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Sample records for adsorption surface area

  1. Specific surface area effect on adsorption of chlorpyrifos and TCP by soils and modeling

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The adsorption of chlorpyrifos and TCP (3,5,6, trichloro-2-pyridinol) was determined in four soils (Mollisol, Inceptisol, Entisol, Alfisol) having different specific surface areas (19–84 m2/g) but rather similar organic matter content (2.4–3.5%). Adsorption isotherms were derived from batch equilibr...

  2. Periodic Mesoporous Organosilica Nanocubes with Ultrahigh Surface Areas for Efficient CO2 Adsorption

    PubMed Central

    Wei, Yong; Li, Xiaomin; Zhang, Renyuan; Liu, Yong; Wang, Wenxing; Ling, Yun; El-Toni, Ahmed Mohamed; Zhao, Dongyuan

    2016-01-01

    Ultrahigh surface area single-crystals of periodic mesoporous organosilica (PMOs) with uniform cubic or truncated-cubic morphology and organic/inorganic components homogeneously distributed over the whole frameworks have successfully been prepared by a sol-gel surfactant-templating method. By tuning the porous feature and polymerization degree, the surface areas of the obtained PMO nanocubes can reach as high as 2370 m2/g, which is the highest for silica-based mesoporous materials. The ultrahigh surface area of the obtained PMO single crystals is mainly resulted from abundant micropores in the mesoporous frameworks. Furthermore, the diameter of the nanocubes can also be well controlled from 150 to 600 nm. The materials show ultrahigh CO2 adsorption capacity (up to 1.42 mmol/g at 273 K) which is much higher than other porous silica materials and comparable to some carbonaceous materials. The adsorption of CO2 into the PMO nanocubes is mainly in physical interaction, therefore the adsorption-desorption process is highly reversible and the adsorption capacity is much dependent on the surface area of the materials. Moreover, the selectivity is also very high (~11 times to N2) towards CO2 adsorption. PMID:26868049

  3. Periodic Mesoporous Organosilica Nanocubes with Ultrahigh Surface Areas for Efficient CO2 Adsorption

    NASA Astrophysics Data System (ADS)

    Wei, Yong; Li, Xiaomin; Zhang, Renyuan; Liu, Yong; Wang, Wenxing; Ling, Yun; El-Toni, Ahmed Mohamed; Zhao, Dongyuan

    2016-02-01

    Ultrahigh surface area single-crystals of periodic mesoporous organosilica (PMOs) with uniform cubic or truncated-cubic morphology and organic/inorganic components homogeneously distributed over the whole frameworks have successfully been prepared by a sol-gel surfactant-templating method. By tuning the porous feature and polymerization degree, the surface areas of the obtained PMO nanocubes can reach as high as 2370 m2/g, which is the highest for silica-based mesoporous materials. The ultrahigh surface area of the obtained PMO single crystals is mainly resulted from abundant micropores in the mesoporous frameworks. Furthermore, the diameter of the nanocubes can also be well controlled from 150 to 600 nm. The materials show ultrahigh CO2 adsorption capacity (up to 1.42 mmol/g at 273 K) which is much higher than other porous silica materials and comparable to some carbonaceous materials. The adsorption of CO2 into the PMO nanocubes is mainly in physical interaction, therefore the adsorption-desorption process is highly reversible and the adsorption capacity is much dependent on the surface area of the materials. Moreover, the selectivity is also very high (~11 times to N2) towards CO2 adsorption.

  4. Effect of surface area and chemisorbed oxygen on the SO2 adsorption capacity of activated char

    USGS Publications Warehouse

    Lizzio, A.A.; DeBarr, J.A.

    1996-01-01

    The objective of this study was to determine whether activated char produced from Illinois coal could be used effectively to remove sulfur dioxide from coal combustion flue gas. Chars were prepared from a high-volatile Illinois bituminous coal under a wide range of pyrolysis and activation conditions. A novel char preparation technique was developed to prepare chars with SO2 adsorption capacities significantly greater than that of a commercial activated carbon. In general, there was no correlation between SO2 adsorption capacity and surface area. Temperature-programmed desorption (TPD) was used to determine the nature and extent of carbon-oxygen (C-O) complexes formed on the char surface. TPD data revealed that SO2 adsorption was inversely proportional to the amount of C-O complex. The formation of a stable C-O complex during char preparation may have served only to occupy carbon sites that were otherwise reactive towards SO2 adsorption. A fleeting C(O) complex formed during SO2 adsorption is postulated to be the reaction intermediate necessary for conversion of SO2 to H2SO4. Copyright ?? 1996 Elsevier Science Ltd.

  5. Adsorption of neon and tetrafluoromethane on carbon nanohorn aggregates: differences in specific surface area values

    NASA Astrophysics Data System (ADS)

    Krungleviciute, Vaiva; Yudasaka, Masako; Iijima, Sumio; Migone, Aldo

    2008-03-01

    We have measured adsorption isotherms for two different adsorbates, neon and tetrafluoromethane, on dahlia-like carbon nanohorn aggregates. The experiments were performed at similar relative temperatures for both gases. The measurements were conducted to explore the effect of adsorbate diameter on the behavior of the resulting adsorbed systems. We measured the effective specific surface area value of the nanohorn sample using both gases, and we found that this quantity was about 22% smaller when we determined this quantity using tetrafluoromethane, the larger molecule. Isosteric heat and binding energy values were also determined from our measurements. We will compare our experimental results with those from a computer simulation study performed by Prof. M. Calbi. The simulations help us understand the source of the observed differences in the measured specific surface values, as well as the coverage dependence of the isosteric heat of adsorption for both gases.

  6. Pore Scale Heterogeneity in the Mineral Distribution, Surface Area and Adsorption in Porous Rocks

    NASA Astrophysics Data System (ADS)

    Lai, P. E. P.; Krevor, S. C.

    2014-12-01

    The impact of heterogeneity in chemical transport and reaction is not understood in continuum (Darcy/Fickian) models of reactive transport. This is manifested in well-known problems such as scale dependent dispersion and discrepancies in reaction rate observations made at laboratory and field scales [1]. Additionally, this is a source of uncertainty for carbon dioxide injection, which produces a reactive fluid-rock system particularly in carbonate rock reservoirs. A potential cause is the inability of the continuum approach to incorporate the impact of heterogeneity in pore-scale reaction rates. This results in part from pore-scale heterogeneities in surface area of reactive minerals [2, 3]. We use x-ray micro tomography to describe the non-normal 3-dimensional distribution of reactive surface area within a porous medium according to distinct mineral groups. Using in-house image processing techniques, thin sections, nitrogen BET surface area, backscattered electron imaging and energy dispersive spectroscopy, we compare the surface area of each mineral phase to those obtained from x-ray CT imagery. In all samples, there is little correlation between the reactive surface area fraction and the volumetric fraction of a mineral in a bulk rock. Berea sandstone was far less heterogeneous and has a characteristic pore size at which a surface area distribution may be used to quantify heterogeneity. In carbonates, heterogeneity is more complex and surface area must be characterized at multiple length scales for an accurate description of reactive transport. We combine the mineral specific surface area characterisation to dynamic tomography, imaging the flow of water and solutes, to observe flow dependent and mineral specific adsorption. The observations may contribute to the incorporation of experimentally based statistical descriptions of pore scale heterogeneity in reactive transport into upscaled models, moving it closer to predictive capabilities for field scale

  7. Facile synthesis of ultrahigh-surface-area hollow carbon nanospheres for enhanced adsorption and energy storage

    PubMed Central

    Xu, Fei; Tang, Zhiwei; Huang, Siqi; Chen, Luyi; Liang, Yeru; Mai, Weicong; Zhong, Hui; Fu, Ruowen; Wu, Dingcai

    2015-01-01

    Exceptionally large surface area and well-defined nanostructure are both critical in the field of nanoporous carbons for challenging energy and environmental issues. The pursuit of ultrahigh surface area while maintaining definite nanostructure remains a formidable challenge because extensive creation of pores will undoubtedly give rise to the damage of nanostructures, especially below 100 nm. Here we report that high surface area of up to 3,022 m2 g−1 can be achieved for hollow carbon nanospheres with an outer diameter of 69 nm by a simple carbonization procedure with carefully selected carbon precursors and carbonization conditions. The tailor-made pore structure of hollow carbon nanospheres enables target-oriented applications, as exemplified by their enhanced adsorption capability towards organic vapours, and electrochemical performances as electrodes for supercapacitors and sulphur host materials for lithium–sulphur batteries. The facile approach may open the doors for preparation of highly porous carbons with desired nanostructure for numerous applications. PMID:26072734

  8. Uranium(VI) adsorption and surface complexation modeling onto background sediments from the F-Area Savannah River Site.

    PubMed

    Dong, Wenming; Tokunaga, Tetsu K; Davis, James A; Wan, Jiamin

    2012-02-01

    The mobility of an acidic uranium waste plume in the F-Area of Savannah River Site is of great concern. In order to understand and predict uranium mobility, U(VI) adsorption experiments were performed as a function of pH using background F-Area aquifer sediments and reference goethite and kaolinite (major reactive phases of F-Area sediments), and a component-additivity (CA) based surface complexation model (SCM) was developed. Our experimental results indicate that the fine fractions (≤45 μm) in sediments control U(VI) adsorption due to their large surface area, although the quartz sands show a stronger adsorption ability per unit surface area than the fine fractions at pH < 5.0. Kaolinite is a more important sorbent for U(VI) at pH < 4.0, while goethite plays a major role at pH > 4.0. Our CA model combines an existing U(VI) SCM for goethite and a modified U(VI) SCM for kaolinite along with estimated relative surface area abundances of these component minerals. The modeling approach successfully predicts U(VI) adsorption behavior by the background F-Area sediments. The model suggests that exchange sites on kaolinite dominate U(VI) adsorption at pH < 4.0, goethite and kaolinite edge sites cocontribute to U(VI) adsorption at pH 4.0-6.0, and goethite dominates U(VI) adsorption at pH > 6.0.

  9. A high surface area Zr(IV)-based metal–organic framework showing stepwise gas adsorption and selective dye uptake

    SciTech Connect

    Lv, Xiu-Liang; Tong, Minman; Huang, Hongliang; Wang, Bin; Gan, Lei; Yang, Qingyuan; Zhong, Chongli; Li, Jian-Rong

    2015-03-15

    Exploitation of new metal–organic framework (MOF) materials with high surface areas has been attracting great attention in related research communities due to their broad potential applications. In this work, a new Zr(IV)-based MOF, [Zr{sub 6}O{sub 4}(OH){sub 4}(eddb){sub 6}] (BUT-30, H{sub 2}eddb=4,4′-(ethyne-1,2-diyl)dibenzoic acid) has been solvothermally synthesized, characterized, and explored for gases and dyes adsorptions. Single-crystal X-ray diffraction analysis demonstrates a three-dimensional cubic framework structure of this MOF, in which each Zr{sub 6}O{sub 4}(OH){sub 4} building unit is linked by 12 linear eddb ligands. BUT-30 has been found stable up to 400 °C and has a Brunauer–Emmett–Teller (BET) surface area as high as 3940.6 m{sup 2} g{sup −1} (based on the N{sub 2} adsorption at 77 K) and total pore volume of 1.55 cm{sup 3} g{sup −1}. It is more interesting that this MOF exhibits stepwise adsorption behaviors for Ar, N{sub 2}, and CO{sub 2} at low temperatures, and selective uptakes towards different ionic dyes. - Graphical abstract: A new Zr(IV)-based MOF with high surface area has been synthesized and structurally characterized, which shows stepwise gas adsorption at low temperature and selective dye uptake from solution. - Highlights: • A new Zr-based MOF was synthesized and structurally characterized. • This MOF shows a higher surface area compared with its analogous UiO-67 and 68. • This MOF shows a rare stepwise adsorption towards light gases at low temperature. • This MOF performs selective uptakes towards cationic dyes over anionic ones. • Using triple-bond spacer is confirmed feasible in enhancing MOF surface areas.

  10. Determination of surface area and porosity of small, nanometer-thick films by quartz crystal microbalance measurement of gas adsorption.

    PubMed

    Aoki, Yoshitaka; Hashizume, Mineo; Onoue, Shinya; Kunitake, Toyoki

    2008-11-20

    The Brunauer-Emmett-Teller (BET) surface area of 15 nm-thick films made of TiO2/polyelectrolyte bilayer was determined by quartz crystal microbalance (QCM) measurement of N2 and Ar adsorption isotherms at 77 K. The measurements were carried out using a home-built vacuum chamber that includes built-in 9 MHz QCM and cryostat units. As little as 1 ng of the adsorbed gas could be detected, and the BET surface area of a flat Au film (ca. 0.5 cm2) on an oscillator was determined within an experimental error of +/-5%. The titania/polymer composite film gives N2 and Ar adsorption isotherms consisting of a less-pronounced type-I curve and a break at around p/p0 = 0.7. This behavior is ascribed to the presence of irregular micropores and 6 nm phi-mesopores in the composite film. An analysis of the isotherms shows that the porosity of the composite film is about 12%, which is much smaller than that of bulk titania gel powder. The greater density appears to be related to the reported superior properties (robustness and resistance to electrical breakdown) of the organic/inorganic multilayer film. We conclude that the QCM-based, high-precision measurement of gas adsorption is a powerful tool for investigation of the detailed morphology of nanometer-thick films.

  11. Molecular surface area based predictive models for the adsorption and diffusion of disperse dyes in polylactic acid matrix.

    PubMed

    Xu, Suxin; Chen, Jiangang; Wang, Bijia; Yang, Yiqi

    2015-11-15

    Two predictive models were presented for the adsorption affinities and diffusion coefficients of disperse dyes in polylactic acid matrix. Quantitative structure-sorption behavior relationship would not only provide insights into sorption process, but also enable rational engineering for desired properties. The thermodynamic and kinetic parameters for three disperse dyes were measured. The predictive model for adsorption affinity was based on two linear relationships derived by interpreting the experimental measurements with molecular structural parameters and compensation effect: ΔH° vs. dye size and ΔS° vs. ΔH°. Similarly, the predictive model for diffusion coefficient was based on two derived linear relationships: activation energy of diffusion vs. dye size and logarithm of pre-exponential factor vs. activation energy of diffusion. The only required parameters for both models are temperature and solvent accessible surface area of the dye molecule. These two predictive models were validated by testing the adsorption and diffusion properties of new disperse dyes. The models offer fairly good predictive ability. The linkage between structural parameter of disperse dyes and sorption behaviors might be generalized and extended to other similar polymer-penetrant systems.

  12. Adsorption of phenol on wood surfaces

    NASA Astrophysics Data System (ADS)

    Mamleeva, N. A.; Lunin, V. V.

    2016-03-01

    Adsorption of phenol on aspen and pine wood is investigated. It is shown that adsorption isotherms are described by the Langmuir model. The woods' specific surface areas and adsorption interaction constants are determined. It is found that the sorption of phenol on surfaces of aspen and pine is due to Van der Waals interactions ( S sp = 45 m2/godw for aspen and 85 m2/godw for pine). The difference between the adsorption characteristics is explained by properties of the wood samples' microstructures.

  13. Lithium inclusion in indium metal-organic frameworks showing increased surface area and hydrogen adsorption

    SciTech Connect

    Bosch, Mathieu; Zhang, Muwei; Feng, Dawei; Yuan, Shuai; Wang, Xuan; Chen, Ying-Pin; Zhou, Hong-Cai

    2014-12-01

    Investigation of counterion exchange in two anionic In-Metal-Organic Frameworks (In-MOFs) showed that partial replacement of disordered ammonium cations was achieved through the pre-synthetic addition of LiOH to the reaction mixture. This resulted in a surface area increase of over 1600% in (Li [In(1,3 − BDC){sub 2}]){sub n} and enhancement of the H{sub 2} uptake of approximately 275% at 80 000 Pa at 77 K. This method resulted in frameworks with permanent lithium content after repeated solvent exchange as confirmed by inductively coupled plasma mass spectrometry. Lithium counterion replacement appears to increase porosity after activation through replacement of bulkier, softer counterions and demonstrates tuning of pore size and properties in MOFs.

  14. Changes in the size of the apparent surface area and adsorption energy of the rye roots by low pH and the presence of aluminium ions induced

    NASA Astrophysics Data System (ADS)

    Szatanik-Kloc, Alicja

    2016-07-01

    The plant reactions on Al-stress include i.a. change of the surface area of the roots, which in the physicochemistry of plants characterizes the transport of water and ions through the root. The object of this study is the specific surface area of the roots of plants which are tolerant to aluminium, such as rye. Plants of rye were grown in a nutrient solution for 14 days at pH 4.5 in the presence of Al3+ ions of concentration 10, 20, and 40 mg dm-3. The control plants were grown continuously at pH 7 or pH 4.5 without Al3+. The apparent surface area and adsorption energy of the plants roots were determined from water vapour adsorption - desorption data. The apparent surface area of roots growing in the aluminium was (with respect to control) statistically significantly lower. There were no statistically significant differences in the apparent surface area of the roots which grew in pH 7, pH 4.5 without Al3+. The average water vapour adsorption energy of the root surface, under stress conditions decreased. In the roots grown in the presence of Al+3, there was a slight decrease in high energy adsorption centres and an increase in the amount of low-energy centres.

  15. The role of counter ions in nano-hematite synthesis: Implications for surface area and selenium adsorption capacity.

    PubMed

    Lounsbury, Amanda W; Yamani, Jamila S; Johnston, Chad P; Larese-Casanova, Philip; Zimmerman, Julie B

    2016-06-01

    Nano metal oxides are of interest for aqueous selenium (Se) remediation, and as such, nano-hematite (nα-Fe2O3) was examined for use as a Se adsorbent. The effect of surface area on adsorption was also studied. nα-Fe2O3 particles were synthesized from Fe(NO3)3 and FeCl3 via forced hydrolysis. The resulting particles have similar sizes, morphologies, aggregate size, pore size, and PZC. The nα-Fe2O3 from FeCl3 (nα-Fe2O3-C) differs from the nα-Fe2O3 from Fe(NO3)3 (nα-Fe2O3-N) with a ∼25±2m(2)/g greater surface area. Selenite Se(IV) adsorption capacity on nα-Fe2O3 has a qmax ∼17mg/g for the freeze-dried and re-suspended nα-Fe2O3. The Δqmax for nα-Fe2O3 from Fe(NO3)3 and FeCl3 that remained in suspension was 4.6mg/g. For selenate Se(VI), the freeze-dried and re-suspended particles realize a Δqmax= 1.5mg/g for nα-Fe2O3 from Fe(NO3)3 and FeCl3. The nα-Fe2O3 from Fe(NO3)3 and FeCl3 that remained in suspension demonstrated Se(VI) Δqmax=5.4mg/g. In situ ATR-FTIR isotherm measurements completed for Se(VI) at a pH 6 suggest that Se(VI) forms primarily outer-sphere complexes with nα-Fe2O3 synthesized from both salts. PMID:26905609

  16. Use of lipophilic ion adsorption isotherms to determine the surface area and the monolayer capacity of a chromatographic packing, as well as the thermodynamic equilibrium constant for its adsorption.

    PubMed

    Cecchi, T

    2005-04-29

    A method that champions the approaches of two independent research groups, to quantitate the chromatographic stationary phase surface available for lipophilic ion adsorption, is presented. For the first time the non-approximated expression of the electrostatically modified Langmuir adsorption isotherm was used. The non approximated Gouy-Chapman (G-C) theory equation was used to give the rigorous surface potential. The method helps model makers, interested in ionic interactions, determine whether the potential modified Langmuir isotherm can be linearized, and, accordingly, whether simplified retention equations can be properly used. The theory cultivated here allows the estimates not only of the chromatographically accessible surface area, but also of the thermodynamic equilibrium constant for the adsorption of the amphiphile, the standard free energy of its adsorption, and the monolayer capacity of the packing. In addition, it establishes the limit between a theoretical and an empirical use of the Freundlich isotherm to determine the surface area. Estimates of the parameters characterising the chromatographic system are reliable from the physical point of view, and this greatly validates the present comprehensive approach.

  17. Synthesis of high surface area carbon adsorbents prepared from pine sawdust-Onopordum acanthium L. for nonsteroidal anti-inflammatory drugs adsorption.

    PubMed

    Álvarez-Torrellas, S; Muñoz, M; Zazo, J A; Casas, J A; García, J

    2016-12-01

    Chemically activated carbon materials prepared from pine sawdust-Onopordum acanthium L. were studied for the removal of diclofenac and naproxen from aqueous solution. Several carbons, using different proportions of precursors were obtained (carbon C1 to carbon C5) and the chemical modification by liquid acid and basic treatments of C1 were carried out. The textural properties of the carbons, evaluated by N2 adsorption-desorption isotherms, revealed that the treatments with nitric acid and potassium hydroxide dramatically reduced the specific surface area and the pore volume of the carbon samples. The surface chemistry characterization, made by thermal programmed decomposition studies, determination of isoelectric point and Boehm's titration, showed the major presence of lactone and phenol groups on the activated carbons surface, being higher the content when the acidic strength of the carbon increased. Diclofenac and naproxen kinetic data onto C1 carbon followed pseudo-second order model. The adsorption equilibrium isotherms of C1 and the modified carbons were well described by both Sips and GAB isotherm equations. The highest adsorption capacity was found for naproxen onto C1 activated carbon, 325 mg g(-1), since the liquid acid and basic functionalization of the carbon led to a severe decreasing in the adsorption removal of the target compounds. PMID:27604753

  18. Synthesis of high surface area carbon adsorbents prepared from pine sawdust-Onopordum acanthium L. for nonsteroidal anti-inflammatory drugs adsorption.

    PubMed

    Álvarez-Torrellas, S; Muñoz, M; Zazo, J A; Casas, J A; García, J

    2016-12-01

    Chemically activated carbon materials prepared from pine sawdust-Onopordum acanthium L. were studied for the removal of diclofenac and naproxen from aqueous solution. Several carbons, using different proportions of precursors were obtained (carbon C1 to carbon C5) and the chemical modification by liquid acid and basic treatments of C1 were carried out. The textural properties of the carbons, evaluated by N2 adsorption-desorption isotherms, revealed that the treatments with nitric acid and potassium hydroxide dramatically reduced the specific surface area and the pore volume of the carbon samples. The surface chemistry characterization, made by thermal programmed decomposition studies, determination of isoelectric point and Boehm's titration, showed the major presence of lactone and phenol groups on the activated carbons surface, being higher the content when the acidic strength of the carbon increased. Diclofenac and naproxen kinetic data onto C1 carbon followed pseudo-second order model. The adsorption equilibrium isotherms of C1 and the modified carbons were well described by both Sips and GAB isotherm equations. The highest adsorption capacity was found for naproxen onto C1 activated carbon, 325 mg g(-1), since the liquid acid and basic functionalization of the carbon led to a severe decreasing in the adsorption removal of the target compounds.

  19. Adsorption of reovirus to clay minerals: effects of cation-exchange capacity, cation saturation, and surface area.

    PubMed Central

    Lipson, S M; Stotzky, G

    1983-01-01

    The adsorption of reovirus to clay minerals has been reported by several investigators, but the mechanisms defining this association have been studied only minimally. The purpose of this investigation was to elucidate the mechanisms involved with this interaction. More reovirus type 3 was adsorbed, in both distilled and synthetic estuarine water, by low concentrations of montmorillonite than by comparable concentrations of kaolinite containing a mixed complement of cations on the exchange complex. Adsorption to the clays was essentially immediate and was correlated with the cation-exchange capacity of the clays, indicating that adsorption was primarily to negatively charged sites on the clays. Adsorption was greater with low concentrations of clays in estuarine water than in distilled water, as the higher ionic strength of the estuarine water reduced the electrokinetic potential of both clay and virus particles. The addition of cations (as chloride salts) to distilled water enhanced adsorption, with divalent cations being more effective than monovalent cations and 10(-2) M resulting in more adsorption than 10(-3) M. Potassium ions suppressed reovirus adsorption to montmorillonite, probably by collapsing the clay lattices and preventing the expression of the interlayer-derived cation-exchange capacity. More virus was adsorbed by montmorillonite made homoionic to various mono-, di-, and trivalent cations (except by montmorillonite homoionic to potassium) than by comparable concentrations of kaolinite homoionic to the same cations. The sequence of the amount of adsorption to homoionic montmorillonite was Al greater than Ca greater than Mg greater than Na greater than K; the sequence of adsorption to kaolinite was Na greater than Al greater than Ca greater than Mg greater than K. The constant partition-type adsorption isotherms obtained when the clay concentration was maintained constant and the virus concentration was varied indicated that a fixed proportion of the

  20. Protein adsorption onto ceramic surfaces.

    PubMed

    Takami, Y; Yamane, S; Makinouchi, K; Otsuka, G; Glueck, J; Benkowski, R; Nosé, Y

    1998-04-01

    Ceramics seldom have been used as blood-contacting materials. However, alumina ceramic (Al2O3) and polyethylene are incorporated into the pivot bearings of the Gyro centrifugal blood pump. This material combination was chosen based on the high durability of the materials. Due to the stagnant flow that often occurs in a continuous flow condition inside a centrifugal pump, pivot bearing system is extremely critical. To evaluate the thombogenicity of pivot bearings in the Gyro pump, this study sought to investigate protein adsorption, particularly albumin, IgG, fibrinogen, and fibronectin onto ceramic surfaces. Al2O3 and silicon carbide ceramic (SiC) were compared with polyethylene (PE) and polyvinylchloride (PVC). Bicinchoninic acid (BCA) protein assay revealed that the amount of adsorbed proteins onto Al2O3 and SiC was significantly less than that on PVC. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated that numerous proteins adsorbed onto PVC compared to PE, Al2O3, and SiC. Identification of adsorbed proteins by Western immunoblotting revealed that the adsorption of albumin was similar on all four materials tested. Western immunoblotting also indicated lesser amounts of IgG, fibrinogen, and fibronectin on Al2O3 and SiC than on PE and PVC. In conclusion, ceramics (Al2O3 and SiC) are expected to be thromboresistant from the viewpoint of protein adsorption. PMID:9511095

  1. Association of the physical and chemical properties and the cytotoxicity of metal oxide nanoparticles: metal ion release, adsorption ability and specific surface area.

    PubMed

    Horie, Masanori; Fujita, Katsuhide; Kato, Haruhisa; Endoh, Shigehisa; Nishio, Keiko; Komaba, Lilian Kaede; Nakamura, Ayako; Miyauchi, Arisa; Kinugasa, Shinichi; Hagihara, Yoshihisa; Niki, Etsuo; Yoshida, Yasukazu; Iwahashi, Hitoshi

    2012-04-01

    Association of cellular influences and physical and chemical properties were examined for 24 kinds of industrial metal oxide nanoparticles: ZnO, CuO, NiO, Sb(2)O(3), CoO, MoO(3), Y(2)O(3), MgO, Gd(2)O(3), SnO(2), WO(3), ZrO(2), Fe(2)O(3), TiO(2), CeO(2), Al(2)O(3), Bi(2)O(3), La(2)O(3), ITO, and cobalt blue pigments. We prepared a stable medium dispersion for each nanoparticle and examined the influence on cell viability and oxidative stress together with physical and chemical characterizations. ZnO, CuO, NiO, MgO, and WO(3) showed a large amount of metal ion release in the culture medium. The cellular influences of these soluble nanoparticles were larger than insoluble nanoparticles. TiO(2), SnO(2), and CeO(2) nanoparticles showed strong protein adsorption ability; however, cellular influences of these nanoparticles were small. The primary particle size and the specific surface area seemed unrelated to cellular influences. Cellular influences of metal oxide nanoparticles depended on the kind and concentrations of released metals in the solution. For insoluble nanoparticles, the adsorption property was involved in cellular influences. The primary particle size and specific surface area of metal oxide nanoparticles did not affect directly cellular influences. In conclusion the most important cytotoxic factor of metal oxide nanoparticles was metal ion release.

  2. Comparison between the loading capacities of columns packed with partially and totally porous fine particles. What is the effective surface area available for adsorption?

    PubMed

    Gritti, Fabrice; Guiochon, Georges

    2007-12-28

    The adsorption isotherms of phenol, caffeine, insulin, and lysozyme were measured on two C(18)-bonded silica columns. The first one was packed with classical totally porous particles (3 microm Luna(2)-C(18)from Phenomenex, Torrance, CA, USA), the second one with shell particles (2.7 microm Halo-C(18) from Advanced Materials Technology, Wilmington, DE, USA). The measurements were made at room temperature (T=295+/-1K), using mainly frontal analysis (FA) and also elution by characteristic points (FACP) when necessary. The adsorption energy distributions (AEDs) were estimated by the iterative numerical expectation-maximization (EM) procedure and served to justify the choice of the best adsorption isotherm model for each compound. The best isotherm parameters were derived from either the best fit of the experimental data to a multi-Langmuir isotherm model (MLRA) or from the AED results (equilibrium constants and saturation capacities), when the convergence of the EM program was achieved. The experiments show than the loading capacity of the Luna column is more than twice that of the Halo column for low-molecular-weight compounds. This result was expected; it is in good agreement with the values of the accessible surface area of these two materials, which were calculated from the pore size volume distributions. The pore size volume distributions are validated by the excellent agreement between the calculated and measured exclusion volumes of polystyrene standards by inverse size exclusion chromatography (ISEC). In contrast, the loading capacity ratio of the two columns is 1.5 or less with insulin and lysozyme. This is due to a significant exclusion of these two proteins from the internal pore volumes of the two packing materials. This result raises the problem of the determination of the effective surface area of the packing material, particularly in the case of proteins. This area is about 40 and 30% of the total surface area for insulin and for lysozyme, respectively

  3. Cd adsorption onto bacterial surfaces: A universal adsorption edge?

    NASA Astrophysics Data System (ADS)

    Yee, Nathan; Fein, Jeremy

    2001-07-01

    In this study, we measure the thermodynamic stability constants for proton and Cd binding onto the Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa, and the Gram-positive bacteria Bacillus megaturium, Streptococcus faecalis, Staphylococcus aureus, Sporosarcina ureae, and Bacillus cereus. Potentiometric titrations and Cd-bacteria adsorption experiments yield average values for the carboxyl site pK a, site concentration, and log stability constant for the bacterial surface Cd-carboxyl complex of 5.0, 2.0 × 10 -3 mol/g and 4.0 respectively. Our results indicate that a wide range of bacterial species exhibit nearly identical Cd adsorption behavior as a function of pH. We propose that metal-bacteria adsorption is not dependent on the bacterial species involved, and we develop a generalized adsorption model which may greatly simplify the task of quantifying the effects of bacterial adsorption on dissolved mass transport in realistic geologic systems.

  4. Formation, Chemistry and Fertility of Extraterrestrial Soils: Cohesion, Water Adsorption and Surface Area of Carbonaceous Chondrite. Prebiotic and Space Resource Applications

    NASA Astrophysics Data System (ADS)

    Mautner, Michael N.

    1999-01-01

    Following microbial and plant responses to Murchison CM2 meteorite nutrients, further soil fertility parameters are examined. Cohesion of the matrix is tested by dissolving in acidic disaggregation agents, 0.4 M CH3COOH, 10% HNO3, H2SO4(pH 3), 50%H2O2+H2SO4(pH 3), and saturated CO2solution. The responses suggest that carbonates and the organic polymer contribute as cementing agents, and that enhanced disaggregation by H2O2and diminished disaggregation in saturated CO2solutions may contribute to the weathering of carbonaceous meteorites in martian or early Earth environments, respectively. The cation exchange capacities (CEC) of the solid (7.2±0.8 meq/100 g) and powdered Murchison (7.8±1.5 meq/100 g) are comparable. The cation exchange capacity is not reduced by oxidation or acetylation, suggesting that the binding sites of exchangeable cations are mostly inorganic. The CEC correlates with water vapor adsorption similar to that for terrestrial soils. For example, at 20°C andP(H2O)=10.8 mbars, 17 mg/g H2O is adsorbed on Murchison (CEC=7.2 meq/100 g) and only 0.6 mg/g on Allende (CEC=0.4 meq/100 g). Under these conditions 13 H2O molecules are adsorbed per surface cation in Murchison and 8 H2O molecules/cation in Allende, similar to 9 H2O molecules/cation in terrestrial soils and in montmorillonite. Adsorption isotherms on the Murchison are convex at low pressures, indicating strong bonding of the first water molecules, and concave at high pressures, indicating a broad pore size distribution. Isotherms at 278, 293, and 311 K yield isosteric heat of adsorption of 56.5±2.5 kJ/mol at 4-8 H2Oadsorbedmolecules/cation, similar to that for montmorillonite. The isotherms yield a specific surface area of Sw=37×103m2/kg for Murchison, larger than the 19×103m2/kg of pure serpentine, suggesting contributions, in addition to the main serpentine-like phyllosilicates, by components equivalent to a 9-12% smectic clay-like content. Water evaporation curves from meteorite surfaces

  5. Graphene-based porous materials with tunable surface area and CO2 adsorption properties synthesized by fluorine displacement reaction with various diamines.

    PubMed

    Li, Baoyin; Fan, Kun; Ma, Xin; Liu, Yang; Chen, Teng; Cheng, Zheng; Wang, Xu; Jiang, Jiaxing; Liu, Xiangyang

    2016-09-15

    A mild, operationally simple and controllable protocol for preparing graphene-based porous materials is essential to achieve a good pore-design development. In this paper, graphene-based porous materials with tunable surface area were constructed by the intercalation of fluorinated graphene (FG) based on the reaction of reactive CF bonds attached to graphene sheets with various amine-terminated molecules. In the porous materials, graphene sheets are like building blocks, and the diamines covalently grafted onto graphene framework act as pillars. Various diamines are successfully grafted onto graphene sheets, but the grafting ratio of diamines and reduction degree of FG differ greatly and depend on the chemical reactivity of diamines. Pillared diamine molecules chemically anchor at one end and are capable of undergoing a different reaction on the other end, resulting in three different conformations of graphene derivatives. Nitrogen sorption isotherms revealed that the surface area and pore distribution of the obtained porous materials depend heavily on the size and structure of diamine pillars. CO2 uptake capacity characterization showed that ethylenediamine intercalated FG achieved a high CO2 uptake density of 18.0 CO2 molecules per nm(2) at 0°C and 1.1bars, and high adsorption heat, up to 46.1kJmol(-1) at zero coverage. PMID:27280538

  6. Graphene-based porous materials with tunable surface area and CO2 adsorption properties synthesized by fluorine displacement reaction with various diamines.

    PubMed

    Li, Baoyin; Fan, Kun; Ma, Xin; Liu, Yang; Chen, Teng; Cheng, Zheng; Wang, Xu; Jiang, Jiaxing; Liu, Xiangyang

    2016-09-15

    A mild, operationally simple and controllable protocol for preparing graphene-based porous materials is essential to achieve a good pore-design development. In this paper, graphene-based porous materials with tunable surface area were constructed by the intercalation of fluorinated graphene (FG) based on the reaction of reactive CF bonds attached to graphene sheets with various amine-terminated molecules. In the porous materials, graphene sheets are like building blocks, and the diamines covalently grafted onto graphene framework act as pillars. Various diamines are successfully grafted onto graphene sheets, but the grafting ratio of diamines and reduction degree of FG differ greatly and depend on the chemical reactivity of diamines. Pillared diamine molecules chemically anchor at one end and are capable of undergoing a different reaction on the other end, resulting in three different conformations of graphene derivatives. Nitrogen sorption isotherms revealed that the surface area and pore distribution of the obtained porous materials depend heavily on the size and structure of diamine pillars. CO2 uptake capacity characterization showed that ethylenediamine intercalated FG achieved a high CO2 uptake density of 18.0 CO2 molecules per nm(2) at 0°C and 1.1bars, and high adsorption heat, up to 46.1kJmol(-1) at zero coverage.

  7. Protein Adsorption on Surfaces with Grafted Polymers

    PubMed Central

    Szleifer, I.

