Science.gov

Sample records for surface chemistry investigation

  1. Investigating the surface chemistry of Mars

    SciTech Connect

    Grunthaner, F.J.; Ricco, A.J.; Butler, A.M.; Lane, A.L.; McKay, C.P.; Zent, A.P.; Quinn, R.C.; Murray, B.; Klein, H.P.; Levin, G.V.; Terhune, R.W.; Homer, M.L.; Ksendzov, A.; Niedermann, P.

    1995-10-01

    One of the primary objectives of the Viking missions to Mars in the 1970s was to search for life. Numerous theories were put forth to explain the Viking data, most of which involved an oxidizing species in the Martian surface material. In December 1992, the Mars Oxidant Experiment (MOx) was selected as the U.S. contribution to the Russian Mars 96 mission. Two landers are scheduled for launch in November 1996 and should arrive at Mars in September 1997. The MOx instrument on the Russian lander is designed to investigate the chemical nature of the Martian surface material, with particular emphasis on its oxidative character. The instrument uses fiber-optic technology to monitor real-time physicochemical changes in a suite of chemically sensitive thin-film materials. This report describes the scientific rationale and basis for the MOx instrument, along with the details of its design and construction. 15 refs., 4 figs., 1 tab.

  2. Laboratory investigations: Low Earth orbit environment chemistry with spacecraft surfaces

    NASA Technical Reports Server (NTRS)

    Cross, Jon B.

    1990-01-01

    Long-term space operations that require exposure of material to the low earth orbit (LEO) environment must take into account the effects of this highly oxidative atmosphere on material properties and the possible contamination of the spacecraft surroundings. Ground-based laboratory experiments at Los Alamos using a newly developed hyperthermal atomic oxygen (AO) source have shown that not only are hydrocarbon based materials effected but that inorganic materials such as MoS2 are also oxidized and that thin protective coatings such as Al2O3 can be breached, producing oxidation of the underlying substrate material. Gas-phase reaction products, such as SO2 from oxidation of MoS2 and CO and CO2 from hydrocarbon materials, have been detected and have consequences in terms of spacecraft contamination. Energy loss through gas-surface collisions causing spacecraft drag has been measured for a few select surfaces and has been found to be highly dependent on the surface reactivity.

  3. Investigating playa surface textures: The impact of chemistry and environment on surface morphology and dust

    NASA Astrophysics Data System (ADS)

    Tollerud, H. J.; Fantle, M. S.

    2010-12-01

    Mineral dust is an important component of geochemical cycles, but its impact on those cycles is not thoroughly understood. For instance, dust inputs to the ocean have been suggested to affect the iron cycle by stimulating natural iron fertilization, which then could modify climate. The influence of dust on geochemical cycles is determined by the chemical and mineralogical composition of dust inputs, which is governed in turn by the composition of dust source regions. A loose, unconsolidated surface texture is more easily ablated by wind, and so a location where composition and environmental characteristics encourage this type of surface is more likely to produce dust and influence geochemical cycles. Also, if evaporation concentrates evaporites such as calcite at the surface of a dust producing region, dust Ca concentrations are likely to be higher. Playas can be regionally significant dust source regions, and they are amenable to study as their surface textures often vary significantly across small areas. This study investigates surface processes experimentally, and compares the results to observations of surface texture in a natural playa system (the Black Rock Desert, Nevada). We dry surfaces with 25% to 75% clay and quartz at 40°C for approximately a day, wet the surface to simulate rain, and then repeat the cycle multiple times. We estimate surface roughness, measure surface strength with a penetrometer, and investigate thermal characteristics with an IR camera (wavelength range 8-12μm). We find that textures similar to those in playas can be reproduced with cycles of wetting and drying, such as might occur in an arid environment with intermittent rain. We investigate the addition of calcite and halite, since their precipitation potentially can disrupt the clay surfaces through the formation and expansion of crystals, thereby linking the chemical composition with the disruption of a strong surface texture and an increased chance of dust production. In the

  4. In-Depth Electrochemical Investigation of Surface Attachment Chemistry via Carbodiimide Coupling.

    PubMed

    Booth, Marsilea Adela; Kannappan, Karthik; Hosseini, Ali; Partridge, Ashton

    2015-07-28

    Aminoferrocene is used as an electroactive indicator to investigate carbodiimide coupling reactions on a carboxylic acid-functionalized self-assembled monolayer. The commonly used attachment chemistry with 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) is used for surface activation. A number of conditions are investigated, including EDC and NHS concentration, buffer solutions, incubation timing, and aminoferrocene concentration. Ferrocene is a well-documented electroactive species, and the number of surface-bound ferrocene species can be calculated using electrochemical methods. This capability allows determination of optimal conditions, as well as providing a method for comparing and investigating novel carboxylated surfaces. An EDC-mediated procedure with ∼5 mM EDC and NHS (1:1) made in water, with a full acid monolayer, with 250 μM aminoferrocene for 40 min was found to give the highest ferrocene attachment. An application of this is demonstrated for preparing a probe-DNA-coated surface for DNA sensing. By backfilling with aminoferrocene, a differential quantification of the amount of probe DNA available for sensing can be obtained. This provides an elegant method to monitor an important aspect, namely, probe surface characterization, which will be highly useful for biosensing purposes. PMID:26107592

  5. Investigating thiol-modification on hyaluronan via carbodiimide chemistry using response surface methodology.

    PubMed

    Santhanam, Sruthi; Liang, Jue; Baid, Rinku; Ravi, Nathan

    2015-07-01

    Hyaluronan (HA) is a naturally occurring glycosaminoglycan widely researched for its use as a biomaterial in tissue engineering, drug delivery, angiogenesis, and ophthalmic surgeries. The mechanical properties of this biomaterial can be altered to a required extent by chemically modifying the pendant reactive groups. However, derivatizing these polymers to a predetermined extent has been the Achilles heel for this process. In this study, we have investigated the factors controlling the derivatization of the carboxyl moieties of HA with amine containing thiol, cystamine dihydrochloride (Cys), via carbodiimide crosslinking chemistry. We used fractional factorial design to screen and identify the significant factor(s) affecting the reaction, and response surface methodology (RSM) to develop a model equation for predicting the degree of thiolation of HA. Also, we analyzed the reaction mechanism for potential side reactions. We observed that N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) (mole ratio with repeat unit of HA) is the significant factor controlling the degree of amidation. The quadratic equations developed from RSM predict the formulation for a desired degree of amidation of HA and percentage of potential side product. Hence, derivatizing HA to a predetermined extent with minimal side product can be achieved using the statistical design of experiments. PMID:25369214

  6. Impact of surface chemistry

    PubMed Central

    Somorjai, Gabor A.; Li, Yimin

    2011-01-01

    The applications of molecular surface chemistry in heterogeneous catalyst technology, semiconductor-based technology, medical technology, anticorrosion and lubricant technology, and nanotechnology are highlighted in this perspective. The evolution of surface chemistry at the molecular level is reviewed, and the key roles of surface instrumentation developments for in situ studies of the gas–solid, liquid–solid, and solid–solid interfaces under reaction conditions are emphasized. PMID:20880833

  7. Getting Physical with Your Chemistry: Mechanically Investigating Local Structure and Properties of Surfaces with the Atomic Force Microscope

    ERIC Educational Resources Information Center

    Heinz, William F.; Hoh, Jan H.

    2005-01-01

    Atomic force microscope (AFM) investigates mechanically the chemical properties of individual molecules, surfaces, and materials using suitably designed probes. The current state of the art of AFM in terms of imaging, force measurement, and sample manipulation and its application to physical chemistry is discussed.

  8. Chemistry of SOFC Cathode Surfaces: Fundamental Investigation and Tailoring of Electronic Behavior

    SciTech Connect

    Yildiz, Bilge; Heski, Clemens

    2013-08-31

    1) Electron tunneling characteristics on La0.7Sr0.3MnO3 (LSM) thin-film surfaces were studied up to 580oC in 10-3mbar oxygen pressure, using scanning tunneling microscopy/ spectroscopy (STM/STS). A threshold-like drop in the tunneling current was observed at positive bias in STS, which is interpreted as a unique indicator for the activation polarization in cation oxygen bonding on LSM cathodes. Sr-enrichment was found on the surface at high temperature using Auger electron spectroscopy, and was accompanied by a decrease in tunneling conductance in STS. This suggests that Sr-terminated surfaces are less active for electron transfer in oxygen reduction compared to Mn-terminated surfaces on LSM. 2) Effects of strain on the surface cation chemistry and the electronic structure are important to understand and control for attaining fast oxygen reduction kinetics on transition metal oxides. Here, we demonstrate and mechanistically interpret the strain coupling to Sr segregation, oxygen vacancy formation, and electronic structure on the surface of La0.7Sr0.3MnO3 (LSM) thin films as a model system. Our experimental results from x-ray photoelectron spectroscopy and scanning tunneling spectroscopy are discussed in light of our first principles-based calculations. A stronger Sr enrichment tendency and a more facile oxygen vacancy formation prevail for the tensile strained LSM surface. The electronic structure of the tensile strained LSM surface exhibits a larger band gap at room temperature, however, a higher tunneling conductance near the Fermi level than the compressively strained LSM at elevated temperatures in oxygen. Our findings suggest lattice strain as a key parameter to tune the reactivity of perovskite transition metal oxides with oxygen in solid oxide fuel cell cathodes. 3) Cation segregation on perovskite oxide surfaces affects vastly the oxygen reduction activity and stability of solid oxide fuel cell (SOFC) cathodes. A unified theory that explains the physical

  9. A solid phase extraction based non-disruptive sampling technique to investigate the surface chemistry of macroalgae.

    PubMed

    Cirri, Emilio; Grosser, Katharina; Pohnert, Georg

    2016-01-01

    The surface chemistry of aquatic organisms determines their biotic interactions. Metabolites in the spatially limited laminar boundary layer mediate processes, such as antifouling, allelopathy and chemical defense against herbivores. However, very few methods are available for the investigation of such surface metabolites. An approach is described in which surfaces are extracted by means of C18 solid phase material. By powdering wet algal surfaces with this material, organic compounds are adsorbed and can be easily recovered for subsequent liquid chromatography/mass spectrometry (LC/MS) and gas chromatography/mass spectrometry (GC/MS) investigations. The method is robust, picks up metabolites of a broad polarity range and is easy to handle. It is more universal compared to established solvent dipping protocols and it does not cause damage to the test organisms. A protocol is introduced for the macroalgae Fucus vesiculosus, Caulerpa taxifolia and Gracilaria vermiculophylla, but it can be easily transferred to other aquatic organisms. PMID:26795737

  10. Interstellar Grain Surface Chemistry

    NASA Technical Reports Server (NTRS)

    Tielens, Alexander G. G. M.; Cuzzi, Jeffrey N. (Technical Monitor)

    1995-01-01

    Chemistry on grain surfaces plays an Important role in the formation of interstellar Ices, It can also influence the composition of the gas phase through outgassing near luminous, newly formed stars. This paper reviews the chemical processes taking place on Interstellar grain surfaces with the emphasis on those transforming CO into other hydrocarbons. At low, molecular cloud temperatures (approximately equal to 10K), physisorption processes dominate interstellar grain surface chemistry and GO is largely hydrogenated through reactions with atomic H and oxidized through reactions with atomic O. The former will lead to the formation of H2CO and CH3OH ices, while the latter results in CO2 ice. The observational evidence for these ices in molecular clouds will be discussed. Very close to protostars, the gas and grain temperatures are much higher (approximately equal to 500K) and chemisorption processes, including catalytic surface reactions, becomes important. This will be illustrated based upon our studies of the Fischer-Tropsch Synthesis of CH4 from CO on metallic surfaces. Likely, this process has played an important role in the early solar nebula. Observational consequences will be pointed out.

  11. Contributions of gas-phase plasma chemistry to surface modifications and gas-surface interactions: investigations of fluorocarbon rf plasmas

    NASA Astrophysics Data System (ADS)

    Cuddy, Michael F., II

    The fundamental aspects of inductively coupled fluorocarbon (FC) plasma chemistry were examined, with special emphasis on the contributions of gas-phase species to surface modifications. Characterization of the gas-phase constituents of single-source CF4-, C2F6-, C3F 8-, and C3F6-based plasmas was performed using spectroscopic and mass spectrometric techniques. The effects of varying plasma parameters, including applied rf power (P) and system pressure (p) were examined. Optical emission spectroscopy (OES) and laser-induced fluorescence (LIF) spectroscopy were employed to monitor the behavior of excited and ground CFx (x = 1,2) radicals, respectively. Mass spectrometric techniques, including ion energy analyses, elucidated behaviors of nascent ions in the FC plasmas. These gas-phase data were correlated with the net effect of substrate processing for Si and ZrO2 surfaces. Surface-specific analyses were performed for post-processed substrates via x-ray photoelectron spectroscopy (XPS) and contact angle goniometry. Generally, precursors with lower F/C ratios tended to deposit robust FC films of high surface energy. Precursors of higher F/C ratio, such as CF4, were associated with etching or removal of material from surfaces. Nonetheless, a net balance between deposition of FC moieties and etching of material exists for each plasma system. The imaging of radicals interacting with surfaces (IRIS) technique provided insight into the phenomena occurring at the interface of the plasma gas-phase and substrate of interest. IRIS results demonstrate that CFx radicals scatter copiously, with surface scatter coefficients, S, generally greater than unity under most experimental conditions. Such considerable S values imply surface-mediated production of the CFx radicals at FC-passivated sites. It is inferred that the primary route to surface production of CFx arises from energetic ion bombardment and ablation of surface FC films. Other factors which may influence the observed CFx

  12. Investigation of IAQ-Relevant Surface Chemistry and Emissions on HVAC Filter Materials

    SciTech Connect

    Destaillats, Hugo; Fisk, William J.

    2010-02-01

    Chemical reactions involving ozone of outdoor origin and indoor materials are known to be significant sources of formaldehyde and other irritant gas-phase oxidation products in the indoor environment. HVAC filters are exposed to particularly high ozone concentrations--close to outdoor levels. In this study, we investigated chemical processes taking place on the surface of filters that included fiberglass, polyester, cotton/polyester blend and synthetic (e.g., polyolefin) filter media. Ozone reactions were studied on unused filter media, and on filters that were deployed for 3 months in two different locations: at the Lawrence Berkeley National Laboratory and at the Port of Oakland. Specimens from each filter were exposed to ozone under controlled conditions in a laboratory flow tube at a constant flow of dry or humidified air (50percent relative humidity). Ozone was generated with a UV source upstream of the flow tube, and monitored using a photometric detector. Ozone breakthrough curves were recorded for each sample exposed to ~;;150 ppbv O3 for periods of ~;;1000 min, from which we estimated their uptake rate. Most experiments were performed at 1.3 L/min (corresponding to a face velocity of 0.013 m/s), except for a few tests performed at a higher airflow rate, to obtain a face velocity of 0.093 m/s, slightly closer to HVAC operation conditions. Formaldehyde and acetaldehyde, two oxidation byproducts, were collected downstream of the filter and quantified. Emissions of these volatile aldehydes were consistently higher under humidified air than under dry conditions, at which levels were near the limit of detection. Our results confirm that there are significant reactions of ozone as air containing ozone flows through HVAC filters, particularly when the filters are loaded with particles and the air is humidified. The amount of ozone reacted was not clearly related to the types of filter media, e.g., fiberglass versus synthetic. Specific fiberglass filters that were

  13. The investigation of the viscoelastic properties of silica/PMMA nanocomposites as a function of silica surface chemistry

    NASA Astrophysics Data System (ADS)

    Conway, Heather; Rende, Deniz; Ozisik, Rahmi

    2013-03-01

    Poly(methyl methacrylate), PMMA, has been used as an economic alternative to glass and polycarbonate in differing situations because of its lightweight, shatter resistance, and ease of processability. The uses of PMMA can be expanded if its weakness to impact force and its scratch resistance are improved. In the current study, viscoelastic properties of silica nanoparticle filled PMMA were investigated via nanoindentation experiments. Silica nanoparticles are known to increase the toughness of PMMA. In the current study, silica nanoparticles were chemically modified with fluorinated alkanes to alter nanofiller-polymer interactions. Results show that viscoelastic properties are strongly affected by silica surface chemistry and silica concentration. This work was partially supported by NSF CMMI-1200270 and DUE-1003574

  14. A two-dimensional atmospheric chemistry modeling investigation of Earth's Phanerozoic O3 and near-surface ultraviolet radiation history

    NASA Astrophysics Data System (ADS)

    Harfoot, Michael B. J.; Beerling, David J.; Lomax, Barry H.; Pyle, John A.

    2007-04-01

    We use the Cambridge two-dimensional (2-D) chemistry-radiation transport model to investigate the implications for column O3 and near-surface ultraviolet radiation (UV), of variations in atmospheric O2 content over the Phanerozoic (last 540 Myr). Model results confirm some earlier 1-D model investigations showing that global annual mean O3 column increases monotonically with atmospheric O2. Sensitivity studies indicate that changes in temperature and N2O exert a minor influence on O3 relative to O2. We reconstructed Earth's O3 history by interpolating the modeled relationship between O3 and O2 onto two Phanerozoic O2 histories. Our results indicate that the largest variation in Phanerozoic column O3 occurred between 400 and 200 Myr ago, corresponding to a rise in atmospheric O2 to ˜1.5 times the present atmospheric level (PAL) and subsequent fall to ˜0.5 PAL. The O3 response to this O2 decline shows latitudinal differences, thinning most at high latitudes (30-40 Dobson units (1 DU = 0.001 atm cm) at 66°N) and least at low latitudes (5-10 DU at 9°N) where a "self-healing" effect is evident. This O3 depletion coincides with significant increases in the near-surface biologically active UV radiation at high latitudes, +28% as weighted by the Thimijan spectral weighting function. O3 and UV changes were exacerbated when we incorporated a direct feedback of the terrestrial biosphere on atmospheric chemistry, through enhanced N2O production as the climate switched from an icehouse to a greenhouse mode. On the basis of a summary of field and laboratory experimental evidence, we suggest that these UV radiation increases may have exerted subtle rather than catastrophic effects on ecosystem processes.

  15. Surface chemistry investigation of colloid transport in packed beds. Final report, August 1, 1989--July 31, 1996

    SciTech Connect

    Olson, T.M.

    1996-12-31

    The importance of colloids as co-transport agents for pollutants in subsurface systems hinges on the extent to which electrostatic or other sources of repulsive colloid-collector interactions inhibit their filtration. When electrostatic interactions are favorable, for example when the colloid and groundwater media have opposite charge, colloids may be expected to travel only a few centimeters in saturated porous media. Repulsive electrostatic interactions between colloids and aquifer media with the same charge sign are postulated to significantly mobilize particles. As it happens, however, theories describing particle filtration from first principles, i.e., DLVO (Derjagin and Landau, Verwey and Overbeek) theory, dramatically underestimate filtration rates when colloid-collector interactions are electrostatically repulsive. One of the primary objectives of the project was to experimentally investigate potential reasons for the historical lack of agreement between particle filtration models based on DLVO theory and observed particle deposition rates. An important hypothesis of the study was to test the validity of the assumption of surface homogeneity, as required by these models. The approach was to focus on collector surfaces that were commonly used as model systems, e.g., glass beads and quartz sand. Laboratory-scale column filtration experiments were conducted with colloidal polystyrene latex spheres. Collector surface preparation and cleaning approaches were examined, as well as the effects of solution chemistry.

  16. Fracture mechanics and surface chemistry investigations of environment-assisted crack growth

    NASA Technical Reports Server (NTRS)

    Wei, R. P.; Klier, K.; Simmons, G. W.; Chou, Y. T.

    1984-01-01

    It is pointed out that environment-assisted subcritical crack growth in high-strength steels and other high-strength alloys (particularly in hydrogen and in hydrogenous environments) is an important technological problem of long standing. This problem is directly related to issues of structural integrity, durability, and reliability. The terms 'hydrogen embrittlement' and 'stress corrosion cracking' have been employed to describe the considered phenomenon. This paper provides a summary of contributions made during the past ten years toward the understanding of environmentally assisted crack growth. The processes involved in crack growth are examined, and details regarding crack growth and chemical reactions are discussed, taking into account crack growth in steels exposed to water/water vapor, the effect of hydrogen, reactions involving hydrogen sulfide, and aspects of fracture surface morphology and composition. Attention is also given to the modeling of crack growth response, crack growth in gas mixtures, and the interaction of solute atoms with the crack-tip stress field.

  17. Surface chemistry of palladium

    SciTech Connect

    Gentle, T.M.

    1984-05-01

    Several classes of catalytically important molecules on Pd single crystals were studied. Influence of surface structure and composition on reactions involving formation and scission of carbon-carbon and carbon-hydrogen bonds was investigated under uhv conditions on single crystals and higher pressures on polycrystalline films. Reactions of acetylene on Pd(111), Pd(100), and Pd(110) were studied using thermal desorption spectroscopy, chemical displacement reactions, and isotopic labeling techniques. Pd single crystals catalyzes trimerization to benzene, hydrogenation to ethylene, and hydrosilation with trimethylsilane. Several atoms such as Si, P, S, and Cl have a profound influence on the catalysis. Single-crystal Pd surfaces catalyzes the dehydrogenation of organosilanes; silacyclohexane chemisorbed on Pd(110) underwent dehydrogenation upon thermal desorption to form silabenzene. Desulfurization products were observed in the thermal desorption spectra chemisorbed thiophene, 3-methylthiophene, and 2,5-dimethylthiophene. Mechanisms of carbon-hydrogen bond scission were investigated for a variety of methyl-substituted benzenes, revealing some degree of regiospecificity in C-H bond scission. Several reactions of unsaturated hydrocarbons were also investigated at higher pressures (10/sup -2/ torr) on polycrystalline Pd films.

  18. Investigations of the structure and "interfacial" surface chemistry of Bioglass (RTM) materials by solid-state multinuclear NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Sarkar, Gautam

    formation of surface silica species and follow the formation of phosphate species, respectively, while cross-polarization magic-angle spinning (CP/MAS) 29Si and 31P NMR have provided information about low intensity NMR peaks due to various silicon- and phosphorus-species present in the vicinity of associated protons on the surface of in vitro reacted BioglassRTM materials. The solid-state NMR investigations of the "interfacial" surface reactions of BioglassRTM materials are discussed in the context of the structure of these materials and the influence of this structure on the kinetics and the mechanism of their "interfacial" surface chemistry. (Abstract shortened by UMI.) BioglassRTM, trademark, University of Florida, Gainesville, FL, 32611.

  19. Cavity ring-down spectroscopy with an automated control feedback system for investigating nitrate radical surface chemistry reactions

    NASA Astrophysics Data System (ADS)

    Flemmer, Michael M.; Ham, Jason E.

    2012-08-01

    Nitrate radical (NO3•) surface chemistry of indoor environments has not been well studied due to the difficulty in generating and maintaining NO3• at low concentrations for long term exposures. This article presents the Surface Chemistry Reactant Air Delivery and Experiment System (SCRADES), a novel feedback controlled system developed to deliver nitrate radicals at specified concentrations (50-500 ppt, ±30 ppt) and flow rates (500-2000 ml min-1) to a variety of indoor surfaces to initiate reaction chemistry for periods of up to 72 h. The system uses a cavity ring-down spectrometer (CRDS), with a detection limit of 1.7 ppt, to measure the concentration of NO3• supplied to a 24 l experiment chamber. Nitrate radicals are introduced via thermal decomposition of N2O5 and diluted with clean dry air until the desired concentration is achieved. Additionally, this article addresses details concerning NO3• loss through the system, consistency of the NO3• concentration delivered, and stability of the CRDS cavity over long exposure durations (72 h).

  20. Visualizing Chemistry: Investigations for Teachers.

    ERIC Educational Resources Information Center

    Ealy, Julie B.; Ealy, James L., Jr.

    This book contains 101 investigations for chemistry classrooms. Topics include: (1) Physical Properties; (2) Reactions of Some Elements; (3) Reactions Involving Gases; (4) Energy Changes; (5) Solutions and Solubility; (6) Transition Metals and Complex Ions; (7) Kinetics and Equilibrium; (8) Acids and Bases; (9) Oxidation-Reduction; (10)…

  1. Experimental and computational investigation of acetic acid deoxygenation over oxophilic molybdenum carbide: Surface chemistry and active site identity

    DOE PAGESBeta

    Schaidle, Joshua A.; Blackburn, Jeffrey; Farberow, Carrie A.; Nash, Connor; Steirer, K. Xerxes; Clark, Jared; Robichaud, David J.; Ruddy, Daniel A.

    2016-01-21

    Ex situ catalytic fast pyrolysis (CFP) is a promising route for producing fungible biofuels; however, this process requires bifunctional catalysts that favor C–O bond cleavage, activate hydrogen at near atmospheric pressure and high temperature (350–500 °C), and are stable under high-steam, low hydrogen-to-carbon environments. Recently, early transition-metal carbides have been reported to selectively cleave C–O bonds of alcohols, aldehydes, and oxygenated aromatics, yet there is limited understanding of the metal carbide surface chemistry under reaction conditions and the identity of the active sites for deoxygenation. In this study, we evaluated molybdenum carbide (Mo2C) for the deoxygenation of acetic acid, anmore » abundant component of biomass pyrolysis vapors, under ex situ CFP conditions, and we probed the Mo2C surface chemistry, identity of the active sites, and deoxygenation pathways using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations.« less

  2. Surface chemistry in photodissociation regions

    NASA Astrophysics Data System (ADS)

    Esplugues, G. B.; Cazaux, S.; Meijerink, R.; Spaans, M.; Caselli, P.

    2016-06-01

    Context. The presence of dust can strongly affect the chemical composition of the interstellar medium. We model the chemistry in photodissociation regions (PDRs) using both gas-phase and dust-phase chemical reactions. Aims: Our aim is to determine the chemical compositions of the interstellar medium (gas/dust/ice) in regions with distinct (molecular) gas densities that are exposed to radiation fields with different intensities. Methods: We have significantly improved the Meijerink PDR code by including 3050 new gas-phase chemical reactions and also by implementing surface chemistry. In particular, we have included 117 chemical reactions occurring on grain surfaces covering different processes, such as adsorption, thermal desorption, chemical desorption, two-body reactions, photo processes, and cosmic-ray processes on dust grains. Results: We obtain abundances for different gas and solid species as a function of visual extinction, depending on the density and radiation field. We also analyse the rates of the formation of CO2 and H2O ices in different environments. In addition, we study how chemistry is affected by the presence/absence of ice mantles (bare dust or icy dust) and the impact of considering different desorption probabilities. Conclusions: The type of substrate (bare dust or icy dust) and the probability of desorption can significantly alter the chemistry occurring on grain surfaces, leading to differences of several orders of magnitude in the abundances of gas-phase species, such as CO, H2CO, and CH3OH. The type of substrate, together with the density and intensity of the radiation field, also determine the threshold extinction to form ices of CO2 and H2O. We also conclude that H2CO and CH3OH are mainly released into the gas phase of low, far-ultraviolet illuminated PDRs through chemical desorption upon two-body surface reactions, rather than through photodesorption.

  3. Surface chemistry of deuterated molecules

    NASA Astrophysics Data System (ADS)

    Tielens, A. G. G. M.

    1983-03-01

    The chemical composition of grain mantles is calculated in order to determine the concentration of deuterated molecules relative to their hydrogenated counterparts in grain mantles. The computation takes into account reactions involving deuterium in the gas phase and on grain surfaces. The results show that the abundance of deuterium molecules in grain mantles is much higher than expected on the basis of the cosmic abundance ratio of D to H. HDCO has a relatively high abundance in grain mantles as compared to other deuterated molecules, due to the fact that H abstraction from HDCO has a lower activation barrier than D abstraction. The infrared characteristics of the calculated grain mantles are discussed and observational tests of the model calcultions are suggested. The contribution of grain surface chemistry to the concentration of molecules in the gas phase is briefly considered.

  4. Surface chemistry of liquid metals

    NASA Technical Reports Server (NTRS)

    Mann, J. Adin, Jr.; Peebles, Henry; Peebles, Diamond; Rye, Robert; Yost, Fred

    1993-01-01

    The fundamental surface chemistry of the behavior of liquid metals spreading on a solid substrate is not at all well understood. Each of these questions involves knowing the details of the structure of interfaces and their dynamics. For example the structure of a monolayer of tin oxide on pure liquid tin is unknown. This is in contrast to the relatively large amount of data available on the structure of copper oxide monolayers on solid, pure copper. However, since liquid tin has a vapor pressure below 10(exp -10)torr for a reasonable temperature range above its melting point, it is possible to use the techniques of surface science to study the geometric, electronic and vibrational structures of these monolayers. In addition, certain techniques developed by surface chemists for the study of liquid systems can be applied to the ultra-high vacuum environment. In particular we have shown that light scattering spectroscopy can be used to study the surface tension tensor of these interfaces. The tin oxide layer in particular is very interesting in that the monolayer is rigid but admits of bending. Ellipsometric microscopy allows the visualization of monolayer thick films and show whether island formation occurs at various levels of dosing.

  5. Influence of pH and Surface Chemistry on Poly(L-lysine) Adsorption onto Solid Supports Investigated by Quartz Crystal Microbalance with Dissipation Monitoring.

    PubMed

    Choi, Jae-Hyeok; Kim, Seong-Oh; Linardy, Eric; Dreaden, Erik C; Zhdanov, Vladimir P; Hammond, Paula T; Cho, Nam-Joon

    2015-08-20

    Poly(L-lysine) (PLL) adsorption onto various materials has been widely applied as a surface modification strategy and layer-by-layer fabrication method. Considering the role of electrostatic charges, a detailed understanding of the influence of solution pH on PLL adsorption process is important for optimization of PLL coating protocols. Herein, PLL adsorption onto different polar and hydrophilic substrates—silica, an amine-terminated self-assembled monolayer (SAM) on gold, and a carboxyl-terminated SAM on gold—across a range of pH conditions was investigated using the quartz crystal microbalance with dissipation. The adsorption kinetics consisted of an initial rapid phase, followed by a second phase where adsorption rate gradually decelerated. These features were interpreted by applying a mean-field kinetic model implying diffusion-limited adsorption in the first phase and reconfiguration of adsorbed PLL molecules in the second phase. The adsorption kinetics and uptake were found to be sensitive to the pH condition, surface chemistry, and flow rate. The strongest PLL adsorption occurred at pH 11 on all three surfaces while weak PLL adsorption generally occurred under acidic conditions. The surface morphology and roughness of adsorbed PLL layers were investigated using atomic force microscopy, and strong PLL adsorption is found to produce a uniform and smooth adlayer while weak adsorption formed a nonuniform and rough adlayer. PMID:26061703

  6. Chemistry. Teacher's Guide. Investigations in Natural Science.

    ERIC Educational Resources Information Center

    Renner, John W.; And Others

    Investigations in Natural Science is a program in secondary school biology, chemistry, and physics based upon the description of science as a quest for knowledge, not the knowledge itself. This teaching guide is designed for use with the 19 chemistry investigations found in the student manual. These investigations focus on concepts related to:…

  7. Surface Chemistry Enhanced Microbial Bioelectrocatalysis

    PubMed Central

    Santoro, Carlo; Babanova, Sofia; Artyushkova, Kateryna; Cornejo, Jose’ A.; Ista, Linnea; Bretschger, Orianna; Marsili, Enrico; Atanassov, Plamen; Schuler, Andrew J.

    2016-01-01

    Self-assembled monolayers (SAMs) modified gold anodes are used in single chamber microbial fuel cells (SCMFC) for organics removal and electricity generation. Hydrophilic (−N(CH3)3+, −OH, −COOH) and hydrophobic (−CH3) SAMs are examined for their effect on bacterial attachment, current and power output. The different substratum chemistry affects both the current and power output and the community composition of the electrochemically active biofilm formed. Of the four SAM-modified anode tested, −N(CH3)3+ results in shortest start up time, highest single electrode polarization and power density, followed by −OH and –COOH SAMs. Hydrophobic SAM decreases bacteria attachment and anodes performance in comparison to hydrophilic SAMs. Electron transfer rate is faster on the N(CH3)3+-surface than on other surfaces, and correlates with a high abundance of δ-Proteobacteria, including electrochemically active species. A consortium of Clostridia and δ-Proteobacteria is found on all the anode surfaces, suggesting a synergistic cooperation under anodic conditions. PMID:26025340

  8. Unexpected surface chemistry in capillaries for electrophoresis.

    PubMed

    Kaupp, S; Bubert, H; Baur, L; Nelson, G; Wätzig, H

    2000-10-13

    Good and reproducible capillary quality is needed to develop robust methods and to facilitate method transfer in CE. Physical surface defects no longer play a major role in variability of fused-silica capillaries. Nevertheless, problems are frequently being reported when buffers in the pH range between 4 and 7 are used. Thus the surface chemistry has been studied by X-ray photoelectron spectroscopy. Silicon-carbon bindings have been found on inner capillary surfaces for electrophoresis. This binding type is not completely removed by pre-conditioning with 1 M NaOH for 30 min. This corresponds to the result, that capillaries provide more stable migration times, especially in the pH range 4-7, when they are pre-conditioned for longer than 1 h. The origin of this Si-C bond is still not quite clear. They could be caused by graphite which is used during the fabrication of the raw cylinders prior to capillary drawing. Further investigations are intended in order to understand if there are any differences in surface carbon content from batch to batch and if this can influence experimental results in CE. A better understanding of the surface chemistry should not only improve robustness in CE, but also help to facilitate and accelerate capillary pre-conditioning and rinsing procedures to remove strongly adsorbed analytes or matrices. PMID:11100849

  9. Chemistry. Student Investigations and Readings. Investigations in Natural Science.

    ERIC Educational Resources Information Center

    Renner, John W.; And Others

    Investigations in Natural Science is a program in secondary school biology, chemistry, and physics based upon the description of science as a quest for knowledge, not the knowledge itself. This student manual contains the 19 chemistry investigations. These investigations focus on concepts related to: interactions with water; salt and calcium;…

  10. The Surface Chemistry of Metal Chalcogenide Nanocrystals

    NASA Astrophysics Data System (ADS)

    Anderson, Nicholas Charles

    The surface chemistry of metal chalcogenide nanocrystals is explored through several interrelated analytical investigations. After a brief discussion of the nanocrystal history and applications, molecular orbital theory is used to describe the electronic properties of semiconductors, and how these materials behave on the nanoscale. Quantum confinement plays a major role in dictating the optical properties of metal chalcogenide nanocrystals, however surface states also have an equally significant contribution to the electronic properties of nanocrystals due to the high surface area to volume ratio of nanoscale semiconductors. Controlling surface chemistry is essential to functionalizing these materials for biological imaging and photovoltaic device applications. To better understand the surface chemistry of semiconducting nanocrystals, three competing surface chemistry models are presented: 1.) The TOPO model, 2.) the Non-stoichiometric model, and 3.) the Neutral Fragment model. Both the non-stoichiometric and neutral fragment models accurately describe the behavior of metal chalcogenide nanocrystals. These models rely on the covalent bond classification system, which divides ligands into three classes: 1.) X-type, 1-electron donating ligands that balance charge with excess metal at the nanocrystal surface, 2.) L-type, 2-electron donors that bind metal sites, and 3.) Z-type, 2-electron acceptors that bind chalcogenide sites. Each of these ligand classes is explored in detail to better understand the surface chemistry of metal chalcogenide nanocrystals. First, chloride-terminated, tri-n-butylphosphine (Bu 3P) bound CdSe nanocrystals were prepared by cleaving carboxylate ligands from CdSe nanocrystals with chlorotrimethylsilane in Bu3P solution. 1H and 31P{1H} nuclear magnetic resonance spectra of the isolated nanocrystals allowed assignment of distinct signals from several free and bound species, including surface-bound Bu3P and [Bu3P-H]+[Cl]- ligands as well as a Bu

  11. The EDM surface: Topography, chemistry, and metallurgy

    SciTech Connect

    Fuller, J.E.

    1991-01-01

    The surface created by the electric discharge machining (EDM) process is of special interest because it has been shown to have a negative effect on the fatigue properties of many alloys. An understanding of the surface metallurgy and chemistry is important in predicting those alloys which are most susceptible to failure. Remedial actions, including thickness minimization, alteration, or removal of the surface layer are addressed.

  12. Laboratory Investigations of Stratospheric Halogen Chemistry

    NASA Technical Reports Server (NTRS)

    Wine, Paul H.; Nicovich, J. Michael; Stickel, Robert E.; Hynes, Anthony J.

    1997-01-01

    A final report for the NASA-supported project on laboratory investigations of stratospheric halogen chemistry is presented. In recent years, this project has focused on three areas of research: (1) kinetic, mechanistic, and thermochemical studies of reactions which produce weakly bound chemical species of atmospheric interest; (2) development of flash photolysis schemes for studying radical-radical reactions of stratospheric interest; and (3) photochemistry studies of interest for understanding stratospheric chemistry. The first section of this paper contains a discussion of work which has not yet been published. All subsequent chapters contain reprints of published papers that acknowledge support from this grant.

