 2} modified with La{sub 2}O{sub 3.} - Abstract: TiO{sub 2} nanoparticles modified with La{sub 2}O{sub 3} were prepared by an impregnation method using anatase TiO{sub 2} support (La{sub 2}O{sub 3}/TiO{sub 2}) or amorphous Ti(OH){sub 4} support (La{sub 2}O{sub 3}/Ti(OH){sub 4}). The bulk and surface crystalline phases of La{sub 2}O{sub 3}/TiO{sub 2} (or La{sub 2}O{sub 3}/Ti(OH){sub 4}) have been characterized by X-ray powder diffraction (XRD) and UV Raman spectroscopy. Besides, morphology and particle size of La{sub 2}O{sub 3}/TiO{sub 2} and La{sub 2}O{sub 3}/Ti(OH){sub 4} samples have been determined by TEM (transmission electron microscope) and Brunauer–Emmett–Teller (BET), respectively. It is found that the phase transformation and increase of the particle size of TiO{sub 2} can be more effectively inhibited in the La{sub 2}O{sub 3}/TiO{sub 2} than in the La{sub 2}O{sub 3}/Ti(OH){sub 4}. Photocatalytic experiments indicated that the La{sub 2}O{sub 3}/TiO{sub 2} (or La{sub 2}O{sub 3}/Ti(OH){sub 4}) samples with surface anatase phase have the similar overall photocatalytic activities. Moreover, it is found that the high crystallinity of surface anatase phase is benefit for the high photocatalytic activity of TiO{sub 2} modified with La{sub 2}O{sub 3}.

  3. Two-phase turbine engines. [using gas-liquid mixture accelerated in nozzles

    NASA Technical Reports Server (NTRS)

    Elliott, D. G.; Hays, L. G.

    1976-01-01

    A description is given of a two-phase turbine which utilizes a uniform mixture of gas and liquid accelerated in nozzles of the types reported by Elliott and Weinberg (1968). The mixture acts directly on an axial flow or tangential impulse turbine or is separated into gas and liquid streams which operate separately on a gas turbine and a hydraulic turbine. The basic two-phase cycles are examined, taking into account working fluids, aspects of nozzle expansion, details of turbine cycle operation, and the effect of mixture ratio variation. Attention is also given to two-phase nozzle efficiency, two-phase turbine operating characteristics and efficiencies, separator turbines, and impulse turbine experiments.

  4. Characterizing the correlations between local phase fractions of gas-liquid two-phase flow with wire-mesh sensor.

    PubMed

    Tan, C; Liu, W L; Dong, F

    2016-06-28

    Understanding of flow patterns and their transitions is significant to uncover the flow mechanics of two-phase flow. The local phase distribution and its fluctuations contain rich information regarding the flow structures. A wire-mesh sensor (WMS) was used to study the local phase fluctuations of horizontal gas-liquid two-phase flow, which was verified through comparing the reconstructed three-dimensional flow structure with photographs taken during the experiments. Each crossing point of the WMS is treated as a node, so the measurement on each node is the phase fraction in this local area. An undirected and unweighted flow pattern network was established based on connections that are formed by cross-correlating the time series of each node under different flow patterns. The structure of the flow pattern network reveals the relationship of the phase fluctuations at each node during flow pattern transition, which is then quantified by introducing the topological index of the complex network. The proposed analysis method using the WMS not only provides three-dimensional visualizations of the gas-liquid two-phase flow, but is also a thorough analysis for the structure of flow patterns and the characteristics of flow pattern transition. This article is part of the themed issue 'Supersensing through industrial process tomography'.

  5. Gas phase heterogeneous catalytic oxidation of alkanes to aliphatic ketones and/or other oxygenates

    SciTech Connect

    Lin, Manhua; Wang, Xiang; Yeom, Younghoon

    2015-03-17

    A catalyst, its method of preparation and its use for producing aliphatic ketones by subjecting alkanes C.sub.3 to C.sub.9 to a gas phase catalytic oxidation in the presence of air or oxygen, and, optionally, steam and/or one or more diluting gases. The catalyst comprises a catalytically active mixed metal oxide phase and a suitable support material onto and/or into which the active catalytic phase id dispersed.

  6. Advanced H2-HCl Gas Dynamic Laser, Phase 2

    DTIC Science & Technology

    1976-01-01

    available in limited quantities on a special order basis, but synthesis is a straightforward and a well-known process. Three candidate propellant...oxidizers. Both oxides react significantly with HL and HC1 at high temperatures to yield H20 and other contaminants (Ca, Mg, CaOH , MgOH, CaCl, CaCl2, MgCip...quantities. However, synthesis of this compound is straight forward and results in a product of good yield and high purity. It is the best H„ gas generator

  7. Electron-beam synthesis of fuel in the gas phase

    NASA Astrophysics Data System (ADS)

    Ponomarev, A. V.; Holodkova, E. M.; Ershov, B. G.

    2012-09-01

    Electron-beam synthesis of liquid fuel from gaseous alkanes was upgraded for formation of conventional and alternative fuel from biomass or pyrolysis oil. Bio-feedstock conversion algorithm includes two consecutive stages: (1) initial macromolecules' transformation to low-molecular-weight intermediates; (2) transformation of these intermediates to stable fuel in gaseous alkanes' atmosphere. Radicals originated from alkanes participate in alkylation/hydrogenation of biomass intermediates. Chemical fixation of gaseous alkanes is amplified in the presence of biomass derivatives due to suppression of gas regeneration reactions, higher molar mass of reagents and lower volatility of radiolytic intermediates.

  8. Simulation of two-phase flow using lattice gas automata methods

    SciTech Connect

    Tsumaya, Akira; Ohashi, Hirotada; Akiyama, Mamoru

    1996-08-01

    Two-phase flow simulation has been primarily based on experimental data in the sense that constitutive relations necessary for solving fundamental equations are experimentally determined. This assures validity of simulation of two-phase flow within the experimental conditions, but it is difficult to predict the behavior of two-phase flow under extreme or complex conditions which occur, for example, in severe accidents of nuclear reactors. Lattice gas automaton (LGA) simulation has recently attracted attention as a method for numerical simulation of multi phase flow. The authors extend phase-separation LGA models and develop methods for two-phase flow simulation. First, they newly added a flow model to the immiscible lattice gas model and applied it to two-dimensional Poiseuille flow. They obtained a result looking like lubricated pipelining of crude oil with water. Also, considering the gravity effect, they introduced a buoyancy force into the liquid-gas model. As a result, they demonstrated that gas bubbles of various diameters rise and gradually coalesce each other turning into larger bubbles. Using these newly developed LGA models, they succeeded in simulating various flow patterns of two-phase flow.

  9. Analysis of Developing Gas/liquid Two-Phase Flows

    SciTech Connect

    Elena A. Tselishcheva; Michael Z. Podowski; Steven P. Antal; Donna Post Guillen; Matthias Beyer; Dirk Lucas

    2010-06-01

    The goal of this work is to develop a mechanistically based CFD model that can be used to simulate process equipment operating in the churn-turbulent regime. The simulations were performed using a state-of-the-art computational multiphase fluid dynamics code, NPHASE–CMFD [Antal et al,2000]. A complete four-field model, including the continuous liquid field and three dispersed gas fields representing bubbles of different sizes, was first carefully tested for numerical convergence and accuracy, and then used to reproduce the experimental results from the TOPFLOW test facility at Forschungszentrum Dresden-Rossendorf e.V. Institute of Safety Research [Prasser et al,2007]. Good progress has been made in simulating the churn-turbulent flows and comparison the NPHASE-CMFD simulations with TOPFLOW experimental data. The main objective of the paper is to demonstrate capability to predict the evolution of adiabatic churn-turbulent gas/liquid flows. The proposed modelling concept uses transport equations for the continuous liquid field and for dispersed bubble fields [Tselishcheva et al, 2009]. Along with closure laws based on interaction between bubbles and continuous liquid, the effect of height on air density has been included in the model. The figure below presents the developing flow results of the study, namely total void fraction at different axial locations along the TOPFLOW facility test section. The complete model description, as well as results of simulations and validation will be presented in the full paper.

  10. Gas-phase and solution-phase polymerization of epoxides by Cr(salen) complexes: evidence for a dinuclear cationic mechanism.

    PubMed

    Schön, Eva; Zhang, Xiangyang; Zhou, Zhiping; Chisholm, Malcolm H; Chen, Peter

    2004-11-15

    The gas-phase reactions of a series of mass-selected mononuclear and dinuclear Cr(salen) complexes with propylene oxide suggest that the enhanced reactivity of the dinuclear complexes in gas-phase and in solution may derive from a dicationic mechanism in which the alkoxide chain is mu(2)-coordinated to two Lewis acidic metal centers. The double coordination is proposed to suppress backbiting, and hence chain-transfer in the gas-phase homopolymerization of epoxides.

  11. Plasma-Sprayed Photocatalytic Zinc Oxide Coatings

    NASA Astrophysics Data System (ADS)

    Navidpour, A. H.; Kalantari, Y.; Salehi, M.; Salimijazi, H. R.; Amirnasr, M.; Rismanchian, M.; Azarpour Siahkali, M.

    2017-03-01

    Fabrication of semiconductor coatings with photocatalytic action for photodegradation of organic pollutants is highly desirable. In this research, pure zinc oxide, which is well known for its promising photocatalytic activity, was deposited on stainless-steel plates by plasma spraying. The phase composition and microstructure of the deposited films were studied by x-ray diffraction analysis and scanning electron microscopy, respectively. Despite the low-energy conditions of the plasma spraying process, the zinc oxide coatings showed good mechanical integrity on the substrate. Their photocatalytic activity was evaluated using aqueous solution of methylene blue at concentration of 5 mg L-1. The results showed the potential of the plasma spraying technique to deposit zinc oxide coatings with photocatalytic action under ultraviolet illumination. Ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy confirmed that the plasma spraying method could deposit zinc oxide films with higher photoabsorption ability relative to the initial powder.

  12. Cold flame on Biofilm - Transport of Plasma Chemistry from Gas to Liquid Phase

    NASA Astrophysics Data System (ADS)

    Kong, Michael

    2014-10-01

    One of the most active and fastest growing fields in low-temperature plasma science today is biological effects of gas plasmas and their translation in many challenges of societal importance such as healthcare, environment, agriculture, and nanoscale fabrication and synthesis. Using medicine as an example, there are already three FDA-approved plasma-based surgical procedures for tissue ablation and blood coagulation and at least five phase-II clinical trials on plasma-assisted wound healing therapies. A key driver for realizing the immense application potential of near room-temperature ambient pressure gas plasmas, commonly known as cold atmospheric plasmas or CAP, is to build a sizeable interdisciplinary knowledge base with which to unravel, optimize, and indeed design how reactive plasma species interact with cells and their key components such as protein and DNA. Whilst a logical objective, it is a formidable challenge not least since existing knowledge of gas discharges is largely in the gas-phase and therefore not directly applicable to cell-containing matters that are covered by or embedded in liquid (e.g. biofluid). Here, we study plasma inactivation of biofilms, a jelly-like structure that bacteria use to protect themselves and a major source of antimicrobial resistance. As 60--90% of biofilm is made of water, we develop a holistic model incorporating physics and chemistry in the upstream CAP-generating region, a plasma-exit region as a buffer for as-phase transport, and a downstream liquid region bordering the gas buffer region. A special model is developed to account for rapid chemical reactions accompanied the transport of gas-phase plasma species through the gas-liquid interface and for liquid-phase chemical reactions. Numerical simulation is used to illustrate how key reactive oxygen species (ROS) are transported into the liquid, and this is supported with experimental data of both biofilm inactivation using plasmas and electron spin spectroscopy (ESR

  13. Effect of rutile TiO2 on the photocatalytic performance of g-C3N4/brookite-TiO2-xNy photocatalyst for NO decomposition

    NASA Astrophysics Data System (ADS)

    Li, Huihui; Wu, Xiaoyong; Yin, Shu; Katsumata, Kenichi; Wang, Yuhua

    2017-01-01

    Novel g-C3N4/rutile-brookite TiO2-xNy composite photocatalysts were fabricated through a facile solvothermal approach. The effect of rutile phase TiO2 with brookite TiO2 and g-C3N4 on the photocatalytic activity of g-C3N4/nitrogen-doped TiO2 composite was studied. The photocatalytic performance of the photocatalyst was evaluated by measuring the degradation of NO gas under visible and UV light irradiation. It is suggested that g-C3N4/rutile-brookite TiO2-xNy forms a Z-scheme photocatalytic system, which shows improvement on the photocatalytic activity than that of g-C3N4/single brookite TiO2-xNy. By importing rutile phase TiO2-xNy, the photogenerated electrons can efficiently transfer from rutile TiO2 to g-C3N4, which results in the separation of electron and hole pairs, enhancing the photocatalytic ability. However, single brookite TiO2-xNy can not remove the photogenerated electrons efficiently and the photocatalytic performances of composites decrease with g-C3N4 amount increase.

  14. Efficient and directed peptide bond formation in the gas phase via ion/ion reactions.

    PubMed

    McGee, William M; McLuckey, Scott A

    2014-01-28

    Amide linkages are among the most important chemical bonds in living systems, constituting the connections between amino acids in peptides and proteins. We demonstrate the controlled formation of amide bonds between amino acids or peptides in the gas phase using ion/ion reactions in a mass spectrometer. Individual amino acids or peptides can be prepared as reagents by (i) incorporating gas phase-labile protecting groups to silence otherwise reactive functional groups, such as the N terminus; (ii) converting the carboxyl groups to the active ester of N-hydroxysuccinimide; and (iii) incorporating a charge site. Protonation renders basic sites (nucleophiles) unreactive toward the N-hydroxysuccinimide ester reagents, resulting in sites with the greatest gas phase basicities being, in large part, unreactive. The N-terminal amines of most naturally occurring amino acids have lower gas phase basicities than the side chains of the basic amino acids (i.e., those of histidine, lysine, or arginine). Therefore, reagents may be directed to the N terminus of an existing "anchor" peptide to form an amide bond by protonating the anchor peptide's basic residues, while leaving the N-terminal amine unprotonated and therefore reactive. Reaction efficiencies of greater than 30% have been observed. We propose this method as a step toward the controlled synthesis of peptides in the gas phase.

  15. In Situ Environmental TEM in Imaging Gas and Liquid Phase Chemical Reactions for Materials Research.

    PubMed

    Wu, Jianbo; Shan, Hao; Chen, Wenlong; Gu, Xin; Tao, Peng; Song, Chengyi; Shang, Wen; Deng, Tao

    2016-11-01

    Gas and liquid phase chemical reactions cover a broad range of research areas in materials science and engineering, including the synthesis of nanomaterials and application of nanomaterials, for example, in the areas of sensing, energy storage and conversion, catalysis, and bio-related applications. Environmental transmission electron microscopy (ETEM) provides a unique opportunity for monitoring gas and liquid phase reactions because it enables the observation of those reactions at the ultra-high spatial resolution, which is not achievable through other techniques. Here, the fundamental science and technology developments of gas and liquid phase TEM that facilitate the mechanistic study of the gas and liquid phase chemical reactions are discussed. Combined with other characterization tools integrated in TEM, unprecedented material behaviors and reaction mechanisms are observed through the use of the in situ gas and liquid phase TEM. These observations and also the recent applications in this emerging area are described. The current challenges in the imaging process are also discussed, including the imaging speed, imaging resolution, and data management.

  16. Effect of additives on gas-phase catalysis with immobilised Thermoanaerobacter species alcohol dehydrogenase (ADH T).

    PubMed

    Trivedi, A H; Spiess, A C; Daussmann, T; Büchs, J

    2006-07-01

    This paper presents a strategy for preparing an efficient immobilised alcohol dehydrogenase preparation for a gas-phase reaction. The effects of additives such as buffers and sucrose on the immobilisation efficiency (residual activity and protein loading) and on the gas-phase reaction efficiency (initial reaction rate and half-life) of Thermoanaerobacter sp. alcohol dehydrogenase were studied. The reduction of acetophenone to 1-phenylethanol under in situ cofactor regeneration using isopropanol as co-substrate was used as a model reaction at fixed reaction conditions (temperature and thermodynamic activities). A strongly enhanced thermostability of the enzyme in the gas-phase reaction was achieved when the enzyme was immobilised with 50 mM phosphate buffer (pH 7) containing sucrose five times the protein amount (on weight/weight basis). This resulted in a remarkable productivity of 200 g L(-1) day(-1) even at non-optimised reaction conditions. The interaction of additives with the enzyme and water affects the immobilisation and gas-phase efficiencies of the enzyme. However, it was not possible to predict the effect of additives on the gas-phase reaction efficiency even after knowing their effect on the immobilisation efficiency.

  17. Gas-phase chemistry of element 114, flerovium

    NASA Astrophysics Data System (ADS)

    Yakushev, Alexander; Eichler, Robert

    2016-12-01

    Element 114 was discovered in 2000 by the Dubna-Livermore collaboration, and in 2012 it was named flerovium. It belongs to the group 14 of the periodic table of elements. A strong relativistic stabilisation of the valence shell 7s27p is expected due to the orbital splitting and the contraction not only of the 7s2 but also of the spherical 7p closed subshell, resulting in the enhanced volatility and inertness. Flerovium was studied chemically by gas-solid chromatography upon its adsorption on a gold surface. Two experimental results on Fl chemistry have been published so far. Based on observation of three atoms, a weak interaction of flerovium with gold was suggested in the first study. Authors of the second study concluded on the metallic character after the observation of two Fl atoms deposited on gold at room temperature.

  18. Air-sea transfer of gas phase controlled compounds

    NASA Astrophysics Data System (ADS)

    Yang, M.; Bell, T. G.; Blomquist, B. W.; Fairall, C. W.; Brooks, I. M.; Nightingale, P. D.

    2016-05-01

    Gases in the atmosphere/ocean have solubility that spans several orders of magnitude. Resistance in the molecular sublayer on the waterside limits the air-sea exchange of sparingly soluble gases such as SF6 and CO2. In contrast, both aerodynamic and molecular diffusive resistances on the airside limit the exchange of highly soluble gases (as well as heat). Here we present direct measurements of air-sea methanol and acetone transfer from two open cruises: the Atlantic Meridional Transect in 2012 and the High Wind Gas Exchange Study in 2013. The transfer of the highly soluble methanol is essentially completely airside controlled, while the less soluble acetone is subject to both airside and waterside resistances. Both compounds were measured concurrently using a proton-transfer-reaction mass spectrometer, with their fluxes quantified by the eddy covariance method. Up to a wind speed of 15 m s-1, observed air-sea transfer velocities of these two gases are largely consistent with the expected near linear wind speed dependence. Measured acetone transfer velocity is ∼30% lower than that of methanol, which is primarily due to the lower solubility of acetone. From this difference we estimate the “zero bubble” waterside transfer velocity, which agrees fairly well with interfacial gas transfer velocities predicted by the COARE model. At wind speeds above 15 m s-1, the transfer velocities of both compounds are lower than expected in the mean. Air-sea transfer of sensible heat (also airside controlled) also appears to be reduced at wind speeds over 20 m s-1. During these conditions, large waves and abundant whitecaps generate large amounts of sea spray, which is predicted to alter heat transfer and could also affect the air-sea exchange of soluble trace gases. We make an order of magnitude estimate for the impacts of sea spray on air-sea methanol transfer.

  19. Strategies for the Gas Phase Modification of Cationized Arginine via Ion/ion Reactions.

    PubMed

    Prentice, Boone M; McGee, William M; Stutzman, John R; McLuckey, Scott A

    2013-11-15

    The gas phase acetylation of cationized arginine residues is demonstrated here using ion/ion reactions with sulfosuccinimidyl acetate (sulfo-NHS acetate) anions. Previous reports have demonstrated the gas phase modification of uncharged primary amine (the N-terminus and ε-amino side chain of lysine) and uncharged guanidine (the arginine side chain) functionalities via sulfo-NHS ester chemistry. Herein, charge-saturated arginine-containing peptides that contain sodium ions as the charge carriers, such as [ac-ARAAARA+2Na](2+), are shown to exhibit strong reactivity towards sulfo-NHS acetate whereas the protonated peptide analogues exhibit no such reactivity. This difference in reactivity is attributed to the lower sodium ion (as compared to proton) affinity of the arginine, which results in increased nucleophilicity of the cationized arginine guanidinium functionality. This increased nucleophilicity improves the arginine residue's reactivity towards sulfo-NHS esters and enhances the gas phase covalent modification pathway. No such dramatic increase in reactivity towards sulfo-NHS acetate has been observed upon sodium cationization of lysine amino acid residues, indicating that this behavior appears to be unique to arginine. The sodium cationization process is demonstrated in the condensed phase by simply spiking sodium chloride into the peptide sample solution and in the gas phase by a peptide-sodium cation exchange process with a sulfo-NHS acetate sodium-bound dimer cluster reagent. This methodology demonstrates several ways by which arginine can be covalently modified in the gas phase even when it is charged. Collisional activation of an acetylated arginine product can result in deguanidination of the residue, generating an ornithine. This gas phase ornithination exhibits similar site-specific fragmentation behavior to that observed with peptides ornithinated in solution and may represent a useful approach for inducing selective peptide cleavages.

  20. Numerical Computation of Flame Spread over a Thin Solid in Forced Concurrent Flow with Gas-phase Radiation

    NASA Technical Reports Server (NTRS)

    Jiang, Ching-Biau; T'ien, James S.

    1994-01-01

    Excerpts from a paper describing the numerical examination of concurrent-flow flame spread over a thin solid in purely forced flow with gas-phase radiation are presented. The computational model solves the two-dimensional, elliptic, steady, and laminar conservation equations for mass, momentum, energy, and chemical species. Gas-phase combustion is modeled via a one-step, second order finite rate Arrhenius reaction. Gas-phase radiation considering gray non-scattering medium is solved by a S-N discrete ordinates method. A simplified solid phase treatment assumes a zeroth order pyrolysis relation and includes radiative interaction between the surface and the gas phase.

  1. Test plan for phase II of the Retained Gas Sampler system

    SciTech Connect

    Hey, B.E.

    1995-06-19

    The Retained Gas Sampler (RGS) system is being developed to permit characterization of the gas phase component of waste tank core samples. Several laboratory experiments have been conducted which have affirmed the proof-of-principle for separating the gas phase materials from waste tank material in a quantitative manner. However, experiments conducted thus far have dealt only with representative materials and simulated hardware mock-ups. This test plan deals with the operation and testing of actual devices in the hot cell environment. This test plan coves all aspects of the RGS system including: sampler load-in, extrusion, gas extraction, quantitative separation, sample collection, and quantitative analysis. Sample material used in this test plan will be waste tank simulants and will not be radioactive. The work environment, however, will be an operating hot cell facility and will have radioactive contaminated surfaces. Operation of the system will therefore require an official radiation work permit (RWP).

  2. Singular effect of crystallite size on the charge carrier generation and photocatalytic activity of nano-TiO2

    NASA Astrophysics Data System (ADS)

    Strauss, Mathias; Pastorello, Murilo; Sigoli, Fernando A.; Silva, Juliana M. de Souza e.; Mazali, Italo O.

    2014-11-01

    Photocatalytic processes on nanometric titanium oxide have been extensively studied from the standpoint of solar energy utilization and remediation of water and gas streams polluted with organic molecules. It is accepted that TiO2 crystallite size and crystalline phase are among the parameters involved in the control of the photocatalytic activity. However, while changing the catalyst nanoparticle size, other attributes important to assess photocatalytic activity may be modified, making thus difficult to define to which extension the photoactivity changes are related only to size differences. Therefore, aiming at studying exclusively the size effect and the parameters directly related to size on the photocatalytic activity of nanometric TiO2, in this work it was explored a method to synthesize TiO2 nanoparticles with controlled size, highly similar morphology and comparable phase and degree of crystallinity. A set composed of four samples of nano-TiO2 loaded porous Vycor glass, each sample having a specific TiO2 nanoparticle size, was tested on the photoactivated process of depollution of solutions of salicylic acid and methylene blue. The photocatalytic activity observed for the organic compounds tested was inversely proportional to the TiO2 nanoparticle size. An opposite tendency was observed for the generation of OH radicals during photocatalyst illumination, as more radicals are formed on the material containing the larger TiO2 nanoparticles. Results of this study suggest that photocatalytic activity of nano-TiO2 is less favored by the enhanced light absorption response and the higher generation of oxidative species observed for the larger nanoparticles. Better catalysts were obtained when nano-TiO2 exhibited high surface-to-volume ratio and had small recombination volumes, which respectively favors pollutant adsorption-desorption on catalyst surface and reduce the number of recombined charge carriers.

  3. Selective removal of ethylene, a deposit precursor, from a "dirty" synthesis gas stream via gas-phase partial oxidation.

    PubMed

    Villano, Stephanie M; Hoffmann, Jessica; Carstensen, Hans-Heinrich; Dean, Anthony M

    2010-06-17

    A fundamental issue in the gasification of biomass is that in addition to the desired synthesis gas product (a mixture of H(2) and CO), the gasifier effluent contains other undesirable products that need to be removed before any further downstream processing can occur. This work assesses the potential to selectively remove hydrocarbons from a synthesis gas stream via gas-phase partial oxidation. Specifically, the partial oxidation of methane-doped, ethylene-doped, and methane/ethylene-doped model synthesis gas mixtures has been investigated at ambient pressures over a temperature range of 760-910 degrees C and at residence times ranging from 0.4 to 2.4 s using a tubular flow reactor. For the synthesis gas mixtures that contain either methane or ethylene, the addition of oxygen substantially reduces the hydrocarbon concentration while only a small reduction in the hydrogen concentration is observed. For the synthesis gas mixtures doped with both methane and ethylene, the addition of oxygen preferentially removes ethylene while the concentrations of methane and hydrogen remain relatively unaffected. These results are compared to the predictions of a plug flow model using a reaction mechanism that is designed to describe the pyrolysis and partial oxidation of small hydrocarbon species. The agreement between the experimental observations and the model predictions is quite good, allowing us to explore the underlying chemistry that leads to the hydrocarbon selective oxidation. The implications of these results are briefly discussed in terms of using synthesis gas to produce liquid fuels and electrical power via a solid oxide fuel cell.