    1997-01-01

    A general theoretical framework for studying the adsorption of protein molecules on surfaces with grafted polymers is presented. The approach is a generalization of the single-chain mean-field theory, in which the grafted polymer-protein-solvent layer is assumed to be inhomogeneous in the direction perpendicular to the grafting surface. The theory enables the calculation of the adsorption isotherms of the protein as a function of the surface coverage of grafted polymers, concentration of protein in bulk, and type of solvent molecules. The potentials of mean force of the protein with the surface are calculated as a function of polymer surface coverage and amount of protein adsorbed. The theory is applied to model lysozyme on surfaces with grafted polyethylene oxide. The protein is modeled as spherical in solution, and it is assumed that the protein-polymer, protein-solvent, and polymer-solvent attractive interactions are all equal. Therefore, the interactions determining the structure of the layer (beyond the bare polymer-surface and protein-surface interactions) are purely repulsive. The bare surface-protein interaction is taken from atomistic calculations by Lee and Park. For surfaces that do not have preferential attractions with the grafted polymer segments, the adsorption isotherms of lysozyme are independent of the polymer length for chains with more than 50 ethylene oxide units. However, the potentials of mean force show strong variations with grafted polymer molecular weight. The competition between different conformations of the adsorbed protein is studied in detail. The adsorption isotherms change qualitatively for surfaces with attractive interactions with ethylene oxide monomers. The protein adsorption is a function of chain length—the longer the polymer the more effective it is in preventing protein adsorption. The structure of the layer and its deformation upon protein adsorption are very important in determining the adsorption isotherms and the

  8. Adsorption Isotherms and Surface Reaction Kinetics

    ERIC Educational Resources Information Center

    Lobo, L. S.; Bernardo, C. A.

    1974-01-01

    Explains an error that occurs in calculating the conditions for a maximum value of a rate expression for a bimolecular reaction. The rate expression is derived using the Langmuir adsorption isotherm to relate gas pressures and corresponding surface coverages. (GS)

  9. Surface area and pore size characteristics of nanoporous gold subjected to thermal, mechanical, or surface modification studied using gas adsorption isotherms, cyclic voltammetry, thermogravimetric analysis, and scanning electron microscopy

    PubMed Central

    Tan, Yih Horng; Davis, Jason A.; Fujikawa, Kohki; Ganesh, N. Vijaya; Demchenko, Alexei V.

    2012-01-01

    Nitrogen adsorption/desorption isotherms are used to investigate the Brunauer, Emmett, and Teller (BET) surface area and Barrett-Joyner-Halenda (BJH) pore size distribution of physically modified, thermally annealed, and octadecanethiol functionalized np-Au monoliths. We present the full adsorption-desorption isotherms for N2 gas on np-Au, and observe type IV isotherms and type H1 hysteresis loops. The evolution of the np-Au under various thermal annealing treatments was examined using scanning electron microscopy (SEM). The images of both the exterior and interior of the thermally annealed np-Au show that the porosity of all free standing np-Au structures decreases as the heat treatment temperature increases. The modification of the np-Au surface with a self-assembled monolayer (SAM) of C18-SH (coverage of 2.94 × 1014 molecules cm−2 based from the decomposition of the C18-SH using thermogravimetric analysis (TGA)), was found to reduce the strength of the interaction of nitrogen gas with the np-Au surface, as reflected by a decrease in the ‘C’ parameter of the BET equation. From cyclic voltammetry studies, we found that the surface area of the np-Au monoliths annealed at elevated temperatures followed the same trend with annealing temperature as found in the BET surface area study and SEM morphology characterization. The study highlights the ability to control free-standing nanoporous gold monoliths with high surface area, and well-defined, tunable pore morphology. PMID:22822294

  10. Adsorption of Polymers on Rough Surfaces

    NASA Astrophysics Data System (ADS)

    Venkatakrishnan, Abishek; Kuppa, Vikram

    2014-03-01

    Most of the surfaces encountered in nature display irregularity and self-similarity at certain length scales. Such real surfaces can be mimicked via fractal surfaces using an algorithm that produces random surfaces. The problem of polymer chains adsorbed on smooth surfaces has been well understood whereas adsorption on rough surfaces still remains unclear due to the complexity involved in equilibration and sampling of molecules in such systems. The enthalpic interactions between the monomers and the entropic penalty arising due to adsorption on rough surfaces are significantly different from smooth surfaces. In this study, we investigate the adsorption of freely rotating polymer chains on fractal surfaces by Monte-Carlo molecular simulations. Random fractal surfaces are generated using the diamond-square algorithm for different values of the Hurst parameter. Properties like monomer-surface interaction, density profiles, chain orientation profiles and distribution of adsorbed chain fractions are investigated. We also demonstrate the significant effect of fractal dimension on adsorption of polymers on rough surfaces.

  11. Adsorption of ammonia on treated stainless steel and polymer surfaces

    NASA Astrophysics Data System (ADS)

    Vaittinen, O.; Metsälä, M.; Persijn, S.; Vainio, M.; Halonen, L.

    2014-05-01

    Adsorption of dynamically diluted ammonia at part-per-billion to low part-per-million concentrations in dry nitrogen was studied with treated and non-treated stainless steel and polymer test tubes. The treatments included electropolishing and two types of coatings based on amorphous silicon. Cavity ring-down spectroscopy with an external cavity diode laser operating in the near-infrared wavelength range was used to monitor the adsorption process in real time in continuous-flow conditions to obtain quantitative assessment of the adsorptive properties of the studied surfaces. The investigated polymers were all less adsorptive than any of the treated or non-treated stainless steel surfaces. Some of the commercial coatings reduced the adsorption loss of stainless steel by a factor of ten or more. Polyvinylidene fluoride was found to be superior (less adsorption) to the four other studied polymer coatings. The number of adsorbed ammonia molecules per surface area obtained at different ammonia gas phase concentrations was modeled with Langmuir and Freundlich isotherms. The time behavior of the adsorption-desorption process occurring in the time scale of seconds and minutes was simulated with a simple kinetic model.

  12. Adsorption of hydroxyacetone on pure ice surfaces.

    PubMed

    Petitjean, Mélanie; Darvas, Maria; Picaud, Sylvain; Jedlovszky, Pál; Le Calvé, Stéphane

    2010-12-17

    The adsorption of hydroxyacetone molecules at the surface of ice is investigated by means of flow-tube reactor measurements in the temperature range: 213-253 K. The number of molecules adsorbed per surface unit is conventionally plotted as a function of the absolute gas concentration of hydroxyacetone and is compared to that previously obtained for acetone and ethanol. The enthalpy of adsorption and the monolayer capacity at the ice surface are determined. In addition, molecular dynamics simulations are performed to support the experimental results. However, it is shown that the available interaction potential between hydroxyacetone and ice is not accurate enough to allow a robust detailed analysis of the adsorption process. Finally, a rapid estimation of the hydroxyacetone partitioning between the gas phase and ice shows that in the densest ice clouds, up to 29% of hydroxyacetone could be adsorbed on pure ice surfaces at 203 K.

  13. Adsorption of Atmospheric Gases on Pu Surfaces

    SciTech Connect

    Nelson, A J; Holliday, K S; Stanford, J A; Grant, W K; Erler, R G; Allen, P G; McLean, W; Roussel, P

    2012-03-29

    Surface adsorption represents a competition between collision and scattering processes that depend on surface energy, surface structure and temperature. The surface reactivity of the actinides can add additional complexity due to radiological dissociation of the gas and electronic structure. Here we elucidate the chemical bonding of gas molecules adsorbed on Pu metal and oxide surfaces. Atmospheric gas reactions were studied at 190 and 300 K using x-ray photoelectron spectroscopy. Evolution of the Pu 4f and O 1s core-level states were studied as a function of gas dose rates to generate a set of Langmuir isotherms. Results show that the initial gas dose forms Pu{sub 2}O{sub 3} on the Pu metal surface followed by the formation of PuO{sub 2} resulting in a layered oxide structure. This work represents the first steps in determining the activation energy for adsorption of various atmospheric gases on Pu.

  14. Random sequential adsorption on partially covered surfaces

    NASA Astrophysics Data System (ADS)

    Adamczyk, Zbigniew; Weroński, Paweł

    1998-06-01

    The random sequential adsorption (RSA) approach was used to analyze adsorption of hard spheres at surfaces precovered with smaller sized particles. Numerical simulations were performed to determine the available surface function φl of larger particles for various particle size ratios λ=al/as and surface concentration of smaller particles θs. It was found that the numerical results were in a reasonable agreement with the formula stemming from the scaled particle theory with the modification for the sphere/sphere geometry. Particle adsorption kinetics was also determined in terms of the RSA simulations. By extrapolating the θl vs τ-1/2 dependencies, the jamming concentrations of larger spheres θl∞ were determined as a function of the initial smaller sphere concentration. It was found that θl∞ were considerably reduced by the presence of smaller sized particles, especially for λ≫1. The pair correlation function g of larger particles in the jamming state was also determined, showing more short range ordering (at the same θl) in comparison with monodisperse systems. The theoretical predictions stemming from our calculations suggest that the presence of trace amounts of very small particles may exert a decisive influence on adsorption of larger particles.

  15. Unsaturated fatty acids in alkane solution: adsorption to steel surfaces.

    PubMed

    Lundgren, Sarah M; Persson, Karin; Mueller, Gregor; Kronberg, Bengt; Clarke, Jim; Chtaib, Mohammed; Claesson, Per M

    2007-10-01

    The adsorption of the unsaturated fatty acids oleic, linoleic, and linolenic acid on steel surfaces has been investigated by means of a quartz crystal microbalance (QCM). Two different solvents were used, n-hexadecane and its highly branched isomer, viz., 2,2,4,4,6,8,8-heptamethylnonane. The area occupied per molecule of oleic acid at 1 wt % corresponds to what is needed for adsorption parallel to the surface. At the same concentration, the adsorbed amount of linoleic acid and linolenic acid indicates that they adsorb in multilayers. The chemisorbed amount estimated from static secondary ion mass spectroscopy (SIMS) measurements was found to be similar for the three unsaturated fatty acids. In the case of linolenic acid, it was found that the presence of water significantly alters the adsorption, most likely because of the precipitation of fatty acid/water aggregates. Furthermore, static SIMS results indicate that the amount of water used here inhibits the chemisorption of linolenic acid.

  16. Adsorption of DNA onto anionic lipid surfaces.

    PubMed

    Martín-Molina, Alberto; Luque-Caballero, Germán; Faraudo, Jordi; Quesada-Pérez, Manuel; Maldonado-Valderrama, Julia

    2014-04-01

    Currently self-assembled DNA delivery systems composed of DNA multivalent cations and anionic lipids are considered to be promising tools for gene therapy. These systems become an alternative to traditional cationic lipid-DNA complexes because of their low cytotoxicity lipids. However, currently these nonviral gene delivery methods exhibit low transfection efficiencies. This feature is in large part due to the poorly understood DNA complexation mechanisms at the molecular level. It is well-known that the adsorption of DNA onto like charged lipid surfaces requires the presence of multivalent cations that act as bridges between DNA and anionic lipids. Unfortunately, the molecular mechanisms behind such adsorption phenomenon still remain unclear. Accordingly a historical background of experimental evidence related to adsorption and complexation of DNA onto anionic lipid surfaces mediated by different multivalent cations is firstly reviewed. Next, recent experiments aimed to characterise the interfacial adsorption of DNA onto a model anionic phospholipid monolayer mediated by Ca(2+) (including AFM images) are discussed. Afterwards, modelling studies of DNA adsorption onto charged surfaces are summarised before presenting preliminary results obtained from both CG and all-atomic MD computer simulations. Our results allow us to establish the optimal conditions for cation-mediated adsorption of DNA onto negatively charged surfaces. Moreover, atomistic simulations provide an excellent framework to understand the interaction between DNA and anionic lipids in the presence of divalent cations. Accordingly,our simulation results in conjunction go beyond the macroscopic picture in which DNA is stuck to anionic membranes by using multivalent cations that form glue layers between them. Structural aspects of the DNA adsorption and molecular binding between the different charged groups from DNA and lipids in the presence of divalent cations are reported in the last part of the study

  17. Surface Tension and Adsorption without a Dividing Surface.

    PubMed

    Marmur, Abraham

    2015-11-24

    The ingenious concept of a dividing surface of zero thickness that was introduced by Gibbs is the basis of the theory of surface tension and adsorption. However, some fundamental questions, mainly those related to the location of the dividing surface and the proper definition of relative adsorption, have remained open over the years. To avoid these questions, the present paper proposes to analyze an interfacial phase by defining a thermodynamic system of constant, but nonzero thickness. The interfacial phase is analyzed as it really is, namely a nonuniform three-dimensional entity. The current analysis redevelops the equation for calculating surface tension, though with different assumptions. However, the main point in the proposed model is that the thermodynamic interfacial system, due to its fixed thickness, conforms to the requirement of first-order homogeneity of the internal energy. This property is the key that allows using the Gibbs adsorption isotherm. It is also characteristic of the Gibbs dividing surface model, but has not always been discussed with regard to subsequent models. The resulting equation leads to a simple, "natural" expression for the relative adsorption. This expression may be compared with simulations and sophisticated surface concentration measurements, and from which the dependence of interfacial tension on the solution composition can be derived. Finally, it is important to point out that in order to calculate the interfacial tension as well as the relative adsorption from data on the properties of the interfacial phase, there is no need to know its exact thickness, as long as it is bigger than the actual thickness but sufficiently small.

  18. 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

  19. 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.

  20. The surface area of soil organic matter

    USGS Publications Warehouse

    Chiou, C.T.; Lee, J.-F.; Boyd, S.A.

    1990-01-01

    The previously reported surface area for soil organic matter (SOM) of 560-800 m2/g as determined by the ethylene glycol (EG) retention method was reexamined by the standard BET method based on nitrogen adsorption at liquid nitrogen temperature. Test samples consisted of two high organic content soils, a freeze-dried soil humic acid, and an oven-dried soil humic acid. The measured BET areas for these samples were less than 1 m2/g, except for the freeze-dried humic acid. The results suggest that surface adsorption of nonionic organic compounds by SOM is practically insignificant in comparison to uptake by partition. The discrepancy between the surface areas of SOM obtained by BET and EG methods was explained in terms of the 'free surface area' and the 'apparent surface area' associated with these measurements.The previously reported surface area for soil organic matter (SOM) of 560-800 m2/g as determined by the ethylene glycol (EG) retention method was reexamined by the standard BET method based on nitrogen adsorption at liquid nitrogen temperature. Test samples consisted of two high organic content soils, a freeze-dried soil humic acid, and an oven-dried soil humic acid. The measured BET areas for these samples were less than 1 m2/g, except for the freeze-dried humic acid. The results suggest that surface adsorption of nonionic organic compounds by SOM is practically insignificant in comparison to uptake by partition. The discrepancy between the surface areas of SOM obtained by BET and EG methods was explained in terms of the 'free surface area' and the 'apparent surface area' associated with these measurements.

  1. Protein adsorption kinetics in different surface potentials

    NASA Astrophysics Data System (ADS)

    Quinn, A.; Mantz, H.; Jacobs, K.; Bellion, M.; Santen, L.

    2008-03-01

    We have studied the adsorption kinetics of the protein amylase at solid/liquid interfaces. Offering substrates with tailored properties, we are able to separate the impact of short- and long-range interactions. By means of a colloidal Monte Carlo approach including conformational changes of the adsorbed proteins induced by density fluctuations, we develop a scenario that is consistent with the experimentally observed three-step kinetics on specific substrates. Our observations show that not only the surface chemistry determines the properties of an adsorbed protein layer but also the van der Waals contributions of a composite substrate may lead to non-negligible effects.

  2. Adsorption-Induced Surface Stresses of the Water/Quartz Interface: Ab Initio Molecular Dynamics Study.

    PubMed

    Gor, Gennady Y; Bernstein, Noam

    2016-05-31

    Adsorption-induced deformation is expansion or contraction of a solid due to adsorption on its surface. This phenomenon is important for a wide range of applications, from chemomechanical sensors to methane recovery from geological formations. The strain of the solid is driven by the change of the surface stress due to adsorption. Using ab initio molecular dynamics, we calculate the surface stresses for the dry α-quartz surfaces, and investigate how these stresses change when the surfaces are exposed to water. We find that the nonhydroxylated surface shows small and approximately isotropic changes in stress, while the hydroxylated surface, which interacts more strongly with the polar water molecules, shows larger and qualitatively anisotropic (opposite sign in xx and yy) surface stress changes. All of these changes are several times larger than the surface tension of water itself. The anisotropy and possibility of positive surface stress change can explain experimentally observed surface area contraction due to adsorption.

  3. Adsorption of flexible polyelectrolytes on charged surfaces.

    PubMed

    Subbotin, A V; Semenov, A N

    2016-08-10

    Adsorption of weakly charged polyelectrolyte (PE) chains from dilute solution on an oppositely charged surface is studied using the self-consistent mean-field approach. The structure of the adsorbed polymer layer and its excess charge are analyzed in the most important asymptotic and intermediate regimes both analytically and numerically. Different regimes of surface charge compensation by PE chains including partial and full charge inversion are identified and discussed in terms of physical parameters like the magnitude of specific short-range interactions of PE segments with the surface, solvent quality and ionic strength. The effect of excluded-volume monomer interactions is considered quantitatively both in the marginally good and poor solvent regimes. PMID:27452184

  4. High surface-area amidoxime-based polymer fibers co-grafted with various acid monomers yielding increased adsorption capacity for the extraction of uranium from seawater.

    PubMed

    Oyola, Yatsandra; Dai, Sheng

    2016-06-01

    Uranium is dissolved in the ocean at a uniform concentration of 3.34 ppb, which translates to approximately 4-5 billion tons of uranium. The development of adsorbents that can extract uranium from seawater has been a long term goal, but the extremely dilute uranium concentration along with the competition of other metal salts (which are at higher concentrations) has hindered the development of an economical adsorption process. Several acid monomers were co-grafted with acrylonitrile (AN) to help increase the hydrophilicity of the adsorbent to improve access to the metal adsorption sites. Grafting various acid monomers on PE fibers was found to significantly affect the uranium adsorption in simulated seawater in the following order: acrylic acid (AA) < vinyl sulfonic acid (VSA) < methacrylic acid (MAA) < itaconic acid (ITA) < vinyl phosphonic acid (VPA). Interestingly, the uranium adsorption capacity significantly increased when Mohr's salt was added with acrylic acid, most likely due to the reduction of co-polymerization of the monomers. When testing under more realistic conditions, the acid-grafted PE fiber adsorbents were exposed to natural seawater (more dilute uranium), the uranium adsorption capacity increased in the following order: MAA < AA (Mohr's salt) < VSA < ITA (Mohr's salt) < ITA < VPA, which agreed well with the simulated seawater results. Characterization of the adsorbents indicated that the increase in uranium adsorption capacity with each acid monomer was related to higher grafting of AN and therefore a higher conversion to amidoxime (AO). PMID:27145863

  5. Surface Adsorption in Nonpolarizable Atomic Models.

    PubMed

    Whitmer, Jonathan K; Joshi, Abhijeet A; Carlton, Rebecca J; Abbott, Nicholas L; de Pablo, Juan J

    2014-12-01

    Many ionic solutions exhibit species-dependent properties, including surface tension and the salting-out of proteins. These effects may be loosely quantified in terms of the Hofmeister series, first identified in the context of protein solubility. Here, our interest is to develop atomistic models capable of capturing Hofmeister effects rigorously. Importantly, we aim to capture this dependence in computationally cheap "hard" ionic models, which do not exhibit dynamic polarization. To do this, we have performed an investigation detailing the effects of the water model on these properties. Though incredibly important, the role of water models in simulation of ionic solutions and biological systems is essentially unexplored. We quantify this via the ion-dependent surface attraction of the halide series (Cl, Br, I) and, in so doing, determine the relative importance of various hypothesized contributions to ionic surface free energies. Importantly, we demonstrate surface adsorption can result in hard ionic models combined with a thermodynamically accurate representation of the water molecule (TIP4Q). The effect observed in simulations of iodide is commensurate with previous calculations of the surface potential of mean force in rigid molecular dynamics and polarizable density-functional models. Our calculations are direct simulation evidence of the subtle but sensitive role of water thermodynamics in atomistic simulations.

  6. Effect of Grain Size on Uranium(VI) Surface Complexation Kinetics and Adsorption Additivity

    SciTech Connect

    Shang, Jianying; Liu, Chongxuan; Wang, Zheming; Zachara, John M.

    2011-07-27

    Laboratory experiments were performed to investigate the contribution of variable grain sizes to uranium adsorption/desorption in a sediment collected from the US DOE Hanford site. The sediment was wet-sieved into four size fractions: coarse sand (1-2 mm), medium sand (0.2-1 mm), fine sand (0.05-0.2 mm), and clay/silt fraction (< 0.05mm). For each size fraction and their composite (sediment), batch experiments were performed to determine uranium adsorption isotherms, and stirred flow-cell experiments were conducted to derive kinetic data of uranium adsorption and subsequent desorption. The results showed that uranium adsorption isotherms and adsorption/desorption kinetics were size-specific, reflecting the effects of size-specific adsorption site concentration and kinetic rate constants. The larger-size fraction had a larger mass percentage in the sediment, but with a smaller adsorption site concentration and generally a slower uranium adsorption/desorption rate. The same equilibrium surface complexation reaction and reaction constant could describe uranium adsorption isotherms for all size fractions and the composite after accounting for the effect of adsorption site concentration. Mass-weighted, linear additivity was observed for both uranium adsorption isotherms and adsorption/desorption kinetics in the composite. Our analysis also showed that uranium adsorption site concentration estimated from the adsorption isotherms was 3 orders of magnitude less than a site concentration estimated from sediment surface area and generic site density. One important implication of this study is that grain size distribution may be used to estimate uranium adsorption site, and adsorption/desorption kinetic rates in heterogeneous sediments from a common location.

  7. Study of Gas Adsorption on Biphasic Nanostructured Surfaces

    NASA Astrophysics Data System (ADS)

    Nader, Rami; Hamieh, Tayssir; Villieras, Frédéric; Angelina. Razafitianamaharav; Toufaily, Joumana; Mcheik, Ali S.; Thomas, Fabien

    This work has carried out on grafted nanoparticles oxide silica to determine the possible existence of "nanoeffect". The textural properties and heterogeneity of surface of the samples were studied at the interface solid-gas. The Geometric properties were discussed in terms of the surface area while the energy properties were discussed in terms of the reactive sites of the surface.In the framework of this study, firstly, the sample was used in the non-grafted state and then in the grafted state using a hydrophilic molecule and a hydrophobic molecule. Several techniques have been used: Infrared spectroscopy, X ray diffraction, the point by point volumetric technique, which enable us to study the interactions between the adsorbate and the solid surface. Finally we have determined the size and electro thermal mobility using zestasizer (Nano ZS). The results obtained show that there are two types of groups silanols and siloxanes on the silica OX5 giving a composite hydrophilic-hydrophobic. This character causes a singular behavior in adsorptive material, the presence of hydrophilic groups, strongly polarized, and is detected by infrared spectroscopy. These groups cause significant differences depending on the polarizability of the probe molecules, and the adsorption of argon shows no heterogeneity of the surface, while nitrogen is adsorbed on the polar sites at low relative pressure, While the volumetric continues to adsorption of argon and nitrogen on combustion silica to obtain and to highlight sites of high energy and polar surface sites. The combustion silica which has been used as adsorbent in this study has an amorphous surface, virtually free of impurities indicates that the sample is not micro porous and grafting of the molecules makes a decrease in high energy sites or to a relative increase in surface low energy.

  8. [Surface characteristics of alkali modified activated carbon and the adsorption capacity of methane].

    PubMed

    Zhang, Meng-Zhu; Li, Lin; Liu, Jun-Xin; Sun, Yong-Jun; Li, Guo-Bin

    2013-01-01

    Coconut shell based activated carbon was modified by alkali with different concentrations. The surface structures of tested carbons were observed and analyzed by SEM and BET methods. Boehm's titration and SEM/EDS methods were applied to assay the functional groups and elements on the carbon surface. The adsorption of methane on tested carbons was investigated and adsorption behavior was described by the adsorption isotherms. Results showed that surface area and pore volume of modified carbon increased and surface oxygen groups decreased as the concentration of the alkali used increased, with no obvious change in pore size. When concentration of alkali was higher than 3.3 mol x L(-1), the specific surface area and pore volume of modified carbon was larger than that of original carbon. Methane adsorption capacity of alkali modified carbon increased 24%. Enlargement of surface area and pore volume, reduction of surface oxygen groups will benefit to enhance the methane adsorption ability on activated carbon. Adsorption behavior of methane followed the Langmuir isotherm and the adsorption coefficient was 163.7 m3 x mg(-1).

  9. Study of lysozyme mobility and binding free energy during adsorption on a graphene surface

    SciTech Connect

    Nakano, C. Masato; Ma, Heng; Wei, Tao

    2015-04-13

    Understanding protein adsorption is a key to the development of biosensors and anti-biofouling materials. Hydration essentially controls the adsorption process on hydrophobic surfaces, but its effect is complicated by various factors. Here, we present an ideal model system to isolate hydration effects—lysozyme adsorption on a flat hydrophobic graphene surface. Our all-atom molecular dynamics and molecular-mechanics/Poisson-Boltzmann surface area computation study reveal that lysozyme on graphene displays much larger diffusivity than in bulk water. Protein's hydration free energy within the first hydration shell is dominated by the protein-water electrostatic interactions and acts as an energy barrier for protein adsorption. On the other hand, the surface tension, especially that from the hydrophobic graphene, can effectively weaken the barrier to promote adsorption.

  10. Enhanced laminin adsorption on nanowires compared to flat surfaces.

    PubMed

    Hammarin, Greger; Persson, Henrik; Dabkowska, Aleksandra P; Prinz, Christelle N

    2014-10-01

    Semiconductor nanowires are widely used to interface living cells, and numerous nanowire-based devices have been developed to manipulate or sense cell behavior. We have, however, little knowledge on the nature of the cell-nanowire interface. Laminin is an extracellular matrix protein promoting cell attachment and growth. Here, we used a method based on fluorescence microscopy and measured the relative amount of laminin adsorbed on nanowires compared to flat surfaces. The amount of adsorbed laminin per surface area is up to 4 times higher on 55nm diameter gallium phosphide nanowires compared to the flat gallium phosphide surface between the nanowires. We show that this enhanced adsorption on nanowires cannot be attributed to electrostatic effects, nor to differences in surface chemistry, but possibly to pure geometrical effects, as increasing the nanowire diameter results in a decreased amount of adsorbed protein. The increased adsorption of laminin on nanowires may explain the exceptionally beneficial properties of nanowire substrates for cellular growth reported in the literature since laminin is often used as surface coating prior to cell cultures in order to promote cell growth, and also because primary cell suspensions contain endogenous laminin.

  11. Influence of activated carbon characteristics on toluene and hexane adsorption: Application of surface response methodology

    NASA Astrophysics Data System (ADS)

    Izquierdo, Mª Teresa; de Yuso, Alicia Martínez; Valenciano, Raquel; Rubio, Begoña; Pino, Mª Rosa

    2013-01-01

    The objective of this study was to evaluate the adsorption capacity of toluene and hexane over activated carbons prepared according an experimental design, considering as variables the activation temperature, the impregnation ratio and the activation time. The response surface methodology was applied to optimize the adsorption capacity of the carbons regarding the preparation conditions that determine the physicochemical characteristics of the activated carbons. The methodology of preparation produced activated carbons with surface areas and micropore volumes as high as 1128 m2/g and 0.52 cm3/g, respectively. Moreover, the activated carbons exhibit mesoporosity, ranging from 64.6% to 89.1% the percentage of microporosity. The surface chemistry was characterized by TPD, FTIR and acid-base titration obtaining different values of surface groups from the different techniques because the limitation of each technique, but obtaining similar trends for the activated carbons studied. The exhaustive characterization of the activated carbons allows to state that the measured surface area does not explain the adsorption capacity for either toluene or n-hexane. On the other hand, the surface chemistry does not explain the adsorption results either. A compromise between physical and chemical characteristics can be obtained from the appropriate activation conditions, and the response surface methodology gives the optimal activated carbon to maximize adsorption capacity. Low activation temperature, intermediate impregnation ratio lead to high toluene and n-hexane adsorption capacities depending on the activation time, which a determining factor to maximize toluene adsorption.

  12. Adsorption of glucose, cellobiose, and cellotetraose onto cellulose model surfaces.

    PubMed

    Hoja, Johannes; Maurer, Reinhard J; Sax, Alexander F

    2014-07-31

    Reliable simulation of molecular adsorption onto cellulose surfaces is essential for the design of new cellulose nanocomposite materials. However, the applicability of classical force field methods to such systems remains relatively unexplored. In this study, we present the adsorption of glucose, cellobiose, and cellotetraose on model surfaces of crystalline cellulose Iα and Iβ. The adsorption of the two large carbohydrates was simulated with the GLYCAM06 force field. To validate this approach, quantum theoretical calculations for the adsorption of glucose were performed: Equilibrium geometries were studied with density functional theory (DFT) and dispersion-corrected DFT, whereas the adsorption energies were calculated with two standard density functional approximations and five dispersion-containing DFT approaches. We find that GLYCAM06 gives a good account of geometries and, in most cases, accurate adsorption energies when compared to dispersion-corrected DFT energies. Adsorption onto the (100) surface of cellulose Iα is, in general, stronger than onto the (100) surface of cellulose Iβ. Contrary to intuition, the adsorption energy is not directly correlated with the number of hydrogen bonds; rather, it is dominated by dispersion interactions. Especially for bigger adsorbates, a neglect of these interactions leads to a dramatic underestimation of adsorption energies.

  13. Adsorption of glucose, cellobiose, and cellotetraose onto cellulose model surfaces.

    PubMed

    Hoja, Johannes; Maurer, Reinhard J; Sax, Alexander F

    2014-07-31

    Reliable simulation of molecular adsorption onto cellulose surfaces is essential for the design of new cellulose nanocomposite materials. However, the applicability of classical force field methods to such systems remains relatively unexplored. In this study, we present the adsorption of glucose, cellobiose, and cellotetraose on model surfaces of crystalline cellulose Iα and Iβ. The adsorption of the two large carbohydrates was simulated with the GLYCAM06 force field. To validate this approach, quantum theoretical calculations for the adsorption of glucose were performed: Equilibrium geometries were studied with density functional theory (DFT) and dispersion-corrected DFT, whereas the adsorption energies were calculated with two standard density functional approximations and five dispersion-containing DFT approaches. We find that GLYCAM06 gives a good account of geometries and, in most cases, accurate adsorption energies when compared to dispersion-corrected DFT energies. Adsorption onto the (100) surface of cellulose Iα is, in general, stronger than onto the (100) surface of cellulose Iβ. Contrary to intuition, the adsorption energy is not directly correlated with the number of hydrogen bonds; rather, it is dominated by dispersion interactions. Especially for bigger adsorbates, a neglect of these interactions leads to a dramatic underestimation of adsorption energies. PMID:25036217

  14. Surfaces of Microparticles in Colloids: Structure and Molecular Adsorption Kinetics

    NASA Astrophysics Data System (ADS)

    Dai, Hai-Lung

    2002-03-01

    Surfaces of micron and sub-micron size particles in liquid solution are probed by second harmonic generation (SHG) facilitated with femtosecond laser pulses. The particles probed include inorganic objects such as carbon black and color pigments, polymeric species like polystyrene beads, and biological systems such as blood cells and ecoli. In the experiments, dye molecules are first adsorbed onto the particle surface to allow generation of second harmonics upon light irradiation. Competition for adsorption between these surface dye molecules and the molecules of interest in the solution is then monitored by the SHG signal to reveal the molecular adsorption kinetics and surface structure. Specifically, surfactant adsorption on polymer surfaces, the structure of carbon black surface, and protein adsorption on biological surfaces, monitored by this technique, will be discussed.

  15. Surface modification of chitin using ultrasound-assisted and supercritical CO2 technologies for cobalt adsorption.

    PubMed

    Dotto, Guilherme L; Cunha, Jeanine M; Calgaro, Camila O; Tanabe, Eduardo H; Bertuol, Daniel A

    2015-09-15

    Ultrasound-assisted (UA) and supercritical CO2 technologies (SCO2) were used to modify the chitin surface and, improve its adsorption characteristics regarding to cobalt. Chitin, before and after the treatments, was characterized by N2 adsorption isotherms (BET), infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Unmodified and surface modified chitins were used as adsorbents to remove cobalt from aqueous solutions. The adsorption study was performed by equilibrium isotherms and kinetic curves. The chitin particle characteristics, such as, surface area, pore volume and porosity were improved by the UA and SCO2 treatments. The crystallinity index decreased after the UA and SCO2 treatments, and also, intense surface modifications were observed. Langmuir and Freundlich models were adequate to represent the adsorption equilibrium. The maximum adsorption capacities were 50.03, 83.94 and 63.08 mg g(-1) for unmodified chitin, UA surface modified chitin and SCO2 surface modified chitin. The adsorption kinetic curves were well represented by the pseudo-second order model. UA and SCO2 technologies are alternatives to modify the chitin surface and improve its adsorption characteristics.

  16. Adsorption mode of cinchonidine on Cu(111) surface.

    PubMed

    Xu, Qing-Min; Wang, Dong; Wan, Li-Jun; Bai, Chun-Li; Wang, Yuan

    2002-12-01

    The adsorption mode of cinchonidine on Cu(111) was directly obtained by in situ STM. The molecules were found to adsorb on the substrate surface and form a long-range ordered adlayer with (4 x 4) symmetry. While the quinoline rings lie parallel to Cu(111), the chiral quinuclidine moiety extends out of the surface. The enantioselectivity of catalysts may relate to this special adsorption conformation of cinchonidine on the surface.

  17. Chlorine adsorption on the InAs (001) surface

    SciTech Connect

    Bakulin, A. V.; Eremeev, S. V.; Tereshchenko, O. E.; Kulkova, S. E.

    2011-01-15

    Chlorine adsorption on the In-stabilized InAs(001) surface with {zeta}-(4 Multiplication-Sign 2) and {beta}3 Prime -(4 Multiplication-Sign 2) reconstructions and on the Ga-stabilized GaAs (001)-{zeta}-(4 Multiplication-Sign 2) surface has been studied within the electron density functional theory. The equilibrium structural parameters of these reconstructions, surface atom positions, bond lengths in dimers, and their changes upon chlorine adsorption are determined. The electronic characteristics of the clean surface and the surface with adsorbed chlorine are calculated. It is shown that the most energetically favorable positions for chlorine adsorption are top positions over dimerized indium or gallium atoms. The mechanism of chlorine binding with In(Ga)-stabilized surface is explained. The interaction of chlorine atoms with dimerized surface atoms weakens surface atom bonds and controls the initial stage of surface etching.

  18. Adsorption of boric acid trimethyl ester on silica surface studied by FT-IR spectroscopy

    NASA Astrophysics Data System (ADS)

    Liu, Jianke; Ying, Pinliang; Xin, Qin; Li, Can

    1998-04-01

    Adsorption of boric acid trimethyl ester (BATE) on high-surface-area silica has been studied by FT-IR spectroscopy. It is found that surface hydroxyls remaining after outgassing at high temperatures act as weak basic sites for BATE adsorption. Coordinate interaction of BATE with isolated hydroxyls dominates the adsorption and induces two splitting B-O vibrational bands at 1375 and 1345 cm -1. In addition, a small amount of BATE reacts with hydrogen-bonded hydroxyls and strained oxygen generated after high-temperature dehydroxylation.

  19. High surface area calcite

    NASA Astrophysics Data System (ADS)

    Schultz, L. N.; Andersson, M. P.; Dalby, K. N.; Müter, D.; Okhrimenko, D. V.; Fordsmand, H.; Stipp, S. L. S.

    2013-05-01

    Calcite (CaCO3) is important in many fields—in nature, because it is a component of aquifers, oil reservoirs and prospective CO2 storage sites, and in industry, where it is used in products as diverse as paper, toothpaste, paint, plastic and aspirin. It is difficult to obtain high purity calcite with a high surface area but such material is necessary for industrial applications and for fundamental calcite research. Commercial powder is nearly always contaminated with growth inhibitors such as sugars, citrate or pectin and most laboratory synthesis methods deliver large precipitates, often containing vaterite or aragonite. To address this problem, we (i) adapted the method of carbonating a Ca(OH)2 slurry with CO2 gas to develop the first simple, cheap, safe and reproducible procedure using common laboratory equipment, to obtain calcite that reproducibly had a surface area of 14-17 m2/g and (ii) conducted a thorough characterization of the product. Scanning electron microscopy (SEM) revealed nanometer scale, rhombohedral crystals. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) confirmed highly crystalline, pure calcite that more closely resembles the dimensions of the biogenic calcite produced by algae in coccoliths than other methods for synthesizing calcite. We suggest that this calcite is useful when purity and high surface area are important.

  20. Random sequential adsorption of human adenovirus 2 onto polyvinylidene fluoride surface influenced by extracellular polymeric substances.