  13. Surface chemistry driven actuation in nanoporous gold

    SciTech Connect

    Biener, J; Wittstock, A; Zepeda-Ruiz, L; Biener, M M; Zielasek, V; Kramer, D; Viswanath, R N; Weissmuller, J; Baumer, M; Hamza, A V

    2008-04-14

    Although actuation in biological systems is exclusively powered by chemical energy, this concept has not been realized in man-made actuator technologies, as these rely on generating heat or electricity first. Here, we demonstrate that surface-chemistry driven actuation can be realized in high surface area materials such as nanoporous gold. For example, we achieve reversible strain amplitudes in the order of a few tenths of a percent by alternating exposure of nanoporous Au to ozone and carbon monoxide. The effect can be explained by adsorbate-induced changes of the surface stress, and can be used to convert chemical energy directly into a mechanical response thus opening the door to surface-chemistry driven actuator and sensor technologies.

  14. Multifunctional Surface Manipulation Using Orthogonal Click Chemistry.

    PubMed

    Brooks, Karson; Yatvin, Jeremy; McNitt, Christopher D; Reese, R Alexander; Jung, Calvin; Popik, Vladimir V; Locklin, Jason

    2016-07-01

    Polymer brushes are excellent substrates for the covalent immobilization of a wide variety of molecules due to their unique physicochemical properties and high functional group density. By using reactive microcapillary printing, poly(pentafluorophenyl acrylate) brushes with rapid kinetic rates toward aminolysis can be partially patterned with other click functionalities such as strained cyclooctyne derivatives and sulfonyl fluorides. This trireactive surface can then react locally and selectively in a one pot reaction via three orthogonal chemistries at room temperature: activated ester aminolysis, strain promoted azide-alkyne cycloaddition, and sulfur(VI) fluoride exchange, all of which are tolerant of ambient moisture and oxygen. Furthermore, we demonstrate that these reactions can also be used to create areas of morphologically distinct surface features on the nanoscale, by inducing buckling instabilities in the films and the grafting of nanoparticles. This approach is modular, and allows for the development of highly complex surface motifs patterned with different chemistry and morphology. PMID:27280689

  15. THE COORDINATION CHEMISTRY OF METAL SURFACES

    SciTech Connect

    Muetterties, Earl L.

    1980-10-01

    In coordinately unsaturated molecular metal complexes, carbon-hydrogen bonds of the peripheral ligands may, if the stereochemistry allows, closely approach a metal center so as to develop a three-center two-electron bond between the carbon, the hydrogen, and the metal atoms, C-H-M. In some instances, the interaction .is followed by a scission of the C-H bond whereby the metal is effectively oxidized and discrete M-H and M-C {sigma} bonds are forrned. This class of metal-hydrogen-carbon interactions and reactions is shown to be a common phenomenon in metal surface chemistry. Ultra high vacuum studies of nickel and platinum with simple organic molecules like olefins, and arenes are described. These surface chemistry studies were done as a function of surface crystallography and surface composition. The discussion is largely limited to the chemistry of methyl isocyanide, acetonitrile, benzene and toluene. Molecular orbital calculations are presented that support the experimental identification of the importance of C-H-M metal bonding for metal surfaces.

  16. Surface chemistry of porphyrins and phthalocyanines

    NASA Astrophysics Data System (ADS)

    Gottfried, J. Michael

    2015-11-01

    This review covers the surface chemistry of porphyrins, phthalocyanines, their metal complexes, and related compounds, with particular focus on chemical reactions at solid/vacuum interfaces. Porphyrins are not only important biomolecules, they also find, together with the artificial phthalocyanines, numerous technological and scientific applications, which often involve surface and interface related aspects. After a brief summary of fundamental properties of these molecules in the context of surface science, the following topics will be discussed: (1) Aspects of geometric structure, including self-assembly, conformation, mobility and manipulation of the adsorbed molecules. (2) Surface-related changes of the electronic structure and the magnetic properties. (3) The role of the metal center in the surface chemical bond. (4) On-surface coordination reactions, such as direct metalation and coordination of axial ligands. (5) The influence of axial ligands on the surface chemical bond and the magnetic properties.

  17. Surface chemistry and structure of beryllium oxide

    SciTech Connect

    Fuller, E.L. Jr.; Eager, M.H.; Smithwick, R.W. III; Smyrl, N.R.

    1982-02-01

    Detailed examination of nitrogen sorption isotherms related to the surface chemistry and structure of high-purity beryllium oxide and the products of alkali treatment aid in a better understanding of the topochemical problems encountered in the production of ceramic items. Details are corroborated by additional techniques: diffuse reflectance infrared Fourier transform (DRIFT); mercury intrusion porosimetry (MIP); and scanning electron microscopy (SEM). The results correlate well with studies on other oxides when the unique thermophysical properties of this material are considered.

  18. Chemistry in the near-surface atmosphere at Ganymede

    NASA Astrophysics Data System (ADS)

    Shematovich, V. I.

    2013-09-01

    Theoretical predictions of the composition and chemical evolution of near-surface atmospheres of the icy satellites in the Jovian and Kronian systems are of great importance for assessing the biological potential of these satellites. Depending on the satellite mass the formation of the rarefied exosphere with the relatively dense near-surface layer is possible as, for example, in the case of the relatively heavy Galilean satellites Europa and Ganymede in the Jovian system [1-3]. Ganymede is of special interest, because observations indicate that Ganymede has a significant O2 near - surface atmosphere, probably subsurface ocean, and is the only satellite with its own magnetosphere. Processes of formation of the rarefied gaseous envelope of Ganymede and chemical exchange between atmosphere and icy surface will be considered. The water vapour is usually the domin ant parent species in such gaseous envelope because of the ejection from the satellite icy surface due to the thermal outgassing, non-thermal photolysis and radiolysis and other active processes at work on the surface. The photochemis try of water vapour in the near - surface atmospheric layer [4] and the radiolysis of icy regolith [5] result in the supplement of the atmosphere by an admixture of H2, O2, OH and O. Returning molecules have species-dependent behaviour on contact with icy surface of the satellite and non-thermal energy distributions for the chemical radicals. The H2 and O2 molecules stick with very low efficiency and are immediately desorbed thermally, but returning H2O, OH, H and O stick to the grains in the icy regolith with unit efficiency. The suprathermal radicals OH, H, and O entering the regolith can drive the surface chemistry. The numerical kinetic model to investigate on the molecular level the chemistry of the atmosphere - surface interface of the rarefied Н2О-dominant gaseous envelope at Ganymede was developed. Such numerical model simulates the gas-phase and diffusive surface

  19. Chemistry of bimetallic and alloys surfaces

    SciTech Connect

    Koel, B.E.

    1991-10-18

    We have continued our work on elucidating the underlying principles that govern chemical reactions occurring on bimetallic and alloy surfaces. Our goal is to aid in the atomic level explanation of the reactivity and selectivity of alloy and bimetallic cluster catalysts and to provide a fundamental basis for the design of new catalysts with improved performance. Our approach is to use a battery of surface science methods to obtain fundamental data on the thermochemistry and kinetics of the adsorption and reaction of molecules on extensively characterized, single-crystal bimetallic surfaces. We measure changes in chemisorption bond strength, adsorption site distributions, and hydrocarbon fragment stability and reactivity and correlate these results with the geometric and electronic structure of the metal atoms on the surface. Often, our aim is to carefully design experiments that isolate the several factors (e.g., ensemble and ligand effects) that control surface chemistry and catalysis on bimetallic and alloy surfaces in order to better understand the importance of each contribution. In the past 18 months, we have continued to study how alkali promoters strongly affect the reactions of hydrocarbons on Pt and Ni surfaces by altering the electronic structure and inducing significant site-blocking effects. We have shown that bismuth coadsorption provides benchmark data on ensemble sizes required for chemical reactions on Pt and Ni surfaces. Surface alloys of Sn/Pt are being used for detailed probing of ensemble sizes and also reactive site requirements. 22 refs.

  20. Acid-base surface chemistry and sorption of some lanthanides on K{sup +}-saturated Marblehead illite: 1. Results of an experimental investigation

    SciTech Connect

    Sinitsyn, V.A.; Aja, S.U.; Kulik, D.A.; Wood, S.A.

    2000-01-01

    The surface reactivity and sorption of Nd and Eu onto K{sup +}-saturated, Marblehead illite has been investigated in 0.01, 0.1, and 1.0 M KCl solutions at 25 C; the potentiometric titrations were conducted using back-titration techniques. Batch experimental protocols were used in both series of studies. The ionic strength-dependent, proton surface charge density ({sigma}{sub H}) varies from {minus}1500 to {minus}1,700 mC/m{sup 2} in 1.0 M KCl solutions and from {minus}1800 to {minus}2,200 mC/m{sup 2} in 0.01 and 0.1 M KCl solutions. An isoelectric point was not defined by the {sigma}{sub H} vs. pH curves, which reflects the multi-phase nature of natural illitic materials. The functional dependence of REE binding constants (log K{sub e}) on surface coverage (log {Gamma}{sub REE}) indicates the existence of a multiplicity of energetically distinct surface types. These surface site types include amphoteric silanol and aluminol sites, basal planar surfaces, and frayed edges; the frayed edges are observed only in low ionic strength solutions (I {le} 0.1 M KCl).

  1. Magmatic and fragmentation controls on volcanic ash surface chemistry

    NASA Astrophysics Data System (ADS)

    Ayris, Paul M.; Diplas, Spyros; Damby, David E.; Hornby, Adrian J.; Cimarelli, Corrado; Delmelle, Pierre; Scheu, Bettina; Dingwell, Donald B.

    2016-04-01

    The chemical effects of silicate ash ejected by explosive volcanic eruptions on environmental systems are fundamentally mediated by ash particle surfaces. Ash surfaces are a composite product of magmatic properties and fragmentation mechanisms, as well as in-plume and atmospheric alteration processes acting upon those surfaces during and after the eruption. Recent attention has focused on the capacity of alteration processes to shape ash surfaces; most notably, several studies have utilised X-ray photoelectron spectroscopy (XPS), a technique probing the elemental composition and coordination state of atoms within the top 10 nm of ash surfaces, to identify patterns of elemental depletions and enrichments relative to bulk ash chemical composition. Under the presumption of surface and bulk equivalence, any disparities have been previously attributed to surface alteration processes, but the ubiquity of some depletions (e.g., Ca, Fe) across multiple ash studies, irrespective of eruptive origin, could suggest these to be features of the surface produced at the instant of magma fragmentation. To investigate this possibility further, we conducted rapid decompression experiments at different pressure conditions and at ambient and magmatic temperature on porous andesitic rocks. These experiments produced fragmented ash material untouched by secondary alteration, which were compared to particles produced by crushing of large clasts from the same experiments. We investigated a restricted size fraction (63-90 μm) from both fragmented and crushed materials, determining bulk chemistry and mineralogy via XRF, SEM-BSE and EPMA, and investigated the chemical composition of the ash surface by XPS. Analyses suggest that fragmentation under experimental conditions partitioned a greater fraction of plagioclase-rich particles into the selected size fraction, relative to particles produced by crushing. Trends in surface chemical composition in fragmented and crushed particles mirror that

  2. Carbon Dioxide Chemistry on Titan's Surface

    NASA Astrophysics Data System (ADS)

    Hodyss, R. P.; Cable, M. L.; Malaska, M. J.; Vu, T. H.

    2015-12-01

    The surfaces of the moons of the outer Solar System are usually considered too cold (30-100 K) for significant chemistry to occur without the input of energy from exogenic sources (such as charged particles or VUV irradiation). In particular, Titan's thick atmosphere prevents significant amounts of high energy radiation from reaching the surface, limiting opportunities for surface chemical reactivity. Recently, we have identified carbamation, the reaction of carbon dioxide with primary amines to form carbamic acids, as a reaction that could occur thermally on Titan's surface. Amines should be present on Titan's surface, formed by photochemical reactions of N2 and CH4 in the upper atmosphere, and amine-containing molecules have been detected as a component of laboratory tholins made in terrestrial laboratories. There is some spectral evidence that CO2 is present on the surface, and CO2 has been definitively identified in the atmosphere. We use a combination of micro-Raman spectroscopy and UHV FTIR spectroscopy to examine the reaction products and kinetics of the carbamation reaction for a variety of primary amines. The reaction occurs readily at Titan surface temperatures (94 K), and leads to both carbamic acids and ammonium carbamate salts. Our kinetic data can be used to estimate the lifetime of CO2 on Titan's surface, and thus constrain the age of possible CO2-bearing cryovolcanic deposits.

  3. Surface modification of Fe2O3 nanoparticles with 3-aminopropyltrimethoxysilane (APTMS): An attempt to investigate surface treatment on surface chemistry and mechanical properties of polyurethane/Fe2O3 nanocomposites

    NASA Astrophysics Data System (ADS)

    Palimi, M. J.; Rostami, M.; Mahdavian, M.; Ramezanzadeh, B.

    2014-11-01

    Fe2O3 nanoparticles were modified with various amounts of 3-amino propyl trimethoxy silane (APTMS). Modified and unmodified nanoparticles were introduced into the polyurethane matrix at different concentrations. Fourier transform infrared radiation (FT-IR) and X-ray photoelectron spectrophotometer (XPS) were employed in order to investigate the APTMS grafting on the nanoparticles field emission-scanning electron microscope (FE-SEM) was utilized in order to investigate nanoparticles dispersion in the polyurethane coating matrix as well as the fracture behavior of the nanocomposites. The mechanical properties of the nanocomposites were investigated by dynamic mechanical thermal analysis (DMTA) and tensile test. The FTIR spectra and XPS analysis clearly showed that APTMS was grafted on the surface of nanoparticles successfully and formed chemical bonds with the surface. Also, surface treatment of the nanoparticles by silane resulted in the significant improvement of the mechanical properties of the polyurethane coating. The improvement was most pronounced when the nanoparticles were modified with 3 gr silane/5 g nanoparticles.

  4. The surface chemistry of iron Fischer-Tropsch catalysts

    SciTech Connect

    Dwyer, D.J.; Hardenburgh, J.H.

    1986-04-01

    The indirect conversion of coal to liquid hydrocarbons via steam gasification followed by synthesis gas (CO/H/sub 2/) chemistry has been the subject of intensive study for a number of decades. A key technological challenge facing researchers in this area is control over the product distribution during the hydrocarbon synthesis step. In the case of iron Fischer-Tropsch catalysts, it has been known that the addition of alkali to the metal catalyst has a significant impact on the product distribution. Iron catalysts treated with alkali produce less methane more alkenes and higher molecular weight products. In spite of numerous investigations, the details of this promotional effect are not understood on a molecular level. To explore the role of alkali in the surface chemistry of iron catalysts, the authors have carried out a combined surface science and catalytic kinetic study of a model iron catalyst with and without surface alkali.

  5. Chemistry of bimetallic and alloy surfaces

    SciTech Connect

    Koel, B.E.

    1991-10-18

    In the first funding period, we continued our work on elucidating the underlying principles that govern chemical reactions occurring on bimetallic and alloy surfaces. Our goal is to aid in the atomic level explanation of the reactivity and selectivity of alloy and bimetallic cluster catalysts and to provide a fundamental basis for the design of new catalysts with improved performance. Our approach is to use a battery of surface science methods to obtain fundamental data on the thermochemistry and kinetics of the adsorption and reaction of molecules on extensively characterized, single-crystal bimetallic surfaces. We measure changes in chemisorption bond strengths, adsorption site distributions, and hydrocarbon fragment stability and reactivity and correlate these results with the geometric and electronic structure of the metal atoms on the surface. Often, our aim is to carefully design experiments that isolate the several factors (e.g., ensemble and ligand effects) that control surface chemistry and catalysis on bimetallic and alloy surfaces in order to better understand the importance of each contribution. Some of the highlights and noteworthy accomplishments made during the first period of this grant are given.

  6. Acidic deposition and surface water chemistry

    NASA Astrophysics Data System (ADS)

    Church, M. R.

    A pair of back-to-back (morning and afternoon) hydrology sessions, held December 10, 1987, at the AGU Fall Meeting in San Francisco, Calif., covered “Predicting the Effects of Acidic Deposition on Surface Water Chemistry.” The combined sessions included four invited papers, 12 contributed papers, and a panel discussion at its conclusion. The gathering dealt with questions on a variety of aspects of modeling the effects of acidic deposition on surface water chemistry.Contributed papers included discussions on the representation of processes in models as well as limiting assumptions in model application (V. S. Tripathi et al., Oak Ridge National Laboratory, Oak Ridge, Tenn., and E. C. Krug, Illinois State Water Survey, Champaign), along with problems in estimating depositional inputs to catchments and thus inputs to be used in the simulation of catchment response (M. M. Reddy et al., U.S. Geological Survey, Lakewood, Colo.; and E. A. McBean, University of Waterloo, Waterloo, Canada). L. A. Baker et al. (University of Minnesota, Minneapolis) dealt with the problem of modeling seepage lake systems, an exceedingly important portion of the aquatic resources in Florida and parts of the upper U.S. Midwest. J. A. Hau and Y. Eckstein (Kent State University, Kent, Ohio) considered equilibrium modeling of two northern Ohio watersheds that receive very different loads of acidic deposition but are highly similar in other respects.

  7. Surface chemistry and mineralogy. [of planet Mars

    NASA Technical Reports Server (NTRS)

    Banin, A.; Clark, B. C.; Waenke, H.

    1992-01-01

    The accumulated knowledge on the chemistry and mineralogy of Martian surface materials is reviewed. Pertinent information obtained by direct analyses of the soil on Mars by the Viking Landers, by remote sensing of Mars from flyby and orbiting spacecraft, by telescopic observations from earth, and through detailed analyses of the SNC meteorites presumed to be Martian rocks are summarized and analyzed. A compositional model for Mars soil, giving selected average elemental concentrations of major and trace elements, is suggested. It is proposed that the fine surface materials on Mars are a multicomponent mixture of weathered and nonweathered minerals. Smectite clays, silicate mineraloids similar to palagonite, and scapolite are suggested as possible major candidate components among the weathered minerals.

  8. Exothermic surface chemistry on aluminum particles promoting reactivity

    NASA Astrophysics Data System (ADS)

    Mulamba, Oliver; Pantoya, Michelle L.

    2014-10-01

    The exothermic surface chemistry associated with the alumina passivation shell surrounding aluminum (Al) particles and fluorine from fluoropolymer materials is investigated. In particular, polytetrafluoroethylene (PTFE) has been synthesized with varying chain lengths and combined with nanometric Al fuel particles. The Al-PTFE kinetics were analyzed using equilibrium diagnostics including differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) for calorific and phase change behavior coupled with additional flame speed measurements. The objective was to understand the effects of varying PTFE molecular structure on the kinetic and energy propagation behaviors of these composites. Results showed a pre-ignition reaction (PIR) with longer chained PTFE samples and not with the shorter chained PTFE samples. The PIR is attributed to fluorine dislodging hydroxyls from the alumina (Al2O3) passivation surface and forming Al-F structures. Composites exhibiting the PIR correspondingly result in significantly higher flame speeds. The PIR surface chemistry may contribute to promoting the melt dispersion mechanism (MDM) responsible for propagating energy in nano Al reactions. Composites with a PIR also have higher heats of combustion in both the PIR and main reaction exotherms. These results help elucidate the influence of molecular scale surface chemistry on macroscopic energy propagation.

  9. Ferroelectric based catalysis: Switchable surface chemistry

    NASA Astrophysics Data System (ADS)

    Kakekhani, Arvin; Ismail-Beigi, Sohrab

    2015-03-01

    We describe a new class of catalysts that uses an epitaxial monolayer of a transition metal oxide on a ferroelectric substrate. The ferroelectric polarization switches the surface chemistry between strongly adsorptive and strongly desorptive regimes, circumventing difficulties encountered on non-switchable catalytic surfaces where the Sabatier principle dictates a moderate surface-molecule interaction strength. This method is general and can, in principle, be applied to many reactions, and for each case the choice of the transition oxide monolayer can be optimized. Here, as a specific example, we show how simultaneous NOx direct decomposition (into N2 and O2) and CO oxidation can be achieved efficiently on CrO2 terminated PbTiO3, while circumventing oxygen (and sulfur) poisoning issues. One should note that NOx direct decomposition has been an open challenge in automotive emission control industry. Our method can expand the range of catalytically active elements to those which are not conventionally considered for catalysis and which are more economical, e.g., Cr (for NOx direct decomposition and CO oxidation) instead of canonical precious metal catalysts. Primary support from Toyota Motor Engineering and Manufacturing, North America, Inc.

  10. Evaluation of Surface Chemistries for Antibody Microarrays

    SciTech Connect

    Seurynck-Servoss, Shannon L.; White, Amanda M.; Baird, Cheryl L.; Rodland, Karin D.; Zangar, Richard C.

    2007-12-01

    Antibody microarrays are an emerging technology that promises to be a powerful tool for the detection of disease biomarkers. The current technology for protein microarrays has been primarily derived from DNA microarrays and is not fully characterized for use with proteins. For example, there are a myriad of surface chemistries that are commercially available for antibody microarrays, but no rigorous studies that compare these different surfaces. Therefore, we have used an enzyme-linked immunosorbent assay (ELISA) microarray platform to analyze 16 different commercially available slide types. Full standard curves were generated for 24 different assays. We found that this approach provides a rigorous and quantitative system for comparing the different slide types based on spot size and morphology, slide noise, spot background, lower limit of detection, and reproducibility. These studies demonstrate that the properties of the slide surface affect the activity of immobilized antibodies and the quality of data produced. Although many slide types can produce useful data, glass slides coated with poly-L-lysine or aminosilane, with or without activation with a crosslinker, consistently produce superior results in the ELISA microarray analyses we performed.

  11. The surface chemistry of cerium oxide

    DOE PAGESBeta

    Mullins, David R.

    2015-01-29

    Our review covers the structure of, and chemical reactions on, well-defined cerium oxide surfaces. Ceria, or mixed oxides containing ceria, are critical components in automotive three-way catalysts due to their well-known oxygen storage capacity. Ceria is also emerging as an important material in a number of other catalytic processes, particularly those involving organic oxygenates and the water–gas shift reaction. Ceria's acid–base properties, and thus its catalytic behavior, are closely related to its surface structure where different oxygen anion and cerium cation environments are present on the low-index structural faces. The actual structure of these various faces has been the focusmore » of a number of theoretical and experimental investigations. Ceria is also easily reducible from CeO2 to CeO2-X. The presence of oxygen vacancies on the surface often dramatically alters the adsorption and subsequent reactions of various adsorbates, either on a clean surface or on metal particles supported on the surface. We conducted surface science studies on the surfaces of thin-films rather than on the surfaces of bulk single crystal oxides. The growth, characterization and properties of these thin-films are also examined.« less

  12. The surface chemistry of cerium oxide

    SciTech Connect

    Mullins, David R.

    2015-01-29

    Our review covers the structure of, and chemical reactions on, well-defined cerium oxide surfaces. Ceria, or mixed oxides containing ceria, are critical components in automotive three-way catalysts due to their well-known oxygen storage capacity. Ceria is also emerging as an important material in a number of other catalytic processes, particularly those involving organic oxygenates and the water–gas shift reaction. Ceria's acid–base properties, and thus its catalytic behavior, are closely related to its surface structure where different oxygen anion and cerium cation environments are present on the low-index structural faces. The actual structure of these various faces has been the focus of a number of theoretical and experimental investigations. Ceria is also easily reducible from CeO2 to CeO2-X. The presence of oxygen vacancies on the surface often dramatically alters the adsorption and subsequent reactions of various adsorbates, either on a clean surface or on metal particles supported on the surface. We conducted surface science studies on the surfaces of thin-films rather than on the surfaces of bulk single crystal oxides. The growth, characterization and properties of these thin-films are also examined.

  13. Nanomaterial surface chemistry design for advancements in capillary electrophoresis modes.

    PubMed

    Ivanov, Michael R; Haes, Amanda J

    2011-01-01

    Tailored surface chemistry impacts nanomaterial function and stability in applications including in various capillary electrophoresis (CE) modes. Although colloidal nanoparticles were first integrated as colouring agents in artwork and pottery over 2000 years ago, recent developments in nanoparticle synthesis and surface modification increased their usefulness and incorporation in separation science. For instance, precise control of surface chemistry is critically important in modulating nanoparticle functionality and stability in dynamic environments. Herein, recent developments in nanomaterial pseudostationary and stationary phases will be summarized. First, nanomaterial core and surface chemistry compositions will be classified. Next, characterization methods will be described and related to nanomaterial function in various CE modes. Third, methods and implications of nanomaterial incorporation into CE will be discussed. Finally, nanoparticle-specific mechanisms likely involved in CE will be related to nanomaterial surface chemistry. Better understanding of surface chemistry will improve nanoparticle design for the integration into separation techniques. PMID:20967383

  14. Engineered microtopographies and surface chemistries direct cell attachment and function

    NASA Astrophysics Data System (ADS)

    Magin, Chelsea Marie

    Harrison, in 1914, first recognized that cells respond to physicochemical cues such as substratum topography when he observed that fibroblasts elongated while cultured on spider silk. Recently, techniques developed in the micro-electronics industry have been used to create molds for producing microscaled topographies with various shapes and spatial arrangements. Although these patterning techniques are well-established, very little is known about the mechanisms underlying cell sensing and response to microtopographies. In this work cellular micro-environments with varying surface topographies and chemistries were evaluated with marine organisms and mammalian cells to investigate cellular sensing and response. Biofouling---the accumulation of micro-organisms, plants, and animals on submerged surfaces---is an environmental and economic concern. Engineered topographies, replicated in polydimethylsiloxane elastomer (PDMSe) and functionalized poly(ethylene glycol)-dimethacrylate (PEGDMA) hydrogels, were evaluated for inhibition of marine fouling organism attachment. Microtopographies replicated in PDMSe inhibited attachment of the marine bacterium, Cobetia marina up to 99% versus smooth. The average normalized attachment densities of cells of C. marina and zoospores of the green algae Ulva on PDMSe topographies scaled inversely with the Engineered Roughness Index (ERIII), a representation of surface energy. Attachment densities of Ulva from four assays and C. marina from two growth phases to PDMSe surfaces scaled inversely with one equation: ERI II multiplied by the Reynolds number of the organism (Re) (R 2 = 0.77). The same microtopographies created in PDMSe reduced the initial attachment density and attachment strength of cells of the diatoms Navicula incerta and Seminavis robusta compared to smooth PDMSe. The average normalized attachment density of Navicula after exposure to shear stress (48 Pa) was correlated with the contact area between the diatom and a

  15. Wet oxidation of ordered mesoporous carbon FDU-15 by using (NH4)2S2O8 for fast adsorption of Sr(II): An investigation on surface chemistry and adsorption mechanism

    NASA Astrophysics Data System (ADS)

    Song, Yang; Ye, Gang; Chen, Jing; Lv, Dachao; Wang, Jianchen

    2015-12-01

    Surface modification of ordered mesoporous carbon (OMC) by wet oxidation provides an oxygen-enriched platform for complexation of metal ions. Here, we present a comprehensive study on the surface chemistry and textual property of OMC FDU-15 modified by wet oxidation using (NH4)2S2O8 as a benign oxidant. And, for the first time, the adsorption behavior and mechanism of wet-oxidized OMC FDU-15 toward Sr(II) in aqueous solutions were investigated. The mesostructural regularity of the OMC FDU-15 was well-reserved under wet oxidation. Compared to OMC CMK-type counterparts prepared via nanocasting, the OMC FDU-15 by soft template method showed much-enhanced structural stability. Due to the introduction of abundant oxygen-containing species, the oxidized OMC FDU-15 exhibited excellent hydrophilicity and dispersibility in aqueous solutions. The adsorption behavior toward Sr(II) was fully investigated, showing a super-fast adsorption kinetics (< 5 min to reach equilibrium) and a Langmuir adsorption isotherm. Moreover, an in-depth X-ray photoelectron spectroscopy analysis through deconvolution of high resolution C1s and O1s spectra was implemented to identify the chemical species of the surface functional groups, while probing the adsorption mechanism. The results suggested that oxygen donor atoms in Csbnd O single bonds mainly contribute to the adsorption of Sr(II) via formation of metal-ligand complexation.

  16. Investigating expanded chemistry in CMAQ clouds

    EPA Science Inventory

    Clouds and fogs significantly impact the amount, composition, and spatial distribution of gas and particulate atmospheric species, not least of which through the chemistry that occurs in cloud droplets.ᅠ Atmospheric sulfate is an important component of fine aerosol mass an...

  17. Impact Driven Chemistry on Europa's Surface

    NASA Astrophysics Data System (ADS)

    Khare, B. N.; NNa Mvondo, D.; Borucki, J. G.; Cruikshank, D. P.; Belisle, W. A.; Wilhite, P.; McKay, C. P.

    2005-08-01

    A new energy source for organic synthesis on simulated Europan surfaces, electrical discharge, light emission, and magnetic phenomena from impacts into the ice, has been studied [Borucki et al. J. Geophys. Res. 107 (E11) 5114 (2002)]. Part of the impactor's kinetic energy is converted into electrical potential. The mechanical disruption causes the release of energy as light, heat, and electrical and magnetic fields as secondary emissions that synthesizes complex organic material named tholin [Sagan and Khare, Nature 277, 102 (1979)] in the area of impact craters. The morphology of the impact craters indicates that tholin is the result of outflow from the fracture zone. Large pool of liquid water may exist for thousands of years as suggested for Titan [Thompson and Sagan, Eur. Space Agency Spec. Publ., ESA-SP, 338, 167 (1992)] and may also apply to Europa potentially driving prebiotic chemistry due to energy pumped in from the secondary emissions. We have detected 8.8 ppm of H2O2 from impact of a 1/4" iron bullet at 5.3 km/s over water ice at ca. -100 C. H2O2 has been detected on the surface of Europa [Carlson et al., Science 283, 2062 (1999)]. Further confirmation by Raman Scattering at 874.5 cm-1 and IR absorbance at 2854 cm-1 is continuing. Since the impactor is limited in the number of experiments we can run, other experiments used a laser induced plasma (LIP) to shock ice mixed with ammonium sulphate and methanol. We detected CH4, CO, N2O, C2H6, CH3CN, CH3COCH3, HCOOCH3 (methyl formate), and traces of HCN. LIP on a mixture of water and methanol ice produced CH4, CO, HCHO, ethanol, formic acid methylester, propanol, acetone, dimethoxyme, and possibly ethanone-1phenyl or other phenyl group. NH3 and methanol could be delivered on impact of comets while sulfur expelled from Io.

  18. Laboratory investigations on the role of sediment surface and ground water chemistry in transport of bacteria through a contaminated Sandy Aquifer

    USGS Publications Warehouse

    Scholl, M.A.; Harvey, R.W.

    1992-01-01

    The effects of pH and sediment surface characteristics on sorption of indigenous groundwater bacteria were determined using contaminated and uncontaminated aquifer material from Cape Cod, MA. Over the pH range of the aquifer (5-7), the extent of bacterial sorption onto sediment in uncontaminated groundwater was strongly pH-dependent, but relatively pH-insensitive in contaminated groundwater from the site. Bacterial sorption was also affected by the presence of oxyhydroxide coatings (iron, aluminum, and manganese). Surface coating effects were most pronounced in uncontaminated groundwater (pH 6.4 at 10??C). Desorption of attached bacteria (up to 14% of the total number of labeled cells added) occurred in both field and laboratory experiments upon adjustment of groundwater to pH 8. The dependence of bacterial sorption upon environmental conditions suggests that bacterial immobilization could change substantially over relatively short distances in contaminated, sandy aquifers and that effects caused by changes in groundwater geochemistry can be significant.

  19. Surface chemistry: Key to control and advance myriad technologies

    PubMed Central

    Yates, John T.; Campbell, Charles T.

    2011-01-01

    This special issue on surface chemistry is introduced with a brief history of the field, a summary of the importance of surface chemistry in technological applications, a brief overview of some of the most important recent developments in this field, and a look forward to some of its most exciting future directions. This collection of invited articles is intended to provide a snapshot of current developments in the field, exemplify the state of the art in fundamental research in surface chemistry, and highlight some possibilities in the future. Here, we show how those articles fit together in the bigger picture of this field. PMID:21245359

  20. INVESTIGATING ENVIRONMENTAL SINKS OF MACROLIDE ANTIBIOTICS WITH ANALYTICAL CHEMISTRY

    EPA Science Inventory

    Possible environmental sinks (wastewater effluents, biosolids, sediments) of macrolide antibiotics (i.e., azithromycin, roxithromycin and clarithromycin)are investigated using state-of-the-art analytical chemistry techniques.

  1. Elementary photocatalytic chemistry on TiO2 surfaces.

    PubMed

    Guo, Qing; Zhou, Chuanyao; Ma, Zhibo; Ren, Zefeng; Fan, Hongjun; Yang, Xueming

    2016-07-01

    Photocatalytic hydrogen production and pollutant degradation provided both great opportunities and challenges in the field of sustainable energy and environmental science. Over the past few decades, we have witnessed fast growing interest and efforts in developing new photocatalysts, improving catalytic efficiency and exploring the reaction mechanism at the atomic and molecular levels. Owing to its relatively high efficiency, nontoxicity, low cost and high stability, TiO2 becomes one of the most extensively investigated metal oxides in semiconductor photocatalysis. Fundamental studies on well characterized single crystals using ultrahigh vacuum based surface science techniques could provide key microscopic insight into the underlying mechanism of photocatalysis. In this review, we have summarized recent progress in the photocatalytic chemistry of hydrogen, water, oxygen, carbon monoxide, alcohols, aldehydes, ketones and carboxylic acids on TiO2 surfaces. We focused this review mainly on the rutile TiO2(110) surface, but some results on the rutile TiO2(011), anatase TiO2(101) and (001) surfaces are also discussed. These studies provided fundamental insights into surface photocatalysis as well as stimulated new investigations in this exciting field. At the end of this review, we have discussed how these studies can help us to develop new photocatalysis models. PMID:26335268

  2. Adsorption of perfluoroalkyl acids by carbonaceous adsorbents: Effect of carbon surface chemistry.

    PubMed

    Zhi, Yue; Liu, Jinxia

    2015-07-01

    Adsorption by carbonaceous sorbents is among the most feasible processes to remove perfluorooctane sulfonic (PFOS) and carboxylic acids (PFOA) from drinking and ground waters. However, carbon surface chemistry, which has long been recognized essential for dictating performance of such sorbents, has never been considered for PFOS and PFOA adsorption. Thus, the role of surface chemistry was systematically investigated using sorbents with a wide range in precursor material, pore structure, and surface chemistry. Sorbent surface chemistry overwhelmed physical properties in controlling the extent of uptake. The adsorption affinity was positively correlated carbon surface basicity, suggesting that high acid neutralizing or anion exchange capacity was critical for substantial uptake of PFOS and PFOA. Carbon polarity or hydrophobicity had insignificant impact on the extent of adsorption. Synthetic polymer-based Ambersorb and activated carbon fibers were more effective than activated carbon made of natural materials in removing PFOS and PFOA from aqueous solutions. PMID:25827692

  3. Surface Chemistry in Heterogeneous Catalysis: An Emerging Discipline.

    ERIC Educational Resources Information Center

    White, J. M.; Campbell, Charles T.

    1980-01-01

    Provides background data on surface chemistry as an emerging discipline. Highlights the important role which surfaces play in catalysis by focusing on the catalyzed oxidation of carbon monoxide. Provides a demonstration of how surfaces exert their influences in heterogeneous phenomena and illustrates how experimental problems in this field are…

  4. Field investigation of FGD system chemistry. Final report

    SciTech Connect

    Litherland, S.T.; Colley, J.D.; Glover, R.L.; Maller, G.; Behrens, G.P.

    1984-12-01

    Three full-scale wet limestone FGD systems were investigated to gain a better understanding of FGD system operation and chemistry. The three plants which participated in the program were South Mississippi Electric Power Association's R. D. Morrow Station, Colorado-Ute Electric Association's Craig Station, and Central Illinois Light Company's Duck Creek Station. Each FGD system was characterized with respect to SO/sub 2/ removal, liquid and solid phase chemistry, and calcium sulfite and calcium sulfate relative saturation. Mist eliminator chemistry and performance were documented at Morrow and Duck Creek. Solutions to severe mist eliminator scaling and pluggage were demonstrated at Duck Creek. A technical and econ

  5. Investigations in Marine Chemistry: Tide Pool Ecology.

    ERIC Educational Resources Information Center

    Schlenker, Richard M.