  4. Insights into diastereoisomeric characterization of tetrahydropyridazine amino acid derivatives: crystal structures and gas phase ion chemistry.

    PubMed

    Giorgi, Gianluca; Favi, Gianfranco; Attanasi, Orazio A

    2013-08-14

    Structural, conformational properties, and gas phase reactivity of two representative diastereoisomeric members of a series of α,α-tetrahydropyridazine amino acid derivatives have been investigated by using X-ray crystallography, tandem mass spectrometry and theoretical calculations. Both diastereoisomers show an unusual screw-boat conformation of the tetrahydropyridazine ring. While protonated molecules mainly decompose in the gas phase by loss of acetamide, the main reactivity of the [M + Na](+) species consists of loss of PhNCO followed by acetamide and it is strictly dependent upon the stereochemistry of the parent compound. The most stable energy minimized structures obtained by theoretical calculations are in full agreement with the experimental data and allowed us to rationalize the gas phase reaction pathways.

  5. Native biomolecules in the gas phase? The case of green fluorescent protein.

    PubMed

    Frankevich, Vladimir; Barylyuk, Konstantin; Chingin, Konstantin; Nieckarz, Robert; Zenobi, Renato

    2013-04-02

    Green fluorescent protein (GFP) was ionized by native electrospray ionization and trapped for many seconds in high vacuum, allowing fluorescence emission to be measured as a probe of its biological function, to answer the question whether GFP exists in the native form in the gas phase or not. Although a narrow charge-state distribution, a collision cross-section very close to that expected for correctly folded GFP, and a large stability against dissociation all support a near-native gas-phase structure, no fluorescence emission was observed. The loss of the native form is attributed to the absence of residual water in the gas phase, which normally stabilizes the para-hydroxybenzylidene imidazolone chromophore of GFP.

  6. Direct observation of the gas-phase Criegee intermediate (CH2OO).

    PubMed

    Taatjes, Craig A; Meloni, Giovanni; Selby, Talitha M; Trevitt, Adam J; Osborn, David L; Percival, Carl J; Shallcross, Dudley E

    2008-09-10

    Carbonyl oxide species play a key role in tropospheric oxidation of organic molecules and in low-temperature combustion processes. In the late 1940s, Criegee first postulated the participation of carbonyl oxides, now often called "Criegee intermediates," in ozonolysis of alkenes. However, despite decades of effort, no gas phase Criegee intermediate has before been observed. As a result, knowledge of gas phase carbonyl oxide reactions has heretofore been inferred by indirect means, with derived rate coefficients spanning orders of magnitude. We have directly detected the primary Criegee intermediate, formaldehyde oxide (CH2OO), in the chlorine-initiated gas-phase oxidation of dimethyl sulfoxide (DMSO). This work not only establishes that the Criegee intermediate is formed in DMSO oxidation also but opens the possibility for explicit kinetics studies on this critical atmospheric species.

  7. Device for two-dimensional gas-phase separation and characterization of ion mixtures

    DOEpatents

    Tang, Keqi; Shvartsburg, Alexandre A.; Smith, Richard D.

    2006-12-12

    The present invention relates to a device for separation and characterization of gas-phase ions. The device incorporates an ion source, a field asymmetric waveform ion mobility spectrometry (FAIMS) analyzer, an ion mobility spectrometry (IMS) drift tube, and an ion detector. In one aspect of the invention, FAIMS operating voltages are electrically floated on top of the IMS drift voltage. In the other aspect, the FAIMS/IMS interface is implemented employing an electrodynamic ion funnel, including in particular an hourglass ion funnel. The present invention improves the efficiency (peak capacity) and sensitivity of gas-phase separations; the online FAIMS/IMS coupling creates a fundamentally novel two-dimensional gas-phase separation technology with high peak capacity, specificity, and exceptional throughput.

  8. Metal-Organic Framework Thin Films as Stationary Phases in Microfabricated Gas-Chromatography Columns.

    SciTech Connect

    Read, Douglas; Sillerud, Colin Halliday

    2016-01-01

    The overarching goal of this project is to integrate Sandia's microfabricated gas-chromatography ( GC) columns with a stationary phase material that is capable of retaining high-volatility chemicals and permanent gases. The successful integration of such a material with GCs would dramatically expand the repertoire of detectable compounds for Sandia's various microanalysis systems. One such promising class of candidate materials is metal-organic frameworks (MOFs). In this report we detail our methods for controlled deposition of HKUST-1 MOF stationary phases within GC columns. We demonstrate: the chromatographic separation of natural gas; a method for determining MOF film thickness from chromatography alone; and the first-reported GC x GC separation of natural gas -- in general -- let alone for two disparate MOF stationary phases. In addition we determine the fundamental thermodynamic constant for mass sorption, the partition coefficient, for HKUST-1 and several light hydrocarbons and select toxic industrial chemicals.

  9. OMVPE growth and gas-phase reactions of AlGaN for UV emitters

    SciTech Connect

    Han, J.; Figiel, J.J.; Crawford, M.H.; Banas, M.A.; Bartram, M.E.; Biefeld, R.M.; Song, Y.K.; Nurmikko, A.V.

    1998-06-01

    Gas-phase parasitic reactions among TMG, TMA, and NH3, are investigated by monitoring of the growth rate/incorporation efficiency of GaN and AlN using an in-situ optical reflectometer. It is suggested that gas phase adduct (TMA: NH{sub 3}) reactions not only reduce the incorporation efficiency of TMA but also affect the incorporation behavior of TMGa. The observed phenomena can be explained by either a synergistic gas-phase scavenging effect or a surface site-blocking effect. Relatively low reactor pressures (30--50 Torr) are employed to grow an AlGaN/GaN QW p-n diode structure. The UV emission at 354 nm (FWHM {approximately} 6 nm) represents the first report of LED operation from an indium-free GaN QW diode.

  10. Abundant gas-phase H2O in absorption toward massive protostars

    NASA Astrophysics Data System (ADS)

    Boonman, A. M. S.; van Dishoeck, E. F.

    2003-06-01

    We present infrared spectra of gas-phase H2O around 6 mu m toward 12 deeply embedded massive protostars obtained with the Short Wavelength Spectrometer on board the Infrared Space Observatory (ISO). The nu2 ro-vibrational band has been detected toward 7 of the sources and the excitation temperatures indicate an origin in the warm gas at Tex>~ 250 K. Typical derived gas-phase H2O abundances are ~ 5*E-6-6*E-5, with the abundances increasing with the temperature of the warm gas. The inferred gas/solid ratios show a similar trend with temperature and suggest that grain-mantle evaporation is important. The increasing gas/solid ratio correlates with other indicators of increased temperatures. If the higher temperatures are due to a larger ratio of source luminosity to envelope mass, this makes gas-phase H2O a good evolutionary tracer. Comparison with chemical models shows that three different chemical processes, ice evaporation, high-T chemistry, and shocks, can reproduce the high inferred gas-phase H2O abundances. In a forthcoming paper each of these processes are investigated in more detail in comparison with data from the Long Wavelength Spectrometer on board ISO and the Submillimeter Wave Astronomy Satellite (SWAS). Comparison with existing SWAS data indicates that a jump in the H2O abundance is present and that the observed nu2 ro-vibrational band traces primarily the warm inner envelope. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

  11. Phase behavior and splitting analysis: An operational tool in gas transmission and distribution

    SciTech Connect

    Martinez A., F.F.; Infantini S., M.

    1998-12-31

    Most of the natural gas produced by Petroleos de Venezuela, S.A. (PDVSA) is associated gas that flows from the gathering systems to the processing plants, before it arrives at the transmission systems. Even if the gas transmission occurs after the necessary processing of the gas has been completed, condensation still happens in the transmission, regulating stations and/or distribution systems. The quantity of condensate will not only depend on composition, pressure and temperature, but also on the unequal splitting phenomenon that takes place at tee junctions in a network system. The splitting phenomenon determines the liquid distribution at the junction. This situation is more drastic when the processing plant is partially or totally shut down in a maintenance program. This work shows how the gas transmission and distribution engineer has to use the phase behavior and splitting analysis as an operational tool, in order to predict and prevent the presence of liquid in the system. Using process simulators, the phase behavior analysis is conducted to determine the bubble and dew point curve and to perform flash calculations at any pressure and temperature. Then, the operational pressure-temperature profile is over-plotted on the phase envelope diagram in order to evaluate the condensation possibility into the gas pipeline. Afterwards, the pressure and temperature drops in regulating stations are incorporated in the phase envelope diagram and the two-phase gas condensate study is completed. Finally, considering the concepts of the splitting phenomenon and the knowledge that it can really happen, the presence of liquid in particular customers can be explained and solved. Operational experiences are included to evaluate the methodology and to present the effectiveness of the results.

  12. Gas adsorption/absorption heat switch, phase 1

    NASA Technical Reports Server (NTRS)

    Chan, C. K.

    1987-01-01

    The service life and/or reliability of far-infrared sensors on surveillance satellites is presently limited by the cryocooler. The life and/or reliability, however, can be extended by using redundant cryocoolers. To reduce parasitic heat leak, each stage of the inactive redundant cryocooler must be thermally isolated from the optical system, while each stage of the active cryocooler must be thermally connected to the system. The thermal break or the thermal contact can be controlled by heat switches. Among different physical mechanisms for heat switching, mechanically activated heat switches tend to have low reliability and, furthermore, require a large contact force. Magnetoresistive heat switches are, except at very low temperatures, of very low efficiency. Heat switches operated by the heat pipe principle usually require a long response time. A sealed gas gap heat switch operated by an adsorption pump has no mechanical motion and should provide the reliability and long lifetime required in long-term space missions. Another potential application of a heat switch is the thermal isolation of the optical plane during decontamination.

  13. Boosting the photocatalytic performance of (001) BiOI: enhancing donor density and separation efficiency of photogenerated electrons and holes.

    PubMed

    Fan, Wenjie; Li, Haibo; Zhao, Fengyi; Xiao, Xujing; Huang, Yongchao; Ji, Hongbing; Tong, Yexiang

    2016-04-18

    Herein, we demonstrate a simple strategy to boost the photocatalytic performance of BiOI by introducing oxygen defects into the BiOI. The oxygen-deficient BiOI exhibits superior photocatalytic performance for the degradation of formaldehyde gas. The enhancement of photocatalytic activity is due to the enhanced separation and migration efficiency of photogenerated electrons and holes.

  14. Gas-phase chemiluminescence and chemi-ionization

    SciTech Connect

    Fontijn, A.

    1985-01-01

    The phenomena of chemiluminescence (or more broadly chemi-excitation) and chemi-ionization have major similarities from a fundamental kinetic and dynamic point of view. However, since the former has primarily been investigated using optical spectroscopic techniques and the latter largely by mass spectroscopic (and other gaseous electronic) methods, the two phenomena have apparently never, explicitly been discussed together in one volume. In addition to a number of review articles on each individual subject, several meetings and books have had chemiluminescence and bioluminescence as their theme and those have been dominated by condensed phase work. On the other hand, chemi-ionization is often discussed in the contest of gaseous electronics, plasma chemistry and combustion. It is the goal of this book to present a more unified understanding of the two phenomena.

  15. Amphipols Outperform Dodecylmaltoside Micelles in Stabilizing Membrane Protein Structure in the Gas Phase

    PubMed Central

    2014-01-01

    Noncovalent mass spectrometry (MS) is emerging as an invaluable technique to probe the structure, interactions, and dynamics of membrane proteins (MPs). However, maintaining native-like MP conformations in the gas phase using detergent solubilized proteins is often challenging and may limit structural analysis. Amphipols, such as the well characterized A8-35, are alternative reagents able to maintain the solubility of MPs in detergent-free solution. In this work, the ability of A8-35 to retain the structural integrity of MPs for interrogation by electrospray ionization-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS) is compared systematically with the commonly used detergent dodecylmaltoside. MPs from the two major structural classes were selected for analysis, including two β-barrel outer MPs, PagP and OmpT (20.2 and 33.5 kDa, respectively), and two α-helical proteins, Mhp1 and GalP (54.6 and 51.7 kDa, respectively). Evaluation of the rotationally averaged collision cross sections of the observed ions revealed that the native structures of detergent solubilized MPs were not always retained in the gas phase, with both collapsed and unfolded species being detected. In contrast, ESI-IMS-MS analysis of the amphipol solubilized MPs studied resulted in charge state distributions consistent with less gas phase induced unfolding, and the presence of lowly charged ions which exhibit collision cross sections comparable with those calculated from high resolution structural data. The data demonstrate that A8-35 can be more effective than dodecylmaltoside at maintaining native MP structure and interactions in the gas phase, permitting noncovalent ESI-IMS-MS analysis of MPs from the two major structural classes, while gas phase dissociation from dodecylmaltoside micelles leads to significant gas phase unfolding, especially for the α-helical MPs studied. PMID:25495802

  16. Probing the energetics of dissociation of carbonic anhydrase-ligand complexes in the gas phase.

    PubMed Central

    Gao, J; Wu, Q; Carbeck, J; Lei, Q P; Smith, R D; Whitesides, G M

    1999-01-01

    This paper describes the use of electrospray ionization-Fourier transform ion cyclotron mass spectrometry (ESI-FTICR-MS) to study the relative stabilities of noncovalent complexes of carbonic anhydrase II (CAII, EC 4.2.1.1) and benzenesulfonamide inhibitors in the gas phase. Sustained off-resonance irradiation collision-induced dissociation (SORI-CID) was used to determine the energetics of dissociation of these CAII-sulfonamide complexes in the gas phase. When two molecules of a benzenesulfonamide (1) were bound simultaneously to one molecule of CAII, one of them was found to exhibit significantly weaker binding (DeltaE50 = 0.4 V, where E50 is defined as the amplitude of sustained off-resonance irradiation when 50% of the protein-ligand complexes are dissociated). In solution, the benzenesulfonamide group coordinates as an anion to a Zn(II) ion bound at the active site of the enzyme. The gas phase stability of the complex with the weakly bound inhibitor was the same as that of the inhibitor complexed with apoCAII (i.e., CAII with the Zn(II) ion removed from the binding site). These results indicate that specific interactions between the sulfonamide group on the inhibitor and the Zn(II) ion on CAII were preserved in the gas phase. Experiments also showed a higher gas phase stability for the complex of para-NO2-benzenesulfonamide-CAII than that for ortho-NO2-benzenesulfonamide-CAII complex. This result further suggests that steric interactions of the inhibitors with the binding pocket of CAII parallel those in solution. Overall, these results are consistent with the hypothesis that CAII retains, at least partially, the structure of its binding pocket in the gas phase on the time scale (seconds to minutes) of the ESI-FTICR measurements. PMID:10354450

  17. Studies of cluster-assembled materials: From gas phase to condensed phase

    NASA Astrophysics Data System (ADS)

    Gao, Lin

    . After being mass gated in a reflectron equipped time-of-flight mass spectrometer (TOF-MS) and deposited onto TEM grids, the resultant specimens can be loaded onto high-resolution TEM investigation via electron diffraction. In conclusion, soft-landing of mass selected clusters has been shown to be a successful approach to obtain structural information on Zr-Met-Car cluster-assembled materials collected from the gas phase. TEM images indicate the richness of the morphologies associated with these cluster crystals. However, passivation methods are expected to be examined further to overcome the limited stabilities of these novel clusters. From this initial study, it's shown the promising opportunity to study other Met-Cars species and more cluster-based materials. Experimental results of reactions run with a solvothermal synthesis method obtained while searching for new Zr-C cluster assembled materials, are reported. One unexpected product in single crystal form was isolated and tentatively identified by X-ray diffraction to be [Zr6i O(OH)O12·2(Bu)4], with space group P2 1/n and lattice parameters of a = 12.44 A, b = 22.06 A, c = 18.40 A, alpha = 90°, beta = 105°, gamma = 90°, V = 4875 A3 and R 1 = 3.15% for the total observed data (I ≥ 2 sigma I) and oR2 = 2.82%. This novel hexanuclear Zr(IV)-oxo-hydroxide cluster anion may be the first member in polyoxometalates class with metal atoms from the IVB group and having Oh symmetry. Alternatively, it may be the first member in {[(Zr6Z)X 12]X6}m- class with halides replaced by oxo- and hydroxyl groups and with an increased oxidation state of Zr. It is predicted to bear application potentials directed by both families. This work could suggest a direction in which the preparation of Zr-C cluster-assembled materials in a liquid environment may be eventually fulfilled. 1,3-Bis(diethylphosphino)propane (depp) protected small gold clusters are studied via multiple techniques, including Electrospray Ionization Mass Spectrometry

  18. Plasma-produced phase-pure cuprous oxide nanowires for methane gas sensing

    SciTech Connect

    Cheng, Qijin Zhang, Fengyan; Yan, Wei; Randeniya, Lakshman; Ostrikov, Kostya

    2014-03-28

    Phase-selective synthesis of copper oxide nanowires is warranted by several applications, yet it remains challenging because of the narrow windows of the suitable temperature and precursor gas composition in thermal processes. Here, we report on the room-temperature synthesis of small-diameter, large-area, uniform, and phase-pure Cu{sub 2}O nanowires by exposing copper films to a custom-designed low-pressure, thermally non-equilibrium, high-density (typically, the electron number density is in the range of 10{sup 11}–10{sup 13} cm{sup −3}) inductively coupled plasmas. The mechanism of the plasma-enabled phase selectivity is proposed. The gas sensors based on the synthesized Cu{sub 2}O nanowires feature fast response and recovery for the low-temperature (∼140 °C) detection of methane gas in comparison with polycrystalline Cu{sub 2}O thin film-based gas sensors. Specifically, at a methane concentration of 4%, the response and the recovery times of the Cu{sub 2}O nanowire-based gas sensors are 125 and 147 s, respectively. The Cu{sub 2}O nanowire-based gas sensors have a potential for applications in the environmental monitoring, chemical industry, mining industry, and several other emerging areas.

  19. Direct Numerical Simulation of biomass pyrolysis and combustion with gas phase reactions

    NASA Astrophysics Data System (ADS)

    Awasthi, A.; Kuerten, J. G. M.; Geurts, B. J.

    2016-09-01

    We present Direct Numerical Simulation of biomass pyrolysis and combustion in a turbulent channel flow. The model includes simplified models for biomass pyrolysis and char combustion along with a model for particle tracking. The gas phase is modelled as a mixture of reacting gas species. The gas-particle interactions for mass, momentum, and energy exchange are included by two-way coupling terms. The effect of two-way coupling on the conversion time of biomass particles is found noticeable for particle volume fractions > 10-5. We also observe that at constant volume fraction the effect of two-way coupling increases as the particle size is reduced, due to the higher total heat exchange area in case of smaller particles. The inclusion of gas phase homogeneous reactions in the DNS model decreases the biomass pyrolysis time due to higher gas temperatures. In contrast, including gas phase reactions increases the combustion time of biomass due to the lower concentration of oxygen at the particle surface.

  20. Distribution of Organophosphate Esters between the Gas and Particle Phase-Model Predictions vs Measured Data.

    PubMed

    Sühring, Roxana; Wolschke, Hendrik; Diamond, Miriam L; Jantunen, Liisa M; Scheringer, Martin

    2016-07-05

    Gas-particle partitioning is one of the key factors that affect the environmental fate of semivolatile organic chemicals. Many organophosphate esters (OPEs) have been reported to primarily partition to particles in the atmosphere. However, because of the wide range of their physicochemical properties, it is unlikely that OPEs are mainly in the particle phase "as a class". We compared gas-particle partitioning predictions for 32 OPEs made by the commonly used OECD POV and LRTP Screening Tool ("the Tool") with the partitioning models of Junge-Pankow (J-P) and Harner-Bidleman (H-B), as well as recently measured data on OPE gas-particle partitioning. The results indicate that half of the tested OPEs partition into the gas phase. Partitioning into the gas phase seems to be determined by an octanol-air partition coefficient (log KOA) < 10 and a subcooled liquid vapor pressure (log PL) > -5 (PL in Pa), as well as the total suspended particle concentration (TSP) in the sampling area. The uncertainty of the physicochemical property data of the OPEs did not change this estimate. Furthermore, the predictions by the Tool, J-P- and H-B-models agreed with recently measured OPE gas-particle partitioning.

  1. Band alignment and enhanced photocatalytic activation of α/β-Bi2O3 heterojunctions via in situ phase transformation.

    PubMed

    Shan, Lianwei; Wang, Guilin; Li, Dan; San, Xingyuan; Liu, Lizhu; Dong, Limin; Wu, Ze

    2015-05-07

    The assembling heterojunction, one of the key topics in photocatalysts and semiconductors (SCs), is generally accomplished in at least two steps, of which the first step is the synthesis of a matrix, and then the growth of the second phase on the matrix. Herein we present the preparation of α/β-Bi2O3 heterojunctions by an in situ phase transformation technique. Under normal pressure, a facile citrate method was used to synthesize β-Bi2O3 nanosheets and α/β-Bi2O3 heterojunctions. The novel features of the process are the mild operating conditions by an appropriate selection of heat treatment temperature and time. Using transmission electron microscopy (TEM), we found that a number of nano-sized α-Bi2O3 form on the β-Bi2O3 nanosheet via a controlled β→α phase transition, generating a large number of heterojunctions. The CM1 (calcining β-Bi2O3 precursor at 363 °C for 4 h) heterojunction achieves a strong visible light absorption and dye absorption capacity and produces a very high reaction rate for Rhodamine B (RhB) photodegradation. Electrochemical impedance spectroscopy (EIS) revealed excellent charge transfer characteristics of the heterojunction, which accounts for its high photoactivity. Using the X-ray electron valence band spectra, it is found that the valence band of α-Bi2O3 is more negative than that of β-Bi2O3. Thus, in heterojunctions, the photogenerated holes in β-Bi2O3 are transferred to α-Bi2O3 with good charge transport characteristics by the intrinsic driving force in the interface field. Furthermore, a separated hole can accomplish a transfer process from α-Bi2O3 to the aqueous solution within its lifetime due to the diameter of α-Bi2O3 being less than 17.6 nm.

  2. Characterization of annular two-phase gas-liquid flows in microgravity

    NASA Astrophysics Data System (ADS)

    Bousman, W. Scott; McQuillen, John B.

    1994-08-01

    A series of two-phase gas-liquid flow experiments were developed to study annular flows in microgravity using the NASA Lewis Learjet. A test section was built to measure the liquid film thickness around the perimeter of the tube permitting the three dimensional nature of the gas-liquid interface to be observed. A second test section was used to measure the film thickness, pressure drop and wall shear stress in annular microgravity two-phase flows. Three liquids were studied to determine the effects of liquid viscosity and surface tension. The result of this study provide insight into the wave characteristics, pressure drop and droplet entrainment in microgravity annular flows.

  3. Study of Hind Limb Tissue Gas Phase Formation in Response to Suspended Adynamia and Hypokinesia

    NASA Technical Reports Server (NTRS)

    Butler, Bruce D.

    1996-01-01

    The purpose of this study was to investigate the hypothesis that reduced joint/muscle activity (hypo kinesia) as well as reduced or null loading of limbs (adynamia) in gravity would result in reduced decompression-induced gas phase and symptoms of decompression sickness (DCS). Finding a correlation between the two phenomena would correspond to the proposed reduction in tissue gas phase formation in astronauts undergoing decompression during extravehicular activity (EVA) in microgravity. The observation may further explain the reported low incidence of DCS in space.

  4. Gas-phase reactions in extraterrestrial environments: laboratory investigations by crossed molecular beams.

    PubMed

    Balucani, Nadia; Casavecchia, Piergiorgio

    2006-12-01

    We have investigated gas-phase reactions of N((2)D) with the most abundant hydrocarbons in the atmosphere of Titan by the crossed molecular beam technique. In all cases, molecular products containing a novel CN bond are formed, thus suggesting possible routes of formation of gas-phase nitriles in the atmosphere of Titan and primordial Earth. The same approach has been recently extended to the study of radical-radical reactions, such as the reaction of atomic oxygen with the CH(3) and C(3)H(5) radicals. Products other than those already considered in the modeling of planetary atmospheres and interstellar medium have been identified.

  5. Gas phase infrared spectra and corresponding DFT calculations of α, ω-diphenylpolyenes

    NASA Astrophysics Data System (ADS)

    Biemann, Lars; Braun, Michaela; Kleinermanns, Karl

    2010-01-01

    We present gas phase Fourier Transform Infrared (FTIR) spectra of the homologue series of α, ω-diphenylpolyenes consisting of trans- and cis-stilbene, diphenylbutadiene (DPB) and diphenylhexatriene (DPH) obtained by a fast thermal heating technique that enables vaporization without decomposition. Infrared marker bands for the cis-isomers of the polyenes have been identified by density functional calculations at the B3LYP/TZVP level of theory. The all trans isomers of DPB and DPH do not interconvert to the cis-isomers in the gas phase at 200 °C.

  6. Characterization of annular two-phase gas-liquid flows in microgravity

    NASA Technical Reports Server (NTRS)

    Bousman, W. Scott; Mcquillen, John B.

    1994-01-01

    A series of two-phase gas-liquid flow experiments were developed to study annular flows in microgravity using the NASA Lewis Learjet. A test section was built to measure the liquid film thickness around the perimeter of the tube permitting the three dimensional nature of the gas-liquid interface to be observed. A second test section was used to measure the film thickness, pressure drop and wall shear stress in annular microgravity two-phase flows. Three liquids were studied to determine the effects of liquid viscosity and surface tension. The result of this study provide insight into the wave characteristics, pressure drop and droplet entrainment in microgravity annular flows.

  7. A microcomputer-controlled gas phase microreactor system

    SciTech Connect

    Morris, R.M.