    PubMed

    Lu, Ruiqing; Li, Qi; Nguyen, Thanh H

    2016-03-15

    Virus removal by membrane bioreactors depends on virus-membrane and virus-foulant interactions. The adsorption of human adenovirus 2 (HAdV-2) on polyvinylidene fluoride (PVDF) membrane and a major membrane foulant, extracellular polymeric substances (EPS), were measured in a quartz crystal microbalance. In 3-100mM CaCl2 solutions, irreversible adsorption of HAdV-2 was observed on both pristine and EPS-fouled PVDF surfaces. The HAdV-2 adsorption kinetics was successfully fitted with the random sequential adsorption (RSA) model. The applicability of the RSA model for HAdV-2 adsorption is confirmed by comparing the two fitting parameters, adsorption rate constant k(a) and area occupied by each adsorbed HAdV-2 particle a, with experimentally measured parameters. A linear correlation between the fitting parameter k(a) and the measured attachment efficiency was found, suggesting that the RSA model correctly describes the interaction forces dominating the HAdV-2 adsorption. By comparing the fitting parameter d(ads) with the hydrodynamic diameter of HAdV-2, we conclude that virus-virus and virus-surface interactions determine the area occupied by each adsorbed HAdV-2 particle, and thus influence the adsorption capacity. These results provide insights into virus retention and will benefit improving virus removal in membrane filtration.

  1. Random sequential adsorption of human adenovirus 2 onto polyvinylidene fluoride surface influenced by extracellular polymeric substances.

    PubMed

    Lu, Ruiqing; Li, Qi; Nguyen, Thanh H

    2016-03-15

    Virus removal by membrane bioreactors depends on virus-membrane and virus-foulant interactions. The adsorption of human adenovirus 2 (HAdV-2) on polyvinylidene fluoride (PVDF) membrane and a major membrane foulant, extracellular polymeric substances (EPS), were measured in a quartz crystal microbalance. In 3-100mM CaCl2 solutions, irreversible adsorption of HAdV-2 was observed on both pristine and EPS-fouled PVDF surfaces. The HAdV-2 adsorption kinetics was successfully fitted with the random sequential adsorption (RSA) model. The applicability of the RSA model for HAdV-2 adsorption is confirmed by comparing the two fitting parameters, adsorption rate constant k(a) and area occupied by each adsorbed HAdV-2 particle a, with experimentally measured parameters. A linear correlation between the fitting parameter k(a) and the measured attachment efficiency was found, suggesting that the RSA model correctly describes the interaction forces dominating the HAdV-2 adsorption. By comparing the fitting parameter d(ads) with the hydrodynamic diameter of HAdV-2, we conclude that virus-virus and virus-surface interactions determine the area occupied by each adsorbed HAdV-2 particle, and thus influence the adsorption capacity. These results provide insights into virus retention and will benefit improving virus removal in membrane filtration. PMID:26720514

  2. Adsorption behaviors of some phenolic compounds onto high specific area activated carbon cloth.

    PubMed

    Ayranci, Erol; Duman, Osman

    2005-09-30

    Adsorption of phenol, hydroquinone, m-cresol, p-cresol and p-nitrophenol from aqueous solutions onto high specific area activated carbon cloth has been studied. The effect of ionization on adsorption of these ionizable phenolic compounds was examined by studying the adsorption from acidic, basic and natural pH solutions. Kinetics of adsorption was followed by in situ UV spectroscopy over a period of 90 min. First-order rate law was found to be valid for the kinetics of adsorption processes and the rate constants were determined. The highest rate constants were obtained for the adsorption from solutions at the natural pH. The lowest rate constants were observed in basic solutions. The rate constants decreased in the order p-nitrophenol approximately m-cresol>p-cresol>hydroquinone approximately phenol. Adsorption isotherms were derived at 30 degrees C and the isotherm data were treated according to Langmuir, Freundlich and Tempkin isotherm equations. The goodness of fit of experimental data to these isotherm equations was tested and the parameters of equations were determined. The possible interactions of compounds with the carbon surface were discussed considering the charge of the surface and the possible ionization of compounds at acidic, basic and natural pH conditions. PMID:15941619

  3. [Surface properties and adsorption characteristics for fluoride of goethite, kaolinite and their association].

    PubMed

    Wei, Shi-Yong; Yang, Xiao-Hong

    2010-09-01

    The basic properties of goethite, kaolinite and their association were characterized using X-ray diffraction (XRD) , scanning electron microscopes (SEM), Fourier transform infrared spectroscopy (FT-IR), potentiometric titrations, specific surface area (SSA) and micropore analysis. Moreover, the adsorption capacity and adsorption models of fluoride by the investigated samples were studied. Results show that when kaolinite and goethite presented simultaneously in the same suspension system, goethite was apt to coat the surface of kaolinite and the interactions between them could occur rapidly. As a result, the binary association containing kaolinite and goethite was formed. The binary association possessed the pore diameter of 0.42 nm and 0.61 nm, specific surface area of 34.08 m2/g, surface fractal dimension of D = 2.726 and the pH(PZNPC) (pH of point of zero net proton charge) in the range of 5.50-6.50. At the initial pH 6. 00, the maximum adsorption capacity (q(max) of goethite, kaolinite and association was 4.506, 0.608 and 3.520 mg/g respectively. The adsorption of fluoride by the single kaolinite or goethite could be attributed to monolayer adsorption and the data of isotherm adsorption could be well fitted by Langmuir model (R2 = 0.991 and R2 = 0.964 respectively). The Freundlich model was suitable for describing the adsorption of fluoride by the binary association (R2 = 0.995), which indicated that the surface of the binary association is heterogeneous and is probably provided with multilayer adsorption sites. The adsorption mechanisms for fluoride by the investigated samples include anion ligand exchange, surface coordination and electrostatic attraction. In addition, F acting as a bond bridge between the surfaces of kaolinite and goethite contributed to the adsorption of fluoride too. Compared to the single goethite or kaolinite, the binary association exhibited the higher specific surface area, surface fractal dimension and adsorption capacity for fluoride

  4. High Surface Area Tunnels in Hexagonal WO₃.

    PubMed

    Sun, Wanmei; Yeung, Michael T; Lech, Andrew T; Lin, Cheng-Wei; Lee, Chain; Li, Tianqi; Duan, Xiangfeng; Zhou, Jun; Kaner, Richard B

    2015-07-01

    High surface area in h-WO3 has been verified from the intracrystalline tunnels. This bottom-up approach differs from conventional templating-type methods. The 3.67 Å diameter tunnels are characterized by low-pressure CO2 adsorption isotherms with nonlocal density functional theory fitting, transmission electron microscopy, and thermal gravimetric analysis. These open and rigid tunnels absorb H(+) and Li(+), but not Na(+) in aqueous electrolytes without inducing a phase transformation, accessing both internal and external active sites. Moreover, these tunnel structures demonstrate high specific pseudocapacitance and good stability in an H2SO4 aqueous electrolyte. Thus, the high surface area created from 3.67 Å diameter tunnels in h-WO3 shows potential applications in electrochemical energy storage, selective ion transfer, and selective gas adsorption.

  5. Albumin adsorption on CoCrMo alloy surfaces

    NASA Astrophysics Data System (ADS)

    Yan, Yu; Yang, Hongjuan; Su, Yanjing; Qiao, Lijie

    2015-12-01

    Proteins can adsorb on the surface of artificial joints immediately after being implanted. Although research studying protein adsorption on medical material surfaces has been carried out, the mechanism of the proteins’ adsorption which affects the corrosion behaviour of such materials still lacks in situ observation at the micro level. The adsorption of bovine serum albumin (BSA) on CoCrMo alloy surfaces was studied in situ by AFM and SKPFM as a function of pH and the charge of CoCrMo alloy surfaces. Results showed that when the specimens were uncharged, hydrophobic interaction could govern the process of the adsorption rather than electrostatic interaction, and BSA molecules tended to adsorb on the surfaces forming a monolayer in the side-on model. Results also showed that adsorbed BSA molecules could promote the corrosion process for CoCrMo alloys. When the surface was positively charged, the electrostatic interaction played a leading role in the adsorption process. The maximum adsorption occurred at the isoelectric point (pH 4.7) of BSA.

  6. Albumin adsorption on CoCrMo alloy surfaces

    PubMed Central

    Yan, Yu; Yang, Hongjuan; Su, Yanjing; Qiao, Lijie

    2015-01-01

    Proteins can adsorb on the surface of artificial joints immediately after being implanted. Although research studying protein adsorption on medical material surfaces has been carried out, the mechanism of the proteins’ adsorption which affects the corrosion behaviour of such materials still lacks in situ observation at the micro level. The adsorption of bovine serum albumin (BSA) on CoCrMo alloy surfaces was studied in situ by AFM and SKPFM as a function of pH and the charge of CoCrMo alloy surfaces. Results showed that when the specimens were uncharged, hydrophobic interaction could govern the process of the adsorption rather than electrostatic interaction, and BSA molecules tended to adsorb on the surfaces forming a monolayer in the side-on model. Results also showed that adsorbed BSA molecules could promote the corrosion process for CoCrMo alloys. When the surface was positively charged, the electrostatic interaction played a leading role in the adsorption process. The maximum adsorption occurred at the isoelectric point (pH 4.7) of BSA. PMID:26673525

  7. Adsorption of chlorophenols from aqueous solutions by pristine and surface functionalized single-walled carbon nanotubes.

    PubMed

    Ding, Han; Li, Xin; Wang, Jun; Zhang, Xiaojian; Chen, Chao

    2016-05-01

    The adsorption of six kinds of chlorophenols on pristine, hydroxylated and carboxylated single-walled carbon nanotubes (SWCNTs) has been investigated. Pseudo-first order and pseudo-second order models were used to describe the kinetic data. All adsorption isotherms were well fitted with Langmuir, Freundlich and Polanyi-Manes models, due to surface adsorption dominating the adsorption process. The close linear relationship between logKow and logKd suggested that hydrophobicity played an important role in the adsorption. The SWCNTs' adsorption capacity for chlorophenols was weakened by addition of oxygen-containing functional groups on the surface, due to the loss of specific surface area, the increase of hydrophilicity and the reduction of π-π interaction. The best adsorption capacity of pristine SWCNTs, SWCNT-OH and SWCNT-COOH for six chlorophenols varied from 19 to 84mg/g, from 19 to 65mg/g and from 17 to 65mg/g, respectively. The effect of pH on the adsorption of 2,6-dichlorophenol (2,6-DCP), was also studied. When pH is over the pKa of 2,6-dichlorophenol (2,6-DCP), its removal dropped sharply. When ionic strength increased (NaCl or KCl concentration from 0 to 0.02mmol/L), the adsorption capacity of 2,6-DCP on pristine SWCNTs decreased slightly. The comparison of chlorophenols adsorption by SWCNTs, MWCNTs and PAC was made, indicating that the adsorption rate of CNTs was much faster than that of PAC. The results provide useful information about the feasibility of SWCNTs as an adsorbent to remove chlorophenols from aqueous solutions.

  8. [Adsorption of Cu on Core-shell Structured Magnetic Particles: Relationship Between Adsorption Performance and Surface Properties].

    PubMed

    Li, Qiu-mei; Chen, Jing; Li, Hai-ning; Zhang, Xiao-lei; Zhang, Gao-sheng

    2015-12-01

    In order to reveal the relationship between the adsorption performance of adsorbents and their compositions, structure, and surface properties, the core-shell structured Fe₃O₄/MnO2 and Fe-Mn/Mn₂2 magnetic particles were systematically characterized using multiple techniques and their Cu adsorption behaviors as well as mechanism were also investigated in details. It was found that both Fe₃O4 and Fe-Mn had spinel structure and no obvious crystalline phase change was observed after coating with MnO₂. The introduction of Mn might improve the affinity between the core and the shell, and therefore enhanced the amount and distribution uniformity of the MnO₂ coated. Consequently, Fe-Mn/MnO₂ exhibited a higher BET specific surface area and a lower isoelectric point. The results of sorption experiments showed that Fe-Mn had a higher maximal Cu adsorption capacity of 33.7 mg · g⁻¹ at pH 5.5, compared with 17.5 mg · g⁻¹ of Fe₃O4. After coating, the maximal adsorption capacity of Fe-Mn/MnO₂ was increased to 58.2 mg · g⁻¹, which was 2.6 times as high as that of Fe₃O₄/MnO₂ and outperformed the majority of magnetic adsorbents reported in literature. In addition, a specific adsorption of Cu occurred at the surface of Fe₃O₄/MnO₂ or Fe-Mn/MnO₂ through the formation of inner-sphere complexes. In conclusion, the adsorption performance of the magnetic particles was positively related to their compositions, structure, and surface properties. PMID:27011990

  9. [Adsorption of Cu on Core-shell Structured Magnetic Particles: Relationship Between Adsorption Performance and Surface Properties].

    PubMed

    Li, Qiu-mei; Chen, Jing; Li, Hai-ning; Zhang, Xiao-lei; Zhang, Gao-sheng

    2015-12-01

    In order to reveal the relationship between the adsorption performance of adsorbents and their compositions, structure, and surface properties, the core-shell structured Fe₃O₄/MnO2 and Fe-Mn/Mn₂2 magnetic particles were systematically characterized using multiple techniques and their Cu adsorption behaviors as well as mechanism were also investigated in details. It was found that both Fe₃O4 and Fe-Mn had spinel structure and no obvious crystalline phase change was observed after coating with MnO₂. The introduction of Mn might improve the affinity between the core and the shell, and therefore enhanced the amount and distribution uniformity of the MnO₂ coated. Consequently, Fe-Mn/MnO₂ exhibited a higher BET specific surface area and a lower isoelectric point. The results of sorption experiments showed that Fe-Mn had a higher maximal Cu adsorption capacity of 33.7 mg · g⁻¹ at pH 5.5, compared with 17.5 mg · g⁻¹ of Fe₃O4. After coating, the maximal adsorption capacity of Fe-Mn/MnO₂ was increased to 58.2 mg · g⁻¹, which was 2.6 times as high as that of Fe₃O₄/MnO₂ and outperformed the majority of magnetic adsorbents reported in literature. In addition, a specific adsorption of Cu occurred at the surface of Fe₃O₄/MnO₂ or Fe-Mn/MnO₂ through the formation of inner-sphere complexes. In conclusion, the adsorption performance of the magnetic particles was positively related to their compositions, structure, and surface properties.

  10. The adsorption of aromatic acids onto the graphite basal surface

    NASA Astrophysics Data System (ADS)

    Martin, David S.

    2003-06-01

    The adsorption of benzoic acid, toluic acid, and salicylic acid from solution onto the graphite basal surface has been studied using atomic force microscopy (AFM). A systematic study of these three related planar aromatic acids is conducted in order to observe the influence of the functional side-group upon adsorption. It is found that upon adsorption all three acids orient with the benzene ring parallel to the graphite surface. On the graphite terraces, the benzoic acid decoration follows a Stranski-Krastanov growth mode whereas toluic acid follows Volmer-Weber growth. Salicylic acid forms a fibrous aggregate network. In addition to the terraces, graphite steps and near-surface bulk defects are found to be important sites for adsorption. The AFM tip is used to create irreversible nanoscale modifications of adsorbate structures.

  11. Protein adsorption to organosiloxane surfaces studied by acoustic wave sensor.

    PubMed

    Cavic, B A; Thompson, M

    1998-10-01

    Surfaces of the two organosiloxanes, polymercaptopropylmethylsiloxane and octaphenylcyclotetrasiloxane, were prepared on the gold electrodes of thickness-shear mode acoustic wave sensors. Compounds containing the siloxane bond are important in the fabrication of medical implants. The flow-through adsorption of the proteins: human serum albumin, alpha-chymotripsinogen A, cytochrome c, fibrinogen, hemoglobin, immunoglobulin G and apo-transferrin to the two siloxane surfaces and a gold electrode were detected by acoustic network analysis. With the exception of minor wash-off by buffer flow, the adsorption of all proteins to the three surfaces is irreversible. Differences observed for the magnitudes of adsorption for the various cases are ascribed to the role played by molecular interactions at the liquid/solid interface. The results confirm that changes in series resonant frequencies caused by macromolecular adsorption differ significantly from the widely accepted "mass based" model usually employed to characterize the response of this type of acoustic wave device.

  12. Surface Curvature Relation to Protein Adsorption for Carbon-based Nanomaterials

    NASA Astrophysics Data System (ADS)

    Gu, Zonglin; Yang, Zaixing; Chong, Yu; Ge, Cuicui; Weber, Jeffrey K.; Bell, David R.; Zhou, Ruhong

    2015-06-01

    The adsorption of proteins onto carbon-based nanomaterials (CBNs) is dictated by hydrophobic and π-π interactions between aliphatic and aromatic residues and the conjugated CBN surface. Accordingly, protein adsorption is highly sensitive to topological constraints imposed by CBN surface structure; in particular, adsorption capacity is thought to increase as the incident surface curvature decreases. In this work, we couple Molecular Dynamics (MD) simulations with fluorescence spectroscopy experiments to characterize this curvature dependence in detail for the model protein bovine serum albumin (BSA). By studying BSA adsorption onto carbon nanotubes of increasing radius (featuring descending local curvatures) and a flat graphene sheet, we confirm that adsorption capacity is indeed enhanced on flatter surfaces. Naïve fluorescence experiments featuring multi-walled carbon nanotubes (MWCNTs), however, conform to an opposing trend. To reconcile these observations, we conduct additional MD simulations with MWCNTs that match those prepared in experiments; such simulations indicate that increased mass to surface area ratios in multi-walled systems explain the observed discrepancies. In reduction, our work substantiates the inverse relationship between protein adsorption capacity and surface curvature and further demonstrates the need for subtle consideration in experimental and simulation design.

  13. Surface topography effects in protein adsorption on nanostructured carbon allotropes.

    PubMed

    Raffaini, Giuseppina; Ganazzoli, Fabio

    2013-04-16

    We report a molecular dynamics (MD) simulation study of protein adsorption on the surface of nanosized carbon allotropes, namely single-walled carbon nanotubes (SWNT) considering both the convex outer surface and the concave inner surface, together with a graphene sheet for comparison. These systems are chosen to investigate the effect of the surface curvature on protein adsorption at the same surface chemistry, given by sp(2) carbon atoms in all cases. The simulations show that proteins do favorably interact with these hydrophobic surfaces, as previously found on graphite which has the same chemical nature. However, the main finding of the present study is that the adsorption strength does depend on the surface topography: in particular, it is slightly weaker on the outer convex surfaces of SWNT and is conversely enhanced on the inner concave SWNT surface, being therefore intermediate for flat graphene. We additionally find that oligopeptides may enter the cavity of common SWNT, provided their size is small enough and the tube diameter is large enough for both entropic and energetic reasons. Therefore, we suggest that proteins can effectively be used to solubilize in water single-walled (and by analogy also multiwalled) carbon nanotubes through adsorption on the outer surface, as indeed experimentally found, and to functionalize them after insertion of oligopeptides within the cavity of nanotubes of appropriate size. PMID:23517008

  14. Molecular Simulation studies of adsorption of polymers on non-planar surfaces: Influence of surface characteristics

    NASA Astrophysics Data System (ADS)

    Venkatakrishnan, Abishek; Shim, Anne; Frost, Aquil; Lewnard, John; Kuppa, Vikram

    2015-03-01

    Molecular simulations are employed to investigate the adsorption of freely rotating polymer chains adsorbing on to non-planar surfaces. Adsorption studies on planar surfaces have been studied extensively and fairly well understood. However, in reality, surfaces are non-planar and cannot be represented using smooth surface models. We investigate the effect of surface characteristics on adsorption via molecular dynamics and Monte Carlo molecular simulations in the NVT ensemble. Both regular (uniform) and irregular (self-affine) roughness parameters are studied. The adsorbed polymer chains are characterized by density and orientation profiles, adsorbed fraction and chain topologies. Our results elucidate the extent to which surface roughness influences adsorption, in competition with other factors such as chain length and monomer-surface interaction. We also demonstrate how both adsorption and desorption can be controlled solely by tuning surface inhomogeneities.

  15. Additive surface complexation modeling of uranium(VI) adsorption onto quartz-sand dominated sediments.

    PubMed

    Dong, Wenming; Wan, Jiamin

    2014-06-17

    Many aquifers contaminated by U(VI)-containing acidic plumes are composed predominantly of quartz-sand sediments. The F-Area of the Savannah River Site (SRS) in South Carolina (USA) is an example. To predict U(VI) mobility and natural attenuation, we conducted U(VI) adsorption experiments using the F-Area plume sediments and reference quartz, goethite, and kaolinite. The sediments are composed of ∼96% quartz-sand and 3-4% fine fractions of kaolinite and goethite. We developed a new humic acid adsorption method for determining the relative surface area abundances of goethite and kaolinite in the fine fractions. This method is expected to be applicable to many other binary mineral pairs, and allows successful application of the component additivity (CA) approach based surface complexation modeling (SCM) at the SRS F-Area and other similar aquifers. Our experimental results indicate that quartz has stronger U(VI) adsorption ability per unit surface area than goethite and kaolinite at pH ≤ 4.0. Our modeling results indicate that the binary (goethite/kaolinite) CA-SCM under-predicts U(VI) adsorption to the quartz-sand dominated sediments at pH ≤ 4.0. The new ternary (quartz/goethite/kaolinite) CA-SCM provides excellent predictions. The contributions of quartz-sand, kaolinite, and goethite to U(VI) adsorption and the potential influences of dissolved Al, Si, and Fe are also discussed.

  16. Adsorption of antimony onto iron oxyhydroxides: adsorption behavior and surface structure.

    PubMed

    Guo, Xuejun; Wu, Zhijun; He, Mengchang; Meng, Xiaoguang; Jin, Xin; Qiu, Nan; Zhang, Jing

    2014-07-15

    Antimony is detected in soil and water with elevated concentration due to a variety of industrial applications and mining activities. Though antimony is classified as a pollutant of priority interest by the United States Environmental Protection Agency (USEPA) and Europe Union (EU), very little is known about its environmental behavior and adsorption mechanism. In this study, the adsorption behaviors and surface structure of antimony (III/V) on iron oxides were investigated using batch adsorption techniques, surface complexation modeling (SCM), X-ray photon spectroscopy (XPS) and extended X-ray absorption fine structure spectroscopy (EXAFS). The adsorption isotherms and edges indicated that the affinity of Sb(V) and Sb(III) toward the iron oxides depended on the Sb species, solution pH, and the characteristics of iron oxides. Sb(V) adsorption was favored at acidic pH and decreased dramatically with increasing pH, while Sb(III) adsorption was constant over a broad pH range. When pH is higher than 7, Sb(III) adsorption by goethite and hydrous ferric oxide (HFO) was greater than Sb(V). EXAFS analysis indicated that the majority of Sb(III), either adsorbed onto HFO or co-precipitated by FeCl3, was oxidized into Sb(V) probably due to the involvement of O2 in the long duration of sample preservation. Only one Sb-Fe subshell was filtered in the EXAFS spectra of antimony adsorption onto HFO, with the coordination number of 1.0-1.9 attributed to bidentate mononuclear edge-sharing ((2)E) between Sb and HFO.

  17. The adsorption of cesium on lanthanum hexaboride surfaces

    NASA Technical Reports Server (NTRS)

    Davis, P. R.; Swanson, L. W.; Chambers, S. A.

    1980-01-01

    The adsorption/desorption characteristics of cesium on clean and oxygen-covered LaB6 (100) surfaces were studied using various surface analysis techniques. On the initially clean surface (phi = 2.77 eV), adsorption produces a minimum work function of 1.96 eV and a saturation work function of 2.07 eV. For the oxygen-saturated surface, the cesium adsorption curve shows no minimum, the lowest work function (1.35 eV) occurring at cesium saturation. The utility of LaB6 (100) as an emitter or collector in thermionic converter applications (particularly for space nuclear electric propulsion) is evaluated.

  18. Adsorption of T4 bacteriophages on planar indium tin oxide surface via controlled surface tailoring.

    PubMed

    Liana, Ayu Ekajayanthi; Chia, Ed Win; Marquis, Christopher P; Gunawan, Cindy; Gooding, J Justin; Amal, Rose

    2016-04-15

    The work investigates the influence of surface physicochemical properties of planar indium tin oxide (ITO) as a model substrate on T4 bacteriophage adsorption. A comparative T4 bacteriophage adsorption study shows a significant difference in bacteriophage adsorption observed on chemically modified planar ITO when compared to similarly modified particulate ITO, which infers that trends observed in virus-particle interaction studies are not necessarily transferrable to predict virus-planar surface adsorption behaviour. We also found that ITO surfaces modified with methyl groups, (resulting in increased surface roughness and hydrophobicity) remained capable of adsorbing T4 bacteriophage. The adsorption of T4 onto bare, amine and carboxylic functionalised planar ITO suggests the presence of a unique binding behaviour involving specific functional groups on planar ITO surface beyond the non-specific electrostatic interactions that dominate phage to particle interactions. The paper demonstrates the significance of physicochemical properties of surfaces on bacteriophage-surface interactions.

  19. Adsorption of charged albumin subdomains on a graphite surface.

    PubMed

    Raffaini, Giuseppina; Ganazzoli, Fabio

    2006-03-01

    We report some new molecular dynamics simulation results about the adsorption on a hydrophobic graphite surface of two albumin subdomains, each formed by three different alpha-helices, considering the correctly charged side groups at pH = 7 instead of the neutral ones as done in our previous exploratory paper (Raffaini and Ganazzoli, Langmuir 2003;19:3403-3412). We find that the presence of charges affects somewhat the initial adsorption stage on the electrostatically neutral surface, but not the final one. Thus, we recover the result that a monolayer of aminoacids is eventually formed, with a rough parallelism of distant strands to optimize both the intramolecular and the surface interactions. This feature is consistent with the adsorption on the hydrophobic surface being driven by dispersion forces only, and with the "soft" nature of albumin. Additional optimizations of the final monolayer carried out at pH = 3 and 11 do not modify appreciably this picture, suggesting that adsorption on graphite is basically independent of pH. The enhanced hydration of the final adsorption state due to the (delocalized) charges of the side groups is also discussed in comparison with similar results of the neutralized subdomains.

  20. Adsorption of sugars on Al- and Ga-doped boron nitride surfaces: A computational study

    NASA Astrophysics Data System (ADS)

    Darwish, Ahmed A.; Fadlallah, Mohamed M.; Badawi, Ashraf; Maarouf, Ahmed A.

    2016-07-01

    Molecular adsorption on surfaces is a key element for many applications, including sensing and catalysis. Non-invasive sugar sensing has been an active area of research due to its importance to diabetes care. The adsorption of sugars on a template surface study is at the heart of matter. Here, we study doped hexagonal boron nitride sheets (h-BNNs) as adsorbing and sensing template for glucose and glucosamine. Using first principles calculations, we find that the adsorption of glucose and glucosamine on h-BNNs is significantly enhanced by the substitutional doping of the sheet with Al and Ga. Including long range van der Waals corrections gives adsorption energies of about 2 eV. In addition to the charge transfer occurring between glucose and the Al/Ga-doped BN sheets, the adsorption alters the size of the band gap, allowing for optical detection of adsorption. We also find that Al-doped boron nitride sheet is better than Ga-doped boron nitride sheet to enhance the adsorption energy of glucose and glucosamine. The results of our work can be potentially utilized when designing support templates for glucose and glucosamine.

  1. Structural Determinants for Protein adsorption/non-adsorption to Silica Surface

    PubMed Central

    Mathé, Christelle; Devineau, Stéphanie; Aude, Jean-Christophe; Lagniel, Gilles; Chédin, Stéphane; Legros, Véronique; Mathon, Marie-Hélène; Renault, Jean-Philippe; Pin, Serge; Boulard, Yves; Labarre, Jean

    2013-01-01

    The understanding of the mechanisms involved in the interaction of proteins with inorganic surfaces is of major interest in both fundamental research and applications such as nanotechnology. However, despite intense research, the mechanisms and the structural determinants of protein/surface interactions are still unclear. We developed a strategy consisting in identifying, in a mixture of hundreds of soluble proteins, those proteins that are adsorbed on the surface and those that are not. If the two protein subsets are large enough, their statistical comparative analysis must reveal the physicochemical determinants relevant for adsorption versus non-adsorption. This methodology was tested with silica nanoparticles. We found that the adsorbed proteins contain a higher number of charged amino acids, particularly arginine, which is consistent with involvement of this basic amino acid in electrostatic interactions with silica. The analysis also identified a marked bias toward low aromatic amino acid content (phenylalanine, tryptophan, tyrosine and histidine) in adsorbed proteins. Structural analyses and molecular dynamics simulations of proteins from the two groups indicate that non-adsorbed proteins have twice as many π-π interactions and higher structural rigidity. The data are consistent with the notion that adsorption is correlated with the flexibility of the protein and with its ability to spread on the surface. Our findings led us to propose a refined model of protein adsorption. PMID:24282583

  2. A key parameter on the adsorption of diluted aniline solutions with activated carbons: The surface oxygen content.

    PubMed

    Pardo, Beatrice; Ferrer, Nabí; Sempere, Julià; Gonzalez-Olmos, Rafael

    2016-11-01

    A total of 11 different commercial activated carbons (AC) with well characterized textural properties and oxygen surface content were tested as adsorbents for the removal of aniline as a target water pollutant. The maximum adsorption capacity of aniline for the studied AC was from 138.9 to 257.9 mg g(-1) at 296.15 K and it was observed to be strongly related to the textural properties of the AC, mainly with the BET surface area and the micropore volume. It was not observed any influence of the oxygen surface content of the AC on the maximum adsorption capacity. However, it was found that at low aniline aqueous concentration, the presence of oxygen surface groups plays a dominant role during the adsorption. A high concentration of oxygen surface groups, mainly carboxylic and phenolic groups, decreases the aniline adsorption regardless of the surface area of the AC. PMID:27497348

  3. A key parameter on the adsorption of diluted aniline solutions with activated carbons: The surface oxygen content.

    PubMed

    Pardo, Beatrice; Ferrer, Nabí; Sempere, Julià; Gonzalez-Olmos, Rafael

    2016-11-01

    A total of 11 different commercial activated carbons (AC) with well characterized textural properties and oxygen surface content were tested as adsorbents for the removal of aniline as a target water pollutant. The maximum adsorption capacity of aniline for the studied AC was from 138.9 to 257.9 mg g(-1) at 296.15 K and it was observed to be strongly related to the textural properties of the AC, mainly with the BET surface area and the micropore volume. It was not observed any influence of the oxygen surface content of the AC on the maximum adsorption capacity. However, it was found that at low aniline aqueous concentration, the presence of oxygen surface groups plays a dominant role during the adsorption. A high concentration of oxygen surface groups, mainly carboxylic and phenolic groups, decreases the aniline adsorption regardless of the surface area of the AC.

  4. Water and Carbon Dioxide Adsorption at Olivine Surfaces

    SciTech Connect

    Kerisit, Sebastien N.; Bylaska, Eric J.; Felmy, Andrew R.

    2013-11-14

    Plane-wave density functional theory (DFT) calculations were performed to simulate water and carbon dioxide adsorption at the (010) surface of five olivine minerals, namely, forsterite (Mg2SiO4), calcio-olivine (Ca2SiO4), tephroite (Mn2SiO4), fayalite (Fe2SiO4), and Co-olivine (Co2SiO4). Adsorption energies per water molecule obtained from energy minimizations varied from -78 kJ mol-1 for fayalite to -128 kJ mol-1 for calcio-olivine at sub-monolayer coverage and became less exothermic as coverage increased. In contrast, carbon dioxide adsorption energies at sub-monolayer coverage ranged from -20 kJ mol-1 for fayalite to -59 kJ mol-1 for calcio-olivine. Therefore, the DFT calculations show a strong driving force for carbon dioxide displacement by water at the surface of all olivine minerals in a competitive adsorption scenario. Additionally, adsorption energies for both water and carbon dioxide were found to be more exothermic for the alkaline-earth (AE) olivines than for the transition-metal (TM) olivines and to not correlate with the solvation enthalpies of the corresponding divalent cations. However, a correlation was obtained with the charge of the surface divalent cation indicating that the more ionic character of the AE cations in the olivine structure relative to the TM cations leads to greater interactions with adsorbed water and carbon dioxide molecules at the surface and thus more exothermic adsorption energies for the AE olivines. For calcio-olivine, which exhibits the highest divalent cation charge of the five olivines, ab initio molecular dynamics simulations showed that this effect leads both water and carbon dioxide to react with the surface and form hydroxyl groups and a carbonate-like species, respectively.

  5. Surface heterogeneity analysis of MCM-41 metallosilicates by using nitrogen adsorption data

    SciTech Connect

    Kruk, M.; Jaroniec, M.; Sayari, A.

    1999-08-31

    MCM-41 silicas with framework-incorporated aluminum and boron heteroatoms were studied using nitrogen adsorption at 77K over a wide range of relative pressures. It was shown that despite significant differences in surface area, pore sizes, and widths of pore size distributions, the framework-substituted MCM-41 materials studied exhibited very similar low-pressure relative adsorption curves and adsorption energy distributions. This indicates that the presence of heteroatoms does not lead to significant changes in the surface properties with respect to nitrogen molecules. However, small but detectable and systematic changes in the low-pressure adsorption were observed for two series of samples with different contents of heteroatoms prepared under similar conditions. It was concluded that low-pressure nitrogen adsorption exhibits rather low sensitivity toward framework-incorporated aluminum and boron heteroatoms, but it may provide some information about contents of heteroatoms for samples prepared under the same conditions. Because of the similarity of nitrogen adsorption processes on surfaces of siliceous ordered mesoporous materials with and without framework-substituted heteroatoms, the methods of micropore analysis (e.g., the comparative plot method) and mesopore size analysis developed and/or calibrated for pure-silica materials are expected to be fully applicable for samples with different kinds of incorporated heteroatoms.

  6. Effect of Dopants on the Adsorption of Carbon Dioxide on Ceria Surfaces

    DOE PAGES

    Li, Meijun; Tumuluri, Uma; Wu, Zili; Dai, Sheng

    2015-09-25

    Here, high-surface-area nanosized CeO2 and M-doped CeO2 (M=Cu, La, Zr, and Mg) prepared by a surfactant-templated method were tested for CO2 adsorption. Cu, La, and Zr are doped into the lattice of CeO2, whereas Mg is dispersed on the CeO2 surface. The doping of Cu and La into CeO2 leads to an increase of the CO2 adsorption capacity, whereas the doping of Zr has little or no effect. The addition of Mg causes a decrease of the CO2 adsorption capacity at a low Mg content and a gradual increase at a higher content. The CO2 adsorption capacity follows the sequencemore » Cu-CeO2>La-CeO2>Zr-CeO2≈CeO2>Mg-CeO2 at low dopant contents, in line with the relative amount of defect sites in the samples. It is the defect sites on the surface, not in the bulk of CeO2, modified by the dopants that play the vital role in CO2 chemisorption. Lastly, the role of surface oxygen vacancies is further supported by an in situ IR spectroscopic study of the surface chemistry during CO2 adsorption on the doped CeO2.« less

  7. Water Adsorption on the LaMnO3 Surface

    NASA Astrophysics Data System (ADS)

    Billman, Chris; Wang, Yan; Cheng, Hai-Ping

    Studying the adsorption of water on the metallic LaMnO3 surface can provide insight into this complicated surface-adsorbate interaction. Using density functional theory, we investigated the adsorption of a water monomer, dimer, trimer and a monolayer on the surface. The electronic structure of ground state configurations is explored using analysis of density of states, charge density, and crystal orbital overlap populations. We found that the interaction between the surface and water molecules is stronger than hydrogen bonding between molecules, which facilitates wetting of the surface. Adsorbed water molecules form very strong hydrogen bonds, with substantially shifted OH stretch modes. For the monolayer of adsorbed water, a hint of a bilayer is observed with a height separation of only 0.2 Å. However, simulated scanning tunneling microscopy (STM) images and vibrational spectra suggest a significant difference between the two layers due to intermolecular bonding and interaction with the substrate.

  8. Water adsorption on the LaMnO3 surface

    NASA Astrophysics Data System (ADS)

    Billman, Chris R.; Wang, Yan; Cheng, Hai-Ping

    2016-02-01

    Studying the adsorption of water on the metallic LaMnO3 surface can provide insight into this complicated surface-adsorbate interaction. Using density functional theory, we investigated the adsorption of a water monomer, dimer, trimer, and a monolayer on the surface. The electronic structure of ground state configurations is explored using analysis of density of states, charge density, and crystal orbital overlap populations. We found that the interaction between the surface and water molecules is stronger than hydrogen bonding between molecules, which facilitates wetting of the surface. Adsorbed water molecules form very strong hydrogen bonds, with substantially shifted OH stretch modes. For the monolayer of adsorbed water, a hint of a bilayer is observed with a height separation of only 0.2 A˚. However, simulated scanning tunneling microscopy images and vibrational spectra suggest a significant difference between the two layers due to intermolecular bonding and interaction with the substrate.