    Students investigated the salinity of tide pools at different levels in the intertidal zone. Data are analyzed collectively. Students graphed and discussed data. Included are suggestions for evaluation and further study. (Author)

  6. Modulation of human osteoblasts by metal surface chemistry.

    PubMed

    Hofstetter, Wilhelm; Sehr, Harald; de Wild, Michael; Portenier, Jeannette; Gobrecht, Jens; Hunziker, Ernst B

    2013-08-01

    The use of metal implants in dental and orthopedic surgery is continuously expanding and highly successful. While today longevity and load-bearing capacity of the implants fulfill the expectations of the patients, acceleration of osseointegration would be of particular benefit to shorten the period of convalescence. To further clarify the options to accelerate the kinetics of osseointegration, within this study, the osteogenic properties of structurally identical surfaces with different metal coatings were investigated. To assess the development and function of primary human osteoblasts on metal surfaces, cell viability, differentiation, and gene expression were determined. Titanium surfaces were used as positive, and surfaces coated with gold were used as negative controls. Little differences in the cellular parameters tested for were found when the cells were grown on titanium discs sputter coated with titanium, zirconium, niobium, tantalum, gold, and chromium. Cell number, activity of cell layer-associated alkaline phosphatase (ALP), and levels of transcripts encoding COL1A1 and BGLAP did not vary significantly in dependence of the surface chemistry. Treatment of the cell cultures with 1,25(OH)2 D3 /Dex, however, significantly increased ALP activity and BGLAP messenger RNA levels. The data demonstrate that the metal layer coated onto the titanium discs exerted little modulatory effects on cell behavior. It is suggested that the microenvironment regulated by the peri-implant tissues is more effective in regulating the tissue response than is the material of the implant itself. PMID:23359530

  7. Water at surfaces with tunable surface chemistries and the chiral imprint of water around DNA

    NASA Astrophysics Data System (ADS)

    Petersen, Poul

    Aqueous interfaces are ubiquitous in atmospheric chemistry and biological systems but are notoriously hard to probe experimentally. Surface-specific vibrational spectroscopy offers an avenue to directly probe the vibrational modes of the water OH stretching band but this method is challenging to implement to buried surfaces. Here we present results from sum-frequency generation (SFG) spectroscopy probing the buried interface between a functionalized surface and aqueous solutions. Studying such buried surfaces offers the advantage of being able to systematically tune the surface chemistry using self-assembled monolayers, i.e. the hydrophobic and hydrophilic character, and examine the effect on the interfacial water. In addition to water at these controlled surfaces, we have initiated studying water at biological surfaces. This includes the solvation structure around DNA. X-ray experiments at cryogenic temperatures have found crystallographic water in the minor grove of DNA giving rise to the notion of a spine of hydration surrounding DNA. Such structured water should exhibit a chiral structure adapted from DNA. We investigate if such a chiral water structure exist around DNA at room temperature using chiral SFG. This work was supported by the National Science Foundation under a NSF CAREER Grant (CHE-1151079).

  8. Investigations in Marine Chemistry: Salinity II.

    ERIC Educational Resources Information Center

    Schlenker, Richard M.

    Presented is a science activity in which the student investigates methods of calibration of a simple conductivity meter via a hands-on inquiry technique. Conductivity is mathematically compared to salinity using a point slope formula and graphical techniques. Sample solutions of unknown salinity are provided so that the students can sharpen their…

  9. Gas Plasma Surface Chemistry for Biological Assays.

    PubMed

    Sahagian, Khoren; Larner, Mikki

    2015-01-01

    Biological systems respond to and interact with surfaces. Gas plasma provides a scalable surface treatment method for designing interactive surfaces. There are many commercial examples of plasma-modified products. These include well plates, filtration membranes, dispensing tools, and medical devices. This chapter presents an overview of gas plasma technology and provides a guide to using gas plasma for modifying surfaces for research or product development. PMID:26160577

  10. Grain surface chemistry in star-forming regions

    NASA Astrophysics Data System (ADS)

    Taquet, Vianney

    2012-12-01

    The first stages of star formation are accompanied by an evolution of the chemistry, starting from simple molecules in cold dark clouds to the detection of complex organic molecules around Class 0 protostars. Although mostly composed of gas, these clouds also contain small amounts of microscopic dust. The contribution of this dust is nevertheless important because it acts as a catalyst for the formation of key molecules seen in cold interstellar ices, such as water or methanol. These ices are believed to be the first step towards the rich chemistry seen in the warm envelope of protostars. During my thesis, I focused on this first step and I did so by taking a twofold approach. i) Modelling. I have developed an astrochemical model coupling the chemistry in the gas phase and on the grain surfaces. This model follows the multilayer formation of interstellar ices and allows us to investigate the influence of key physical, chemical, and surface parameters, such as the grain porosity, on the chemical composition of ices via a multiparameter approach. The model has been applied to predict the chemical differentiation and the deuteration of interstellar ices. To this end, I have built up a chemical network taking into account the most recent experimental and theoretical works. I applied then the model to various cases. For example, I showed that ices are heterogeneous and their composition are sensitive to the physical conditions as well as several grain surface parameters. The high deuteration of formaldehyde, and methanol observed around low-mass protostars has been predicted by a dense (nH ∼ 5 × 10^6 cm-3) and fast (∼ 5000 years) phase while the lower deuteration of water is predicted for typical molecular cloud conditions. The deuterium fractionation is very sensitive and can be used as a tracer of the physical conditions. ii) Observations. I have been involved in observational projects whose goals are related to the grain surface chemical problems. I obtained the

  11. The chemistry and physics of zinc oxide surfaces

    NASA Astrophysics Data System (ADS)

    Wöll, Christof

    Metal oxides are virtually everywhere - only gold has the property not to form an oxide on its surface when exposed to the ambient. As a result, understanding the physics and chemistry of oxide surfaces is a topic of pronounced general interest and, of course, also a necessary prerequisite for many technical applications. The most important of these is certainly heterogeneous catalysis, but one has to realize that - under ambient conditions - virtually all phenomena occurring at liquid/metal and gas/metal interfaces are determined by the corresponding oxide. This applies in particular to friction phenomena, adhesion and corrosion. A necessary - but not necessarily sufficient - condition for unravelling the fundamentals governing this complex field is to analyze in some detail elementary chemical and physical processes at oxide surfaces. Although the Surface Science of metal surfaces has seen a major progress in the past decades, for oxides detailed experimental investigations for well-defined single crystal surfaces still represent a formidable challenge - mostly because of technical difficulties (charging), but to some extent also due to fundamental problems related to the stabilization of polar surfaces. As a result, the amount of information available for this class of materials is - compared to that at hand for metals - clearly not satisfactory. A particular disturbing lack of information is that about the presence of hydrogen at oxide surfaces - either as hydroxy-species or in form of metal hydrides. In the present review we will summarize recent experimental and theoretical information which has become available from single crystal studies on ZnO surfaces. While the number of papers dealing with another oxide, rutile TiO 2, is significantly larger (although titania does not exhibit a polar surface), also for zinc oxide a basis of experimental and theoretical knowledge as been accumulated, which - at least for the non-polar surfaces - allows to understand

  12. Scattering and Chemical Investigations of Semiconductor Surfaces.

    NASA Astrophysics Data System (ADS)

    Wallace, Robert Milo

    1988-12-01

    This two-part thesis describes: (i) the design of an ion scattering system to examine the surface and near-surface region of semiconductors, and (ii) the chemical reaction channels of unsaturated hydrocarbons on the silicon (100) surface. Details on the design and construction of an ultrahigh vacuum, high-energy ion scattering system are presented. The use of MeV ion scattering to investigate surface and near -surface regions of materials is described and the combination of ion scattering with complimentary surface science techniques is stressed. The thermal activation of chemical bonds of the adsorbed unsaturated hydrocarbon molecules ethylene, propylene, and acetylene is investigated on the Si(100)-(2 times 11) surface with a goal of understanding the surface chemistry of Si-C formation. The use of precision dosing techniques, Low Energy Electron Diffraction, Auger Electron Spectroscopy, and Temperature Programmed Desorption in the investigation of the remaining carbonaceous species is described. Comparisons of the adsorption and desorption behavior of these molecules is made in terms of the carbon -carbon double and triple bonds (ethylene to acetylene) and the methyl functional group (ethylene to propylene). We find that the monolayer saturation coverage of these hydrocarbons is in very good agreement with the number of dimer sites on the surface estimated from scanning-tunneling microscopy, which suggests that the bonding of these hydrocarbons to the Si(100) surface is similar. It is also found that ethylene, in particular, does not provide an efficient Si-C reaction channel upon thermal activation, with nearly 100% of the ethylene molecules desorbing. In contrast, acetylene is found to be very efficient in SiC formation: >=q90% of the adsorbed acetylene thermally dissociates and eventually leads to SiC formation. Propylene has an efficiency of roughly 70% upon heating. Evidence for the diffusion of carbon into the bulk is seen at >=q850 K for propylene and

  13. Chemistry of bimetallic and alloy surfaces

    SciTech Connect

    Koel, B.E.

    1992-01-01

    Recent research accomplishments included: a method for estimating surface reaction energetics, and application to ethylene decomposition on Pt(111); carbon Auger line shapes for adsorption/decomposition of ethylene on Ni(100) and C-C bonding in ''carbidic'' layers on metals; surface structure of Sn deposited on Pt(111) and Pt(100); chemisorption of CO, H[sub 2], O[sub 2] on ordered Sn/Pt(111) surface alloys; effects of K adatoms on H[sub 2] adsorption on Pt(111); effects of adsorbed K, O, and H on CO adsorption on Pt(111); hydrocarbon trapping, condensation on Pt(111); effects of C on cyclohexane dehydrogenation on Pt(111) surfaces; and SnPt(111) catalysis of benzene production from acetylene under uhv conditions.

  14. Supported organometallic complexes: Surface chemistry, spectroscopy, and catalysis

    SciTech Connect

    Marks, T.J.

    1991-01-01

    Adsorbing organometallic molecules onto the surfaces of inorganic supports such as Al{sub 2}O{sub 3}, MgCl{sub 2}, SiO{sub 2}, etc. can result in dramatic enhancements in catalytic activity. The reasons for this and the structures of the resulting surface organometallic centers are not well understood. We have addressed this problem using actinide and early transition metal complexes as model adsorbates. Characterization tools include catalytic and stoichiometric reaction chemistry, reaction kinetics and isotopic labeling, quantitative poisoning studies, model solution chemistry, and a wide array of surface-sensitive spectroscopies such as CPMAS NMR, EPR, and UV-VIS as well as titration calorimetry. These chemical and physical experiments are closely coupled to model solution chemistry to provide maximum information yield. 4 refs., 2 figs.

  15. The surface coat of chylomicrons: lipid chemistry.

    PubMed

    Zilversmit, D B

    1968-03-01

    Chylomicrons from the thoracic duct lymph of dogs fed corn oil were isolated by centrifugation and disrupted by either freezing and thawing or rotary evaporation and rehydration. A pellet, representing the surface coat, was isolated by centrifugation. Pellets isolated by freezing and thawing contained a higher percentage of saturated triglycerides than pellets isolated by rotary evaporation; the presence of saturated triglyceride in the pellet was probably an artifact of the preparation of the surface coat material at low temperature. Exchange of free cholesterol between surface and core lipid of chylomicrons was complete within 1 hr. The percentage of cholesterol in pellets of surface material isolated by freezing and thawing was about twice that found for pellets after rotary evaporation at 25-40 degrees C. Cholesteryl ester was not present in the surface lipid and that present in the core lipid did not exchange with serum lipoprotein cholesteryl ester. For phosphatidyl choline, the percentage of linoleic acid in lymph chylomicrons was markedly higher than that in clear lymph or plasma, while the percentage of arachidonic acid was lower. Sphingomyelin of lymph chylomicrons was characterized by very high levels of 16:0 and relatively small percentages of very long-chain fatty acids as compared with clear lymph or plasma. The data are consistent with the view that in lymph chylomicrons: (a) cholesteryl esters are dissolved in a core of triglycerides which contain fatty acids derived primarily from dietary fatty acids, (b) free cholesterol is partitioned between core and surface and is freely exchangeable between the two, (c) the phospholipid fractions are present on the surface and are intracellular in origin. PMID:5640497

  16. A model of Martian surface chemistry

    NASA Technical Reports Server (NTRS)

    Oyama, V. I.; Berdahl, B. J.

    1979-01-01

    Alkaline earth and alkali metal superoxides and peroxides, gamma-Fe2O3 and carbon suboxide polymer, are proposed to be constituents of the Martian surface material. These reactive substances explain the water modified reactions and thermal behaviors of the Martian samples demonstrated by all of the Viking Biology Experiments. It is also proposed that the syntheses of these substances result mainly from electrical discharges between wind-mobilized particles at Martian pressures; plasmas are initiated and maintained by these discharges. Active species in the plasma either combine to form or react with inorganic surfaces to create the reactive constituents.

  17. Supported organometallic complexes: Surface chemistry, spectroscopy, and catalysis

    SciTech Connect

    Marks, T.J.

    1992-02-01

    The long-range goal of this project is to elucidate and understand the surface chemistry and catalytic properties of well-defined, highly-reactive organometallic molecules (principally based upon abundant actinide, lanthanide, and early transition elements) adsorbed on metal oxides and halides. The nature of the adsorbed species is probed by a battery of chemical and physicochemical techniques, to understand the nature of the molecular-surface coordination chemistry and how this can give rise to extremely high catalytic activity. A complementary objective is to delineate the scope and mechanisms of the heterogeneous catalytic reactions, as well as to relate them both conceptually and functionally to model systems generated in solution.

  18. Organic chemistry on Titan: Surface interactions

    NASA Technical Reports Server (NTRS)

    Thompson, W. Reid; Sagan, Carl

    1992-01-01

    The interaction of Titan's organic sediments with the surface (solubility in nonpolar fluids) is discussed. How Titan's sediments can be exposed to an aqueous medium for short, but perhaps significant, periods of time is also discussed. Interactions with hydrocarbons and with volcanic magmas are considered. The alteration of Titan's organic sediments over geologic time by the impacts of meteorites and comets is discussed.

  19. Investigating the Effectiveness of Computer Simulations for Chemistry Learning

    ERIC Educational Resources Information Center

    Plass, Jan L.; Milne, Catherine; Homer, Bruce D.; Schwartz, Ruth N.; Hayward, Elizabeth O.; Jordan, Trace; Verkuilen, Jay; Ng, Florrie; Wang, Yan; Barrientos, Juan

    2012-01-01

    Are well-designed computer simulations an effective tool to support student understanding of complex concepts in chemistry when integrated into high school science classrooms? We investigated scaling up the use of a sequence of simulations of kinetic molecular theory and associated topics of diffusion, gas laws, and phase change, which we designed…

  20. Molecular Surface Chemistry by Metal Single Crystals and Nanoparticles from Vacuum to High Pressure.

    SciTech Connect

    Somorjai, Gabor A.; Park, Jeong Y.

    2008-04-05

    Model systems for studying molecular surface chemistry have evolved from single crystal surfaces at low pressure to colloidal nanoparticles at high pressure. Low pressure surface structure studies of platinum single crystals using molecular beam surface scattering and low energy electron diffraction techniques probe the unique activity of defects, steps and kinks at the surface for dissociation reactions (H-H, C-H, C-C, O{double_bond}O bonds). High-pressure investigations of platinum single crystals using sum frequency generation vibrational spectroscopy have revealed the presence and the nature of reaction intermediates. High pressure scanning tunneling microscopy of platinum single crystal surfaces showed adsorbate mobility during a catalytic reaction. Nanoparticle systems are used to determine the role of metal-oxide interfaces, site blocking and the role of surface structures in reactive surface chemistry. The size, shape and composition of nanoparticles play important roles in determining reaction activity and selectivity.

  1. Quantification of air plasma chemistry for surface disinfection

    NASA Astrophysics Data System (ADS)

    Pavlovich, Matthew J.; Clark, Douglas S.; Graves, David B.

    2014-12-01

    Atmospheric-pressure air plasmas, created by a variety of discharges, are promising sources of reactive species for the emerging field of plasma biotechnology because of their convenience and ability to operate at ambient conditions. One biological application of ambient-air plasma is microbial disinfection, and the ability of air plasmas to decontaminate both solid surfaces and liquid volumes has been thoroughly established in the literature. However, the mechanism of disinfection and which reactive species most strongly correlate with antimicrobial effects are still not well understood. We describe quantitative gas-phase measurements of plasma chemistry via infrared spectroscopy in confined volumes, focusing on air plasma generated via surface micro-discharge (SMD). Previously, it has been shown that gaseous chemistry is highly sensitive to operating conditions, and the measurements we describe here extend those findings. We quantify the gaseous concentrations of ozone (O3) and nitrogen oxides (NO and NO2, or NOx) throughout the established ‘regimes’ for SMD air plasma chemistry: the low-power, ozone-dominated mode; the high-power, nitrogen oxides-dominated mode; and the intermediate, unstable transition region. The results presented here are in good agreement with previously published experimental studies of aqueous chemistry and parameterized models of gaseous chemistry. The principal finding of the present study is the correlation of bacterial inactivation on dry surfaces with gaseous chemistry across these time and power regimes. Bacterial decontamination is most effective in ‘NOx mode’ and less effective in ‘ozone mode’, with the weakest antibacterial effects in the transition region. Our results underscore the dynamic nature of air plasma chemistry and the importance of careful chemical characterization of plasma devices intended for biological applications.

  2. Lunar surface chemistry: A new imaging technique

    USGS Publications Warehouse

    Andre, C.G.; Bielefeld, M.J.; Eliason, E.; Soderblom, L.A.; Adler, I.; Philpotts, J.A.

    1977-01-01

    Detailed chemical maps of the lunar surface have been constructed by applying a new weighted-filter imaging technique to Apollo 15 and Apollo 16 x-ray fluorescence data. The data quality improvement is amply demonstrated by (i) modes in the frequency distribution, representing highland and mare soil suites, which are not evident before data filtering and (ii) numerous examples of chemical variations which are correlated with small-scale (about 15 kilometer) lunar topographic features.

  3. Surface chemistry at the nanometer scale

    NASA Astrophysics Data System (ADS)

    Cao, Peigen

    This thesis describes research towards understanding surface chemical and physical processes, as well as their effects on the underlying substrate properties, at the nanometer and atomic scales. We demonstrate a method to tune the density of etch pits on Si(111) during the chlorination process so as to change the surface reactivity. Subsequent grafting of an azide group to replace chlorine demonstrates an example of non-oxidative passivation of silicon surfaces with new functionalities. Depending upon the solvent used in the azidation process, it is shown to yield different azidation kinetic rates, different final azide coverages, and different surface-area distributions. Scanning tunneling spectroscopy studies show that both chlorination and azidation processes significantly modify the surface electronic structures, with the former leading to a non-zero density of states at the Fermi level. Our studies on a new class of corrugation, i.e., wrinkles, in exfoliated graphene on SiO2 show that a "three-for-six" triangular pattern of atoms is exclusively and consistently observed on wrinkles, suggesting the local curvature of the wrinkle is a perturbation that breaks the six-fold symmetry of the graphene lattice. Lower electrical conductance is also found on the top of wrinkles compared to other regions of graphene. The wrinkles are characterized by the presence of midgap states, which is in agreement with recent theoretical predictions. A general method is also reported for reliably fabricating ultrahigh-density graphene nanoribbon (GNR) arrays. We have clearly observed how the properties of GNRs evolve as a function of number of graphene layers. The band gap (and so the on-off ratio) decreases as the number of layers increases. These results suggest that, in addition to single layer graphene, properties of GNRs of different thicknesses can also be harnessed for engineering GNRs as different building blocks towards FET applications. A novel imaging technique, graphene

  4. Role of Surface Chemistry in Nanoscale Electrokinetic Transport

    NASA Astrophysics Data System (ADS)

    Atalay, Selcuk

    This dissertation work presents the efforts to study the electrofluidics phenomena, with a focus on surface charge properties in nanoscale systems with the potential applications in imaging, energy conversion, ultrafiltration, DNA analysis/sequencing, DNA and protein transport, drug delivery, biological/chemical agent detection and micro/nano chip sensors. Since the ion or molecular or particle transport and also liquid confinement in nano-structures are strongly dominated by the surface charge properties, in regards of the fundamental understanding of electrofluidics at nanoscale, we have used surface charge chemistry properties based on 2-pK charging mechanism. Using this mechanism, we theoretically and analytically showed the surface charge properties of silica nanoparticles as a function of their size, pH level and salt ionic strength of aqueous solution. For a fixed particle size, the magnitude of the surface charge typically increases with an increase in pH or background salt concentration. Furthermore, we investigated the surface charge properties of a charged dielectric nanoparticle and flat wall in electrostatic interactions. According to the theoretical results strong interactions cause a non-uniform surface charge density on the nanoparticle and the plate as a result of the enhancement of proton concentration in the gap between the particle and the plate. This effect increases with decreased separation distance (Kh). We moreover investigated the ion confinement inside the nanospaces and using a continuum model, we showed the proton enhancement in extended nanochannels. The proton enrichment at the center of the nanochannel is significant when the bulk pH is medium high and the salt concentration is relatively low. The results gathered are informative for the development of biomimetic nanofluidic apparatuses and the interpretation of relevant experimental data. Later, we have developed an analytical model for electroosmotic ion transport inside p

  5. Effect of accelerated weathering on surface chemistry of modified wood

    NASA Astrophysics Data System (ADS)

    Temiz, Ali; Terziev, Nasko; Eikenes, Morten; Hafren, Jonas

    2007-04-01

    In this study, the effects of UV-light irradiation and water spray on colour and surface chemistry of scots pine sapwood samples were investigated. The specimens were treated with chromated copper arsenate (CCA), a metal-free propiconazol-based formulation, chitosan, furfuryl alcohol and linseed and tall oils. The weathering experiment was performed by cycles of 2 h UV-light irradiation followed by water spray for 18 min. The changes at the surface of the weathered samples were characterised by Fourier transform infrared spectroscopy (FT-IR); colour characterizations were performed by measuring CIELab parameters. The results show that all treatment methods except chitosan treatment provided lower colour changes than the control groups after 800 h exposure in weathering test cycle, but differences between chitosan and control were also small. The lowest colour changes were found on linseed oil (full cell process) and CCA treated wood. FT-IR results show that oil treatment (linseed and tall oil) decreased the intensities of a lignin specific peak (1500-1515 cm -1). Absorption band changes at 1630-1660 cm -1 were reduced by all treatments.

  6. The surface chemistry of dissolving labradorite feldspar

    NASA Astrophysics Data System (ADS)

    Casey, William H.; Westrich, Henry R.; Arnold, George W.; banfield, Jillian F.

    1989-04-01

    Elastic recoil detection (ERD) analysis was used in conjunction with Rutherford backscattering (RBS) analysis to determine depth profiles of hydrogen, silicon, aluminum and calcium in labradorite crystals reacted under various pH conditions. The inventory of hydrogen in the mineral is strongly affected by solution pH. Hydrogen extensively infiltrates the mineral during reaction for 264 hours with solutions in the pH range 1-3. Infiltration is accompanied by extensive removal of sodium, calcium and aluminum from the mineral. This incongruent reaction proceeds to several hundreds of angstroms of depth and produces a silicon-rich surface which is amorphous to electron diffraction. The amount of hydrogen in the reacted layer is much less than is predicted from knowledge of the quantity of cations leached from the feldspar. These low inventories of hydrogen suggest that hydrogen-bearing groups in the reacted layer repolymermize subsequent to ion exchange and depolymerization reactions. This repolymerization eliminates hydrogen from the layer. At higher pH conditions (pH > 5), hydrogen inventories in the crystals decrease with time relative to an unreacted reference crystal. Hydrogen does not infiltrate beyond the first few unit cells of feldspar. Thus, dissolution in slightly acid, near-neutral, and basic solutions proceeds at the immediate surface of the feldspar. Within the limit of the RBS technique, there is no evidence for incongruent dissolution at these conditions.

  7. Density functional theory in surface chemistry and catalysis

    PubMed Central

    Nørskov, Jens K.; Abild-Pedersen, Frank; Studt, Felix; Bligaard, Thomas

    2011-01-01

    Recent advances in the understanding of reactivity trends for chemistry at transition-metal surfaces have enabled in silico design of heterogeneous catalysts in a few cases. The current status of the field is discussed with an emphasis on the role of coupling theory and experiment and future challenges. PMID:21220337

  8. Density Functional Theory in Surface Chemistry and Catalysis

    SciTech Connect

    Norskov, Jens

    2011-05-19

    Recent advances in the understanding of reactivity trends for chemistry at transition metal surfaces have enabled in silico design of heterogeneous catalysts in a few cases. Current status of the field is discussed with an emphasis on the role of coupling between theory and experiment and future challenges.

  9. Long-term trends in precipitation and surface water chemistry

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This chapter shows long-term data and trends in precipitation and surface water chemistry for each site. It contains a brief introduction to the topic, and methods of measurements, selection of variables, and their data source. It consists primarily of a large number of figures showing long-term da...

  10. Investigating the students' understanding of surface phenomena

    NASA Astrophysics Data System (ADS)

    Hamed, Kastro Mohamad

    1999-11-01

    This study investigated students' understanding of surface phenomena. The main purpose for conducting this research endeavor was to understand how students think about a complex topic about which they have little direct or formal instruction. The motivation for focusing on surface phenomena stemmed from an interest in integrating research and education. Despite the importance of surfaces and interfaces in research laboratories, in technological applications, and in everyday experiences, no previous systematic effort was done on pedagogy related to surface phenomena. The design of this research project was qualitative, exploratory, based on a Piagetian semi-structured clinical piloted interview, focused on obtaining a longitudinal view of the intended sample. The sampling was purposeful and the sample consisted of forty-four undergraduate students at Kansas State University. The student participants were enrolled in physics classes that spanned a wide academic spectrum. The data were analyzed qualitatively. The main themes that emerged from the analysis were: (a) students used analogies when confronted with novel situations, (b) students mixed descriptions and explanations, (c) students used the same explanation for several phenomena, (d) students manifested difficulties transferring the meaning of vocabulary across discipline boundaries, (e) in addition to the introductory chemistry classes, students used everyday experiences and job-related experiences as sources of knowledge, and (f) students' inquisitiveness and eagerness to investigate and discuss novel phenomena seemed to peak about the time students were enrolled in second year physics classes.

  11. Quantum Chemistry for Surface Segregation in Metal Alloys

    SciTech Connect

    Sholl, David

    2006-08-31

    Metal alloys are vital materials for the fabrication of high-flux, high-selectivity hydrogen separation membranes. A phenomenon that occurs in alloys that does not arise in pure metals is surface segregation, where the composition of the surface differs from the bulk composition. Little is known about the strength of surface segregation in the alloys usually considered for hydrogen membranes. Despite this lack of knowledge, surface segregation may play a decisive role in the ability of appropriately chosen alloys to be resistant to chemical poisoning, since membrane poisoning is controlled by surface chemistry. The aim of this Phase I project is to develop quantum chemistry approaches to assess surface segregation in a prototypical hydrogen membrane alloy, fcc Pd{sub 75}Cu{sub 25}. This alloy is known experimentally to have favorable surface properties as a poison resistant H{sub 2} purification membrane (Kamakoti et al., Science 307 (2005) 569-573), but previous efforts at modeling surfaces of this alloy have ignored the possible role of surface segregation (Alfonso et al., Surf. Sci. 546 (2003) 12-26).

  12. Surface Chemistry and Properties of Oxides as Catalyst Supports

    SciTech Connect

    DeBusk, Melanie Moses; Narula, Chaitanya Kumar; Contescu, Cristian I

    2015-01-01

    Heterogeneous catalysis relies on metal-oxides as supports for the catalysts. Catalyst supports are an indispensable component of most heterogeneous catalysts, but the role of the support is often minimized in light of the one played by the catalytically active species it supports. The active species of supported catalysts are located on the surface of the support where their contact with liquid or gas phase reactants will be greatest. Considering that support plays a major role in distribution and stability of active species, the absorption and retention of reactive species, and in some cases in catalytic reaction, the properties and chemistry that can occur at the surface of an oxide support are important for understanding their impact on the activity of a supported catalyst. This chapter examines this rich surface chemistry and properties of oxides used as catalyst supports, and explores the influence of their interaction with the active species.

  13. On the use of SPM to probe the interplay between polymer surface chemistry and polymer surface mechanics

    NASA Astrophysics Data System (ADS)

    Brogly, Maurice; Noel, Olivier; Awada, Houssein; Castelein, Gilles

    2007-03-01

    Adhesive properties of a polymer surface results from the complex contribution of surface chemistry and activation of sliding and dissipating mechanisms within the polymer surface layer. The purpose of this study is to dissociate the different contributions (chemical and mechanical) included in an AFM force-distance curve in order to establish relationships between the surface viscoelastic properties of the polymer, the surface chemistry of functionalized polymer surfaces and the adhesive forces, as determined by C-AFM experiments. Indeed we are interested in the measurements of local attractive or adhesive forces in AFM contact mode, of controlled chemical and mechanical model substrates. In order to investigate the interplay between mechanical or viscoelastic mechanisms and surface chemistry during the tip - polymer contact, we achieved force measurements on model PDMS polymer networks, whose surfaces are chemically controlled with the same functional groups as before (silicon substrates). On the basis of AFM nano-indentation experiments, surface Young moduli have been determined. The results show that the viscoelastic contribution is dominating in the adhesion force measurement. We propose an original model, which express the local adhesion force to the energy dissipated within the contact and the surface properties of the material (thermodynamic work of adhesion). Moreover we show that the dissipation function is related to Mc, the mass between crosslinks of the network.

  14. Microstructure and surface chemistry of amorphous alloys important to their friction and wear behavior

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1983-01-01

    An investigation was conducted to examine the microstructure and surface chemistry of amorphous alloys, and their effects on tribological behavior. The results indicate that the surface oxide layers present on amorphous alloys are effective in providing low friction and a protective film against wear in air. Clustering and crystallization in amorphous alloys can be enhanced as a result of plastic flow during the sliding process at a low sliding velocity, at room temperature. Clusters or crystallines with sizes to 150 nm and a diffused honeycomb-shaped structure are produced on the wear surface. Temperature effects lead to drastic changes in surface chemistry and friction behavior of the alloys at temperatures to 750 C. Contaminants can come from the bulk of the alloys to the surface upon heating and impart to the surface oxides at 350 C and boron nitride above 500 C. The oxides increase friction while the boron nitride reduces friction drastically in vacuum.

  15. Cell preparation methods influence Escherichia coli D21g surface chemistry and transport in saturated sand

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The effect of cell preparation methods on the surface chemistry and deposition of Escherichia coli D21g was investigated over a range of ionic strength conditions. The cell preparation methods, which were considered, included filtration and centrifugation (at various speeds and for different duratio...

  16. Influence of surface structure and chemistry on water droplet splashing.

    PubMed

    Koch, Kerstin; Grichnik, Roland

    2016-08-01

    Water droplet splashing and aerosolization play a role in human hygiene and health systems as well as in crop culturing. Prevention or reduction of splashing can prevent transmission of diseases between animals and plants and keep technical systems such as pipe or bottling systems free of contamination. This study demonstrates to what extent the surface chemistry and structures influence the water droplet splashing behaviour. Smooth surfaces and structured replicas of Calathea zebrina (Sims) Lindl. leaves were produced. Modification of their wettability was done by coating with hydrophobizing and hydrophilizing agents. Their wetting was characterized by contact angle measurement and splashing behaviour was observed with a high-speed video camera. Hydrophobic and superhydrophilic surfaces generally showed fewer tendencies to splash than hydrophobic ones. Structuring amplified the underlying behaviour of the surface chemistries, increasing hydrophobic surfaces' tendency to splash and decreasing splash on hydrophilic surfaces by quickly transporting water off the impact point by capillary forces. The non-porous surface structures found in C. zebrina could easily be applied to technical products such as plastic foils or mats and coated with hydrophilizing agents to suppress splash in areas of increased hygiene requirements or wherever pooling of liquids is not desirable.This article is part of the themed issue 'Bioinspired hierarchically structured surfaces for green science'. PMID:27354737

  17. Aryl Diazonium Chemistry for the Surface Functionalization of Glassy Biosensors.

    PubMed

    Zheng, Wei; van den Hurk, Remko; Cao, Yong; Du, Rongbing; Sun, Xuejun; Wang, Yiyu; McDermott, Mark T; Evoy, Stephane

    2016-03-01

    Nanostring resonator and fiber-optics-based biosensors are of interest as they offer high sensitivity, real-time measurements and the ability to integrate with electronics. However, these devices are somewhat impaired by issues related to surface modification. Both nanostring resonators and photonic sensors employ glassy materials, which are incompatible with electrochemistry. A surface chemistry approach providing strong and stable adhesion to glassy surfaces is thus required. In this work, a diazonium salt induced aryl film grafting process is employed to modify a novel SiCN glassy material. Sandwich rabbit IgG binding assays are performed on the diazonium treated SiCN surfaces. Fluorescently labelled anti-rabbit IgG and anti-rabbit IgG conjugated gold nanoparticles were used as markers to demonstrate the absorption of anti-rabbit IgG and therefore verify the successful grafting of the aryl film. The results of the experiments support the effectiveness of diazonium chemistry for the surface functionalization of SiCN surfaces. This method is applicable to other types of glassy materials and potentially can be expanded to various nanomechanical and optical biosensors. PMID:26985910

  18. Aryl Diazonium Chemistry for the Surface Functionalization of Glassy Biosensors

    PubMed Central

    Zheng, Wei; van den Hurk, Remko; Cao, Yong; Du, Rongbing; Sun, Xuejun; Wang, Yiyu; McDermott, Mark T.; Evoy, Stephane

    2016-01-01

    Nanostring resonator and fiber-optics-based biosensors are of interest as they offer high sensitivity, real-time measurements and the ability to integrate with electronics. However, these devices are somewhat impaired by issues related to surface modification. Both nanostring resonators and photonic sensors employ glassy materials, which are incompatible with electrochemistry. A surface chemistry approach providing strong and stable adhesion to glassy surfaces is thus required. In this work, a diazonium salt induced aryl film grafting process is employed to modify a novel SiCN glassy material. Sandwich rabbit IgG binding assays are performed on the diazonium treated SiCN surfaces. Fluorescently labelled anti-rabbit IgG and anti-rabbit IgG conjugated gold nanoparticles were used as markers to demonstrate the absorption of anti-rabbit IgG and therefore verify the successful grafting of the aryl film. The results of the experiments support the effectiveness of diazonium chemistry for the surface functionalization of SiCN surfaces. This method is applicable to other types of glassy materials and potentially can be expanded to various nanomechanical and optical biosensors. PMID:26985910

  19. Ferroelectrics: A pathway to switchable surface chemistry and catalysis

    NASA Astrophysics Data System (ADS)

    Kakekhani, Arvin; Ismail-Beigi, Sohrab; Altman, Eric I.

    2016-08-01

    It has been known for more than six decades that ferroelectricity can affect a material's surface physics and chemistry thereby potentially enhancing its catalytic properties. Ferroelectrics are a class of materials with a switchable electrical polarization that can affect surface stoichiometry and electronic structure and thus adsorption energies and modes; e.g., molecular versus dissociative. Therefore, ferroelectrics may be utilized to achieve switchable surface chemistry whereby surface properties are not fixed but can be dynamically controlled by, for example, applying an external electric field or modulating the temperature. Several important examples of applications of ferroelectric and polar materials in photocatalysis and heterogeneous catalysis are discussed. In photocatalysis, the polarization direction can control band bending at water/ferroelectric and ferroelectric/semiconductor interfaces, thereby facilitating charge separation and transfer to the electrolyte and enhancing photocatalytic activity. For gas-surface interactions, available results suggest that using ferroelectrics to support catalytically active transition metals and oxides is another way to enhance catalytic activity. Finally, the possibility of incorporating ferroelectric switching into the catalytic cycle itself is described. In this scenario, a dynamic collaboration of two polarization states can be used to drive reactions that have been historically challenging to achieve on surfaces with fixed chemical properties (e.g., direct NOx decomposition and the selective partial oxidation of methane). These predictions show that dynamic modulation of the polarization can help overcome some of the fundamental limitations on catalytic activity imposed by the Sabatier principle.

  20. The Role of Surface Chemistry in Filter Feeding by Zooplankton

    NASA Astrophysics Data System (ADS)

    Gerritsen, Jeroen; Porter, Karen G.

    1982-06-01

    Surface chemistry of both particles and animals is important in filter feeding at low Reynolds number. Daphnia magna, fed mixtures of three sizes of polystyrene particles, retained particles that were smaller than the mesh size of the animals (1.0 micrometer) at greater efficiencies than predicted by a sieving model. Retention efficiency of the smallest particles (0.5 micrometer) was increased when negative surface charge on the particles was neutralized, and retention was decreased when a nonionic surfactant was added to reduce wettability.