    1983-08-01

    Although automated reactors are effective tools for studying a single type of reaction or optimizing catalyst performance, they may not be well suited for exploratory research. These reactors generally have several shortcomings. First, they may have limited versatility since they are usually designed with a single application in mind. Second, computer systems used for process control and data acquisition are often expensive and complex, so that once they are set up for a given application, it is quite difficult to adapt them for another. Because of these restrictions, experimental reactors are often operated manually, requiring a full-time operator to monitor operations and acquire data. This is a greater problem in laboratories where projects are often short-term, and the costs of setting up an automated reactor may outweigh the benefits of automation. For an automated reactor to be cost-effective in such an environment, both reactor hardware and control software must be versatile enough that they can be easily modified and adapted for different experiments. An automated gas-flow microreactor has been designed and constructed which is both inexpensive and flexible. The reactor is capable of performing three different types of experiments, 1) continuous reagent feed with analysis of the product stream, 2) pulsed-flow experiments, and 3) temperature-programmed desorption (TPD) and reaction (TPR). Conversion of the reactor from one configuration to another requires less than one hour. Process control and data acquisition are performed using an Apple II Plus microcomputer (Apple Computer Corp., Cupertino, Calif.) and an ISAAC interface device (Cyborg Corp., Newton, Mass.).

  8. Measurements of liquid-phase turbulence in gas-liquid two-phase flows using particle image velocimetry

    NASA Astrophysics Data System (ADS)

    Zhou, Xinquan; Doup, Benjamin; Sun, Xiaodong

    2013-12-01

    Liquid-phase turbulence measurements were performed in an air-water two-phase flow loop with a circular test section of 50 mm inner diameter using a particle image velocimetry (PIV) system. An optical phase separation method--planar laser-induced fluorescence (PLIF) technique—which uses fluorescent particles and an optical filtration technique, was employed to separate the signals of the fluorescent seeding particles from those due to bubbles and other noises. An image pre-processing scheme was applied to the raw PIV images to remove the noise residuals that are not removed by the PLIF technique. In addition, four-sensor conductivity probes were adopted to measure the radial distribution of the void fraction. Two benchmark tests were performed: the first was a comparison of the PIV measurement results with those of similar flow conditions using thermal anemometry from previous studies; the second quantitatively compared the superficial liquid velocities calculated from the local liquid velocity and void fraction measurements with the global liquid flow rate measurements. The differences of the superficial liquid velocity obtained from the two measurements were bounded within ±7% for single-phase flows and two-phase bubbly flows with the area-average void fraction up to 18%. Furthermore, a preliminary uncertainty analysis was conducted to investigate the accuracy of the two-phase PIV measurements. The systematic uncertainties due to the circular pipe curvature effects, bubble surface reflection effects and other potential uncertainty sources of the PIV measurements were discussed. The purpose of this work is to facilitate the development of a measurement technique (PIV-PLIF) combined with image pre-processing for the liquid-phase turbulence in gas-liquid two-phase flows of relatively high void fractions. The high-resolution data set can be used to more thoroughly understand two-phase flow behavior, develop liquid-phase turbulence models, and assess high

  9. Modeling the final phase of landfill gas generation from long-term observations.

    PubMed

    Tintner, Johannes; Kühleitner, Manfred; Binner, Erwin; Brunner, Norbert; Smidt, Ena

    2012-06-01

    For waste management, methane emissions from landfills and their effect on climate change are of serious concern. Current models for biogas generation that focus on the economic use of the landfill gas are usually based on first order chemical reactions (exponential decay), underestimating the long-term emissions of landfills. The presented study concentrated on the curve fitting and the quantification of the gas generation during the final degradation phase under optimal anaerobic conditions. For this purpose the long-term gas generation (240-1,830 days) of different mechanically biologically treated (MBT) waste materials was measured. In this study the late gas generation was modeled by a log-normal distribution curve to gather the maximum gas generation potential. According to the log-normal model the observed gas sum curve leads to higher values than commonly used exponential decay models. The prediction of the final phase of landfill gas generation by a fitting model provides a basis for CO(2) balances in waste management and some information to which extent landfills serve as carbon sink.

  10. Molecular simulation of excess isotherm and excess enthalpy change in gas-phase adsorption.

    PubMed

    Do, D D; Do, H D; Nicholson, D

    2009-01-29

    We present a new approach to calculating excess isotherm and differential enthalpy of adsorption on surfaces or in confined spaces by the Monte Carlo molecular simulation method. The approach is very general and, most importantly, is unambiguous in its application to any configuration of solid structure (crystalline, graphite layer or disordered porous glass), to any type of fluid (simple or complex molecule), and to any operating conditions (subcritical or supercritical). The behavior of the adsorbed phase is studied using the partial molar energy of the simulation box. However, to characterize adsorption for comparison with experimental data, the isotherm is best described by the excess amount, and the enthalpy of adsorption is defined as the change in the total enthalpy of the simulation box with the change in the excess amount, keeping the total number (gas + adsorbed phases) constant. The excess quantities (capacity and energy) require a choice of a reference gaseous phase, which is defined as the adsorptive gas phase occupying the accessible volume and having a density equal to the bulk gas density. The accessible volume is defined as the mean volume space accessible to the center of mass of the adsorbate under consideration. With this choice, the excess isotherm passes through a maximum but always remains positive. This is in stark contrast to the literature where helium void volume is used (which is always greater than the accessible volume) and the resulting excess can be negative. Our definition of enthalpy change is equivalent to the difference between the partial molar enthalpy of the gas phase and the partial molar enthalpy of the adsorbed phase. There is no need to assume ideal gas or negligible molar volume of the adsorbed phase as is traditionally done in the literature. We illustrate this new approach with adsorption of argon, nitrogen, and carbon dioxide under subcritical and supercritical conditions.

  11. An approximate calculation of advective gas-phase transport of 14C at Yucca Mountain, Nevada

    NASA Astrophysics Data System (ADS)

    Knapp, R. B.

    1990-01-01

    A quasilinear partial differential equation, which describes gas-phase transport of a 14C kinematic wave through a porous medium, is derived, its sensitivity to system variables is analyzed and it is applied to one possible release scenarion at the porposed Yucca Mountain, Nevada high-level radioactive waste repository. Advection, isotope exchange between CO 2 in a flowing gas phase and HCO 3- in a static aqueous phase, and radioactive decay are incorporated. The governing equation is solved analytically by the method of characteristics. The mass fraction of 14C in the gas phase,X 14g, is controlled by radioactive decay. The relatively long half-line of 14C, about 5720 years, and the relatively shallow proposed burial depth of the radioactive waste, about 350m, requires significant retardation of the 14C wave velocity for significant reduction in X 14g. 14C wave velocity is most sensitive to temperature and pH which control the distribution of total carbon between gas and liquid phase; the greater the partitioning of carbon into the liquid phase, the greater the retardation of the 14C wave velocity and the greater the ultimate reduction in X 14g from initial conditions. Partitioning of total carbon into the liquid phase is greatest at low temperatures, < 100° C, and high pH values, > 8. Increasing water saturation also tends to retard 14C wave velocity but to a lesser extent. The governing equation has been applied using conditions that may possibly occur at the proposed Yucca Mountain repository. Calculations indicate that the 14C wave takes about 5900 years to reach the surface with a X 14g equal to 25 ppm. Diffusion and dispersion are not of major importance for these conditions. These calculations are approximate due to the number of assumptions involved. Discharge of 14C into the gas before the selected time would accelerate wave arrival and increase the amount of 14C reaching the surface.

  12. Effect of liquid distribution on gas-water phase mass transfer in an unsaturated sand during infiltration

    NASA Astrophysics Data System (ADS)

    Imhoff, Paul T.; Jaffé, Peter R.

    1994-09-01

    Gas-water phase mass transfer was examined in a homogeneous sand with both the gas and water phase mobile: water was infiltrated from the top of the sand column while benzene-laden air flowed upward from the bottom. Mass-transfer limitations for this situation may be important for applications of bioventing, where water and nutrients are added at the ground surface simultaneously with induced air movement to carry oxygen and volatile organics to microbial populations. Gas- and water-phase samples indicate that gas-water phase mass transfer was sufficiently fast that equilibrium between gas and water phases was achieved at all sampling locations within the porous medium. Lower-bound estimates for the gas-water mass-transfer rate coefficient show that mass transfer was at least 10-40 times larger than predictions made from an empirical model developed for gas-water phase mass transfer in an identical porous medium. A water-phase tracer test demonstrates that water flow was much more uniform in this study than in those earlier experiments, which is a likely explanation for the differing rates of gas-water phase mass transfer. It is hypothesized that the liquid distribution in previous laboratory experiments was less uniform because of preferential flow paths due to wetting front instabilities. Gas-water phase mass-transfer rate coefficients reported in this investigation are for an ideal situation of uniform water infiltration: mass-transfer rates in field soils are expected to be significantly smaller.

  13. Tricrystalline TiO2 with enhanced photocatalytic activity and durability for removing volatile organic compounds from indoor air.

    PubMed

    Chen, Kunyang; Zhu, Lizhong; Yang, Kun

    2015-06-01

    It is important to develop efficient and economic techniques for removing volatile organic compounds (VOCs) in indoor air. Heterogeneous TiO2-based semiconductors are a promising technology for achieving this goal. Anatase/brookite/rutile tricrystalline TiO2 with mesoporous structure was synthesized by a low-temperature hydrothermal route in the presence of HNO3. The obtained samples were characterized by X-ray diffraction and N2 adsorption-desorption isotherm. The photocatalytic activity was evaluated by photocatalytic decomposition of toluene in air under UV light illumination. The results show that tricrystalline TiO2 exhibited higher photocatalytic activity and durability toward gaseous toluene than bicrystalline TiO2, due to the synergistic effects of high surface area, uniform mesoporous structure and junctions among mixed phases. The tricrystalline TiO2 prepared at RHNO3=0.8, containing 80.7% anatase, 15.6% brookite and 3.7% rutile, exhibited the highest photocatalytic activity, about 3.85-fold higher than that of P25. The high activity did not significantly degrade even after five reuse cycles. In conclusion, it is expected that our study regarding gas-phase degradation of toluene over tricrystalline TiO2 will enrich the chemistry of the TiO2-based materials as photocatalysts for environmental remediation and stimulate further research interest on this intriguing topic.

  14. Coated mesh photocatalytic reactor for air treatment applications: comparative study of support materials.

    PubMed

    Passalía, Claudio; Nocetti, Emanuel; Alfano, Orlando; Brandi, Rodolfo

    2016-06-14

    An experimental comparative study of different meshes as support materials for photocatalytic applications in gas phase is presented. The photocatalytic oxidation of dichloromethane in air was addressed employing different coated meshes in a laboratory-scale, continuous reactor. Two fiberglass meshes and a stainless steel mesh were studied regarding the catalyst load, adherence, and catalytic activity. Titanium dioxide photocatalyst was immobilized on the meshes by dip-coating cycles. Results indicate the feasibility of the dichloromethane elimination in the three cases. When the number of coating cycles was doubled, the achieved conversion levels were increased twofold for stainless steel and threefold for the fiberglass meshes. One of the fiberglass meshes (FG2) showed the highest reactivity per mass of catalyst and per catalytic surface area.

  15. In situ measurements of gas/particle-phase transitions for atmospheric semivolatile organic compounds

    PubMed Central

    Williams, Brent J.; Goldstein, Allen H.; Kreisberg, Nathan M.; Hering, Susanne V.

    2010-01-01

    An understanding of the gas/particle-phase partitioning of semivolatile compounds is critical in determining atmospheric aerosol formation processes and growth rates, which in turn affect global climate and human health. The Study of Organic Aerosol at Riverside 2005 campaign was performed to gain a better understanding of the factors responsible for aerosol formation and growth in Riverside, CA, a region with high concentrations of secondary organic aerosol formed through the phase transfer of low-volatility reaction products from the oxidation of precursor gases. We explore the ability of the thermal desorption aerosol gas chromatograph (TAG) to measure gas-to-particle-phase transitioning for several organic compound classes (polar and nonpolar) found in the ambient Riverside atmosphere by using in situ observations of several hundred semivolatile organic compounds. Here we compare TAG measurements to modeled partitioning of select semivolatile organic compounds. Although TAG was not designed to quantify the vapor phase of semivolatile organics, TAG measurements do distinguish when specific compounds are dominantly in the vapor phase, are dominantly in the particle phase, or have both phases present. Because the TAG data are both speciated and time-resolved, this distinction is sufficient to see the transition from vapor to particle phase as a function of carbon number and compound class. Laboratory studies typically measure the phase partitioning of semivolatile organic compounds by using pure compounds or simple mixtures, whereas hourly TAG phase partitioning measurements can be made in the complex mixture of thousands of polar/nonpolar and organic/inorganic compounds found in the atmosphere. PMID:20142511

  16. Effect of surfactants on gas holdup of two-phase bubble columns

    SciTech Connect

    Estevez, L.A. ); Saez, E.; Pachino, J.; Cavicchioli, I. )

    1988-01-01

    Two-phase experiments have been carried out using organic liquids with a surfactant and air in a bubble column 30 (cm) inside diameter and 3 (m) tall. Under the presence of the surfactant, two distinct regions are observed: a bubbling region is the lower part, and a froth zone in the upper part of the column. Intrinsic gas holdups were measured in each region. Results showed that intrinsic gas holdup did not change significantly with surfactant concentration. However, the position of the limiting surface separating the two regions varied considerably with surfactant concentration, thus affecting strongly the overall gas holdup. Based on the described experimental observations, correlations for intrinsic and overall gas holdups have been proposed. Intrinsic gas holdups have been correlated and a function of gas and liquid superficial velocities, and not as functions of surfactant concentration. Overall gas holdups have been expressed in terms of intrinsic gas holdup and of the fraction PHI of the column that is occupied by the froth region. The variable PHI is the one that has been correlated in terms of the surfactant concentration.

  17. Photocatalytic water splitting

    NASA Astrophysics Data System (ADS)

    Kuo, Yenting

    New photocatalystic materials Ti-In oxy(nitride) and nanosized Ru-loaded strontium titanate doped with Rh (Ru/SrTiO3:Rh) have been synthesized. The textural and surface characteristic properties were studied by nitrogen BET analysis, diffuse reflectance UV-vis spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy and powder XRD. The photocatalytic properties were enhanced by the binary metal oxides of titanium dioxide and indium oxide. The XRD patterns confirmed the oxygen exchange between two metal oxides during the synthesis. Moreover, the presence of titanium dioxide can help the stabilization of InN during hot NH3(g) treatment. On the other hand, the particle sizes of aerogel prepared Ru/SrTiO3:Rh varied from 12 to 25 nm depended on different Rh doping. A mixture of ethanol and toluene was found to be the best binary solvent for supercritical drying, which yielded a SrTiO3 sample with a surface area of 130 m2/g and an average crystallite size of 6 nm. Enhanced photocatalytic hydrogen production under UV-vis light irradiation was achieved by ammonolysis of intimately mixed titanium dioxide and indium oxide at high temperatures. Gas chromatography monitored steadily the formation of hydrogen when sacrificial (methanol or ethanol) were present. XRD patterns confirmed that the photocatalysts maintain crystalline integrity before and after water splitting experiments. Moreover, the presence of InN may be crucial for the increase of hydrogen production activities. These Ru/SrTiO3:Rh photocatalysts have been studied for photocatalytic hydrogen production under visible light. The band gap of the bulk SrTiO 3 (3.2 eV) does not allow response to visible light. However, after doping with rhodium and loaded with ruthenium, the modified strontium titanates can utilize light above 400 nm due to the formation of valence band or electron donor levels inside of the band gap. Moreover, the surface areas of these

  18. SELECTIVE OXIDATION OF ALCOHOLS IN GAS PHASE USING LIGHT-ACTIVATED TITANIUM DIOXIDE

    EPA Science Inventory

    Selective oxidations of various primary and secondary alcohols were studied in a gas phase photochemical reactor using immobilized TiO2 catalyst. An annular photoreactor was used at 463K with an average contact time of 32sec. The system was found to be specifically suited for the...

  19. SPECIATION OF GAS-PHASE AND FINE PARTICLE EMISSIONS FROM BURNING OF FOLIAR FUELS

    EPA Science Inventory

    Particle size distributions (10-1000 nm aerodynamic diameter), physical and chemical properties of fine particle matter (PM2.5) with aerodynamic diameter <2.5 micrometers, and gas-phase emissions from controlled open burning of assorted taxa were measured. Chemical speciation of ...

  20. GAS-PHASE OXIDATION PRODUCTS OF BIPHENYL AND POLYCHLORINATED BIPHENYLS (R825377)

    EPA Science Inventory

    Our laboratory recently measured the gas-phase reaction rate constants of
    polychlorinated biphenyls (PCBs) with the hydroxyl radical (OH) and concluded
    that OH reactions are the primary removal pathway of PCBs from the atmosphere.
    With the reaction system previousl...

  1. Humidity independent mass spectrometry for gas phase chemical analysis via ambient proton transfer reaction.

    PubMed

    Zhu, Hongying; Huang, Guangming

    2015-03-31

    In this work, a humidity independent mass spectrometric method was developed for rapid analysis of gas phase chemicals. This method is based upon ambient proton transfer reaction between gas phase chemicals and charged water droplets, in a reaction chamber with nearly saturate humidity under atmospheric pressure. The humidity independent nature enables direct and rapid analysis of raw gas phase samples, avoiding time- and sample-consuming sample pretreatments in conventional mass spectrometry methods to control sample humidity. Acetone, benzene, toluene, ethylbenzene and meta-xylene were used to evaluate the analytical performance of present method. The limits of detection for benzene, toluene, ethylbenzene and meta-xylene are in the range of ∼0.1 to ∼0.3 ppbV; that of benzene is well below the present European Union permissible exposure limit for benzene vapor (5 μg m(-3), ∼1.44 ppbV), with linear ranges of approximately two orders of magnitude. The majority of the homemade device contains a stainless steel tube as reaction chamber and an ultrasonic humidifier as the source of charged water droplets, which makes this cheap device easy to assemble and facile to operate. In addition, potential application of this method was illustrated by the real time identification of raw gas phase chemicals released from plants at different physiological stages.

  2. OH REACTION KINETICS OF GAS-PHASE A- AND G-HEXACHLOROCYCLOHEXANE AND HEXACHLOROBENZENE. (R825377)

    EPA Science Inventory

    Rate constants for the gas-phase reactions of the hydroxyl
    radical (OH) with - and -hexachlorocyclohexane (-
    and Ozonation of coal vitrinites of different metamorphism degrees in gas and liquid phases

    SciTech Connect

    S.A. Semenova; Y.F. Patrakov

    2007-02-15

    The comparative analysis of the dynamics of accumulation of oxygen-containing groups in coals of different metamorphism degrees under their ozonation in the gas phase and in chloroform has been performed. The coals of the middle stage of metamorphism demonstrate the highest reactivity. The ozonation in chloroform proceeds with a higher intensity.

  3. Chemical studies of elements with Z ⩾ 104 in gas phase

    NASA Astrophysics Data System (ADS)

    Türler, Andreas; Eichler, Robert; Yakushev, Alexander

    2015-12-01

    Chemical investigations of superheavy elements in the gas-phase, i.e. elements with Z ≥ 104, allow assessing the influence of relativistic effects on their chemical properties. Furthermore, for some superheavy elements and their compounds quite unique gas-phase chemical properties were predicted. The experimental verification of these properties yields supporting evidence for a firm assignment of the atomic number. Prominent examples are the high volatility observed for HsO4 or the very weak interaction of Cn with gold surfaces. The unique properties of HsO4 were exploited to discover the doubly-magic even-even nucleus 270Hs and the new isotope 271Hs. The combination of kinematic pre-separation and gas-phase chemistry allowed gaining access to a new class of relatively fragile compounds, the carbonyl complexes of elements Sg through Mt. A not yet resolved issue concerns the interaction of Fl with gold surfaces. While competing experiments agree on the fact that Fl is a volatile element, there are discrepancies concerning its adsorption on gold surfaces with respect to its daughter Cn. The elucidation of these and other questions amounts to the fascination that gas-phase chemical investigations exert on current research at the extreme limits of chemistry today.

  4. Planar gas chromatography column on aluminum plate with multi-walled carbon nanotubes as stationary phase

    NASA Astrophysics Data System (ADS)

    Platonov, I. A.; Platonov, V. I.; Pavelyev, V. S.

    2016-04-01

    The high selectivity of the adsorption layer for low-boiling alkanes is shown, the separation factor (α) couple iso-butane / butane is 1.9 at a column temperature of 50 °C.The paper presents sorption and selective properties of planar gas chromatography column on aluminum plate with multi-walled carbon nanotubes as the stationary phase.

  5. Multiple Multidentate Halogen Bonding in Solution, in the Solid State, and in the (Calculated) Gas Phase.

    PubMed

    Jungbauer, Stefan H; Schindler, Severin; Herdtweck, Eberhardt; Keller, Sandro; Huber, Stefan M

    2015-09-21

    The binding properties of neutral halogen-bond donors (XB donors) bearing two multidentate Lewis acidic motifs toward halides were investigated. Employing polyfluorinated and polyiodinated terphenyl and quaterphenyl derivatives as anion receptors, we obtained X-ray crystallographic data of the adducts of three structurally related XB donors with tetraalkylammonium chloride, bromide, and iodide. The stability of these XB complexes in solution was determined by isothermal titration calorimetry (ITC), and the results were compared to X-ray analyses as well as to calculated binding patterns in the gas phase. Density functional theory (DFT) calculations on the gas-phase complexes indicated that the experimentally observed distortion of the XB donors during multiple multidentate binding can be reproduced in 1:1 complexes with halides, whereas adducts with two halides show a symmetric binding pattern in the gas phase that is markedly different from the solid state structures. Overall, this study demonstrates the limitations in the transferability of binding data between solid state, solution, and gas phase in the study of complex multidentate XB donors.

  6. Generation of naphthoquinone radical anions by electrospray ionization: solution, gas-phase, and computational chemistry studies.

    PubMed

    Vessecchi, Ricardo; Naal, Zeki; Lopes, José N C; Galembeck, Sérgio E; Lopes, Norberto P

    2011-06-02

    Radical anions are present in several chemical processes, and understanding the reactivity of these species may be described by their thermodynamic properties. Over the last years, the formation of radical ions in the gas phase has been an important issue concerning electrospray ionization mass spectrometry studies. In this work, we report on the generation of radical anions of quinonoid compounds (Q) by electrospray ionization mass spectrometry. The balance between radical anion formation and the deprotonated molecule is also analyzed by influence of the experimental parameters (gas-phase acidity, electron affinity, and reduction potential) and solvent system employed. The gas-phase parameters for formation of radical species and deprotonated species were achieved on the basis of computational thermochemistry. The solution effects on the formation of radical anion (Q(•-)) and dianion (Q(2-)) were evaluated on the basis of cyclic voltammetry analysis and the reduction potentials compared with calculated electron affinities. The occurrence of unexpected ions [Q+15](-) was described as being a reaction between the solvent system and the radical anion, Q(•-). The gas-phase chemistry of the electrosprayed radical anions was obtained by collisional-induced dissociation and compared to the relative energy calculations. These results are important for understanding the formation and reactivity of radical anions and to establish their correlation with the reducing properties by electrospray ionization analyses.

  7. Regio-Selective Intramolecular Hydrogen/Deuterium Exchange in Gas-Phase Electron Transfer Dissociation

    NASA Astrophysics Data System (ADS)

    Hamuro, Yoshitomo

    2017-02-01

    Protein backbone amide hydrogen/deuterium exchange mass spectrometry (HDX-MS) typically utilizes enzymatic digestion after the exchange reaction and before MS analysis to improve data resolution. Gas-phase fragmentation of a peptic fragment prior to MS analysis is a promising technique to further increase the resolution. The biggest technical challenge for this method is elimination of intramolecular hydrogen/deuterium exchange (scrambling) in the gas phase. The scrambling obscures the location of deuterium. Jørgensen's group pioneered a method to minimize the scrambling in gas-phase electron capture/transfer dissociation. Despite active investigation, the mechanism of hydrogen scrambling is not well-understood. The difficulty stems from the fact that the degree of hydrogen scrambling depends on instruments, various parameters of mass analysis, and peptide analyzed. In most hydrogen scrambling investigations, the hydrogen scrambling is measured by the percentage of scrambling in a whole molecule. This paper demonstrates that the degree of intramolecular hydrogen/deuterium exchange depends on the nature of exchangeable hydrogen sites. The deuterium on Tyr amide of neurotensin (9-13), Arg-Pro-Tyr-Ile-Leu, migrated significantly faster than that on Ile or Leu amides, indicating the loss of deuterium from the original sites is not mere randomization of hydrogen and deuterium but more site-specific phenomena. This more precise approach may help understand the mechanism of intramolecular hydrogen exchange and provide higher confidence for the parameter optimization to eliminate intramolecular hydrogen/deuterium exchange during gas-phase fragmentation.

  8. Methylation of 2-Naphthol Using Dimethyl Carbonate under Continuous-Flow Gas-Phase Conditions

    ERIC Educational Resources Information Center

    Tundo, Pietro; Rosamilia, Anthony E.; Arico, Fabio

    2010-01-01

    This experiment investigates the methylation of 2-naphthol with dimethyl carbonate. The volatility of the substrates, products, and co-products allows the reaction to be performed using a continuous-flow gas-phase setup at ambient pressure. The reaction uses catalytic quantities of base, achieves high conversion, produces little waste, and…

  9. Bond-Specific Dissociation Following Excitation Energy Transfer for Distance Constraint Determination in the Gas Phase

    PubMed Central

    2015-01-01

    Herein, we report chemistry that enables excitation energy transfer (EET) to be accurately measured via action spectroscopy on gaseous ions in an ion trap. It is demonstrated that EET between tryptophan or tyrosine and a disulfide bond leads to excited state, homolytic fragmentation of the disulfide bond. This phenomenon exhibits a tight distance dependence, which is consistent with Dexter exchange transfer. The extent of fragmentation of the disulfide bond can be used to determine the distance between the chromophore and disulfide bond. The chemistry is well suited for the examination of protein structure in the gas phase because native amino acids can serve as the donor/acceptor moieties. Furthermore, both tyrosine and tryptophan exhibit unique action spectra, meaning that the identity of the donating chromophore can be easily determined in addition to the distance between donor/acceptor. Application of the method to the Trpcage miniprotein reveals distance constraints that are consistent with a native-like fold for the +2 charge state in the gas phase. This structure is stabilized by several salt bridges, which have also been observed to be important previously in proteins that retain native-like structures in the gas phase. The ability of this method to measure specific distance constraints, potentially at numerous positions if combined with site-directed mutagenesis, significantly enhances our ability to examine protein structure in the gas phase. PMID:25174489

  10. Bond-specific dissociation following excitation energy transfer for distance constraint determination in the gas phase.