  9. The adsorption and oxidation of cyanogen on copper surfaces

    NASA Astrophysics Data System (ADS)

    Carley, A. F.; Chinn, M.; Parkinson, C. R.

    2003-07-01

    The adsorption of cyanogen on clean and oxygen pre-treated graphite supported copper films, and a polycrystalline copper surface, and the co-adsorption of cyanogen and oxygen on graphite supported copper films, and a polycrystalline copper surface has been studied using X-ray photoelectron spectroscopy. Cyanogen dissociates on the copper surfaces at 300 K, yielding an adsorbed cyano group, CN (a). On the oxygen pre-treated copper surface cyanogen reacts quantitatively with the adsorbed oxygen at 300 K to form a surface cyanate species, NCO. On annealing to 600 K this species decomposes, leaving only N adatoms and residual adsorbed CN on the surface. The co-adsorption of cyanogen and oxygen from a cyanogen-oxygen mixture enhances the formation of NCO to the extent that all available surface oxygen is consumed to form NCO on annealing at 450 K. In the absence of available atomic surface oxygen NCO does not decompose at temperatures up to 600 K. NCO and NCO 2 are shown to be the intermediates in the oxidation of cyanogen on copper films and a polycrystalline copper foil.

  10. A chemical equilibrium model for metal adsorption onto bacterial surfaces

    NASA Astrophysics Data System (ADS)

    Fein, Jeremy B.; Daughney, Christopher J.; Yee, Nathan; Davis, Thomas A.

    1997-08-01

    This study quantifies metal adsorption onto cell wall surfaces of Bacillus subtilis by applying equilibrium thermodynamics to the specific chemical reactions that occur at the water-bacteria interface. We use acid/base titrations to determine deprotonation constants for the important surface functional groups, and we perform metal-bacteria adsorption experiments, using Cd, Cu, Pb, and Al, to yield site-specific stability constants for the important metal-bacteria surface complexes. The acid/base properties of the cell wall of B. subtilis can best be characterized by invoking three distinct types of surface organic acid functional groups, with pK a values of 4.82 ± 0.14, 6.9 ± 0.5, and 9.4 ± 0.6. These functional groups likely correspond to carboxyl, phosphate, and hydroxyl sites, respectively, that are displayed on the cell wall surface. The results of the metal adsorption experiments indicate that both the carboxyl sites and the phosphate sites contribute to metal uptake. The values of the log stability constants for metal-carboxyl surface complexes range from 3.4 for Cd, 4.2 for Pb, 4.3 for Cu, to 5.0 for Al. These results suggest that the stabilities of the metal-surface complexes are high enough for metal-bacterial interactions to affect metal mobilities in many aqueous systems, and this approach enables quantitative assessment of the effects of bacteria on metal mobilities.

  11. Reversible Adsorption Kinetics of Near Surface Dimer Colloids.

    PubMed

    Salipante, Paul F; Hudson, Steven D

    2016-08-30

    We investigate the effect of shape on reversible adsorption kinetics using colloidal polystyrene dimers near a solid glass surface as a model system. The interaction between colloid and wall is tuned using electrostatic, depletion, and gravity forces to produce a double-well potential. The dwell time in each of the potential wells is measured from long duration particle trajectories. The height of each monomer relative to the glass surface is measured to a resolution of <20 nm by in-line holographic microscopy. The measured transition probability distributions are used in kinetic equations to describe the flux of particles to and from the surface. The dimers are compared to independent isolated monomers to determine the effects of shape on adsorption equilibria and kinetics. To elucidate these differences, we consider both mass and surface coverage and two definitions of surface coverage. The results show that dimers with single coverage produce slower adsorption, lower surface coverage, and higher mass coverage in comparison to those of monomers, while dimers with double coverage adsorb faster and result in higher surface coverage. PMID:27483023

  12. Differential adsorption of CHON isomers at interstellar grain surfaces

    NASA Astrophysics Data System (ADS)

    Lattelais, M.; Pauzat, F.; Ellinger, Y.; Ceccarelli, C.

    2015-06-01

    Context. The CHON generic chemical formula covers different isomers such as isocyanic acid (HNCO), cyanic acid (HOCN), fulminic acid (HCNO), and isofulminic acid (HONC); the first three have been identified in a large variety of environments in the interstellar medium (ISM). Several phenomena could be at the origin of the observed abundances, such as different pathways of formation and destruction involving gas phase reactions with different possible activation barriers and/or surface processes depending on the local temperature and the nature of the support. Aims: The scope of this article is to shed some light on the interaction of the CHON isomers with interstellar grains as a function of the nature of the surface and to determine the corresponding adsorption energies in order to find whether this phenomenon could play a role in the abundances observed in the ISM. Methods: The question was addressed by means of numerical simulations using first principle periodic density functional theory (DFT) to represent the grain support as a solid of infinite dimension. Results: Regardless of the nature of the model surface (water ice, graphene, silica), two different classes of isomers were identified: weakly bound (HNCO and HCNO) and strongly bound (HOCN and HONC), with the adsorption energies of the latter group being about twice those of the former. The range of the adsorption energies is (from highest to lowest) HOCN > HONC > HNCO > HCNO. They are totally disconnected from the relative stabilities, which range from HNCO > HOCN > HCNO > HONC. Conclusions: The possibility of hydrogen bonding is the discriminating factor in the trapping of CHON species on grain surfaces. Whatever the environment, differential adsorption is effective and its contribution to the molecular abundances should not be ignored. The theoretical adsorption energies provided here could be profitably used for a more realistic modeling of molecule-surfaces interactions.

  13. [Effect of acid-base two steps surface modification on the adsorption of Cr(VI) onto activated carbon].

    PubMed

    Liu, Shou-xin; Chen, Xiao-yun; Chen, Xi; Sun, Cheng-lin

    2005-11-01

    Effect of HNO3-NaOH two steps surface modification on the adsorption of Cr(VI) from aqueous solution onto activated carbon was evaluated. Activated carbon was oxidized in HNO3 aqueous solution at first (AC1), then treated in the mixture of NaOH and NaCl solution (AC2). Batch equilibrium and continuous adsorption experiments were conducted to determine the adsorption characteristics. Boehm titration method, element analysis were used to characterize the surface properties. N2/77 K adsorption isotherm method was used to characterize the pore structure. The results reveal that adsorption capacity and adsorption rate increase significantly, which in the following order: AC2>AC1>AC0. Surface modification caused BET surface area decreased and the total number of surface oxygen acid groups increased. First oxidation modification in HNO3 solution produced positive acid groups on the surface of activated carbon. Subsequent 2nd modification replaced H+ of carbon surface groups by Na+, the acidity of AC2 was decreased. The main cause of higher Cr(VI) adsorption capacity and rate for AC2 was the more oxygen surface acid groups, and suitable solution pH provide by surface groups.

  14. Effect of surface strain on oxygen adsorption on Zr (0001) surface

    SciTech Connect

    Wang, Xing; Khafizov, Marat; Szlufarska, Izabela

    2014-02-01

    The effect of surface strain on oxygen adsorption on Zr (0 0 0 1) surface is investigated by density functional theory (DFT) calculations. It is demonstrated that both surface strain and interactions between oxygen adsorbates influence the adsorption process. Oxygen binding to zirconium becomes stronger as the strain changes from compressive to tensile. When oxygen coverage is low and the oxygen interactions are negligible, surface face-centered cubic sites are the most stable for O binding. At high coverage and under compression, octahedral sites between second and third Zr layers become most favorable because the interactions between adsorbates are weakened by positive charge screening. Calculations with both single-layer adsorption model and multiple-layer adsorption model demonstrate that compressive strain at the Zr/oxide interface will provide a thermodynamic driving force for oxygen to incorporate from the surface into the bulk of Zr, while binding oxygen to the Zr surface will be easier when tensile strain is applied.

  15. Surface adsorption of Cs137 ions on quartz crystals

    USGS Publications Warehouse

    Antkiw, Stephen; Waesche, H.; Senftle, F.

    1954-01-01

    Adsorption tests were made on four large synthetic and three natural quartz crystals to see if surface defects might be detected by subsequent autoradiography techniques. The adsorbent used was radioactive Cs137 in a solution of Cs 137Cl. Natural quartz crystals adsorbed more cesium than the synthetic crystals. Certain surface defects were made evident by this method, but twinning features could not be detected.

  16. Surface free energy analysis of adsorbents used for radioiodine adsorption

    NASA Astrophysics Data System (ADS)

    González-García, C. M.; Román, S.; González, J. F.; Sabio, E.; Ledesma, B.

    2013-10-01

    In this work, the surface free energy of biomass-based activated carbons, both fresh and impregnated with triethylenediamine, has been evaluated. The contribution of Lifshitz van der Waals components was determined by the model proposed by van Oss et al. The results obtained allowed predicting the most probable configurations of the impregnant onto the carbon surface and its influence on the subsequent adsorption of radioactive methyl iodide.

  17. Zwitteration: Coating Surfaces with Zwitterionic Functionality to Reduce Nonspecific Adsorption

    PubMed Central

    2015-01-01

    Coating surfaces with thin or thick films of zwitterionic material is an effective way to reduce or eliminate nonspecific adsorption to the solid/liquid interface. This review tracks the various approaches to zwitteration, such as monolayer assemblies and polymeric brush coatings, on micro- to macroscopic surfaces. A critical summary of the mechanisms responsible for antifouling shows how zwitterions are ideally suited to this task. PMID:24754399

  18. CO adsorption on cobalt: Prediction of stable surface phases

    NASA Astrophysics Data System (ADS)

    Gunasooriya, G. T. Kasun Kalhara; van Bavel, Alexander P.; Kuipers, Herman P. C. E.; Saeys, Mark

    2015-12-01

    Adsorption is often described by a Langmuir isotherm, sometimes accounting for a gradual decrease in the adsorption energy with coverage. Using density functional theory, we show that CO adsorption on cobalt does not follow this typical behavior. Instead, adsorption on Co(0001) is dominated by two surface phases. At low pressures, the (√3 × √3)R30°-CO structure is the stable phase, and CO forms (√3 × √3)R30°-CO islands for coverages below 1/3 ML because of attractive CO-CO interactions. Increasing the pressure does not gradually increase the coverage beyond 1/3 ML. Instead, a transition to a high coverage (2√3 × 2√3)R30°-7CO surface structure occurs at 0.1 mbar at room temperature and at 21 bar at 500 K. These two phases are also the dominant structures that have been characterized experimentally on Co(0001), and the conditions where each phase was observed match the first principle surface phase diagram.

  19. Surface Analysis of 4-Aminothiophenol Adsorption at Polycrystalline Platinum Electrodes

    NASA Technical Reports Server (NTRS)

    Rosario-Castro, Belinda I.; Fachini, Estevao R.; Contes, Enid J.; Perez-Davis, Marla E.; Cabrera, Carlos R.

    2008-01-01

    Formation of self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) on polycrystalline platinum electrodes has been studied by surface analysis and electrochemistry techniques. The 4-ATP monolayer was characterized by cyclic voltammetry (CV), Raman spectroscopy, reflection absorption infrared (RAIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) experiments give an idea about the packing quality of the monolayer. RAIR and Raman spectra for 4-ATP modified platinum electrodes showed the characteristic adsorption bands for neat 4-ATP indicating the adsorption of 4-ATP molecules on platinum surface. The adsorption on platinum was also evidenced by the presence of sulfur and nitrogen peaks by XPS survey spectra of the modified platinum electrodes. High resolution XPS studies and RAIR spectrum for platinum electrodes modified with 4-ATP indicate that molecules are sulfur-bonded to the platinum surface. The formation of S-Pt bond suggests that ATP adsorption gives up an amino terminated SAM. Thickness of the monolayer was evaluated via angle-resolved XPS (AR-XPS) analyses. Derivatization of 4-ATP SAM was performed using 16-Br hexadecanoic acid.

  20. Computer program calculates and plots surface area and pore size distribution data

    NASA Technical Reports Server (NTRS)

    Halpert, G.

    1968-01-01

    Computer program calculates surface area and pore size distribution of powders, metals, ceramics, and catalysts, and prints and plots the desired data directly. Surface area calculations are based on the gas adsorption technique of Brunauer, Emmett, and Teller, and pore size distribution calculations are based on the gas adsorption technique of Pierce.

  1. Ethanol adsorption on the Si (111) surface: First principles study

    NASA Astrophysics Data System (ADS)

    Gavrilenko, Alexander V.; Bonner, Carl E.; Gavrilenko, Vladimir I.

    2012-03-01

    Equilibrium atomic configurations and electron energy structure of ethanol adsorbed on the Si (111) surface are studied by the first principles density functional theory. Geometry optimization is performed by the total energy minimization method. Equilibrium atomic geometries of ethanol, both undissociated and dissociated, on the Si (111) surface are found and analysed. Reaction pathways and predicted transition states are discussed in comparison with available experimental data in terms of the feasibility of the reactions occurring. Analysis of atom and orbital resolved projected density of states indicates substantial modifications of the Si surface valence and conduction electron bands due to the adsorption of ethanol affecting the electronic properties of the surface.

  2. Initial Processes of Sulfur Adsorption on Si(100) Surface

    NASA Astrophysics Data System (ADS)

    Ma, Li; Wang, Jian-Guang; Wang, Guang-Hou

    2005-10-01

    The adsorption of one monolayer S atoms on ideal Si(100) surface is studied by using the self-consistent tight binding linear muffin-tin orbital method. Energies of adsorption systems of S atoms on different sites are calculated. It is found that the adsorbed S atoms are more favorable on B1 site (bridge site) with a distance 0.131 nm above the Si surface. The S, Si mixed layer might exist at S/Si(100) interface. The layer projected density of states are calculated and compared with that of the clean surface. The charge transfers are also investigated. The project supported by National Natural Science Foundation of China under Grant Nos. 90206033 and 10274031

  3. Cell surface engineering of microorganisms towards adsorption of heavy metals.

    PubMed

    Li, Peng-Song; Tao, Hu-Chun

    2015-06-01

    Heavy metal contamination has become a worldwide environmental concern due to its toxicity, non-degradability and food-chain bioaccumulation. Conventional physical and chemical treatment methods for heavy metal removal have disadvantages such as cost-intensiveness, incomplete removal, secondary pollution and the lack of metal specificity. Microbial biomass-based biosorption is one of the approaches gaining increasing attention because it is effective, cheap, and environmental friendly and can work well at low concentrations. To enhance the adsorption properties of microbial cells to heavy metal ions, the cell surface display of various metal-binding proteins/peptides have been performed using a cell surface engineering approach. The surface engineering of Gram-negative bacteria, Gram-positive bacteria and yeast towards the adsorption of heavy metals are reviewed in this article. The problems and future perspectives of this technology are discussed.

  4. Reversible adsorption of hydrogen chloride to ice surfaces

    NASA Astrophysics Data System (ADS)

    Zimmermann, Stefan; Kippenberger, Matthias; Crowley, John

    2015-04-01

    Hydrogen chloride is the most important reservoir of gaseous, reactive chlorine in the atmosphere. Although several laboratory investigations of the interaction of HCl with ice surfaces have been conducted, there is still great uncertainty associated with the adsorption isotherms of HCl on ice, which is largely a consequence of most previous studies being unable to work at concentrations relevant for the atmosphere and to explore the non-saturated part of the isotherm at sub-monolayer coverage. We have conducted experiments on HCl uptake on ice surfaces at temperatures between 190 and 220 K, using a coated wall flow tube. HCl at concentrations as low as 2 × 109 molecule cm3 (~10-8 Torr) was detected using a chemical-ionization, quadrupole mass spectrometer. The equilibrium surface coverage of HCl on ice could be interpreted using the Langmuir-model to derive partition coefficients (KLang). We find that the dissociative Langmuir isotherm describes our data significantly better than the non-dissociative type. Surprisingly, and in contrast to the behavior of the majority of traces-gases which adsorb reversibly on ice surfaces, the partition-coefficients we derive for HCl do not show a systematic dependence on temperature, precluding the simple derivation of an adsorption enthalpy and indicating the presence of more complex adsorption and desorption mechanisms for strong acids ionizing on the surface compared to H-bonded trace gases.

  5. Arginine Inhibits Adsorption of Proteins on Polystyrene Surface

    PubMed Central

    Shikiya, Yui; Tomita, Shunsuke; Arakawa, Tsutomu; Shiraki, Kentaro

    2013-01-01

    Nonspecific adsorption of protein on solid surfaces causes a reduction of concentration as well as enzyme inactivation during purification and storage. However, there are no versatile inhibitors of the adsorption between proteins and solid surfaces at low concentrations. Therefore, we examined additives for the prevention of protein adsorption on polystyrene particles (PS particles) as a commonly-used material for vessels such as disposable test tubes and microtubes. A protein solution was mixed with PS particles, and then adsorption of protein was monitored by the concentration and activity of protein in the supernatant after centrifugation. Five different proteins bound to PS particles through electrostatic, hydrophobic, and aromatic interactions, causing a decrease in protein concentration and loss of enzyme activity in the supernatant. Among the additives, including arginine hydrochloride (Arg), lysine hydrochloride, guanidine hydrochloride, NaCl, glycine, and glucose, Arg was most effective in preventing the binding of proteins to PS particles as well as activity loss. Moreover, even after the mixing of protein and PS particles, the addition of Arg caused desorption of the bound protein from PS particles. This study demonstrated a new function of Arg, which expands the potential for application of Arg to proteins. PMID:23967100

  6. Adsorption of benzaldehyde at the surface of ice, studied by experimental method and computer simulation.

    PubMed

    Petitjean, Mélanie; Hantal, György; Chauvin, Coline; Mirabel, Philippe; Le Calvé, Stéphane; Hoang, Paul N M; Picaud, Sylvain; Jedlovszky, Pál

    2010-06-15

    Adsorption study of benzaldehyde on ice surfaces is performed by combining experimental and theoretical approaches. The experiments are conducted over the temperature range 233-253 K using a coated wall flow tube coupled to a mass spectrometric detector. Besides the experimental way, the adsorption isotherm is also determined by performing a set of grand canonical Monte Carlo simulations at 233 K. The experimental and calculated adsorption isotherms show a very good agreement within the corresponding errors. Besides, both experimental and theoretical studies permit us to derive the enthalpy of adsorption of benzaldehyde on ice surfaces DeltaH(ads), which are in excellent agreement: DeltaH(ads) = -61.4 +/- 9.7 kJ/mol (experimental) and DeltaH(ads) = -59.4 +/- 5.1 kJ/mol (simulation). The obtained results indicate a much stronger ability of benzaldehyde of being adsorbed at the surface of ice than that of small aliphatic aldehydes, such as formaldehyde or acetaldehyde. At low surface coverages the adsorbed molecules exclusively lie parallel with the ice surface. With increasing surface coverage, however, the increasing competition of the adsorbed molecules for the surface area to be occupied leads to the appearance of two different perpendicular orientations relative to the surface. In the first orientation, the benzaldehyde molecule turns its aldehyde group toward the ice phase, and, similarly to the molecules in the lying orientation, forms a hydrogen bond with a surface water molecule. In the other perpendicular orientation the aldehyde group turns to the vapor phase, and its O atom interacts with the delocalized pi system of the benzene ring of a nearby lying benzaldehyde molecule of the second molecular layer. In accordance with this observed scenario, the saturated adsorption layer, being stable in a roughly 1 kJ/mol broad range of chemical potentials, contains, besides the first molecular layer, also traces of the second molecular layer of adsorbed

  7. Adsorption of aromatic organic acids onto high area activated carbon cloth in relation to wastewater purification.

    PubMed

    Ayranci, Erol; Duman, Osman

    2006-08-25

    Adsorption of aromatic organic acids: benzoic acid (BA), salicylic acid (SA), p-aminobenzoic acid (pABA) and nicotinic acid (NA), onto high area activated carbon cloth from solutions in 0.4 M H(2)SO(4), in water at natural pH, in 0.1 M NaOH and also from solutions having pH 7.0 were studied by in situ UV-spectroscopic technique. The first-order rate law was found to be applicable for the kinetic data of adsorption. The rates and extents of adsorption of the organic acids were the highest from water or 0.4 M H(2)SO(4) solutions and the lowest from 0.1 M NaOH solution. The order of rates and extents of adsorption of the four organic acids in each of the four solutions (0.4 M H(2)SO(4), water, solution of pH 7.0 and 0.1 M NaOH) was determined as SA>BA>NA approximately pABA. These observed orders were explained in terms of electrostatic, dispersion and hydrogen bonding interactions between the surface and the adsorbate species, taking the charge of the carbon surface and the adsorbate in each solution into account. Adsorption of BA in molecular form or in benzoate form was analyzed by treating the solution as a mixture of two components and applying Lambert-Beer law to two-component system. The adsorption isotherm data of the systems studied were derived at 30 degrees C and fitted to Langmuir and Freundlich equations. PMID:16442224

  8. Adsorption of poly(ethylene glycol)-modified ribonuclease A to a poly(lactide-co-glycolide) surface.

    PubMed

    Daly, Susan M; Przybycien, Todd M; Tilton, Robert D

    2005-06-30

    Protein adsorption is a source of variability in the release profiles of therapeutic proteins from biodegradable microspheres. We employ optical reflectometry and total internal reflection fluorescence to explore the extent and kinetics of ribonuclease A (RNase A) adsorption to spin-cast films of poly(lactide-co-glycolide) (PLG) and, in particular, to determine how covalent grafting of polyethylene glycol (PEG) to RNase A affects adsorption. Adsorption kinetics on PLG surfaces are surface-limited for RNase A but transport-limited for unconjugated PEG homopolymers and for PEG-modified RNase A, indicating that PEG anchors the conjugates to the surface during the transport-limited regime. PEG modification of RNase A decreases the total number of adsorbed molecules per unit area but increases the areal surface coverage because the grafted PEG chains exclude additional surface area. Total internal reflection fluorescence-based exchange measurements show that there is no exchange between adsorbed and solution-phase protein molecules. This indicates an unusually tenacious adsorption. Streaming current measurements indicate that the zeta potential of the PLG surface becomes increasingly negative as the film is exposed to water for several weeks, as expected. Aging of the PLG surface results in increased adsorption of unmodified RNase A but decreased adsorption of unconjugated PEG homopolymers and of PEG-RNase A conjugates, relative to the extent of adsorption on freshly prepared PLG surfaces. Adsorption results correlate well with an increase in the rate, total extent and preservation of bioactivity of RNase A released from PLG microspheres for the PEG-modified version of RNase A.

  9. Adsorption of Amelogenin onto Self-Assembled and Fluoroapatite Surfaces

    SciTech Connect

    Tarasevich, Barbara J.; Lea, Alan S.; Bernt, William; Engelhard, Mark H.; Shaw, Wendy J.

    2009-02-19

    Abstract. The interactions of proteins at surfaces are of great importance to biomineralizaton processes and to the development and function of biomaterials. Amelogenin is a unique biomineralization protein because it self-assembles to form supramolecular structures called “nanospheres,” spherical aggregates of monomers that are 20-60 nm in diameter. Although the nanosphere quaternary structure has been observed in solution, the quaternary structure of amelogenin adsorbed onto surfaces is also of great interest because the surface structure is critical to its function. We report studies of the adsorption of the amelogenin onto self-assembled monolayers (SAMs) with COOH and CH3 end group functionality and single crystal fluoroapatite (FAP). Dynamic light scattering (DLS) experiments showed that the solutions contained nanospheres and aggregates of nanospheres. Protein adsorption onto the various substrates was evidenced by null ellipsometry, x-ray photoelectron spectroscopy (XPS), and external reflectance Fourier transform infrared spectroscopy (ERFTIR). Although only nanospheres were observed in solution, ellipsometry and atomic force microscopy (AFM) indicated that the protein adsorbates were much smaller structures than the original nanospheres, from monomers to small oligomers in size. Monomer adsorption was promoted onto the CH3 surfaces and small oligomer adsorption was promoted onto the COOH and FAP substrates. In some cases, remnants of the original nanospheres adsorbed as multilayers on top of the underlying subnanosphere layers. This work suggests that amelogenin can adsorb by the “shedding” or disassembling of substructures from the nanospheres onto substrates and indicates that amelogenin may have a range of possible quaternary structures depending on whether it is in solution or interacting with surfaces.

  10. Surface-modified magnetic colloids for affinity adsorption of immunoglobulins

    NASA Astrophysics Data System (ADS)

    Martins, Fernanda; Pinho, Samantha C.; Zollner, Terezinha C. A.; Zollner, Ricardo L.; de Cuyper, Marcel; Santana, Maria Helena A.

    This work describes the preparation, characterization and in vitro adsorption tests of surface-modified magnetoliposomes for affinity binding of (i) anticardiolipin (isotype G) antibodies and (ii) specific isotype E antibodies generated by hypersensitivity reactions in humans with respiratory allergy. In the first case, cardiolipin embedded in the bilayer of magnetoliposomes was used as specific ligand. In the second case, antigenic proteins present in an extract of Dermatophagoids pteronyssinus and Blomia tropicalis mites were covalently coupled on the surface of magnetoliposomes via a diglycolic spacer arm, and used as specific ligands for IgE. Antibody adsorption was performed in a high-gradient magnetophoresis system, using either sera of healthy individuals or a pool of sera from autoimmune or allergic patients. The selectivity and capacity of the system were quantified by a frontal analysis in a capillary column, and by constructing breakthrough curves. The results show that the highest yield and selectivity were obtained if the ligand was extended into the aqueous layer surrounding the magnetoliposome surface. A 100% selectivity was obtained for adsorption of specific IgE, and 8% for IgG. These results demonstrate the potentialities of both types of surface-modified magnetic biocolloids in the field of in vitro diagnosis tests for allergic or autoimmune conditions.

  11. High surface area, high permeability carbon monoliths

    SciTech Connect

    Lagasse, R.R.; Schroeder, J.L.

    1994-12-31

    The goal of this work is to prepare carbon monoliths having precisely tailored pore size distribution. Prior studies have demonstrated that poly(acrylonitrile) can be processed into a precursor having tailored macropore structure. Since the macropores were preserved during pyrolysis, this synthetic process provided a route to porous carbon having macropores with size =0.1 to 10{mu}m. No micropores of size <2 nm could be detected in the carbon, however, by nitrogen adsorption. In the present work, the authors have processed a different polymer, poly(vinylidene chloride) into a macroporous precursor, Pyrolysis produced carbon monoliths having macropores derived from the polymer precursor as well as extensive microporosity produced during the pyrolysis of the polymer. One of these carbons had BET surface area of 1,050 m{sup 2}/g and about 1.2 cc/g total pore volume, with about 1/3 of the total pore volume in micropores and the remainder in 1{mu}m macropores. No mesopores in the intermediate size range could be detected by nitrogen adsorption. Carbon materials having high surface area as well as micron size pores have potential applications as electrodes for double layer supercapacitors containing liquid electrolyte, or as efficient media for performing chemical separations.

  12. Atomic hydrogen adsorption on lithium-doped graphite surfaces

    SciTech Connect

    Allouche, Alain

    2012-01-01

    The effects of lithium doping of pristine and defective graphite surfaces on hydrogen adsorption are studied by the first-principles Plane-Wave Density Functional Theory. The surface defects are simulated by a single atomic vacancy. The DFT calculation is corrected for long-range effects through semi-empirical London terms for each constituent of the system. The lithium doping of the graphite surfaces notably reinforces hydrogen atom binding. Qualitative comparison with experimental results is given using the lithium 1s energy level shifts induced by the atomic vacancy and/or hydrogen trapping.

  13. Adsorption structure of water molecules on the Be(0001) surface

    SciTech Connect

    Yang, Yu; Li, Yanfang; Wang, Shuangxi; Zhang, Ping

    2014-06-07

    By using density functional theory calculations, we systematically investigate the adsorption of water molecules at different coverages on the Be(0001) surface. The coverage dependence of the prototype water structures and energetics for water adlayer growth are systematically studied. The structures, energetics, and electronic properties are calculated and compared with other available studies. Through our systematic investigations, we find that water molecules form clusters or chains on the Be(0001) surface at low coverages. When increasing the water coverage, water molecules tend to form a 2 × 2 hexagonal network on the Be(0001) surface.

  14. Adsorption of Te on the Si(001) Surface

    NASA Astrophysics Data System (ADS)

    Sen, Prasenjit; Batra, Inder P.; Grein, C. H.; Fong, C. Y.; Ciraci, S.

    2001-03-01

    To understand the interface between CdTe and Si and to reveal the atomistic mechanism for the surfactant behavior of adsorbed Te we have investigated the adsorption of Te on the Si(001) surface. This interface is also of crucial importance in developing CdTe/Si as a composite substance for the growth of HgCdTe. We carried out first-principles plane wave calculations within density-functional theory. The adsorption sites and corresponding binding energies are calculated on fully relaxed geometries by using the conjugate gradient method. We found that, at monolayer coverage, Te adatoms do not dimerize. At very low coverage, the top site above the Si-Si surface dimer bond is energetically favorable relative to cave, hollow and bridge sites. Finally, the atomistic mechanism of the surfactant role of Te has been investigated by finite temperature ab-initio molecular dynamics calculations.

  15. Adsorption and Coupling of 4-aminophenol on Pt(111) surfaces

    PubMed Central

    Otero-Irurueta, G.; Martínez, J. I.; Bueno, R.A.; Palomares, F. J.; Salavagione, H. J.; Singh, M. K.; Méndez, J.; Ellis, G. J.; López, M. F.; Martín-Gago, J. A.

    2016-01-01

    We have deposited 4-aminophenol on Pt(111) surfaces in ultra-high vacuum and studied the strength of its adsorption through a combination of STM, LEED, XPS and ab initio calculations. Although an ordered (2√3×2√3)R30° phase appears, we have observed that molecule-substrate interaction dominates the adsorption geometry and properties of the system. At RT the high catalytic activity of Pt induces aminophenol to lose the H atom from the hydroxyl group, and a proportion of the molecules lose the complete hydroxyl group. After annealing above 420K, all deposited aminophenol molecules have lost the OH moiety and some hydrogen atoms from the amino groups. At this temperature, short single-molecule oligomer chains can be observed. These chains are the product of a new reaction that proceeds via the coupling of radical species that is favoured by surface diffusion. PMID:27279673

  16. Adsorption and desorption studies of cesium on sapphire surfaces

    SciTech Connect

    Zavadil, K.R.; Ing, J.L.

    1993-12-01

    Adsorption/desorption were studied using combined surface analytical techniques. An approximate initial sticking coefficient for Cs on sapphire was measured using reflection mass spectrometry and found to be 0.9. Thermal Desorption Mass Spectrometry (TDMS) and Auger Electron Spectroscopy (AES) were used to verify that a significant decrease in sticking coefficient occurs as the Cs coverage reaches a critical submonolayer value. TDMS analysis demonstrates that Cs is stabilized on a clean sapphire surface at temperatures (1200 K) in excess of the temperatures experienced by sapphire in a TOPAZ-2 thermionic fuel element (TFE). Surface contaminants on sapphire can enhance Cs adsorption relative to the clean surface. C contamination eliminates the high temperature state of Cs desorption found on clean sapphire but shifts the bulk of the C desorption from 400 to 620 K. Surface C is a difficult contaminant to remove from sapphire, requiring annealing above 1400 K. Whether Cs is stabilized on sapphire in a TFE environment will most likely depend on relation between surface contamination and surface structure.

  17. Goethite surface reactivity: III. Unifying arsenate adsorption behavior through a variable crystal face - Site density model

    NASA Astrophysics Data System (ADS)

    Salazar-Camacho, Carlos; Villalobos, Mario

    2010-04-01

    We developed a model that describes quantitatively the arsenate adsorption behavior for any goethite preparation as a function of pH and ionic strength, by using one basic surface arsenate stoichiometry, with two affinity constants. The model combines a face distribution-crystallographic site density model for goethite with tenets of the Triple Layer and CD-MUSIC surface complexation models, and is self-consistent with its adsorption behavior towards protons, electrolytes, and other ions investigated previously. Five different systems of published arsenate adsorption data were used to calibrate the model spanning a wide range of chemical conditions, which included adsorption isotherms at different pH values, and adsorption pH-edges at different As(V) loadings, both at different ionic strengths and background electrolytes. Four additional goethite-arsenate systems reported with limited characterization and adsorption data were accurately described by the model developed. The adsorption reaction proposed is: lbond2 FeOH +lbond2 SOH +AsO43-+H→lbond2 FeOAsO3[2-]…SOH+HO where lbond2 SOH is an adjacent surface site to lbond2 FeOH; with log K = 21.6 ± 0.7 when lbond2 SOH is another lbond2 FeOH, and log K = 18.75 ± 0.9, when lbond2 SOH is lbond2 Fe 2OH. An additional small contribution of a protonated complex was required to describe data at low pH and very high arsenate loadings. The model considered goethites above 80 m 2/g as ideally composed of 70% face (1 0 1) and 30% face (0 0 1), resulting in a site density for lbond2 FeOH and for lbond2 Fe 3OH of 3.125/nm 2 each. Below 80 m 2/g surface capacity increases progressively with decreasing area, which was modeled by considering a progressively increasing proportion of faces (0 1 0)/(1 0 1), because face (0 1 0) shows a much higher site density of lbond2 FeOH groups. Computation of the specific proportion of faces, and thus of the site densities for the three types of crystallographic surface groups present in

  18. Polymer Adsorption on Graphite and CVD Graphene Surfaces Studied by Surface-Specific Vibrational Spectroscopy.

    PubMed

    Su, Yudan; Han, Hui-Ling; Cai, Qun; Wu, Qiong; Xie, Mingxiu; Chen, Daoyong; Geng, Baisong; Zhang, Yuanbo; Wang, Feng; Shen, Y R; Tian, Chuanshan

    2015-10-14

    Sum-frequency vibrational spectroscopy was employed to probe polymer contaminants on chemical vapor deposition (CVD) graphene and to study alkane and polyethylene (PE) adsorption on graphite. In comparing the spectra from the two surfaces, it was found that the contaminants on CVD graphene must be long-chain alkane or PE-like molecules. PE adsorption from solution on the honeycomb surface results in a self-assembled ordered monolayer with the C-C skeleton plane perpendicular to the surface and an adsorption free energy of ∼42 kJ/mol for PE(H(CH2CH2)nH) with n ≈ 60. Such large adsorption energy is responsible for the easy contamination of CVD graphene by impurity in the polymer during standard transfer processes. Contamination can be minimized with the use of purified polymers free of PE-like impurities.

  19. DNA adsorption onto calcium aluminate and silicate glass surfaces.

    PubMed

    Carlson, Krista; Flick, Lisa; Hall, Matthew

    2014-05-01

    A common technique for small-scale isolation of genomic DNA is via adsorption of the DNA molecules onto a silica scaffold. In this work, the isolation capacities of calcium aluminate based glasses were compared against a commercially available silica scaffold. Silica scaffolds exhibit a negative surface at the physiological pH values used during DNA isolation (pH 5-9), while the calcium aluminate glass microspheres exhibit a positive surface charge. Isolation data demonstrates that the positively charged surface enhanced DNA adsorption over the negatively charged surface. DNA was eluted from the calcium aluminate surface by shifting the pH of the solution to above its IEP at pH 8. Iron additions to the calcium aluminate glass improved the chemical durability without compromising the surface charge. Morphology of the glass substrate was also found to affect DNA isolation; 43-106 μm diameter soda lime silicate microspheres adsorbed a greater quantity of genomic DNA than silica fibers with an average diameter of ∼2 μm.

  20. Surface charge effects in protein adsorption on nanodiamonds

    NASA Astrophysics Data System (ADS)

    Aramesh, M.; Shimoni, O.; Ostrikov, K.; Prawer, S.; Cervenka, J.