  1. QM/MM investigations of organic chemistry oriented questions.

    PubMed

    Schmidt, Thomas C; Paasche, Alexander; Grebner, Christoph; Ansorg, Kay; Becker, Johannes; Lee, Wook; Engels, Bernd

    2014-01-01

    About 35 years after its first suggestion, QM/MM became the standard theoretical approach to investigate enzymatic structures and processes. The success is due to the ability of QM/MM to provide an accurate atomistic picture of enzymes and related processes. This picture can even be turned into a movie if nuclei-dynamics is taken into account to describe enzymatic processes. In the field of organic chemistry, QM/MM methods are used to a much lesser extent although almost all relevant processes happen in condensed matter or are influenced by complicated interactions between substrate and catalyst. There is less importance for theoretical organic chemistry since the influence of nonpolar solvents is rather weak and the effect of polar solvents can often be accurately described by continuum approaches. Catalytic processes (homogeneous and heterogeneous) can often be reduced to truncated model systems, which are so small that pure quantum-mechanical approaches can be employed. However, since QM/MM becomes more and more efficient due to the success in software and hardware developments, it is more and more used in theoretical organic chemistry to study effects which result from the molecular nature of the environment. It is shown by many examples discussed in this review that the influence can be tremendous, even for nonpolar reactions. The importance of environmental effects in theoretical spectroscopy was already known. Due to its benefits, QM/MM can be expected to experience ongoing growth for the next decade.In the present chapter we give an overview of QM/MM developments and their importance in theoretical organic chemistry, and review applications which give impressions of the possibilities and the importance of the relevant effects. Since there is already a bunch of excellent reviews dealing with QM/MM, we will discuss fundamental ingredients and developments of QM/MM very briefly with a focus on very recent progress. For the applications we follow a similar

  2. Effects of surface chemistry on hot corrosion life: Overview

    NASA Technical Reports Server (NTRS)

    Merutka, J.

    1982-01-01

    This program concentrates on analyzing a limited number of hot corroded components from the field and the carrying out of a series of controlled laboratory experiments to establish the effects of oxide scale and coating chemistry on hot corrosion life. This is to be determined principally from the length of the incubation period, the investigation of the mechanisms of hot corrosion attack, and the fitting of the data generated from the test exposure experiments to an empirical life prediction model.

  3. Grain Surface Chemistry and the Composition of Interstellar Ices

    NASA Technical Reports Server (NTRS)

    Tielens, A. G. G. M.

    2006-01-01

    Submicron sized dust grains are an important component of the interstellar medium. In particular they provide surface where active chemistry can take place. At the low temperatures (-10 K) of the interstellar medium, colliding gas phase species will stick, diffuse, react, and form an icy mantle on these dust grains. This talk will review the principles of grain surface chemistry and delineate important grain surface routes, focusing on reactions involving H, D, and O among each other and with molecules such as CO. Interstellar ice mantles can be studied through the fundamental vibrations of molecular species in the mid-infrared spectra of sources embedded in or located behind dense molecular clouds. Analysis of this type of data has provided a complex view of the composition of these ices and the processes involved. Specifically, besides grain surface chemistry, the composition of interstellar ices is also affected by thermal processing due to nearby newly formed stars. This leads to segregation between different ice components as well as outgassing. The latter results in the formation of a so-called Hot Core region with a gas phase composition dominated by evaporated mantle species. Studies of such regions provide thus a different view on the ice composition and the chemical processes involved. Interstellar ices can also be processed by FUV photons and high energy cosmic ray ions. Cosmic ray processing likely dominates the return of accreted species to the gas phase where further gas phase reactions can take place. These different chemical routes towards molecular complexity in molecular clouds and particularly regions of star formation will be discussed.

  4. A Chamber Investigation of Nitric Acid-Soot Aerosol Chemistry at 298 K

    SciTech Connect

    Disselkamp, Robert S.; Carpenter, Michael A.; Cowin, James P.

    2000-10-02

    Long-pathlength infrared absorption spectroscopy was used to investigate nitric acid-soot aerosol chemistry at 298 K and 0.5 % relative humidity. Experiments were performed by introducing nitric acid vapor (PHNO3~3 Pa, Ptotal~40 kPa) into a teflon-coated chamber and initiating acquisition of infrared spectra at 3 minute time intervals. After 36 minutes of data collection, soot powder was rapidly expanded into nitric acid contained in the chamber to generate a soot-HNO3 aerosol. Infrared spectra collected before, and after, soot introduction to the chamber were used to characterize chamber wall reaction processes and soot aerosol chemistry, respectively. Three soot types were investigated (Degussa FW2, Cabot Monarch 1000, and crystalline graphite), each yielding similar chemistry. Upon soot introduction to the chamber both HNO3 uptake and NO2 production occurred, with the molar ratio of HNO3 uptake to NO2 production varying from 1.2 to 2.9 for the three soot types studied. Unreacted HNO3 was present at the conclusion of each of the aerosol experiments, indicating incomplete conversion of HNO3 into NO2. This observation suggested that "active" sites at the soot surface responsible for the reduction of HNO3 are not regenerated (i.e., formed) in the reaction process. In essence, a titration occurred between these active sites and HNO3. The NO2 concentrations produced, the soot mass concentrations used, and the BET measured specific surface area of the powders allowed computation of the surface density of active sites of ~4.0x10-18 m2/active site (describing all three powders studied). This is the first reported measurement of surface density of active sites for nitric acid chemistry on soot. Since atmospheric heterogeneous reactions that exhibit surface deactivation may, in principle, affect trace gas concentration, we perform an assessment in this regard.

  5. Surface Chemistry and Water Dispersability of Carbon Black Materials

    SciTech Connect

    Contescu, Cristian I; Baker, Frederick S; Burchell, Timothy D

    2006-01-01

    Formulation of water-stable carbon black dispersions is a double-sided task, which requires selection of a proper dispersing agents and matching it with the properties of a specific carbon black. Among other properties that affect water dispersability of carbon blacks (particle size, surface area, and aggregate structure), surface chemistry plays a prime-order role. We have characterized physical and chemical properties of several carbon black materials, and correlated them with the stability of dispersions formed with ionic and non-ionic surfactants. In particular, chemical characterization of surface functional groups on carbon blacks based on potentiometric titration measurements (pKa spectra) provided a comprehensive picture of pH effects on dispersion stability. The results obtained were complemented by information from physical characterization methods, such as XPS and FTIR. The selection of a suitable dispersing agent able to withstand large pH variations will be discussed.

  6. Role of surface chemistry in the ignition of pyrotechnic materials

    SciTech Connect

    Moddeman, W.E.; Collins, L.W.; Wang, P.S.; Wittberg, T.N.

    1980-01-01

    The surface chemistry of fuels has been shown to play a key role in the ignition of pyrotechnic materials. Since these fuels are usually easily oxidized, the surface must provide protection from undesirable oxidation processes such as pyrophoricity while permitting the desirable pyrotechnic reactions. For both titanium and aluminum, these criteria are met by metal oxide coatings which control the accessibility of the fuel to the oxidizer. However, we have shown that the mechanisms through which this control is exerted are substantially different. The ignition of titanium based pyrotechnics seems to be kinetically controlled by the dissolution of the titanium oxide coating to generate a reactive surface for the pyrotechnic reaction. Reactions of aluminum seem to depend on diffusion of aluminum (or oxygen at higher temperatures) through its oxide coating. It was also shown that the accessibility of aluminum can be improved by alloying.

  7. Isothermal microcalorimetry to investigate non specific interactions in biophysical chemistry.

    PubMed

    Ball, Vincent; Maechling, Clarisse

    2009-10-01

    Isothermal titration microcalorimetry (ITC) is mostly used to investigate the thermodynamics of "specific" host-guest interactions in biology as well as in supramolecular chemistry. The aim of this review is to demonstrate that ITC can also provide useful information about non-specific interactions, like electrostatic or hydrophobic interactions. More attention will be given in the use of ITC to investigate polyelectrolyte-polyelectrolyte (in particular DNA-polycation), polyelectrolyte-protein as well as protein-lipid interactions. We will emphasize that in most cases these "non specific" interactions, as their definition will indicate, are favoured or even driven by an increase in the entropy of the system. The origin of this entropy increase will be discussed for some particular systems. We will also show that in many cases entropy-enthalpy compensation phenomena occur. PMID:20111693

  8. Isothermal Microcalorimetry to Investigate Non Specific Interactions in Biophysical Chemistry

    PubMed Central

    Ball, Vincent; Maechling, Clarisse

    2009-01-01

    Isothermal titration microcalorimetry (ITC) is mostly used to investigate the thermodynamics of “specific” host-guest interactions in biology as well as in supramolecular chemistry. The aim of this review is to demonstrate that ITC can also provide useful information about non-specific interactions, like electrostatic or hydrophobic interactions. More attention will be given in the use of ITC to investigate polyelectrolyte-polyelectrolyte (in particular DNA-polycation), polyelectrolyte-protein as well as protein-lipid interactions. We will emphasize that in most cases these “non specific” interactions, as their definition will indicate, are favoured or even driven by an increase in the entropy of the system. The origin of this entropy increase will be discussed for some particular systems. We will also show that in many cases entropy-enthalpy compensation phenomena occur. PMID:20111693

  9. Saltwater icephobicity: Influence of surface chemistry on saltwater icing

    PubMed Central

    Carpenter, Katherine; Bahadur, Vaibhav

    2015-01-01

    Most studies on icephobicity focus on ice formation with pure water. This manuscript presents studies to understand the influence of surfaces on saltwater ice nucleation and propagation. Experiments are conducted to quantify the influence of surface chemistry on saltwater ice nucleation and to understand the utility of superhydrophobic surfaces for saltwater icephobicity. These experiments are conducted with pure water and two sodium chloride solutions, which represent the salinity of seawater and briny produced water. It is seen that the presence of salt slows down the ice front propagation velocity significantly. Saltwater droplet impact dynamics on superhydrophobic surfaces are also different from pure water. Saltwater droplets retract more and a greater fraction of impacting liquid is repelled from the superhydrophobic surface. It is seen that the greater bounciness of saltwater droplets is a result of slower ice nucleation propagation kinetics. These experiments indicate that superhydrophobic surfaces will have better resistance to impact icing with saltwater than pure water and can remain useful at temperatures as low as −40 °C. Overall, this work is a starting point for further studies on heterogeneous nucleation in saltwater and serves as a bridge between the widely studied freshwater icephobic surfaces and saltwater-related applications. PMID:26626958

  10. Saltwater icephobicity: Influence of surface chemistry on saltwater icing

    NASA Astrophysics Data System (ADS)

    Carpenter, Katherine; Bahadur, Vaibhav

    2015-12-01

    Most studies on icephobicity focus on ice formation with pure water. This manuscript presents studies to understand the influence of surfaces on saltwater ice nucleation and propagation. Experiments are conducted to quantify the influence of surface chemistry on saltwater ice nucleation and to understand the utility of superhydrophobic surfaces for saltwater icephobicity. These experiments are conducted with pure water and two sodium chloride solutions, which represent the salinity of seawater and briny produced water. It is seen that the presence of salt slows down the ice front propagation velocity significantly. Saltwater droplet impact dynamics on superhydrophobic surfaces are also different from pure water. Saltwater droplets retract more and a greater fraction of impacting liquid is repelled from the superhydrophobic surface. It is seen that the greater bounciness of saltwater droplets is a result of slower ice nucleation propagation kinetics. These experiments indicate that superhydrophobic surfaces will have better resistance to impact icing with saltwater than pure water and can remain useful at temperatures as low as -40 °C. Overall, this work is a starting point for further studies on heterogeneous nucleation in saltwater and serves as a bridge between the widely studied freshwater icephobic surfaces and saltwater-related applications.

  11. Bacterial response to different surface chemistries fabricated by plasma polymerization on electrospun nanofibers.

    PubMed

    Abrigo, Martina; Kingshott, Peter; McArthur, Sally L

    2015-01-01

    Control over bacterial attachment and proliferation onto nanofibrous materials constitutes a major challenge for a variety of applications, including filtration membranes, protective clothing, wound dressings, and tissue engineering scaffolds. To develop effective devices, the interactions that occur between bacteria and nanofibers with different morphological and physicochemical properties need to be investigated. This paper explores the influence of fiber surface chemistry on bacterial behavior. Different chemical functionalities were generated on the surface of electrospun polystyrene nanofibers through plasma polymerization of four monomers (acrylic acid, allylamine, 1,7-octadiene, and 1,8-cineole). The interactions of Escherichia coli with the surface modified fibers were investigated through a combination of scanning electron microscopy and confocal laser scanning microscopy. Fiber wettability, surface charge, and chemistry were found to affect the ability of bacterial cells to attach and proliferate throughout the nanofiber meshes. The highest proportion of viable cells attachment occurred on the hydrophilic amine rich coating, followed by the hydrophobic octadiene. The acrylic acid coating rich in carboxyl groups showed a significantly lower attraction of bacterial cells. The 1,8-cineole retained the antibacterial activity of the monomer, resulting with a high proportion of dead isolated cells attached onto the fibers. Results showed that the surface chemistry properties of nanofibrous membranes can be strategically tuned to control bacterial behavior. PMID:26251319

  12. Investigating Multireference Character and Correlation in Quantum Chemistry.

    PubMed

    Coe, J P; Paterson, M J

    2015-09-01

    We review a range of multireference diagnostics for quantum chemistry and discuss them in terms of choices of the molecular orbitals. We show how an approach1 of P.-O. Löwdin can also be viewed as quantifying the electron correlation via the spatial entanglement relative to a single determinant. We consider three example systems from quantum chemistry that exhibit three different combinations of multireference character and correlation: not strongly multireference and not strongly correlated, strongly multireference but not strongly correlated, and strongly multireference together with strong correlation. We find that a multireference measure (MR) does not change substantially with the cutoff used for a Monte Carlo configuration interaction calculation and investigate the effect of using natural orbitals. We see that a coupled-cluster singles and doubles diagnostic and a density-functional theory diagnostic give a correct general prediction of the multireference character for these systems. We also look at the issue of multireference character for a collection of noninteracting hydrogen molecules and the effect of basis size on the multireference character of a stretched hydrogen molecule. PMID:26575914

  13. The surface chemistry of GaAs atomic layer epitaxy

    SciTech Connect

    Creighton, J.R.; Banse, B.A.

    1991-01-01

    In this paper we review three proposed mechanisms for GaAs ALE and review or present data support or contradiction of these mechanisms. Surface chemistry results clearly demonstrated that TMGa irreversibly chemisorbs on the Ga-rich GaAs(100) surface. The reactive sticking coefficient (RSC) of TMGa on the adsorbate-free Ga-rich GaAs(100) surface was measured to be {approximately}0.5, conclusively demonstrating that the selective adsorption'' mechanism of ALE is not valid. We describe kinetic evidence for methyl radical desorption in support of the adsorbate inhibition'' mechanism. The methyl radical desorption rates determined by temperature programmed desorption (TPD) demonstrate that desorption is at least a factor of {approximately}10 faster from the As-rich c(2 {times} 8)/(2 {times} 4) surface than from the Ga-rich surface. It is disparity in CH{sub 3} desorption rates between the As-rich and Ga-rich surfaces that is largely responsible for GaAs ALE behavior. A gallium alkyl radical (e.g. MMGa) is also observed during TPD and molecular beam experiments, in partial support of the flux balance'' mechanism. Stoichiometry issues of ALE are also discussed. We have discovered that arsine exposures typical of atmospheric pressure and reduced pressure ALE lead to As coverages {ge} 1 ML, which provides the likely solution to the stoichiometry question regarding the arsine cycle. 32 refs., 6 figs.

  14. Gridded global surface ozone metrics for atmospheric chemistry model evaluation

    NASA Astrophysics Data System (ADS)

    Sofen, E. D.; Bowdalo, D.; Evans, M. J.; Apadula, F.; Bonasoni, P.; Cupeiro, M.; Ellul, R.; Galbally, I. E.; Girgzdiene, R.; Luppo, S.; Mimouni, M.; Nahas, A. C.; Saliba, M.; Tørseth, K.

    2016-02-01

    The concentration of ozone at the Earth's surface is measured at many locations across the globe for the purposes of air quality monitoring and atmospheric chemistry research. We have brought together all publicly available surface ozone observations from online databases from the modern era to build a consistent data set for the evaluation of chemical transport and chemistry-climate (Earth System) models for projects such as the Chemistry-Climate Model Initiative and Aer-Chem-MIP. From a total data set of approximately 6600 sites and 500 million hourly observations from 1971-2015, approximately 2200 sites and 200 million hourly observations pass screening as high-quality sites in regionally representative locations that are appropriate for use in global model evaluation. There is generally good data volume since the start of air quality monitoring networks in 1990 through 2013. Ozone observations are biased heavily toward North America and Europe with sparse coverage over the rest of the globe. This data set is made available for the purposes of model evaluation as a set of gridded metrics intended to describe the distribution of ozone concentrations on monthly and annual timescales. Metrics include the moments of the distribution, percentiles, maximum daily 8-hour average (MDA8), sum of means over 35 ppb (daily maximum 8-h; SOMO35), accumulated ozone exposure above a threshold of 40 ppbv (AOT40), and metrics related to air quality regulatory thresholds. Gridded data sets are stored as netCDF-4 files and are available to download from the British Atmospheric Data Centre (doi: 10.5285/08fbe63d-fa6d-4a7a-b952-5932e3ab0452). We provide recommendations to the ozone measurement community regarding improving metadata reporting to simplify ongoing and future efforts in working with ozone data from disparate networks in a consistent manner.

  15. Gridded global surface ozone metrics for atmospheric chemistry model evaluation

    NASA Astrophysics Data System (ADS)

    Sofen, E. D.; Bowdalo, D.; Evans, M. J.; Apadula, F.; Bonasoni, P.; Cupeiro, M.; Ellul, R.; Galbally, I. E.; Girgzdiene, R.; Luppo, S.; Mimouni, M.; Nahas, A. C.; Saliba, M.; Tørseth, K.; Wmo Gaw, Epa Aqs, Epa Castnet, Capmon, Naps, Airbase, Emep, Eanet Ozone Datasets, All Other Contributors To

    2015-07-01

    The concentration of ozone at the Earth's surface is measured at many locations across the globe for the purposes of air quality monitoring and atmospheric chemistry research. We have brought together all publicly available surface ozone observations from online databases from the modern era to build a consistent dataset for the evaluation of chemical transport and chemistry-climate (Earth System) models for projects such as the Chemistry-Climate Model Initiative and Aer-Chem-MIP. From a total dataset of approximately 6600 sites and 500 million hourly observations from 1971-2015, approximately 2200 sites and 200 million hourly observations pass screening as high-quality sites in regional background locations that are appropriate for use in global model evaluation. There is generally good data volume since the start of air quality monitoring networks in 1990 through 2013. Ozone observations are biased heavily toward North America and Europe with sparse coverage over the rest of the globe. This dataset is made available for the purposes of model evaluation as a set of gridded metrics intended to describe the distribution of ozone concentrations on monthly and annual timescales. Metrics include the moments of the distribution, percentiles, maximum daily eight-hour average (MDA8), SOMO35, AOT40, and metrics related to air quality regulatory thresholds. Gridded datasets are stored as netCDF-4 files and are available to download from the British Atmospheric Data Centre (doi:10.5285/08fbe63d-fa6d-4a7a-b952-5932e3ab0452). We provide recommendations to the ozone measurement community regarding improving metadata reporting to simplify ongoing and future efforts in working with ozone data from disparate networks in a consistent manner.

  16. Quantifying the surface chemistry of 3D matrices in situ

    NASA Astrophysics Data System (ADS)

    Tzeranis, Dimitrios S.; So, Peter T. C.; Yannas, Ioannis V.

    2014-03-01

    Despite the major role of the matrix (the insoluble environment around cells) in physiology and pathology, there are very few and limited methods that can quantify the surface chemistry of a 3D matrix such as a biomaterial or tissue ECM. This study describes a novel optical-based methodology that can quantify the surface chemistry (density of adhesion ligands for particular cell adhesion receptors) of a matrix in situ. The methodology utilizes fluorescent analogs (markers) of the receptor of interest and a series of binding assays, where the amount of bound markers on the matrix is quantified via spectral multi-photon imaging. The study provides preliminary results for the quantification of the ligands for the two major collagen-binding integrins (α1β1, α2β1) in porous collagen scaffolds that have been shown to be able to induce maximum regeneration in transected peripheral nerves. The developed methodology opens the way for quantitative descriptions of the insoluble microenvironment of cells in physiology and pathology, and for integrating the matrix in quantitative models of cell signaling. α

  17. The hydrochemistry of glacial Ebba River (Petunia Bay, Central Spitsbergen): Groundwater influence on surface water chemistry

    NASA Astrophysics Data System (ADS)

    Dragon, Krzysztof; Marciniak, Marek; Szpikowski, Józef; Szpikowska, Grażyna; Wawrzyniak, Tomasz

    2015-10-01

    The article presents the investigation of surface water chemistry changes of the glacial Ebba River (Central Spitsbergen) during three melting seasons of 2008, 2009 and 2010. The twice daily water chemistry analyses allow recognition of the surface water chemistry differentiation. The surface water chemistry changes are related to the river discharge and changes in the influence of different water balance components during each melting season. One of the most important process that influence river water component concentration increase is groundwater inflow from active layer occurring on the valley area. The significance of this process is the most important at the end of the melting season when temperatures below 0 °C occur on glaciers (resulting in a slowdown of melting of ice and snow and a smaller recharge of the river by the water from the glaciers) while the flow of groundwater is still active, causing a relatively higher contribution of groundwater to the total river discharge. The findings presented in this paper show that groundwater contribution to the total polar river water balance is more important than previously thought and its recognition allow a better understanding of the hydrological processes occurring in a polar environment.

  18. Surface chemistry, morphological analysis and properties of cellulose nanocrystals with gradiented sulfation degrees.

    PubMed

    Lin, Ning; Dufresne, Alain

    2014-05-21

    The process of sulfuric acid-hydrolysis of cellulose fibers for the preparation of cellulose nanocrystals (CNs) includes an esterification reaction between acid and cellulose molecules, which induces the covalent coupling of sulfate groups on the surface of prepared CNs. Negatively charged sulfate groups play an important role in both surface chemistry and physical properties of CNs. This study explored the strategy of introducing a gradient of sulfate groups on the surface of CNs, and further investigated the effect of the sulfation degree on surface chemistry, morphology, dimensions, and physical properties of different CN samples. Based on the discussion of their surface chemistry, the selection of different cross-section models was reported to significantly affect the calculation of the degree of substitution of sulfate groups on CNs. A new ellipsoid cross-section model was proposed on the basis of AFM observations. The effect of sulfate groups on crystal properties and thermal stability was discussed and validated, and the birefringence behavior of nanocrystal suspensions was observed. PMID:24706023

  19. Early osseointegration driven by the surface chemistry and wettability of dental implants

    PubMed Central

    SARTORETTO, Suelen Cristina; ALVES, Adriana Terezinha Neves Novellino; RESENDE, Rodrigo Figueiredo Britto; CALASANS-MAIA, José; GRANJEIRO, José Mauro; CALASANS-MAIA, Mônica Diuana

    2015-01-01

    Objective The objective of this study was to investigate the impact of two different commercially available dental implants on osseointegration. The surfaces were sandblasting and acid etching (Group 1) and sandblasting and acid etching, then maintained in an isotonic solution of 0.9% sodium chloride (Group 2). Material and Methods X-ray photoelectron spectroscopy (XPS) was employed for surface chemistry analysis. Surface morphology and topography was investigated by scanning electron microscopy (SEM) and confocal microscopy (CM), respectively. Contact angle analysis (CAA) was employed for wetting evaluation. Bone-implant-contact (BIC) and bone area fraction occupied (BAFO) analysis were performed on thin sections (30 μm) 14 and 28 days after the installation of 10 implants from each group (n=20) in rabbits’ tibias. Statistical analysis was performed by ANOVA at the 95% level of significance considering implantation time and implant surface as independent variables. Results Group 2 showed 3-fold less carbon on the surface and a markedly enhanced hydrophilicity compared to Group 1 but a similar surface roughness (p>0.05). BIC and BAFO levels in Group 2 at 14 days were similar to those in Group 1 at 28 days. After 28 days of installation, BIC and BAFO measurements of Group 2 were approximately 1.5-fold greater than in Group 1 (p<0.05). Conclusion The surface chemistry and wettability implants of Group 2 accelerate osseointegration and increase the area of the bone-to-implant interface when compared to those of Group 1. PMID:26221922

  20. Surface chemistry of CO2 - Adsorption of carbon dioxide on clean surfaces at ultrahigh vacuum

    NASA Astrophysics Data System (ADS)

    Burghaus, Uwe

    2014-05-01

    Carbon dioxide chemistry has attracted significant interest in recent years. Although the field is diverse, a current and more comprehensive review of the surface science literature may be of interest for a variety of communities since environmental chemistry, energy technology, materials science, catalysis, and nanocatalysis are certainly affected by gas-surface properties. The review describes surface phenomena and characterization strategies highlighting similarities and differences, instead of providing only a list of system-specific information. The various systems are roughly distinguished as those that clearly form carbonates and those that merely physisorb CO2 at ultra-high vacuum conditions. Nevertheless, extended sections about specific systems including rarely studied surfaces and unusual materials are included, making this review also useful as a reference.

  1. Surface Enzyme Chemistries for Ultrasensitive Microarray Biosensing with SPR Imaging.

    PubMed

    Fasoli, Jennifer B; Corn, Robert M

    2015-09-01

    The sensitivity and selectivity of surface plasmon resonance imaging (SPRI) biosensing with nucleic acid microarrays can be greatly enhanced by exploiting various nucleic acid ligases, nucleases, and polymerases that manipulate the surface-bound DNA and RNA. We describe here various examples from each of these different classes of surface enzyme chemistries that have been incorporated into novel detection strategies that either drastically enhance the sensitivity of or create uniquely selective methods for the SPRI biosensing of proteins and nucleic acids. A dual-element generator-detector microarray approach that couples a bioaffinity adsorption event on one microarray element to nanoparticle-enhanced SPRI measurements of nucleic acid hybridization adsorption on a different microarray element is used to quantitatively detect DNA, RNA, and proteins at femtomolar concentrations. Additionally, this dual-element format can be combined with the transcription and translation of RNA from surface-bound double-stranded DNA (dsDNA) templates for the on-chip multiplexed biosynthesis of aptamer and protein microarrays in a microfluidic format; these microarrays can be immediately used for real-time SPRI bioaffinity sensing measurements. PMID:25641598

  2. Surface Enzyme Chemistries for Ultrasensitive Microarray Biosensing with SPR Imaging

    PubMed Central

    2015-01-01

    The sensitivity and selectivity of surface plasmon resonance imaging (SPRI) biosensing with nucleic acid microarrays can be greatly enhanced by exploiting various nucleic acid ligases, nucleases, and polymerases that manipulate the surface-bound DNA and RNA. We describe here various examples from each of these different classes of surface enzyme chemistries that have been incorporated into novel detection strategies that either drastically enhance the sensitivity of or create uniquely selective methods for the SPRI biosensing of proteins and nucleic acids. A dual-element generator–detector microarray approach that couples a bioaffinity adsorption event on one microarray element to nanoparticle-enhanced SPRI measurements of nucleic acid hybridization adsorption on a different microarray element is used to quantitatively detect DNA, RNA, and proteins at femtomolar concentrations. Additionally, this dual-element format can be combined with the transcription and translation of RNA from surface-bound double-stranded DNA (dsDNA) templates for the on-chip multiplexed biosynthesis of aptamer and protein microarrays in a microfluidic format; these microarrays can be immediately used for real-time SPRI bioaffinity sensing measurements. PMID:25641598

  3. Effects of wood fiber surface chemistry on strength of wood-plastic composites

    NASA Astrophysics Data System (ADS)

    Migneault, Sébastien; Koubaa, Ahmed; Perré, Patrick; Riedl, Bernard

    2015-07-01

    Because wood-plastic composites (WPC) strength relies on fiber-matrix interaction at fiber surface, it is likely that fiber surface chemistry plays an important role in WPC strength development. The objective of the present study is to investigate the relationships between fiber surface chemical characteristics and WPC mechanical properties. Different fibers were selected and characterized for surface chemical characteristics using X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIR). WPC samples were manufactured at 40% fiber content and with six different fibers. High density polyethylene was used as matrix and maleated polyethylene (MAPE) was used as compatibility agent. WPC samples were tested for mechanical properties and fiber-matrix interface was observed with scanning electron microscope. It was found WPC strength decreases as the amount of unoxidized carbon (assigned to lignin and extractives) measured with XPS on fiber surface increases. In the opposite case, WPC strength increases with increasing level of oxidized carbon (assigned to carbohydrates) on fiber surface. The same conclusions were found with FTIR where WPC strength decreases as lignin peaks intensity increases. Esterification reaction of fibers with MAPE occurs on polar sites of carbohydrates, such as hydroxyls (Osbnd H). Thus, fibers with carbohydrates-rich surface, such as cellulose pulp, produced stronger WPC samples. Other factors such as mechanical interlocking and fiber morphology interfered with the effects of fiber surface chemistry.

  4. Genotoxicity of Copper Oxide Nanoparticles with Different Surface Chemistry on Rat Bone Marrow Mesenchymal Stem Cells.

    PubMed

    Zhang, Wenjing; Jiang, Pengfei; Chen, Wei; Zheng, Botuo; Mao, Zhengwei; Antipov, Alexei; Correia, Manuel; Larsen, Erik H; Gao, Changyou

    2016-06-01

    The surface chemistry of nanoparticles (NPs) is one of the critical factors determining their cellular responses. In this study, the cytotoxicity and genotoxicity of copper oxide (CuO) NPs with a similar size but different surface chemistry to rat bone marrow mesenchymal stem cells (MSCs) were investigated. The morphology, size and surface charge of four types of CuO NPs, i.e., CuO-core, CuO-COOH, CuO-NH2 and CuO-PEG NPs, were characterized by TEM, dynamic light scattering (DLS) and zeta-potential measurement, respectively. All of the four CuO NPs had a negative surface charge around -10 mV and showed a similar tendency to form agglomerates with a size of -200 nm in cell culture environment. The cytotoxicity of CuO NPs to MSCs at various concentrations and incubation periods were firstly evaluated. The CuO NPs showed dose-dependent and time-dependent toxicity to MSCs, and their surface chemistry had influence on the toxicity to some extent too. The intracellular reactive oxygen species (ROS) level of MSCs was then quantified. Finally, the genotoxicity of the CuO NPs was studied by comet assay. The results suggest that the genotoxicity of CuO NPs was mainly dependent on NPs concentration, and was only slightly influenced by their surface chemistry. The osteogenic and adipogenic differentiation abilities of the MSCs exposed to different CuO NPs were studied by Alizarin Res S and Oil Red O staining. The preliminary results showed that the exposure to 10 μg/mL CuO NPs will, not lead to significant impact on the differentiation potential of the MSCs. PMID:27427588

  5. What's on the Surface? Physics and Chemistry of Delta-Doped Surfaces

    NASA Technical Reports Server (NTRS)

    Hoenk, Michael

    2011-01-01

    Outline of presentation: 1. Detector surfaces and the problem of stability 2. Delta-doped detectors 3. Physics of Delta-doped Silicon 4. Chemistry of the Si-SiO2 Interface 5. Physics and Chemistry of Delta-doped Surfaces a. Compensation b. Inversion c. Quantum exclusion. Conclusions: 1. Quantum confinement of electrons and holes dominates the behavior of delta-doped surfaces. 2. Stability of delta-doped detectors: Delta-layer creates an approx 1 eV tunnel barrier between bulk and surface. 3. At high surface charge densities, Tamm-Shockley states form at the surface. 4. Surface passivation by quantum exclusion: Near-surface delta-layer suppresses T-S trapping of minority carriers. 5. The Si-SiO2 interface compensates the surface 6. For delta-layers at intermediate depth, surface inversion layer forms 7. Density of Si-SiO2 interface charge can be extremely high (>10(exp 14)/sq cm)

  6. Correlation between surface chemistry and ion energy dependence of the etch yield in multicomponent oxides etching

    SciTech Connect

    Berube, P.-M.; Poirier, J.-S.; Margot, J.; Stafford, L.; Ndione, P. F.; Chaker, M.; Morandotti, R.

    2009-09-15

    The influence of surface chemistry in plasma etching of multicomponent oxides was investigated through measurements of the ion energy dependence of the etch yield. Using pulsed-laser-deposited Ca{sub x}Ba{sub (1-x)}Nb{sub 2}O{sub 6} (CBN) and SrTiO{sub 3} thin films as examples, it was found that the etching energy threshold shifts toward values larger or smaller than the sputtering threshold depending on whether or not ion-assisted chemical etching is the dominant etching pathway and whether surface chemistry is enhancing or inhibiting desorption of the film atoms. In the case of CBN films etched in an inductively coupled Cl{sub 2} plasma, it is found that the chlorine uptake is inhibiting the etching reaction, with the desorption of nonvolatile NbCl{sub 2} and BaCl{sub 2} compounds being the rate-limiting step.

  7. Students' Written Arguments in General Chemistry Laboratory Investigations

    ERIC Educational Resources Information Center

    Choi, Aeran; Hand, Brian; Greenbowe, Thomas

    2013-01-01

    This study aimed to examine the written arguments developed by college freshman students using the Science Writing Heuristic approach in inquiry-based general chemistry laboratory classrooms and its relationships with students' achievement in chemistry courses. Fourteen freshman students participated in the first year of the study while 19…

  8. The impact of surface chemistry on the performance of localized solar-driven evaporation system

    PubMed Central

    Yu, Shengtao; Zhang, Yao; Duan, Haoze; Liu, Yanming; Quan, Xiaojun; Tao, Peng; Shang, Wen; Wu, Jianbo; Song, Chengyi; Deng, Tao

    2015-01-01

    This report investigates the influence of surface chemistry (or wettability) on the evaporation performance of free-standing double-layered thin film on the surface of water. Such newly developed evaporation system is composed of top plasmonic light-to-heat conversion layer and bottom porous supporting layer. Under solar light illumination, the induced plasmonic heat will be localized within the film. By modulating the wettability of such evaporation system through the control of surface chemistry, the evaporation rates are differentiated between hydrophilized and hydrophobized anodic aluminum oxide membrane-based double layered thin films. Additionally, this work demonstrated that the evaporation rate mainly depends on the wettability of bottom supporting layer rather than that of top light-to-heat conversion layer. The findings in this study not only elucidate the role of surface chemistry of each layer of such double-layered evaporation system, but also provide additional design guidelines for such localized evaporation system in applications including desalination, distillation and power generation. PMID:26337561

  9. The impact of surface chemistry on the performance of localized solar-driven evaporation system.

    PubMed

    Yu, Shengtao; Zhang, Yao; Duan, Haoze; Liu, Yanming; Quan, Xiaojun; Tao, Peng; Shang, Wen; Wu, Jianbo; Song, Chengyi; Deng, Tao

    2015-01-01

    This report investigates the influence of surface chemistry (or wettability) on the evaporation performance of free-standing double-layered thin film on the surface of water. Such newly developed evaporation system is composed of top plasmonic light-to-heat conversion layer and bottom porous supporting layer. Under solar light illumination, the induced plasmonic heat will be localized within the film. By modulating the wettability of such evaporation system through the control of surface chemistry, the evaporation rates are differentiated between hydrophilized and hydrophobized anodic aluminum oxide membrane-based double layered thin films. Additionally, this work demonstrated that the evaporation rate mainly depends on the wettability of bottom supporting layer rather than that of top light-to-heat conversion layer. The findings in this study not only elucidate the role of surface chemistry of each layer of such double-layered evaporation system, but also provide additional design guidelines for such localized evaporation system in applications including desalination, distillation and power generation. PMID:26337561

  10. The impact of surface chemistry on the performance of localized solar-driven evaporation system

    NASA Astrophysics Data System (ADS)

    Yu, Shengtao; Zhang, Yao; Duan, Haoze; Liu, Yanming; Quan, Xiaojun; Tao, Peng; Shang, Wen; Wu, Jianbo; Song, Chengyi; Deng, Tao

    2015-09-01

    This report investigates the influence of surface chemistry (or wettability) on the evaporation performance of free-standing double-layered thin film on the surface of water. Such newly developed evaporation system is composed of top plasmonic light-to-heat conversion layer and bottom porous supporting layer. Under solar light illumination, the induced plasmonic heat will be localized within the film. By modulating the wettability of such evaporation system through the control of surface chemistry, the evaporation rates are differentiated between hydrophilized and hydrophobized anodic aluminum oxide membrane-based double layered thin films. Additionally, this work demonstrated that the evaporation rate mainly depends on the wettability of bottom supporting layer rather than that of top light-to-heat conversion layer. The findings in this study not only elucidate the role of surface chemistry of each layer of such double-layered evaporation system, but also provide additional design guidelines for such localized evaporation system in applications including desalination, distillation and power generation.