    PubMed

    Hendricks, Nathan G; Lareau, Nichole M; Stow, Sarah M; McLean, John A; Julian, Ryan R

    2014-09-24

    Herein, we report chemistry that enables excitation energy transfer (EET) to be accurately measured via action spectroscopy on gaseous ions in an ion trap. It is demonstrated that EET between tryptophan or tyrosine and a disulfide bond leads to excited state, homolytic fragmentation of the disulfide bond. This phenomenon exhibits a tight distance dependence, which is consistent with Dexter exchange transfer. The extent of fragmentation of the disulfide bond can be used to determine the distance between the chromophore and disulfide bond. The chemistry is well suited for the examination of protein structure in the gas phase because native amino acids can serve as the donor/acceptor moieties. Furthermore, both tyrosine and tryptophan exhibit unique action spectra, meaning that the identity of the donating chromophore can be easily determined in addition to the distance between donor/acceptor. Application of the method to the Trpcage miniprotein reveals distance constraints that are consistent with a native-like fold for the +2 charge state in the gas phase. This structure is stabilized by several salt bridges, which have also been observed to be important previously in proteins that retain native-like structures in the gas phase. The ability of this method to measure specific distance constraints, potentially at numerous positions if combined with site-directed mutagenesis, significantly enhances our ability to examine protein structure in the gas phase.

  11. The 'sticky business' of cleaning gas-phase membrane proteins: a detergent oriented perspective.

    PubMed

    Borysik, Antoni J; Robinson, Carol V

    2012-11-14

    In recent years the properties of gas-phase detergent clusters have come under close scrutiny due in part to their participation in the analysis of intact membrane protein complexes by mass spectrometry. The detergent molecules that cover the protein complex are removed in the gas-phase by thermally agitating the ions by collision-induced dissociation. This process however, is not readily controlled and can frequently result in the disruption of protein structure. Improved methods of releasing proteins from detergent clusters are clearly required. To facilitate this the structural properties of detergent clusters along with the mechanistic details of their dissociation need to be understood. Pivotal to understanding the properties of gas-phase detergent clusters is the technique of ion mobility mass spectrometry. This technique can be used to assign polydisperse detergent clusters and provide information about their geometries and packing densities. In this article we consider the shapes of detergent clusters and show that these clusters possess geometries that are inconsistent with those in solution. We analyse the distributions of clusters in detail using tandem mass spectrometry and suggest that the mean charge of clusters formed from certain detergents is governed by electrostatic repulsion. We discuss the dissociation of detergent clusters and propose that detergent evaporation it a key process in the protection of protein complexes during high energy collisions in the gas-phase.

  12. ECO LOGIC INTERNATIONAL GAS-PHASE CHEMICAL REDUCTION PROCESS - THE THERMAL DESORPTION UNIT - APPLICATIONS ANALYSIS REPORT

    EPA Science Inventory

    ELI ECO Logic International, Inc.'s Thermal Desorption Unit (TDU) is specifically designed for use with Eco Logic's Gas Phase Chemical Reduction Process. The technology uses an externally heated bath of molten tin in a hydrogen atmosphere to desorb hazardous organic compounds fro...

  13. Why do disk galaxies present a common gas-phase metallicity gradient?

    NASA Astrophysics Data System (ADS)

    Chang, R.; Zhang, Shuhui; Shen, Shiyin; Yin, Jun; Hou, Jinliang

    2017-03-01

    CALIFA data show that isolated disk galaxies present a common gas-phase metallicity gradient, with a characteristic slope of -0.1dex/re between 0.3 and 2 disk effective radius re (Sanchez et al. 2014). Here we construct a simple model to investigate which processes regulate the formation and evolution.

  14. Dominant factors controlling concentrations of aldehydes in rain, fog, dew water, and in the gas phase

    NASA Astrophysics Data System (ADS)

    Matsumoto, Kiyoshi; Kawai, Shunji; Igawa, Manabu

    Low-molecular weight aldehyde compounds in rain, fog, dew water, and in the gas phase were measured at urban and suburban mountain sites, to characterize the chemical composition of aldehydes in liquid droplets and in the gas phase in the ambient atmosphere, and discuss the factors controlling wet removal processes of aldehydes. Higher concentrations of total aldehydes were found in dew water than in rain and fog water due to the small amount of water volume. Both formaldehyde and acetaldehyde were detected as dominant aldehydes in the gas phase. Secondary formation processes are dominant sources for both aldehydes in the suburban site, whereas primary sources are relatively important for the urban atmosphere. In rainwater, by contrast, formaldehyde was the most abundant aldehyde, followed by glyoxal. Glyoxal was detected as the most dominant aldehyde in fog and dew water. Acetaldehyde was not detected as a main component in liquid droplets in spite of its abundance in the gas phase. Water solubility of each aldehyde compound and dilution effect by water are critical factors that control the compositions and concentrations of these aldehydes in ambient liquid droplets.

  15. Multi-scale symbolic time reverse analysis of gas-liquid two-phase flow structures

    NASA Astrophysics Data System (ADS)

    Wang, Hongmei; Zhai, Lusheng; Jin, Ningde; Wang, Youchen

    Gas-liquid two-phase flows are widely encountered in production processes of petroleum and chemical industry. Understanding the dynamic characteristics of multi-scale gas-liquid two-phase flow structures is of great significance for the optimization of production process and the measurement of flow parameters. In this paper, we propose a method of multi-scale symbolic time reverse (MSTR) analysis for gas-liquid two-phase flows. First, through extracting four time reverse asymmetry measures (TRAMs), i.e. Euclidean distance, difference entropy, percentage of constant words and percentage of reversible words, the time reverse asymmetry (TRA) behaviors of typical nonlinear systems are investigated from the perspective of multi-scale analysis, and the results show that the TRAMs are sensitive to the changing of dynamic characteristics underlying the complex nonlinear systems. Then, the MSTR analysis is used to study the conductance signals from gas-liquid two-phase flows. It is found that the multi-scale TRA analysis can effectively reveal the multi-scale structure characteristics and nonlinear evolution properties of the flow structures.

  16. Onset conditions for gas phase reaction and nucleation in the CVD of transition metal oxides

    NASA Technical Reports Server (NTRS)

    Collins, J.; Rosner, D. E.; Castillo, J.

    1992-01-01

    A combined experimental/theoretical study is presented of the onset conditions for gas phase reaction and particle nucleation in hot substrate/cold gas CVD of transition metal oxides. Homogeneous reaction onset conditions are predicted using a simple high activation energy reacting gas film theory. Experimental tests of the basic theory are underway using an axisymmetric impinging jet CVD reactor. No vapor phase ignition has yet been observed in the TiCl4/O2 system under accessible operating conditions (below substrate temperature Tw = 1700 K). The goal of this research is to provide CVD reactor design and operation guidelines for achieving acceptable deposit microstructures at the maximum deposition rate while simultaneously avoiding homogeneous reaction/nucleation and diffusional limitations.

  17. Finite-time thermodynamics and the gas-liquid phase transition

    NASA Astrophysics Data System (ADS)

    Santoro, M.; Schön, J. C.; Jansen, M.

    2007-12-01

    In this paper, we study the application of the concept of finite-time thermodynamics to first-order phase transitions. As an example, we investigate the transition from the gaseous to the liquid state by modeling the liquification of the gas in a finite time. In particular, we introduce, state, and solve an optimal control problem in which we aim at achieving the gas-liquid first-order phase transition through supersaturation within a fixed time in an optimal fashion, in the sense that the work required to supersaturate the gas, called excess work, is minimized by controlling the appropriate thermodynamic parameters. The resulting set of coupled nonlinear differential equations is then solved for three systems, nitrogen N2 , oxygen O2 , and water vapor H2O .

  18. Microfluidic generation of uniform water droplets using gas as the continuous phase.

    PubMed

    Jiang, Kunqiang; Lu, Annie Xi; Dimitrakopoulos, Panagiotis; DeVoe, Don L; Raghavan, Srinivasa R

    2015-06-15

    Microfluidic schemes for forming uniform aqueous microdroplets usually rely on contacting the aqueous liquid (dispersed phase) with an immiscible oil (continuous phase). Here, we demonstrate that the oil can be substituted with gas (nitrogen or air) while still retaining the ability to generate discrete and uniform aqueous droplets. Our device is a capillary co-flow system, with the inner flow of water getting periodically dispersed into droplets by the external flow of gas. The droplet size and different formation modes can be tuned by varying the liquid and gas flow rates. Importantly, we identify the range of conditions that correspond to the "dripping mode", i.e., where discrete droplets are consistently generated with no satellites. We believe this is a significant development that will be beneficial for chemical and biological applications requiring clean and contaminant-free droplets, including DNA amplification, drug encapsulation, and microfluidic cell culture.

  19. Chemical models of interstellar gas-grain processes. II - The effect of grain-catalysed methane on gas phase evolution

    NASA Technical Reports Server (NTRS)

    Brown, Paul D.; Charnley, S. B.

    1991-01-01

    The effects on gas phase chemistry which result from the continuous desorption of methane molecules from grain surfaces are studied. Significant and sustained enhancements in the abundances of several complex hydrocarbon molecules are found, in good agreement with their observed values in TMC-1. The overall agreement is, however, just as good for the case of zero CH4 desorption efficiency. It is thus impossible to determine from the models whether or not the grain-surface production of methane is responsible for the observed abundances of some hydrocarbon molecules.

  1. Design of composite photocatalyst of TiO2 and Y-zeolite for degradation of 2-propanol in the gas phase under UV and visible light irradiation.

    PubMed

    Kamegawa, Takashi; Ishiguro, Yasushi; Kido, Ryota; Yamashita, Hiromi

    2014-10-13

    Hydrophobic Y-zeolite (SiO2/Al2O3 = 810) and TiO2 composite photocatalysts were designed by using two different types of TiO2 precursors, i.e., titanium ammonium oxalate and ammonium hexafluorotitanate. The porous structure, surface property and state of TiO2 were investigated by various characterization techniques. By using an ammonium hexafluorotitanate as a precursor, hydrophobic modification of the Y-zeolite surface and realizing visible light sensitivity was successfully achieved at the same time after calcination at 773 K in the air. The prepared sample still maintained the porous structure of Y-zeolite and a large surface area. Highly crystalline anatase TiO2 was also formed on the Y-zeolite surface by the role of fluorine in the precursor. The usages of ammonium hexafluorotitanate were effective for the improvement of the photocatalytic performance of the composite in the degradation of 2-propanol in the gas phase under UV and visible light (λ > 420 nm) irradiation.

  2. Synergistic manipulation of micro-nanostructures and composition: anatase/rutile mixed-phase TiO2 hollow micro-nanospheres with hierarchical mesopores for photovoltaic and photocatalytic applications.

    PubMed

    Zhu, Qing; Qian, Jieshu; Pan, Hao; Tu, Luo; Zhou, Xingfu

    2011-09-30

    The construction of nanocrystals with controllable composition and desirable micro-nanostructures is a well-known challenge. A combination of favorable composition and optimized micro-nanostructures can enhance the performance of a material significantly. Using TiO(2) as an example, we demonstrate here a facile approach to prepare anatase/rutile mixed-phase TiO(2) hollow micro-nanospheres with hierarchical mesopores. Our strategy relies on polymer-assisted assembly of ∼ 5 nm nano-building blocks into three-dimensional hierarchical hollow micro-nanospheres in a mixed alcohol-water solution. This superior micro-nanostructure endows the sample with hierarchical mesopores and a high surface area of 106 m(2) g(-1). We also show that, due to the synergetic effects of the mixed-phase composition and the micro-nanostructures, the sample exhibited significantly improved photovoltaic performance and similar photocatalytic performance compared with the commercial Degussa P25. These results suggested that our sample has great potential for future photovoltaic and photocatalytic applications.

  3. Anatase TiO2 sheet-assisted synthesis of Ti(3+) self-doped mixed phase TiO2 sheet with superior visible-light photocatalytic performance: Roles of anatase TiO2 sheet.

    PubMed

    Zhang, Xiaojie; Zuo, Guoqing; Lu, Xin; Tang, Changqing; Cao, Shuo; Yu, Miao

    2017-03-15

    On the basis of measurements, such as field emission scanning electron microscope, UV-Vis diffuse reflectance spectra, X-ray diffraction, electron paramagnetic resonance, photoluminescence spectra, and photocurrent measurements, the roles of anatase TiO2 sheet on synthesizing Ti(3+) self-doped mixed phase TiO2 nanosheets (doped TiO2 (A/R, TiO2 (A))) and on improving the performance for photocatalytic CO2 reduction were explored systematically. High surface area anatase TiO2 nanosheets (TiO2 (A)) as a substrate, structure directing agent, and inhibitor, mediated the synthesis of Ti(3+) self-doped mixed phase TiO2 nanosheets. Addition of TiO2 (A) significantly improved not only visible light absorption of doped TiO2 (A/R, TiO2 (A)), but also the efficiency of photo-excited charges separations due to the existence of interfacial regions of anatase-rutile TiO2 junctions. Finally, a possible mechanism for interfacial charge transfer at the anatase-rutile TiO2 interface and for photocatalytic CO2 reduction over Pt loaded doped TiO2 (A/R, TiO2 (A)) were proposed.

  4. Influence of the coulomb interaction on the liquid-gas phase transition and nuclear multifragmentation.

    PubMed

    Gulminelli, F; Chomaz, Ph; Raduta, Al H; Raduta, Ad R

    2003-11-14

    The liquid-gas phase transition is analyzed from the topologic properties of the event distribution in the observables space. A multicanonical formalism allows one to directly relate the standard phase transition with neutral particles to the case where the nonsaturating Coulomb interaction is present, and to interpret the Coulomb effect as a deformation of the probability distributions and a rotation of the order parameter. This formalism is applied to a statistical multifragmentation model and consequences for the nuclear multifragmentation phase transitions are drawn.

  5. Comparison of different gas-phase mechanisms and aerosol modules for simulating particulate matter formation.

    PubMed

    Kim, Youngseob; Couvidat, Florian; Sartelet, Karine; Seigneur, Christian

    2011-11-01

    The effects of two gas-phase chemical kinetic mechanisms, Regional Atmospheric Chemistry Mechanism version 2 (RACM2) and Carbon-Bond 05 (CB05), and two secondary organic aerosol (SOA) modules, the Secondary Organic Aerosoi Model (SORGAM) and AER/EPRI/Caltech model (AEC), on fine (aerodynamic diameter < or =2.5 microm) particulate matter (PM2.5) formation is studied. The major sources of uncertainty in the chemistry of SOA formation are investigated. The use of all major SOA precursors and the treatment of SOA oligomerization are found to be the most important factors for SOA formation, leading to 66% and 60% more SOA, respectively. The explicit representation of high-NO, and low-NOx gas-phase chemical regimes is also important with increases in SOA of 30-120% depending on the approach used to implement the distinct SOA yields within the gas-phase chemical kinetic mechanism; further work is needed to develop gas-phase mechanisms that are fully compatible with SOA formation algorithms. The treatment of isoprene SOA as hydrophobic or hydrophilic leads to a significant difference, with more SOA being formed in the latter case. The activity coefficients may also be a major source of uncertainty, as they may differ significantly between atmospheric particles, which contain a myriad of SOA, primary organic aerosol (POA), and inorganic aerosol species, and particles formed in a smog chamber from a single precursor under dry conditions. Significant interactions exist between the uncertainties of the gas-phase chemistry and those of the SOA module.

  6. Gas-phase transformation of phosphatidylcholine cations to structurally informative anions via ion/ion chemistry.

    PubMed

    Stutzman, John R; Blanksby, Stephen J; McLuckey, Scott A

    2013-04-02

    Gas-phase transformation of synthetic phosphatidylcholine (PC) monocations to structurally informative anions is demonstrated via ion/ion reactions with doubly deprotonated 1,4-phenylenedipropionic acid (PDPA). Two synthetic PC isomers, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (PC(16:0/18:1)) and 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (PC(18:1/16:0)), were subjected to this ion/ion chemistry. The product of the ion/ion reaction is a negatively charged complex, [PC + PDPA - H](-). Collisional activation of the long-lived complex causes transfer of a proton and methyl cation to PDPA, generating [PC - CH3](-). Subsequent collisional activation of the demethylated PC anions produces abundant fatty acid carboxylate anions and low-abundance acyl neutral losses as free acids and ketenes. Product ion spectra of [PC - CH3](-) suggest favorable cleavage at the sn-2 position over the sn-1 due to distinct differences in the relative abundances. In contrast, collisional activation of PC cations is absent of abundant fatty acid chain-related product ions and typically indicates only the lipid class via formation of the phosphocholine cation. A solution phase method to produce the gas-phase adducted PC anion is also demonstrated. Product ion spectra derived from the solution phase method are similar to the results generated via ion/ion chemistry. This work demonstrates a gas-phase means to increase structural characterization of phosphatidylcholines via ion/ion chemistry.

  7. Gas-Phase Oxidation, Particle Uptake, and Product Studies of Isoprene Epoxydiols

    NASA Astrophysics Data System (ADS)

    Bates, K. H.; Nguyen, T. B.; St Clair, J. M.; Crounse, J.; Zhang, X.; Coggon, M.; Schwantes, R.; Bennett, N.; Stoltz, B.; Wennberg, P. O.; Seinfeld, J.

    2013-12-01

    Isoprene epoxydiols (IEPOX), discovered in 2009 as low-NOx atmospheric oxidation products of the ubiquitous biogenic precursor isoprene, are key intermediates in the formation of secondary organic aerosol (SOA) from biogenic emissions. Recent studies carried out in the Caltech environmental chambers have elucidated the gas-phase OH oxidation rates and products, particle uptake rates, and particle-phase OH oxidation products of three isomers of IEPOX synthesized in-house. Gas-phase oxidation studies were conducted in 1 m3 chambers at both high- and low-NOx conditions, and were monitored by GC-FID, two types of chemical ionization mass spectrometry (CIMS), and GC-CIMS. Comparisons with previous studies on isoprene showed that the two β-IEPOX isomers dominate over the ∂ isomers under atmospheric conditions, and the use of propene as an internal standard provided a robust estimate of OH oxidation rates between 0.99*10-11 and 1.67*10-11 cm3molec-1s-1 for the three isomers. Particle uptake and oxidation studies were conducted in 28 m3 chambers, and were monitored by GC-FID, CIMS, an aerosol mass spectrometer (AMS), and a differential mobility analyzer (DMA). Particle uptake showed a strong dependence on humidity, with no uptake on dry seed, and was faster on ammonium sulfate seed than sodium chloride seed. Particle-phase oxidation gave similar products to gas-phase oxidation by OH radicals.

  8. Shadow imaging in bubbly gas-liquid two-phase flow in porous structures

    NASA Astrophysics Data System (ADS)

    Altheimer, Marco; Häfeli, Richard; Wälchli, Carmen; Rudolf von Rohr, Philipp

    2015-09-01

    Shadow imaging is used for the investigation of bubbly gas-liquid two-phase flow in a porous structure. The porous structure is made of Somos WaterShed XC 11122, a clear epoxy resin used in rapid prototyping. Optical access is provided by using an aqueous solution of sodium iodide and zinc iodide having the same refractive index as the structure material (). Nitrogen is injected into the continuous phase at volumetric transport fractions in the range of resulting in a hold-up of . The obtained images of overlapping bubble shadows are processed to measure the bubble dimensions. Therefore, a new processing sequence is developed to determine bubble dimensions from overlapping bubble shadows by ellipse fitting. The accuracy of the bubble detection and sizing routine is assessed processing synthetic images. It is shown that the developed technique is suitable for volumetric two-phase flow measurements. Important global quantities such as gas hold-up and total interfacial area can be measured with only one camera. Operation parameters for gas-liquid two-phase flows are determined to improve mass and heat transfer between the phases.

  9. Lattice model theory of the equation of state covering the gas, liquid, and solid phases

    NASA Technical Reports Server (NTRS)

    Bonavito, N. L.; Tanaka, T.; Chan, E. M.; Horiguchi, T.; Foreman, J. C.

    1975-01-01

    The three stable states of matter and the corresponding phase transitions were obtained with a single model. Patterned after Lennard-Jones and Devonshires's theory, a simple cubic lattice model containing two fcc sublattices (alpha and beta) is adopted. The interatomic potential is taken to be the Lennard-Jones (6-12) potential. Employing the cluster variation method, the Weiss and the pair approximations on the lattice gas failed to give the correct phase diagrams. Hybrid approximations were devised to describe the lattice term in the free energy. A lattice vibration term corresponding to a free volume correction is included semi-phenomenologically. The combinations of the lattice part and the free volume part yield the three states and the proper phase diagrams. To determine the coexistence regions, the equalities of the pressure and Gibbs free energy per molecule of the coexisting phases were utilized. The ordered branch of the free energy gives rise to the solid phase while the disordered branch yields the gas and liquid phases. It is observed that the triple point and the critical point quantities, the phase diagrams and the coexistence regions plotted are in good agreement with the experimental values and graphs for argon.

  10. Enhancement in the photocatalytic nature of nitrogen-doped PVD-grown titanium dioxide thin films

    NASA Astrophysics Data System (ADS)

    Tavares, C. J.; Marques, S. M.; Viseu, T.; Teixeira, V.; Carneiro, J. O.; Alves, E.; Barradas, N. P.; Munnik, F.; Girardeau, T.; Rivière, J.-P.

    2009-12-01

    Nitrogen-doped titanium dioxide semiconductor photocatalytic thin films have been deposited by unbalanced reactive magnetron physical vapor deposition on glass substrates for self-cleaning applications. In order to increase the photocatalytic efficiency of the titania coatings, it is important to enhance the catalysts absorption of light from the solar spectra. Bearing this fact in mind, a reduction in the titania semiconductor band-gap has been attempted by using nitrogen doping from a coreactive gas mixture of N2:O2 during the titanium sputtering process. Rutherford backscattering spectroscopy was used in order to assess the composition of the titania thin films, whereas heavy-ion elastic recoil detection analysis granted the evaluation of the doping level of nitrogen. X-ray photoelectron spectroscopy provided valuable information about the cation-anion binding within the semiconductor lattice. The as-deposited thin films were mostly amorphous, however, after a thermal annealing in vacuum at 500 °C the crystalline polymorph anatase and rutile phases have been developed, yielding an enhancement in the crystallinity. Spectroscopic ellipsometry experiments enabled the determination the refractive index of the thin films as a function of the wavelength, while from the optical transmittance it was possible to estimate the semiconductor indirect band-gap of these coatings, which has been proven to decrease as the N-doping increases. The photocatalytic performance of the titania films has been characterized by the degradation rate of an organic reactive dye under UV/visible irradiation. It has been found that for a certain critical limit of 1.19 at. % of nitrogen doping in the titania anatase crystalline lattice enhances the photocatalytic behavior of the thin films and it is in accordance with the observed semiconductor band-gap narrowing to 3.18 eV. By doping the titania lattice with nitrogen, the photocatalytic activity is enhanced under both UV and visible light.

  11. Enhancement in the photocatalytic nature of nitrogen-doped PVD-grown titanium dioxide thin films

    SciTech Connect

    Tavares, C. J.; Marques, S. M.; Viseu, T.; Teixeira, V.; Carneiro, J. O.; Alves, E.; Barradas, N. P.; Munnik, F.; Girardeau, T.; Riviere, J.-P.

    2009-12-01

    Nitrogen-doped titanium dioxide semiconductor photocatalytic thin films have been deposited by unbalanced reactive magnetron physical vapor deposition on glass substrates for self-cleaning applications. In order to increase the photocatalytic efficiency of the titania coatings, it is important to enhance the catalysts absorption of light from the solar spectra. Bearing this fact in mind, a reduction in the titania semiconductor band-gap has been attempted by using nitrogen doping from a coreactive gas mixture of N{sub 2}:O{sub 2} during the titanium sputtering process. Rutherford backscattering spectroscopy was used in order to assess the composition of the titania thin films, whereas heavy-ion elastic recoil detection analysis granted the evaluation of the doping level of nitrogen. X-ray photoelectron spectroscopy provided valuable information about the cation-anion binding within the semiconductor lattice. The as-deposited thin films were mostly amorphous, however, after a thermal annealing in vacuum at 500 deg. C the crystalline polymorph anatase and rutile phases have been developed, yielding an enhancement in the crystallinity. Spectroscopic ellipsometry experiments enabled the determination the refractive index of the thin films as a function of the wavelength, while from the optical transmittance it was possible to estimate the semiconductor indirect band-gap of these coatings, which has been proven to decrease as the N-doping increases. The photocatalytic performance of the titania films has been characterized by the degradation rate of an organic reactive dye under UV/visible irradiation. It has been found that for a certain critical limit of 1.19 at. % of nitrogen doping in the titania anatase crystalline lattice enhances the photocatalytic behavior of the thin films and it is in accordance with the observed semiconductor band-gap narrowing to 3.18 eV. By doping the titania lattice with nitrogen, the photocatalytic activity is enhanced under both UV and

  12. Gas-phase reactivity of [Ca(formamide)](2+) complex: an example of different dynamical behaviours.

    PubMed

    Martin-Somer, Ana; Spezia, Riccardo; Yáñez, Manuel

    2017-04-28

    In the present contribution, we have summarized our recent work on the comprehension of [Ca(formamide)](2+) complex gas-phase unimolecular dissociation. By using different theoretical approaches, we were able to revise the original (and typical for such kind of problems) understanding given in terms of stationary points on the potential energy surface, which did not provide a satisfactory explanation of the experimentally observed reactivity. In particular, we point out how non-statistical and non-intrinsic reaction coordinate mechanisms are of fundamental importance.This article is part of the themed issue 'Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces'.