    2015-03-01

    Understanding the interaction of proteins with charged diamond nanoparticles is of fundamental importance for diverse biomedical applications. Here we present a thorough study of protein binding, adsorption kinetics and structure on strongly positively (hydrogen-terminated) and negatively (oxygen-terminated) charged nanodiamond particles using a quartz crystal microbalance by dissipation and infrared spectroscopy. By using two model proteins (bovine serum albumin and lysozyme) of different properties (charge, molecular weight and rigidity), the main driving mechanism responsible for the protein binding to the charged nanoparticles was identified. Electrostatic interactions were found to dominate the protein adsorption dynamics, attachment and conformation. We developed a simple electrostatic model that can qualitatively explain the observed adsorption behaviour based on charge-induced pH modifications near the charged nanoparticle surfaces. Under neutral conditions, the local pH around the positively and negatively charged nanodiamonds becomes very high (11-12) and low (1-3) respectively, which has a profound impact on the protein charge, hydration and affinity to the nanodiamonds. Small proteins (lysozyme) were found to form multilayers with significant conformational changes to screen the surface charge, while larger proteins (albumin) formed monolayers with minor conformational changes. The findings of this study provide a step forward toward understanding and eventually predicting nanoparticle interactions with biofluids.Understanding the interaction of proteins with charged diamond nanoparticles is of fundamental importance for diverse biomedical applications. Here we present a thorough study of protein binding, adsorption kinetics and structure on strongly positively (hydrogen-terminated) and negatively (oxygen-terminated) charged nanodiamond particles using a quartz crystal microbalance by dissipation and infrared spectroscopy. By using two model proteins

  1. DFT modelling of hydrogen sulphide adsorption on α-Cr2O3 (0001) surface

    NASA Astrophysics Data System (ADS)

    Maldonado, Frank; Stashans, Arvids

    2016-05-01

    Density functional theory has been used to predict properties of hydrogen sulphide, H2S, adsorption on the α-Cr2O3 (0001) surface. Five energetically most favourable adsorption configurations have been selected for the study. Our work reveals adsorption geometries as well as discusses electronic and magnetic properties of the adsorbate on chromium oxide surface. It is shown that two different adsorption types, namely molecular adsorption and dissociative adsorption, can take place leading to two sets of adsorption energies. The most favourable arrangement is found to correspond to the case of dissociative adsorption with molecular hydrogen forming OH group at the α-Cr2O3 (0001) surface. Initial geometry for the adsorption configurations

  2. [Surface organic modification of acid vermiculite and its adsorption of hydrophobic micro pollutants in aqueous solutions].

    PubMed

    Jiang, Zheng-Ming; Yu, Xu-Biao; Hu, Yun; Ren, Yuan; Li, Xue-Hui; Wei, Chao-Hai

    2013-07-01

    To solve the problems of intercalated organoclay such as low surface area and inhomogeneous organic loading, natural vermiculite was activated by acid leaching and then modified by trimethylchlorosilane (CTMS) and triethylchlorosilane (CTES). The modified materials were characterized by FTIR, BET, SEM and TG. Experimental results indicated that the surface area of the modified acid vermiculite (361.0 m2 x g(-1)) was much larger than that of the intercalated organovermiculite (6.0 m2 x g(-1)), moreover, the organic groups were grafted onto the surface covalently. Diethyl phthalate (DEP), a typical hydrophobic micro-organic pollutant, was used to test the adsorption capacity of different adsorbents. The adsorption amounts of DEP were 63.7, 51.2 and 15.7 mg x g(-1) for CTES, CTMS and intercalated organovermiculite in this study, respectively. The high organic affinity of modified acid vermiculite was due to both the bigger surface area and the homogeneous organic loading. The adsorption kinetics was found to follow the pseudosecond-order model. The isotherms exhibited linear characteristics and could be described by Henry and Freundlich equations, indicating that the partition process is the main control mechanism of the removal of DEP.

  3. Halogens on Semiconductor Surfaces: Adsorption, Oxidation, and Etching.

    NASA Astrophysics Data System (ADS)

    Stepniak, Frank

    This dissertation presents studies of Si, GaAs, and InP surfaces following exposure to the halogens Cl _2 and Br_2. Synchrotron radiation photoemission is used to investigate the oxidation states of Si near the Si/SiO_2 interface as a function of Cl_2 exposure. Oxidation of highly ordered surfaces shows no dependence of the oxidation state concentration on Cl_2 inclusion in the gas mixture. For less-than-ideal Si surfaces, oxidation with O_2 -only results in a broader transition region, and presumably, inferior electrical properties. The addition of Cl_2 in the oxidizing gas reduced the concentration of intermediate oxides by a factor of two for these disordered starting Si surfaces. A new feature is also measured from Cl-Si bonds that we associate with passivation of Si defects at the oxide interface. The adsorption and reactivity of Br_2 and Cl_2 on GaAs(110) and InP(110) was studied in the temperature range of 25 K < T < 625 K with photoemission spectroscopy and scanning tunneling microscopy. Initial halogen adsorption was dissociative at all temperatures and we find that a simple model where the halogen atoms bond to a single Ga or As surface site can not account for the complex surface chemistry and morphology. Thermally-activated etching was observed after warming a surface with chemisorbed Br or Cl. Etching resulted from the formation and eventual temperature dependent desorption of the trihalides of Ga and As. For halogen exposures where T < 650 K, monohalide-like surface bonding persist during the etching process and the etched surface is rough. For T > 700 K, the surface is essentially free of halogen and etching occurs in a nearly layer-by-layer fashion.

  4. Zinc isotope fractionation during surface adsorption by bacteria

    NASA Astrophysics Data System (ADS)

    Kafantaris, F. A.; Borrok, D. M.

    2011-12-01

    The cycling and transport of zinc (Zn) in natural waters is partly controlled by its adsorption and uptake by bacterial communities. These reactions are reflected in changes in the ratios of stable Zn isotopes; however, the magnitudes and directions of these changes are largely unconstrained. In the current work, we attempt to define Zn isotope fractionation factors for bacteria-Zn interactions by performing adsorption experiments with representative Gram-positive (Bacillus subtilis) and Gram-negative (Pseudomonas mendocina) bacteria. Experiments included, (1) pH-dependent adsorption using differing bacteria:Zn ratios, (2) Zn loading at constant pH, and (3) kinetics and reversibility experiments. Results indicate that Zn adsorption is fully reversible for both bacterial species. Moreover, under the same experimental conditions both bacterial species adsorbed Zn to similar extents. Initial isotopic analysis (using a Nu Instruments MC-ICP-MS) demonstrates that, as the extent of adsorption increases, the heavier Zn isotopes are preferentially incorporated as bacterial-surface complexes. Under conditions of low bacteria:Zn ratio, the Δ66Znbacteria-solution was about 0.3% for both bacterial species. This separation factor is similar to that found in other studies involving the complexation of Zn with biologic or organic components. For example, the complexation of Zn with Purified Humic Acid (PHA) resulted in a Δ66ZnPHA-solution of +0.24% [1], and sorption of Zn onto two separate diatom species resulted in Δ66Znsolid-solution of +0.43% and +0.27%, respectively [2]. These results suggest that Zn complexation with functional groups common to bacteria and natural organic matter may be a process that universally incorporates the heavier Zn isotopes. Our current work is focused on quantifying Zn isotope fractionation during metabolic incorporation by separating this effect from surface adsorption reactions. [1] Jouvin et al., (2009) Environ. Sci. Technol., 43(15) 5747

  5. Surface complexation modeling of Cu(II) adsorption on mixtures of hydrous ferric oxide and kaolinite

    PubMed Central

    Lund, Tracy J; Koretsky, Carla M; Landry, Christopher J; Schaller, Melinda S; Das, Soumya

    2008-01-01

    Background The application of surface complexation models (SCMs) to natural sediments and soils is hindered by a lack of consistent models and data for large suites of metals and minerals of interest. Furthermore, the surface complexation approach has mostly been developed and tested for single solid systems. Few studies have extended the SCM approach to systems containing multiple solids. Results Cu adsorption was measured on pure hydrous ferric oxide (HFO), pure kaolinite (from two sources) and in systems containing mixtures of HFO and kaolinite over a wide range of pH, ionic strength, sorbate/sorbent ratios and, for the mixed solid systems, using a range of kaolinite/HFO ratios. Cu adsorption data measured for the HFO and kaolinite systems was used to derive diffuse layer surface complexation models (DLMs) describing Cu adsorption. Cu adsorption on HFO is reasonably well described using a 1-site or 2-site DLM. Adsorption of Cu on kaolinite could be described using a simple 1-site DLM with formation of a monodentate Cu complex on a variable charge surface site. However, for consistency with models derived for weaker sorbing cations, a 2-site DLM with a variable charge and a permanent charge site was also developed. Conclusion Component additivity predictions of speciation in mixed mineral systems based on DLM parameters derived for the pure mineral systems were in good agreement with measured data. Discrepancies between the model predictions and measured data were similar to those observed for the calibrated pure mineral systems. The results suggest that quantifying specific interactions between HFO and kaolinite in speciation models may not be necessary. However, before the component additivity approach can be applied to natural sediments and soils, the effects of aging must be further studied and methods must be developed to estimate reactive surface areas of solid constituents in natural samples. PMID:18783619

  6. Effect of Dopants on the Adsorption of Carbon Dioxide on Ceria Surfaces

    SciTech Connect

    Li, Meijun; Tumuluri, Uma; Wu, Zili; Dai, Sheng

    2015-09-25

    Here, high-surface-area nanosized CeO2 and M-doped CeO2 (M=Cu, La, Zr, and Mg) prepared by a surfactant-templated method were tested for CO2 adsorption. Cu, La, and Zr are doped into the lattice of CeO2, whereas Mg is dispersed on the CeO2 surface. The doping of Cu and La into CeO2 leads to an increase of the CO2 adsorption capacity, whereas the doping of Zr has little or no effect. The addition of Mg causes a decrease of the CO2 adsorption capacity at a low Mg content and a gradual increase at a higher content. The CO2 adsorption capacity follows the sequence Cu-CeO2>La-CeO2>Zr-CeO2≈CeO2>Mg-CeO2 at low dopant contents, in line with the relative amount of defect sites in the samples. It is the defect sites on the surface, not in the bulk of CeO2, modified by the dopants that play the vital role in CO2 chemisorption. Lastly, the role of surface oxygen vacancies is further supported by an in situ IR spectroscopic study of the surface chemistry during CO2 adsorption on the doped CeO2.

  7. The effect of the nanosize on surface properties of NiO nanoparticles for the adsorption of Quinolin-65.

    PubMed

    Marei, Nedal N; Nassar, Nashaat N; Vitale, Gerardo

    2016-03-01

    Using Quinolin-65 (Q-65) as a model-adsorbing compound for polar heavy hydrocarbons, the nanosize effect of NiO nanoparticles on the adsorption of Q-65 was investigated. Different-sized NiO nanoparticles with sizes between 5 and 80 nm were prepared by the controlled thermal dehydroxylation of Ni(OH)2. The properties of the nanoparticles were characterized using XRD, BET, FTIR, HRTEM and TGA. The effects of the nanosize on the textural properties, the shape and the morphology were studied. The adsorption of Q-65 molecules onto different-sized nanoparticles was tested in toluene-based solutions. On a normalized surface area basis, the number of Q-65 molecules adsorbed per nm(2) of the NiO surface was the highest for NiO nanoparticles of size 80 nm, while that for 5 nm sized NiO nanoparticles was the lowest. Excitingly, the adsorption capacity of other NiO sizes varied from loading suggesting different adsorption behavior, which exhibits the significance of textural properties during the adsorption of Q-65. Computational modeling of the interaction between the Q-65 molecule and the NiO nanoparticle surface was carried out to get more understanding of its adsorption behavior. A number of factors contributing to the enhanced adsorption capacity of nanoscale NiO were determined. These include surface reactivity, topology, morphology and textural properties.

  8. Structural phases of adsorption for flexible polymers on nanocylinder surfaces.

    PubMed

    Gross, Jonathan; Vogel, Thomas; Bachmann, Michael

    2015-11-11

    By means of generalized-ensemble Monte Carlo simulations, we investigate the thermodynamic behavior of a flexible, elastic polymer model in the presence of an attractive nanocylinder. We systematically identify the structural phases that are formed by competing monomer-monomer and monomer-substrate interactions. The influence of the relative surface attraction strength on the structural phases in the hyperphase diagram, parameterized by cylinder radius and temperature, is discussed as well. In the limiting case of the infinitely large cylinder radius, our results coincide with previous outcomes of studies of polymer adsorption on planar substrates.

  9. Density functional theory study of mercury adsorption on metal surfaces

    SciTech Connect

    Steckel, J.A.

    2008-01-01

    Density functional theory _DFT_ calculations are used to characterize the interaction of mercury with copper, nickel, palladium, platinum, silver, and gold surfaces. Mercury binds relatively strongly to all the metal surfaces studied, with binding energies up to _1 eV for Pt and Pd. DFT calculations underestimate the energy of adsorption with respect to available experimental data. Plane-wave DFT results using the local density approximation and the Perdew-Wang 1991 and Perdew-Burke-Ernzerhof parametrizations of the generalized gradient approximation indicate that binding of mercury at hollow sites is preferred over binding at top orbridge sites. The interaction with mercury in order of increasing reactivity over the six metals studied is Ag_Au_Cu_Ni_Pt_Pd. Binding is stronger on the _001_ faces of the metal surfaces, where mercury issituated in fourfold hollow sites as opposed to the threefold hollow sites on _111_ faces. In general, mercury adsorption leads to decreases in the work function; adsorbate-induced work function changes are particularly dramatic on Pt.

  10. Density functional theory study of mercury adsorption on metal surfaces

    SciTech Connect

    Steckel, Janice A.

    2008-03-10

    Density functional theory (DFT) calculations are used to characterize the interaction of mercury with copper, nickel, palladium, platinum, silver, and gold surfaces. Mercury binds relatively strongly to all the metal surfaces studied, with binding energies up to ~1eV for Pt and Pd. DFT calculations underestimate the energy of adsorption with respect to available experimental data. Plane-wave DFT results using the local density approximation and the Perdew-Wang 1991 and Perdew-Burke-Ernzerhof parametrizations of the generalized gradient approximation indicate that binding of mercury at hollow sites is preferred over binding at top or bridge sites. The interaction with mercury in order of increasing reactivity over the six metals studied is Agsurfaces, where mercury is situated in fourfold hollow sites as opposed to the threefold hollow sites on (111) faces. Finally, in general, mercury adsorption leads to decreases in the work function; adsorbate-induced work function changes are particularly dramatic on Pt.

  11. Adsorption of boron on a Mo(110) surface

    NASA Astrophysics Data System (ADS)

    Magkoev, Tamerlan T.; Turiev, Anatolij M.; Tsidaeva, Natal'ja I.; Panteleev, Dmitrij G.; Vladimirov, Georgij G.; Rump, Gennadij A.

    2008-12-01

    Adsorption of boron atoms in submonolayer to multilayer coverage on atomically clean Mo(110) surfaces has been studied by Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS) and work function measurements. According to Auger results there is a layer-by-layer growth mode of the film on the substrate held at room temperature. In the submonolayer region the work function gradually increases with boron coverage until a saturation value of 5.8 eV is achieved after completion of the first monoatomic layer. The B-Mo(110) adsorbate system formed on the substrate at room temperature is not stable, dominated by a strong tendency of the boron atoms to diffuse into the bulk of the crystal. The latter is manifested by dramatic Mo(110) surface plasmon mode transformation upon boron adsorption, presumably as a result of penetration of boron atoms into the topmost substrate layer even at T = 300 K. Slight annealing up to 450 K facilitates this trend, leading to total dissolution of deposited boron atoms in the bulk of the crystal under further annealing, restoring the initial state of the Mo(110) surface after achieving a temperature of approximately 2000 K.

  12. Surface Complexation Modeling of U(VI) Adsorption onto Savannah River Site Sediments

    NASA Astrophysics Data System (ADS)

    Dong, W.; Wan, J.; Tokunaga, T. K.; Denham, M.; Davis, J.; Hubbard, S. S.

    2011-12-01

    The Savannah River Site (SRS) was a U.S. Department of Energy facility for plutonium production during the Cold War. Waste plumes containing low-level radioactivity and acidic waste solutions were discharged to a series of unlined seepage basins in the F-Area of the SRS from 1955 to 1988. Although the site has undergone many years of active remediation, the groundwater remains acidic, and the concentrations of U and other radionuclides are still significantly higher than their Maximum Contaminant Levels (MCLs). The objective of this effort is to understand and predict U(VI) mobility in acidic waste plumes through developing surface complexation models (SCMs). Laboratory batch experiments were conducted to evaluate U adsorption behavior over the pH range of 3.0 to 9.5. Ten sorbent samples were selected including six contaminated sediment samples from three boreholes drilled within the plume and along the groundwater flow direction, two uncontaminated (pristine) sediment samples from a borehole outside of the plume, and two reference minerals, goethite and kaolinite (identified as the dominant minerals in the clay size fraction of the F-Area sediments). The results show that goethite and kaolinite largely control U partitioning behavior. In comparison with the pristine sediment, U(VI) adsorption onto contaminated sediments exhibits adsorption edges shifted toward lower pH by about 1.0 unit (e.g., from pH≈4.5 to pH≈3.5). We developed a SCMs based component additivity (CA) approach, which can successfully predict U(VI) adsorption onto uncontaminated SRS sediments. However, application of the same SCMs based CA approach to contaminated sediments resulted in underestimates of U(VI) adsorption at acidic pH conditions. The model sensitivity analyses indicate that both goethite and kaolinite surfaces co-contributed to U(VI) adsorption under acidic pH conditions. In particular, the exchange sites of clay minerals might play an important role in adsorption of U(VI) at p

  13. Kinetics and thermodynamics studies on the BMP-2 adsorption onto hydroxyapatite surface with different multi-morphological features.

    PubMed

    Lu, Zhiwei; Huangfu, Changxin; Wang, Yanying; Ge, Hongwei; Yao, Yao; Zou, Ping; Wang, Guangtu; He, Hua; Rao, Hanbing

    2015-01-01

    The effect of the surface topography on protein adsorption process is of great significance for designing hydroxyapatite (HA) ceramic material surfaces. In this work, three different topographies of HA materials HA-sheet, HA-rod, and HA-whisker were synthesized and testified by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Brunauer-Emmett-Teller (BET) and a field emission scanning electron microscopy (FE-SEM). We have systematically investigated the adsorption kinetics and thermodynamics of bone morphogenetic proteins (BMP-2) on the three different topography surfaces of HA, respectively. The results showed that the maximum adsorption capacities of HA-sheet, HA-rod and HA-whisker were (219.96 ± 10.18), (247.13 ± 12.35), and (354.67 ± 17.73) μg · g(-1), respectively. Kinetic parameters, rate constants, equilibrium adsorption capacities and related correlation coefficients, for each kinetic model were calculated as well as discussed. It demonstrated that the adsorption of BMP-2 onto HA could be described by the pseudo second-order equation. Adsorption of BMP-2 onto HA followed the Langmuir isotherm. It confirmed that compared with other samples HA-whisker had more adsorption sites for its high specific surface area which could provide more opportunities for protein molecules. The adsorption processes were endothermic (ΔH > 0), spontaneous (ΔG < 0) and entropy increasing (ΔS > 0). A possible adsorption mechanism has been proposed. In addition, the BMP-2 could be adsorbed to the surface which existed slight conformational changes by FT-IR. PMID:25953565

  14. Study of DNA adsorption on mica surfaces using a surface force apparatus

    NASA Astrophysics Data System (ADS)

    Kan, Yajing; Tan, Qiyan; Wu, Gensheng; Si, Wei; Chen, Yunfei

    2015-02-01

    We report our studies on the adsorption properties of double-stranded DNA molecules on mica surfaces in a confined environment using a surface force apparatus. Specifically, we studied the influence of cation species and concentrations on DNA adsorption properties. Our results indicated that divalent cations (Mg2+ and Co2+) preferred to form uniform and moderately dense DNA layers on a mica substrate. By measuring the interactions between DNA-coated mica and bare mica in an aqueous solution, obvious adhesion was observed in a cobalt chloride solution, possibly due to the ion-correlation attraction between negatively charged DNA and the mica surface. Furthermore, the interaction differences that were observed with MgCl2 and CoCl2 solutions reveal that the specific adsorption behaviors of DNA molecules on a mica substrate were mediated by these two salts. Our results are helpful to elucidate the dynamics of DNA binding on a solid substrate.

  15. Study of DNA adsorption on mica surfaces using a surface force apparatus.

    PubMed

    Kan, Yajing; Tan, Qiyan; Wu, Gensheng; Si, Wei; Chen, Yunfei

    2015-02-13

    We report our studies on the adsorption properties of double-stranded DNA molecules on mica surfaces in a confined environment using a surface force apparatus. Specifically, we studied the influence of cation species and concentrations on DNA adsorption properties. Our results indicated that divalent cations (Mg(2+) and Co(2+)) preferred to form uniform and moderately dense DNA layers on a mica substrate. By measuring the interactions between DNA-coated mica and bare mica in an aqueous solution, obvious adhesion was observed in a cobalt chloride solution, possibly due to the ion-correlation attraction between negatively charged DNA and the mica surface. Furthermore, the interaction differences that were observed with MgCl2 and CoCl2 solutions reveal that the specific adsorption behaviors of DNA molecules on a mica substrate were mediated by these two salts. Our results are helpful to elucidate the dynamics of DNA binding on a solid substrate.

  16. An example in surface area.

    PubMed

    Goffman, C

    1969-05-01

    For length and area, a central fact is that the value of the length of a curve or the area of a surface, as given by the Lebesgue theory, is at least as great as that given by the classical formula, whenever the latter has meaning. This is now found not to be valid in higher dimensions. We give an example of a continuous mapping of the unit cube into itself for which the value given by the formula exceeds the three-dimensional Lebesgue area of the corresponding suface.

  17. Adsorption of annealed branched polymers on curved surfaces.

    PubMed

    Wagner, Jef; Erdemci-Tandogan, Gonca; Zandi, Roya

    2015-12-16

    The behavior of annealed branched polymers near adsorbing surfaces plays a fundamental role in many biological and industrial processes. Most importantly single stranded RNA in solution tends to fold up and self-bind to form a highly branched structure. Using a mean field theory, we both perturbatively and numerically examine the adsorption of branched polymers on surfaces of several different geometries in a good solvent. Independent of the geometry of the wall, we observe that as branching density increases, surface tension decreases. However, we find a coupling between the branching density and curvature in that a further lowering of surface tension occurs when the wall curves towards the polymer, but the amount of lowering of surface tension decreases when the wall curves away from the polymer. We find that for branched polymers confined into spherical cavities, most of branch-points are located in the vicinity of the interior wall and the surface tension is minimized for a critical cavity radius. For branch polymers next to sinusoidal surfaces, we find that branch-points accumulate at the valleys while end-points on the peaks.

  18. Adsorption study of antibiotics on silver nanoparticle surfaces by surface-enhanced Raman scattering spectroscopy

    NASA Astrophysics Data System (ADS)

    Filgueiras, Aline Luciano; Paschoal, Diego; Dos Santos, Hélio F.; Sant'Ana, Antonio C.

    2015-02-01

    In this work the adsorption of the antibiotics levofloxacin (LV), tetracycline (TC) and benzylpenicillin (BP) on the surface of silver nanoparticles (AgNP) have been investigated through both surface-enhanced Raman scattering (SERS) and UV-VIS-NIR spectroscopies. The SERS spectra were obtained using 1064 nm exciting radiation. Theoretical models for the antibiotic molecules were obtained from DFT calculations, and used in the vibrational assignment. The adsorption geometries were proposed based on the changes in the spectral patterns. The LV compound adsorbs through carboxylate group, TC compound interacts with silver atoms through carbonyl from intermediate ring, and BP compound adsorbs by carbonyl moieties from carboxylate and acyclic amide.

  19. Protonation of water clusters induced by hydroperoxyl radical surface adsorption.

    PubMed

    Torrent-Sucarrat, Miquel; Ruiz-Lopez, Manuel F; Martins-Costa, Marilia; Francisco, Joseph S; Anglada, Josep M

    2011-04-26

    We have investigated the HO(2) adsorption and acid dissociation process on the surface of (H(2)O)(20) and (H(2)O)(21) clusters by using quantum-chemistry calculations. Our results show that the radical forms a stable hydrogen-bond complex on the cluster. The HO(2) acid dissociation is more favorable in the case of the (H(2)O)(21) cluster, for which the inner water molecule plays a crucial role. In fact, acid dissociation of HO(2) is found to occur in two steps. The first step involves H(2) O autoionization in the cluster, and the second one involves the proton transfer from the HO(2) radical to the hydroxide anion. The presence of the HO(2) radicals on the surface of the cluster facilitates water autoionization in the cluster. PMID:21433120

  20. Rainfastness and adsorption of herbicides on hard surfaces.

    PubMed

    Spanoghe, Pieter; Claeys, Johan; Pinoy, Luc; Steurbaut, Walter

    2005-08-01

    Herbicides are still used to control weeds on hard surfaces, including municipal, private and industrial sites. Used under unfavourable conditions, especially when rain occurs shortly after application, herbicides may run off to surface waters. Such losses of herbicides from hard surfaces are estimated to be much higher than for herbicides used in arable fields. In this study, three kinds of hard surface were evaluated: asphalt, concrete surface and gravel (fine and coarse). Three herbicides were applied: glyphosate, diuron and diflufenican. Adsorption isotherms of diuron and diflufenican to the three surfaces were determined. At different times after treatment with the herbicides, rainfall was simulated by use of a rain-droplet spray nozzle, and the run-off was collected for analysis. After this run-off event, the materials were immersed in water to measure desorption which, together with the compound in the run-off, gave a measure of the dislodgable residues. The apolar herbicides diuron and especially diflufenican adsorbed strongly to asphalt. The polar herbicide glyphosate lost 75% in run-off from asphalt but was adsorbed strongly to soil and concrete pavement.

  1. Adsorption of V on a Hematite (0001) Surface and its Oxidation: Submonolayer Coverage

    SciTech Connect

    Jin, J.; Ma, X.; Kim, C.-Y.; Ellis, D.E.; Bedzyk, M.J.

    2008-10-06

    The adsorption of submonolayer V on an idealized model hematite (0 0 0 1) surface and subsequent oxidation under atomic O adsorption are studied by density functional theory. The preferred adsorption sites, adsorption energy and configuration changes due to V and O adsorption are investigated. It is found that in most cases V forms threefold bonds with surface O atoms, inducing a large geometry change at the hematite surface and near surface region and a bond stretch between surface Fe and O. The adsorption energy is mainly decided by interplay between adsorbed metal-surface oxygen bonding and adsorbed metal - subsurface metal interaction. The relative energy of subsequent O adsorption and geometry depends on the reformed V/hematite structure. Electronic properties such as projected densities of states and chemical state change upon V adsorption are studied through both periodic slab and embedded cluster localized orbital calculations; both strong vanadium-oxygen and vanadium-iron interactions are found. While V generally donates electrons to a hematite surface, causing nearby Fe to be partially reduced, the Fe and V oxidization state depends very much on the coverage and detailed adsorption configuration. When the V/hematite system is exposed to atomic O, V is further oxidized and surface/near surface Fe is re-oxidized. Our theoretical results are compared with X-ray surface standing wave and X-ray photoelectron spectroscopic measurements. The influence of d-electron correlation on the predicted structures is briefly discussed, making use of the DFT + U scheme.

  2. Specific surface area as a maturity index of lunar fines

    NASA Technical Reports Server (NTRS)

    Gammage, R. B.; Holmes, H. F.

    1975-01-01

    Mature surface fines have an equilibrium specific surface area of about 0.6 sq m/g the equivalent mean particle size being about 3 microns. The adsorption behavior of inert gases (reversible isotherms) indicates that the particles are also nonporous in the size range of pores from 10 to 3000 A. Apparently, in mature soils there is a balance in the forces which cause fining, attrition, pore filling, and growth of lunar dust grains. Immature, lightly irradiated soils usually have coarser grains which reduce in size as aging proceeds. The specific surface area, determined by nitrogen or krypton sorption at 77 K, is a valuable index of soil maturity.

  3. Measurements of BET Surface Area on Silica Nanosprings

    SciTech Connect

    Karkamkar, Abhijeet J.

    2008-09-01

    Nitrogen adsorption desorption isotherm for Silica nanosprings (GoNano2) samples deposited on substrate. The isotherm was obtained at 77 K using liquid N2 bath. The area of the substrate is 16 cm2. The amount of the sample is 0.44 mg/cm2. Amount of silica nanosprings= 7.04 mg. There is no indication of substantial micro or mesoporosity in the sample based on the nature of the isotherm. Eleven point BET surface area was measured. Nine points plotted. Goodness if fit R= 0.9992. BET surface area for silica nanosprings= 262 cm2/g

  4. Alteration of urinary macromolecules by adsorption on surfaces, probably an important factor in urolithiasis.

    PubMed

    Baumann, J M; Affolter, B; von Arx, U; Noël, M

    2013-11-01

    To get information on the consequences of adsorption of urinary macromolecules (UMs) on crystals, Ca phosphate (CaP) precipitation was performed in urine of 15 stone patients and 15 controls. In solutions of dissolved precipitates (DPU), Ca oxalate (CaOx) crystallization and aggregation (AGN) of latex beads were spectrophotometrically studied and compared to results obtained in urine and in UMs isolated by hemofilter dialysis (HD). Tests were repeated with a 20 μg/mL albumin solution (AS). Inhibition of CaOx growth and AGN was significantly reduced in DPU as well as in HD. Furthermore, DPU and HD showed an AGN of latex beads which in patients was more pronounced than in controls. Identical effects observed in DPU and HD can be explained by temporary high concentrations of UMs by adsorption on surfaces favoring self AGN. Temporary adsorption of AS on CaP produced polymers of a limited size, significantly reduced the inhibition of CaOx AGN and accelerated latex AGN. In DPU, AGN of latex beads occurred despite a surface potential of -37 mV, which within short distances produces areas of massive electrostatic repulsion and normally inhibits AGN. Such areas might be bridged by self-aggregated UMs. The retardation of CaOx AGN measured in DPU could be decisive whether during crystalluria crystals are washed out from the kidney by diuresis or are attached to kidney calcifications or pre-existing stones.

  5. Bacterial locomotion, adsorption and growth over chemically patterned surfaces

    NASA Astrophysics Data System (ADS)

    Jalali, Maryam; Molaei, Mehdi; Sheng, Jian

    2013-11-01

    Complex dynamic interactions between bacteria and chemically patched interface that mimics the heterogeneous energy landscape of a real-life interfacial environment are studied in the paper. We explore effects of these spatially varying chemical patches on bacterial locomotion, adsorption, biofilm formation and the film growth rate. Using micro-fabrication and soft-lithography, we have fabricated PDMS microfluidic channels with a solid substrate covered by micro-scale chemical patches. Arrays of 2D geometries of characteristic scales varying from 10 to 50 μm are transferred onto a glass substrate by soft-lithography. The substrate is functionalized to generate alternating hydrophobic and hydrophilic regions and bonded with the channel. The 3D swimming characteristics near these surfaces, such as swimming velocity, linear and angular dispersions, are measured in-situ using 3D digital holographic microscopy. The observations are used to examine the mechanisms involved in adsorption and desorption of swimming bacteria onto the substrate. Long-term experiments are conducted to quantify the growth rate and structures of colony. A correlation between various length scales of the substrate and bacteria motility are observed.

  6. Determination of the amount of physical adsorption of water vapour on platinum-iridium surfaces

    NASA Astrophysics Data System (ADS)

    Mizushima, S.; Ueda, K.; Ooiwa, A.; Fujii, K.

    2015-08-01

    This paper presents the measurement of the physical adsorption of water vapour on platinum-iridium surfaces using a vacuum mass comparator. This value is of importance for redefining the kilogram, which will be realized under vacuum in the near future. Mirror-polished artefacts, consisting of a reference artefact and a test artefact, were manufactured for this experiment. The surface area difference between the reference and test artefacts was 226.2 cm2. This surface area difference was approximately 3.2 times the geometric surface area of the prototype of the kilogram made of platinum-iridium (71.7 cm2). The measurement results indicate that the amount of physical adsorption at a relative humidity of 50% is 0.0129 μg cm{{-}2} , with a standard uncertainty of 0.0016 μg cm{{-}2} . This value is 0.03 to 0.16 times that observed in other studies.

  7. Adsorption of air pollutants on the grain surface of Japanese cedar pollen

    NASA Astrophysics Data System (ADS)

    Okuyama, Yuji; Matsumoto, Kiyoshi; Okochi, Hiroshi; Igawa, Manabu

    The contaminants adsorbed on the surface of pollen may affect the development of hay fever, because the patients of the fever are larger in areas with much air pollution than in nonpolluted areas and the fine particles and gases are susceptible to deposit on the nasal cavities and eyes by their transfer on the pollen. Since Japanese cedar pollinosis is the most common hay fever in Japan, we analyzed the air pollutants adsorbed on the surface of dispersed Japanese cedar pollen in the urban and mountainous districts. Fine anthropogenic particles were significantly adsorbed and many elements were concentrated on the surface of the pollen in the urban site of Yokohama, while they were not concentrated on the surface of the pollen collected at a mountainous site. The acid gases are also adsorbed and acidify the surface, and their amounts increase with their concentrations in the ambient air. The high adsorption of nitric acid on the pollen determined by an exposure experiment of nitric acid gas suggests that nitric acid is dissolved in the inner part of the pollen. The adsorption amounts of the gases on the pollen were especially greater than those on other natural particles, humic acid and yellow sand.

  8. Response mechanism for surface acoustic wave gas sensors based on surface-adsorption.

    PubMed

    Liu, Jiansheng; Lu, Yanyan

    2014-04-16

    A theoretical model is established to describe the response mechanism of surface acoustic wave (SAW) gas sensors based on physical adsorption on the detector surface. Wohljent's method is utilized to describe the relationship of sensor output (frequency shift of SAW oscillator) and the mass loaded on the detector surface. The Brunauer-Emmett-Teller (BET) formula and its improved form are introduced to depict the adsorption behavior of gas on the detector surface. By combining the two methods, we obtain a theoretical model for the response mechanism of SAW gas sensors. By using a commercial SAW gas chromatography (GC) analyzer, an experiment is performed to measure the frequency shifts caused by different concentration of dimethyl methylphosphonate (DMMP). The parameters in the model are given by fitting the experimental results and the theoretical curve agrees well with the experimental data.