  11. Ionic Liquids Can Permanently Modify Porous Silicon Surface Chemistry.

    PubMed

    Trivedi, Shruti; Coombs, Sidney G; Wagle, Durgesh V; Bhawawet, Nakara; Baker, Gary A; Bright, Frank V

    2016-08-01

    To develop ionic liquid/porous silicon (IL/pSi) microarrays we have contact pin-printed 20 hydrophobic and hydrophilic ionic liquids onto as-prepared, hydrogen-passivated porous silicon (ap-pSi) and then determined the individual IL spot size, shape and associated pSi surface chemistry. The results reveal that the hydrophobic ionic liquids oxidize the ap-pSi slightly. In contrast, the hydrophilic ionic liquids lead to heavily oxidized pSi (i.e., ox-pSi). The strong oxidation arises from residual water within the hydrophilic ILs that is delivered from these ILs into the ap-pSi matrix causing oxidation. This phenomenon is less of an issue in the hydrophobic ILs because their water solubility is substantially lower. PMID:27405109

  12. Control of pyrite surface chemistry in physical coal cleaning

    SciTech Connect

    Luttrell, G.H.; Yoon, R.H.; Zachwieja, J.; Lagno, M.

    1992-06-24

    To better understand the surface chemical properties of coal and mineral pyrite, studies on the effect of flotation surfactants (frother and kerosene) on the degree of hydrophobicity have been conducted. The presence of either frother or kerosene enhanced the flotability of coal and mineral pyrite with a corresponding decrease in induction time over the pH range examined. Scanning electron microscopy (SEM) results indicate a correlation exists between the sample surface morphology and crystal structure and the observed hydrophobicity. As a result of the data obtained from the surface characterization studies, controlled surface oxidation was investigated as a possible pyrite rejection scheme in microbubble column flotation.

  13. Investigation of Venus Surface Properties

    NASA Technical Reports Server (NTRS)

    Ford, Peter G.

    2002-01-01

    Strong localized radar echoes have been observed at decimeter wavelengths from the highlands of Venus since the earliest radar maps were obtained over 30 years ago. These echoes are some five to ten times stronger than those from the presumably basaltic rocks seen at lower altitudes elsewhere on Venus. Observations of thermal emission from the visible disk of Venus at wavelengths corresponding to those used in the radar mapping confirm that the regions of high reflectivity also exhibit low emissivity, as expected from considerations of detailed thermodynamic balance. Two possibilities have been put forward to explain this unexpected aspect of the Venus highlands: 1) surface materials of high effective dielectric constant, probably associated with finite electrical conductivity, and 2) volume scattering associated with multiple scattering from a layer of very-low-loss material containing voids and extending down a few hundred wavelengths beneath the surface. Analogs to these two mechanisms are found elsewhere in the solar system, and each is capable of explaining the basic observations. as of the early 1990's. In 1993, however, it became possible to carry out a bistatic observation of the anomalous highland regions using the Magellan spacecraft, then in orbit about Venus. In this experiment the on-board telemetry transmitter was aimed at the planet's surface with its linear S-band polarization vector oriented at 45 deg to the spacecraft-Venus-Earth scattering plane. The pointing of the transmitting antenna was adjusted so that the spacecraft-to-illuminated-surface incidence angle equalled the Earth-to-Venus-surface incidence angle. In this way, the experiment emphasized the specular scattering component. A full Stokes-Vector analysis of the reflected signal as received on Earth was carried out as the illuminated region scanned across the highland regions of Venus. From the observed position angle of the echo, it was possible to calculate the Fresnel reflectivity of

  14. In Situ Quantification of Surface Chemistry in Porous Collagen Biomaterials.

    PubMed

    Tzeranis, Dimitrios S; Soller, Eric C; Buydash, Melissa C; So, Peter T C; Yannas, Ioannis V

    2016-03-01

    Cells inside a 3D matrix (such as tissue extracellular matrix or biomaterials) sense their insoluble environment through specific binding interactions between their adhesion receptors and ligands present on the matrix surface. Despite the critical role of the insoluble matrix in cell regulation, there exist no widely-applicable methods for quantifying the chemical stimuli provided by a matrix to cells. Here, we describe a general-purpose technique for quantifying in situ the density of ligands for specific cell adhesion receptors of interest on the surface of a 3D matrix. This paper improves significantly the accuracy of the procedure introduced in a previous publication by detailed marker characterization, optimized staining, and improved data interpretation. The optimized methodology is utilized to quantify the ligands of integrins α 1 β 1, α 2 β 1 on two kinds of matched porous collagen scaffolds, which are shown to possess significantly different ligand density, and significantly different ability to induce peripheral nerve regeneration in vivo. Data support the hypothesis that cell adhesion regulates contractile cell phenotypes, recently shown to be inversely related to organ regeneration. The technique provides a standardized way to quantify the surface chemistry of 3D matrices, and a means for introducing matrix effects in quantitative biological models. PMID:26369635

  15. Cassini atmospheric chemistry mapper. Volume 1. Investigation and technical plan

    NASA Technical Reports Server (NTRS)

    Smith, William Hayden; Baines, Kevin Hays; Drossart, Pierre; Fegley, Bruce; Orton, Glenn; Noll, Keith; Reitsema, Harold; Bjoraker, Gordon L.

    1990-01-01

    The Cassini Atmospheric Chemistry Mapper (ACM) enables a broad range of atmospheric science investigations for Saturn and Titan by providing high spectral and spatial resolution mapping and occultation capabilities at 3 and 5 microns. ACM can directly address the major atmospheric science objectives for Saturn and for Titan, as defined by the Announcement of Opportunity, with pivotal diagnostic measurements not accessible to any other proposed Cassini instrument. ACM determines mixing ratios for atmospheric molecules from spectral line profiles for an important and extensive volume of the atmosphere of Saturn (and Jupiter). Spatial and vertical profiles of disequilibrium species abundances define Saturn's deep atmosphere, its chemistry, and its vertical transport phenomena. ACM spectral maps provide a unique means to interpret atmospheric conditions in the deep (approximately 1000 bar) atmosphere of Saturn. Deep chemistry and vertical transport is inferred from the vertical and horizontal distribution of a series of disequilibrium species. Solar occultations provide a method to bridge the altitude range in Saturn's (and Titan's) atmosphere that is not accessible to radio science, thermal infrared, and UV spectroscopy with temperature measurements to plus or minus 2K from the analysis of molecular line ratios and to attain an high sensitivity for low-abundance chemical species in the very large column densities that may be achieved during occultations for Saturn. For Titan, ACM solar occultations yield very well resolved (1/6 scale height) vertical mixing ratios column abundances for atmospheric molecular constituents. Occultations also provide for detecting abundant species very high in the upper atmosphere, while at greater depths, detecting the isotopes of C and O, constraining the production mechanisms, and/or sources for the above species. ACM measures the vertical and horizontal distribution of aerosols via their opacity at 3 microns and, particularly, at 5

  16. Plant surface reactions: an ozone defence mechanism impacting atmospheric chemistry

    NASA Astrophysics Data System (ADS)

    Jud, W.; Fischer, L.; Canaval, E.; Wohlfahrt, G.; Tissier, A.; Hansel, A.

    2015-07-01

    Elevated tropospheric ozone concentrations are considered a toxic threat to plants, responsible for global crop losses with associated economic costs of several billion dollars per year. Plant injuries have been linked to the uptake of ozone through stomatal pores and oxidative damage of the internal leaf tissue. But a striking question remains: how much ozone effectively enters the plant through open stomata and how much is lost by chemical reactions at the plant surface? In this laboratory study we could show that semi-volatile organic compounds exuded by the glandular trichomes of different Nicotiana tabacum varieties are an efficient ozone sink at the plant surface. In our experiments, different diterpenoid compounds were responsible for a strongly variety dependent ozone uptake of plants under dark conditions, when stomatal pores are almost closed. Surface reactions of ozone were accompanied by prompt release of oxygenated volatile organic compounds, which could be linked to the corresponding precursor compounds: ozonolysis of cis-abienol (C20H34O) - a diterpenoid with two exocyclic double bonds - caused emissions of formaldehyde (HCHO) and methyl vinyl ketone (C4H6O). The ring-structured cembratrien-diols (C20H34O2) with three endocyclic double bonds need at least two ozonolysis steps to form volatile carbonyls such as 4-oxopentanal (C5H8O2), which we could observe in the gas phase, too. Fluid dynamic calculations were used to model ozone distribution in the diffusion limited leaf boundary layer under daylight conditions. In the case of an ozone-reactive leaf surface, ozone gradients in the vicinity of stomatal pores are changed in such a way, that ozone flux through the open stomata is strongly reduced. Our results show that unsaturated semi-volatile compounds at the plant surface should be considered as a source of oxygenated volatile organic compounds, impacting gas phase chemistry, as well as efficient ozone sink improving the ozone tolerance of plants.

  17. Effect of Surface Chemistry on Gene Transfer Efficiency Mediated by Surface-induced DNA-doped Nanocomposites

    PubMed Central

    Sun, Bingbing; Yi, Minchang; Yacoob, Christina C.; Nguyen, Hai T.; Shen, Hong

    2011-01-01

    Surface-induced biomineralization represents an effective way to immobilize DNA molecules onto biomaterial surfaces for introducing DNA into cells in contact with or in an approximate distance to biomaterial surfaces. Our previous studies have investigated how the composition of mineralizing solutions affects the composition and pH responsiveness of nanocomposites and thus gene transfer efficiency in different cell types. In this study, we investigated how the functional groups of a biomaterial surface would affect the induction and crystallographic properties of nanocomposites and thus the gene transfer efficiency. Self-assembled monolayers (SAMs) with different terminus were used to control the functional groups of a surface. We demonstrated that the induction of DNA-doped nanocomposites depended on the surface functional groups, which is consistent with previous studies. The crystallographic properties did not vary significantly with the functional groups. DNA-doped nanocomposites induced by different surface functional groups resulted in different cellular uptake of DNA and thus gene transfer efficiency. The differential cellular uptake may be attributed to the interactions between nanocomposites and functional groups. The weaker inducer resulted in higher cellular uptake thus higher gene transfer efficiency. Together with others and our previous studies, our current results suggest that surface-mediated gene transfer by DNA-doped nanocomposites can be modulated through both mineralizing solutions and surface chemistries. PMID:22198137

  18. Adsorption of pentacene on (100) vicinal surfaces: role of coordination, surface chemistry and vdWs effects

    NASA Astrophysics Data System (ADS)

    Matos, Jeronimo; Kara, Abdelkader

    2015-03-01

    In contrast to low miller index surfaces, vicinal surfaces are characterized by steps and step edges that not only present an interesting atomic landscape for the adsorption organic molecules, but also a unique electronic structure resulting in part from the low coordinated atoms at the step edges. The adsorption of pentacene on the stepped (511), (711), (911) surfaces (respectively 3, 4 and 5-atom wide terraces) of Cu and Ag (coinage transition metals); Pt (reactive transition metal); and Ni (reactive, magnetic transition metal) are studied using density functional theory, in order to investigate the support effects arising from differing surface chemistry. We compare the adsorption energy, adsorption geometry and electronic structure predicted by the PBE functional with those obtained from one of the optimized vdW-DF methods: optB88-vdW. Work supported by the U.S. Department of Energy Basic Energy Science under Contract No. DE-FG02-11ER16243.

  19. Surface-Enhanced Raman Spectroscopy as a Probe of the Surface Chemistry of Nanostructured Materials.

    PubMed

    Dick, Susan; Konrad, Magdalena P; Lee, Wendy W Y; McCabe, Hannah; McCracken, John N; Rahman, Taifur M D; Stewart, Alan; Xu, Yikai; Bell, Steven E J

    2016-07-01

    Surface-enhanced Raman spectroscopy (SERS) is now widely used as a rapid and inexpensive tool for chemical/biochemical analysis. The method can give enormous increases in the intensities of the Raman signals of low-concentration molecular targets if they are adsorbed on suitable enhancing substrates, which are typically composed of nanostructured Ag or Au. However, the features of SERS that allow it to be used as a chemical sensor also mean that it can be used as a powerful probe of the surface chemistry of any nanostructured material that can provide SERS enhancement. This is important because it is the surface chemistry that controls how these materials interact with their local environment and, in real applications, this interaction can be more important than more commonly measured properties such as morphology or plasmonic absorption. Here, the opportunity that this approach to SERS provides is illustrated with examples where the surface chemistry is both characterized and controlled in order to create functional nanomaterials. PMID:26822589

  20. Functional surface chemistry of carbon-based nanostructures

    NASA Astrophysics Data System (ADS)

    Abdula, Daner

    The recently discovered abilities to synthesize single-walled carbon nanotubes and prepare single layer graphene have spurred interest in these sp2-bonded carbon nanostructures. In particular, studies of their potential use in electronic devices are many as silicon integrated circuits are encountering processing limitations, quantum effects, and thermal management issues due to rapid device scaling. Nanotube and graphene implementation in devices does come with significant hurdles itself. Among these issues are the ability to dope these materials and understanding what influences defects have on expected properties. Because these nanostructures are entirely all-surface, with every atom exposed to ambient, introduction of defects and doping by chemical means is expected to be an effective route for addressing these issues. Raman spectroscopy has been a proven characterization method for understanding vibrational and even electronic structure of graphene, nanotubes, and graphite, especially when combined with electrical measurements, due to a wealth of information contained in each spectrum. In Chapter 1, a discussion of the electronic structure of graphene is presented. This outlines the foundation for all sp2-bonded carbon electronic properties and is easily extended to carbon nanotubes. Motivation for why these materials are of interest is readily gained. Chapter 2 presents various synthesis/preparation methods for both nanotubes and graphene, discusses fabrication techniques for making devices, and describes characterization methods such as electrical measurements as well as static and time-resolved Raman spectroscopy. Chapter 3 outlines changes in the Raman spectra of individual metallic single-walled carbon nantoubes (SWNTs) upon sidewall covalent bond formation. It is observed that the initial degree of disorder has a strong influence on covalent sidewall functionalization which has implications on developing electronically selective covalent chemistries and

  1. Molecular potential energy surfaces for interstellar chemistry and fusion applications

    NASA Astrophysics Data System (ADS)

    Braams, Bastiaan J.; Huang, Xinchuan; Jin, Zhong; Xie, Zhen; Zhang, Xiubin; Bowman, Joel M.; Sharma, Amit Raj; Scheider, Ralf

    2006-04-01

    In the Born-Oppenheimer approximation the electronic Schr"odinger equation is solved given the nuclear positions as parameters, and this defines the potential energy surface. We have used computational invariant theory and the MAGMA computer algebra system as an aid to develop representations for the potential energy and dipole moment surfaces that are fully invariant under permutations of like nuclei, extending an approach that for 3-body and 4-body systems has a long history, e.g. [J. N. Murrell et al. Molecular Potential Energy Functions, Wiley, 1984]. A many-body (cluster) expansion is used to describe reaction complexes. The methods have been applied in an almost routine way for systems of up to 7 nuclei, including several molecules that are of interest for interstellar chemistry and for the issue of hydrocarbon breakdown in fusion edge plasma: H5^+, CH5, CH5^+, C2H3^+, and their fragments, with C2H5^+ on the way. The mathematical and computional methods and the hydrocarbon applications will be presented.

  2. Surface Chemistry at Size-Selected Nano-Aerosol Particles

    NASA Astrophysics Data System (ADS)

    Roberts, Jeffrey

    2005-03-01

    A method has been developed to conduct surface chemistry and extract surface kinetic rates from size-selected aerosol nanoparticles. The measurements encompass broad ranges of particle size, phase, and composition. Results will be presented on the uptake of water by aerosolized soot nanoparticles of radius between 10 and 40 nm. Water uptake was monitored by tandem differential mobility analysis (T-DMA), which is capable of measuring changes in particle diameter as little as 0.2 nm. Soot particles were produced in an ethene diffusion flame and extracted into an atmospheric pressure aerosol flow tube reactor. The particles were subjected to various thermal and oxidative treatments, and the effects of these treatments on the ability of soot to adsorb monolayer quantities of water was determined. The results are important because soot nucleates atmospheric cloud particles. More generally, the results represent one of the first kinetic and mechanistic studies of gas-phase nanoparticle reactivity. Co-author: Henry Ajo, University of Minnesota

  3. Surface chemistry of gold nanorods: origin of cell membrane damage and cytotoxicity

    NASA Astrophysics Data System (ADS)

    Wang, Liming; Jiang, Xiumei; Ji, Yinglu; Bai, Ru; Zhao, Yuliang; Wu, Xiaochun; Chen, Chunying

    2013-08-01

    We investigated how surface chemistry influences the interaction between gold nanorods (AuNRs) and cell membranes and the subsequent cytotoxicity arising from them in a serum-free cell culture system. Our results showed that the AuNRs coated with cetyl trimethylammonium bromide (CTAB) molecules can generate defects in the cell membrane and induce cell death, mainly due to the unique bilayer structure of CTAB molecules on the surface of the rods rather than their charge. Compared to CTAB-capped nanorods, positively charged polyelectrolyte-coated, i.e. poly(diallyldimethyl ammonium chloride) (PDDAC), AuNRs show improved biocompatibility towards cells. Thus, the present results indicate that the nature of surface molecules, especially their packing structures on the surface of AuNRs rather than surface charge, play a more crucial role in determining cytotoxicity. These findings about interfacial interactions could also explain the effects of internalized AuNRs on the structures or functions of organelles. This study will help understanding of the toxic nature of AuNRs and guide rational design of the surface chemistry of AuNRs for good biocompatibility in pharmaceutical therapy.

  4. Atomic Scale Structure-Chemistry Relationships at Oxide Catalyst Surfaces and Interfaces

    NASA Astrophysics Data System (ADS)

    McBriarty, Martin E.

    Oxide catalysts are integral to chemical production, fuel refining, and the removal of environmental pollutants. However, the atomic-scale phenomena which lead to the useful reactive properties of catalyst materials are not sufficiently understood. In this work, the tools of surface and interface science and electronic structure theory are applied to investigate the structure and chemical properties of catalytically active particles and ultrathin films supported on oxide single crystals. These studies focus on structure-property relationships in vanadium oxide, tungsten oxide, and mixed V-W oxides on the surfaces of alpha-Al2O3 and alpha-Fe2O 3 (0001)-oriented single crystal substrates, two materials with nearly identical crystal structures but drastically different chemical properties. In situ synchrotron X-ray standing wave (XSW) measurements are sensitive to changes in the atomic-scale geometry of single crystal model catalyst surfaces through chemical reaction cycles, while X-ray photoelectron spectroscopy (XPS) reveals corresponding chemical changes. Experimental results agree with theoretical calculations of surface structures, allowing for detailed electronic structure investigations and predictions of surface chemical phenomena. The surface configurations and oxidation states of V and W are found to depend on the coverage of each, and reversible structural shifts accompany chemical state changes through reduction-oxidation cycles. Substrate-dependent effects suggest how the choice of oxide support material may affect catalytic behavior. Additionally, the structure and chemistry of W deposited on alpha-Fe 2O3 nanopowders is studied using X-ray absorption fine structure (XAFS) measurements in an attempt to bridge single crystal surface studies with real catalysts. These investigations of catalytically active material surfaces can inform the rational design of new catalysts for more efficient and sustainable chemistry.

  5. Surface chemistry dependent immunostimulative potential of porous silicon nanoplatforms.

    PubMed

    Shahbazi, Mohammad-Ali; Fernández, Tahia D; Mäkilä, Ermei M; Le Guével, Xavier; Mayorga, Cristobalina; Kaasalainen, Martti H; Salonen, Jarno J; Hirvonen, Jouni T; Santos, Hélder A

    2014-11-01

    Nanoparticles (NPs) have been suggested for immunotherapy applications in order to optimize the delivery of immuno-stimulative or -suppressive molecules. However, low attention towards the impact of the NPs' physicochemical properties has presented a major hurdle for developing efficient immunotherapeutic agents. Here, the effects of porous silicon (PSi) NPs with different surface chemistries were evaluated on human monocyte-derived dendritic cells (MDDCs) and lymphocytes in order to highlight the importance of the NPs selection in immuno-stimulative or -suppressive treatment. Although all the PSi NPs showed high biocompatibility, only thermally oxidized PSi (TOPSi) and thermally hydrocarbonized PSi (THCPSi) NPs were able to induce very high rate of immunoactivation by enhancing the expression of surface co-stimulatory markers of the MDDCs (CD80, CD83, CD86, and HLA-DR), inducing T-cell proliferation, and also the secretion of interleukins (IL-1β, IL-4, IL-6, IL-10, IL-12, IFN-γ, and TNF-α). These results indicated a balanced increase in the secretion of Th1, Th2, and Treg cytokines. Moreover, undecylenic acid functionalized THCPSi, as well as poly(methyl vinyl ether-alt-maleic acid) conjugated to (3-aminopropyl)triethoxysilane functionalized thermally carbonized PSi and polyethyleneimine conjugated undecylenic acid functionalized THCPSi NPs showed moderate immunoactivation due to the mild increase in the above-mentioned markers. By contrast, thermally carbonized PSi (TCPSi) and (3-aminopropyl)triethoxysilane functionalized TCPSi NPs did not induce any immunological responses, suggesting that their application could be in the delivery of immunosuppressive molecules. Overall, our findings suggest all the NPs containing more nitrogen or oxygen on the outermost backbone layer have lower immunostimulatory effect than NPs with higher C-H structures on the surface. PMID:25123922

  6. Analysis of temporal evolution of quantum dot surface chemistry by surface-enhanced Raman scattering

    PubMed Central

    Doğan, İlker; Gresback, Ryan; Nozaki, Tomohiro; van de Sanden, Mauritius C. M.

    2016-01-01

    Temporal evolution of surface chemistry during oxidation of silicon quantum dot (Si-QD) surfaces were probed using surface-enhanced Raman scattering (SERS). A monolayer of hydrogen and chlorine terminated plasma-synthesized Si-QDs were spin-coated on silver oxide thin films. A clearly enhanced signal of surface modes, including Si-Clx and Si-Hx modes were observed from as-synthesized Si-QDs as a result of the plasmonic enhancement of the Raman signal at Si-QD/silver oxide interface. Upon oxidation, a gradual decrease of Si-Clx and Si-Hx modes, and an emergence of Si-Ox and Si-O-Hx modes have been observed. In addition, first, second and third transverse optical modes of Si-QDs were also observed in the SERS spectra, revealing information on the crystalline morphology of Si-QDs. An absence of any of the abovementioned spectral features, but only the first transverse optical mode of Si-QDs from thick Si-QD films validated that the spectral features observed from Si-QDs on silver oxide thin films are originated from the SERS effect. These results indicate that real-time SERS is a powerful diagnostic tool and a novel approach to probe the dynamic surface/interface chemistry of quantum dots, especially when they involve in oxidative, catalytic, and electrochemical surface/interface reactions. PMID:27389331

  7. Analysis of temporal evolution of quantum dot surface chemistry by surface-enhanced Raman scattering

    NASA Astrophysics Data System (ADS)

    Doğan, Ilker; Gresback, Ryan; Nozaki, Tomohiro; van de Sanden, Mauritius C. M.

    2016-07-01

    Temporal evolution of surface chemistry during oxidation of silicon quantum dot (Si-QD) surfaces were probed using surface-enhanced Raman scattering (SERS). A monolayer of hydrogen and chlorine terminated plasma-synthesized Si-QDs were spin-coated on silver oxide thin films. A clearly enhanced signal of surface modes, including Si-Clx and Si-Hx modes were observed from as-synthesized Si-QDs as a result of the plasmonic enhancement of the Raman signal at Si-QD/silver oxide interface. Upon oxidation, a gradual decrease of Si-Clx and Si-Hx modes, and an emergence of Si-Ox and Si-O-Hx modes have been observed. In addition, first, second and third transverse optical modes of Si-QDs were also observed in the SERS spectra, revealing information on the crystalline morphology of Si-QDs. An absence of any of the abovementioned spectral features, but only the first transverse optical mode of Si-QDs from thick Si-QD films validated that the spectral features observed from Si-QDs on silver oxide thin films are originated from the SERS effect. These results indicate that real-time SERS is a powerful diagnostic tool and a novel approach to probe the dynamic surface/interface chemistry of quantum dots, especially when they involve in oxidative, catalytic, and electrochemical surface/interface reactions.

  8. Chemoselective modification of viral surfaces via bioorthogonal click chemistry.

    PubMed

    Rubino, Frederick A; Oum, Yoon Hyeun; Rajaram, Lakshmi; Chu, Yanjie; Carrico, Isaac S

    2012-01-01

    The modification of virus particles has received a significant amount of attention for its tremendous potential for impacting gene therapy, oncolytic applications and vaccine development. Current approaches to modifying viral surfaces, which are mostly genetics-based, often suffer from attenuation of virus production, infectivity and cellular transduction. Using chemoselective click chemistry, we have developed a straightforward alternative approach which sidesteps these issues while remaining both highly flexible and accessible. The goal of this protocol is to demonstrate the effectiveness of using bioorthogonal click chemistry to modify the surface of adenovirus type 5 particles. This two-step process can be used both therapeutically or analytically, as it allows for chemoselective ligation of targeting molecules, dyes or other molecules of interest onto proteins pre-labeled with azide tags. The three major advantages of this method are that (1) metabolic labeling demonstrates little to no impact on viral fitness, (2) a wide array of effector ligands can be utilized, and (3) it is remarkably fast, reliable and easy to access. In the first step of this procedure, adenovirus particles are produced bearing either azidohomoalanine (Aha, a methionine surrogate) or the unnatural sugar O-linked N-azidoacetylglucosamine (O-GlcNAz), both of which contain the azide (-N3) functional group. After purification of the azide-modified virus particles, an alkyne probe containing the fluorescent TAMRA moiety is ligated in a chemoselective manner to the pre-labeled proteins or glycoproteins. Finally, an SDS-PAGE analysis is performed to demonstrate the successful ligation of the probe onto the viral capsid proteins. Aha incorporation is shown to label all viral capsid proteins (Hexon, Penton and Fiber), while O-GlcNAz incorporation results in labeling of Fiber only. In this evolving field, multiple methods for azide-alkyne ligation have been successfully developed; however only the

  9. Investigation of Varied Strontium-Transuranic Precipitation Chemistries for Crossflow

    SciTech Connect

    Nash, C.A.

    2000-07-27

    Precipitation chemistries for strontium and transuranic (TRU) removal have been tested for crossflow filterability and lanthanide removal with simulants of Hanford tank 241-AN-107 supernate. This is the initial work indicating the usefulness of a strontium and permanganate precipitation process as applied to the Hanford River Protection Project. Precipitations with both ferric and ferrous iron were shown to be at least two orders of magnitude less filterable than a 0.1 gpm/ft target average flux that was desired at the time. A precipitate from a strontium nitrate strike alone was found to filter easily and to make the desired average flux. Other chemistries tested included precipitant of lanthanum(III), nickel (II), calcium (II), and a redox chemistry using sodium permanganate. Of these chemistries a strontium and permanganate strike including calcium provided the highest filter flux compared to the other chemistries. It showed the most promise in lanthanide removal as well. This work provides a promising direction for further work to achieve both acceptable filterability and decontamination for Envelope C wastes to be treated by the Hanford River Protection Project. The work reported here was originally intended to satisfy needs for crossflow filter testing of a strontium and ferric precipitation method for treating Envelope C using a 241-AN-107 simulant.

  10. Chromate removal by surface-modified nanoscale zero-valent iron: Effect of different surface coatings and water chemistry.

    PubMed

    Dong, Haoran; He, Qi; Zeng, Guangming; Tang, Lin; Zhang, Chang; Xie, Yankai; Zeng, Yalan; Zhao, Feng; Wu, Yanan

    2016-06-01

    This study investigated the correlation between the colloidal stability and reactivity of surface-modified nano zero-valent iron (SM-nZVI) as affected by the surface coating (i.e., polyacrylic acid [PAA] and starch) under various geochemical conditions. Generally, the colloidal stability of nZVI was enhanced with increasing loading of surface coating, while there is an optimum loading for the most efficient Cr(VI) removal by SM-nZVI. At lower loadings than the optimum loading, the surface coating could enhance the particle stabilization, facilitating the Cr(VI) reduction by providing more available surface sites. However, the over-loaded surface coating on the surface of nZVI particles decreased the Cr(VI) reduction due to the occupation of the reactive sites and the inhibition of the mass transfer of Cr(VI) ions from water to the particle surface by providing the electrostatic or steric repulsion. The effects of Ca(2+) ions or humic acid (HA) on the colloidal stability and reactivity of PAA-modified nZVI (P-nZVI) and starch-modified nZVI (S-nZVI) were examined. Differing stability behavior and reactivity were observed for different SM-nZVI. It was found that the presence of Ca(2+) or HA altered surface chemistry of SM-nZVI, the particle-particle interaction and the particle-contaminant interaction, and hence influencing the stability behavior and reactivity of the particles. PMID:26970032

  11. Capturing Conformation-Dependent Molecule-Surface Interactions When Surface Chemistry Is Heterogeneous.

    PubMed

    Mabry, Joshua N; Kastantin, Mark; Schwartz, Daniel K

    2015-07-28

    Molecular building blocks, such as carbon nanotubes and DNA origami, can be fully integrated into electronic and optical devices if they can be assembled on solid surfaces using biomolecular interactions. However, the conformation and functionality of biomolecules depend strongly on the local chemical environment, which is highly heterogeneous near a surface. To help realize the potential of biomolecular self-assembly, we introduce here a technique to spatially map molecular conformations and adsorption, based on single-molecule fluorescence microscopy. On a deliberately patterned surface, with regions of varying hydrophobicity, we characterized the conformations of adsorbed helicogenic alanine-lysine copeptides using Förster resonance energy transfer. The peptides adopted helical conformations on hydrophilic regions of the surface more often than on hydrophobic regions, consistent with previous ensemble-averaged observations of α-helix surface stability. Interestingly, this dependence on surface chemistry was not due to surface-induced unfolding, as the apparent folding and unfolding dynamics were usually much slower than desorption. The most significant effect of surface chemistry was on the adsorption rate of molecules as a function of their initial conformational state. In particular, regions with higher adsorption rates attracted more molecules in compact, disordered coil states, and this difference in adsorption rates dominated the average conformation of the ensemble. The correlation between adsorption rate and average conformation was also observed on nominally uniform surfaces. Spatial variations in the functional state of adsorbed molecules would strongly affect the success rates of surface-based molecular assembly and can be fully understood using the approach developed in this work. PMID:26079177

  12. Don Quixote Pond Sediments: Surface and Subsurface Chemistry and Mineralogy

    NASA Astrophysics Data System (ADS)

    Englert, P. A. J.; Bishop, J. L.; Patel, S.; Gibson, E. K.; Koeberl, C.

    2014-12-01

    Don Quixote Pond, like Don Juan Pond in the South Fork of Wright Valley, Antarctica, is a model for calcium and chlorine weathering and distribution on Mars. It is located in the western part of the North Fork about 100 m above Mean Seawater Level; its brine is seasonally frozen [1]. Field observations show zones of discoloration which grow lighter with distance from the pond edges. Four sediment cores, a set of radial surface samples, special surface samples, and samples of local rocks were obtained [2]. We report on chemical and mineral analyses of traverse samples and on two cores. Core DQ20 is a northeastern shoreline core. Its soluble salt concentration exceeds 200 micromoles/g in the top 5 cm, and then falls to less than 70 micromoles/g at the permafrost depth of 15 cm. These concentrations are low when compared to similarly positioned locations at Don Juan Pond and to cores from Prospect Mesa close to Lake Vanda, Wright Valley. Halite, soda niter, tachyhydrite and/bischovite are suggested from the ionic molar relationships Measured halite concentrations of surface samples, collected along a traverse of 35 m from the pond outwards, range from over 5% to trace amounts, decreasing with distance. Gypsum is also present in almost all of these samples ranging from 0.2% to 2.6%, but does not exhibit a trend. However, in core DQ35, located at a distance of 15 m along the traverse, gypsum decreases from 2.5% to 0.6% from the surface to the permafrost depth of 12 cm. While DQ35 and radial samples show high quartz and albite abundance, samples that contained visible encrustations and evaporites are low in these minerals and rich in highly diverse alteration products. Don Juan Basin ponds may have formed by a complex surface water mobilization of weathering products [3] and local groundwater action [4,5]. In contrast, Don Quixote pond mineralogy and chemistry may be consistent with a less complex shallow and deep groundwater system origin [1]. [1] Harris H

  13. An Investigation into the Effectiveness of Problem-Based Learning in a Physical Chemistry Laboratory Course

    ERIC Educational Resources Information Center

    Gurses, Ahmet; Acikyildiz, Metin; Dogar, Cetin; Sozbilir, Mustafa

    2007-01-01

    The aim of this study was to investigate the effectiveness of a problem-based learning (PBL) approach in a physical chemistry laboratory course. The parameters investigated were students' attitudes towards a chemistry laboratory course, scientific process skills of students and their academic achievement. The design of the study was one group…

  14. Surface chemistry and physics of deuterium retention in lithiated graphite

    SciTech Connect

    Taylor, C. N.; Krstic, Predrag S; Allain, J. P.; Heim, B.; Skinner, C. H.; Kugel, H.

    2011-01-01

    Lithium wall conditioning in TFTR, CDX-U, T-11M, TJ-II and NSTX is found to yield enhanced plasma performance manifest, in part, through improved deuterium particle control. X-ray photoelectron spectroscopy (XPS) experiments examine the affect of D irradiation on lithiated graphite and show that the surface chemistry of lithiated graphite after D ion bombardment (500 eV/amu) is fundamentally different from that of non-Li conditioned graphite. Instead of simple LiD bonding seen in pure liquid Li, graphite introduces additional complexities. XPS spectra show that Li-O-D (533.0 {+-} 0.6 eV) and Li-C-D (291.4 {+-} 0.6 eV) bonds, for a nominal Li dose of 2 {micro}m, become 'saturated' with D at fluences between 3.8 and 5.2 x 10{sup 17} cm{sup -2}. Atomistic modeling indicate that Li-O-D-C interactions may be a result of multibody effects as opposed to molecular bonding.

  15. Influence of anode surface chemistry on microbial fuel cell operation.

    PubMed

    Santoro, Carlo; Babanova, Sofia; Artyushkova, Kateryna; Cornejo, Jose A; Ista, Linnea; Bretschger, Orianna; Marsili, Enrico; Atanassov, Plamen; Schuler, Andrew J

    2015-12-01

    Self-assembled monolayers (SAMs) modified gold anodes are used in single chamber microbial fuel cells for organic removal and electricity generation. Hydrophilic (N(CH3)3(+), OH, COOH) and hydrophobic (CH3) SAMs are examined for their effect on bacterial attachment, current and power output. The different substratum chemistry affects the community composition of the electrochemically active biofilm formed and thus the current and power output. Of the four SAM-modified anodes tested, N(CH3)3(+) results in the shortest start up time (15 days), highest current achieved (225 μA cm(-2)) and highest MFC power density (40 μW cm(-2)), followed by COOH (150 μA cm(-2) and 37 μW cm(-2)) and OH (83 μA cm(-2) and 27 μW cm(-2)) SAMs. Hydrophobic SAM decreases electrochemically active bacteria attachment and anode performance in comparison to hydrophilic SAMs (CH3 modified anodes 7 μA cm(-2) anodic current and 1.2 μW cm(-2) MFC's power density). A consortium of Clostridia and δ-Proteobacteria is found on all the anode surfaces, suggesting a synergistic cooperation under anodic conditions. PMID:26025340

  16. Surface-chemistry-sensitive spectral features of In-Ga-Zn-O thin film: Cleaned, air-passivated, and sputter-phase-separated surfaces

    NASA Astrophysics Data System (ADS)

    Kang, Se Jun; Baik, Jae Yoon; Thakur, Anup; Kim, Hyeong-Do; Shin, Hyun-Joon; Chung, JaeGwan; Lee, Jaecheol; Lee, JaeHak

    2011-07-01

    The photoelectron spectral features and corresponding energy band diagrams of amorphous indium gallium zinc oxide ( a-IGZO) thin films were investigated for different surface chemistries. Cleaned-IGZO surface had a deep subgap state (DSS), the binding energy (BE) of which expanded to ˜1.5 eV. When stored in air, IGZO surface became contaminant passivated and DSS became negligible. Sputtering resulted in phase separation of surface into metallic In and lesser In and Zn containing IGZO. Compared with IGZO, the air-passivated surface and phase-separated surface, respectively, had a more weakly conducting environment and a higher BE spectral shift.

  17. Students' Written Arguments in General Chemistry Laboratory Investigations

    NASA Astrophysics Data System (ADS)

    Choi, Aeran; Hand, Brian; Greenbowe, Thomas

    2012-11-01

    This study aimed to examine the written arguments developed by college freshman students using the Science Writing Heuristic approach in inquiry-based general chemistry laboratory classrooms and its relationships with students' achievement in chemistry courses. Fourteen freshman students participated in the first year of the study while 19 freshman students participated in the second year of the study. Two frameworks, an analytical and a holistic argument framework, were developed to evaluate the written argument generated by students. The analytical framework scored each argument component separately and allocated a Total Argument score while the holistic framework evaluated the arguments holistically. Three hundred and sixty-eight samples from 33 students were evaluated. Stepwise regression analyses revealed that the evidence and the claims-evidence relationship components were identified as the most important predictors of the Total Argument and the Holistic Argument scores. Students' argument scores were positively correlated with their achievement, as measured by the final grade received for the general chemistry laboratory and the general chemistry lecture course.