  13. Computer code for gas-liquid two-phase vortex motions: GLVM

    NASA Technical Reports Server (NTRS)

    Yeh, T. T.

    1986-01-01

    A computer program aimed at the phase separation between gas and liquid at zero gravity, induced by vortex motion, is developed. It utilizes an explicit solution method for a set of equations describing rotating gas-liquid flows. The vortex motion is established by a tangential fluid injection. A Lax-Wendroff two-step (McCormack's) numerical scheme is used. The program can be used to study the fluid dynamical behavior of the rotational two-phase fluids in a cylindrical tank. It provides a quick/easy sensitivity test on various parameters and thus provides the guidance for the design and use of actual physical systems for handling two-phase fluids.

  14. Recent progress of chiral stationary phases for separation of enantiomers in gas chromatography.

    PubMed

    Xie, Sheng-Ming; Yuan, Li-Ming

    2017-01-01

    Chromatography techniques based on chiral stationary phases are widely used for the separation of enantiomers. In particular, gas chromatography has developed rapidly in recent years due to its merits such as fast analysis speed, lower consumption of stationary phases and analytes, higher column efficiency, making it a better choice for chiral separation in diverse industries. This article summarizes recent progress of novel chiral stationary phases based on cyclofructan derivatives and chiral porous materials including chiral metal-organic frameworks, chiral porous organic frameworks, chiral inorganic mesoporous materials, and chiral porous organic cages in gas chromatography, covering original research papers published since 2010. The chiral recognition properties and mechanisms of separation toward enantiomers are also introduced.

  15. Effect of duty-cycles on the air plasma gas-phase of dielectric barrier discharges

    NASA Astrophysics Data System (ADS)

    Barni, R.; Biganzoli, I.; Dell'Orto, E. C.; Riccardi, C.

    2015-10-01

    An experimental investigation concerning the effects of a duty-cycle in the supply of a dielectric barrier discharge in atmospheric pressure air has been performed. Electrical characteristics of the discharge have been measured, focusing mainly on the statistical properties of the current filaments and on dielectric surface charging, both affected by the frequent repetition of breakdown imposed by the duty-cycle. Information on the gas-phase composition was gathered too. In particular, a strong enhancement in the ozone formation rate is observed when suitable long pauses separate the active discharge phases. A simulation of the chemical kinetics in the gas-phase, based on a simplified discharge modeling, is briefly described in order to shed light on the observed increase in ozone production. The effect of a duty-cycle on surface modification of polymeric films in order to increase their wettability has been investigated too.

  16. MOVPE GaN gas phase chemistry for reactor design and optimization

    SciTech Connect

    Safvi, S.A.; Thon, A.; Kuech, T.F.; Redwing, J.M.; Flynn, J.S.; Tischler, M.A.

    1997-12-31

    The results of gas phase decomposition studies are used to construct a chemistry model which is compared to data obtained from an experimental MOVPE reactor. A flow tube reactor is used to study gas phase reactions between trimethylgallium (TMG) and ammonia at high temperatures, characteristic to the metalorganic vapor phase epitaxy (MOVPE) of GaN. Experiments were performed to determine the effect of the mixing of the Group III precursors and Group V precursors on the growth rate, growth uniformity and film properties. Growth rates are predicted for simple reaction mechanisms and compared to those obtained experimentally. Quantification of the loss of reacting species due to oligomerization is made based on experimentally observed growth rates. The model is used to obtain trends in growth rate and uniformity with the purpose of moving towards better operating conditions.

  17. Gas phase catalytic hydrodechlorination of chlorobenzene over cobalt phosphide catalysts with different P contents.

    PubMed

    Cecilia, J A; Infantes-Molina, A; Rodríguez-Castellón, E; Jiménez-López, A

    2013-09-15

    The gas phase catalytic hydrodechlorination (HDC) of chlorobenzene (CB) at atmospheric pressure was investigated over silica-supported cobalt and cobalt phosphide catalysts containing different P loading and a fixed amount of cobalt (5 wt.%). The effect of the initial P/Co molar ratio on the stoichiometry of the cobalt phosphide phase, the acidity and the hydrogen activation capability were discussed and these properties correlated with the catalytic activity. Catalytic results indicated that the cobalt phosphide phase is much more active than the monometallic cobalt one. The activity raised with the P content present in the sample due to the formation of the CoP phase instead of the Co₂P one, which favored the formation of hydrogen spillover species, increased the amount of weak acid sites and the number of exposed superficial cobalt atoms probably related to a better dispersion of the active phase. All the catalysts gave rise benzene as the main reaction product.

  18. Fluid Phase Separation (FPS) experiment for flight on a space shuttle Get Away Special (GAS) canister

    NASA Technical Reports Server (NTRS)

    Peters, Bruce; Wingo, Dennis; Bower, Mark; Amborski, Robert; Blount, Laura; Daniel, Alan; Hagood, Bob; Handley, James; Hediger, Donald; Jimmerson, Lisa

    1990-01-01

    The separation of fluid phases in microgravity environments is of importance to environmental control and life support systems (ECLSS) and materials processing in space. A successful fluid phase separation experiment will demonstrate a proof of concept for the separation technique and add to the knowledge base of material behavior. The phase separation experiment will contain a premixed fluid which will be exposed to a microgravity environment. After the phase separation of the compound has occurred, small samples of each of the species will be taken for analysis on the Earth. By correlating the time of separation and the temperature history of the fluid, it will be possible to characterize the process. The experiment has been integrated into space available on a manifested Get Away Special (GAS) experiment, CONCAP 2, part of the Consortium for Materials Complex Autonomous Payload (CAP) Program, scheduled for STS-42. The design and the production of a fluid phase separation experiment for rapid implementation at low cost is presented.

  19. A generalized expression for lag-time in the gas-phase permeation of hollow tubes

    NASA Technical Reports Server (NTRS)

    Shah, K. K.; Nelson, H. G.; Johnson, D. L.; Hamaker, F. M.

    1975-01-01

    A generalized expression for the nonsteady-state parameter, lag-time, has been obtained from Fick's second law for gas-phase transport through hollow, cylindrical membranes. This generalized expression is simplified for three limiting cases of practical interest: (1) diffusion controlled transport, (2) phase boundary reaction control at the inlet surface, and (3) phase boundary reaction control at the outlet surface. In all three cases the lag-time expressions were found to be inversely proportional only to the diffusion coefficient and functionally dependent on the membrane radii. Finally, the lag-time expressions were applied to experimentally obtained lag-time data for alpha-phase titanium and alpha-phase iron.

  20. Temperature dependence of the particle/gas partition coefficient: An application to predict indoor gas-phase concentrations of semi-volatile organic compounds.

    PubMed

    Wei, Wenjuan; Mandin, Corinne; Blanchard, Olivier; Mercier, Fabien; Pelletier, Maud; Le Bot, Barbara; Glorennec, Philippe; Ramalho, Olivier

    2016-09-01

    The indoor gas-phase concentrations of semi-volatile organic compounds (SVOCs) can be predicted from their respective concentrations in airborne particles by applying the particle/gas partitioning equilibrium. The temperature used for partitioning is often set to 25°C. However, indoor temperatures frequently differ from this reference value. This assumption may result in errors in the predicted equilibrium gas-phase SVOC concentrations. To improve the prediction model, the temperature dependence of the particle/gas partition coefficient must be addressed. In this paper, a theoretical relationship between the particle/gas partition coefficient and temperature was developed based on the SVOC absorptive mechanism. The SVOC particle/gas partition coefficients predicted by employing the derived theoretical relationship agree well with the experimental data retrieved from the literature (R>0.93). The influence of temperature on the equilibrium gas-phase SVOC concentration was quantified by a dimensionless analysis of the derived relationship between the SVOC particle/gas partition coefficient and temperature. The predicted equilibrium gas-phase SVOC concentration decreased by between 31% and 53% when the temperature was lowered by 6°C, while it increased by up to 750% when the indoor temperature increased from 15°C to 30°C.

  1. A chamber study on the reactions of O3, NO, NO2 and selected VOCs with a photocatalytically active cementitious coating material.

    PubMed

    Mothes, F; Böge, O; Herrmann, H

    2016-08-01

    Chamber studies were performed to investigate the efficiency of a photocatalytically active cementitious coating material to depollute contaminated air. The results showed a photocatalytic effect on ozone (O3), proven by an increase of the geometric uptake coefficient from 5.2 × 10(-6) for the inactive to 7.7 × 10(-6) for the active material under irradiation. Measured first-order rate constants for nitrogen oxides (NOx) under irradiation are in the range of 2.6-5.9 × 10(-4) s(-1), which is significantly higher compared to the inactive material (7.3-9.7 × 10(-5) s(-1)) demonstrating the photocatalytic effect. However, no significant photocatalytic degradation was observed for the studied volatile organic compounds (VOCs) toluene and isoprene resulting in only an upper limit uptake coefficient of 5.0 × 10(-7) for both VOCs. In all experiments using the photocatalytically active material, a clear formation of small carbonyl (C1-C5) gas phase compounds was identified which is suggested to result from the photocatalytic degradation of organic additives. In contrast to the uptake observed for pure O3, during the experiments with NOx (≥50 % relative humidity), a clear photocatalytic formation of O3 was observed. For the material investigated, an empirically derived overall zero-order rate constant of k 0 (O3) ≈ 5 × 10(7) molecules cm(-3) s(-1) was determined. The results demonstrate the necessity of detailed studies of heterogeneous reactions on such surfaces under more complex simulated atmospheric conditions as enabled by simulation chambers.

  2. The role of gas phase reactions in the deflagration-to-detonation transition of high energy propellants

    NASA Technical Reports Server (NTRS)

    Boggs, T. L.; Price, C. F.; Atwood, A. I.; Zurn, D. E.; Eisel, J. L.; Derr, R. L.

    1980-01-01

    The inadequacies of the two commonly used assumptions are shown, along with the need for considering gas phase reactions. Kinetic parameters that describe the gas phase reactions for several ingredients are provided, and the first steps in convective combustion leading to deflagration to detonation transition are described.

  3. Graphene quantum dots modified silicon nanowire array for ultrasensitive detection in the gas phase

    NASA Astrophysics Data System (ADS)

    Li, T. Y.; Duan, C. Y.; Zhu, Y. X.; Chen, Y. F.; Wang, Y.

    2017-03-01

    Si nanostructure-based gas detectors have attracted much attention due to their huge surface areas, relatively high carrier mobility, maneuverability for surface functionalization and compatibility to modern electronic industry. However, the unstable surface of Si, especially for the nanostructures in a corrosive atmosphere, hinders their sensitivity and reproducibility when used for detection in the gas phase. In this study, we proposed a novel strategy to fabricate a Si-based gas detector by using the vertically aligned Si nanowire (SiNW) array as a skeleton and platform, and decorated chemically inert graphene quantum dots (GQDs) to protect the SiNWs from oxidation and promote the carriers’ interaction with the analytes. The radial core–shell structures of the GQDs/SiNW array were then assembled into a resistor-based gas detection system and evaluated by using nitrogen dioxide (NO2) as the model analyte. Compared to the bare SiNW array, our novel sensor exhibited ultrahigh sensitivity for detecting trace amounts of NO2 with the concentration as low as 10 ppm in room temperature and an immensely reduced recovery time, which is of significant importance for their practical application. Meanwhile, strikingly, reproducibility and stability could also be achieved by showing no sensitivity decline after storing the GQDs/SiNW array in air for two weeks. Our results demonstrate that protecting the surface of the SiNW array with chemically inert GQDs is a feasible strategy to realize ultrasensitive detection in the gas phase.

  4. Effect of annealing treatment on the photocatalytic activity of TiO2 thin films deposited by dc reactive magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Arias, L. M. Franco; Arias Duran, A.; Cardona, D.; Camps, E.; Gómez, M. E.; Zambrano, G.

    2015-07-01

    Titanium dioxide (TiO2) thin films have been deposited by DC reactive magnetron sputtering on silicon and quartz substrates with different Ar/O2 ratios in the gas mixture. Substrate temperature was kept constant at 400 °C during the deposition process, and the TiO2 thin films were later annealed at 700 °C for 3 h. The effect of the Ar/O2 ratio in the gas flow and the annealing treatment on the phase composition, deposition rate, crystallinity, surface morphology and the resulting photocatalytic properties were investigated. For photocatalytic measurements, the variation of the concentration of the methylene blue (MB) dye under UV irradiation was followed by a change in the intensity of the characteristic MB band in the UV- Vis transmittance spectra. We report here that the as-grown TiO2 films showed only the anatase phase, whereas after annealing, the samples exhibited both the anatase and rutile phases in proportions that varied with the Ar/O2 ratio in the mixture of gases used during growth. In particular, the annealed TiO2 thin film deposited at a 50/50 ratio of Ar/O2, composed of both anatase (80%) and rutile phases (20%), exhibited the highest photocatalytic activity (30% of MB degradation) compared with the samples without annealing and composed of only the anatase phase.

  5. FIELD METHODS TO MEASURE CONTAMINANT REMOVAL EFFECTIVENESS OF GAS-PHASE AIR FILTRATION EQUIPMENT - PHASE 1: SEARCH OF LITERATURE AND PRIOR ART

    EPA Science Inventory

    The report, Phase 1 of a two-phase research project, gives results of a literature search into the
    effectiveness of in-field gas-phase air filtration equipment (GPAFE) test methods, including required instrumentation and costs. GPAFE has been used in heating, ventilation, and ...

  6. Comprehensive Gas-Phase Peptide Ion Structure Studies Using Ion Mobility Techniques: Part 2. Gas-Phase Hydrogen/Deuterium Exchange for Ion Population Estimation.

    PubMed

    Khakinejad, Mahdiar; Ghassabi Kondalaji, Samaneh; Tafreshian, Amirmahdi; Valentine, Stephen J

    2017-03-17

    Gas-phase hydrogen/deuterium exchange (HDX) using D2O reagent and collision cross-section (CCS) measurements are utilized to monitor the ion conformers of the model peptide acetyl-PAAAAKAAAAKAAAAKAAAAK. The measurements are carried out on a home-built ion mobility instrument coupled to a linear ion trap mass spectrometer containing electron transfer dissociation (ETD) capabilities. ETD is utilized to obtain per-residue deuterium uptake data for select ion conformers, and a new algorithm is presented for interpreting the HDX data. Using molecular dynamics (MD) production data and a hydrogen accessibility scoring (HAS)-number of effective collisions (NEC) model, hypothetical HDX behavior is attributed to various in-silico candidate (CCS match) structures. The HAS-NEC model is applied to all candidate structures, and non-negative linear regression is employed to determine structure contributions resulting in the best match to deuterium uptake. The accuracy of the HAS-NEC model is tested with the comparison of predicted and experimental isotopic envelopes for several of the observed c-ions. It is proposed that gas-phase HDX can be utilized effectively as a second criterion (after CCS matching) for filtering suitable MD candidate structures. In this study, the second step of structure elucidation, 13 nominal structures were selected (from a pool of 300 candidate structures) and each with a population contribution proposed for these ions. Graphical Abstract ᅟ.

  7. Comprehensive Gas-Phase Peptide Ion Structure Studies Using Ion Mobility Techniques: Part 2. Gas-Phase Hydrogen/Deuterium Exchange for Ion Population Estimation

    NASA Astrophysics Data System (ADS)

    Khakinejad, Mahdiar; Ghassabi Kondalaji, Samaneh; Tafreshian, Amirmahdi; Valentine, Stephen J.

    2017-03-01

    Gas-phase hydrogen/deuterium exchange (HDX) using D2O reagent and collision cross-section (CCS) measurements are utilized to monitor the ion conformers of the model peptide acetyl-PAAAAKAAAAKAAAAKAAAAK. The measurements are carried out on a home-built ion mobility instrument coupled to a linear ion trap mass spectrometer containing electron transfer dissociation (ETD) capabilities. ETD is utilized to obtain per-residue deuterium uptake data for select ion conformers, and a new algorithm is presented for interpreting the HDX data. Using molecular dynamics (MD) production data and a hydrogen accessibility scoring (HAS)-number of effective collisions (NEC) model, hypothetical HDX behavior is attributed to various in-silico candidate (CCS match) structures. The HAS-NEC model is applied to all candidate structures, and non-negative linear regression is employed to determine structure contributions resulting in the best match to deuterium uptake. The accuracy of the HAS-NEC model is tested with the comparison of predicted and experimental isotopic envelopes for several of the observed c-ions. It is proposed that gas-phase HDX can be utilized effectively as a second criterion (after CCS matching) for filtering suitable MD candidate structures. In this study, the second step of structure elucidation, 13 nominal structures were selected (from a pool of 300 candidate structures) and each with a population contribution proposed for these ions.

  8. Transport of Gas Phase Radionuclides in a Fractured, Low-Permeability Reservoir

    NASA Astrophysics Data System (ADS)

    Cooper, C. A.; Chapman, J.

    2001-12-01

    The U.S. Atomic Energy Commission (predecessor to the Department of Energy, DOE) oversaw a joint program between industry and government in the 1960s and 1970s to develop technology to enhance production from low-permeability gas reservoirs using nuclear stimulation rather than conventional means (e.g., hydraulic and/or acid fracturing). Project Rio Blanco, located in the Piceance Basin, Colorado, was the third experiment under the program. Three 30-kiloton nuclear explosives were placed in a 2134 m deep well at 1780, 1899, and 2039 m below the land surface and detonated in May 1973. Although the reservoir was extensively fractured, complications such as radionuclide contamination of the gas prevented production and subsequent development of the technology. Two-dimensional numerical simulations were conducted to identify the main transport processes that have occurred and are currently occurring in relation to the detonations, and to estimate the extent of contamination in the reservoir. Minor modifications were made to TOUGH2, the multiphase, multicomponent reservoir simulator developed at Lawrence Berkeley National Laboratories. The simulator allows the explicit incorporation of fractures, as well as heat transport, phase change, and first order radionuclide decay. For a fractured two-phase (liquid and gas) reservoir, the largest velocities are of gases through the fractures. In the gas phase, tritium and one isotope of krypton are the principle radionuclides of concern. However, in addition to existing as a fast pathway, fractures also permit matrix diffusion as a retardation mechanism. Another retardation mechanism is radionuclide decay. Simulations show that incorporation of fractures can significantly alter transport rates, and that radionuclides in the gas phase can preferentially migrate upward due to the downward gravity drainage of liquid water in the pores. This project was funded by the National Nuclear Security Administration, Nevada Operations Office

  9. Transport of gas-phase radionuclides in a fractured, low-permeability reservoir

    SciTech Connect

    Clay Cooper; Jenny Chapman

    2001-12-01

    The U.S. Atomic Energy Commission (predecessor to the U.S. Department of Energy, DOE) oversaw a joint program between industry and government in the 1960s and 1970s to develop technology to enhance production from low-permeability gas reservoirs using nuclear stimulation rather than conventional means (e.g., hydraulic and/or acid fracturing). Project Rio Blanco, located in the Piceance Basin, Colorado, was the third experiment under the program. Three 30-kiloton nuclear explosives were placed in a 2,134-m-deep well at 1,780, 1,899, and 2,039 m below the land surface and detonated in May 1973. Although the reservoir was extensively fractured, complications such as radionuclide contamination of the gas prevented production and subsequent development of the technology. Two-dimensional numerical simulations were conducted to identify the main transport processes that have occurred and are currently occurring in relation to the detonations, and to estimate the extent of contamination in the reservoir. Minor modifications were made to TOUGH2, the multiphase, multicomponent reservoir simulator developed at Lawrence Berkeley National Laboratories. The simulator allows the explicit incorporation of fractures, as well as heat transport, phase change, and first-order radionuclide decay. For a fractured, two-phase (liquid and gas) reservoir, the largest velocities are of gases through the fractures. In the gas phase, tritium and one isotope of krypton are the principal radionuclides of concern. However, in addition to existing as a fast pathway, fractures also permit matrix diffusion as a retardation mechanism. Another retardation mechanism is radionuclide decay. Simulations show that incorporation of fractures can significantly alter transport rates, and that radionuclides in the gas phase can preferentially migrate upward due to the downward gravity drainage of liquid water in the pores.

  10. Missing gas-phase source of HONO inferred from Zeppelin measurements in the troposphere

    NASA Astrophysics Data System (ADS)

    Li, Xin; Rohrer, Franz; Hofzumahaus, Andreas; Brauers, Theo; Häseler, Rolf; Bohn, Birger; Broch, Sebastian; Fuchs, Hendrik; Gomm, Sebastian; Holland, Frank; Jäger, Julia; Kaiser, Jennifer; Keutsch, Frank N.; Lohse, Insa; Tillmann, Ralf; Wegener, Robert; Wolfe, Glenn M.; Mentel, Thomas F.; Kiendler-Scharr, Astrid; Wahner, Andreas

    2014-05-01

    Nitrous acid (HONO) is an important trace gas in the atmosphere due to its contribution to the cycles of nitrogen oxides (NOX) and hydrogen oxides (HOX). In the past decades, ground-based observations of HONO around the world showed much higher daytime concentrations than can be explained by the known gas-phase chemistry (i.e., HONO + hν → OH + NO, HONO + OH → NO2 + H2O, OH + NO + M → HONO + M). Different light-dependent reactions on ground surfaces have been proposed as additional daytime HONO sources. However, due to lack of measurements, little is known about the concentrations of HONO and its sources in the planetary boundary layer (PBL) at higher altitudes above the earth's surface. The airship Zeppelin NT is an ideal platform to investigate the chemistry and dynamics of the PBL. During the PEGASOS field campaigns in 2012 and 2013, HONO and its gas-phase sources and sinks were measured simultaneously on-board the airship Zeppelin NT, for the lowest 1 km of the PBL. In the upper part of the altitude range during morning hours, when the airmass is still isolated from processes at the earth's surface by the remaining nocturnal boundary layer, we find unexpectedly large concentrations of HONO which can neither be explained by heterogeneous reactions on aerosol and ground surfaces, nor by known gas-phase reactions. Our observations show evidence for an unknown gas-phase light-dependent HONO production which dominates the overall HONO formation in the lower troposphere. This new HONO source requires NOX and possibly OH or HO2 radicals. As a result, the general impact of HONO on the OH formation is likely overestimated.

  11. Design and Development of Gas-Liquid Cylindrical Cyclone Compact Separators for Three-Phase Flow

    SciTech Connect

    Mohan, Ram S.; Shoham, Ovadia

    1999-10-28

    The objective of this five-year project (October, 1997--September, 2002) is to expand the current research activities of Tulsa University Separation Technology Projects (TUSTP) to multiphase oil/water/gas separation. This project will be executed in two phases. Phase I (1997--2000) will focus on the investigations of the complex multiphase hydrodynamic flow behavior in a three-phase Gas-Liquid Cylindrical Cyclone (GLCC) Separator. The activities of this phase will include the development of a mechanistic model, a computational fluid dynamics (CFD) simulator, and detailed experimentation on the three-phase GLCC. The experimental and CFD simulation results will be suitably integrated with the mechanistic model. In Phase II (2000--2002), the developed GLCC separator will be tested under high pressure and real crudes conditions. This is crucial for validating the GLCC design for field application and facilitating easy and rapid technology deployment. Design criteria for industrial applications will be developed based on these results and will be incorporated into the mechanistic model by TUSTP.

  12. Design and Development of Gas-Liquid Cylindrical Cyclone Compact Separators for Three-Phase Flow

    SciTech Connect

    Mohan, R.S.; Shoham, O.

    2001-01-18

    The objective of this five-year project (October 1997 - September 2002) was to expand the current research activities of Tulsa University Separation Technology Projects (TUSTP) to multiphase oil/water/gas separation. This project was executed in two phases. Phase I (1997 - 2000) focused on the investigations of the complex multiphase hydrodynamic flow behavior in a three-phase Gas-Liquid Cylindrical Cyclone (GLCC) Separator. The activities of this phase included the development of a mechanistic model, a computational fluid dynamics (CFD) simulator, and detailed experimentation on the three-phase GLCC. The experimental and CFD simulation results will be suitably integrated with the mechanistic model. In Phase II (2000 - 2002), the developed GLCC separator will be tested under high pressure and real crude conditions. This is crucial for validating the GLCC design for field application and facilitating easy and rapid technology deployment. Design criteria for industrial applications will be developed based on these results and will be incorporated into the mechanistic model by TUSTP.

  13. Design and Development of Gas-Liquid Cylindrical Cyclone Compact Separators for Three-Phase Flow

    SciTech Connect

    Mohan, R.S.; Shoham, O.

    2001-01-10

    The objective of this five-year project (October 1997--September 2002) was to expand the current research activities of Tulsa University Separation Technology Projects (TUSTP) to multiphase oil/water/gas separation. This project was executed in two phases. Phase I (1997--2000) focused on the investigations of the complex multiphase hydrodynamic flow behavior in a three-phase Gas-Liquid Cylindrical Cyclone (GLCC) Separator. The activities of this phase included the development of a mechanistic model, a computational fluid dynamics (CFD) simulator, and detailed experimentation on the three-phase GLCC. The experimental and CFD simulation results will be suitably integrated with the mechanistic model. In Phase II (2000--2002), the developed GLCC separator will be tested under high pressure and real crude conditions. This is crucial for validating the GLCC design for field application and facilitating easy and rapid technology deployment. Design criteria for industrial applications will be developed based on these results and will be incorporated into the mechanistic model by TUSTP.