  9. Humic acid adsorption and surface charge effects on schwertmannite and goethite in acid sulphate waters.

    PubMed

    Kumpulainen, Sirpa; von der Kammer, Frank; Hofmann, Thilo

    2008-04-01

    In acid conditions, as in acid mine drainage waters, iron oxide particles are positively charged, attracting negatively charged organic particles present in surrounding natural waters. Schwertmannite (Fe8O8(OH)6SO4) and goethite (alpha-FeOOH) are the most typical iron oxide minerals found in mine effluents. We studied schwertmannite formation in the presence of humic acid. Further, surface charge and adsorption of humic acid on synthetic schwertmannite and goethite surfaces in pH 2-9 and in humic acid concentrations of 0.1-100 mg/L C were examined. Schwertmannite did precipitate despite the presence of humic acid, although it contained more sulphate and had higher specific surface area than ordinary schwertmannite. Specific surface area weighted results showed that schwertmannite and goethite had similar humic acid adsorption capacities. Sulphate was released from schwertmannite surfaces with increasing pH, resulting in an increase in specific surface area. Presence of sulphate in solution decreased the surface charge of schwertmannite and goethite similarly, causing coagulation. In acid conditions (pH 2-3.5), according to the zeta potential, schwertmannite is expected to coagulate even in the presence of high concentrations of humic acid (< or = 100 mg/L C). However, at high humic acid concentrations (10-100 mg/L C) with moderate acid conditions (pH>3.5), both schwertmannite and goethite surfaces are strongly negatively charged (zeta potential < -30 mV) thus posing a risk for colloid stabilization and colloidal transport. PMID:18221768

  10. Modeling adsorption and reactions of organic molecules at metal surfaces.

    PubMed

    Liu, Wei; Tkatchenko, Alexandre; Scheffler, Matthias

    2014-11-18

    CONSPECTUS: The understanding of adsorption and reactions of (large) organic molecules at metal surfaces plays an increasingly important role in modern surface science and technology. Such hybrid inorganic/organic systems (HIOS) are relevant for many applications in catalysis, light-emitting diodes, single-molecule junctions, molecular sensors and switches, and photovoltaics. Obviously, the predictive modeling and understanding of the structure and stability of such hybrid systems is an essential prerequisite for tuning their electronic properties and functions. At present, density-functional theory (DFT) is the most promising approach to study the structure, stability, and electronic properties of complex systems, because it can be applied to both molecules and solids comprising thousands of atoms. However, state-of-the-art approximations to DFT do not provide a consistent and reliable description for HIOS, which is largely due to two issues: (i) the self-interaction of the electrons with themselves arising from the Hartree term of the total energy that is not fully compensated in approximate exchange-correlation functionals, and (ii) the lack of long-range part of the ubiquitous van der Waals (vdW) interactions. The self-interaction errors sometimes lead to incorrect description of charge transfer and electronic level alignment in HIOS, although for molecules adsorbed on metals these effects will often cancel out in total energy differences. Regarding vdW interactions, several promising vdW-inclusive DFT-based methods have been recently demonstrated to yield remarkable accuracy for intermolecular interactions in the gas phase. However, the majority of these approaches neglect the nonlocal collective electron response in the vdW energy tail, an effect that is particularly strong in condensed phases and at interfaces between different materials. Here we show that the recently developed DFT+vdW(surf) method that accurately accounts for the collective electronic

  11. Modeling adsorption and reactions of organic molecules at metal surfaces.

    PubMed

    Liu, Wei; Tkatchenko, Alexandre; Scheffler, Matthias

    2014-11-18

    CONSPECTUS: The understanding of adsorption and reactions of (large) organic molecules at metal surfaces plays an increasingly important role in modern surface science and technology. Such hybrid inorganic/organic systems (HIOS) are relevant for many applications in catalysis, light-emitting diodes, single-molecule junctions, molecular sensors and switches, and photovoltaics. Obviously, the predictive modeling and understanding of the structure and stability of such hybrid systems is an essential prerequisite for tuning their electronic properties and functions. At present, density-functional theory (DFT) is the most promising approach to study the structure, stability, and electronic properties of complex systems, because it can be applied to both molecules and solids comprising thousands of atoms. However, state-of-the-art approximations to DFT do not provide a consistent and reliable description for HIOS, which is largely due to two issues: (i) the self-interaction of the electrons with themselves arising from the Hartree term of the total energy that is not fully compensated in approximate exchange-correlation functionals, and (ii) the lack of long-range part of the ubiquitous van der Waals (vdW) interactions. The self-interaction errors sometimes lead to incorrect description of charge transfer and electronic level alignment in HIOS, although for molecules adsorbed on metals these effects will often cancel out in total energy differences. Regarding vdW interactions, several promising vdW-inclusive DFT-based methods have been recently demonstrated to yield remarkable accuracy for intermolecular interactions in the gas phase. However, the majority of these approaches neglect the nonlocal collective electron response in the vdW energy tail, an effect that is particularly strong in condensed phases and at interfaces between different materials. Here we show that the recently developed DFT+vdW(surf) method that accurately accounts for the collective electronic

  12. Modeling Adsorption and Reactions of Organic Molecules at Metal Surfaces

    PubMed Central

    2014-01-01

    Conspectus The understanding of adsorption and reactions of (large) organic molecules at metal surfaces plays an increasingly important role in modern surface science and technology. Such hybrid inorganic/organic systems (HIOS) are relevant for many applications in catalysis, light-emitting diodes, single-molecule junctions, molecular sensors and switches, and photovoltaics. Obviously, the predictive modeling and understanding of the structure and stability of such hybrid systems is an essential prerequisite for tuning their electronic properties and functions. At present, density-functional theory (DFT) is the most promising approach to study the structure, stability, and electronic properties of complex systems, because it can be applied to both molecules and solids comprising thousands of atoms. However, state-of-the-art approximations to DFT do not provide a consistent and reliable description for HIOS, which is largely due to two issues: (i) the self-interaction of the electrons with themselves arising from the Hartree term of the total energy that is not fully compensated in approximate exchange-correlation functionals, and (ii) the lack of long-range part of the ubiquitous van der Waals (vdW) interactions. The self-interaction errors sometimes lead to incorrect description of charge transfer and electronic level alignment in HIOS, although for molecules adsorbed on metals these effects will often cancel out in total energy differences. Regarding vdW interactions, several promising vdW-inclusive DFT-based methods have been recently demonstrated to yield remarkable accuracy for intermolecular interactions in the gas phase. However, the majority of these approaches neglect the nonlocal collective electron response in the vdW energy tail, an effect that is particularly strong in condensed phases and at interfaces between different materials. Here we show that the recently developed DFT+vdWsurf method that accurately accounts for the collective electronic

  13. Molecular dynamics simulation study on controlling the adsorption behavior of polyethylene by fine tuning the surface nanodecoration of graphite.

    PubMed

    Wang, Xiao-Lin; Lu, Zhong-Yuan; Li, Ze-Sheng; Sun, Chia-Chung

    2007-01-16

    Molecular dynamics simulations are applied to study the adsorption of polyethylene with different chain lengths on patterned graphite surfaces that contain nanoscale protrusions. The influence of the nanostructure on the strong attractive interaction inherently in the hydrophobic polyethylene and hydrophobic graphite system is investigated by modifying the top surface area and the height and the shape of the protrusions. The results are analyzed in terms of the chain configuration, the adsorption energy, the global orientational order parameter, and the normalized surface-chain contacting pair number in the first adsorption layer. When the size of the protrusion increases, the adsorption energy, the order parameter, and the normalized surface-chain contacting pair number decrease at a fixed chain length. When the size of the protrusion is fixed, the average adsorption energy per monomer and the order parameter decrease with increasing chain length because of the stronger intramolecular interactions between the monomers. Changing the protrusion shape in a suitable way will effectively reduce the strong surface-chain interaction.

  14. Selective adsorption of benzoic acid species on patterned OH/Si(100) surface

    SciTech Connect

    Ihm, Kyuwook; Han, Jin Hee; Kim, Bongsoo; Chung, Sukmin; Hwang, Chan-Cuk; Kang, Tai-Hee; Kim, Ki-Jeong; Jung, Yu Jin; An, Ki-Seok

    2006-08-15

    It has recently been observed that benzoic acid strongly reacts with OH group on the silicon surface. Here, by defining the area in which OH group is adsorbed on the Si surface, the selective adsorption of benzoic acid species was attempted. The patterned OH/Si surface was prepared by irradiating the zeroth order beam from the bending magnet of the synchrotron facility through the gold mesh placed in front of the OH/Si sample. For discerning the selectively adsorbed molecule by x-ray photoelectron emission microscopy (X-PEEM) at N k edge, 4-nitrobenzoic acid was utilized instead of benzoic acid. Near edge x-ray absorption fine structure spectra at carbon and oxygen k edges were in good accord with the previous results obtained from the benzoic acid system. The X-PEEM images around N k edge clearly showed that the molecules adsorb only on the area in which OH groups remain.

  15. Adsorption of imidazole on Au(111) surface: Dispersion corrected density functional study

    NASA Astrophysics Data System (ADS)

    Izzaouihda, Safia; Mahjoubi, Khaled; Abou El Makarim, Hassna; Komiha, Najia; Benoit, David M.

    2016-10-01

    We use density functional theory in the generalized gradient approximation to study the adsorption of imidazole on the Au(111) surface and account for dispersion effect using Grimme's empirical dispersion correction technique. Our results show that the adsorption energy of imidazole depends on the slab size and on the adsorption site. In agreement with other studies, we find the largest adsorption energy for imidazole on a top site of Au(111). However, we also note that the adsorption energy at other sites is substantial.

  16. High Surface Area Inorganic Membrane for Water Removal

    SciTech Connect

    2008-12-01

    This factsheet describes a research project whose objective is to demonstrate the fabrication and performance advantages of minichannel planar membrane modules made of porous metallic supports of surface area packing density one order of magnitude higher than the conventional membrane tube. The new, transformational, ceramic/metallic, hybrid membrane technology will be used for water/ethanol separations and reduce energy consumption by >20% over distillation and adsorption.

  17. Surface stoichiometry of zinc sulfide and its effect on the adsorption behaviors of xanthate

    PubMed Central

    2011-01-01

    In this paper, the surface stoichiometry, acid-base properties as well as the adsorption of xanthate at ZnS surfaces were studied by means of potentiometric titration, adsorption and solution speciation modeling. The surface proton binding site was determined by using Gran plot to evaluate the potentiometric titration data. Testing results implied that for stoichiometric surfaces of zinc sulfide, the proton and hydroxide determine the surface charge. For the nonstoichiometric surfaces, the surface charge is controlled by proton, hydroxide, zinc and sulfide ions depending on specific conditions. The xanthate adsorption decreases with increasing solution pH, which indicates an ion exchange reaction at the surfaces. Based on experimental results, the surface protonation, deprotonation, stoichiometry and xanthate adsorption mechanism were discussed. PMID:22112283

  18. Molecular Dynamics Simulations of the Initial Adsorption Stages of Fibrinogen on Mica and Graphite Surfaces.

    PubMed

    Köhler, Stephan; Schmid, Friederike; Settanni, Giovanni

    2015-12-01

    Fibrinogen, a blood glycoprotein of vertebrates, plays an essential role in blood clotting by polymerizing into fibrin when activated. Upon adsorption on material surfaces, it also contributes to determine their biocompatibility and has been implicated in the onset of thrombosis and inflammation at medical implants. Here we present the first fully atomistic simulations of the initial stages of the adsorption process of fibrinogen on mica and graphite surfaces. The simulations reveal a weak adsorption on mica that allows frequent desorption and reorientation events. This adsorption is driven by electrostatic interactions between the protein and the silicate surface as well as the counterion layer. Preferred adsorption orientations for the globular regions of the protein are identified. The adsorption on graphite is found to be stronger with fewer reorientation and desorption events and shows the onset of denaturation of the protein.

  19. Non-equilibrium Thermodynamic Dissolution Theory for Multi-Component Solid/Liquid Surfaces Involving Surface Adsorption and Radiolysis Kinetics

    SciTech Connect

    Stout, R B

    2001-04-01

    A theoretical expression is developed for the dissolution rate response for multi-component radioactive materials that have surface adsorption kinetics and radiolysis kinetics when wetted by a multi-component aqueous solution. An application for this type of dissolution response is the performance evaluation of multi-component spent nuclear fuels (SNFs) for long term interim storage and for geological disposition. Typically, SNF compositions depend on initial composition, uranium oxide and metal alloys being most common, and on reactor burnup which results in a wide range of fission product and actinide concentrations that decay by alpha, beta, and gamma radiation. These compositional/burnup ranges of SNFs, whether placed in interim storage or emplaced in a geologic repository, will potentially be wetted by multi-component aqueous solutions, and these solutions may be further altered by radiolytic aqueous species due to three radiation fields. The solid states of the SNFs are not thermodynamically stable when wetted and will dissolve, with or without radiolysis. The following development of a dissolution theory is based on a non-equilibrium thermodynamic analysis of energy reactions and energy transport across a solid-liquid phase change discontinuity that propagates at a quasi-steady, dissolution velocity. The integral form of the energy balance equation is used for this spatial surface discontinuity analysis. The integral formulation contains internal energy functional of classical thermodynamics for both the SNFs' solid state and surface adsorption species, and the adjacent liquid state, which includes radiolytic chemical species. The steady-state concentrations of radiolytic chemical species are expressed by an approximate analysis of the decay radiation transport equation. For purposes of illustration a modified Temkin adsorption isotherm was assumed for the surface adsorption kinetics on an arbitrary, finite area of the solid-liquid dissolution interface. For

  20. A unifying model for adsorption and nucleation of vapors on solid surfaces.

    PubMed

    Laaksonen, Ari

    2015-04-23

    Vapor interaction with solid surfaces is traditionally described with adsorption isotherms in the undersaturated regime and with heterogeneous nucleation theory in the supersaturated regime. A class of adsorption isotherms is based on the idea of vapor molecule clustering around so-called active sites. However, as the isotherms do not account for the surface curvature effects of the clusters, they predict an infinitely thick adsorption layer at saturation and do not recognize the existence of the supersaturated regime. The classical heterogeneous nucleation theory also builds on the idea of cluster formation, but describes the interactions between the surface and the cluster with a single parameter, the contact angle, which provides limited information compared with adsorption isotherms. Here, a new model of vapor adsorption on nonporous solid surfaces is derived. The basic assumption is that adsorption proceeds via formation of molecular clusters, modeled as liquid caps. The equilibrium of the individual clusters with the vapor phase is described with the Frenkel-Halsey-Hill (FHH) adsorption theory modified with the Kelvin equation that corrects for the curvature effect on vapor pressure. The new model extends the FHH adsorption isotherm to be applicable both at submonolayer surface coverages and at supersaturated conditions. It shows good agreement with experimental adsorption data from 12 different adsorbent-adsorbate systems. The model predictions are also compared against heterogeneous nucleation data, and they show much better agreement than predictions of the classical heterogeneous nucleation theory. PMID:25831213

  1. Molecular Dynamics Simulations of Uranyl and Uranyl Carbonate Adsorption at Alumino-silicate Surfaces

    SciTech Connect

    Kerisit, Sebastien N.; Liu, Chongxuan

    2014-03-03

    Adsorption at mineral surfaces is a critical factor controlling the mobility of uranium(VI) in aqueous environments. Therefore, molecular dynamics (MD) simulations were performed to investigate uranyl(VI) adsorption onto two neutral alumino-silicate surfaces, namely the orthoclase (001) surface and the octahedral aluminum sheet of the kaolinite (001) surface. Although uranyl preferentially adsorbed as a bi-dentate innersphere complex on both surfaces, the free energy of adsorption at the orthoclase surface (-15 kcal mol-1) was significantly more favorable than that at the kaolinite surface (-3 kcal mol-1), which was attributed to differences in surface functional groups and to the ability of the orthoclase surface to dissolve a surface potassium ion upon uranyl adsorption. The structures of the adsorbed complexes compared favorably with X-ray absorption spectroscopy results. Simulations of the adsorption of uranyl complexes with up to three carbonate ligands revealed that uranyl complexes coordinated to up to 2 carbonate ions are stable on the orthoclase surface whereas uranyl carbonate surface complexes are unfavored at the kaolinite surface. Combining the MD-derived equilibrium adsorption constants for orthoclase with aqueous equilibrium constants for uranyl carbonate species indicates the presence of adsorbed uranium complexes with one or two carbonates in alkaline conditions, in support of current uranium(VI) surface complexation models.

  2. Modeling of thorium (IV) ions adsorption onto a novel adsorbent material silicon dioxide nano-balls using response surface methodology.

    PubMed

    Kaynar, Ümit H; Şabikoğlu, Israfil; Kaynar, Sermin Çam; Eral, Meral

    2016-09-01

    The silicon dioxide nano-balls (nano-SiO2) were prepared for the adsorption of thorium (IV) ions from aqueous solution. The synthesized silicon dioxide nano-balls were characterized by Scanning Electron Microscopy/Energy Dispersive X-ray, X-ray Diffraction, Fourier Transform Infrared and BET surface area measurement spectroscopy. The effects of pH, concentration, temperature and the solid-liquid ratio on the adsorption of thorium by nano-balls were optimized using central composite design of response surface methodology. The interaction between four variables was studied and modelled. Furthermore, the statistical analysis of the results was done. Analysis of variance revealed that all of the single effects found statistically significant on the sorption of Th(IV). Probability F-values (F=4.64-14) and correlation coefficients (R(2)=0.99 for Th(IV)) indicate that model fit the experimental data well. The ability of this material to remove Th(IV) from aqueous solution was characterized by Langmuir, Freunlinch and Temkin adsorption isotherms. The adsorption capacity of thorium (IV) achieved 188.2mgg(-1). Thermodynamic parameters were determined and discussed. The batch adsorption condition with respect to interfering ions was tested. The results indicated that silicon dioxide nano-balls were suitable as sorbent material for adsorption and recovery of Th(IV) ions from aqueous solutions. PMID:27451112

  3. Modeling of thorium (IV) ions adsorption onto a novel adsorbent material silicon dioxide nano-balls using response surface methodology.

    PubMed

    Kaynar, Ümit H; Şabikoğlu, Israfil; Kaynar, Sermin Çam; Eral, Meral

    2016-09-01

    The silicon dioxide nano-balls (nano-SiO2) were prepared for the adsorption of thorium (IV) ions from aqueous solution. The synthesized silicon dioxide nano-balls were characterized by Scanning Electron Microscopy/Energy Dispersive X-ray, X-ray Diffraction, Fourier Transform Infrared and BET surface area measurement spectroscopy. The effects of pH, concentration, temperature and the solid-liquid ratio on the adsorption of thorium by nano-balls were optimized using central composite design of response surface methodology. The interaction between four variables was studied and modelled. Furthermore, the statistical analysis of the results was done. Analysis of variance revealed that all of the single effects found statistically significant on the sorption of Th(IV). Probability F-values (F=4.64-14) and correlation coefficients (R(2)=0.99 for Th(IV)) indicate that model fit the experimental data well. The ability of this material to remove Th(IV) from aqueous solution was characterized by Langmuir, Freunlinch and Temkin adsorption isotherms. The adsorption capacity of thorium (IV) achieved 188.2mgg(-1). Thermodynamic parameters were determined and discussed. The batch adsorption condition with respect to interfering ions was tested. The results indicated that silicon dioxide nano-balls were suitable as sorbent material for adsorption and recovery of Th(IV) ions from aqueous solutions.

  4. Surface Charge Transfer Doping of Monolayer Phosphorene via Molecular Adsorption.

    PubMed

    He, Yuanyuan; Xia, Feifei; Shao, Zhibin; Zhao, Jianwei; Jie, Jiansheng

    2015-12-01

    Monolayer phosphorene has attracted much attention owing to its extraordinary electronic, optical, and structural properties. Rationally tuning the electrical transport characteristics of monolayer phosphorene is essential to its applications in electronic and optoelectronic devices. Herein, we study the electronic transport behaviors of monolayer phosphorene with surface charge transfer doping of electrophilic molecules, including 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), NO2, and MoO3, using density functional theory combined with the nonequilibrium Green's function formalism. F4TCNQ shows optimal performance in enhancing the p-type conductance of monolayer phosphorene. Static electronic properties indicate that the enhancement is originated from the charge transfer between adsorbed molecule and phosphorene layer. Dynamic transport behaviors demonstrate that additional channels for hole transport in host monolayer phosphorene were generated upon the adsorption of molecule. Our work unveils the great potential of surface charge transfer doping in tuning the electronic properties of monolayer phosphorene and is of significance to its application in high-performance devices.

  5. High coverage hydrogen adsorption on the Fe3O4(1 1 0) surface

    NASA Astrophysics Data System (ADS)

    Yu, Xiaohu; Zhang, Xuemei; Wang, Shengguang

    2015-10-01

    Hydrogen adsorption on the A and B termination layers of the Fe3O4(1 1 0) surface at different coverage has been systematically studied by density functional theory calculations including an on-site Hubbard term (GGA + U). The adsorption of hydrogen prefers surface oxygen atoms on both layers. The more stable A layer has stronger adsorption energy than the less stable B layer. The saturation coverage has two dissociatively adsorbed H2 on the A layer, and one dissociatively adsorbed H2 on the B layer. The adsorption mechanism has been analyzed on the basis of projected density of states (PDOS).

  6. Cd adsorption onto Anoxybacillus flavithermus: Surface complexation modeling and spectroscopic investigations

    SciTech Connect

    Burnett, Peta-Gaye; Daughney, Christopher J.; Peak, Derek

    2008-06-09

    Several recent studies have applied surface complexation theory to model metal adsorption behaviour onto mesophilic bacteria. However, no investigations have used this approach to characterise metal adsorption by thermophilic bacteria. In this study, we perform batch adsorption experiments to quantify cadmium adsorption onto the thermophile Anoxybacillus flavithermus. Surface complexation models (incorporating the Donnan electrostatic model) are developed to determine stability constants corresponding to specific adsorption reactions. Adsorption reactions and stoichiometries are constrained using spectroscopic techniques (XANES, EXAFS, and ATR-FTIR). The results indicate that the Cd adsorption behaviour of A. flavithermus is similar to that of other mesophilic bacteria. At high bacteria-to-Cd ratios, Cd adsorption occurs by formation of a 1:1 complex with deprotonated cell wall carboxyl functional groups. At lower bacteria-to-Cd ratios, a second adsorption mechanism occurs at pH > 7, which may correspond to the formation of a Cd-phosphoryl, CdOH-carboxyl, or CdOH-phosphoryl surface complex. X-ray absorption spectroscopic investigations confirm the formation of the 1:1 Cd-carboxyl surface complex, but due to the bacteria-to-Cd ratio used in these experiments, other complexation mechanism(s) could not be unequivocally resolved by the spectroscopic data.

  7. Phosphate adsorption on aluminum-impregnated mesoporous silicates: surface structure and behavior of adsorbents.

    PubMed

    Shin, Eun Woo; Han, James S; Jang, Min; Min, Soo-Hong; Park, Jae Kwang; Rowell, Roger M

    2004-02-01

    Phosphorus from excess fertilizers and detergents ends up washing into lakes, creeks, and rivers. This overabundance of phosphorus causes excessive aquatic plant and algae growth and depletes the dissolved oxygen supply in the water. In this study, aluminum-impregnated mesoporous adsorbents were tested for their ability to remove phosphate from water. The surface structure of the materials was investigated with X-ray diffraction (XRD), a N2 adsorption-desorption technique, Fourier transform-infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS) to understand the effect of surface properties on the adsorption behavior of phosphate. The mesoporous materials were loaded with Al components by reaction with surface silanol groups. In the adsorption test, the Al-impregnated mesoporous materials showed fast adsorption kinetics as well as high adsorption capacities, compared with activated alumina. The uniform mesopores of the Al-impregnated mesoporous materials caused the diffusion rate in the adsorption process to increase, which in turn caused the fast adsorption kinetics. High phosphate adsorption capacities of the Al-impregnated mesoporous materials were attributed to not only the increase of surface hydroxyl density on Al oxide due to well-dispersed impregnation of Al components but also the decrease in stoichiometry of surface hydroxyl ions to phosphate by the formation of monodentate surface complexes. PMID:14968882

  8. Oxygen adsorption on the Al₉Co₂(001) surface: first-principles and STM study.

    PubMed

    Villaseca, S Alarcón; Loli, L N Serkovic; Ledieu, J; Fournée, V; Gille, P; Dubois, J-M; Gaudry, E

    2013-09-01

    Atomic oxygen adsorption on a pure aluminum terminated Al9Co2(001) surface is studied by first-principle calculations coupled with STM measurements. Relative adsorption energies of oxygen atoms have been calculated on different surface sites along with the associated STM images. The local electronic structure of the most favourable adsorption site is described. The preferential adsorption site is identified as a 'bridge' type site between the cluster entities exposed at the (001) surface termination. The Al-O bonding between the adsorbate and the substrate presents a covalent character, with s-p hybridization occurring between the states of the adsorbed oxygen atom and the aluminum atoms of the surface. The simulated STM image of the preferential adsorption site is in agreement with experimental observations. This work shows that oxygen adsorption generates important atomic relaxations of the topmost surface layer and that sub-surface cobalt atoms strongly influence the values of the adsorption energies. The calculated Al-O distances are in agreement with those reported in Al2O and Al2O3 oxides and for oxygen adsorption on Al(111). PMID:23883551

  9. Oxygen adsorption on the Al₉Co₂(001) surface: first-principles and STM study.

    PubMed

    Villaseca, S Alarcón; Loli, L N Serkovic; Ledieu, J; Fournée, V; Gille, P; Dubois, J-M; Gaudry, E

    2013-09-01

    Atomic oxygen adsorption on a pure aluminum terminated Al9Co2(001) surface is studied by first-principle calculations coupled with STM measurements. Relative adsorption energies of oxygen atoms have been calculated on different surface sites along with the associated STM images. The local electronic structure of the most favourable adsorption site is described. The preferential adsorption site is identified as a 'bridge' type site between the cluster entities exposed at the (001) surface termination. The Al-O bonding between the adsorbate and the substrate presents a covalent character, with s-p hybridization occurring between the states of the adsorbed oxygen atom and the aluminum atoms of the surface. The simulated STM image of the preferential adsorption site is in agreement with experimental observations. This work shows that oxygen adsorption generates important atomic relaxations of the topmost surface layer and that sub-surface cobalt atoms strongly influence the values of the adsorption energies. The calculated Al-O distances are in agreement with those reported in Al2O and Al2O3 oxides and for oxygen adsorption on Al(111).

  10. Effect of the surface oxygen groups on methane adsorption on coals

    NASA Astrophysics Data System (ADS)

    Hao, Shixiong; Wen, Jie; Yu, Xiaopeng; Chu, Wei

    2013-01-01

    To investigate the influence of surface oxygen groups on methane adsorption on coals, one bituminous coal was modified with H2O2, (NH4)2S2O8 and HNO3 respectively, to prepare coal samples with different surface properties. The oxygen groups on coal surface were characterized by X-ray photoelectron spectroscopy (XPS). The textures of the coal samples were investigated by N2 adsorption at 77 K. Their surface morphologies were analyzed by scanning electron microscopy (SEM). The methane adsorption behaviors of these coal samples were measured at 303 K in pressure range of 0-5.3 MPa by volumetric method. The adsorption data of methane were fitted to the Langmuir model and Dubinin-Astakhov (D-A) model. The fitting results showed that the D-A model fitted the isotherm data better than the Langmuir model. It was observed that there was, in general, a positive correlation between the methane saturated adsorption capacity and the micropore volume of coals while a negative correlation between methane saturated adsorption capacity and the Ototal/Ctotal. The methane adsorption capacity was determined by the coal surface chemistry when the microporosity parameters of two samples were similar. Coal with a higher amount of oxygen surface groups, and consequently with a less hydrophobic character, had lower methane adsorption capacity.

  11. Initial heats of H{sub 2}S adsorption on activated carbons: Effect of surface features

    SciTech Connect

    Bagreev, A.; Adib, F.; Bandosz, T.J.

    1999-11-15

    The sorption of hydrogen sulfide was studied on activated carbons of various origins by means of inverse gas chromatography at infinite dilution. The conditions of the experiment were dry and anaerobic. Prior to the experiments the surface of some carbon samples was oxidized using either nitric acid or ammonium persulfate. Then the structural parameters of carbons were evaluated from the sorption of nitrogen. From the IGC experiments at various temperatures, heats of adsorption were calculated. The results showed that the heat of H{sub 2}S adsorption under dry anaerobic conditions does not depend on surface chemistry. The dependence of the heat of adsorption on the characteristic energy of nitrogen adsorption calculated from the Dubinin-Raduskevich equation was found. This correlation can be used to predict the heat of H{sub 2}S adsorption based on the results obtained from nitrogen adsorption.

  12. Fermi level pinning and the charge transfer contribution to the energy of adsorption at semiconducting surfaces

    SciTech Connect

    Krukowski, Stanisław; Kempisty, Paweł; Strak, Paweł; Sakowski, Konrad

    2014-01-28

    It is shown that charge transfer, the process analogous to formation of semiconductor p-n junction, contributes significantly to adsorption energy at semiconductor surfaces. For the processes without the charge transfer, such as molecular adsorption of closed shell systems, the adsorption energy is determined by the bonding only. In the case involving charge transfer, such as open shell systems like metal atoms or the dissociating molecules, the energy attains different value for the Fermi level differently pinned. The Density Functional Theory (DFT) simulation of species adsorption at different surfaces, such as SiC(0001) or GaN(0001) confirms these predictions: the molecular adsorption is independent on the coverage, while the dissociative process adsorption energy varies by several electronvolts.

  13. The dynamics of adsorption on clean and adsorbate-modified transition metal surfaces

    SciTech Connect

    Madix, R.J.

    1991-06-01

    Research is being carried out on both nondissociative and dissociative adsorption of gases on transition metal surfaces, with emphasis on alkanes. Particular attention is be placed on understanding the effects of adsorbed species on adsorption probabilities and on clarifying the role of energy exchange processes at the surface in both dissociative and nondissociative adsorption. Molecular beam methods are coupled with methods of surface science to gain the greatest control of the variables of the problem, including the incident kinetic energy, vibrational energy and angle of incidence of the incoming molecules. The dynamics of both direct and precursor-influenced dissociative adsorption routes are examined. Surface intermediates formed by activated adsorption are identified by vibrational spectroscopy and temperature programmed reaction. Emphasis is on comparative studies of low molecular weight alkanes in order to understand the origin of the differences in their reactivities on different metals.

  14. Phosphate adsorption on aluminum-coordinated functionalized macroporous–mesoporous silica: Surface structure and adsorption behavior

    SciTech Connect

    Huang, Weiya; Li, Dan; Zhu, Yi; Xu, Kai; Li, Jianqiang; Han, Boping; Zhang, Yuanming

    2013-12-15

    Graphical abstract: - Highlights: • Al-coordinated functionalized macroporous–mesoporous silica for phosphate removal. • It had the maximum adsorption capacity of 23.59 mg P/g. • Over 95% of the final adsorption capacity reached in the first 1 min. - Abstract: In this study, Al(III)-coordinated diamino-functionalized macroporous–mesoporous silica was synthesized and characterized by X-ray diffraction, N{sub 2} adsorption–desorption, Fourier transform infrared spectroscopy, scanning and transmission electron microscopy. Because of well-defined and interconnecting macroporous–mesoporous networks, the resulting adsorbent (MM-SBA) exhibited a significantly better phosphate adsorption performance and faster removal rate, as compared with the mesoporous adsorbent (M-SBA). Based on the Freundlich and Langmuir models, the phosphate adsorption capacity and the maximum adsorption capacity of MM-SBA were 7.99 mg P/g and 23.59 mg P/g, respectively. In the kinetic study of MM-SBA, over 95% of its final adsorption capacity reached in the first 1 min; whereas that of M-SBA was less than 79%.

  15. Adsorption and surface-enhanced Raman of dyes on silver and gold sols

    SciTech Connect

    Lee, P.C.; Meisel, D.

    1982-08-19

    Several negatively charged dyes were investigated for their possible adsorption on the surface of silver and gold colloidal particles. Those dyes that were found to adsorb on the particles were then checked for surface enhancement of Raman scattering. Highly efficient surface-enhanced Raman scattering (SERS) was observed from a carbocyanine dye in both sols. Excitation-dependence studies as well as adsorption studies confirm the SERS nature of the Raman spectra obtained. The dye is probably aggregated on adsorption and is probably attached through the naphthalene side moiety to the surface. Less efficient SERS was also observed for copper phthalocyanine.

  16. Co-adsorption of phosphate and zinc(II) on the surface of ferrihydrite.

    PubMed

    Liu, Jing; Zhu, Runliang; Xu, Tianyuan; Xu, Yin; Ge, Fei; Xi, Yunfei; Zhu, Jianxi; He, Hongping

    2016-02-01

    Ferrihydrite (Fh) is of great importance in affecting the migration and transformation of heavy-metal cations and oxyanions. To advance the understanding of co-adsorption reactions on Fh surface, the co-adsorption of phosphate and Zn(II) from aqueous solution to a synthesized Fh was determined. The batch experiments demonstrated a synergistic adsorption of phosphate and Zn(II) on Fh. In the pH range of 3.5-6, the adsorption of the two contaminants showed strong pH dependence in the single solute adsorption systems, but the dependence alleviated in the simultaneous adsorption system. X-ray photoelectron spectroscopy (XPS) revealed that the chemical shifts of Zn 2p1/2 and Zn 2p3/2 binding energies were more significant than that of P 2p in the single and simultaneous adsorption systems. On the other side, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) observed increased formation of outer- and inner-sphere complexes of phosphate in the simultaneous system. Thus, the synergistic adsorption of the two contaminants could be attributed to the formation of ternary complexes as well as electrostatic interactions, while surface precipitation could not be completely ruled out. On the basis of the results from both the batch adsorption experiments and structural characterization, these two contaminants were likely to form phosphate-bridged ternary complexes (≡Fe-P-Zn) in the simultaneous adsorption system.

  17. Co-adsorption of phosphate and zinc(II) on the surface of ferrihydrite.

    PubMed

    Liu, Jing; Zhu, Runliang; Xu, Tianyuan; Xu, Yin; Ge, Fei; Xi, Yunfei; Zhu, Jianxi; He, Hongping

    2016-02-01

    Ferrihydrite (Fh) is of great importance in affecting the migration and transformation of heavy-metal cations and oxyanions. To advance the understanding of co-adsorption reactions on Fh surface, the co-adsorption of phosphate and Zn(II) from aqueous solution to a synthesized Fh was determined. The batch experiments demonstrated a synergistic adsorption of phosphate and Zn(II) on Fh. In the pH range of 3.5-6, the adsorption of the two contaminants showed strong pH dependence in the single solute adsorption systems, but the dependence alleviated in the simultaneous adsorption system. X-ray photoelectron spectroscopy (XPS) revealed that the chemical shifts of Zn 2p1/2 and Zn 2p3/2 binding energies were more significant than that of P 2p in the single and simultaneous adsorption systems. On the other side, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) observed increased formation of outer- and inner-sphere complexes of phosphate in the simultaneous system. Thus, the synergistic adsorption of the two contaminants could be attributed to the formation of ternary complexes as well as electrostatic interactions, while surface precipitation could not be completely ruled out. On the basis of the results from both the batch adsorption experiments and structural characterization, these two contaminants were likely to form phosphate-bridged ternary complexes (≡Fe-P-Zn) in the simultaneous adsorption system. PMID:26461439

  18. Surface modifications of illite in concentrated lime solutions investigated by pyridine adsorption.

    PubMed

    Konan, K L; Peyratout, C; Smith, A; Bonnet, J-P; Magnoux, P; Ayrault, P

    2012-09-15

    The surface properties and functionality of an illite-containing clay mineral in alkaline solutions containing increasing quantities of calcium hydroxide were investigated using FTIR monitored pyridine adsorption at various temperatures. Results showed that the binding behavior of electron donor pyridine molecules to illite platelets is mostly governed by electron acceptor sites located at the edges of the clay particles. The binding of bulky hydrated calcium ions at the surface of the illite platelets decreases the surface area of illite. Moderate thermal treatments up to 450°C do not affect the structure of the clay mineral but strongly decrease the number of Lewis and Brönsted sites available at the edges of the clay platelets. PMID:22748428

  19. Adsorption/electrosorption of catechol and resorcinol onto high area activated carbon cloth.

    PubMed

    Bayram, Edip; Hoda, Numan; Ayranci, Erol

    2009-09-15

    Removal of catechol and resorcinol from aqueous solutions by adsorption and electrosorption onto high area activated carbon cloth (ACC) was investigated. Kinetics of both adsorption and electrosorption were followed by in-situ UV-spectroscopic method and the data were treated according to pseudo-first-order, pseudo-second-order and intraparticle diffusion models. It was found that the adsorption and electrosorption of these compounds onto ACC follows pseudo-second-order model. pH changes during adsorption and electrosorption were followed and discussed with regard to the interaction between ACC and adsorbate molecules, utilizing the pH(pzc) value of ACC. An electrodesorption experiment was conducted to explore the possibility of regeneration of ACC. Adsorption isotherms were derived at 25 degrees C on the basis of batch analysis. The fits of experimental isotherm data to the well-known Freundlich, Langmuir and Tempkin models were examined. PMID:19345487

  20. A Study of DNA Adsorption Kinetics on OTS Surfaces

    NASA Astrophysics Data System (ADS)

    Barone, Joseph; Fang, Xiaohua; Li, Bingquan; Seo, Young-Soo; Samuilov, Vladimir; Rafailovich, Miriam; Sokolov, Jonathan

    2003-03-01

    The evaporation kinetics of droplets containing DNA were studied as a function of DNA molecular weight, DNA concentration, and buffer concentration.The contact angle and overall droplet morphology were observed using a KSV contact angle goniometer as a function of time. Simultaneously, the DNA distribution and adsorption kinetics were measured with confocal microscopy. The DNA droplets were deposited on hydrophobic OTS-covered silicon surfaces and stained with ethidium bromide solution. Up to three stages were found during DNA droplet drying process, depending on the DNA concentration. The results also show that a ring is formed at the air/solid /liquid interface in a manner similar to that reported for a colloidal suspension by Robert D. Deegan et.a. [Physical Review E, Vol 62, No.1, July 2000, p756-765] The absorbed amount of DNA was obtained by measuring the intensity in the ring. The dynamics and DNA morphology are affected by both the molecular weight and the DNA concentration. Supported by NSF-MRSEC program (DMR-9632525)

  1. Surface complexation modeling of uranyl adsorption on corrensite from the Waste Isolation Pilot Plant Site

    SciTech Connect

    Park, Sang-Won; Leckie, J.O.; Siegel, M.D.