  18. Effects of Tailored Surface Chemistry on Desorption Electrospray Ionization Mass Spectrometry: a Surface-Analytical Study by XPS and AFM

    NASA Astrophysics Data System (ADS)

    Penna, Andrea; Careri, Maria; Spencer, Nicholas D.; Rossi, Antonella

    2015-08-01

    Since it was proposed for the first time, desorption electrospray ionization-mass spectrometry (DESI-MS) has been evaluated for applicability in numerous areas. Elucidations of the ionization mechanisms and the subsequent formation of isolated gas-phase ions have been proposed so far. In this context, the role of both surface and pneumatic effects on ion-formation yield has recently been investigated. Nevertheless, the effect of the surface chemistry has not yet been completely understood. Functionalized glass surfaces have been prepared, in order to tailor surface performance for ion formation. Three substrates were functionalized by depositing three different silanes [3-mercaptopropyltriethoxysilane (MTES), octyltriethoxysilane (OTES), and 1H,1H,2H,2H-perfluorooctyltriethoxy-silane (FOTES)] from toluene solution onto standard glass slides. Surface characterization was carried out by contact-angle measurements, tapping-mode atomic force microscopy, and X-ray photoelectron spectroscopy. Morphologically homogeneous and thickness-controlled films in the nm range were obtained, with surface free energies lying between 15 and 70 mJ/m2. These results are discussed, together with those of DESI-MS on low-molecular-weight compounds such as melamine, tetracycline, and lincomycin, also taking into account the effects of the sprayer potential and its correlation with surface wettability. The results demonstrate that ion-formation efficiency is affected by surface wettability, and this was demonstrated operating above and below the onset of the electrospray.

  19. LABORATORY AND COMPUTATIONAL CHEMISTRY INVESTIGATIONS OF THE GAS PHASE ATMOSPHERIC CHEMISTRY OF AIR TOXIC COMPOUNDS

    EPA Science Inventory

    A full assessment of the impact of the release of air toxic compounds into the atmospheric requires a detailed understanding of their atmospheres lifetimes and fates. To address this issue a detailed review of the atmospheric chemistry of each of these classes was carried out t...

  20. Preliminary findings of the Viking gas exchange experiment and a model for Martian surface chemistry

    NASA Technical Reports Server (NTRS)

    Oyama, V. I.; Berdahl, B. J.; Carle, G. C.

    1977-01-01

    Earlier results reported from the Viking Lander-1 experiment are reexamined and interpreted in terms of a model of the Martian soil surface morphology and chemistry. Major events in the gas exchange experiment (GEX) first cycle are tabulated and data are presented on the sample processing and transport environments experienced by the soil samples. Oxygen and CO2 evolved from humidified Martian soil in GEX and slight changes in N2 present are investigated. A soil model involving iron oxide coating on silicate material is entertained to yield a mechanistic explanation of the experimental findings, and invocation of biotic processes is eschewed.

  1. Surface chemistry and surface electronic properties of ZnO single crystals and nanorods

    SciTech Connect

    Uhlrich, J. J.; Olson, D. C.; Hsu, J. W. P.; Kuech, T. F.

    2009-03-15

    The surface chemistry of ZnO single crystals of (0001) and (1010) orientations and ZnO nanorods was studied using x-ray and ultraviolet photoelectron spectroscopies. Air drying and UV-ozone preparations were studied in particular as chemical treatments that could be applied to poly(3-hexylthiophene) (P3HT)-ZnO solar cells to enhance performance. The UV-ozone treatment showed negligible effect by photoelectron spectroscopy on the ZnO single crystal surfaces, but brought about electronic shifts consistent with increased upward band bending by {approx}0.25 eV on the ZnO nanorod surface. Modest interface dipoles of {approx}0.15 and {approx}0.25 eV were measured between P3HT and the (1010) and (0001) single crystal orientations, respectively, with the dipole moment pointing from ZnO to the P3HT layer. The sol-gel films showed evidence of forming a small interface dipole in the opposite direction, which illustrates the difference in surface chemistry between the solution-grown ZnO and the ZnO single crystals.

  2. The influence of carbon surface chemistry on supported palladium nanoparticles in heterogeneous reactions.

    PubMed

    Ding, Yuxiao; Zhang, Liyun; Wu, Kuang-Hsu; Feng, Zhenbao; Shi, Wen; Gao, Qiang; Zhang, Bingsen; Su, Dang Sheng

    2016-10-15

    The surface chemistry of nanocarbon support can tailor chemical properties of precious metal nanoparticle/nanocarbon hybrid catalyst in heterogeneous reactions. We report on modified reduced graphene oxide (rGO) support with ionic liquid-derived carbonaceous surface for palladium nanoparticle (Pd NPs) decoration and their actions in different heterogeneous reactions. The surface chemistry of support materials was characterized in detail, and the influence of which on the formation and distribution of metal particles was further investigated. Three different types of reactions including Suzuki-Miyaura coupling reaction, CO oxidation and phenol reduction were examined in terms of reactivity and selectivity. The roles of substituted nitrogen in graphitic lattice and grafted groups on the carbon surface were exploited. Nitrogen-doping can give rise to changes in electronic properties of supported metals, and the Lewis basicity of the doped nitrogen atoms can favor the adsorption of acidic reactants in phenol reduction. The grafted groups derived a negative impact to the Suzuki-Miyaura coupling reaction, due to the involvement of larger reactant molecules, despite that they could prevent significant sintering of Pd NPs in the CO oxidation. PMID:27442144

  3. Surface chemistry relevant to material processing for semiconductor devices

    NASA Astrophysics Data System (ADS)

    Okada, Lynne Aiko

    Metal-oxide-semiconductor (MOS) structures are the core of many modern integrated circuit (IC) devices. Each material utilized in the different regions of the device has its own unique chemistry. Silicon is the base semiconductor material used in the majority of these devices. With IC device complexity increasing and device dimensions decreasing, understanding material interactions and processing becomes increasingly critical. Hsb2 desorption is the rate-limiting step in silicon growth using silane under low temperature conditions. Activation energies for Hsb2 desorption measured during Si chemical vapor deposition (CVD) versus single-crystal studies are found to be significantly lower. It has been proposed that defect sites on the silicon surface could explain the observed differences. Isothermal Hsb2 desorption studies using laser induced thermal desorption (LITD) techniques have addressed this issue. The growth of low temperature oxides is another relevant issue for fabrication of IC devices. Recent studies using 1,4-disilabutane (DSB) (SiHsb3CHsb2CHsb2SiHsb3) at 100sp°C in ambient Osb2 displayed the successful low temperature growth of silicon dioxide (SiOsb2). However, these studies provided no information about the deposition mechanism. We performed LITD and Fourier transform infrared (FTIR) studies on single-crystal and porous silicon surfaces to examine the adsorption, decomposition, and desorption processes to determine the deposition mechanism. Titanium nitride (TiN) diffusion barriers are necessary in modern metallization structures. Controlled deposition using titanium tetrachloride (TiClsb4) and ammonia (NHsb3) has been demonstrated using atomic layered processing (ALP) techniques. We intended to study the sequential deposition method by monitoring the surface intermediates using LITD techniques. However, formation of a Cl impurity source, ammonium chloride (NHsb4sp+Clsp-), was observed, thereby, limiting our ability for effective studies. Tetrakis

  4. ATR-FTIR Spectroscopy in the Undergraduate Chemistry Laboratory: Part II--A Physical Chemistry Laboratory Experiment on Surface Adsorption

    ERIC Educational Resources Information Center

    Schuttlefield, Jennifer D.; Larsen, Sarah C.; Grassian, Vicki H.

    2008-01-01

    Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy is a useful technique for measuring the infrared spectra of solids and liquids as well as probing adsorption on particle surfaces. The use of FTIR-ATR spectroscopy in organic and inorganic chemistry laboratory courses as well as in undergraduate research was presented…

  5. Biophysical evaluation of cells on nanotubular surfaces: the effects of atomic ordering and chemistry

    PubMed Central

    Shokuhfar, Tolou; Hamlekhan, Azhang; Chang, Jen-Yung; Choi, Chang Kyoung; Sukotjo, Cortino; Friedrich, Craig

    2014-01-01

    After the implantation of a biomaterial in the body, the first interaction occurs between the cells in contact with the biomaterial surface. Therefore, evaluating the cell–substrate interface is crucial for designing a successful implant. In this study, the interaction of MC3T3 osteoblasts was studied on commercially pure and alloy (Ti6Al4V) Ti surfaces treated with amorphous and crystalline titanium dioxide nanotubes. The results indicated that the presence of nanotubes increased the density of osteoblast cells in comparison to bare surfaces (no nanotubes). More importantly, our finding shows that the chemistry of the substrate affects the cell density rather than the morphology of the cells. A novel approach based on the focused ion beam technique was used to investigate the biophysical cell–substrate interaction. The analysis revealed that portions of the cells migrated inside the crystalline nanotubes. This observation was correlated with the super hydrophilic properties of the crystalline nanotubes. PMID:25143725

  6. Chemistry and catalysis at the surface of nanomaterials

    NASA Astrophysics Data System (ADS)

    White, Brian Edward

    This thesis will delve into three main areas of nanomaterials research: (I) Designing, building, and utilizing a chemical vapor deposition (CVD) system for the growth of CNTs; (II) Aqueous suspensions of carbon nanotubes (CNT) solubilized by various surfactants, and the oxidative chemistry that can occur at CNT surfaces; (III) Catalytic CO oxidation over supported Cu2O nanoparticle systems. An introduction to nanomaterials in general, with a particular emphasis on carbon nanotubes and nanoparticles will be given in Chapter one. Chapter two provides a summary of common techniques used to grow carbon nanotubes, and introduces a new method we have developed. This method is based on previous chemical vapor deposition techniques, but uses liquids, specifically ethanol, as the carbon source. Using ethanol has several advantages, including ease of use and safety, as well as chemical benefits. Our new process affords long, aligned, single-walled nanotubes, with a relatively narrow diameter distribution. This method can also be used to grow CNTs across slits, which can then be studied spectroscopically. In Chapter three CNT-surfactant aqueous suspensions will be discussed in depth, including a new robust polymer surfactant. Poly(maleic acid/octyl vinyl ether) (PMAOVE) is stable over a large range of temperatures and pH values, and is well suited for the study of the oxidative chemistry that can occur on SWNT surfaces. Our aqueous suspensions were found to be quite stable by zeta potential studies and their emissive properties exhibited a pH dependence, quenching at higher concentrations of H+. We attribute this dependence to chemisorbed oxygen and its protonation at lower pH values. By heating the suspensions of SWNTs, O2 can be driven off, thus eliminating the dependence on pH. We also reproducibly add oxygen back into the system in the form of 1DeltaO2 , obtained from an endoperoxide. This method allows us to calculate the number of oxygen molecules needed for

  7. Research program to investigate the fundamental chemistry of technetium

    SciTech Connect

    Shuh, David K.; Lukens, Wayne W.; Burns, Carol J.

    2003-12-19

    The objective of this research is to increase the knowledge of the fundamental technetium chemistry that is necessary to address challenges to the safe, long-term remediation of high-level waste posed by this element. These challenges may be divided into two categories: unexpected behavior of technetium in high-level waste tanks at the Hanford and Savannah River Sites and the behavior of technetium in waste forms.

  8. Pattern recognition used to investigate multivariate data in analytical chemistry

    SciTech Connect

    Jurs, P.C.

    1986-06-06

    Pattern recognition and allied multivariate methods provide an approach to the interpretation of the multivariate data often encountered in analytical chemistry. Widely used methods include mapping and display, discriminant development, clustering, and modeling. Each has been applied to a variety of chemical problems, and examples are given. The results of two recent studies are shown, a classification of subjects as normal or cystic fibrosis heterozygotes and simulation of chemical shifts of carbon-13 nuclear magnetic resonance spectra by linear model equations.

  9. Properties Data for Adhesion and Surface Chemistry of Aluminum: Sapphire-Aluminum, Single-Crystal Couple

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Pohlchuck, Bobby; Whitle, Neville C.; Hector, Louis G., Jr.; Adams, Jim

    1998-01-01

    An investigation was conducted to examine the adhesion and surface chemistry of single-crystal aluminum in contact with single-crystal sapphire (alumina). Pull-off force (adhesion) measurements were conducted under loads of 0. I to I mN in a vacuum of 10(exp -1) to 10(exp -9) Pa (approx. 10(exp -10) to 10(exp -11) torr) at room temperature. An Auger electron spectroscopy analyzer incorporated directly into an adhesion-measuring vacuum system was primarily used to define the chemical nature of the surfaces before and after adhesion measurements. The surfaces were cleaned by argon ion sputtering. With a clean aluminum-clean -sapphire couple the mean value and standard deviation of pull-off forces required to separate the surfaces were 3015 and 298 micro-N, respectively. With a contaminated aluminum-clean sapphire couple these values were 231 and 241 micro-N. The presence of a contaminant film on the aluminum surface reduced adhesion by a factor of 13. Therefore, surfaces cleanliness, particularly aluminum cleanliness, played an important role in the adhesion of the aluminum-sapphire couples. Pressures on the order of 10(exp -8) to 10(exp -9) Pa (approx. 10(exp -10) to 10(exp -11) torr) maintained a clean aluminum surface for only a short time (less then 1 hr) but maintained a clean sapphire surface, once it was achieved, for a much longer time.

  10. Combined effects of surface conditions, boundary layer dynamics and chemistry on diurnal SOA evolution

    NASA Astrophysics Data System (ADS)

    Janssen, R. H. H.; Vilà-Guerau de Arellano, J.; Ganzeveld, L. N.; Kabat, P.; Jimenez, J. L.; Farmer, D. K.; van Heerwaarden, C. C.; Mammarella, I.

    2012-08-01

    We study the combined effects of land surface conditions, atmospheric boundary layer dynamics and chemistry on the diurnal evolution of biogenic secondary organic aerosol in the atmospheric boundary layer, using a model that contains the essentials of all these components. First, we evaluate the model for a case study in Hyytiälä, Finland, and find that it is able to satisfactorily reproduce the observed dynamics and gas-phase chemistry. We show that the exchange of organic aerosol between the free troposphere and the boundary layer (entrainment) must be taken into account in order to explain the observed diurnal cycle in organic aerosol (OA) concentration. An examination of the budgets of organic aerosol and terpene concentrations show that the former is dominated by entrainment, while the latter is mainly driven by emission and chemical transformation. We systematically investigate the role of the land surface, which governs both the surface energy balance partitioning and terpene emissions, and the large-scale atmospheric process of vertical subsidence. Entrainment is especially important for the dilution of organic aerosol concentrations under conditions of dry soils and low terpene emissions. Subsidence suppresses boundary layer growth while enhancing entrainment. Therefore, it influences the relationship between organic aerosol and terpene concentrations. Our findings indicate that the diurnal evolution of secondary organic aerosols (SOA) in the boundary layer is the result of coupled effects of the land surface, dynamics of the atmospheric boundary layer, chemistry, and free troposphere conditions. This has potentially some consequences for the design of both field campaigns and large-scale modeling studies.

  11. Investigating Titan's Atmospheric Chemistry at Low Temperature with the Titan Haze Simulation Experiment

    NASA Astrophysics Data System (ADS)

    Sciamma-O'Brien, E. M.; Salama, F.

    2012-12-01

    Titan, Saturn's largest satellite, possesses a dense atmosphere (1.5 bar at the surface) composed mainly of N2 and CH4. The solar radiation and electron bombardment from Saturn's magnetosphere induces a complex organic chemistry between these two constituents leading to the production of more complex molecules and subsequently to solid aerosols. These aerosols in suspension in the atmosphere form the haze layers giving Titan its characteristic orange color. Since 2004, the instruments onboard the Cassini orbiter have produced large amounts of observational data, unraveling a chemistry much more complex than what was first expected, particularly in Titan's upper atmosphere. Neutral, positively and negatively charged heavy molecules have been detected in the ionosphere of Titan, including benzene (C6H6) and toluene (C6H5CH3). The presence of these critical precursors of polycyclic aromatic hydrocarbon (PAH) compounds suggests that PAHs might play a role in the production of Titan's aerosols. The aim of the Titan Haze Simulation (THS) experiment, developed at the NASA Ames COSmIC facility, is to study the chemical pathways that link the simple molecules resulting from the first steps of the N2-CH4 chemistry to benzene, and to PAHs and nitrogen-containing PAHs (PANHs) as precursors to the production of solid aerosols. In the THS experiment, Titan's atmospheric chemistry is simulated by plasma in the stream of a supersonic expansion. With this unique design, the gas mixture is cooled to Titan-like temperature (~150K) before inducing the chemistry by plasma discharge. Due to the short residence time of the gas in the plasma discharge, the THS experiment can be used to probe the first and intermediate steps of Titan's chemistry by injecting different gas mixtures in the plasma. The products of the chemistry are detected and studied using two complementary techniques: Cavity Ring Down Spectroscopy and Time-Of-Flight Mass Spectrometry. Thin tholin deposits are also produced

  12. Mimicking enzymatic active sites on surfaces for energy conversion chemistry.

    PubMed

    Gutzler, Rico; Stepanow, Sebastian; Grumelli, Doris; Lingenfelder, Magalí; Kern, Klaus

    2015-07-21

    Metal-organic supramolecular chemistry on surfaces has matured to a point where its underlying growth mechanisms are well understood and structures of defined coordination environments of metal atoms can be synthesized in a controlled and reproducible procedure. With surface-confined molecular self-assembly, scientists have a tool box at hand which can be used to prepare structures with desired properties, as for example a defined oxidation number and spin state of the transition metal atoms within the organic matrix. From a structural point of view, these coordination sites in the supramolecular structure resemble the catalytically active sites of metallo-enzymes, both characterized by metal centers coordinated to organic ligands. Several chemical reactions take place at these embedded metal ions in enzymes and the question arises whether these reactions also take place using metal-organic networks as catalysts. Mimicking the active site of metal atoms and organic ligands of enzymes in artificial systems is the key to understanding the selectivity and efficiency of enzymatic reactions. Their catalytic activity depends on various parameters including the charge and spin configuration in the metal ion, but also on the organic environment, which can stabilize intermediate reaction products, inhibits catalytic deactivation, and serves mostly as a transport channel for the reactants and products and therefore ensures the selectivity of the enzyme. Charge and spin on the transition metal in enzymes depend on the one hand on the specific metal element, and on the other hand on its organic coordination environment. These two parameters can carefully be adjusted in surface confined metal-organic networks, which can be synthesized by virtue of combinatorial mixing of building synthons. Different organic ligands with varying functional groups can be combined with several transition metals and spontaneously assemble into ordered networks. The catalytically active metal

  13. Molecular metal catalysts on supports: organometallic chemistry meets surface science.

    PubMed

    Serna, Pedro; Gates, Bruce C

    2014-08-19

    -support bonding and structure, which identify the supports as ligands with electron-donor properties that influence reactivity and catalysis. Each of the catalyst design variables has been varied independently, illustrated by mononuclear and tetranuclear iridium on zeolite HY and on MgO and by isostructural rhodium and iridium (diethylene or dicarbonyl) complexes on these supports. The data provide examples resolving the roles of the catalyst design variables and place the catalysis science on a firm foundation of organometallic chemistry linked with surface science. Supported molecular catalysts offer the advantages of characterization in the absence of solvents and with surface-science methods that do not require ultrahigh vacuum. Families of supported metal complexes have been made by replacement of ligands with others from the gas phase. Spectroscopically identified catalytic reaction intermediates help to elucidate catalyst performance and guide design. The methods are illustrated for supported complexes and clusters of rhodium, iridium, osmium, and gold used to catalyze reactions of small molecules that facilitate identification of the ligands present during catalysis: alkene dimerization and hydrogenation, H-D exchange in the reaction of H2 with D2, and CO oxidation. The approach is illustrated with the discovery of a highly active and selective MgO-supported rhodium carbonyl dimer catalyst for hydrogenation of 1,3-butadiene to give butenes. PMID:25036259

  14. Spatial And Temporal Variation In The Dissolved Trace Element Chemistry Of Chesapeake Bay Surface Waters

    NASA Astrophysics Data System (ADS)

    Dorval, E.; Hannigan, R.; Jones, C.

    2001-12-01

    Surface waters were collected from sea grass beds around the Chesapeake Bay of Virginia as well as from the mouths of the York, James, Potomac and Rappahannock rivers and Tangier and Smith islands. These sea grass beds represent the nursery habitats for a variety of sport fish including Spotted Sea Trout and Weakfish. Trace element ratios of fish otoliths record the unique chemistries of bodies of water in which the fish live. The data presented here represent the initial results of a "ground-truthing" investigation of the relationships between the water and otolith chemistry. Waters were collected bi-monthly (July through September) from 30 sites around the western and eastern shore of Chesapeake Bay including major tributaries and Tangier and Smith islands. Water was collected using trace metal clean procedures including filtration through a 0.45 uM filter and acidification in the field to pH < 2 with ultra-pure nitric acid. Dissolved trace element composition was measured by sector field ICP-MS. The trace element chemistry of samples show both spatial and temporal variation. Using discriminant analysis it is not possible to statistically classify samples to the respective zones (western shore, eastern shore or islands) but it is possible to separate samples from the Tangier and Smith island sites from the eastern and western shore sites. Elements that allow this classification include Ce and Th, which are found in higher concentration in the samples from the island sites than in the eastern and western shore samples. These relationships follow the trends observed in pH and dissolved oxygen likely related to a restricted flow regime between the islands and the eastern shore. Mg/Ca and Sr/Ca ratios are unique for the sea grass beds along the western shore and allow the distinction of beds located between the York and Rappahannock rivers from those between the Rappahannock and Potomac rivers. Sr and Ba concentrations are variable between sites along the eastern

  15. Tuning of nanoparticle biological functionality through controlled surface chemistry and characterisation at the bioconjugated nanoparticle surface

    NASA Astrophysics Data System (ADS)

    Hristov, Delyan R.; Rocks, Louise; Kelly, Philip M.; Thomas, Steffi S.; Pitek, Andrzej S.; Verderio, Paolo; Mahon, Eugene; Dawson, Kenneth A.

    2015-12-01

    We have used a silica - PEG based bionanoconjugate synthetic scheme to study the subtle connection between cell receptor specific recognition and architecture of surface functionalization chemistry. Extensive physicochemical characterization of the grafted architecture is capable of capturing significant levels of detail of both the linker and grafted organization, allowing for improved reproducibility and ultimately insight into biological functionality. Our data suggest that scaffold details, propagating PEG layer architecture effects, determine not only the rate of uptake of conjugated nanoparticles into cells but also, more significantly, the specificity of pathways via which uptake occurs.

  16. The Consequences of Surface Confinement on Free Radical Chemistry

    SciTech Connect

    Birtt, P.F.; Buchanan, A.C., III

    1999-08-22

    Mass transport limitations impact the thermochemical processing of fossil and renewable energy resources, which involves the breakdown of cross-linked, macromolecular networks. To Investigate the molecular level details of the consequences of molecular confinement on high temperature (275-500°C) free-radical reaction pathways, we have been examining the pyrolysis of model compounds attached to the surface of non-porous silica nanoparticles through a thermally robust Si-O-Caryl, tetha. Pyrolysis of silica-immobilized diphenylalkanes and related ethers have been studied in detail and compared with the corresponding behavior in fluid phases. The diffusional constraints can lead to reduced rates of radical termination on the surface, and enhancement of neophyl-like rearrangements, cyclization-dehydrogenation pathways, and ipso- aromatic substitutions. Furthermore, studies of two-component surfaces have revealed the importance of a radical relay mechanism involving rapid serial hydrogen transfer steps resulting from the molecular pre-organization on the low fractal dimension silica surface. Key findings are reviewed in this paper, and the implications of these results for fuel processing are described.

  17. Aluminum in acidic surface waters: chemistry, transport, and effects.

    PubMed Central

    Driscoll, C T

    1985-01-01

    Ecologically significant concentrations of Al have been reported in surface waters draining "acid-sensitive" watersheds that are receiving elevated inputs of acidic deposition. It has been hypothesized that mineral acids from atmospheric deposition have remobilized Al previously precipitated within the soil during soil development. This Al is then thought to be transported to adjacent surface waters. Dissolved mononuclear Al occurs as aquo Al, as well as OH-, F-, SO4(2-), and organic complexes. Although past investigations have often ignored non-hydroxide complexes of Al, it appears that organic and F complexes are the predominant forms of Al in dilute (low ionic strength) acidic surface waters. The concentration of inorganic forms of Al increases exponentially with decreases in solution pH. This response is similar to the theoretical pH dependent solubility of Al mineral phases. The concentration of organic forms of Al, however, is strongly correlated with variations in organic carbon concentration of surface waters rather than pH. Elevated concentrations of Al in dilute acidic waters are of interest because: Al is an important pH buffer; Al may influence the cycling of important elements like P, organic carbon, and trace metals; and Al is potentially toxic to aquatic organisms. An understanding of the aqueous speciation of Al is essential for an evaluation of these processes. PMID:3935428

  18. Roles of surface chemistry on safety and electrochemistry in lithium ion batteries.

    PubMed

    Lee, Kyu Tae; Jeong, Sookyung; Cho, Jaephil

    2013-05-21

    Motivated by new applications including electric vehicles and the smart grid, interest in advanced lithium ion batteries has increased significantly over the past decade. Therefore, research in this field has intensified to produce safer devices with better electrochemical performance. Most research has focused on the development of new electrode materials through the optimization of bulk properties such as crystal structure, ionic diffusivity, and electric conductivity. More recently, researchers have also considered the surface properties of electrodes as critical factors for optimizing performance. In particular, the electrolyte decomposition at the electrode surface relates to both a lithium ion battery's electrochemical performance and safety. In this Account, we give an overview of the major developments in the area of surface chemistry for lithium ion batteries. These ideas will provide the basis for the design of advanced electrode materials. Initially, we present a brief background to lithium ion batteries such as major chemical components and reactions that occur in lithium ion batteries. Then, we highlight the role of surface chemistry in the safety of lithium ion batteries. We examine the thermal stability of cathode materials: For example, we discuss the oxygen generation from cathode materials and describe how cells can swell and heat up in response to specific conditions. We also demonstrate how coating the surfaces of electrodes can improve safety. The surface chemistry can also affect the electrochemistry of lithium ion batteries. The surface coating strategy improved the energy density and cycle performance for layered LiCoO2, xLi2MnO3·(1 - x)LiMO2 (M = Mn, Ni, Co, and their combinations), and LiMn2O4 spinel materials, and we describe a working mechanism for these enhancements. Although coating the surfaces of cathodes with inorganic materials such as metal oxides and phosphates improves the electrochemical performance and safety properties of

  19. Degradation of Environmental Contaminants with Water-Soluble Cobalt Catalysts: An Integrative Inorganic Chemistry Investigation

    ERIC Educational Resources Information Center

    Evans, Alexandra L.; Messersmith, Reid E.; Green, David B.; Fritsch, Joseph M.

    2011-01-01

    We present an integrative laboratory investigation incorporating skills from inorganic chemistry, analytical instrumentation, and physical chemistry applied to a laboratory-scale model of the environmental problem of chlorinated ethylenes in groundwater. Perchloroethylene (C[subscript 2]Cl[subscript 4], PCE) a common dry cleaning solvent,…

  20. Using Think-Aloud Protocols to Investigate Secondary School Chemistry Teachers' Misconceptions about Chemical Equilibrium

    ERIC Educational Resources Information Center

    Cheung, Derek

    2009-01-01

    Secondary school chemistry teachers' understanding of chemical equilibrium was investigated through interviews using the think-aloud technique. The interviews were conducted with twelve volunteer chemistry teachers in Hong Kong. Their teaching experience ranged from 3 to 18 years. They were asked to predict what would happen to the equilibrium…

  1. An Investigation of College Chemistry Students' Understanding of Structure-Property Relationships

    ERIC Educational Resources Information Center

    Cooper, Melanie M.; Corley, Leah M.; Underwood, Sonia M.

    2013-01-01

    The connection between the molecular-level structure of a substance and its macroscopic properties is a fundamental concept in chemistry. Students in college-level general and organic chemistry courses were interviewed to investigate how they used structure-property relationships to predict properties such as melting and boiling points. Although…

  2. Electronically non-adiabatic influences in surface chemistry and dynamics.

    PubMed

    Wodtke, Alec M

    2016-07-01

    Electronically nonadiabatic interactions between molecules and metal surfaces are now well known. Evidence is particularly clear from studies of diatomic molecules that molecular vibration can be strongly coupled to electrons of the metal leading to efficient energy transfer between these two kinds of motion. Since molecular vibration is the same motion needed for bond breaking, it is logical to postulate that electronically nonadiabatic influences on surface chemical reaction probabilities would be strong. Still there are few if any examples where such influences have been clearly investigated. This review recounts the evidence for and against the aforementioned postulate emphasizing reacting systems that have yet to receive full attention and where electronically nonadiabatic influence of reaction probabilities might be clearly demonstrated. PMID:27152489

  3. Ice surface chemistry relevant to stratospheric ozone depletion

    NASA Astrophysics Data System (ADS)

    Geiger, Franz Martin

    The surface specific nonlinear laser spectroscopy method second harmonic generation (SHG) is used to investigate the heterogeneously catalyzed hydrolysis of chlorine nitrate (ClONO2) on ice, a key reaction in stratospheric ozone depletion occurring in the presence of polar stratospheric cloud (PSC) ice particles formed during the polar winter. The reaction, yielding hypochlorous acid (HOCl) and nitric acid (HNO3), is studied directly and in real time on a single crystal basal ice (Ih) surface maintained under typical conditions of the polar stratosphere. The ice crystal is kept in equilibrium with its vapor pressure. Polarization studies are consistent with the clean basal ice surface at 158K being 3m symmetric, in contrast to proposals by others that the surface is disordered. The symmetry is retained upon HNO3 adsorption; this observation disagrees with proposals by others that this could cause surface melting. A SHG spectrum from 290 to 310 nm is obtained from HOCl on ice; this spectrum resembles the electronic spectrum of HOCl and serves as an identification tool for adsorbed HOCl. HOCl adsorption onto ice is instantaneous and occurs in registry with the underlying ice lattice. Measured isothermal rate constants for HOCl desorption from ice result in an activation energy for desorption of 36 +/- 2 kJ/mol. When submonolayer amounts of ClONO2 are hydrolyzed on the ice surface, the SHG vs. time traces show no changes for hundreds of seconds, then a sigmoidal increase, and eventually a constant value. The SHG increase is related to the appearance of HOCl. Predosing experiments show that the delay times are due to autocatalysis, with the HOCl product being a possible autocatalyst. The HNO3 co-product, on the other hand, acts as a surface poison and inhibits HOCl desorption. A molecular reaction mechanism, based on one proposed by Bianco and Hynes, is presented and discussed in light of the obtained experimental data, supporting ab initio calculations, and numerical

  4. Elementary surface chemistry during CuO/Al nanolaminate-thermite synthesis: copper and oxygen deposition on aluminum (111) surfaces.

    PubMed

    Lanthony, Cloé; Guiltat, Mathilde; Ducéré, Jean Marie; Verdier, Agnes; Hémeryck, Anne; Djafari-Rouhani, Mehdi; Rossi, Carole; Chabal, Yves J; Estève, Alain

    2014-09-10

    The surface chemistry associated with the synthesis of energetic nanolaminates controls the formation of the critical interfacial layers that dominate the performances of nanothermites. For instance, the interaction of Al with CuO films or CuO with Al films needs to be understood to optimize Al/CuO nanolaminates. To that end, the chemical mechanisms occurring during early stages of molecular CuO adsorption onto crystalline Al(111) surfaces are investigated using density functional theory (DFT) calculations, leading to the systematic determination of their reaction enthalpies and associated activation energies. We show that CuO undergoes dissociative chemisorption on Al(111) surfaces, whereby the Cu and O atoms tend to separate from each other. Both Cu and O atoms form islands with different properties. Copper islanding fosters Cu insertion (via surface site exchange mechanism) into the subsurface, while oxygen islands remain stable at the surface. Above a critical local oxygen coverage, aluminum atoms are extracted from the Al surface, leading to oxygen-aluminum intermixing and the formation of aluminum oxide (γ-alumina). For Cu and O co-deposition, copper promotes oxygen-aluminum interaction by oxygen segregation and separates the resulting oxide from the Al substrate by insertion into Al and stabilization below the oxide front, preventing full mixing of Al, Cu, and O species. PMID:25089744

  5. Monsoon Season Surface Water Chemistry Response Following Wildfire: 2003 Aspen Fire in Sabino Canyon, Arizona

    NASA Astrophysics Data System (ADS)

    Einloth, S. L.; Chief, K. D.; Ekwurzel, B.; Nijssen, B.; Ferré, P. A.

    2003-12-01

    The Aspen Fire in the Coronado National Forest north of Tucson burned in excess of 80,000 acres and destroyed more than 300 structures. Exposed, burned soils are highly vulnerable to intense monsoon rains, leading to increases in surface runoff, peak flows, and erosion rates. As part of an integrated investigation of the hydrologic impacts of this fire, we rapidly mobilized a field sampling campaign during the 2003 monsoon season that began immediately following the resolution of the fire. Stream water chemistry serves as an integrated signal of many watershed processes: precipitation, runoff, infiltration, soil hydrophobic layers, ash deposition in the stream, debris flows, and subsequent water/ash chemical equilibrium reactions. The portion of the watershed that has been burned by the Aspen fire covers a wide range of elevation and vegetation zones of the Santa Catalina Mountains. Many biogeochemical and hydrological processes within this area were altered by a sudden lack of vegetation and changes in soil properties following a fire: evapotranspiration, litter volume, organic decomposition, leaching, cation exchange, anion sorption, nutrient uptake, and soil hydrophobic layers. Surface water and precipitation samples were collected following an event-based sampling strategy, while soil samples were collected in each vegetation and burn severity regime. Precipitation samples were collected to characterize temperature and elevation effects on precipitation chemistry, in particular stable isotopes. The surface water chemistry changes measured throughout each hydrograph event can be linked to air permeameter results, a rapid measurement for soil hydraulic conductivity, for the different burn severity and vegetation zone regimes. Both nutrient and suspended sediment loads greatly increased following the fire. A debris flow mobilized large diameter boulders. Stream gauge flow event peaks were larger than expected given concurrent extensive precipitation gauge network

  6. Surface Chemistry of Nanocellulose Fibers Directs Monocyte/Macrophage Response.

    PubMed

    Hua, Kai; Ålander, Eva; Lindström, Tom; Mihranyan, Albert; Strømme, Maria; Ferraz, Natalia

    2015-09-14

    The effect of surface functionalization of nanofibrillated cellulose (NFC) on monocyte/macrophage (MM) behavior is investigated to understand how the physicochemical properties of nanocelluloses influence the interactions of such materials with biological systems. Films of anionic (a-), cationic (c-), and unmodified (u-) NFC were synthesized and characterized in terms of surface charge. THP-1 monocytes were cultured on the surface of the films for 24 h in the presence and absence of lipopolysaccharide, and the cell response was evaluated in terms of cell adhesion, morphology, and secretion of TNF-α, IL-10, and IL-1ra. The results show that MMs cultured on carboxymethylated-NFC films (a-NFC) are activated toward a proinflammatory phenotype, whereas u-NFC promotes a mild activation of the studied cells. The presence of hydroxypropyltrimethylammonium groups on c-NFC, however, does not promote the activation of MMs, indicating that c-NFC closely behaves as an inert material in terms of MM activation. None of the materials is able to directly activate the MMs toward an anti-inflammatory response. These results may provide a foundation for the design of future NFC-based materials with the ability to control MM activation and may expand the use of NFC in biomedical applications. PMID:26247827

  7. Surface chemistry of hierarchical nanosprings for sensing and catalysis

    NASA Astrophysics Data System (ADS)

    Fouetio Kengne, Blaise-Alexis

    Silica nanosprings (NS) were grown and their surface chemistry was modified depending upon the application. For explosive detection, NS were subsequently coated with ZnO, decorated with metal nanoparticles, and functionalized with thiols; while NS supported cobalt catalysts (Co/NS) were prepared for Fischer-Tropsch synthesis (FTS). Scanning and transmission electron microscopies (SEM and TEM), X-ray diffraction (XRD), N2 physisorption, H2-temperatature programmed reduction (H2-TPR, and X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) have been used to characterize the hierarchical NS. Based on XPS analysis of the thiolated NS, a single S 2p core level is observed for 4-mercaptobenzoic acid and11-(1-pyrenyl)-1-undecathiol, which is assigned to the S-Au bond. The S 2p core level of L-cysteine, 6-mercaptohexanol and DL-thioctic acid consists of two doublets, where one is S-Au bond and the other is the S-Zn bond. UPS analysis shows that the hybridization of the S 3p states and the Au d-bands produces antibonding and bonding states, above and below the Au d-bands, which is characteristic of molecular chemisorption on Au nanoparticles. Gas sensors functionalized with functionalized with 4-mercaptobenzoic acid and 6-mercaptohexanol showed the strongest responses to ammonium nitrate by factors of 4 to 5, respectively, relative to the less responsive thiols. For FTS, even though Co/NS had 75 times less gravimetric Co content than the reference catalyst, without being fully reduced, it still showed higher activity. This is attributed to higher Co dispersion on NS and greater gases acessibility. In situ XPS has been used to monitor the reduction of Co/NS. The analysis shows that cobalt is present in the starting catalyst as a Co 3O4 spinel phase. At 385 ºC and 10-6 Torr of H2 a two-step reduction from Co3O4 to CoO and then to Co0 is observed, which is consistent with H2-TPR results. The two reduction steps are concurrent. The reduction saturates at the value

  8. Investigating the impact of adding an environmental focus to a developmental chemistry class

    NASA Astrophysics Data System (ADS)

    Robelia, Beth A.