  14. DYNAMIC MODELING STRATEGY FOR FLOW REGIME TRANSITION IN GAS-LIQUID TWO-PHASE FLOWS

    SciTech Connect

    X. Wang; X. Sun; H. Zhao

    2011-09-01

    In modeling gas-liquid two-phase flows, the concept of flow regime has been used to characterize the global interfacial structure of the flows. Nearly all constitutive relations that provide closures to the interfacial transfers in two-phase flow models, such as the two-fluid model, are often flow regime dependent. Currently, the determination of the flow regimes is primarily based on flow regime maps or transition criteria, which are developed for steady-state, fully-developed flows and widely applied in nuclear reactor system safety analysis codes, such as RELAP5. As two-phase flows are observed to be dynamic in nature (fully-developed two-phase flows generally do not exist in real applications), it is of importance to model the flow regime transition dynamically for more accurate predictions of two-phase flows. The present work aims to develop a dynamic modeling strategy for determining flow regimes in gas-liquid two-phase flows through the introduction of interfacial area transport equations (IATEs) within the framework of a two-fluid model. The IATE is a transport equation that models the interfacial area concentration by considering the creation and destruction of the interfacial area, such as the fluid particle (bubble or liquid droplet) disintegration, boiling and evaporation; and fluid particle coalescence and condensation, respectively. For the flow regimes beyond bubbly flows, a two-group IATE has been proposed, in which bubbles are divided into two groups based on their size and shape (which are correlated), namely small bubbles and large bubbles. A preliminary approach to dynamically identifying the flow regimes is provided, in which discriminators are based on the predicted information, such as the void fraction and interfacial area concentration of small bubble and large bubble groups. This method is expected to be applied to computer codes to improve their predictive capabilities of gas-liquid two-phase flows, in particular for the applications in

  15. PHASE-FIELD SIMULATION OF IRRADIATED METALS: PART II: GAS BUBBLE KINETICS

    SciTech Connect

    Paul C Millett; Anter El-Azab

    2011-01-01

    We present a phase-field model for inert gas bubble formation and evolution in irradiated metals. The model evolves vacancy, self-interstitial, and fission gas atoms through a coupled set of Cahn-Hilliard and Allen-Cahn equations, capturing the processes of defect generation, recombination, annihilation at GB sinks, as well as intragranular and intergranular bubble nucleation and growth in polycrystalline microstructures. Illustrative results are presented that characterize bubble growth and shrinkage, as well as the bubble density, size and nucleation rate as a function of varying irradiation conditions. Finally, intergranular bubble characteristics such as shape, pinning energy on GB motion, and bubble density are investigated.

  16. Phase 1-B development of kinematic Stirling/Rankine commercial gas-fired heat pump system

    NASA Astrophysics Data System (ADS)

    Johansson, L.; Agno, J. G.; Percival, W. H.

    1985-07-01

    The goal of this project is to develop a commercial size Stirling engine-driven gas heat pump with a cooling capacity of 10-ton, and a COP (heating) of 1.8 and COP (cooling) of 1.1. The project is a multi-phase development with commercialization planned for 1989. To date, a piston type open shaft refrigeration compressor has been selected as the best match for the engine. Both the engine and compressor have been tested and characterized by performance maps, and the experimental heat pump systems designed. The manufacturer has continued to focus on improving the Stirling engine performance and reliability for the gas heat pump application.

  17. Review: gas-phase ion chemistry of the noble gases: recent advances and future perspectives.

    PubMed

    Grandinetti, Felice

    2011-01-01

    This review article surveys recent experimental and theoretical advances in the gas-phase ion chemistry of the noble gases. Covered issues include the interaction of the noble gases with metal and non-metal cations, the conceivable existence of covalent noble-gas anions, the occurrence of ion-molecule reactions involving singly-charged xenon cations, and the occurrence of bond-forming reactions involving doubly-charged cations. Research themes are also highlighted, that are expected to attract further interest in the future.

  18. Gas-Phase Photochemical Overall H2 S Splitting by UV Light Irradiation.

    PubMed

    Baldovi, Herme G; Albero, Josep; Ferrer, Belen; Mateo, Diego; Alvaro, Mercedes; García, Hermenegildo

    2017-04-11

    Splitting of hydrogen sulfide is achieved to produce value-added chemicals. Upon irradiation at 254 nm in the gas phase and in the absence of catalysts or photocatalysts at near room temperature, H2 S splits into stoichiometric amounts of H2 and S with a quantum efficiency close to 50 %. No influence of the presence of CH4 and CO2 (typical components in natural gas and biogas in which H2 S is an unwanted component) on the efficiency of overall H2 S splitting was observed. A mechanism for the H2 and S formation is proposed.

  19. Risk Assessment Related to Atmospheric Polycyclic Aromatic Hydrocarbons in Gas and Particle Phases near Industrial Sites

    PubMed Central

    Ramírez, Noelia; Cuadras, Anna; Marcé, Rosa Maria

    2011-01-01

    Background: Inhalation is one of the main means of human exposure to polycyclic aromatic hydrocarbons (PAHs) because of their ubiquitous presence in the atmosphere. However, most studies have considered only PAHs found in the particle phase and have omitted the contribution of the gas-phase PAHs to the risk. Objective: We estimated the lifetime lung cancer risk from PAH exposure by inhalation in people living next to the largest chemical site in Southern Europe and the Mediterranean area. Methods: We determined 18 PAHs in the atmospheric gas and particle phase. We monitored the PAHs for 1 year in three locations near the chemical site in different seasons. We used toxic equivalence factors to calculate benzo[a]pyrene (BaP) equivalents (BaP-eq) for individual PAHs and applied the World Health Organization unit risk (UR) for BaP (UR = 8.7 × 10–5) to estimate lifetime cancer risks due to PAH exposures. Results: We observed some spatial and seasonal variability in PAH concentrations. The contribution of gas-phase PAHs to the total BaP-eq value was between 34% and 86%. The total estimated average lifetime lung cancer risk due to PAH exposure in the study area was 1.2 × 10–4. Conclusions: The estimated risk was higher than values recommended by the World Health Organization and U.S. Environmental Protection Agency but lower than the threshold value of 10–3 that is considered an indication of definite risk according to similar risk studies. The results also showed that risk may be underestimated if the contributions of gas-phase PAHs are not considered. PMID:21478082

  20. Gas-phase IR spectra of intact [alpha]-helical coiled coil protein complexes

    NASA Astrophysics Data System (ADS)

    Pagel, Kevin; Kupser, Peter; Bierau, Frauke; Polfer, Nicolas C.; Steill, Jeffrey D.; Oomens, Jos; Meijer, Gerard; Koksch, Beate; von Helden, Gert

    2009-06-01

    Electrospray ionization (ESI) is the softest ionization method that is currently available and it is widely accepted, that ESI generated ions of proteins and protein assemblies at certain conditions retain characteristic aspects of their solution-state conformation. ESI mass spectrometry (MS) therefore evolved as a useful tool to obtain information on composition, stoichiometry, and dynamics of non-covalently associated protein complexes. While tertiary structure information of proteins can be obtained from ion mobility spectrometry (IMS), only a few techniques yield direct information on the secondary structure of gas-phase peptides and proteins. We present here the mid-IR spectroscopic secondary structural analysis of three de novo designed [alpha]-helical coiled coil model peptides and their non-covalently associated complexes in the gas-phase. The conformational stability of such coiled coil peptides in solution is primarily driven by aggregation. Isolated monomers usually remain unfolded. Two of the investigated peptides were designed to assemble into stable [alpha]-helical complexes in acidic solution, while the third one remains monomeric and unfolded at these conditions. Monomer ions of all three peptides show comparable photodissociation IR spectra and therefore suggest an unfolded conformation in the gas phase. In contrast, considerable CO stretch (amide-I) and N-H bend (amide-II) band shifts have been observed for the dimers which is consistent with an elevated H-bond content. These findings provide evidence that at least a fraction of the condensed phase [alpha]-helical structure is retained in the gas-phase coiled coil complexes.

  1. Gas-phase chemistry in dense interstellar clouds including grain surface molecular depletion and desorption

    NASA Technical Reports Server (NTRS)

    Bergin, E. A.; Langer, W. D.; Goldsmith, P. F.

    1995-01-01

    We present time-dependent models of the chemical evolution of molecular clouds which include depletion of atoms and molecules onto grain surfaces and desorption, as well as gas-phase interactions. We have included three mechanisms to remove species from the grain mantles: thermal evaporation, cosmic-ray-induced heating, and photodesorption. A wide range of parameter space has been explored to examine the abundance of species present both on the grain mantles and in the gas phase as a function of both position in the cloud (visual extinction) and of evolutionary state (time). The dominant mechanism that removes molecules from the grain mantles is cosmic-ray desorption. At times greater than the depletion timescale, the abundances of some simple species agree with abundances observed in the cold dark cloud TMC-1. Even though cosmic-ray desorption preserves the gas-phase chemistry at late times, molecules do show significant depletions from the gas phase. Examination of the dependence of depletion as a function of density shows that when the density increases from 10(exp 3)/cc to 10(exp 5)/cc several species including HCO(+), HCN, and CN show gas-phase abundance reductions of over an order of magnitude. The CO: H2O ratio in the grain mantles for our standard model is on the order of 10:1, in reasonable agreement with observations of nonpolar CO ice features in rho Ophiuchus and Serpens. We have also examined the interdependence of CO depletion with the space density of molecular hydrogen and binding energy to the grain surface. We find that the observed depletion of CO in Taurus in inconsistent with CO bonding in an H2O rich mantle, in agreement with observations. We suggest that if interstellar grains consist of an outer layer of CO ice, then the binding energies for many species to the grain mantle may be lower than commonly used, and a significant portion of molecular material may be maintained in the gas phase.

  2. Determination of gas phase protein ion densities via ion mobility analysis with charge reduction.

    PubMed

    Maisser, Anne; Premnath, Vinay; Ghosh, Abhimanyu; Nguyen, Tuan Anh; Attoui, Michel; Hogan, Christopher J

    2011-12-28

    We use a charge reduction electrospray (ESI) source and subsequent ion mobility analysis with a differential mobility analyzer (DMA, with detection via both a Faraday cage electrometer and a condensation particle counter) to infer the densities of single and multiprotein ions of cytochrome C, lysozyme, myoglobin, ovalbumin, and bovine serum albumin produced from non-denaturing (20 mM aqueous ammonium acetate) and denaturing (1 : 49.5 : 49.5, formic acid : methanol : water) ESI. Charge reduction is achieved through use of a Po-210 radioactive source, which generates roughly equal concentrations of positive and negative ions. Ions produced by the source collide with and reduce the charge on ESI generated drops, preventing Coulombic fissions, and unlike typical protein ESI, leading to gas-phase protein ions with +1 to +3 excess charges. Therefore, charge reduction serves to effectively mitigate any role that Coulombic stretching may play on the structure of the gas phase ions. Density inference is made via determination of the mobility diameter, and correspondingly the spherical equivalent protein volume. Through this approach it is found that for both non-denaturing and denaturing ESI-generated ions, gas-phase protein ions are relatively compact, with average densities of 0.97 g cm(-3) and 0.86 g cm(-3), respectively. Ions from non-denaturing ESI are found to be slightly more compact than predicted from the protein crystal structures, suggesting that low charge state protein ions in the gas phase are slightly denser than their solution conformations. While a slight difference is detected between the ions produced with non-denaturing and denaturing ESI, the denatured ions are found to be much more dense than those examined previously by drift tube mobility analysis, in which charge reduction was not employed. This indicates that Coulombic stretching is typically what leads to non-compact ions in the gas-phase, and suggests that for gas phase

  3. A comparative study of optical absorption and photocatalytic properties of nanocrystalline single-phase anatase and rutile TiO2 doped with transition metal cations

    NASA Astrophysics Data System (ADS)

    Kernazhitsky, L.; Shymanovska, V.; Gavrilko, T.; Naumov, V.; Kshnyakin, V.; Khalyavka, T.

    2013-02-01

    The effect of nanocrystalline TiO2 doping with transition metal cations (Cu2+, Fe3+, Co2+, Cr3+) on their optical absorption and photocatalytic properties was investigated. The obtained metal-doped TiO2 samples were characterized by X-ray diffraction, scanning electron microscopy, and UV-vis absorption spectroscopy. It is shown that doping effect on anatase (A) and rutile (R) properties is quite different, being much stronger and complicated on A than on R. Contrary to doped R, doped A revealed a significant red shift of the absorption edge along with the band gap narrowing. Photocatalytic activity of anatase increases upon doping in the order: Aphotocatalytic activity of rutile samples decreases upon doping in the series R>R/Co>R/Cu>R/Fe>R/Cr, indicating the inhibitory effect of impurity cations. This fact correlates with the decrease in the UV absorption of the doped rutile in the region of the Hg-lamp irradiation at 4.88 eV.

  4. Surface induced dissociation: dissecting noncovalent protein complexes in the gas phase.

    PubMed

    Zhou, Mowei; Wysocki, Vicki H

    2014-04-15

    The quaternary structures of proteins are both important and of interest to chemists, because many proteins exist as complexes in vivo, and probing these structures allows us to better understand their biological functions. Conventional structural biology methods such as X-ray crystallography and nuclear magnetic resonance provide high-resolution information on the structures of protein complexes and are the gold standards in the field. However, other emerging biophysical methods that only provide low-resolution data (e.g. stoichiometry and subunit connectivity) on the structures of the protein complexes are also becoming more important to scientists. Mass spectrometry is one of these approaches that provide lower than atomic structural resolution, but the approach is higher throughput and provides not only better mass information than other techniques but also stoichiometry and topology. Fragile noncovalent interactions within the protein complexes can be preserved in the gas phase of MS under gentle ionization and transfer conditions. Scientists can measure the masses of the complexes with high confidence to reveal the stoichiometry and composition of the proteins. What makes mass spectrometry an even more powerful method is that researchers can further isolate the protein complexes and activate them in the gas phase to release subunits for more structural information. The caveat is that, upon gas-phase activation, the released subunits need to faithfully reflect the native topology so that useful information on the proteins can be extracted from mass spectrometry experiments. Unfortunately, many proteins tend to favor unfolding upon collision with neutral gas (the most common activation method in mass spectrometers). Therefore, this typically results in limited insights on the quaternary structure of the precursor without further manipulation of other experimental factors. Scientists have observed, however, that valuable structural information can be obtained

  5. Dissolution of two-phase microsystems: Gas and liquid microparticle dissolution and dehydration of biomaterials

    NASA Astrophysics Data System (ADS)

    Duncan, Phillip Brent

    A main focus of this research is to develop techniques to study the dissolution process of two-phase microsystems on a single microparticle basis. This dissertation introduces a systematic approach to investigate the formation of microparticles to fulfill the need for rational design of microspheres for a range of applications. This novel method is based on the micropipet manipulation technique and can essentially test any system, where the continuous phase is a liquid and the dispersed phase is practically any phase, a gas (foam), a liquid (emulsion), or a solid (suspension). It is possible to study single microparticle volumes in the picoliter to nanoliter scale, which is on the same size-scale as particles created in bulk suspensions, microsphere processes, and applications. The ability to create, isolate, observe, and manipulate individual gas, liquid or solid microparticles in a well-defined and controlled liquid environment was found to be ideal to study gas microbubbles and microparticles, liquid microdroplets, and the dehydration of dissolved solutes. Subsequently, one can directly measure the dissolution rate and, when a solute is present, calculate its concentration during the dissolution process. Microbubble or microdroplet dissolution in a second phase is driven by two independent factors, a concentration gradient (undersaturation of the dispersed phase in the continuous phase) and a pressure gradient (due to the Laplace-overpressure inside the microparticle created by the surface tension). Experimentally, each of these driving forces can be independently tested. Both the gas microparticle and pure liquid microdroplet dissolution can be predicted by a simple theory based on the diffusion coefficient and solubility limit of the dispersed phase in the continuous phase. The dehydration of a salt ion solution microdroplet results in the nucleation and growth of a crystal, while the dehydration of proteins leads to glassification of the protein. The water

  6. Single-shot gas-phase thermometry by time-to-frequency mapping of coherence dephasing.

    PubMed

    Yue, Orin; Bremer, Marshall T; Pestov, Dmitry; Gord, James R; Roy, Sukesh; Dantus, Marcos

    2012-08-09

    We demonstrate a single-beam coherent anti-Stokes Raman scattering (CARS) technique for gas-phase thermometry that assesses the species-specific local gas temperature by single-shot time-to-frequency mapping of Raman-coherence dephasing. The proof-of-principle experiments are performed with air in a temperature-controlled gas cell. Impulsive excitation of molecular vibrations by an ultrashort pump/Stokes pulse is followed by multipulse probing of the 2330 cm(-1) Raman transition of N(2). This sequence of colored probe pulses, delayed in time with respect to each other and corresponding to three isolated spectral bands, imprints the coherence dephasing onto the measured CARS spectrum. For calibration purposes, the dephasing rates are recorded at various gas temperatures, and the relationship is fitted to a linear regression. The calibration data are then used to determine the gas temperature and are shown to provide better than 15 K accuracy. The described approach is insensitive to pulse energy fluctuations and can, in principle, gauge the temperature of multiple chemical species in a single laser shot, which is deemed particularly valuable for temperature profiling of reacting flows in gas-turbine combustors.

  7. CFD simulation of gas and non-Newtonian fluid two-phase flow in anaerobic digesters.

    PubMed

    Wu, Binxin

    2010-07-01

    This paper presents an Eulerian multiphase flow model that characterizes gas mixing in anaerobic digesters. In the model development, liquid manure is assumed to be water or a non-Newtonian fluid that is dependent on total solids (TS) concentration. To establish the appropriate models for different TS levels, twelve turbulence models are evaluated by comparing the frictional pressure drops of gas and non-Newtonian fluid two-phase flow in a horizontal pipe obtained from computational fluid dynamics (CFD) with those from a correlation analysis. The commercial CFD software, Fluent12.0, is employed to simulate the multiphase flow in the digesters. The simulation results in a small-sized digester are validated against the experimental data from literature. Comparison of two gas mixing designs in a medium-sized digester demonstrates that mixing intensity is insensitive to the TS in confined gas mixing, whereas there are significant decreases with increases of TS in unconfined gas mixing. Moreover, comparison of three mixing methods indicates that gas mixing is more efficient than mixing by pumped circulation while it is less efficient than mechanical mixing.

  8. Gas phase laser synthesis and processing of calcium phosphate nanoparticles for biomedical applications

    NASA Astrophysics Data System (ADS)

    Bapat, Parimal V.

    Biochemical processes make pervasive use of calcium and phosphate ions. Calcium phosphate salts that are naturally nontoxic and bioactive have been used for several medical applications in form of coatings and micropowders. Nanoparticle-based calcium phosphates have been shown to be internalized by living cells and be effective in DNA transfection, drug delivery, and transport of fluorophores for imaging of intracellular processes. They are also expected to interact strongly with cell adhesive proteins and are therefore promising elements in approaches to mimic the complex environment of the extra cellular matrix of bone. Harnessing this biomedical potential requires the ability to control the numerous characteristics of nanophase calcium phosphates that affect biological response, including nanoparticle chemical composition, crystal phase, crystallinity, crystallographic orientation of exposed faces, size, shape, surface area, number concentration, and degree of aggregation. This dissertation focuses on the use of laser-induced gas-phase synthesis for creation of calcium phosphate nanoparticles, and corresponding nanoparticle-based substrates that could offer new opportunities for guiding biological responses through well-controlled biochemical and topological cues. Gas-phase synthesis of nanoparticles has several characteristics that could enhance control over particle morphology, crystallinity, and surface area, compared to liquid-phase techniques. Synthesis from gas-phase precursors can be carried out at high temperatures and in high-purity inert or reactive gas backgrounds, enabling good control of chemistry, crystal structure, and purity. Moreover, the particle mean free path and number concentration can be controlled independently. This allows regulation of interparticle collision rates, which can be adjusted to limit aggregation. High-temperature synthesis of well-separated particles is therefore possible. In this work high power lasers are employed to

  9. Influences of various Pt dopants over surface platinized TiO2 on the photocatalytic oxidation of nitric oxide.

    PubMed

    Wang, Haiqiang; Wu, Zhongbiao; Liu, Yue; Wang, Yuejun

    2009-02-01

    Various surface platinized TiO(2) were prepared by four different preparation methods and investigated with respect to their behaviors in UV photocatalytic oxidation of nitric oxide. The physicochemical properties of the Pt modified TiO(2) were investigated by X-ray diffraction analysis, X-ray photoelectron spectrum analysis, transmission electron microscopy, and photoluminescence spectra. From the experimental results, it was found that new electronic states were observed above the valence bands of PtOx-TiO(2) and PtClx-TiO(2). And the lifetime of electrons and holes was found prolonged in the PtOx-TiO(2) catalysts. The activity tests showed that the dopants existed as metallic Pt and platinum chloride had little contribution to the photocatalytic oxidation of NO in gas phase. However, the dopant which existed as PtOx could improve the NO photocatalytic oxidation efficiency and the reaction rate. The photocatalytic activity of the 0.05 at% PtOx-TiO(2) was nearly three times higher than that of the pure Degussa P25 with an inlet NO concentration of 200 ppm.

  10. ASSESSMENT OF SUBSURFACE FATE OF MONOETHANOLAMINE AT SOUR GAS PROCESSING PLANT SITES-PHASE III

    SciTech Connect

    James A. Sorensen

    1999-02-01

    Alkanolamines are commonly used by the natural gas industry to remove hydrogen sulfide, carbon dioxide, and other acid gases from the natural gas in which they occur (''sour'' gas if hydrogen sulfide is present). At sour gas-processing plants, as at all plants that use alkanolamines for acid gas removal (AGR), spills and on-site management of wastes containing alkanolamines and associated reaction products have occasionally resulted in subsurface contamination that is presently the focus of some environmental concern. In 1994, the Energy and Environmental Research Center (EERC) initiated a three-phase program to investigate the natural attenuation processes that control the subsurface transport and fate of the most commonly used alkanolamine in Canada, monoethanolamine (MEA). Funding for the MEA research program was provided by the U.S. Department of Energy (DOE), Canadian Association of Petroleum Producers (CAPP), Canadian Occidental Petroleum Ltd. (CanOxy), Gas Research Institute (GRI), Environment Canada, and the National Energy Board of Canada. The MEA research program focused primarily on examining the biodegradability of MEA and MEA-related waste materials in soils and soil-slurries under a variety of environmentally relevant conditions, evaluating the mobility of MEA in soil and groundwater and the effectiveness of bioremediation techniques for removing contaminants and toxicity from MEA-contaminated soil. The presently inactive Okotoks sour gas-processing plant, owned by CanOxy in Alberta, Canada, was the source of samples and field data for much of the laboratory-based experimental work and was selected to be the location for the field-based efforts to evaluate remediation techniques. The objective of the research program is to provide the natural gas industry with ''real world'' data and insights developed under laboratory and field conditions regarding the effective and environmentally sound use of biological methods for the remediation of soil

  11. MOLECULAR SPECTROSCPY AND REACTIONS OF ACTINIDES IN THE GAS PHASE AND CRYOGENIC MATRICES

    SciTech Connect

    Heaven, Michael C.; Gibson, John K.; Marcalo, Joaquim

    2009-02-01

    In this chapter we review the spectroscopic data for actinide molecules and the reaction dynamics for atomic and molecular actinides that have been examined in the gas phase or in inert cryogenic matrices. The motivation for this type of investigation is that physical properties and reactions can be studied in the absence of external perturbations (gas phase) or under minimally perturbing conditions (cryogenic matrices). This information can be compared directly with the results from high-level theoretical models. The interplay between experiment and theory is critically important for advancing our understanding of actinide chemistry. For example, elucidation of the role of the 5f electrons in bonding and reactivity can only be achieved through the application of experimentally verified theoretical models. Theoretical calculations for the actinides are challenging due the large numbers of electrons that must be treated explicitly and the presence of strong relativistic effects. This topic has been reviewed in depth in Chapter 17 of this series. One of the goals of the experimental work described in this chapter has been to provide benchmark data that can be used to evaluate both empirical and ab initio theoretical models. While gas-phase data are the most suitable for comparison with theoretical calculations, there are technical difficulties entailed in generating workable densities of gas-phase actinide molecules that have limited the range of species that have been characterized. Many of the compounds of interest are refractory, and problems associated with the use of high temperature vapors have complicated measurements of spectra, ionization energies, and reactions. One approach that has proved to be especially valuable in overcoming this difficulty has been the use of pulsed laser ablation to generate plumes of vapor from refractory actinide-containing materials. The vapor is entrained in an inert gas, which can be used to cool the actinide species to room

  12. Intracavity phase-matched coherent anti-Stokes Raman spectroscopy for trace gas detection.

    PubMed

    Zaitsu, Shin-ichi; Imasaka, Totaro

    2014-01-01

    We present a novel, cavity-enhanced spectroscopic technique based on a phase-matched Raman process to detect trace quantities of gas. The essence of this technique is the careful control of cavity dispersion to satisfy the phase-matching condition of coherent anti-Stokes Raman scattering (CARS) enhanced in a high-finesse optical cavity. A 6000-fold improvement of the CARS signal is observed under optimized conditions, indicating that this is a promising tool to quantify Raman-active molecules with an extremely low detection limit.

  13. Gas phase NMR spectra of N,N-dimethylnitrosamine. Environmental effects on kinetic parameters

    NASA Astrophysics Data System (ADS)

    Chauvel, J. Paul; Leung, Doris Y.; True, Nancy S.

    1984-04-01

    Gas phase 1H NMR spectra of N,N-dimethylnitrosamine are consistent with first order chemical exchange rate constants which are ca. 25 times faster than those observed in neat liquids at corresponding temperatures. The associated kinetic parameters: Eact(∞), 20.5(1.1) kcal mol -1, Δ H‡, 19.7(1.0) kcal mol -1 and Δ G‡, 21.1(0.4) kcal mol -1 are approximately 2.5 kcal mol -1 lower than the most recently reported values for the neat liquid. The observed phase dependence is consistent with a process proceeding via a freely rotating transition state.

  14. Finite-momentum superfluidity and phase transitions in a p-wave resonant Bose gas

    SciTech Connect

    Choi, Sungsoo; Radzihovsky, Leo

    2011-10-15

    We study a degenerate two-species gas of bosonic atoms interacting through a p-wave Feshbach resonance as, for example, realized in a {sup 85}Rb-{sup 87}Rb mixture. We show that, in addition to a conventional atomic and a p-wave molecular spinor-1 superfluidity at large positive and negative detunings, respectively, the system generically exhibits a finite-momentum atomic-molecular superfluidity at intermediate detuning around the unitary point. We analyze the detailed nature of the corresponding phases and the associated quantum and thermal phase transitions.