    1995-09-01

    Corrensite is the dominant clay mineral in the Culebra Dolomite at the Waste Isolation Pilot Plant. The surface characteristics of corrensite, a mixed chlorite/smectite clay mineral, have been studied. Zeta potential measurements and titration experiments suggest that the corrensite surface contains a mixture of permanent charge sites on the basal plane and SiOH and AlOH sites with a net pH-dependent charge at the edge of the clay platelets. Triple-layer model parameters were determined by the double extrapolation technique for use in chemical speciation calculations of adsorption reactions using the computer program HYDRAQL. Batch adsorption studies showed that corrensite is an effective adsorbent for uranyl. The pH-dependent adsorption behavior indicates that adsorption occurs at the edge sites. Adsorption studies were also conducted in the presence of competing cations and complexing ligands. The cations did not affect uranyl adsorption in the range studied. This observation lends support to the hypothesis that uranyl adsorption occurs at the edge sites. Uranyl adsorption was significantly hindered by carbonate. It is proposed that the formation of carbonate uranyl complexes inhibits uranyl adsorption and that only the carbonate-free species adsorb to the corrensite surface. The presence of the organic complexing agents EDTA and oxine also inhibits uranyl sorption.

  2. [Simulation study on the effect of salinity on the adsorption behavior of mercury in wastewater-irrigated area].

    PubMed

    Zheng, Shun-An; Li, Xiao-Hua; Xu, Zhi-Yu

    2014-05-01

    This study was designed to pinpoint the impact of salinity ( NaCl and Na2SO4, added at salinity levels of 0-5%, respectively) on the adsorption behavior of mercury in wastewater-irrigated areas of Tianjin City by batch and kinetic experiments. The results showed that, the Langmuir isotherm and the Elovich equation can well fitted batch and kinetic experimental data, respectively. As NaCI spiked in soil, Hg( II) adsorption capacity and strength had marked decreases, from 868.64 mgkg-1 and 1. 32 at control to 357.48 mgkg-1 and 0.63 at 5% salinity level of NaCI, respectively. As Na2SO4 spiked in soil, Hg(II) adsorption capacity (parameter qm in Langmuir isotherm) and strength (parameter k in Langmuir isotherm) changed slightly, from 868.64 mg kg-1 and 1.32 at control to 739.44 mg.kg-1 and 1. 18 at 5% salinity level of Na2 SO4, respectively. Kinetic data showed that, Hg( II) adsorption rate (parameter b in Elovich equation) in soil was not influenced by Na2SO, addition. However, the addition of NaC1 had a great effect on mercury adsorption rate. Hg(II ) adsorption capacity as a function of CI- or SO(2-)(4) content in soil could be simulated by the natural logarithm model, while Hg( II ) adsorption rate as a function of CI- content in soil could be simulated by the linear model. The study manifested that NaCI can significantly increase migration of Hg( II ) in the soil irrigated with wastewater, which may enhance Hg( II) bioavailability in the soil and cause a hazard to surface water. Especially, it will be harmful to human body through the food chain. PMID:25055690

  3. The effects of pH and surface composition on Pb adsorption to natural freshwater biofilms.

    PubMed

    Wilson, A R; Lion, L W; Nelson, Y M; Shuler, M L; Ghiorse, W C

    2001-08-01

    Two dominant variables that control the adsorption of toxic trace metals to suspended particulate materials and aquatic surface coatings are surface composition and solution pH. A model for the pH-dependent adsorption of Pbto heterogeneous particulate surface mixtures was derived from experimental evaluation of Pb adsorption to laboratory-derived surrogates. The surrogate materials were selected to represent natural reactive surface components. Pb adsorption to both the laboratory surrogates and natural biofilms was determined in chemically defined solutions under controlled laboratory conditions. Pb adsorption was measured over a pH range of 5-8, with an initial Pb concentration in solution of 2.0 microM. The surface components considered include amorphous Fe oxide, biogenic Mn oxide produced by a Mn(II) oxidizing bacterium (Leptothrix discophora SS-1), Al oxide, the common green alga Chlorella vulgaris, and Leptothrix discophora SS-1 cells. A linearization of Pb adsorption data for each adsorbent was used to quantify the relationship between Pb adsorption and pH. The parameters for individual adsorbents were incorporated into an additive model to predict the total Pb adsorption in multiple-adsorbent natural surface coatings that were collected from Cayuga Lake, NY. Pb adsorption experiments on the natural surface coatings at variable pH were utilized to verify the additive model predictions based on the pH dependent behavior of the experimental laboratory surrogates. Observed Pb adsorption is consistent with the model predictions (within 1-24%) over the range of solution pH values considered. The experimental results indicate that the combination of Fe and biogenic Mn oxides can contribute as much as 90% of Pb adsorbed on Cayuga Lake biofilms, with the dominant adsorbent switching from Mn to Fe oxide with increasing pH. PMID:11505999

  4. Adsorption of the antimicrobial peptide tritrpticin onto solid and liquid surfaces: Ion-specific effects.

    PubMed

    Salay, Luiz C; Petri, Denise F S; Nakaie, Clovis R; Schreier, Shirley

    2015-12-01

    Developing functional biointerfaces is important for technological applications. We investigated the interaction and adsorption of the antimicrobial peptide tritrpticin (VRRFPWWWPFLRR, TRP3) onto solid and liquid surfaces and the influence of ions on these processes by several techniques. Surface tension measurements showed that salt addition to TRP3 solution causes a high decrease of surface tension due to the adsorption of TRP3 at air-liquid surface. Ellipsometry studies show the TRP3 adsorption on silicon surfaces forming nanometric films that are able to further interact with liposomes. Contact angle measurements gave insight on the nature of thin film and its roughness. AFM shows the topology of the film on the solid substrates. In addition, those techniques also showed that anions can act as modulators on adsorption phenomena and are correlated with the Hofmeister series. The findings of the current work are relevant for the development of functional interfaces such as biocidal surfaces. PMID:26529674

  5. Site-Specific Scaling Relations for Hydrocarbon Adsorption on Hexagonal Transition Metal Surfaces

    SciTech Connect

    Montemore, Matthew M.; Medlin, James W.

    2013-10-03

    Screening a large number of surfaces for their catalytic performance remains a challenge, leading to the need for simple models to predict adsorption properties. To facilitate rapid prediction of hydrocarbon adsorption energies, scaling relations that allow for calculation of the adsorption energy of any intermediate attached to any symmetric site on any hexagonal metal surface through a carbon atom were developed. For input, these relations require only simple electronic properties of the surface and of the gas-phase reactant molecules. Determining adsorption energies consists of up to four steps: (i) calculating the adsorption energy of methyl in the top site using density functional theory or by simple relations based on the electronic structure of the surface; (ii) using modified versions of classical scaling relations to scale between methyl in the top site and C₁ species with more metal-surface bonds (i.e., C, CH, CH₂) in sites that complete adsorbate tetravalency; (iii) using gas-phase bond energies to predict adsorption energies of longer hydrocarbons (i.e., CR, CR₂, CR₃); and (iv) expressing energetic changes upon translation of hydrocarbons to various sites in terms of the number of agostic interactions and the change in the number of carbon-metal bonds. Combining all of these relations allows accurate scaling over a wide range of adsorbates and surfaces, resulting in efficient screening of catalytic surfaces and a clear elucidation of adsorption trends. The relations are used to explain trends in methane reforming, hydrocarbon chain growth, and propane dehydrogenation.

  6. Adsorption of lysozyme on base metal surfaces in the presence of an external electric potential.

    PubMed

    Ei Ei, Htwe; Nakama, Yuhi; Tanaka, Hiroshi; Imanaka, Hiroyuki; Ishida, Naoyuki; Imamura, Koreyoshi

    2016-11-01

    The impact of external electric potential on the adsorption of a protein to base metal surfaces was examined. Hen egg white lysozyme (LSZ) and six types of base metal plates (stainless steel SUS316L (St), Ti, Ta, Zr, Cr, or Ni) were used as the protein and adsorption surface, respectively. LSZ was allowed to adsorb on the surface under different conditions (surface potential, pH, electrolyte type and concentration, surface material), which was monitored using an ellipsometer. LSZ adsorption was minimized in the potential range above a certain threshold and, in the surface potential range below the threshold, decreasing the surface potential increased the amount of protein adsorbed. The threshold potential for LSZ adsorption was shifted toward a positive value with increasing pH and was lower for Ta and Zr than for the others. A divalent anion salt (K2SO4) as an electrolyte exhibited the adsorption of LSZ in the positive potential range while a monovalent salt (KCl) did not. A comprehensive consideration of the obtained results suggests that two modes of interactions, namely the electric force by an external electric field and electrostatic interactions with ionized surface hydroxyl groups, act on the LSZ molecules and determine the extent of suppression of LSZ adsorption. All these findings appear to support the view that a base metal surface can be controlled for the affinity to a protein by manipulating the surface electric potential as has been reported on some electrode materials. PMID:27478958

  7. Adsorption of lysozyme on base metal surfaces in the presence of an external electric potential.

    PubMed

    Ei Ei, Htwe; Nakama, Yuhi; Tanaka, Hiroshi; Imanaka, Hiroyuki; Ishida, Naoyuki; Imamura, Koreyoshi

    2016-11-01

    The impact of external electric potential on the adsorption of a protein to base metal surfaces was examined. Hen egg white lysozyme (LSZ) and six types of base metal plates (stainless steel SUS316L (St), Ti, Ta, Zr, Cr, or Ni) were used as the protein and adsorption surface, respectively. LSZ was allowed to adsorb on the surface under different conditions (surface potential, pH, electrolyte type and concentration, surface material), which was monitored using an ellipsometer. LSZ adsorption was minimized in the potential range above a certain threshold and, in the surface potential range below the threshold, decreasing the surface potential increased the amount of protein adsorbed. The threshold potential for LSZ adsorption was shifted toward a positive value with increasing pH and was lower for Ta and Zr than for the others. A divalent anion salt (K2SO4) as an electrolyte exhibited the adsorption of LSZ in the positive potential range while a monovalent salt (KCl) did not. A comprehensive consideration of the obtained results suggests that two modes of interactions, namely the electric force by an external electric field and electrostatic interactions with ionized surface hydroxyl groups, act on the LSZ molecules and determine the extent of suppression of LSZ adsorption. All these findings appear to support the view that a base metal surface can be controlled for the affinity to a protein by manipulating the surface electric potential as has been reported on some electrode materials.

  8. Surface modification of activated carbon for enhanced adsorption of perfluoroalkyl acids from aqueous solutions.

    PubMed

    Zhi, Yue; Liu, Jinxia

    2016-02-01

    The objective of the research was to examine the effect of increasing carbon surface basicity on uptake of perfluorooctane sulfonic (PFOS) and carboxylic acids (PFOA) by activated carbon. Granular activated carbons made from coal, coconut shell, wood, and phenolic-polymer-based activated carbon fibers were modified through high-temperature and ammonia gas treatments to facilitate systematical evaluation of the impact of basicity of different origins. Comparison of adsorption isotherms and adsorption distribution coefficients showed that the ammonia gas treatment was more effective than the high-temperature treatment in enhancing surface basicity. The resultant higher point of zero charges and total basicity (measured by total HCl uptake) correlated with improved adsorption affinity for PFOS and PFOA. The effectiveness of surface modification to enhance adsorption varied with carbon raw material. Wood-based carbons and activated carbon fibers showed enhancement by one to three orders of magnitudes while other materials could experience reduction in adsorption towards either PFOS or PFOA.

  9. Surface modification of activated carbon for enhanced adsorption of perfluoroalkyl acids from aqueous solutions.

    PubMed

    Zhi, Yue; Liu, Jinxia

    2016-02-01

    The objective of the research was to examine the effect of increasing carbon surface basicity on uptake of perfluorooctane sulfonic (PFOS) and carboxylic acids (PFOA) by activated carbon. Granular activated carbons made from coal, coconut shell, wood, and phenolic-polymer-based activated carbon fibers were modified through high-temperature and ammonia gas treatments to facilitate systematical evaluation of the impact of basicity of different origins. Comparison of adsorption isotherms and adsorption distribution coefficients showed that the ammonia gas treatment was more effective than the high-temperature treatment in enhancing surface basicity. The resultant higher point of zero charges and total basicity (measured by total HCl uptake) correlated with improved adsorption affinity for PFOS and PFOA. The effectiveness of surface modification to enhance adsorption varied with carbon raw material. Wood-based carbons and activated carbon fibers showed enhancement by one to three orders of magnitudes while other materials could experience reduction in adsorption towards either PFOS or PFOA. PMID:26469934

  10. Surface Structural Ion Adsorption Modeling of Competitive Binding of Oxyanions by Metal (Hydr)oxides.

    PubMed

    Hiemstra; Van Riemsdijk WH

    1999-02-01

    Spectroscopy has provided a progressive flow of information concerning the binding mechanism(s) of ions and their surface-complex structure. An important challenge in surface complexation models (SCM) is to connect the molecular microscopic reality to macroscopic adsorption phenomena. This is important because SCM alone provide insufficient insight in the binding mechanisms, and moreover, it is a priori not obvious that SCM, which describe the pH dependent adsorption correctly in simple systems, will predict the ion interaction under multicomponent conditions. This study elucidates the primary factor controlling the adsorption process by analysing the adsorption and competition of PO4, AsO4, and SeO3. We show that the structure of the surface-complex acting in the dominant electrostatic field can be ascertained as the primary controlling adsorption factor. The surface species of arsenate are identical with those of phosphate and the adsorption behavior is very similar. On the basis of the selenite adsorption, we show that the commonly used 2pK models are incapable to incorporate in the adsorption modeling the correct bidentate binding mechanism found by spectroscopy. The use of the bidentate mechanism leads to a proton-oxyanion ratio and corresponding pH dependency that are too large. The inappropriate intrinsic charge attribution to the primary surface groups and the condensation of the inner sphere surface complex to a point charge are responsible for this behavior of commonly used 2pK models. Both key factors are differently defined in the charge distributed multi site complexation (CD-MUSIC) model and are based in this model on a surface structural approach. The CD-MUSIC model can successfully describe the macroscopic adsorption phenomena using the surface speciation and binding mechanisms as found by spectroscopy. The model is also able to predict the anion competition well. The charge distribution in the interface is in agreement with the observed structure

  11. Application of surface complexation models to anion adsorption by natural materials

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Various chemical models of ion adsorption will be presented and discussed. Chemical models, such as surface complexation models, provide a molecular description of anion adsorption reactions using an equilibrium approach. Two such models, the constant capacitance model and the triple layer model w...

  12. Adsorption of alkenyl succinic anhydride from solutions in carbon tetrachloride on a fine magnetite surface

    NASA Astrophysics Data System (ADS)

    Balmasova, O. V.; Ramazanova, A. G.; Korolev, V. V.

    2016-06-01

    The adsorption of alkenyl succinic anhydride from a solution in carbon tetrachloride on a fine magnetite surface at a temperature of 298.15 K is studied using fine magnetite, which forms the basis of magnetic fluids, as the adsorbent. An adsorption isotherm is recorded and interpreted in terms of the theory of the volume filling of micropores (TVFM). Adsorption process parameters are calculated on the basis of the isotherm. It is shown that at low equilibrium concentrations, the experimental adsorption isotherm is linear in the TVFM equation coordinates.

  13. Volumetric Interpretation of Protein Adsorption: Capacity Scaling with Adsorbate Molecular Weight and Adsorbent Surface Energy

    PubMed Central

    Parhi, Purnendu; Golas, Avantika; Barnthip, Naris; Noh, Hyeran; Vogler, Erwin A.

    2009-01-01

    Silanized-glass-particle adsorbent capacities are extracted from adsorption isotherms of human serum albumin (HSA, 66 kDa), immunoglobulin G (IgG, 160 kDa), fibrinogen (Fib, 341 kDa), and immunoglobulin M (IgM, 1000 kDa) for adsorbent surface energies sampling the observable range of water wettability. Adsorbent capacity expressed as either mass-or-moles per-unit-adsorbent-area increases with protein molecular weight (MW) in a manner that is quantitatively inconsistent with the idea that proteins adsorb as a monolayer at the solution-material interface in any physically-realizable configuration or state of denaturation. Capacity decreases monotonically with increasing adsorbent hydrophilicity to the limit-of-detection (LOD) near τo = 30 dyne/cm (θ~65o) for all protein/surface combinations studied (where τo≡γlvocosθ is the water adhesion tension, γlvo is the interfacial tension of pure-buffer solution, and θ is the buffer advancing contact angle). Experimental evidence thus shows that adsorbent capacity depends on both adsorbent surface energy and adsorbate size. Comparison of theory to experiment implies that proteins do not adsorb onto a two-dimensional (2D) interfacial plane as frequently depicted in the literature but rather partition from solution into a three-dimensional (3D) interphase region that separates the physical surface from bulk solution. This interphase has a finite volume related to the dimensions of hydrated protein in the adsorbed state (defining “layer” thickness). The interphase can be comprised of a number of adsorbed-protein layers depending on the solution concentration in which adsorbent is immersed, molecular volume of the adsorbing protein (proportional to MW), and adsorbent hydrophilicity. Multilayer adsorption accounts for adsorbent capacity over-and-above monolayer and is inconsistent with the idea that protein adsorbs to surfaces primarily through protein/surface interactions because proteins within second (or higher

  14. Application of surface complexation models to anion adsorption by natural materials.

    PubMed

    Goldberg, Sabine

    2014-10-01

    Various chemical models of ion adsorption are presented and discussed. Chemical models, such as surface complexation models, provide a molecular description of anion adsorption reactions using an equilibrium approach. Two such models, the constant capacitance model and the triple layer model, are described in the present study. Characteristics common to all the surface complexation models are equilibrium constant expressions, mass and charge balances, and surface activity coefficient electrostatic potential terms. Methods for determining parameter values for surface site density, capacitances, and surface complexation constants also are discussed. Spectroscopic experimental methods of establishing ion adsorption mechanisms include vibrational spectroscopy, nuclear magnetic resonance spectroscopy, electron spin resonance spectroscopy, X-ray absorption spectroscopy, and X-ray reflectivity. Experimental determinations of point of zero charge shifts and ionic strength dependence of adsorption results and molecular modeling calculations also can be used to deduce adsorption mechanisms. Applications of the surface complexation models to heterogeneous natural materials, such as soils, using the component additivity and the generalized composite approaches are described. Emphasis is on the generalized composite approach for predicting anion adsorption by soils. Continuing research is needed to develop consistent and realistic protocols for describing ion adsorption reactions on soil minerals and soils. The availability of standardized model parameter databases for use in chemical speciation-transport models is critical. PMID:24619924

  15. 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.

  16. Designing transition metal surfaces for their adsorption properties and chemical reactivity

    NASA Astrophysics Data System (ADS)

    Montemore, Matthew M.

    Many technological processes, such as catalysis, electrochemistry, corrosion, and some materials synthesis techniques, involve molecules bonding to and/or reacting on surfaces. For many of these applications, transition metals have proven to have excellent chemical reactivity, and this reactivity is strongly tied to the surface's adsorption properties. This thesis focuses on predicting adsorption properties for use in the design of transition metal surfaces for various applications. First, it is shown that adsorption through a particular atom (e.g, C or O) can be treated in a unified way. This allows predictions of all C-bound adsorbates from a single, simple adsorbate, such as CH3. In particular, consideration of the adsorption site can improve the applicability of previous approaches, and gas-phase bond energies correlate with adsorption energies for similarly bound adsorbates. Next, a general framework is presented for understanding and predicting adsorption through any atom. The energy of the adsorbate's highest occupied molecular orbital (HOMO) determines the strength of the repulsion between the adsorbate and the surface. Because adsorbates with similar HOMO energies behave similarly, their adsorption energies correlate. This can improve the efficiency of predictions, but more importantly it constrains catalyst design and suggests strategies for circumventing these constraints. Further, the behavior of adsorbates with dissimilar HOMO energies varies in a systematic way, allowing predictions of adsorption energy differences between any two adsorbates. These differences are also useful in surface design. In both of these cases, the dependence of adsorption energies on surface electronic properties is explored. This dependence is used to justify the unified treatments mentioned above, and is used to gain further insight into adsorption. The properties of the surface's d band and p band control variations in adsorption energy, as does the strength of the

  17. Comparative Study of Water Adsorption on a H(+) and K(+) Ion Exposed Mica Surface: Monte Carlo Simulation Study.

    PubMed

    Debbarma, Rousan; Malani, Ateeque

    2016-02-01

    Clay minerals are used in variety of applications ranging from composites to electronic devices. For their efficient use in such areas, understanding the effect of surface-active agents on interfacial properties is essential. We investigated the role of surface ions in the adsorption of water molecules by using a muscovite mica surface populated with two different, H(+) and K(+), surface ions. A series of grand canonical Monte Carlo (GCMC) simulations at various relative vapor pressures (p/p0) were performed to obtain the water structure and adsorption isotherm on the H(+)-exposed mica (H-mica) surface. The obtained results were compared to the recent simulation data of water adsorption on the K(+)-exposed mica (K-mica) surface reported by Malani and Ayyappa (Malani, A.; Ayappa, K. G. J. Phys. Chem. B 2009, 113, 1058-1067). Water molecules formed two prominent layers adjacent to the H-mica surface, whereas molecular layering was observed adjacent to the K-mica surface. The adsorption isotherm of water on the K-mica surface was characterized by three stages that corresponded to rapid adsorption in the initial regime below p/p0 = 0.1, followed by a linear development regime for p/p0 = 0.1-0.7 and rapid film thickening for p/p0 ≥ 0.7, whereas only latter two regimes were observed in the H-mica system. In addition, the film thickness of adsorbed water molecules for p/p0 < 0.7 was lower as compared to that for the K-mica surface and comparable beyond. The film thickness obtained from the MC simulations was in excellent agreement with the interferometry experimental data of Balmer et al. (Balmer, T. E.; Christenson, H. K.; Spencer, N. D.; Heuberger, M. Langmuir 2008, 24, 1566-1569). It was observed that the hydration behaviors of the two ions were completely different and depended on the size of their hydration shell and their ability to form hydrogen bonds. The behavior of water adsorption between these two cases was illustrated using the water density distribution

  18. Surface plasmon coupled chemiluminescence during adsorption of oxygen on magnesium surfaces

    SciTech Connect

    Hagemann, Ulrich; Nienhaus, Hermann

    2015-12-28

    The dissociative adsorption of oxygen molecules on magnesium surfaces represents a non-adiabatic reaction exhibiting exoelectron emission, chemicurrent generation, and weak chemiluminescence. Using thin film Mg/Ag/p-Si(111) Schottky diodes with 1 nm Mg on a 10-60 nm thick Ag layer as 2π-photodetectors, the chemiluminescence is internally detected with a much larger efficiency than external methods. The chemically induced photoyield shows a maximum for a Ag film thickness of 45 nm. The enhancement is explained by surface plasmon coupled chemiluminescence, i.e., surface plasmon polaritons are effectively excited in the Ag layer by the oxidation reaction and decay radiatively leading to the observed photocurrent. Model calculations of the maximum absorption in attenuated total reflection geometry support the interpretation. The study demonstrates the extreme sensitivity and the practical usage of internal detection schemes for investigating surface chemiluminescence.

  19. Adsorption Mechanism of Inhibitor and Guest Molecules on the Surface of Gas Hydrates.

    PubMed

    Yagasaki, Takuma; Matsumoto, Masakazu; Tanaka, Hideki

    2015-09-23

    The adsorption of guest and kinetic inhibitor molecules on the surface of methane hydrate is investigated by using molecular dynamics simulations. We calculate the free energy profile for transferring a solute molecule from bulk water to the hydrate surface for various molecules. Spherical solutes with a diameter of ∼0.5 nm are significantly stabilized at the hydrate surface, whereas smaller and larger solutes exhibit lower adsorption affinity than the solutes of intermediate size. The range of the attractive force is subnanoscale, implying that this force has no effect on the macroscopic mass transfer of guest molecules in crystal growth processes of gas hydrates. We also examine the adsorption mechanism of a kinetic hydrate inhibitor. It is found that a monomer of the kinetic hydrate inhibitor is strongly adsorbed on the hydrate surface. However, the hydrogen bonding between the amide group of the inhibitor and water molecules on the hydrate surface, which was believed to be the driving force for the adsorption, makes no contribution to the adsorption affinity. The preferential adsorption of both the kinetic inhibitor and the spherical molecules to the surface is mainly due to the entropic stabilization arising from the presence of cavities at the hydrate surface. The dependence of surface affinity on the size of adsorbed molecules is also explained by this mechanism.

  20. Nanometer polymer surface features: the influence on surface energy, protein adsorption and endothelial cell adhesion

    NASA Astrophysics Data System (ADS)

    Carpenter, Joseph; Khang, Dongwoo; Webster, Thomas J.

    2008-12-01

    Current small diameter (<5 mm) synthetic vascular graft materials exhibit poor long-term patency due to thrombosis and intimal hyperplasia. Tissue engineered solutions have yielded functional vascular tissue, but some require an eight-week in vitro culture period prior to implantation—too long for immediate clinical bedside applications. Previous in vitro studies have shown that nanostructured poly(lactic-co-glycolic acid) (PLGA) surfaces elevated endothelial cell adhesion, proliferation, and extracellular matrix synthesis when compared to nanosmooth surfaces. Nonetheless, these studies failed to address the importance of lateral and vertical surface feature dimensionality coupled with surface free energy; nor did such studies elicit an optimum specific surface feature size for promoting endothelial cell adhesion. In this study, a series of highly ordered nanometer to submicron structured PLGA surfaces of identical chemistry were created using a technique employing polystyrene nanobeads and poly(dimethylsiloxane) (PDMS) molds. Results demonstrated increased endothelial cell adhesion on PLGA surfaces with vertical surface features of size less than 18.87 nm but greater than 0 nm due to increased surface energy and subsequently protein (fibronectin and collagen type IV) adsorption. Furthermore, this study provided evidence that the vertical dimension of nanometer surface features, rather than the lateral dimension, is largely responsible for these increases. In this manner, this study provides key design parameters that may promote vascular graft efficacy.

  1. IR surface electromagnetic-wave measurement of hydrogen adsorption and surface reconstruction on W(100)

    SciTech Connect

    Hanssen, L.M.

    1985-01-01

    Both the clean and hydrogen covered W(100) surfaces are probed with an inhomogenous electromagnetic mode which is bound to the metal surface. This Surface Electromagnetic Wave (SEW) is generated from a plane-wave spectrum by means of a grating directly etched into the metal surface. A second grating, spaced about 5 cm from the first, transforms the SEW back into a plane wave infrared beam. Near room temperature, the temperature dependence of the magnitude of the SEW signal agrees with the Drude model prediction using the d.c. resistivity. At high temperatures (>1000K) however, SEW signal is attenuated to such a large extent that plane wave radiation generated at the first grating can be detected as well. The first SEW spectrum of surface reconstruction was observed upon hydrogen adsorption on a W(100) sample maintained near room temperature. The reconstruction of the W(100)-H surface is checked and calibrated through LEED observations and thermal desorption measurements. The SEW signal is found to follow a sigmoid curve as a function of coverage. Intensity changes as large as 30% of the clean surface value occur as the state of the W(100)-H surface changes. This extreme sensitivity of the SEW attentuation length to surface reconstruction is shown to be consistent with changes in the diffuse surface scattering component of the conduction electron scattering time.

  2. Determination of Reactive Surface Area of Melt Glass

    SciTech Connect

    Bourcier,W.L.; Roberts, S.; Smith, D.K.; Hulsey, S.; Newton,L.; Sawvel, A.; Bruton, C.; Papelis, C.; Um, W.; Russell, C. E.; Chapman,J.

    2000-10-01

    A comprehensive investigation of natural and manmade silicate glasses, and nuclear melt glass was undertaken in order to derive an estimate of glass reactive surface area. Reactive surface area is needed to model release rates of radionuclides from nuclear melt glass in the subsurface. Because of the limited availability of nuclear melt glasses, natural volcanic glass samples were collected which had similar textures and compositions as those of melt glass. A flow-through reactor was used to measure the reactive surface area of the analog glasses in the presence of simplified NTS site ground waters. A measure of the physical surface area of these glasses was obtained using the BET gas-adsorption method. The studies on analog glasses were supplemented by measurement of the surface areas of pieces of actual melt glass using the BET method. The variability of the results reflect the sample preparation and measurement techniques used, as well as textural heterogeneity inherent to these samples. Based on measurements of analog and actual samples, it is recommended that the hydraulic source term calculations employ a range of 0.001 to 0.01 m{sup 2}/g for the reactive surface area of nuclear melt glass.

  3. Sputter deposited bioceramic coatings: surface characterisation and initial protein adsorption studies using surface-MALDI-MS.

    PubMed

    Boyd, A R; Burke, G A; Duffy, H; Holmberg, M; O' Kane, C; Meenan, B J; Kingshott, P

    2011-01-01

    Protein adsorption onto calcium phosphate (Ca-P) bioceramics utilised in hard tissue implant applications has been highlighted as one of the key events that influences the subsequent biological response, in vivo. This work reports on the use of surface-matrix assisted laser desorption ionisation mass spectrometry (Surface-MALDI-MS) as a technique for the direct detection of foetal bovine serum (FBS) proteins adsorbed to hybrid calcium phosphate/titanium dioxide surfaces produced by a novel radio frequency (RF) magnetron sputtering method incorporating in situ annealing between 500°C and 700°C during deposition. XRD and XPS analysis indicated that the coatings produced at 700°C were hybrid in nature, with the presence of Ca-P and titanium dioxide clearly observed in the outer surface layer. In addition to this, the Ca/P ratio was seen to increase with increasing annealing temperature, with values of between 2.0 and 2.26 obtained for the 700°C samples. After exposure to FBS solution, surface-MALDI-MS indicated that there were significant differences in the protein patterns as shown by unique peaks detected at masses below 23.1 kDa for the different surfaces. These adsorbates were assigned to a combination of growth factors and lipoproteins present in serum. From the data obtained here it is evident that surface-MALDI-MS has significant utility as a tool for studying the dynamic nature of protein adsorption onto the surfaces of bioceramic coatings, which most likely plays a significant role in subsequent bioactivity of the materials.

  4. A combined QCM and XPS investigation of asphaltene adsorption on metal surfaces.

    PubMed

    Rudrake, Amit; Karan, Kunal; Horton, J Hugh

    2009-04-01

    To investigate asphaltene-metal interactions, a combined quartz crystal microbalance (QCM) and X-ray photoelectron spectroscopy (XPS) study of asphaltene adsorption on a gold surface was conducted. Adsorption experiments were conducted at 25 degrees C with solutions of asphaltenes in toluene at concentrations ranging from 50 to 1500 ppm. QCM measurements yielded information on the kinetics of adsorption and further assessment of the data allowed the estimation of equilibrium adsorption levels. XPS analysis of adsorbed and bulk asphaltene demonstrated the presence of carboxylic, thiophenic, sulfide, pyridinic and pyrrolic type functional groups. The intensity of the main carbon (C-H) peak was related to surface coverage of adsorbed asphaltene as a function of asphaltene concentration by a simple mathematical model. The mass adsorption data from the QCM experiments also allowed estimation of the surface coverage, which was compared to those from XPS analyses. Surface coverage estimates as a function of asphaltene concentration could be described by a Langmuir (type-I) isotherm. The free energy of asphaltene adsorption was estimated to be -26.8+/-0.1 and -27.3+/-0.1 kJ/mol from QCM and XPS data, respectively assuming asphaltene molar mass of 750 g/gmol. QCM and XPS data was also analyzed to estimate adsorbed layer thickness after accounting for surface coverage. The thickness of the adsorbed asphaltene estimated from both XPS and QCM data analyses ranged from 6-8 nm over the entire range of adsorption concentrations investigated.

  5. Adsorption of oxygen atom on MoSi2 (110) surface

    NASA Astrophysics Data System (ADS)

    Sun, S. P.; Li, X. P.; Wang, H. J.; Jiang, Y.; Yi, D. Q.

    2016-09-01

    The adsorption energy, structural relaxation and electronic properties of oxygen atom on MoSi2 (110) surface have been investigated by first-principles calculations. The energetic stability of MoSi2 low-index surfaces was analyzed, and the results suggested that MoSi2 (110) surface had energetically stability. The site of oxygen atom adsorbed on MoSi2 (110) surface were discussed, and the results indicated that the preference adsorption site of MoSi2 (110) surface for oxygen atom was H site (hollow position). Our calculated work should help to understand further the interaction between oxygen atoms and MoSi2 surfaces.

  6. Selective homopolymer adsorption on structured surfaces as a model for pattern recognition.

    PubMed

    Gemünden, Patrick; Behringer, Hans

    2013-01-14

    Homopolymer adsorption onto chemically structured periodic surfaces and its potential for pattern recognition is investigated using Monte Carlo simulations. To analyze the surface-induced selective adsorption on a fundamental geometric level polymer chains are represented by freely jointed chains with a fixed bond length whose monomers are attracted by the sites of regular lattice patterns. The structural properties of the adsorbed low-temperature state are comprehensively discussed for different lattices by looking at the radius of gyration and the inter bond angle distributions. These observables show a non-trivial dependence on the commensurability of characteristic lengths given by the lattice constant and by the bond length. Reasons for this behavior are given by exploiting geometric and entropic arguments. The findings are examined in the context of pattern recognition by polymer adsorption. Furthermore, the adsorption transition is discussed briefly. For certain incommensurable situations the adsorption occurs in two steps due to entropic restrictions.

  7. On the hydrogen adsorption and dissociation on Cu surfaces and nanorows

    NASA Astrophysics Data System (ADS)

    Álvarez-Falcón, Leny; Viñes, Francesc; Notario-Estévez, Almudena; Illas, Francesc

    2016-04-01

    Here we present a thorough density functional theory study, including and excluding dispersive forces interaction description, on the adsorption and dissociation of H2 molecule on the low-index Miller Cu (111), (100), and (110) surfaces and two different surface Cu nanorows, all displaying a different number of surface nearest neighbors, nn. The computational setup has been optimized granting an accuracy below 0.04 eV. Surface and nanorow energies-for which a new methodology to extract them is presented- are found to follow the nn number. However, the adsorption strength is found not to. Thus, the adsorption energies seem to be governed by a particular orbital ↔ band interaction rather than by the simple nn surface saturation. The van der Waals (vdW) forces are found to play a key role in the adsorption of H2, and merely an energetic adjustment on chemisorbed H adatoms. Neither clear trends are observed for H2 and H adsorption energies, and H2 dissociation energy with respect nn, and nor Brønsted-Evans-Polanyi, making H2 adsorption and dissociation a trend outlier compared to other cases. H2 is found to adsorb and dissociate on Cu(100) surface. On the Cu(111) surface, the rather small H2 adsorption energy would prevent H2 dissociation, regardless if it is thermodynamically driven. On Cu(110) surface, the H2 dissociation process would be endothermic and achievable if adsorption energy is released on surpassing the dissociation energy barrier. On low-coordinated sites on Cu nanorows, vdW plays a key role in the H2 dissociation process, which otherwise is found to be endothermic. Indeed, dispersive forces turn the process markedly exothermic. Nanoparticle Cu systems must display Cu(100) surfaces or facets in order to dissociate H2, vital in many hydrogenation processes.

  8. Periodic Density Functional Theory Study of Water Adsorption on the a-Quartz (101) Surface.

    SciTech Connect

    Bandura, Andrei V.; Kubicki, James D.; Sofo, Jorge O.

    2011-01-01

    Plane wave density functional theory (DFT) calculations have been performed to study the atomic structure, preferred H2O adsorption sites, adsorption energies, and vibrational frequencies for water adsorption on the R-quartz (101) surface. Surface energies and atomic displacements on the vacuum-reconstructed, hydrolyzed, and solvated surfaces have been calculated and compared with available experimental and theoretical data. By considering different initial positions of H2O molecules, the most stable structures of water adsorption at different coverages have been determined. Calculated H2O adsorption energies are in the range -55 to -65 kJ/mol, consistent with experimental data. The lowest and the highest O-H stretching vibrational bands may be attributed to different states of silanol groups on the watercovered surface. The dissociation energy of the silanol group on the surface covered by the adsorption monolayer is estimated to be 80 kJ/mol. The metastable states for the protonated surface bridging O atoms (Obr), which may lead to hydrolysis of siloxane bonds, have been investigated. The calculated formation energy of a Q2 center from a Q3 center on the (101) surface with 2/3 dense monolayer coverage is equal to 70 kJ/mol which is in the range of experimental activation energies for quartz dissolution.