    Making chemistry more relevant to students has been a goal of many curriculum projects. None of these projects have investigated how specific applications of chemistry impact student learning or environmental mindset. The goal of this study was to examine how focusing attention on environmental issues as applications of chemistry concepts would affect students' understanding of general chemistry or environmental chemistry as well environmental attitudes, behaviors and knowledge. Special attention was paid to how women responded to the addition of an environmental focus because prior research indicated women hold more pro-environmental attitudes but are less knowledgeable about environmental topics. The quasi-experimental design used two treatment groups and a comparison group. Both treatment groups received instruction with a Science-Technology-Society orientation, one group focused on environmental applications of chemistry while the other drew applications of chemistry from a number of different fields students might be familiar with such as health care, food science and forensics. The comparison groups used mainly traditional examples from chemistry laboratories. In order to avoid testing the effect of the instructor, two people co-taught both treatment sections. Students in all three groups took a general chemistry assessment at the beginning and end of the course. The treatment groups took a pre and post environmental chemistry assessment and a survey of their environmental attitudes, behaviors and knowledge. Results indicate that students in the environmentally focused section may have made slight gains in general chemistry knowledge. Gains in environmental chemistry knowledge were not significantly different. Students also made modest gains in environmental attitude. Results for women mirrored results for the classes as a whole.

  9. Research Program to Investigate the Fundamental Chemistry of Technetium

    SciTech Connect

    Edelstein, Norman M.; Burns, Carol J.; Shuh, David D.; Lukens, Wayne

    2000-06-01

    Technetium (99Tc, half-life = 2.13x105 years, b-emitter) is one of the radionuclides of major concern for nuclear waste disposal. This concern is due to the long half-life of 99Tc, the ease with which pertechnetate, TcO4 -, migrates in the geosphere, and the corresponding regulatory considerations. The problem of mobility of pertechnetate in the environment is compounded by the fact that pertechnetate is the thermodynamically stable form of technetium in aerobic environments. These two factors present challenges for the safe, long term immobilization of technetium in waste forms. Because of the stability of pertechnetate, technetium has been assumed to exist as pertechnetate in the aqueous phase of nuclear waste tanks. However, recent studies indicate that a significant fraction of the technetium is in a different chemical form. This program addresses the fundamental solution chemistry of technetium in the waste tank environment, and in a second part, the stability of technetium in various waste forms. The chemistry of this element will be studied in aqueous solutions at high pH, with various added salts such as nitrate, nitrite, and organic complexants, and as a function of radiation dose, to determine whether radiolysis effects can reduce TcO4 -. A separate facet of this research is the search for chemical forms of technetium that may be thermodynamically and/or kinetically stable and may be incorporated in various waste forms for long term storage. This phase of the program will address the problem of the possible oxidation of lower valent technetium species in various waste form matrices and the subsequent leaching of the highly soluble TcO4 -.

  10. FROZEN GROUND CONTROL ON SNOWMELT FLOWPATHS AND SURFACE WATER CHEMISTRY IN TWO ALPINE BASINS

    EPA Science Inventory

    This study will increase our understanding of how snowmelt flowpaths are influenced by frozen ground in mid-latitude alpine basins. It also will elucidate how these flowpaths dictate surface water chemistry in relation to snowmelt.

  11. Regional relationships between geomorphic/hydrologic parameters and surface water chemistry relative to acidic deposition

    SciTech Connect

    Rochelle, B.P.; Liff, C.I.; Campbell, W.G.; Cassell, D.L.; Church, M.R.

    1989-01-01

    The authors determined geomorphic and hydrologic parameters for 144 forested, lake watersheds in the Northeast (NE) of the United States based primarily on measurements from topographic maps. These parameters were used to test for relationships with selected surface water chemistry relevant to acidic deposition. Analyses were conducted on regional and subregional scales delineated based on soils, land use, physiography, total sulfur deposition and statistical clustering of selected geomorphic/hydrologic parameters. Significant relationships were found among the geomorphic/hydrologic parameters and the surface water chemistry for the NE. Elevation had the most significant relationship with surface water chemistry, particularly in the mountainous areas of the NE. Other factors occurring consistently as significant predictors of surface water chemistry were maximum relief, relief ratio, runoff, and estimates of basin elongation. Results suggest that elevational parameters might be surrogates for other watershed characteristics, such as soils or spatial deposition patterns.

  12. Bactericidal effects of plasma-modified surface chemistry of silicon nanograss

    NASA Astrophysics Data System (ADS)

    Ostrikov, Kola; Macgregor-Ramiasa, Melanie; Cavallaro, Alex; (Ken Ostrikov, Kostya; Vasilev, Krasimir

    2016-08-01

    The surface chemistry and topography of biomaterials regulate the adhesion and growth of microorganisms in ways that are still poorly understood. Silicon nanograss structures prepared via inductively coupled plasma etching were coated with plasma deposited nanometer-thin polymeric films to produce substrates with controlled topography and defined surface chemistry. The influence of surface properties on Staphylococcus aureus proliferation is demonstrated and explained in terms of nanograss substrate wetting behaviour. With the combination of the nanograss topography; hydrophilic plasma polymer coatings enhanced antimicrobial activity while hydrophobic coatings reduced it. This study advances the understanding of the effects of surface wettability on the bactericidal properties of reactive nano-engineered surfaces.

  13. Combining hierarchical surface roughness with fluorinated surface chemistry to preserve superhydrophobicity after organic contamination

    NASA Astrophysics Data System (ADS)

    Wang, Chih-Feng; Hung, Shih-Wei; Kuo, Shiao-Wei; Chang, Chi-Jung

    2014-11-01

    Surfaces exhibiting superhydrophobicity are attracting commercial and academic attention because of their potential applications in, for example, self-cleaning utensils, microfluidic systems, and microelectronic devices. In this study, we prepared a fluorinated superhydrophobic surface displaying nanoscale roughness, a superhydrophobic surface possessing a micro- and nanoscale binary structure, and a fluorinated superhydrophobic surface possessing such a binary structure. We investigated the effects of the (i) hierarchy of the surface topography and (ii) the surface chemical composition of the superhydrophobic carbon nanotube/polybenzoxazine coatings on their ability to retain superhydrophobicity upon contamination with particles and organic matter, an important characteristic for maintaining non-wetting properties under outdoor conditions. We have found that the topographical microstructure and the surface chemical composition are both important factors for preservation of the non-wetting properties of such superhydrophobic surfaces upon contamination with organic matter.

  14. Rosetta/VIRTIS investigation of the chemistry and activity of comet 67P/Churyumov-Gerasimenko

    NASA Astrophysics Data System (ADS)

    Bockelee-Morvan, Dominique; Drossart, Pierre; Piccioni, Giuseppe; Migliorini, Alessandra; Erard, Stéphane; Capaccioni, Fabrizio; Filacchione, Gianrico; Fougere, Nicolas; Leyrat, Cedric; Crovisier, Jacques; Capaccioni, Fabrizio

    2016-07-01

    The composition of cometary ices inside cometary nuclei provides clues to the chemistry of the protoplanetary disk where they formed, 4.6 Gyr ago. These ices sublimate when the body approches the Sun, so that the coma molecular species give insights on the nucleus surface and sub-surface composition. So far, most investigations of the coma chemical composition were performed from telescopic observations from the ground or space plateforms. Since August 2014, the ESA/Rosetta spacecraft has been investigating the nucleus and inner coma of 67P/Churyumov-Gerasimenko. This talk will present an overview of the results obtained by the Visual and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument onboard Rosetta, focussing on observations of molecular species. VIRTIS is composed of two channels. The VIRTIS-M channel is a spectro-imager covering the 0.27-5.1 microns range, which allowed us to map the spatial distribution of H2O and CO2 (Migliorini et al. 2016, A&A in press). VIRTIS-H is a high-spectral resolution spectrometer covering the 2-5 microns range. Spectra obtained with VIRTIS-H show signatures of H2O, CO2 (both fundamental and hot bands), 13CO2, CH4 and other C-H bearing species (Bockelee-Morvan et al. A&A, 583, A6,2015). VIRTIS is a key instrument to investigate regional, diurnal and seasonal variations of the comet outgassing.

  15. Influence of the carbon fiber surface microstructure on the surface chemistry generated by a thermo-chemical surface treatment

    NASA Astrophysics Data System (ADS)

    Vautard, F.; Ozcan, S.; Paulauskas, F.; Spruiell, J. E.; Meyer, H.; Lance, M. J.

    2012-11-01

    Carbon fibers made of textile and aerospace grade polyacrylonitrile precursor fibers were surface treated by a continuous gas phase thermochemical treatment. The surface chemistry generated by the surface treatment was characterized by X-ray photoelectron spectroscopy. The surface and the average entire microstructure of the fibers were characterized by Raman spectroscopy and X-ray diffraction, respectively. Depending on the grade of the precursor, the final surface concentration of oxygen was comprised between 14% and 24%, whereas the typical commercial electrochemical surface treatments led to concentrations of around 8% with the same fibers. The final concentration of oxygen was directly correlated to the size of the crystallites which was a function of the grade of the polyacrylonitrile precursor and to the corresponding surface microstructure. The thermochemical surface treatment enabled a better control of the nature of the oxygen-containing functionalities as well. Whatever the grade of the precursor, desired hydroxyl groups and carboxylic acid functionalities were preferably generated, which is observed to be difficult with electrochemical surface treatments.

  16. Influence of the carbon fiber surface microstructure on the surface chemistry generated by a thermo-chemical surface treatment

    SciTech Connect

    Vautard, Frederic; Ozcan, Soydan; Paulauskas, Felix L; Spruiell, J. E.; Meyer III, Harry M; Lance, Michael J

    2012-01-01

    Carbon fibers made of textile and aerospace grade polyacrylonitrile precursor fibers were surface treated by a continuous gas phase thermo-chemical treatment. The surface chemistry generated by the surface treatment was characterized by X-ray photoelectron spectroscopy. The surface and the average entire micro-structure of the fibers were characterized by Raman spectroscopy and X-ray diffraction, respectively. Depending on the grade of the precursor, the final surface concentration of oxygen was comprised between 14% and 24%, whereas the typical commercial electro-chemical surface treatments led to concentrations of around 8% with the same fibers. The final concentration of oxygen was directly correlated to the size of the crystallites which was a function of the grade of the polyacrylonitrile precursor and to the corresponding surface micro-structure. The thermo-chemical surface treatment enabled a better control of the nature of the oxygen-containing functionalities as well. Whatever the grade of the precursor, desired hydroxyl groups and carboxylic acid functionalities were preferably generated, which was not observed with electro-chemical surface treatments.

  17. Random Phase Approximation in Surface Chemistry: Water Splitting on Iron.

    PubMed

    Karlický, František; Lazar, Petr; Dubecký, Matúš; Otyepka, Michal

    2013-08-13

    The reaction of water with zero-valent iron (anaerobic corrosion) is a complex chemical process involving physisorption and chemisorption events. We employ random phase approximation (RPA) along with gradient-corrected and hybrid density functional theory (DFT) functionals to study the reaction of water with the Fe atom and Fe(100) surface. We show that the involvement of the exact electron exchange and nonlocal correlation effects in RPA improves the description of all steps of the reaction on the Fe surface with respect to standard [meaning local density approximation (LDA) or generalized gradient approximation (GGA)] DFT methods. The reaction profile calculated by range-separated hybrid functional HSE06 agrees reasonably well with the RPA profile, which makes HSE06 a computationally less demanding alternative to RPA. We also investigate the reaction of the Fe atom with water using DFT, RPA, and coupled-cluster through the perturbative triples complete basis set [CCSD(T)-3s3p-DKH/CBS] method. Local DFT methods significantly underestimate reaction barriers, while the reaction kinetics and thermodynamics from RPA agree with the reference CCSD(T) data. Both systems, i.e., the Fe atom and Fe(100), provide the same reaction mechanism, indicating that anaerobic corrosion is a stepwise process involving one-electron steps, with the first reaction step (formation of the HFeOH intermediate) representing the rate-limiting step. PMID:26584120

  18. Effect of Surface Chemistry on Water Interaction with Cu(111).

    PubMed

    Antony, Andrew C; Liang, Tao; Akhade, Sneha A; Janik, Michael J; Phillpot, Simon R; Sinnott, Susan B

    2016-08-16

    The interfacial dynamics of water in contact with bare, oxidized, and hydroxylated copper surfaces are examined using classical molecular dynamics (MD) simulations. A third-generation charge-optimized many-body (COMB3) potential is used in the MD simulations to investigate the adsorption of water molecules on Cu(111), and the results are compared to the findings of density functional theory (DFT) calculations. The adsorption energies and structures predicted by COMB3 are generally consistent with those determined with DFT. The COMB3 potential is then used to investigate the wetting behavior of water nanodroplets on Cu(111) at 20, 130, and 300 K. At room temperature, the simulations predict that the spreading rate of the base radius, R0, of a water droplet with a diameter of about 1.5 nm exhibits a spreading rate of R0 ≈ t(0.16) and a final base radius of 3.5 nm. At 20 and 130 K, water droplets are predicted to retain their structure after adsorption on Cu(111) and to undergo minimal spreading in agreement with scanning tunneling microscopy data. When the same water droplet encounters a reconstructed, oxidized Cu(111) surface, the classical MD simulations predict wetting with a spreading rate of R ≈ t(0.14) and a final base radius of 3.0 nm. Similarly, our MD simulations predict a spreading rate of R ≈ t(0.14) and a final base radius of 2.5 nm when water encounters OH-covered Cu(111). These results indicate that oxidation and hydroxylation cause a reduction in the degree of spreading and final base radius that is directly associated with a decreased spreading rate for water nanodroplets on copper. PMID:27442055

  19. Comparison of surface modification chemistries in mouse, porcine, and human islets.

    PubMed

    SoRelle, Jeffrey A; Kanak, Mazhar A; Itoh, Takeshi; Horton, Joshua M; Naziruddin, Bashoo; Kane, Robert R

    2015-03-01

    Beta cell replacement therapy, the transplantation of isolated pancreatic islets by intraportal infusion, offers patients with brittle type 1 diabetes blood glucose regulation with a minimally invasive technique. Chemical modification of islets prior to transplantation, providing a nanothin barrier that potentially includes active protective compounds, has been proposed as a strategy to minimize the inflammatory and immune reactions that often significantly limit graft function and duration. Chemical modification also has the potential to allow the use of alternative sources of islets, such as porcine islets, for transplantation. This investigation compared three orthogonal covalent islet modification techniques across three species (human, porcine, and murine), using multiple measures to determine biocompatibility and effectiveness. All three conjugation chemistries were well tolerated, and the overall efficiency, gross uniformity, and stability of the surface modifications were dependent upon the conjugation chemistry as well as the islet source (human, porcine, or murine). Notably, the reductive modification of surface disulfides was shown to afford intense and long-lasting modification of human islets. This study demonstrates that murine, human, and porcine islets tolerate a variety of covalent modifications, that these modifications are relatively stable, and that the murine islet model may not be predictive for some chemical contexts. PMID:24829144

  20. Seventh BES (Basic Energy Sciences) catalysis and surface chemistry research conference

    SciTech Connect

    Not Available

    1990-03-01

    Research programs on catalysis and surface chemistry are presented. A total of fifty-seven topics are included. Areas of research include heterogeneous catalysis; catalysis in hydrogenation, desulfurization, gasification, and redox reactions; studies of surface properties and surface active sites; catalyst supports; chemical activation, deactivation; selectivity, chemical preparation; molecular structure studies; sorption and dissociation. Individual projects are processed separately for the data bases. (CBS)

  1. Surface and coordination chemistry related to GaAs

    NASA Astrophysics Data System (ADS)

    Keys, Andrea

    The vapor phase structures of Al(tBU)3 and Ga(tBU)3 have been investigated by gas phase electron diffraction and consist of planar three-coordinate monomers. Salient structural parameters (ra) include: Al-C = 2.005(3) A, Ga-C = 2.034(2) A. The geometries are controlled by inter-ligand interactions. The electron diffraction structures are compared to those determined by ab initio calculations for M(tBU)3 (M = Al, Ga, In). To understand the most suitable linkages for the surface of GaAs, model compounds were synthesized by reacting Ga(tBU)3 and [tBu2Ga(mu-Cl]2 with one molar equivalent of varying ligands. The synthesized compounds include chlorides, benzenethiolate, dithiocarbamates, carboxylates, amides, benzohydroxamate, and phenylphosphonate. The Ga ⋯ Ga and Ga-ligand interatomic distances for these compounds, as well as Group 15 and 16 donor bridging ligands, are compared to the values for the surface of GaAs and cubic-GaS in order to determine their suitability as linkage groups for self-assembled monolayers. The most suitable linkages were determined to be benzenethiol and phenylphophonic acid, and these were used to grow self-assembled monolayers on {100} GaAs. Carboxylic acid was also used, to determine the success of the organometallic model compounds in predicting the suitability of ligands for surface reaction. Self-assembled monolayers were also grown on Al2O3, using carboxylic acids and phenylphosphonic acids as the surface linkages. Metallo-organic chemical vapor deposition was performed using single-source precursors ( tBU)2Ga(S2CNR2). The tert -butyl gallium bis-dialkyl-dithiocarbamate compounds, (tBu)Ga(S2CNR2)2, are formed as minor products via ligand disproportionation reactions. Gallium sulfide (GaS) thin films have been grown at 375-425°C by atmospheric pressure metal-organic chemical vapor deposition using compounds (tBu) 2Ga(S2CNMe2) and (tBu)2Ga(S 2CNEt2) as single source precursors. Polycrystalline samples of the chalcogenides InSe, In2Se3

  2. Research program to investigate the fundamental chemistry of technetium

    SciTech Connect

    McKeown, David A.; Buechele, Andrew C.; Lukens, Wayne W.; Muller, Isabelle S.; Shuh, David K.; Pegg, Ian L.

    2007-10-12

    The objective of this research is to increase the knowledge of the fundamental technetium chemistry necessary to address challenges to the safe, long-term disposal of high-level nuclear waste posed by this element. The primary issues examined during the course of this project were the behavior of technetium and its surrogate rhenium during waste vitrification and glass corrosion. Since the redox behavior of technetium can play a large role in determining its volatility, one goal of this research was to better understand the behavior of technetium in glass as a function of the redox potential of the glass melt. In addition, the behavior of rhenium was examined, since rhenium is commonly used as a surrogate for technetium in waste vitrification studies. A number of glasses similar to Hanford Low Activity Waste (LAW) glasses were prepared under controlled atmospheres. The redox state of the glass was determined from the Fe(II)/Fe(III) ratio in the cooled glass, and the speciation of technetium and rhenium was determined by x-ray absorption fine structure (XAFS) spectroscopy. The behavior of rhenium and technetium during glass alteration was also examined using the vapor hydration test (VHT).

  3. Spectroscopic and computational investigation of actinium coordination chemistry.

    PubMed

    Ferrier, Maryline G; Batista, Enrique R; Berg, John M; Birnbaum, Eva R; Cross, Justin N; Engle, Jonathan W; La Pierre, Henry S; Kozimor, Stosh A; Lezama Pacheco, Juan S; Stein, Benjamin W; Stieber, S Chantal E; Wilson, Justin J

    2016-01-01

    Actinium-225 is a promising isotope for targeted-α therapy. Unfortunately, progress in developing chelators for medicinal applications has been hindered by a limited understanding of actinium chemistry. This knowledge gap is primarily associated with handling actinium, as it is highly radioactive and in short supply. Hence, Ac(III) reactivity is often inferred from the lanthanides and minor actinides (that is, Am, Cm), with limited success. Here we overcome these challenges and characterize actinium in HCl solutions using X-ray absorption spectroscopy and molecular dynamics density functional theory. The Ac-Cl and Ac-OH2O distances are measured to be 2.95(3) and 2.59(3) Å, respectively. The X-ray absorption spectroscopy comparisons between Ac(III) and Am(III) in HCl solutions indicate Ac(III) coordinates more inner-sphere Cl(1-) ligands (3.2±1.1) than Am(III) (0.8±0.3). These results imply diverse reactivity for the +3 actinides and highlight the unexpected and unique Ac(III) chemical behaviour. PMID:27531582

  4. Spectroscopic and computational investigation of actinium coordination chemistry

    PubMed Central

    Ferrier, Maryline G.; Batista, Enrique R.; Berg, John M.; Birnbaum, Eva R.; Cross, Justin N.; Engle, Jonathan W.; La Pierre, Henry S.; Kozimor, Stosh A.; Lezama Pacheco, Juan S.; Stein, Benjamin W.; Stieber, S. Chantal E.; Wilson, Justin J.

    2016-01-01

    Actinium-225 is a promising isotope for targeted-α therapy. Unfortunately, progress in developing chelators for medicinal applications has been hindered by a limited understanding of actinium chemistry. This knowledge gap is primarily associated with handling actinium, as it is highly radioactive and in short supply. Hence, AcIII reactivity is often inferred from the lanthanides and minor actinides (that is, Am, Cm), with limited success. Here we overcome these challenges and characterize actinium in HCl solutions using X-ray absorption spectroscopy and molecular dynamics density functional theory. The Ac–Cl and Ac–OH2O distances are measured to be 2.95(3) and 2.59(3) Å, respectively. The X-ray absorption spectroscopy comparisons between AcIII and AmIII in HCl solutions indicate AcIII coordinates more inner-sphere Cl1– ligands (3.2±1.1) than AmIII (0.8±0.3). These results imply diverse reactivity for the +3 actinides and highlight the unexpected and unique AcIII chemical behaviour. PMID:27531582

  5. Nanostructured surfaces investigated by quantitative morphological studies

    NASA Astrophysics Data System (ADS)

    Perani, Martina; Carapezzi, Stefania; Rani Mutta, Geeta; Cavalcoli, Daniela

    2016-05-01

    The morphology of different surfaces has been investigated by atomic force microscopy and quantitatively analyzed in this paper. Two different tools have been employed to this scope: the analysis of the height-height correlation function and the determination of the mean grain size, which have been combined to obtain a complete characterization of the surfaces. Different materials have been analyzed: SiO x N y , InGaN/GaN quantum wells and Si nanowires, grown with different techniques. Notwithstanding the presence of grain-like structures on all the samples analyzed, they present very diverse surface design, underlying that this procedure can be of general use. Our results show that the quantitative analysis of nanostructured surfaces allows us to obtain interesting information, such as grain clustering, from the comparison of the lateral correlation length and the grain size.

  6. Nanostructured surfaces investigated by quantitative morphological studies.

    PubMed

    Perani, Martina; Carapezzi, Stefania; Mutta, Geeta Rani; Cavalcoli, Daniela

    2016-05-01

    The morphology of different surfaces has been investigated by atomic force microscopy and quantitatively analyzed in this paper. Two different tools have been employed to this scope: the analysis of the height-height correlation function and the determination of the mean grain size, which have been combined to obtain a complete characterization of the surfaces. Different materials have been analyzed: SiO x N y , InGaN/GaN quantum wells and Si nanowires, grown with different techniques. Notwithstanding the presence of grain-like structures on all the samples analyzed, they present very diverse surface design, underlying that this procedure can be of general use. Our results show that the quantitative analysis of nanostructured surfaces allows us to obtain interesting information, such as grain clustering, from the comparison of the lateral correlation length and the grain size. PMID:27004458

  7. PES Surface Modification Using Green Chemistry: New Generation of Antifouling Membranes.

    PubMed

    Nady, Norhan

    2016-01-01

    A major limitation in using membrane-based separation processes is the loss of performance due to membrane fouling. This drawback can be addressed thanks to surface modification treatments. A new and promising surface modification using green chemistry has been recently investigated. This modification is carried out at room temperature and in aqueous medium using green catalyst (enzyme) and nontoxic modifier, which can be safely labelled "green surface modification". This modification can be considered as a nucleus of new generation of antifouling membranes and surfaces. In the current research, ferulic acid modifier and laccase bio-catalyst were used to make poly(ethersulfone) (PES) membrane less vulnerable to protein adsorption. The blank and modified PES membranes are evaluated based on e.g., their flux and protein repellence. Both the blank and the modified PES membranes (or laminated PES on silicon dioxide surface) are characterized using many techniques e.g., SEM, EDX, XPS and SPM, etc. The pure water flux of the most modified membranes was reduced by 10% on average relative to the blank membrane, and around a 94% reduction in protein adsorption was determined. In the conclusions section, a comparison between three modifiers-ferulic acid, and two other previously used modifiers (4-hydroxybenzoic acid and gallic acid)-is presented. PMID:27096873

  8. PES Surface Modification Using Green Chemistry: New Generation of Antifouling Membranes

    PubMed Central

    Nady, Norhan

    2016-01-01

    A major limitation in using membrane-based separation processes is the loss of performance due to membrane fouling. This drawback can be addressed thanks to surface modification treatments. A new and promising surface modification using green chemistry has been recently investigated. This modification is carried out at room temperature and in aqueous medium using green catalyst (enzyme) and nontoxic modifier, which can be safely labelled “green surface modification”. This modification can be considered as a nucleus of new generation of antifouling membranes and surfaces. In the current research, ferulic acid modifier and laccase bio-catalyst were used to make poly(ethersulfone) (PES) membrane less vulnerable to protein adsorption. The blank and modified PES membranes are evaluated based on e.g., their flux and protein repellence. Both the blank and the modified PES membranes (or laminated PES on silicon dioxide surface) are characterized using many techniques e.g., SEM, EDX, XPS and SPM, etc. The pure water flux of the most modified membranes was reduced by 10% on average relative to the blank membrane, and around a 94% reduction in protein adsorption was determined. In the conclusions section, a comparison between three modifiers—ferulic acid, and two other previously used modifiers (4-hydroxybenzoic acid and gallic acid)—is presented. PMID:27096873

  9. Adsorption of hydrogen sulfide onto activated carbon fibers: effect of pore structure and surface chemistry.

    PubMed

    Feng, Wenguo; Kwon, Seokjoon; Borguet, Eric; Vidic, Radisav

    2005-12-15

    To understand the nature of H2S adsorption onto carbon surfaces under dry and anoxic conditions, the effects of carbon pore structure and surface chemistry were studied using activated carbon fibers (ACFs) with different pore structures and surface areas. Surface pretreatments, including oxidation and heattreatment, were conducted before adsorption/desorption tests in a fixed-bed reactor. Raw ACFs with higher surface area showed greater adsorption and retention of sulfur, and heat treatment further enhanced adsorption and retention of sulfur. The retained amount of hydrogen sulfide correlated well with the amount of basic functional groups on the carbon surface, while the desorbed amount reflected the effect of pore structure. Temperature-programmed desorption (TPD) and thermal gravimetric analysis (TGA) showed that the retained sulfurous compounds were strongly bonded to the carbon surface. In addition, surface chemistry of the sorbent might determine the predominant form of adsorbate on the surface. PMID:16475362

  10. Physics and chemistry on well-defined semiconductor and oxide surfaces

    SciTech Connect

    Chen, Peijun

    1992-12-31

    High resolution electron energy loss spectroscopy (HREELS) and other surface spectroscopic techniques have been employed to investigate the following two classes of surface/interface phenomena on well-defined semiconductor and oxide surfaces: (i) the fundamental physical and chemical processes involved in gas-solid interaction on silicon single crystal surfaces, and (ii) the physical and chemical properties of metal-oxide interfaces. The particular systems reported in this dissertation are: NH{sub 3}, PH{sub 3} and B{sub 10}H{sub 14} on Si(111)-(7 x 7); NH{sub 3} on Si(100)-(2 x 1); atomic H on Si(111)-(7 x 7) and boron-modified Si(111); Al on Al{sub 2}O{sub 3} and Sn on SiO{sub 2}. On silicon surfaces, the surface dangling bonds function as the primary adsorption sites where surface chemical processes take place. The unambiguous identification of surface species by vibrational spectroscopy allow the elementary steps involved in these surface chemical processes to be followed on a molecular level. For adsorbate such as NH{sub 3} and PH{sub 3}, the nature of the initial low temperature (100-300 K) adsorption is found to be dissociative, while that for B{sub 10}H{sub 14} is non-dissociative. This has been deduced based upon the presence (or absence) of specific characteristic vibrational mode(s) on surface. By following the evolution of surface species as a function of temperature, the elementary steps leading to silicon nitride thin film growth and doping of silicon are elucidated. In the case of NH{sub 3} on Si(111)-(7 x7) and Si(100)-(2 x 1), a detailed understanding on the role of substrate surface structure is controlling the surface reactivity has been gained on the basis of a Si adatom backbond-strain relief mechanism on the Si(111)-(7 x 7). The electronic modification to Si(111) surface by subsurface boron doping has been shown to quench its surface chemistry, even for the most aggressive atomic H.

  11. The Role of Surface Chemistry in Adhesion and Wetting of Gecko Toe Pads

    PubMed Central

    Badge, Ila; Stark, Alyssa Y.; Paoloni, Eva L.; Niewiarowski, Peter H.; Dhinojwala, Ali

    2014-01-01

    An array of micron-sized setal hairs offers geckos a unique ability to walk on vertical surfaces using van der Waals interactions. Although many studies have focused on the role of surface morphology of the hairs, very little is known about the role of surface chemistry on wetting and adhesion. We expect that both surface chemistry and morphology are important, not only to achieve optimum dry adhesion but also for increased efficiency in self-cleaning of water and adhesion under wet conditions. Here, we used a plasma-based vapor deposition process to coat the hairy patterns on gecko toe pad sheds with polar and non-polar coatings without significantly perturbing the setal morphology. By a comparison of wetting across treatments, we show that the intrinsic surface of gecko setae has a water contact angle between 70–90°. As expected, under wet conditions, adhesion on a hydrophilic surface (glass) was lower than that on a hydrophobic surface (alkyl-silane monolayer on glass). Surprisingly under wet and dry conditions the adhesion was comparable on the hydrophobic surface, independent of the surface chemistry of the setal hairs. This work highlights the need to utilize morphology and surface chemistry in developing successful synthetic adhesives with desirable adhesion and self-cleaning properties. PMID:25323067

  12. The Role of Surface Chemistry in Adhesion and Wetting of Gecko Toe Pads

    NASA Astrophysics Data System (ADS)

    Badge, Ila; Stark, Alyssa Y.; Paoloni, Eva L.; Niewiarowski, Peter H.; Dhinojwala, Ali

    2014-10-01

    An array of micron-sized setal hairs offers geckos a unique ability to walk on vertical surfaces using van der Waals interactions. Although many studies have focused on the role of surface morphology of the hairs, very little is known about the role of surface chemistry on wetting and adhesion. We expect that both surface chemistry and morphology are important, not only to achieve optimum dry adhesion but also for increased efficiency in self-cleaning of water and adhesion under wet conditions. Here, we used a plasma-based vapor deposition process to coat the hairy patterns on gecko toe pad sheds with polar and non-polar coatings without significantly perturbing the setal morphology. By a comparison of wetting across treatments, we show that the intrinsic surface of gecko setae has a water contact angle between 70-90°. As expected, under wet conditions, adhesion on a hydrophilic surface (glass) was lower than that on a hydrophobic surface (alkyl-silane monolayer on glass). Surprisingly under wet and dry conditions the adhesion was comparable on the hydrophobic surface, independent of the surface chemistry of the setal hairs. This work highlights the need to utilize morphology and surface chemistry in developing successful synthetic adhesives with desirable adhesion and self-cleaning properties.

  13. Role(s) of adsorbed water in the surface chemistry of environmental interfaces.

    PubMed

    Rubasinghege, Gayan; Grassian, Vicki H

    2013-04-18

    The chemistry of environmental interfaces such as oxide and carbonate surfaces under ambient conditions of temperature and relative humidity is of great interest from many perspectives including heterogeneous atmospheric chemistry, heterogeneous catalysis, photocatalysis, sensor technology, corrosion science, and cultural heritage science. As discussed here, adsorbed water plays important roles in the reaction chemistry of oxide and carbonate surfaces with indoor and outdoor pollutant molecules including nitrogen oxides, sulfur dioxide, carbon dioxide, ozone and organic acids. Mechanisms of these reactions are just beginning to be unraveled and found to depend on the details of the reaction mechanism as well as the coverage of water on the surface. As discussed here, adsorbed water can: (i) alter reaction pathways and surface speciation relative to the dry surface; (ii) hydrolyze reactants, intermediates and products; (iii) enhance surface reactivity by providing a medium for ionic dissociation; (iv) inhibit surface reactivity by blocking sites; (v) solvate ions; (vi) enhance ion mobility on surfaces and (vii) alter the stability of surface adsorbed species. In this feature article, drawing on research that has been going on for over a decade on the reaction chemistry of oxide and carbonate surfaces under ambient conditions of temperature and relative humidity, a number of specific examples showing the multi-faceted roles of adsorbed water are presented. PMID:23417201

  14. The role of surface chemistry in adhesion and wetting of gecko toe pads.

    PubMed

    Badge, Ila; Stark, Alyssa Y; Paoloni, Eva L; Niewiarowski, Peter H; Dhinojwala, Ali

    2014-01-01

    An array of micron-sized setal hairs offers geckos a unique ability to walk on vertical surfaces using van der Waals interactions. Although many studies have focused on the role of surface morphology of the hairs, very little is known about the role of surface chemistry on wetting and adhesion. We expect that both surface chemistry and morphology are important, not only to achieve optimum dry adhesion but also for increased efficiency in self-cleaning of water and adhesion under wet conditions. Here, we used a plasma-based vapor deposition process to coat the hairy patterns on gecko toe pad sheds with polar and non-polar coatings without significantly perturbing the setal morphology. By a comparison of wetting across treatments, we show that the intrinsic surface of gecko setae has a water contact angle between 70-90°. As expected, under wet conditions, adhesion on a hydrophilic surface (glass) was lower than that on a hydrophobic surface (alkyl-silane monolayer on glass). Surprisingly under wet and dry conditions the adhesion was comparable on the hydrophobic surface, independent of the surface chemistry of the setal hairs. This work highlights the need to utilize morphology and surface chemistry in developing successful synthetic adhesives with desirable adhesion and self-cleaning properties. PMID:25323067

  15. Analytical Chemistry of Surfaces: Part III. Ion Spectroscopy.

    ERIC Educational Resources Information Center

    Hercules, David M.; Hercules, Shirley H.

    1984-01-01

    The fundamentals of two surface techniques--secondary-ion mass spectrometry (SIMS) and ion-scattering spectrometry (ISS)--are discussed. Examples of how these techniques have been applied to surface problems are provided. (JN)

  16. Analytical Chemistry of Surfaces: Part I. General Aspects.

    ERIC Educational Resources Information Center

    Hercules, David M.; Hercules, Shirley H.

    1984-01-01

    Reviews various spectroscopic techniques currently used to analyze real physical surfaces that bound two actual phases. Problems inherent in analyzing these surfaces and possible approaches that may be taken are considered. (JN)

  17. Supported organometallic complexes: Surface chemistry, spectroscopy, and catalysis

    SciTech Connect

    Marks, T.J.

    1990-02-01

    The goal of our program is to define those modes of interaction that take place between organometallic molecules and inorganic surfaces and, ultimately, to correlate various molecule-surface structures with catalytic properties.

  18. Transient Catalytic Combustor Model With Detailed Gas and Surface Chemistry

    NASA Technical Reports Server (NTRS)

    Struk, Peter M.; Dietrich, Daniel L.; Mellish, Benjamin P.; Miller, Fletcher J.; Tien, James S.