  15. Fluorometric method for the determination of gas-phase hydrogen peroxide

    NASA Technical Reports Server (NTRS)

    Kok, Gregory L.; Lazrus, Allan L.

    1986-01-01

    The fluorometric gas-phase hydrogen peroxide procedure is based on the technique used by Lazrus et. al. for the determination of H2O2 in the liquid phase. The analytical method utilizes the reaction of H2O2 with horseradish peroxidase and p-hydroxphenylacetic acid (POPHA) to form the fluorescent dimer of POPHA. The analytical reaction responds stoichiometrically to both H2O2 and some organic hydroperoxides. To discriminate H2O2 from organic hydroperoxides, catalase is used to preferentially destroy H2O2. Using a dual-channel flow system the H2O2 concentration is determined by difference.

  16. Gas-Phase Molecular Dynamics: Theoretical Studies In Spectroscopy and Chemical Dynamics

    SciTech Connect

    Yu H. G.; Muckerman, J.T.

    2012-05-29

    The main goal of this program is the development and application of computational methods for studying chemical reaction dynamics and molecular spectroscopy in the gas phase. We are interested in developing rigorous quantum dynamics algorithms for small polyatomic systems and in implementing approximate approaches for complex ones. Particular focus is on the dynamics and kinetics of chemical reactions and on the rovibrational spectra of species involved in combustion processes. This research also explores the potential energy surfaces of these systems of interest using state-of-the-art quantum chemistry methods, and extends them to understand some important properties of materials in condensed phases and interstellar medium as well as in combustion environments.

  17. Interactions of molecules with HCl in the gas and matrix phases

    NASA Astrophysics Data System (ADS)

    George, W. O.; Lewis, Rh.; Hussain, G.; Rees, G. J.

    1988-10-01

    The FT-IR spectra of mixtures of HCl and the following compounds have been recorded in the gaseous and matrix isolated phases: argon, ethene, ethyne, d 6-benzene, fluorobenzene, CO, CO 2, SO 2, CCl 4, CHCl 3, d 6-acetone, ethanal, HCN, acrylonitrile. The features which are measured are: firstly the changes in the integrated intensity of lines in the rotation—vibration spectrum of the fundamental HCl band as a function of non-specific interactions with other components of the mixture and secondly bands associated with specific interactions forming hydrogen bonded complexes in the gas and matrix isolated phases. The relationship between the two kinds of interactions is discussed.

  18. Numerical simulation study on gas solid two-phase flow in pre-calciner

    NASA Astrophysics Data System (ADS)

    Hu, Zhijuan; Lu, Jidong; Huang, Lai; Wang, Shijie

    2006-06-01

    A three-dimensional numerical simulation of DD (dual combustion and denitratior process) pre-calciner for cement production was conducted in this paper. In Euler coordinate system, the fluid phase is expressed with RNG k- ɛ two-equation model and the solid phase is expressed with particle stochastic trajectory model in Lagrange coordinate system. Four mixture fractions are deduced in this article to simulate the gas compositions. The results of numerical simulation predicted the burn-out ratio of coal and the decomposition ratio of limestone particles along with particle trajectories. It also supplied theoretical foundation for industrial analysis of the coupling relation between coal combustion and calcium carbonate decomposition.

  19. Nanoparticle films made by gas phase synthesis: comparison of various techniques and sensor applications

    NASA Astrophysics Data System (ADS)

    Heszler, Peter; Reyes, L. F.; Hoel, Anders; Landstrom, Lars; Lantto, V.; Granqvist, Claes-Goran

    2003-07-01

    Nanoparticles can be generated by several different gas phase methods, such as gas deposition, laser-assisted chemical vapor deposition, and laser ablation. Some of the most important aspects - such as size-distribution, structure, and chemical composition of the generated nanoparticles (specifically W and WO3) - are presented and compared. WO3 nanoparticle films were deposited by an advanced gas deposition technique and were tested for sensor applications. Two different sensor devices were fabricated: Firstly, a thin Au-WO3 nanoparticle sandwich film was constructed, and conductance fluctuations of the Au film were measured as the sensor was exposed to alcohol vapor. Secondly, conductivity changes of a thick WO3 nanoparticle film were detected as it was exposed to test gases (H2S, NO2, and CO).

  20. Analysis of organic gas phase compounds formed by hydrothermal liquefaction of Dried Distillers Grains with Solubles.

    PubMed

    Madsen, René B; Christensen, Per S; Houlberg, Kasper; Lappa, Elpiniki; Mørup, Anders J; Klemmer, Maika; Olsen, Eva M; Jensen, Mads M; Becker, Jacob; Iversen, Bo B; Glasius, Marianne

    2015-09-01

    This work provides a comprehensive characterization of the gas phase from hydrothermal liquefaction of Dried Distillers Grains with Solubles (DDGS) collected during a 24-h continuous experiment. The gas consisted mainly of CO2, CO, H2, CH4 and C2H6 accounting for 96 v/v% while further analysis by gas chromatography coupled to mass spectrometry (GC-MS) showed additionally 62 compounds of which 54 were tentatively identified. These products included methanethiol, dimethyl sulfide, various olefins and several aromatic compounds. The composition provided clear indication of the steady state of the system. Apart from CO2, olefins were the most abundant compound class and could provide a source of revenue.

  1. Selective covalent bond formation in polypeptide ions via gas-phase ion/ion reaction chemistry.

    PubMed

    Han, Hongling; McLuckey, Scott A

    2009-09-16

    Primary amines present in protonated polypeptides can be covalently modified via gas-phase ion/ion reactions using bifunctional reagent ions. The use of reagent anions with a charge-bearing site that leads to strong interactions with the polypeptide, such as sulfonic acid, gives rise to the formation of a long-lived adduct. A distinct reactive functional group, an aldehyde in the present case, can then undergo reaction with the peptide. Collisional activation of the adduct ion formed from a reagent with an aldehyde group and a peptide ion with a primary amine gives rise to water loss in conjunction with imine (Schiff base) formation. The covalently bound modification is retained upon subsequent collisional activation. This work demonstrates the ability to selectively modify polypeptide ions in the gas phase within the context of a multistage mass spectrometry experiment.

  2. Decay of the 3D inviscid liquid-gas two-phase flow model

    NASA Astrophysics Data System (ADS)

    Zhang, Yinghui

    2016-06-01

    We establish the optimal {Lp-L2(1 ≤ p < 6/5)} time decay rates of the solution to the Cauchy problem for the 3D inviscid liquid-gas two-phase flow model and analyze the influences of the damping on the qualitative behaviors of solution. Compared with the viscous liquid-gas two-phase flow model (Zhang and Zhu in J Differ Equ 258:2315-2338, 2015), our results imply that the friction effect of the damping is stronger than the dissipation effect of the viscosities and enhances the decay rate of the velocity. Our proof is based on Hodge decomposition technique, the {Lp-L2} estimates for the linearized equations and an elaborate energy method.

  3. Unusual hydroxyl migration in the fragmentation of β-alanine dication in the gas phase.

    PubMed

    Piekarski, Dariusz Grzegorz; Delaunay, Rudy; Maclot, Sylvain; Adoui, Lamri; Martín, Fernando; Alcamí, Manuel; Huber, Bernd A; Rousseau, Patrick; Domaracka, Alicja; Díaz-Tendero, Sergio

    2015-07-14

    We present a combined experimental and theoretical study of the fragmentation of doubly positively charged β-alanine molecules in the gas phase. The dissociation of the produced dicationic molecules, induced by low-energy ion collisions, is analysed by coincidence mass spectrometric techniques; the coupling with ab initio molecular dynamics simulations allows rationalisation of the experimental observations. The present strategy gives deeper insights into the chemical mechanisms of multiply charged amino acids in the gas phase. In the case of the β-alanine dication, in addition to the expected Coulomb explosion and hydrogen migration processes, we have found evidence of hydroxyl-group migration, which leads to unusual fragmentation products, such as hydroxymethyl cation, and is necessary to explain some of the observed dominant channels.

  4. Gas-Phase Femtosecond Particle Spectroscopy: A Bottom-Up Approach to Nucleotide Dynamics

    NASA Astrophysics Data System (ADS)

    Stavros, Vasilios G.; Verlet, Jan R. R.

    2016-05-01

    We summarize how gas-phase ultrafast charged-particle spectroscopy has been used to provide an understanding of the photophysics of DNA building blocks. We focus on adenine and discuss how, following UV excitation, specific interactions determine the fates of its excited states. The dynamics can be probed using a systematic bottom-up approach that provides control over these interactions and that allows ever-larger complexes to be studied. Starting from a chromophore in adenine, the excited state decay mechanisms of adenine and chemically substituted or clustered adenine are considered and then extended to adenosine mono-, di-, and trinucleotides. We show that the gas-phase approach can offer exquisite insight into the dynamics observed in aqueous solution, but we also highlight stark differences. An outlook is provided that discusses some of the most promising developments in this bottom-up approach.

  5. Photoelectron Velocity Map Imaging of Vibrationally Excited, Gas-Phase Biomolecules and Their Anions

    NASA Astrophysics Data System (ADS)

    Bakker, Daniël; Bakels, Sjors; van der Made, Rutger; Peters, Atze; Rijs, Anouk

    2016-06-01

    A powerful method in spectroscopy to characterize the structure of large, gas phase molecules is to probe the ionization yield upon irradiating the molecules with infrared (IR) and/or ultraviolet (UV) radiation. When this spectroscopic technique is employed, the photodetached electrons are usually ignored, although they contain information on, for example, the ionization threshold of the molecule and the excited states of the formed ions. Here, the novel combination of a molecular beam mass spectrometer equipped with a laser desorption source, the free electron laser FELIX and the powerful velocity map imaging (VMI) technique is presented. With this extended set of tools we can bring large molecules intact into the gas phase and prepare them in specific vibrationally excited states. UV or VUV radiation can subsequently be used to ionize the molecules. The kinetic energy and the radial distribution of the photoelectrons can be measured using VMI combined with ion detection using a time-of-flight mass spectrometer.

  6. Gas-Phase Synthesis of 1-Silacyclopenta-2,4-diene.

    PubMed

    Yang, Tao; Dangi, Beni B; Thomas, Aaron M; Sun, Bing-Jian; Chou, Tzu-Jung; Chang, Agnes H H; Kaiser, Ralf I

    2016-07-04

    Silole (1-silacyclopenta-2,4-diene) was synthesized for the first time by the bimolecular reaction of the simplest silicon-bearing radical, silylidyne (SiH), with 1,3-butadiene (C4 H6 ) in the gas phase under single-collision conditions. The absence of consecutive collisions of the primary reaction product prevents successive reactions of the silole by Diels-Alder dimerization, thus enabling the clean gas-phase synthesis of this hitherto elusive cyclic species from acyclic precursors in a single-collision event. Our method opens up a versatile and unconventional path to access a previously rather obscure class of organosilicon molecules (substituted siloles), which have been difficult to access through classical synthetic methods.

  7. Simplification of the CBS-QB3 method for predicting gas-phase deprotonation free energies

    NASA Astrophysics Data System (ADS)

    Casasnovas, Rodrigo; Frau, Juan; Ortega-Castro, Joaquín; Salvà, Antoni; Donoso, Josefa; Muñoz, Francisco

    Simplified versions of CBS-QB3 model chemistry were used to calculate the free energies of 36 deprotonation reactions in the gas phase. The best such version, S9, excluded coupled cluster calculation [CCSD(T)], and empirical (ΔEemp) and spin-orbit (ΔEint) correction terms. The mean absolute deviation and root mean square thus obtained (viz. 1.24 and 1.56 kcal/mol, respectively) were very-close to those provided by the original CBS-QB3 method (1.19 and 1.52 kcal/mol, respectively). The high-accuracy of the proposed simplification and its computational expeditiousness make it an excellent choice for energy calculations on gas-phase deprotonation reactions in complex systems.

  8. Transport simulations of the pre-thermal-quench phase in ASDEX Upgrade massive gas injection experiments

    NASA Astrophysics Data System (ADS)

    Fable, E.; Pautasso, G.; Lehnen, M.; Dux, R.; Bernert, M.; Mlynek, A.; the ASDEX Upgrade Team

    2016-02-01

    The pre-thermal-quench (PTQ) phase of the massive gas injection (MGI) scenario to terminate the tokamak plasma discharge is studied by means of one-dimensional (1D) transport simulations. This phase is characterized by the cold-front penetration in the hot plasma after the gas has been released from the valves, and before the actual thermal quench takes place, with consequent plasma disruption at lower stored energy. The comparison between the simulations and the ASDEX Upgrade (AUG) experiments allows to gain insight in the observed dependencies and time scales. Despite the genuine three-dimensional structure of the problem, it is shown that the 1D simulations are already giving experimentally relevant answers, the reason for which will be discussed in detail. Influence of unknown parameters and simplifying assumptions are also discussed.

  9. Taming molecular beams; towards a gas-phase molecular laboratory on a chip

    NASA Astrophysics Data System (ADS)

    Meek, Samuel A.; Santambrogio, Gabriele; Conrad, Horst; Meijer, Gerard

    2009-11-01

    The manipulation of gas-phase molecules with electric and magnetic fields above a chip is an emerging field of research. Miniaturization of the electric and magnetic field structures allows for the creation of large field gradients and tight traps above the chip. Present-day microelectronics technology enables the integration of complicated tools and devices on a compact surface area. The molecules can be positioned extremely accurately and reproducibly above the chip where they can be held isolated from their environment and where there is excellent access to them. It is expected that several of the gas-phase molecular beam experiments that are currently being done in machines that are up to several meters in length can in the future be performed on a surface area of a few cm2 and that many new experiments will become possible.

  10. Infrared Action Spectroscopy of Low-Temperature Neutral Gas-Phase Molecules of Arbitrary Structure

    NASA Astrophysics Data System (ADS)

    Yatsyna, Vasyl; Bakker, Daniël J.; Salén, Peter; Feifel, Raimund; Rijs, Anouk M.; Zhaunerchyk, Vitali

    2016-09-01

    We demonstrate a technique for IR action spectroscopy that enables measuring IR spectra in a background-free fashion for low-temperature neutral gas-phase molecules of arbitrary structure. The method is exemplified experimentally for N -methylacetamide molecules in the mid-IR spectral range of 1000 - 1800 cm-1 , utilizing the free electron laser FELIX. The technique involves the resonant absorption of multiple mid-IR photons, which induces molecular dissociation. The dissociation products are probed with 10.49 eV vacuum ultraviolet photons and analyzed with a mass spectrometer. We also demonstrate the capability of this method to record, with unprecedented ease, mid-IR spectra for the molecular associates, such as clusters and oligomers, present in a molecular beam. In this way the mass-selected spectra of low-temperature gas-phase dimers and trimers of N -methylacetamide are measured in the full amide I-III range.

  11. Multifunctional acid formation from the gas-phase ozonolysis of beta-pinene.

    PubMed

    Ma, Yan; Marston, George

    2008-10-28

    The gas-phase ozonolysis of beta-pinene was studied in static chamber experiments, using gas chromatography coupled to mass spectrometric and flame ionisation detection to separate and detect products. A range of multifunctional organic acids-including pinic acid, norpinic acid, pinalic-3-acid, pinalic-4-acid, norpinalic acid and OH-pinalic acid-were identified in the condensed phase after derivatisation. Formation yields for these products under systematically varying reaction conditions (by adding different OH radical scavengers and Criegee intermediate scavengers) were investigated and compared with those observed from alpha-pinene ozonolysis, allowing detailed information on product formation mechanisms to be elucidated. In addition, branching ratios for the initial steps of the reaction were inferred from quantitative measurements of primary carbonyl formation. Atmospheric implications of this work are discussed.

  12. Luther-Emery Phase and Atomic-Density Waves in a Trapped Fermion Gas

    NASA Astrophysics Data System (ADS)

    Xianlong, Gao; Rizzi, M.; Polini, Marco; Fazio, Rosario; Tosi, M. P.; Campo, V. L., Jr.; Capelle, K.

    2007-01-01

    The Luther-Emery liquid is a state of matter that is predicted to occur in one-dimensional systems of interacting fermions and is characterized by a gapless charge spectrum and a gapped spin spectrum. In this Letter we discuss a realization of the Luther-Emery phase in a trapped cold-atom gas. We study by means of the density-matrix renormalization-group technique a two-component atomic Fermi gas with attractive interactions subject to parabolic trapping inside an optical lattice. We demonstrate how this system exhibits compound phases characterized by the coexistence of spin pairing and atomic-density waves. A smooth crossover occurs with increasing magnitude of the atom-atom attraction to a state in which tightly bound spin-singlet dimers occupy the center of the trap. The existence of atomic-density waves could be detected in the elastic contribution to the light-scattering diffraction pattern.

  13. Hydration energies of deprotonated amino acids from gas phase equilibria measurements.

    PubMed

    Wincel, Henryk

    2008-08-01

    Singly hydrated clusters of deprotonated amino acids were studied using an electrospray high-pressure mass spectrometer equipped with a pulsed ion-beam reaction chamber. Thermochemical data, DeltaH(o), DeltaS(o), and DeltaG(o), for the hydration reaction [AA - H](-) + H(2)O = [AA - H](-).(H(2)O) were obtained from gas-phase equilibria determinations for AA = Gly, Ala, Val, Pro, Phe, Lys, Met, Trp, Gln, Arg, and Asp. The hydration free-energy changes are found to depend significantly on the side-chain substituents. The water binding energy in [AA - H](-).(H(2)O) increases with the gas-phase acidity of AA. The anionic hydrogen bond strengths in [AA - H](-).(H(2)O) are compared with those of the cationic bonds in the corresponding AAH(+).(H(2)O) systems.

  14. Imaging molecular structure through femtosecond photoelectron diffraction on aligned and oriented gas-phase molecules.

    PubMed

    Boll, Rebecca; Rouzée, Arnaud; Adolph, Marcus; Anielski, Denis; Aquila, Andrew; Bari, Sadia; Bomme, Cédric; Bostedt, Christoph; Bozek, John D; Chapman, Henry N; Christensen, Lauge; Coffee, Ryan; Coppola, Niccola; De, Sankar; Decleva, Piero; Epp, Sascha W; Erk, Benjamin; Filsinger, Frank; Foucar, Lutz; Gorkhover, Tais; Gumprecht, Lars; Hömke, André; Holmegaard, Lotte; Johnsson, Per; Kienitz, Jens S; Kierspel, Thomas; Krasniqi, Faton; Kühnel, Kai-Uwe; Maurer, Jochen; Messerschmidt, Marc; Moshammer, Robert; Müller, Nele L M; Rudek, Benedikt; Savelyev, Evgeny; Schlichting, Ilme; Schmidt, Carlo; Scholz, Frank; Schorb, Sebastian; Schulz, Joachim; Seltmann, Jörn; Stener, Mauro; Stern, Stephan; Techert, Simone; Thøgersen, Jan; Trippel, Sebastian; Viefhaus, Jens; Vrakking, Marc; Stapelfeldt, Henrik; Küpper, Jochen; Ullrich, Joachim; Rudenko, Artem; Rolles, Daniel

    2014-01-01

    This paper gives an account of our progress towards performing femtosecond time-resolved photoelectron diffraction on gas-phase molecules in a pump-probe setup combining optical lasers and an X-ray free-electron laser. We present results of two experiments aimed at measuring photoelectron angular distributions of laser-aligned 1-ethynyl-4-fluorobenzene (C(8)H(5)F) and dissociating, laser-aligned 1,4-dibromobenzene (C(6)H(4)Br(2)) molecules and discuss them in the larger context of photoelectron diffraction on gas-phase molecules. We also show how the strong nanosecond laser pulse used for adiabatically laser-aligning the molecules influences the measured electron and ion spectra and angular distributions, and discuss how this may affect the outcome of future time-resolved photoelectron diffraction experiments.

  15. Distinct Fragmentation Pathways of Anticancer Drugs Induced by Charge-Carrying Cations in the Gas Phase

    NASA Astrophysics Data System (ADS)

    Hong, Areum; Lee, Hong Hee; Heo, Chae Eun; Cho, Yunju; Kim, Sunghwan; Kang, Dukjin; Kim, Hugh I.

    2016-12-01

    With the growth of the pharmaceutical industry, structural elucidation of drugs and derivatives using tandem mass spectrometry (MS2) has become essential for drug development and pharmacokinetics studies because of its high sensitivity and low sample requirement. Thus, research seeking to understand fundamental relationships between fragmentation patterns and precursor ion structures in the gas phase has gained attention. In this study, we investigate the fragmentation of the widely used anticancer drugs, doxorubicin (DOX), vinblastine (VBL), and vinorelbine (VRL), complexed by a singly charged proton or alkali metal ion (Li+, Na+, K+) in the gas phase. The drug-cation complexes exhibit distinct fragmentation patterns in tandem mass spectra as a function of cation size. The trends in fragmentation patterns are explicable in terms of structures derived from ion mobility mass spectrometry (IM-MS) and theoretical calculations.

  16. Fundamental studies of gas phase ionic reactions by ion mobility spectrometry

    NASA Technical Reports Server (NTRS)

    Giles, K.; Knighton, W. B.; Sahlstrom, K. E.; Grimsrud, E. P.

    1995-01-01

    Ion mobility spectrometry (IMS) provides a promising approach to the study of gas phase ionic reactions in buffer gases at unusually high pressures. This point is illustrated here by studies of the Sn2 nucleophilic displacement reaction, Cl(-) + CH3Br yields Br + CH3Br, using IMS at atmospheric pressure. The equilibrium clustering reaction, Cl(-)(CHCI3)(n - 1) + CHCI3 yields Cl(-)(CHCI3)(n), where n = 1 and 2, and the effect of clustering on the Sn2 reaction with CH3Br have also been characterized by this IMS-based kinetic method. Present problems and anticipated improvements in the application of ion mobility spectrometry to studies of other gas phase ionic processes are discussed.

  17. Gas-Phase Chemistry of Multiply Charged Bioions in Analytical Mass Spectrometry

    PubMed Central

    Huang, Teng-Yi; McLuckey, Scott A.

    2011-01-01

    Ion chemistry has long played an important role in molecular mass spectrometry (MS), as it is central to the use of MS as a structural characterization tool. With the advent of ionization methods capable of producing gaseous ions from large biomolecules, the chemistry of gaseous bioions has become a highly active area of research. Gas-phase biomolecule-ion reactions are usually driven by interactions with neutral molecules, photons, electrons, ions, or surfaces. Ion dissociation or transformation into different ion types can be achieved. The types of reaction products observed depend on the characteristics of the ions, the transformation methods, and the time frame of observation. This review focuses on the gas-phase chemistries of ions derived from the electrospray ionization of peptides, proteins, and oligonucleotides, with particular emphasis on their utility in bioanalysis. Various ion-transformation strategies, which further facilitate structural interrogation by converting ions from one type to another, are also summarized. PMID:20636047

  18. Gas-phase catalysis by atomic and cluster metal ions: the ultimate single-site catalysts.

    PubMed

    Böhme, Diethard K; Schwarz, Helmut

    2005-04-15

    Gas-phase experiments with state-of-the-art techniques of mass spectrometry provide detailed insights into numerous elementary processes. The focus of this Review is on elementary reactions of ions that achieve complete catalytic cycles under thermal conditions. The examples chosen cover aspects of catalysis pertinent to areas as diverse as atmospheric chemistry and surface chemistry. We describe how transfer of oxygen atoms, bond activation, and coupling of fragments can be mediated by atomic or cluster metal ions. In some cases truly unexpected analogies of the idealized gas-phase ion catalysis can be drawn with related chemical transformations in solution or the solid state, and so improve our understanding of the intrinsic operation of a practical catalyst at a strictly molecular level.

  19. Anchoring the gas-phase acidity scale: From formic acid to methanethiol

    NASA Astrophysics Data System (ADS)

    Eyet, Nicole; Villano, Stephanie M.; Bierbaum, Veronica M.

    2009-06-01

    We have measured the gas-phase acidities of nine compounds: formic acid, acetic acid, 1,3-propanedithiol, 2-methyl-2-propanethiol, 3-methyl-1-butanethiol, 2-propanethiol, 1-propanethiol, ethanethiol, and methanethiol, with acidities ranging from 338.6 to 351.1 kcal mol-1 using proton transfer kinetics and the resulting equilibrium constants. These acids were anchored to the well-known acidity of hydrogen sulfide; the measured acidities are in good agreement with previous experimental values, but error bars are significantly reduced. The gas-phase acidity of 3-methyl-1-butanethiol was determined to be 347.1 (5) kcal mol-1; there were no previous measurements of this value. Entropies of deprotonation were calculated and enthalpies of deprotonation were determined.

  20. Methods and apparatus for using gas and liquid phase cathodic depolarizers

    NASA Technical Reports Server (NTRS)

    Murphy, Oliver J. (Inventor); Hitchens, G. Duncan (Inventor)

    1998-01-01

    The invention provides methods for using gas and liquid phase cathodic depolarizers in an electrochemical cell having a cation exchange membrane in intimate contact with the anode and cathode. The electrochemical conversion of cathodic depolarizers at the cathode lowers the cell potential necessary to achieve a desired electrochemical conversion, such as ozone evolution, at the anode. When gaseous cathodic depolarizers, such as oxygen, are used, a gas diffusion cathode having the cation exchange membrane bonded thereto is preferred. When liquid phase cathodic depolarizers are used, the cathode may be a flow-by electrode, flow-through electrode, packed-bed electrode or a fluidized-bed electrode in intimate contact with the cation exchange membrane.

  1. Gas-phase acidities of tetrahedral oxyacids from ab initio electronic structure theory

    SciTech Connect

    Rustad, J.R.; Dixon, D.A.; Kubicki, J.D.; Felmy, A.R.