    2005-01-01

    In this work, we numerically investigate the transient combustion of a premixed gas mixture in a narrow, perfectly-insulated, catalytic channel which can represent an interior channel of a catalytic monolith. The model assumes a quasi-steady gas-phase and a transient, thermally thin solid phase. The gas phase is one-dimensional, but it does account for heat and mass transfer in a direction perpendicular to the flow via appropriate heat and mass transfer coefficients. The model neglects axial conduction in both the gas and in the solid. The model includes both detailed gas-phase reactions and catalytic surface reactions. The reactants modeled so far include lean mixtures of dry CO and CO/H2 mixtures, with pure oxygen as the oxidizer. The results include transient computations of light-off and system response to inlet condition variations. In some cases, the model predicts two different steady-state solutions depending on whether the channel is initially hot or cold. Additionally, the model suggests that the catalytic ignition of CO/O2 mixtures is extremely sensitive to small variations of inlet equivalence ratios and parts per million levels of H2.

  19. Chemistry of Stream Sediments and Surface Waters in New England

    USGS Publications Warehouse

    Robinson, Gilpin R., Jr.; Kapo, Katherine E.; Grossman, Jeffrey N.

    2004-01-01

    Summary -- This online publication portrays regional data for pH, alkalinity, and specific conductance for stream waters and a multi-element geochemical dataset for stream sediments collected in the New England states of Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. A series of interpolation grid maps portray the chemistry of the stream waters and sediments in relation to bedrock geology, lithology, drainage basins, and urban areas. A series of box plots portray the statistical variation of the chemical data grouped by lithology and other features.

  20. Complex surface concentration gradients by stenciled "electro click chemistry".

    PubMed

    Hansen, Thomas S; Lind, Johan U; Daugaard, Anders E; Hvilsted, Søren; Andresen, Thomas L; Larsen, Niels B

    2010-10-19

    Complex one- or two-dimensional concentration gradients of alkynated molecules are produced on azidized conducting polymer substrates by stenciled "electro click chemistry". The latter describes the local electrochemical generation of catalytically active Cu(I) required to complete a "click reaction" between alkynes and azides at room temperature. A stencil on the counter electrode defines the shape and multiplicity of the gradient(s) on the conducting polymer substrate, while the specific reaction conditions control gradient steepness and the maximum concentration deposited. Biologically active ligands including cell binding peptides are patterned in gradients by this method without losing their biological function or the conductivity of the polymer. PMID:20860406

  1. THE INTEGRATED USE OF COMPUTATIONAL CHEMISTRY, SCANNING PROBE MICROSCOPY, AND VIRTUAL REALITY TO PREDICT THE CHEMICAL REACTIVITY OF ENVIRONMENTAL SURFACES

    EPA Science Inventory

    In the last decade three new techniques scanning probe microscopy (SPM), virtual reality (YR) and computational chemistry ave emerged with the combined capability of a priori predicting the chemically reactivity of environmental surfaces. Computational chemistry provides the cap...

  2. Effect of surface chemistry on the integrin induced pathway in regulating vascular endothelial cells migration.

    PubMed

    Shen, Yang; Gao, Min; Ma, Yunlong; Yu, Hongchi; Cui, Fu-zhai; Gregersen, Hans; Yu, Qingsong; Wang, Guixue; Liu, Xiaoheng

    2015-02-01

    The migration of vascular endothelial cells (ECs) is essential for reendothelialization after implantation of cardiovascular biomaterials. Reendothelialization is largely determined by surface properties of implants. In this study, surfaces modified with various chemical functional groups (CH3, NH2, COOH, OH) prepared by self-assembled monolayers (SAMs) were used as model system. Expressions and distributions of critical proteins in the integrin-induced signaling pathway were examined to explore the mechanisms of surface chemistry regulating EC migration. The results showed that SAMs modulated cell migration were in the order CH3>NH2>OH>COOH, determined by differences in the expressions of focal adhesion components and Rho GTPases. Multiple integrin subunits showed difference in a surface chemistry-dependent manner, which induced a stepwise activation of signaling cascades associated with EC migration. This work provides a broad overview of surface chemistry regulated endothelial cell migration and establishes association among the surface chemistry, cell migration behavior and associated integrin signaling events. Understanding the relationship between these factors will help us to understand the surface/interface behavior between biomaterials and cells, reveal molecular mechanism of cells sensing surface characterization, and guide surface modification of cardiovascular implanted materials. PMID:25575348

  3. Research Program to Investigate the Fundamental Chemistry of Technetium

    SciTech Connect

    Pegg, Ian

    2005-06-01

    Research Progress and Implications Portions of two Tc glasses, LBNL-118 (Hanford AP-101 tank formulation) and LBNL-121 (higher organic content Hanford AN-107 tank formulation), were placed in vapor hydration test (VHT) stainless steel pressure vessels and exposed to a hydrous atmosphere at 238 C for 24.9 days. After being removed from the vessels, complete sample alteration is clearly visible for both samples. X-ray absorption spectra were then collected on these samples to characterize the Tc speciation within the alteration layers. The X-ray fluorescence signal was significantly improved for both VHT samples compared with that collected for the corresponding unaltered glasses, so much so that X ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data could be collected for each VHT sample. This signal improvement for the VHT samples indicates that a significant amount of the Tc in the original glasses has migrated closer to the VHT sample surface; this surface enrichment results in a stronger Tc X ray signal than is the case for the more homogeneously distributed Tc in the original glasses.

  4. Surface modification of nanoporous 1,2-polybutadiene by atom transfer radical polymerization or click chemistry.

    PubMed

    Guo, Fengxiao; Jankova, Katja; Schulte, Lars; Vigild, Martin E; Ndoni, Sokol

    2010-02-01

    Surface-initiated atom transfer radical polymerization (ATRP) and click chemistry were used to obtain functional nanoporous polymers based on nanoporous 1,2-polybutadiene (PB) with gyroid morphology. The ATRP monolith initiator was prepared by immobilizing bromoester initiators onto the pore walls through two different methodologies: (1) three-step chemical conversion of double bonds of PB into bromoisobutyrate, and (2) photochemical functionalization of PB with bromoisobutyrate groups. Azide functional groups were attached onto the pore walls before click reaction with alkynated MPEG. Following ATRP-grafting of hydrophilic polyacrylates and click of MPEG, the originally hydrophobic samples transformed into hydrophilic nanoporous materials. The successful modification was confirmed by infrared spectroscopy, contact angle measurements and measurements of spontaneous water uptake, while the morphology was investigated by small-angle X-ray scattering and transmission electron microscopy. PMID:20099923

  5. (90377) SEDNA: INVESTIGATION OF SURFACE COMPOSITIONAL VARIATION

    SciTech Connect

    Barucci, M. A.; De Bergh, C.; Merlin, F.; Morea Dalle Ore, C.; Cruikshank, D.; Alvarez-Candal, A.; Dumas, C.

    2010-12-15

    The dwarf planet (90377) Sedna is one of the most remote solar system objects accessible to investigations. To better constrain its surface composition and to investigate the possible heterogeneity of the surface of Sedna, several observations have been carried out at ESO-VLT with the powerful spectrometer SINFONI observing simultaneously the H and K bands. The analyzed spectra (obtained in 2005, 2007, and 2008) show a non-uniform spectral signature, particularly in the K band. Spectral modeling using the Shkuratov radiative transfer code for surface scattering has been performed using the various sets of data, including previous observations at visible wavelengths and photometry at 3.6 and 4.5 {mu}m by the Spitzer Space Telescope. The visible and near-infrared spectra can be modeled with organic materials (triton and titan tholin), serpentine, and H{sub 2}O ice in fairly significant amounts, and CH{sub 4}, N{sub 2}, and C{sub 2}H{sub 6} in varying trace amounts. One of the spectra obtained in 2005 October shows a different signature in the K band and is best modeled with CH{sub 3}OH in place of CH{sub 4}, with reduced amounts of serpentine and with the addition of olivine. The compositional surface heterogeneity can give input on the past history as well clues to the origin of this peculiar, distant object.

  6. Hierarchical Hydrodynamic Flow Confinement: Efficient Use and Retrieval of Chemicals for Microscale Chemistry on Surfaces

    PubMed Central

    2014-01-01

    We devised, implemented, and tested a new concept for efficient local surface chemistry that we call hierarchical hydrodynamic flow confinement (hierarchical HFC). This concept leverages the hydrodynamic shaping of multiple layers of liquid to address challenges inherent to microscale surface chemistry, such as minimal dilution, economical consumption of reagent, and fast liquid switching. We illustrate two modes of hierarchical HFC, nested and pinched, by locally denaturing and recovering a 26 bp DNA with as little as 2% dilution and by efficiently patterning an antibody on a surface, with a 5 μm resolution and a 100-fold decrease of reagent consumption compared to microcontact printing. In addition, valveless switching between nanoliter volumes of liquids was achieved within 20 ms. We believe hierarchical HFC will have broad utility for chemistry on surfaces at the microscale. PMID:24625080

  7. NOx Binding and Dissociation: Enhanced Ferroelectric Surface Chemistry by Catalytic Monolayers

    NASA Astrophysics Data System (ADS)

    Kakekhani, Arvin; Ismail-Beigi, Sohrab

    2013-03-01

    NOx molecules are regulated air pollutants produced during automotive combustion. As part of an effort to design viable catalysts for NOx decomposition operating at higher temperatures that would allow for improved fuel efficiency, we examine NOx chemistry on ferroelectric perovskite surfaces. Changing the direction of ferroelectric polarization can modify surface electronic properties and may lead to switchable surface chemistry. Here, we describe our recent work on potentially enhanced surface chemistry using catalytic RuO2 monolayers on perovskite ferroelectric substrates. In addition to thermodynamic stabilization of the RuO2 layer, we present results on the polarization-dependent binding of NO, O2, N2, and atomic O and N. We present results showing that one key problem with current catalysts, involving the difficulty of releasing dissociation products (especially oxygen), can be ameliorated by this method. Primary support from Toyota Motor Engineering and Manufacturing, North America, Inc.

  8. Geothermal chemistry/exploration investigations at Dixie Valley, Nevada

    SciTech Connect

    Goff, F.; Bergfeld, D.; Counce, D.; Janik, C.J.; Bruton, C.J.; Nimz, G.

    1998-12-01

    Dixie Valley geothermal field has continuously produced electric power since 1988. At the request of Oxbow Geothermal Corp. and the US Department of Energy, the authors have organized an inter-agency team of investigators to examine several topics of concern regarding management and behavior of the resource. These topics include scaling of the injection system, recharge of the reservoir, geochemical monitoring of the reservoir, and development of increased fumarolic activity north of the power plant.

  9. The Effects of Surface Chemistry on the Properties of Proteins Confined in Nano-porous Materials

    SciTech Connect

    Garrett, Latasha M; O'Neill, Hugh Michael

    2007-01-01

    The entrapment of proteins using the sol-gel route provides a means to retain its native properties and artificially reproduce the molecular crowding and confinement experienced by proteins in the cell allowing investigation of the physico-chemical and structural properties of biomolecules at the biotic/abiotic interface. The biomolecules are spatially separated and 'caged' in the gel structure but solutes can freely permeate the matrix. Thus, properties such as the folding of ensembles of individual molecules can be examined in the absence of aggregation effects that can occur in solution studies. Green fluorescent protein from Aequorea coerulescens was used as a model protein to examine the unfolding/re-folding properties of protein in silica gels. The recombinant protein was isolated and purified from Escherichia coli extracts by cell lysis, three-phase partitioning, dialysis, and anion exchange chromatography. The purity of the protein was greater than 90% as judged by SDS PAGE gel analysis. Sol-gels were synthesized using tetramethylorthosilicate (TMOS) in combination with, methyltrimethoxyorthosilane (MTMOS), ethyltrimethoxyorthosilane (ETMOS), 3-aminopropyltriethoxysilane (APTES), and 3-glycidoxypropyltrimethoxysilane (GPTMS). The acid induced denaturation and renaturation of GFP was analyzed by UV-visible, fluorescence, and circular dichroism (CD) spectroscopies. No renaturation was observed in gels that were made with TMOS only, and in the presence of APTES, MTMOS, and ETMOS. However, in gels that were made with GPTMS, the CD and UV-visible spectra indicated that the protein had refolded. The fluorescence emission spectrum indicated that approximately 20% of fluorescence had returned. This study highlights the importance of the surface chemistry of the silica gels for the refolding properties of the entrapped GFP. Future studies will investigate the effect of surface chemistry on the thermal and solvent stability of the entrapped protein.

  10. THE EFFECTS OF SURFACE CHEMISTRY ON THE PROPERTIES OF PROTEINS CONFINED IN NANO-POROUS MATERIALS

    SciTech Connect

    Garrett, L. M.; O'Neill, H.

    2007-01-01

    The entrapment of proteins using the sol-gel route provides a means to retain its native properties and artifi cially reproduce the molecular crowding and confi nement experienced by proteins in the cell allowing investigation of the physico-chemical and structural properties of biomolecules at the biotic/abiotic interface. The biomolecules are spatially separated and ‘caged’ in the gel structure but solutes can freely permeate the matrix. Thus, properties such as the folding of ensembles of individual molecules can be examined in the absence of aggregation effects that can occur in solution studies. Green fl uorescent protein from Aequorea coerulescens was used as a model protein to examine the unfolding/re-folding properties of protein in silica gels. The recombinant protein was isolated and purifi ed from Escherichia coli extracts by cell lysis, three-phase partitioning, dialysis, and anion exchange chromatography. The purity of the protein was greater than 90% as judged by SDS PAGE gel analysis. Sol-gels were synthesized using tetramethylorthosilicate (TMOS) in combination with, methyltrimethoxyorthosilane (MTMOS), ethyltrimethoxyorthosilane (ETMOS), 3-aminopropyltriethoxysilane (APTES), and 3-glycidoxypropyltrimethoxysilane (GPTMS). The acid induced denaturation and renaturation of GFP was analyzed by UV-visible, fl uorescence, and circular dichroism (CD) spectroscopies. No renaturation was observed in gels that were made with TMOS only, and in the presence of APTES, MTMOS, and ETMOS. However, in gels that were made with GPTMS, the CD and UV-visible spectra indicated that the protein had refolded. The fl uorescence emission spectrum indicated that approximately 20% of fl uorescence had returned. This study highlights the importance of the surface chemistry of the silica gels for the refolding properties of the entrapped GFP. Future studies will investigate the effect of surface chemistry on the thermal and solvent stability of the entrapped protein.

  11. Surface chemistry and catalysis on well-defined epitaxial iron-oxide layers

    NASA Astrophysics Data System (ADS)

    Weiss, Werner; Ranke, Wolfgang

    2002-03-01

    Metal-oxide-based catalysts are used for many important synthesis reactions in the chemical industry. A better understanding of the catalyst operation can be achieved by studying elementary reaction steps on well-defined model catalyst systems. For the dehydrogenation of ethylbenzene to styrene in the presence of steam both unpromoted and potassium promoted iron-oxide catalysts are active. Here we review the work done over unpromoted single-crystalline FeO(1 1 1), Fe3O4(1 1 1) and α- Fe2O3(0 0 0 1) films grown epitaxially on Pt(1 1 1) substrates. Their geometric and electronic surface structures were characterized by STM, LEED, electron microscopy and electron spectroscopic techniques. In an integrative approach, the interaction of water, ethylbenzene and styrene with these films was investigated mainly by thermal desorption and photoelectron emission spectroscopy. The adsorption-desorption energetics and kinetics depend on the oxide surface terminations and are correlated to the electronic structures and acid-base properties of the corresponding oxide phases, which reveal insight into the nature of the active sites and into the catalytic function of semiconducting oxides in general. Catalytic studies, using a batch-reactor arrangement at high gas pressures and post-reaction surface analysis, showed that only α- Fe2O3(0 0 0 1) containing surface defects is catalytically active, whereas Fe3O4(1 1 1) is always inactive. This can be related to the elementary adsorption and desorption properties observed in ultrahigh vacuum, which indicates that the surface chemical properties of the iron-oxide films do not change significantly across the “pressure-gap”. A model is proposed according to which the active site involves a regular acidic surface site and a defect site next to it. The results on metal-oxide surface chemistry also have implications for other fields such as environmental science, biophysics and chemical sensors.

  12. Control of pyrite surface chemistry in physical coal cleaning. Final report

    SciTech Connect

    Luttrell, G.H.; Yoon, R.H.; Richardson, P.E.

    1993-05-19

    In Part I, Surface Chemistry of Coal Pyrite the mechanisms responsible for the inefficient rejection of coal pyrite were investigated using a number of experimental techniques. The test results demonstrate that the hydrophobicity of coal pyrite is related to the surface products formed during oxidation in aqueous solutions. During oxidation, a sulfur-rich surface layer is produced in near neutral pH solutions. This surface layer is composed mainly of sulfur species in the form of an iron-polysulfide along with a smaller amount of iron oxide/hydroxides. The floatability coal pyrite increases dramatically in the presence of frothers and hydrocarbon collectors. These reagents are believed to absorb on the weakly hydrophobic pyrite surfaces as a result of hydrophobic interaction forces. In Part III, Developing the Best Possible Rejection Schemes, a number of pyrite depressants were evaluated in column and conventional flotation tests. These included manganese (Mn) metal, chelating agents quinone and diethylenetriamine (DETA), and several commercially-available organic depressants. Of these, the additives which serve as reducing agents were found to be most effective. Reducing agents were used to prevent pyrite oxidation and/or remove oxidation products present on previously oxidized surfaces. These data show that Mn is a significantly stronger depressant for pyrite than quinone or DETA. Important factors in determining the pyrite depression effect of Mn include the slurry solid content during conditioning, the addition of acid (HCl), and the amount of Mn. The acid helps remove the oxide layer from the surface of Mn and promotes the depression of pyrite by Mn.

  13. Chemistry of atmosphere-surface interactions on Venus and Mars

    NASA Technical Reports Server (NTRS)

    Fegley, Bruce, Jr.; Treiman, Allan H.

    1992-01-01

    Earth-based, earth-orbital, and spacecraft observational data are used in the present evaluation of Venus atmosphere-surface interactions to quantitatively characterize the reactions between C, H, S, Cl, F, and N gases and plausible surface minerals. Calculation results are used to predict stable minerals and mineral assemblages on the Venus surface, in order to ascertain which (if any) of the atmospheric gases are buffeted by mineral assemblages. Chemical equilibrium calculations using extant thermodynamic data on scapolite minerals predict that carbonate-bearing scapolite and sulfate meionite are unstable on the surface of Venus, while chloride-bearing scapolite is stable.

  14. NATIONAL SURFACE WATER SURVEY: WESTERN LAKE SURVEY (PHASE 1 - SYNOPTIC CHEMISTRY) QUALITY ASSURANCE PLAN

    EPA Science Inventory

    The purpose of the National Surface Water Survey of the National Acid Precipitation Assessment Program is to evaluate the present water chemistry of lakes and streams, to determine the status of certain biotic resources, and to select regionally representative surface waters for ...

  15. 3D Printed Potential and Free Energy Surfaces for Teaching Fundamental Concepts in Physical Chemistry

    ERIC Educational Resources Information Center

    Kaliakin, Danil S.; Zaari, Ryan R.; Varganov, Sergey A.

    2015-01-01

    Teaching fundamental physical chemistry concepts such as the potential energy surface, transition state, and reaction path is a challenging task. The traditionally used oversimplified 2D representation of potential and free energy surfaces makes this task even more difficult and often confuses students. We show how this 2D representation can be…

  16. Analytical Chemistry of Surfaces: Part II. Electron Spectroscopy.

    ERIC Educational Resources Information Center

    Hercules, David M.; Hercules, Shirley H.

    1984-01-01

    Discusses two surface techniques: X-ray photoelectron spectroscopy (ESCA) and Auger electron spectroscopy (AES). Focuses on fundamental aspects of each technique, important features of instrumentation, and some examples of how ESCA and AES have been applied to analytical surface problems. (JN)

  17. Geochemistry and Organic Chemistry on the Surface of Titan

    NASA Technical Reports Server (NTRS)

    Lunine, J. I.; Beauchamp, P.; Beauchamp, J.; Dougherty, D.; Welch, C.; Raulin, F.; Shapiro, R.; Smith, M.

    2001-01-01

    Titan's atmosphere produces a wealth of organic products from methane and nitrogen. These products, deposited on the surface in liquid and solid form, may interact with surface ices and energy sources to produce compounds of exobiological interest. Additional information is contained in the original extended abstract.

  18. Control of pyrite surface chemistry in physical coal cleaning

    SciTech Connect

    Luttrell, G.H.; Yoon, R.H.; Zachwieja, J.B.; Lagno, M.L.

    1992-06-24

    Correlation of the hydrophobicity measurements of coal and mineral pyrite with changes in the surface composition of the samples as determined by x-ray photoelectron spectroscopy (XPS) reveals that similar surface oxidation products are found on both mineral and coal pyrite samples. The surface oxidation layer of these samples is comprised of different amounts of hydrophilic species (iron hydroxy-oxides and/or iron oxides) and hydrophobic species (polysulfide or elemental sulfur). The resulting hydrophobicity of these samples may be attributed to the ratio of hydrophilic (surface oxides) to hydrophobic (sulfur-containing) species in the surface oxidation layer. Also, coal pyrite samples were found to exhibit a greater degree of superficial oxidation and a less hydrophobic character as compared to the mineral pyrite samples.

  19. Effects of surface chemistry and microstructure of electrolyte on oxygen reduction kinetics of solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Park, Joong Sun; An, Jihwan; Lee, Min Hwan; Prinz, Fritz B.; Lee, Wonyoung

    2015-11-01

    We report systematic investigation of the surface properties of yttria-stabilized zirconia (YSZ) electrolytes with the control of the grain boundary (GB) density at the surface, and its effects on electrochemical activities. The GB density of thin surface layers deposited on single crystal YSZ substrates is controlled by changing the annealing temperature (750-1450 °C). Higher oxygen reduction reactions (ORR) kinetics is observed in samples annealed at lower temperatures. The higher ORR activity is ascribed to the higher GB density at the YSZ surface where 'mobile' oxide ion vacancies are more populated. Meanwhile, oxide ion vacancies concurrently created with yttrium segregation at the surface at the higher annealing temperature are considered inactive to oxygen incorporation reactions. Our results provide additional insight into the interplay between the surface chemistry, microstructures, and electrochemical activity. They potentially provide important guidelines for engineering the electrolyte-electrode interfaces of solid oxide fuel cells for higher electrochemical performance.

  20. Effects of surface chemistry and microstructure of electrolyte on oxygen reduction kinetics of solid oxide fuel cells

    SciTech Connect

    Park, Joong Sun; An, Jihwan; Lee, Min Hwan; Prinz, Friedrich B.; Lee, Wonyoung

    2015-07-10

    In this study, we report systematic investigation of the surface properties of yttria-stabilized zirconia (YSZ) electrolytes with the control of the grain boundary (GB) density at the surface, and its effects on electrochemical activities. The GB density of thin surface layers deposited on single crystal YSZ substrates is controlled by changing the annealing temperature (750-1450 °C). Higher oxygen reduction reactions (ORR) kinetics is observed in samples annealed at lower temperatures. The higher ORR activity is ascribed to the higher GB density at the YSZ surface where 'mobile' oxide ion vacancies are more populated. Meanwhile, oxide ion vacancies concurrently created with yttrium segregation at the surface at the higher annealing temperature are considered inactive to oxygen incorporation reactions. Our results provide additional insight into the interplay between the surface chemistry, microstructures, and electrochemical activity. They potentially provide important guidelines for engineering the electrolyte electrode interfaces of solid oxide fuel cells for higher electrochemical performance.

  1. Hexametaphosphate effects on tooth surface conditioning film chemistry--in vitro and in vivo studies.

    PubMed

    Busscher, Henk J; White, Donald J; van der Mei, Henny C; Baig, Arif A; Kozak, Kathy M

    2002-01-01

    These studies compared the effects of Crest Dual Action Whitening dentifrice with sodium hexametaphosphate and control commercial dentifrices on the surface chemistry of conditioning film-coated dental enamel in vitro and in vivo. Conditioning film chemistry was studied by measurements of film thickness, ability to wet the surface/surface energy, conditioning film chemical composition and zeta potential. Laboratory and in vivo studies demonstrated that brushing and chemical-only treatment of pellicle-coated enamel surfaces produced marked changes in surface chemistry. Brushing of surfaces with all commercial dentifrices significantly reduced pellicle film quantity. Effects on non-brushed areas, of significance in the clinical situation, were different for different dentifrices. For dentifrice chemical treatments, calcium phosphate surface active builders, such as pyrophosphate and hexametaphosphate, produced stronger effects than standard (non-tartar control) dentifrices, peroxide baking soda dentifrices and dentifrices formulated with carboxylate polymers, viz. Colgate Total with copolymer. Crest Dual Action Whitening hexametaphosphate dentifrice removed more pellicle conditioning film, produced a lower zeta potential, produced the largest changes in film composition and had the greatest impact on surface free energies of the tested dentifrices. Crest Dual Action Whitening dentifrice also produced lasting changes in the reacquisition of pellicle conditioning film, as established by in vitro cycling immersion studies. Crest Dual Action Whitening dentifrice produced stronger and more lasting effects on surface film chemistry than low molecular weight pyrophosphate (Crest Tartar Control) or other polymeric-based dentifrice systems (Colgate Total). These surface chemistries may contribute to the unique clinical actions of hexametaphosphate established in recently reported, randomized clinical studies of tartar control, stain prevention and stain removal effects. PMID

  2. Surface chemistry controls crystallinity of ZnSnanoparticles

    SciTech Connect

    Gilbert, Benjamin; Huang, Feng; Lin, Zhang; Goodell, Carmen; Zhang, Hengzhong; Banfield Jillian F.

    2005-12-20

    Combined small-angle and high energy wide-angle x-ray scattering measurements of nanoparticle size and structure permit interior strain and disorder to be directly observed in the real-space pair distribution function (PDF). PDF analysis showed that samples of ZnS nanoparticle with similar mean diameters (3.2-3.6 nm) but synthesized and treated differently possess a dramatic range of interior disorder. We used Fourier transform infra-red spectroscopy to detect the surface species and the nature of surface chemical interactions. Our results suggest that there is a direct correlation between the strength of surface-ligand interactions and interior crystallinity.

  3. The surface chemistry of metal-organic frameworks.

    PubMed

    McGuire, Christina V; Forgan, Ross S

    2015-03-28

    Metal-organic frameworks (MOFs) have received particular attention over the last 20 years as a result of their attractive properties offering potential applications in a number of areas. Typically, these characteristics are tuned by functionalisation of the bulk of the MOF material itself. This Feature Article focuses instead on modification of MOF particles at their surfaces only, which can also offer control over the bulk properties of the material. The differing surface modification techniques available to the synthetic chemist will be discussed, with a focus on the effect of surface modification of MOFs on their fundamental properties and application in adsorption, catalysis, drug delivery and other areas. PMID:25116412

  4. Effects of Surface Chemistry on the Porous Structure of Coal

    SciTech Connect

    Radovic, Ljubisa R; Hatcher, Patrick G

    1997-05-01

    In this report, 129 Xe nuclear magnetic resonance spectroscopy of xenon gas adsorbed in coal is used to describe some poorly understood features of coal microporous structure, particularly in establishing that a connected network exists, the type of connectivity, and its changes with the rank of coal. Micropore size scale and distribution are also considered. Two methods are developed which are new and versatile tools for the investigation of porous structure. Both utilize xenon gas that is in motion, while undergoing diffusion or exchange in coal, to describe the connectivity of the micropore structure of coal. Time tracking of the adsorption process by NMR, selective saturation, and saturation transfer techniques were used to obtain new information on the coal rank dependence of porous structure. In addition, an existing 129 Xe chemical shift-pore diameter model was used to calculate micropore diameters for coals, as well as for a microporous carbon, before and after pore-size alteration. In the initial study performed, straightforward 129 Xe NMR spectra at equilibrium xenon adsorption at a series of pressures were acquired for a rank-varied set of six coals. Acquisition of the NMR signal as an echo was tested and found to improve spectral quality. The spectra were used to calculate micropore diameters for the six coals. These range from 5.6 to 7.5 and exhibit a minimum value for the intermediate coal rank. The smallest pores occur in coals of about 82-85% carbon; at both lower and higher coal ranks, the average micropore size tends to be larger. The changes in the spectra with coal rank and surface area were explored. Signal linewidths were found to decrease with increasing coal rank and were interpreted in terms of increasing chemical or physical homogeneity of the coal as rank increases. The packing density of powdered coal was found to alter the spectral appearance in a high volatile bituminous coal, which is preliminary evidence that exchange affects the

  5. Research Program to Investigate the Fundamental Chemistry of Technetium

    SciTech Connect

    Shuh, David K.; Burns, Carol J.; Lukens, Wayne W. Jr.

    2001-06-15

    Technetium (99Tc, half-life = 2.13x105 years, b-emitter) is one of the radionuclides of major concern for nuclear waste disposal. This concern is due to the long half-life of 99Tc, the ease with which pertechnetate, TcO4 -, migrates in the geosphere, difficulties in incorporating technetium into glass waste forms, and the corresponding regulatory considerations. The problem of mobility of pertechnetate in the environment is compounded by the fact that pertechnetate is the thermodynamically stable form of technetium in oxidizing environments. Because of this stability, pertechnetate was presumed to be the predominant chemical form of technetium in the aqueous phase of nuclear waste tanks. However, studies have indicated that a significant fraction of the technetium is in a different chemical form. These factors present challenges the separation and immobilization of technetium. The objective of this project is to investigate the chemical behavior of technetium so that the se problems may be understood and the challenges addressed.

  6. Reaction chemistry and ligand exchange at cadmium selenide nanocrystal surfaces

    SciTech Connect

    Owen, Jonathan; Park, Jungwon; Trudeau, Paul-Emile; Alivisatos, A. Paul

    2008-12-02

    Chemical modification of nanocrystal surfaces is fundamentally important to their assembly, their implementation in biology and medicine, and greatly impacts their electrical and optical properties. However, it remains a major challenge owing to a lack of analytical tools to directly determine nanoparticle surface structure. Early nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) studies of CdSe nanocrystals prepared in tri-n-octylphosphine oxide (1) and tri-n-octylphosphine (2), suggested these coordinating solvents are datively bound to the particle surface. However, assigning the broad NMR resonances of surface-bound ligands is complicated by significant concentrations of phosphorus-containing impurities in commercial sources of 1, and XPS provides only limited information about the nature of the phosphorus containing molecules in the sample. More recent reports have shown the surface ligands of CdSe nanocrystals prepared in technical grade 1, and in the presence of alkylphosphonic acids, include phosphonic and phosphinic acids. These studies do not, however, distinguish whether these ligands are bound datively, as neutral, L-type ligands, or by X-type interaction of an anionic phosphonate/phosphinate moiety with a surface Cd{sup 2+} ion. Answering this question would help clarify why ligand exchange with such particles does not proceed generally as expected based on a L-type ligand model. By using reagents with reactive silicon-chalcogen and silicon-chlorine bonds to cleave the ligands from the nanocrystal surface, we show that our CdSe and CdSe/ZnS core-shell nanocrystal surfaces are likely terminated by X-type binding of alkylphosphonate ligands to a layer of Cd{sup 2+}/Zn{sup 2+} ions, rather than by dative interactions. Further, we provide spectroscopic evidence that 1 and 2 are not coordinated to our purified nanocrystals.

  7. Affinity Induced Surface Functionalization of Liposomes Using Cu-Free Click Chemistry.

    PubMed

    Bak, Martin; Jølck, Rasmus I; Eliasen, Rasmus; Andresen, Thomas L

    2016-07-20

    Functionalization of nanoparticles is a key element for improving specificity of drug delivery systems toward diseased tissue or cells. In the current study we report a highly efficient and chemoselective method for post-functionalization of liposomes with biomacromolecules, which equally well can be used for functionalization of other nanoparticles or solid surfaces. The method exploits a synergistic effect of having both affinity and covalent anchoring tags on the surface of the liposome. This was achieved by synthesizing a peptide linker system that uses Cu-free strain-promoted click chemistry in combination with histidine affinity tags. The investigation of post-functionalization of PEGylated liposomes was performed with a cyclic RGDfE peptide. By exploring both affinity and covalent tags a 98 ± 2.0% coupling efficiency was achieved, even a diluted system showed a coupling efficiency of 87 ± 0.2%. The reaction kinetics and overall yield were quantified by HPLC. The results presented here open new possibilities for constructing complex nanostructures and functionalized surfaces. PMID:27269516

  8. Surface chemistry and spectroscopy of the β-galactosidase Langmuir monolayer.

    PubMed

    Crawford, Nicholas F; Micic, Miodrag; Orbulescu, Jhony; Weissbart, Daniel; Leblanc, Roger M

    2015-09-01

    The changes of interfacial properties of β-galactosidase introduced into different pH environments are investigated through surface chemistry and in situ spectroscopy. Conditions for an optimal Langmuir monolayer formation were firstly obtained by varying the subphase salt concentration and the surface-pressure area isotherm was used to extrapolate the limiting molecular area of the enzyme monolayer to be around 42,000 Å(2) molecule(-1). Surface pressure stability measurements held at 20 mN/m for 90 min along with compression-decompression cycles revealed no aggregate formation at the air-water interface. Consistent with the data obtained from the isotherm, in situ UV-Vis and fluorescence spectroscopy shows a steep rise in absorbance and photoluminescence intensity correlating to with a switch from a liquid-expanded to a liquid-condensed phase. A decrease in subphase pH increased the electrostatic repulsion as the enzyme was protonated, leading to an expanded monolayer. Infrared absorption-reflection spectroscopy demonstrates that the enzyme adopts mainly β-sheet conformation at the air-water interface before and during the compression. PMID:25985424

  9. Macroform and microform-induced change in redox-sensitive chemistries of river channel surface sediments

    NASA Astrophysics Data System (ADS)

    Byrne, P.; Zhang, H.; Heathwaite, A. L.; Binley, A.; Ullah, S.; Kaeser, D.; Heppell, C. M.; Lansdown, K.; Trimmer, M.

    2012-04-01

    In-stream geomorphological features such as riffle-pool sequences (macroforms) can produce steep hydraulic gradients which induce flow in and out of the riverbed - hyporheic exchange flow (HEF). The acceleration of flow over channel obstacles such as large cobbles and boulders (microforms) can create variation in surface-subsurface pressure gradients and generation of HEF. HEF in shallow surface sediments affect the transformation of redox-sensitive chemical forms and, therefore, the attenuation or release of nutrients in river systems. Here, we examine the relationship between stream geomorphological environment (microform and macroform) and concentration profiles of redox-sensitive species (nitrate, sulphate, iron, manganese) in shallow (15cm) subsurface sediments. In-situ passive samplers (diffusive equilibrium in thin films - DET) are used to obtain biogeochemical data from armoured environments at fine scale (cm) depth resolution where there is strong upwelling. The probes were deployed in a 50m reach of the River Eden, Cumbria, UK, during baseflow conditions. The experimental setup allowed for the assessment of differences in redox-sensitive chemistries between a riffle and pool environment and between smooth and rough bed surfaces in the pool. The passive sensing basis of the DET methodology provided a means for investigating how HEF systems generated at two different geomorphological scales influence the concentration and spatial patterns of redox-sensitive species. DET's capability of measuring at high spatial resolution allowed the extent of hyporheic mixing to be targeted, even though it is often limited to the top few centimetres of sediment.

  10. Biotite surface chemistry as a function of aqueous fluid composition

    NASA Astrophysics Data System (ADS)

    Bray, Andrew W.; Benning, Liane G.; Bonneville, Steeve; Oelkers, Eric H.

    2014-03-01

    The chemical composition and charge of the biotite near-surface, in contact with NaCl bearing aqueous solutions at 25 °C from pH 1 to 12, have been derived via zeta potential measurements and potentiometric titrations performed for 20 and 60 min in batch reactors. Zeta potential measurements yielded an isoelectric point of pH 3.0 (±0.2) and batch potentiometric titrations yielded a pH of immersion of 9.66 (S.D. 0.24). From batch potentiometric titrations we determined both the proton consumption and the metal release from the biotite surface as a function of pH. Potassium removal from the near-surface of biotite is only slightly dependent on pH with a minimum of ˜6 atoms nm-2 removed at the immersion pH, corresponding to an average depletion depth of ˜1.5 nm. In contrast, the release of Mg, Al and Fe is strongly pH-dependent as those metals are preferentially removed from the biotite surface at pH less than 9 (Mg) and 4 (Al, Fe). The average depletion depth of Mg, Al, and Fe increases with decreasing pH, reaching on average ˜2 nm at pH ˜1. The removal of K, Mg, Al, and Fe is not charge conservative, resulting in a relative negative charge in the biotite near-surface. Taken together, our results indicate that the composition of the biotite surface varies dramatically as a function of pH. At basic conditions, the biotite near-surface is K depleted and likely hydrogen enriched. At near-neutral conditions, the biotite near-surface is comprised of only the Si and Al tetrahedral, and the Fe(II) octahedral framework, following the removal of both alkali metals and Mg. Finally, at acidic conditions, the biotite near-surface is comprised exclusively of a remnant Si, O and H framework. The results of these experiments give an indication of the composition and charge of the biotite surface in the natural environment, following contact with water, for example in the vadose zone, and can help us understand weathering reactions in these systems.