    2000-05-04

    Density functional calculations have been performed on several protonation states of the oxyacids of Si, P, V, As, Cr, and S. Structures and vibrational frequencies are in good agreement with experimental values where these are available. A reasonably well-defined correlation between the calculated gas-phase acidities and the measured pK{sub a} in aqueous solution has been found. The pK{sub a}/gas-phase acidity slopes are consistent with those derived from previous molecular mechanics calculations on ferric hydrolysis and the first two acidity constants for orthosilicic acid. The successive deprotonation of other H{sub n}TO{sub 4} species, for a given tetrahedral anion T are roughly consistent with this slope, but not to the extent that there is a universal correlation among all species.

  2. Online Measurements of Highly Oxidized Organics in the Gas and Particle phase during SOAS and SENEX

    NASA Astrophysics Data System (ADS)

    Lopez-Hilfiker, F.; Lee, B. H.; Mohr, C.; Ehn, M.; Rubach, F.; Mentel, T. F.; Kleist, E.; Thornton, J. A.

    2014-12-01

    We present measurements of a large suite of gas and particle phase organic compounds made with a Filter Inlet for Gas and AEROsol (FIGAERO) coupled to a high resolution time of flight chemical ionization mass spectrometer (HR-ToF-CIMS) developed at the University of Washington and with airborne HR-ToF-CIMS measurements. The FIGAERO instrument was deployed on the Jülich Plant Atmosphere Chamber to study α-pinene oxidation, and subsequently at the SMEAR II forest station in Hyytiälä, Finland and the SOAS ground site, in Brent Alabama. During the Southern Atmosphere Study, a gas-phase only version of the HR-ToF-CIMS was deployed on the NOAA WP-3 aircraft as part of SENEX. We focus here on highly oxygenated organic compounds derived from monoterpene oxidation detected both aloft during SENEX and at the ground-based site during SOAS. In both chamber and the atmosphere, many highly oxidized, low volatility compounds were observed in the gas and particles and many of the same compositions detected in the gas-phase were detected in the particles upon temperature programmed thermal desorption. The fraction of a given compound measured in the particle phase follows expected trends with elemental composition such as O/C ratios, but many compounds would not be well described by an absorptive partitioning model assuming unity activity coefficients. The detailed structure in the thermograms reveals a significant contribution from large molecular weight organics and/or oligomers in both chamber and ambient aerosol samples. Approximately 50% of the measured organics in the particle phase are associated with compounds having effective vapour pressures 4 or more orders of magnitude lower than commonly measured monoterpene oxidation products. We discuss the implications of these findings for measurements of gas-particle partitioning and for evaluating the contribution of monoterpene oxidation to organic aerosol formation and growth. We also use the aircraft measurements and a

  3. Source reconciliation of atmospheric gas-phase and particle-phase pollutants during a severe photochemical smog episode.

    PubMed

    Schauer, James J; Fraser, Matthew P; Cass, Glen R; Simoneit, Bernd R T

    2002-09-01

    A comprehensive organic compound-based receptor model is developed that can simultaneously apportion the source contributions to atmospheric gas-phase organic compounds, semivolatile organic compounds, fine particle organic compounds, and fine particle mass. The model is applied to ambient data collected at four sites in the south coast region of California during a severe summertime photochemical smog episode, where the model determines the direct primary contributions to atmospheric pollutants from 11 distinct air pollution source types. The 11 sources included in the model are gasoline-powered motor vehicle exhaust, diesel engine exhaust, whole gasoline vapors, gasoline headspace vapors, organic solvent vapors, whole diesel fuel, paved road dust, tire wear debris, meat cooking exhaust, natural gas leakage, and vegetative detritus. Gasoline engine exhaust plus whole gasoline vapors are the predominant sources of volatile organic gases, while gasoline and diesel engine exhaust plus diesel fuel vapors dominate the emissions of semivolatile organic compounds from these sources during the episode studied at all four air monitoring sites. The atmospheric fine particle organic compound mass was composed of noticeable contributions from gasoline-powered motor vehicle exhaust, diesel engine exhaust, meat cooking, and paved road dust with smaller but quantifiable contributions from vegetative detritus and tire wear debris. In addition, secondary organic aerosol, which is formed from the low-vapor pressure products of gas-phase chemical reactions, is found to be a major source of fine particle organic compound mass under the severe photochemical smog conditions studied here. The concentrations of secondary organic aerosol calculated in the present study are compared with previous fine particle source apportionment results for less intense photochemical smog conditions. It is shown that estimated secondary organic aerosol concentrations correlate fairly well with the

  4. Initiation of the ice phase by marine biogenic surfaces in supersaturated gas and supercooled aqueous phases.

    PubMed

    Alpert, Peter A; Aller, Josephine Y; Knopf, Daniel A

    2011-11-28

    Biogenic particles have the potential to affect the formation of ice crystals in the atmosphere with subsequent consequences for the hydrological cycle and climate. We present laboratory observations of heterogeneous ice nucleation in immersion and deposition modes under atmospherically relevant conditions initiated by Nannochloris atomus and Emiliania huxleyi, marine phytoplankton with structurally and chemically distinct cell walls. Temperatures at which freezing, melting, and water uptake occur are observed using optical microscopy. The intact and fragmented unarmoured cells of N. atomus in aqueous NaCl droplets enhance ice nucleation by 10-20 K over the homogeneous freezing limit and can be described by a modified water activity based ice nucleation approach. E. huxleyi cells covered by calcite plates do not enhance droplet freezing temperatures. Both species nucleate ice in the deposition mode at an ice saturation ratio, S(ice), as low as ~1.2 and below 240 K, however, for each, different nucleation modes occur at warmer temperatures. These observations show that markedly different biogenic surfaces have both comparable and contrasting effects on ice nucleation behaviour depending on the presence of the aqueous phase and the extent of supercooling and water vapour supersaturation. We derive heterogeneous ice nucleation rate coefficients, J(het), and cumulative ice nuclei spectra, K, for quantification and analysis using time-dependent and time-independent approaches, respectively. Contact angles, α, derived from J(het)via immersion freezing depend on T, a(w), and S(ice). For deposition freezing, α can be described as a function of S(ice) only. The different approaches yield different predictions of atmospheric ice crystal numbers primarily due to the time evolution allowed for the time-dependent approach with implications for the evolution of mixed-phase and ice clouds.

  5. Test and Characterization of Some Zeolite Supported Gas Phase Desulfurization Sorbents

    DTIC Science & Technology

    2009-06-01

    of-the-art SOFC electrode material is improving, the gas phase desulfurization step at high temperature is still essential to SOFCs . Our report ...NOTICES Disclaimers The findings in this report are not to be construed as an official Department of the Army position unless so...the use thereof. Destroy this report when it is no longer needed. Do not return it to the originator. Army Research Laboratory Adelphi, MD

  6. Comparison of ozone determinations by ultraviolet photometry and gas-phase titration

    NASA Technical Reports Server (NTRS)

    Demore, W. B.; Patapoff, M.

    1976-01-01

    A comparison of ozone determinations based on ultraviolet absorption photometry and gas-phase titration (GPT) shows good agreement between the two methods. Together with other results, these findings indicate that three candidate reference methods for ozone, UV photometry, IR photometry, and GPT are in substantial agreement. However, the GPT method is not recommended for routine use by air pollution agencies for calibration of ozone monitors because of susceptibility to experimental error.

  7. Position for determining gas-phase volatile organic compound concentrations in transuranic waste containers. Revision 2

    SciTech Connect

    Connolly, M.J.; Liekhus, K.J.; Djordjevic, S.M.; Loehr, C.A.; Spangler, L.R.

    1998-06-01

    In the conditional no-migration determination (NMD) for the test phase of the Waste Isolation Pilot Plant (WIPP), the US Environmental Protection Agency (EPA) imposed certain conditions on the US Department of Energy (DOE) regarding gas phase volatile organic compound (VOC) concentrations in the void space of transuranic (TRU) waste containers. Specifically, the EPA required the DOE to ensure that each waste container has no layer of confinement that contains flammable mixtures of gases or mixtures of gases that could become flammable when mixed with air. The EPA also required that sampling of the headspace of waste containers outside inner layers of confinement be representative of the entire void space of the container. The EPA stated that all layers of confinement in a container would have to be sampled until DOE can demonstrate to the EPA that sampling of all layers is either unnecessary or can be safely reduced. A test program was conducted at the Idaho National Engineering and Environmental Laboratory (INEEL) to demonstrate that the gas phase VOC concentration in the void space of each layer of confinement in vented drums can be estimated from measured drum headspace using a theoretical transport model and that sampling of each layer of confinement is unnecessary. This report summarizes the studies performed in the INEEL test program and extends them for the purpose of developing a methodology for determining gas phase VOC concentrations in both vented and unvented TRU waste containers. The methodology specifies conditions under which waste drum headspace gases can be said to be representative of drum gases as a whole and describes a method for predicting drum concentrations in situations where the headspace concentration is not representative. The methodology addresses the approach for determining the drum VOC gas content for two purposes: operational period drum handling and operational period no-migration calculations.

  8. Method and apparatus for selective capture of gas phase analytes using metal .beta.-diketonate polymers

    DOEpatents

    Harvey, Scott D [Kennewick, WA

    2011-06-21

    A process and sensor device are disclosed that employ metal .beta.-diketonate polymers to selectively capture gas-phase explosives and weaponized chemical agents in a sampling area or volume. The metal .beta.-diketonate polymers can be applied to surfaces in various analytical formats for detection of: improvised explosive devices, unexploded ordinance, munitions hidden in cargo holds, explosives, and chemical weapons in public areas.

  9. a Nucleoside Under Observation in the Gas Phase: a Rotational Study of Uridine

    NASA Astrophysics Data System (ADS)

    Peña, Isabel; Alonso, José L.

    2014-06-01

    The nucleoside of uridine has been placed in the gas phase by laser ablation and the most stable C2{'}-anti conformation characterized by broadband chirped pulse (CP-FTMW) and narrowband molecular beam Fourier transform microwave (LA-MB-FTMW) spectroscopies. The quadrupole hyperfine structure, originated by two 14N nuclei, has been completely resolved. Intramolecular hydrogen bonds involving uracil and ribose moieties have been found to play an important role in the stabilization of the nucleoside.

  10. Mass Spectrometry of Protein-Ligand Complexes: Enhanced Gas Phase Stability of Ribonuclease-Nucleotide Complexes

    PubMed Central

    Yin, Sheng; Xie, Yongming; Loo, Joseph A.

    2008-01-01

    Noncovalent protein-ligand complexes are readily detected by electrospray ionization mass spectrometry (ESI-MS). Ligand binding stoichiometry can be determined easily by the ESI-MS method. The ability to detect noncovalent protein-ligand complexes depends, however, on the stability of the complexes in the gas phase environment. Solution binding affinities may or may not be accurate predictors of their stability in vacuo. Complexes composed of cytidine nucleotides bound to ribonuclease A (RNase A) and ribonuclease S (RNase S) were detected by ESI-MS and were further analyzed by MS/MS. RNase A and RNase S share similar structures and biological activity. Subtilisin-cleavage of RNase A yields an S-peptide and an S-protein; the S-peptide and S-protein interact through hydrophobic interactions with a solution binding constant in the nanomolar range to generate an active RNase S. Cytidine nucleotides bind to the ribonucleases through electrostatic interactions with a solution binding constant in the micromolar range. Collisionally activated dissociation (CAD) of the 1:1 RNase A-CDP and CTP complexes yields cleavage of the covalent phosphate bonds of the nucleotide ligands, releasing CMP from the complex. CAD of the RNase S-CDP and CTP complexes dissociates the S-peptide from the remaining S-protein/nucleotide complex; further dissociation of the S-protein/nucleotide complex fragments a covalent phosphate bond of the nucleotide with subsequent release of CMP. Despite a solution binding constant favoring the S-protein/S-peptide complex, CDP/CTP remains electrostatically bound to the S-protein in the gas phase dissociation experiment. This study highlights the intrinsic stability of electrostatic interactions in the gas phase and the significant differences in solution and gas phase stabilities of noncovalent complexes that can result. PMID:18565758

  11. Synthesis, crystal structure, and photocatalytic activity of the new three-layer aurivillius phases, Bi{sub 2}ASrTi{sub 2}TaO{sub 12} (A=Bi, La)

    SciTech Connect

    Wang Dong; Tang Kaibin; Liang Zhenhua; Zheng Huagui

    2010-02-15

    Two new three-layer Aurivillius phases Bi{sub 2}ASrTi{sub 2}TaO{sub 12} (A=Bi, La) have been synthesized. The detailed structure determination of Bi{sub 2}ASrTi{sub 2}TaO{sub 12} (A=Bi, La) performed by powder X-ray diffraction (XRD) and selected area electron microscopy (SAED) shows that they all crystallize in the space group I/4mmm. UV-visible diffuse reflection spectrum of the prepared Bi{sub 2}ASrTi{sub 2}TaO{sub 12} (A=Bi, La) indicates that it had absorption in the ultraviolet (UV) region. The photocatalytic activity of the Bi{sub 2}ASrTi{sub 2}TaO{sub 12} (A=Bi, La) powders was evaluated by degradation of rhodamine B (RB) molecules in water under UV light irradiation. The results showed that Bi{sub 2}ASrTi{sub 2}TaO{sub 12} (A=Bi, La) has high photocatalytic activity at room temperature. Therefore, the preparation and properties studies of Bi{sub 2}ASrTi{sub 2}TaO{sub 12} (A=Bi, La) with a three-layer Aurivillius structure suggest potential future applications in photocatalysis. - Graphical abstract: Two new three-layer Aurivillius phases Bi{sub 2}ASrTi{sub 2}TaO{sub 12} (A=Bi, La) have been synthesized by a conventional solid state reaction method. And this is the crystal structure of the three-layer Aurivillius phases, Bi{sub 2}ASrTi{sub 2}TaO{sub 12}.

  12. A Gas-phase Formation Route to Interstellar Trans-methyl Formate

    NASA Astrophysics Data System (ADS)

    Cole, Callie A.; Wehres, Nadine; Yang, Zhibo; Thomsen, Ditte L.; Snow, Theodore P.; Bierbaum, Veronica M.

    2012-07-01

    The abundance of methyl formate in the interstellar medium has previously been underpredicted by chemical models. Additionally, grain surface chemistry cannot account for the relative abundance of the cis- and trans-conformers of methyl formate, and the trans-conformer is not even formed at detectable abundance on these surfaces. This highlights the importance of studying formation pathways to methyl formate in the gas phase. The rate constant and branching fractions are reported for the gas-phase reaction between protonated methanol and formic acid to form protonated trans-methyl formate and water as well as adduct ion: Rate constants were experimentally determined using a flowing afterglow-selected ion flow tube apparatus at 300 K and a pressure of 530 mTorr helium. The results indicate a moderate overall rate constant of (3.19 ± 0.39) × 10-10 cm3 s-1 (± 1σ) and an average branching fraction of 0.05 ± 0.04 for protonated trans-methyl formate and 0.95 ± 0.04 for the adduct ion. These experimental results are reinforced by ab initio calculations at the MP2(full)/aug-cc-pVTZ level of theory to examine the reaction coordinate and complement previous density functional theory calculations. This study underscores the need for continued observational studies of trans-methyl formate and for the exploration of other gas-phase formation routes to complex organic molecules.

  13. Gas-Phase Structure Determination of Dihydroxycarbene, One of the Smallest Stable Singlet Carbenes

    NASA Astrophysics Data System (ADS)

    Womack, Carrie; Crabtree, Kyle N.; McCaslin, Laura; Martinez, Oscar, Jr.; Field, Robert W.; Stanton, John F.; McCarthy, Michael C.

    2014-06-01

    Carbenes (R1-C-R2) are a reactive class of compounds, usually characterized by an electron-deficient divalent carbon atom, found in applications ranging from organic synthesis to gas phase oxidation chemistry. Carbenes with 2- or 3-atom substituents often undergo rapid unimolecular isomerization, but may be stabilized if these substituents are electron-donating. Dihydroxycarbene (HO-C-OH) is one of the smallest singlet carbenes to be afforded this stability, due to its two electron-donating hydroxyl groups. We report the first gas-phase detection and structural characterization of this reactive species, using a combination of Fourier transform microwave spectroscopy and high level electronic structure calculations. Detection in the gas phase indicates that it is fairly stable relative to its isomers, formic acid (HCOOH) and the simplest Criegee intermediate (CH_2OO), the latter of which has recently received a great deal of attention for its role in the atmospheric ozonolysis of alkenes. Our experimental results yield a precise structure of HO-C-OH, and we comment on upcoming experiments investigating its stability and reactivity with other common atmospheric species.

  14. Gas-phase reactivity of carboxylic acid functional groups with carbodiimides.

    PubMed

    Prentice, Boone M; Gilbert, Joshua D; Stutzman, John R; Forrest, William P; McLuckey, Scott A

    2013-01-01

    Gas-phase modification of carboxylic acid functionalities is performed via ion/ion reactions with carbodiimide reagents [N-cyclohexyl-N'-(2-morpholinoethyl)carbodiimide (CMC) and [3-(3-Ethylcarbodiimide-1-yl)propyl]trimethylaminium (ECPT)]. Gas-phase ion/ion covalent chemistry requires the formation of a long-lived complex. In this instance, the complex is stabilized by an electrostatic interaction between the fixed charge quaternary ammonium group of the carbodiimide reagent cation and the analyte dianion. Subsequent activation results in characteristic loss of an isocyanate derivative from one side of the carbodiimide functionality, a signature for this covalent chemistry. The resulting amide bond is formed on the analyte at the site of the original carboxylic acid. Reactions involving analytes that do not contain available carboxylic acid groups (e.g., they have been converted to sodium salts) or reagents that do not have the carbodiimide functionality do not undergo a covalent reaction. This chemistry is demonstrated using PAMAM generation 0.5 dendrimer, ethylenediaminetetraacetic acid (EDTA), and the model peptide DGAILDGAILD. This work demonstrates the selective gas-phase covalent modification of carboxylic acid functionalities.

  15. All-gas-phase synthesis of UiO-66 through modulated atomic layer deposition

    PubMed Central

    Lausund, Kristian Blindheim; Nilsen, Ola

    2016-01-01

    Thin films of stable metal-organic frameworks (MOFs) such as UiO-66 have enormous application potential, for instance in microelectronics. However, all-gas-phase deposition techniques are currently not available for such MOFs. We here report on thin-film deposition of the thermally and chemically stable UiO-66 in an all-gas-phase process by the aid of atomic layer deposition (ALD). Sequential reactions of ZrCl4 and 1,4-benzenedicarboxylic acid produce amorphous organic–inorganic hybrid films that are subsequently crystallized to the UiO-66 structure by treatment in acetic acid vapour. We also introduce a new approach to control the stoichiometry between metal clusters and organic linkers by modulation of the ALD growth with additional acetic acid pulses. An all-gas-phase synthesis technique for UiO-66 could enable implementations in microelectronics that are not compatible with solvothermal synthesis. Since this technique is ALD-based, it could also give enhanced thickness control and the possibility to coat irregular substrates with high aspect ratios. PMID:27876797

  16. Gas-phase structures and thermochemistry of neutral histidine and its conjugated acid and base.

    PubMed

    Riffet, Vanessa; Bouchoux, Guy

    2013-04-28

    Extensive exploration of the conformational space of neutral, protonated and deprotonated histidine has been conducted at the G4MP2 level. Theoretical protonation and deprotonation thermochemistry as well as heats of formation of gaseous histidine and its ionized forms have been calculated at the G4 level considering either the most stable conformers or an equilibrium population of conformers at 298 K. These theoretical results were compared to evaluated experimental determinations. Recommended proton affinity and protonation entropy deduced from these comparisons are PA(His) = 980 kJ mol(-1) and ΔpS(His) ∼ 0 J mol(-1) K(-1), thus leading to a gas-phase basicity value of GB(His) = 947.5 kJ mol(-1). Similarly, gas phase acidity parameters are ΔacidH(o)(His) = 1373 kJ mol(-1), ΔacidS(His) ∼ 10 J mol(-1) K(-1) and ΔacidG(o)(His) = 1343 kJ mol(-1). Computed G4 heats of formation values are equal to -290, 265 and -451 kJ mol(-1) for gaseous neutral histidine and its protonated and deprotonated forms, respectively. The present computational data correct, and complete, previous thermochemical parameter estimates proposed for gas-phase histidine and its acido-basic properties.

  17. Gas-phase self-assembly of uniform silica nanostructures decorated and doped with silver nanoparticles

    NASA Astrophysics Data System (ADS)

    Lai, Chao-Shun; Chen, Yi-Chen; Wang, Hsiao-Fang; Ho, Hsin-Chia; Ho, Rong-Ming; Tsai, De-Hao

    2017-01-01

    We report a systematic study of the controlled gas-phase synthesis of silver-silica hybrid nanostructures (Ag-SiO2 NP) using the concept of evaporation-induced self-assembly. The approach includes the use of a direct gas-phase electrophoresis for size classification and in situ characterization of mobility size. Transmission electron microscopy and ultraviolet-visible light spectroscopy were employed complementarily to determine the morphology and surface plasmon resonance of Ag-SiO2 NP. Results show that two types of Ag-SiO2 NPs were successfully synthesized: (1) AgNPs decorated on a SiO2-NP (Ag-T-SiO2 NP), and (2) AgNPs doped in a cluster of SiO2-NPs (Ag-C-SiO2 NP). The physical size, morphology, and compositions of Ag-SiO2 NPs were tunable through the adjustments of precursor concentrations and the selected mobility sizes. The results also show that SPR performance, colloidal stability, and dispersibility of AgNPs enhanced significantly in an aqueous environment after the hybridization with SiO2-NP (especially for Ag-C-SiO2 NP). The results and corresponding methodology summarized here provide the proof of concept to fabricate high-purity AgNP-based hybrid nanostructures through gas-phase evaporation-induced self-assembly for future biomedical applications (e.g., hyperthermal therapy, targeted drug delivery, and antibacterial applications).

  18. Gas-phase Ion Isomer Analysis Reveals the Mechanism of Peptide Sequence Scrambling

    PubMed Central

    Jia, Chenxi; Wu, Zhe; Lietz, Christopher B.; Liang, Zhidan; Cui, Qiang; Li, Lingjun

    2014-01-01

    Peptide sequence scrambling during mass spectrometry-based gas-phase fragmentation analysis causes misidentification of peptides and proteins. Thus, there is a need to develop an efficient approach to probing the gas-phase fragment ion isomers related to sequence scrambling and the underlying fragmentation mechanism, which will facilitate the development of bioinformatics algorithm for proteomics research. Herein, we report on the first use of electron transfer dissociation (ETD)-produced diagnostic fragment ions to probe the components of gas-phase peptide fragment ion isomers. In combination with ion mobility spectrometry (IMS) and formaldehyde labeling, this novel strategy enables qualitative and quantitative analysis of b-type fragment ion isomers. ETD fragmentation produced diagnostic fragment ions indicative of the precursor ion isomer components, and subsequent IMS analysis of b ion isomers provided their quantitative and structural information. The isomer components of three representative b ions (b9, b10, and b33 from three different peptides) were accurately profiled by this method. IMS analysis of the b9 ion isomers exhibited dynamic conversion among these structures. Furthermore, molecular dynamics simulation predicted theoretical drift time values which were in good agreement with experimentally measured values. Our results strongly support the mechanism of peptide sequence scrambling via b ion cyclization, and provide the first experimental evidence to support that the conversion from molecular precursor ion to cyclic b ion (M→cb) pathway is less energetically (or kinetically) favored. PMID:24313304

  19. Thermodynamic analysis of fuels in gas phase: ethanol, gasoline and ethanol - gasoline predicted by DFT method.

    PubMed

    Neto, A F G; Lopes, F S; Carvalho, E V; Huda, M N; Neto, A M J C; Machado, N T

    2015-10-01

    This paper presents a theoretical study using density functional theory to calculate thermodynamics properties of major molecules compounds at gas phase of fuels like gasoline, ethanol, and gasoline-ethanol mixture in thermal equilibrium on temperature range up to 1500 K. We simulated a composition of gasoline mixture with ethanol for a thorough study of thermal energy, enthalpy, Gibbs free energy, entropy, heat capacity at constant pressure with respect to temperature in order to study the influence caused by ethanol as an additive to gasoline. We used semi-empirical computational methods as well in order to know the efficiency of other methods to simulate fuels through this methodology. In addition, the ethanol influence through the changes in percentage fractions of chemical energy released in combustion reaction and the variations on thermal properties for autoignition temperatures of fuels was analyzed. We verified how ethanol reduces the chemical energy released by gasoline combustion and how at low temperatures the gas phase fuels in thermal equilibrium have similar thermodynamic behavior. Theoretical results were compared with experimental data, when available, and showed agreement. Graphical Abstract Thermodynamic analysis of fuels in gas phase.

  20. The Decomposition of Hydrazine in the Gas Phase and over an Iridium Catalyst

    SciTech Connect

    Schmidt, Michael W.; Gordon, Mark S.

    2013-09-30

    Hydrazine is an important rocket fuel, used as both a monopropellant and a bipropellant. This paper presents theoretical results to complement the extensive experimental studies of the gas phase and Ir catalyzed decompositions involved in the monopropellant applications of hydrazine. Gas phase electronic structure theory calculations that include electron correlation predict that numerous molecular and free radical reactions occur within the same energy range as the basic free radical pathways: NN bond breaking around 65 kcal/mol and NH bond breaking around 81 kcal/mol. The data suggest that a revision to existing kinetics modeling is desirable, based on the energetics and the new elementary steps reported herein. A supported Ir-6 octahedron model for the Shell 405 Iridium catalyst used in thrusters was developed. Self-Consistent Field and electron correlation calculations (with core potentials and associated basis sets) find a rich chemistry for hydrazine on this catalyst model. The model catalyst provides dramatically lower NN and NH bond cleavage energies and an even smaller barrier to breaking the NH bond by NH2 abstractions. Thus, the low temperature decomposition over the catalyst is interpreted in terms of consecutive NH2 abstractions to produce ammonia and nitrogen. The higher temperature channel, which has hydrogen and nitrogen products, may be due to a mixture of two mechanisms. These two mechanisms are successive NH cleavages with surface H + H recombinations, and the same type of assisted H-2 eliminations found to occur in the gas phase part of this study.