  9. Study of water adsorption on activated carbons with different degrees of surface oxidation

    SciTech Connect

    Salame, I.I.; Bandosz, T.J. |

    1999-02-15

    A carbon of wood origin was oxidized with different oxidizing agents (nitric acid, hydrogen peroxide, and ammonium persulfate). The microstructural properties of the starting material and the oxidized samples were characterized using sorption of nitrogen. The surface acidity was determined using Boehm titration and potentiometric titration. The changes in the surface chemistry were also studied by diffuse reflectance FTIR. Water adsorption isotherms were measured at three different temperatures close to ambient (relative pressure from 0.001 to 0.3). From the isotherms the heats of adsorption were calculated using a virial equation. The results indicated that the isosteric heats of water adsorption are affected by the surface heterogeneity only at low surface coverage. In all cases the limiting heat of adsorption was equal to the heat of water condensation (45 kJ/mol).

  10. Laboratory Studies of Perchlorate Deliquescence and Water Adsorption at the Surface of Mars with Raman Scattering

    NASA Astrophysics Data System (ADS)

    Nikolakakos, G.; Whiteway, J. A.

    2016-09-01

    Laser Raman scattering has been applied in order to experimentally study the exchange of water between the surface and atmosphere on Mars. Results show that both deliquescence of salts and adsorption by minerals are likely currently active processes.

  11. Effectiveness of charged noncovalent polymer coatings against protein adsorption to silica surfaces studied by evanescent-wave cavity ring-down spectroscopy and capillary electrophoresis.

    PubMed

    Haselberg, Rob; van der Sneppen, Lineke; Ariese, Freek; Ubachs, Wim; Gooijer, Cees; de Jong, Gerhardus J; Somsen, Govert W

    2009-12-15

    Protein adsorption to silica surfaces is a notorious problem in analytical separations. Evanescent-wave cavity ring-down spectroscopy (EW-CRDS) and capillary electrophoresis (CE) were employed to investigate the capability of positively charged polymer coatings to minimize the adsorption of basic proteins. Adsorption of cytochrome c (cyt c) to silica coated with a single layer of polybrene (PB), or a triple layer of PB, dextran sulfate (DS), and PB, was studied and compared to bare silica. Direct analysis of silica surfaces by EW-CRDS revealed that both coatings effectively reduce irreversible protein adsorption. Significant adsorption was observed only for protein concentrations above 400 microM, whereas the PB-DS-PB coating was shown to be most effective and stable. CE analyses of cyt c were performed with and without the respective coatings applied to the fused-silica capillary wall. Monitoring of the electroosmotic flow and protein peak areas indicated a strong reduction of irreversible protein adsorption by the positively charged coatings. Determination of the electrophoretic mobility and peak width of cyt c revealed reversible protein adsorption to the PB coating. It is concluded that the combination of results from EW-CRDS and CE provides highly useful information on the adsorptive characteristics of bare and coated silica surfaces toward basic proteins.

  12. Adsorption of oxazole and isoxazole on BNNT surface: A DFT study

    NASA Astrophysics Data System (ADS)

    Kaur, Jasleen; Singla, Preeti; Goel, Neetu

    2015-02-01

    The adsorption behavior of oxazole and isoxazole heterocycles over the (6,0) zigzag and (5,5) armchair boron nitride nanotube (BNNT) has been studied within the formalism of density functional theory (DFT). The adsorption energies, the frontier molecular orbital (FMO) analysis and the structural changes at the adsorption site are indicative of covalent adsorption on the zigzag BNNT surface, while the adsorption is physical in nature on the armchair BNNT surface. The role of solvent in improving the adsorption properties over the BNNT surface is elucidated by reoptimizing the structures in aqueous phase. The solvation energy is indicative of remarkable increase in the solubility of BNNTs after adsorption of heterocyclic rings. The Density of states (DOS) Plots, natural bond orbital (NBO) analysis and the quantum molecular descriptors (QMD) are witness to the substantial changes in the electronic properties of the BNNT systems following the attachment of these heterocycles with the tube surface. The study envisages the functionalization of the BNNT as well as its applicability as carrier of the drugs containing heterocyclic rings oxazole and isoxazole with marked sensitivity to the type of adsorbate and the adsorbent.

  13. Effect of surface property of activated carbon on adsorption of nitrate ion.

    PubMed

    Iida, Tatsuya; Amano, Yoshimasa; Machida, Motoi; Imazeki, Fumio

    2013-01-01

    In this study, the removal of acidic functional groups and introduction of basic groups/sites on activated carbons (ACs) by outgassing and ammonia gas treatment were respectively carried out to enhance the nitrate ion adsorption in aqueous solution. Then, the relationships between nitrate ion adsorption and solution pH as well as surface charge of AC were investigated to understand the basic mechanisms of nitrate ion adsorption by AC. The result showed that the nitrate ion adsorption depended on the equilibrium solution pH (pHe) and the adsorption amount was promoted with decreasing pHe. The ACs treated by outgassing and ammonia gas treatment showed larger amount of nitrate ion adsorption than that by untreated AC. These results indicated that, since basic groups/sites could adsorb protons in the solution, the AC surface would be charged positively, and that the nitrate ion would be electrically interacted with positively charged carbon surface. Accordingly, it was concluded that basic groups/sites on the surface of AC could promote nitrate ion adsorption.

  14. Surface structural ion adsorption modeling of competitive binding of oxyanions by metal (hydr)oxides

    SciTech Connect

    Hiemstra, T.; Riemsdijk, W.H. van

    1999-02-01

    An important challenge in surface complexation models (SCM) is to connect the molecular microscopic reality to macroscopic adsorption phenomena. This study elucidates the primary factor controlling the adsorption process by analyzing the adsorption and competition of PO{sub 4}, AsO{sub 4}, and SeO{sub 3}. The authors show that the structure of the surface-complex acting in the dominant electrostatic field can be ascertained as the primary controlling adsorption factor. The surface species of arsenate are identical with those of phosphate and the adsorption behavior is very similar. On the basis of the selenite adsorption, The authors show that the commonly used 1pK models are incapable to incorporate in the adsorption modeling the correct bidentate binding mechanism found by spectroscopy. The use of the bidentate mechanism leads to a proton-oxyanion ratio and corresponding pH dependence that are too large. The inappropriate intrinsic charge attribution to the primary surface groups and the condensation of the inner sphere surface complex to a point charge are responsible for this behavior of commonly used 2pK models. Both key factors are differently defined in the charge distributed multi-site complexation (CD-MUSIC) model and are based in this model on a surface structural approach. The CD-MUSIC model can successfully describe the macroscopic adsorption phenomena using the surface speciation and binding mechanisms as found by spectroscopy. The model is also able to predict the anion competition well. The charge distribution in the interface is in agreement with the observed structure of surface complexes.

  15. Glutathione-coated luminescent gold nanoparticles: a surface ligand for minimizing serum protein adsorption.

    PubMed

    Vinluan, Rodrigo D; Liu, Jinbin; Zhou, Chen; Yu, Mengxiao; Yang, Shengyang; Kumar, Amit; Sun, Shasha; Dean, Andrew; Sun, Xiankai; Zheng, Jie

    2014-08-13

    Ultrasmall glutathione-coated luminescent gold nanoparticles (GS-AuNPs) are known for their high resistance to serum protein adsorption. Our studies show that these NPs can serve as surface ligands to significantly enhance the physiological stability and lower the serum protein adsorption of superparamagnetic iron oxide nanoparticles (SPIONs), in addition to rendering the NPs the luminescence property. After the incorporation of GS-AuNPs onto the surface of SPIONs to form the hybrid nanoparticles (HBNPs), these SPIONs' protein adsorption was about 10-fold lower than those of the pure glutathione-coated SPIONs suggesting that GS-AuNPs are capable of providing a stealth effect against serum proteins.

  16. Adsorption of PTCDA on Si(001) − 2 × 1 surface

    SciTech Connect

    Suzuki, Takayuki Yagyu, Kazuma; Tochihara, Hiroshi; Yoshimoto, Yoshihide

    2015-03-14

    Adsorption structures of the 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) molecule on the clean Si(001) − 2 × 1 surface were investigated using scanning tunneling microscopy (STM) experiments in conjunction with first principles theoretical calculations. Four dominant adsorption structures were observed in the STM experiments and their atomic coordinates on the Si(001) surface were determined by comparison between the experimental STM images and the theoretical simulations. Maximizing the number of the Si—O bonds is more crucial than that of the Si—C bonds in the PTCDA adsorption.

  17. Approaches to surface complexation modeling of Uranium(VI) adsorption on aquifer sediments

    USGS Publications Warehouse

    Davis, J.A.; Meece, D.E.; Kohler, M.; Curtis, G.P.

    2004-01-01

    Uranium(VI) adsorption onto aquifer sediments was studied in batch experiments as a function of pH and U(VI) and dissolved carbonate concentrations in artificial groundwater solutions. The sediments were collected from an alluvial aquifer at a location upgradient of contamination from a former uranium mill operation at Naturita, Colorado (USA). The ranges of aqueous chemical conditions used in the U(VI) adsorption experiments (pH 6.9 to 7.9; U(VI) concentration 2.5 ?? 10-8 to 1 ?? 10-5 M; partial pressure of carbon dioxide gas 0.05 to 6.8%) were based on the spatial variation in chemical conditions observed in 1999-2000 in the Naturita alluvial aquifer. The major minerals in the sediments were quartz, feldspars, and calcite, with minor amounts of magnetite and clay minerals. Quartz grains commonly exhibited coatings that were greater than 10 nm in thickness and composed of an illite-smectite clay with occluded ferrihydrite and goethite nanoparticles. Chemical extractions of quartz grains removed from the sediments were used to estimate the masses of iron and aluminum present in the coatings. Various surface complexation modeling approaches were compared in terms of the ability to describe the U(VI) experimental data and the data requirements for model application to the sediments. Published models for U(VI) adsorption on reference minerals were applied to predict U(VI) adsorption based on assumptions about the sediment surface composition and physical properties (e.g., surface area and electrical double layer). Predictions from these models were highly variable, with results overpredicting or underpredicting the experimental data, depending on the assumptions used to apply the model. Although the models for reference minerals are supported by detailed experimental studies (and in ideal cases, surface spectroscopy), the results suggest that errors are caused in applying the models directly to the sediments by uncertain knowledge of: 1) the proportion and types of

  18. Accelerated Molecular Dynamics Study of the Effects of Surface Hydrophilicity on Protein Adsorption.

    PubMed

    Mücksch, Christian; Urbassek, Herbert M

    2016-09-13

    The adsorption of streptavidin is studied on two surfaces, graphite and titanium dioxide, using accelerated molecular dynamics. Adsorption on graphite leads to strong conformational changes while the protein spreads out over the surface. Interestingly, also adsorption on the highly hydrophilic rutile surface induces considerable spreading of the protein. We pin down the cause for this unfolding to the interaction of the protein with the ordered water layers above the rutile surface. For special orientations, the protein penetrates the ordered water layers and comes into direct contact with the surface where the positively charged amino acids settle in places adjacent to the negatively charged top surface atom layer of rutile. We conclude that for both surface materials studied, streptavidin changes its conformation so strongly that it loses its potential for binding biotin. Our results are in good qualitative agreement with available experimental studies. PMID:27533302

  19. Surface chemistry of ferrihydrite: Part 2. Kinetics of arsenate adsorption and coprecipitation

    USGS Publications Warehouse

    Fuller, C.C.; Dadis, J.A.; Waychunas, G.A.

    1993-01-01

    The kinetics of As(V) adsorption by ferrihydrite was investigated in coprecipitation and postsynthesis adsorption experiments conducted in the pH range 7.5-9.0. In coprecipitation experiments, As(V) was present in solution during the hydrolysis and precipitation of iron. In adsorption experiments, a period of rapid (<5 min) As(V) uptake from solution was followed by continued uptake for at least eight days, as As(V) diffused to adsorption sites on ferrihydrite surfaces within aggregates of colloidal particles. The time dependence of As(V) adsorption is well described by a general model for diffusion into a sphere if a subset of surface sites located near the exterior of aggregates is assumed to attain adsorptive equilibrium rapidly. The kinetics of As(V) desorption after an increase in pH were also consistent with diffusion as a rate-limiting process. Aging of pure ferrihydrite prior to As(V) adsorption caused a decrease in adsorption sites on the precipitate owing to crystallite growth. In coprecipitation experiments, the initial As(V) uptake was significantly greater than in post-synthesis adsorption experiments, and the rate of uptake was not diffusion limited because As(V) was coordinated by surface sites before crystallite growth and coagulation processes could proceed. After the initial adsorption, As(V) was slowly released from coprecipitates for at least one month, as crystallite growth caused desorption of As(V). Adsorption densities as high as 0.7 mole As(V) per mole of Fe were measured in coprecipitates, in comparison to 0.25 mole As(V) per mole of Fe in post-synthesis adsorption experiments. Despite the high Concentration of As(V) in the precipitates, EXAFS spectroscopy (Waychunas et al., 1993) showed that neither ferric arsenate nor any other As-bearing surface precipitate or solid solution was formed. The high adsorption densities are possible because the ferrihydrite particles are extremely small, approaching the size of small dioctahedral chains at

  20. Polymer adsorption phenomena at the surface of delayed tack toner images in a photopolymer proofing concept

    NASA Astrophysics Data System (ADS)

    Pinto, Gerard R.; Fine, Laurence D.

    1992-05-01

    The photopolymers discussed here utilize a photo-initiated crosslinking mechanism to detackify the imaged regions. The latent image can be rendered visible by applying micron- sized pigmented toner particles to the tacky non-imaged areas of the photopolymer. Because the toner contains a solid plasticizer, it serves as a latent ink particle; heating activates the delayed tack state, characterized by prolonged adhesiveness. The creation of a liquid ink enables the rendered image to be printed onto a paper substrate. Photopolymer components, migrating into the melted toner layer, preferentially adsorb to the polymer/air interface after printing to paper, thus influencing the delayed tack adhesive state, during which excess plasticizer crystallizes. We examine competitive adsorption phenomena at the polymer solution/air interface, via a model four-component system, containing two oligomeric surfactant molecules from the film, both characterized by ethylene-oxide linkages, but distinguished by the fact that one, is linear, while the second, is composed of three branches. The concentrations of these long-chain constituents are varied in an otherwise constant bulk polymer solution of triphenylphosphate and the toner polymer, simulating typical compositions in the actual melted toner layer. We apply two techniques of surface analysis, SIMS and ESCA (XPS), in order to reveal the identity of the adsorbing film species. Although both molecules are capable of a surface excess, the structure imposed upon the interfacial region is clearly different, depending on the excess surfactant at the surface. This difference is explained by assuming that the linear molecule lies flat on the surface while the branched oligomer adsorbs vertically. Specific SIMS/ESCA signals exhibit spectral intensities that are nonlinearly proportional to the bulk oligomer concentration; from the shapes of the adsorption isotherms, we deduce that the single chain surfactant is displaced at the surface by

  1. Surface energetics of alkaline-earth metal oxides: Trends in stability and adsorption of small molecules

    NASA Astrophysics Data System (ADS)

    Bajdich, Michal; Nørskov, Jens K.; Vojvodic, Aleksandra

    2015-04-01

    We present a systematic theoretical investigation of the surface properties, stability, and reactivity of rocksalt type alkaline-earth metal oxides including MgO, CaO, SrO, and BaO. The accuracy of commonly used exchange-correlation density functionals (LDA, PBE, RPBE, PBEsol, BEEF-vdW, and hybrid HSE) and random-phase approximation (RPA) is evaluated and compared to existing experimental values. Calculated surface energies of the four most stable surface facets under vacuum conditions, the (100) surface, the metal and oxygen terminated octopolar (111), and the (110) surfaces, exhibit a monotonic increase in stability from MgO to BaO. On the MgO(100) surface, adsorption of CO, NO, and CH4 is characterized by physisorption while H2O chemisorbs, which is in agreement with experimental findings. We further use the on-top metal adsorption of CO and NO molecules to map out the surface energetics of each alkaline-earth metal oxide surface. The considered functionals all qualitatively predict similar adsorption energy trends. The ordering between the adsorption energies on different surface facets can be attributed to differences in the local geometrical surface structure and the electronic structure of the metal constituent of the alkaline-earth metal oxide. The striking observation that CO adsorption strength is weaker than NO adsorption on the (100) terraces as the period of the alkaline-earth metal in the oxide increases is analyzed in detail in terms of charge redistribution within the σ and π channels of adsorbates. Finally, we also present oxygen adsorption and oxygen vacancy formation energies in these oxide systems.

  2. Ferroelectric triggering of carbon monoxide adsorption on lead zirco-titanate (001) surfaces

    PubMed Central

    Tănase, Liviu Cristian; Apostol, Nicoleta Georgiana; Abramiuc, Laura Elena; Tache, Cristian Alexandru; Hrib, Luminița; Trupină, Lucian; Pintilie, Lucian; Teodorescu, Cristian Mihail

    2016-01-01

    Atomically clean lead zirco-titanate PbZr0.2Ti0.8O3 (001) layers exhibit a polarization oriented inwards P(−), visible by a band bending of all core levels towards lower binding energies, whereas as introduced layers exhibit P(+) polarization under air or in ultrahigh vacuum. The magnitude of the inwards polarization decreases when the temperature is increased at 700 K. CO adsorption on P(−) polarized surfaces saturates at about one quarter of a monolayer of carbon, and occurs in both molecular (oxidized) and dissociated (reduced) states of carbon, with a large majority of reduced state. The sticking of CO on the surface in ultrahigh vacuum is found to be directly related to the P(−) polarization state of the surface. A simple electrostatic mechanism is proposed to explain these dissociation processes and the sticking of carbon on P(−) polarized areas. Carbon desorbs also when the surface is irradiated with soft X-rays. Carbon desorption when the polarization is lost proceeds most probably in form of CO2. Upon carbon desorption cycles, the ferroelectric surface is depleted in oxygen and at some point reverses its polarization, owing to electrons provided by oxygen vacancies which are able to screen the depolarization field produced by positive fixed charges at the surface. PMID:27739461

  3. Ferroelectric triggering of carbon monoxide adsorption on lead zirco-titanate (001) surfaces

    NASA Astrophysics Data System (ADS)

    Tănase, Liviu Cristian; Apostol, Nicoleta Georgiana; Abramiuc, Laura Elena; Tache, Cristian Alexandru; Hrib, Luminița; Trupină, Lucian; Pintilie, Lucian; Teodorescu, Cristian Mihail

    2016-10-01

    Atomically clean lead zirco-titanate PbZr0.2Ti0.8O3 (001) layers exhibit a polarization oriented inwards P(‑), visible by a band bending of all core levels towards lower binding energies, whereas as introduced layers exhibit P(+) polarization under air or in ultrahigh vacuum. The magnitude of the inwards polarization decreases when the temperature is increased at 700 K. CO adsorption on P(‑) polarized surfaces saturates at about one quarter of a monolayer of carbon, and occurs in both molecular (oxidized) and dissociated (reduced) states of carbon, with a large majority of reduced state. The sticking of CO on the surface in ultrahigh vacuum is found to be directly related to the P(‑) polarization state of the surface. A simple electrostatic mechanism is proposed to explain these dissociation processes and the sticking of carbon on P(‑) polarized areas. Carbon desorbs also when the surface is irradiated with soft X-rays. Carbon desorption when the polarization is lost proceeds most probably in form of CO2. Upon carbon desorption cycles, the ferroelectric surface is depleted in oxygen and at some point reverses its polarization, owing to electrons provided by oxygen vacancies which are able to screen the depolarization field produced by positive fixed charges at the surface.

  4. Separation and concentration of natural products by fast forced adsorption using well-dispersed velvet-like graphitic carbon nitride with response surface methodology optimisation.

    PubMed

    Ding, Xinru; Zhu, Jun; Zhang, Yue; Xia, Qian; Bi, Wentao; Yang, Xiaodi; Yang, Jinfei

    2016-07-01

    Well-dispersed velvet-like graphitic carbon nitride nanoparticles with a large surface area were prepared and utilized for separation and concentration of bioactive compounds from fruit extracts by fast (20s) forced adsorption. The large surface area, enhanced non-covalent interactions of this nanoparticle with bioactive compounds and good dispersity in different solvents benefited its application as a good sorbent. To evaluate their adsorption capabilities, these carbon nitride nanoparticles were used for separation and concentration of flavonoids from fruit extracts by a forced-adsorption dispersive solid phase extraction method. The combined use of this nanoparticle and our experimental conditions showed excellent precision (3.6-4.7%) and sensitivity (limits of detection (S/N=3): 0.6-3.75ng/mL). This research provides an alternative strategy to prepare suitable sorbents for adsorption, separation and concentration of various compounds from different extracts. PMID:27154656

  5. Separation and concentration of natural products by fast forced adsorption using well-dispersed velvet-like graphitic carbon nitride with response surface methodology optimisation.

    PubMed

    Ding, Xinru; Zhu, Jun; Zhang, Yue; Xia, Qian; Bi, Wentao; Yang, Xiaodi; Yang, Jinfei

    2016-07-01

    Well-dispersed velvet-like graphitic carbon nitride nanoparticles with a large surface area were prepared and utilized for separation and concentration of bioactive compounds from fruit extracts by fast (20s) forced adsorption. The large surface area, enhanced non-covalent interactions of this nanoparticle with bioactive compounds and good dispersity in different solvents benefited its application as a good sorbent. To evaluate their adsorption capabilities, these carbon nitride nanoparticles were used for separation and concentration of flavonoids from fruit extracts by a forced-adsorption dispersive solid phase extraction method. The combined use of this nanoparticle and our experimental conditions showed excellent precision (3.6-4.7%) and sensitivity (limits of detection (S/N=3): 0.6-3.75ng/mL). This research provides an alternative strategy to prepare suitable sorbents for adsorption, separation and concentration of various compounds from different extracts.

  6. Single-nanoparticle near-infrared surface plasmon resonance microscopy for real-time measurements of DNA hybridization adsorption.

    PubMed

    Halpern, Aaron R; Wood, Jennifer B; Wang, Yong; Corn, Robert M

    2014-01-28

    A novel 814 nm near-infrared surface plasmon resonance (SPR) microscope is used for the real-time detection of the sequence-selective hybridization adsorption of single DNA-functionalized gold nanoparticles. The objective-coupled, high numerical aperture SPR microscope is capable of imaging in situ the adsorption of single polystyrene and gold particles with diameters ranging from 450 to 20 nm onto a 90 μm × 70 μm area of a gold thin film with a time resolution of approximately 1-3 s. Initial real-time SPR imaging (SPRI) measurements were performed to detect the accumulation of 40 nm gold nanoparticles for 10 min onto a gold thin film functionalized with a 100% complementary DNA surface at concentrations from 5 pM to 100 fM by counting individual particle binding events. A 100% noncomplementary DNA surface exhibited virtually no nanoparticle adsorption. In contrast, in a second set of SPRI measurements, two component complementary/noncomplementary mixed DNA monolayers that contained a very small percentage of complementary sequences ranging from 0.1 to 0.001%, showed both permanent and transient hybridization adsorption of the gold nanoparticles that could be tracked both temporally and spatially with the SPR microscope. These experiments demonstrate that SPR imaging measurements of single biofunctionalized nanoparticles can be incorporated into bioaffinity biosensing methods at subpicomolar concentrations.

  7. Molecular simulation of fibronectin adsorption onto polyurethane surfaces

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Polyethylene glycol-based polyurethanes have been widely used in biomedical applications, however are prone to swelling. A natural polyol, castor oil can be incorporated into these polyurethanes to control the degree of the swelling, which alters mechanical properties and protein adsorption characte...

  8. Predicting enzyme adsorption to lignin films by calculating enzyme surface hydrophobicity.

    PubMed

    Sammond, Deanne W; Yarbrough, John M; Mansfield, Elisabeth; Bomble, Yannick J; Hobdey, Sarah E; Decker, Stephen R; Taylor, Larry E; Resch, Michael G; Bozell, Joseph J; Himmel, Michael E; Vinzant, Todd B; Crowley, Michael F

    2014-07-25

    The inhibitory action of lignin on cellulase cocktails is a major challenge to the biological saccharification of plant cell wall polysaccharides. Although the mechanism remains unclear, hydrophobic interactions between enzymes and lignin are hypothesized to drive adsorption. Here we evaluate the role of hydrophobic interactions in enzyme-lignin binding. The hydrophobicity of the enzyme surface was quantified using an estimation of the clustering of nonpolar atoms, identifying potential interaction sites. The adsorption of enzymes to lignin surfaces, measured using the quartz crystal microbalance, correlates to the hydrophobic cluster scores. Further, these results suggest a minimum hydrophobic cluster size for a protein to preferentially adsorb to lignin. The impact of electrostatic contribution was ruled out by comparing the isoelectric point (pI) values to the adsorption of proteins to lignin surfaces. These results demonstrate the ability to predict enzyme-lignin adsorption and could potentially be used to design improved cellulase cocktails, thus lowering the overall cost of biofuel production. PMID:24876380

  9. Predicting Enzyme Adsorption to Lignin Films by Calculating Enzyme Surface Hydrophobicity*

    PubMed Central

    Sammond, Deanne W.; Yarbrough, John M.; Mansfield, Elisabeth; Bomble, Yannick J.; Hobdey, Sarah E.; Decker, Stephen R.; Taylor, Larry E.; Resch, Michael G.; Bozell, Joseph J.; Himmel, Michael E.; Vinzant, Todd B.; Crowley, Michael F.

    2014-01-01

    The inhibitory action of lignin on cellulase cocktails is a major challenge to the biological saccharification of plant cell wall polysaccharides. Although the mechanism remains unclear, hydrophobic interactions between enzymes and lignin are hypothesized to drive adsorption. Here we evaluate the role of hydrophobic interactions in enzyme-lignin binding. The hydrophobicity of the enzyme surface was quantified using an estimation of the clustering of nonpolar atoms, identifying potential interaction sites. The adsorption of enzymes to lignin surfaces, measured using the quartz crystal microbalance, correlates to the hydrophobic cluster scores. Further, these results suggest a minimum hydrophobic cluster size for a protein to preferentially adsorb to lignin. The impact of electrostatic contribution was ruled out by comparing the isoelectric point (pI) values to the adsorption of proteins to lignin surfaces. These results demonstrate the ability to predict enzyme-lignin adsorption and could potentially be used to design improved cellulase cocktails, thus lowering the overall cost of biofuel production. PMID:24876380

  10. DFT MODELING OF BENZOYL PEROXIDE ADSORPTION ON α-Cr2O3 (0001) SURFACE

    NASA Astrophysics Data System (ADS)

    Maldonado, Frank; Stashans, Arvids

    2016-04-01

    Density functional theory (DFT) within the generalized gradient approximation (GGA) has been used to investigate possible adsorption configurations of benzoyl peroxide (BPO) molecule on the chromium oxide (α-Cr2O3) (0001) surface. Two configurations are found to lead to the molecular adsorption with corresponding adsorption energies being equal to -0.16 and -0.48eV, respectively. Our work describes in detail atomic displacements for both crystalline surface and adsorbate as well as discusses electronic and magnetic properties of the system. The most favorable adsorption case is found when the chemical bond between one of the molecular oxygens and one of the surface Cr atoms has been formed.

  11. Adsorption of heterobifunctional 4-nitrophenol on the Ge(100)-2 × 1 surface

    NASA Astrophysics Data System (ADS)

    Shong, Bonggeun; Hellstern, Thomas R.; Bent, Stacey F.

    2016-08-01

    We report the adsorption chemistry of a heterobifunctional molecule, 4-nitrophenol, on the Ge(100)-2 × 1 surface. X-ray photoelectron and infrared spectroscopy experiments and density functional theory calculations were used to determine the adsorption products. The results show that 4-nitrophenol reacts with the Ge surface through either one or both of the sbnd OH or sbnd NO2 functionalities. It was found that the fraction of dually and singly tethered adsorbates varies according to reaction conditions: namely, singly tethered adsorbates are favored at higher adsorbate coverages and lower adsorption temperatures. These variations are explained by a two-step adsorption mechanism for 4-nitrophenol, in which geometrical limitations of the adsorbates on the surface affect the product distribution.

  12. Adsorption rate of phenol from aqueous solution onto organobentonite: surface diffusion and kinetic models.

    PubMed

    Ocampo-Perez, Raul; Leyva-Ramos, Roberto; Mendoza-Barron, Jovita; Guerrero-Coronado, Rosa M

    2011-12-01

    The concentration decay curves for the adsorption of phenol on organobentonite were obtained in an agitated tank batch adsorber. The experimental adsorption rate data were interpreted with diffusional models as well as first-order, second-order and Langmuir kinetic models. The surface diffusion model adjusted the data quite well, revealing that the overall rate of adsorption was controlled by surface diffusion. Furthermore, the surface diffusion coefficient increased raising the mass of phenol adsorbed at equilibrium and was independent of the particle diameter in the range 0.042-0.0126 cm. It was demonstrated that the overall rate of adsorption was essentially not affected by the external mass transfer. The second-order and the Langmuir kinetic models fitted the experimental data quite well; however, the kinetic constants of both models varied without any physical meaning while increasing the particle size and the mass of phenol adsorbed at equilibrium.

  13. High-temperature adsorption of n-octane, benzene, and chloroform onto silica gel surface

    SciTech Connect

    Bilinski, B.

    2000-05-01

    The adsorption properties of silica gel surface for compounds differing in types of intermolecular interactions were studied under conditions in which the same silica was investigated by means of a gas phase titration method, i.e., at high temperature and low surface coverage. Adsorption isotherms of n-octane, benzene, and chloroform were determined at 373, 363, and 353 K. Based on these isotherms the isosteric heat of adsorption was calculated. Moreover, the adsorption energy distribution function and the derivative of film pressure with respect to the adsorbed amount were computed from the isotherms determined at 373 K. The obtained results were compared to those determined by gas phase titration. It was stated that on the dependencies of film pressure derivative some linear sections appeared that corresponded to the inflection points on gas phase titration curves. The results are discussed in terms of both the type and the strength of surface-molecule interactions.

  14. Adsorption at the liquid-vapor surface of a binary liquid mixture

    NASA Astrophysics Data System (ADS)

    Whitmer, J. K.; Kiselev, S. B.; Law, B. M.

    2005-11-01

    In a binary liquid mixture, the component possessing the lowest surface tension preferentially adsorbs at the liquid-vapor surface. In the past this adsorption behavior has been extensively investigated for critical binary liquid mixtures near the mixture's critical temperature Tc. In this fluctuation-dominated regime the adsorption is described by a universal function of the dimensionless depth z /ξ where ξ is the bulk correlation length. Fewer studies have quantitatively examined adsorption for off-critical mixtures because, in this case, one must carefully account for both the bulk and surface crossover from the fluctuation-dominated regime (close to Tc) to the mean-field dominated regime (far from Tc). In this paper we compare extensive liquid-vapor ellipsometric adsorption measurements for the mixture aniline+cyclohexane at a variety of critical and noncritical compositions with the crossover theory of Kiselev and co-workers [J. Chem. Phys. 112, 3370 (2000)].

  15. Mechanistic investigation of the on-surface enzymatic digestion (oSED) protein adsorption detection method using targeted mass spectrometry.

    PubMed

    Undin, Torgny; Dahlin, Andreas; Hörnaeus, Katarina; Bergquist, Jonas; Lind, Sara Bergström

    2016-03-01

    This study describes our efforts to study some of the mechanistic aspects of the earlier established on-surface enzymatic digestion (oSED) method. In a multitude of application areas, it has become important to be able to fully characterize and understand selective protein adsorption to biomaterial surfaces for various applications, including biomedicine (implants), nanotechnology (microchip surfaces and sensors) and materials sciences. Herein, the investigation of the mechanistic aspects was based on microdialysis catheter tubes that were flushed with controlled protein solutions mimicking the extracellular fluid of the brain. The protein adsorption properties were monitored using high-resolution liquid chromatography tandem mass spectrometry (LC-MS/MS) with a targeted method. The temporally resolved results show that most proteins stay adsorbed onto the surface during the entire digestion process and are only cut away piece by piece, whereas smaller proteins and peptides seem to desorb rather easily from the surface. This information will simplify the interpretation of data generated using the oSED method and can also be used for the characterization of the physicochemical properties controlling the adsorption of individual proteins to specific surfaces.

  16. Surface modification of electrospun cellulose acetate nanofibers via RAFT polymerization for DNA adsorption.

    PubMed

    Demirci, Serkan; Celebioglu, Asli; Uyar, Tamer

    2014-11-26

    We report on a facile and robust method by which surface of electrospun cellulose acetate (CA) nanofibers can be chemically modified with cationic polymer brushes for DNA adsorption. The surface of CA nanofibers was functionalized by growing poly[(ar-vinylbenzyl)trimethylammonium chloride)] [poly(VBTAC)] brushes through a multi-step chemical sequence that ensures retention of mechanically robust nanofibers. Initially, the surface of the CA nanofibers was modified with RAFT chain transfer agent. Poly(VBTAC) brushes were then prepared via RAFT-mediated polymerization from the nanofiber surface. DNA adsorption capacity of CA nanofibrous web surface functionalized with cationic poly(VBTAC) brushes was demonstrated. The reusability of these webs was investigated by measuring the adsorption capacity for target DNA in a cyclic manner. In brief, CA nanofibers surface-modified with cationic polymer brushes can be suitable as membrane materials for filtration, purification, and/or separation processes for DNA.

  17. Polyelectrolyte adsorption onto like-charged surfaces mediated by trivalent counterions: a Monte Carlo simulation study.

    PubMed

    Luque-Caballero, Germán; Martín-Molina, Alberto; Quesada-Pérez, Manuel

    2014-05-01

    Both experiments and theory have evidenced that multivalent cations can mediate the interaction between negatively charged polyelectrolytes and like-charged objects, such as anionic lipoplexes (DNA-cation-anionic liposome complexes). In this paper, we use Monte Carlo simulations to study the electrostatic interaction responsible for the trivalent-counterion-mediated adsorption of polyelectrolytes onto a like-charged planar surface. The evaluation of the Helmholtz free energy allows us to characterize both the magnitude and the range of the interaction as a function of the polyelectrolyte charge, surface charge density, [3:1] electrolyte concentration, and cation size. Both polyelectrolyte and surface charge favor the adsorption. It should be stressed, however, that the adsorption will be negligible if the surface charge density does not exceed a threshold value. The effect of the [3:1] electrolyte concentration has also been analyzed. In certain range of concentrations, the counterion-mediated attraction seems to be independent of this parameter, whereas very high concentrations of salt weaken the adsorption. If the trivalent cation diameter is doubled the adsorption moderates due to the excluded volume effects. The analysis of the integrated charge density and ionic distributions suggests that a delicate balance between charge inversion and screening effects governs the polyelectrolyte adsorption onto like-charged surfaces mediated by trivalent cations. PMID:24811649

  18. Molecular dynamics simulation of free and forced BSA adsorption on a hydrophobic graphite surface.

    PubMed

    Mücksch, Christian; Urbassek, Herbert M

    2011-11-01

    The adsorption of bovine serum albumin (BSA) onto a hydrophobic graphite surface is studied using molecular-dynamics simulation. In addition to the free, that is, unsteered, adsorption, we also investigate forced adsorption, in which the action of an AFM tip pushing the protein with constant force to the surface is modeled. Using an implicit inviscid water model, the adsorption dynamics and energetics are monitored for two different initial protein orientations toward the surface. In all cases, we find that the protein partially unfolds and spreads on the surface. The spreading is in agreement with the well-known high biocompatibility of graphite-based implants. The denaturation is, however, greatly enhanced in the case of forced adsorption. We follow the position of the so-called lipid-binding pocket found in subdomain IIIA (Sudlow site II) during adsorption and find that it is tilted and moved toward the graphite surface in all cases, in agreement with its hydrophobic character. The relevance of our findings for the common measurement procedure of studying protein adhesion using AFM experiments is discussed.

  19. Protein adsorption on a hydrophobic surface: a molecular dynamics study of lysozyme on graphite.

    PubMed

    Raffaini, Giuseppina; Ganazzoli, Fabio

    2010-04-20

    Adsorption of human lysozyme on hydrophobic graphite is investigated through atomistic computer simulations with molecular mechanics (MM) and molecular dynamics (MD) techniques. The chosen strategy follows a simulation protocol proposed by the authors to model the initial and the final adsorption stage on a bare surface. Adopting an implicit solvent and considering 10 starting molecular orientations so that all the main sides of the protein can face the surface, we first carry out an energy minimization to investigate the initial adsorption stage, and then long MD runs of selected arrangements to follow the surface spreading of the protein maximizing its adsorption strength. The results are discussed in terms of the kinetics of surface spreading, the interaction energy, and the molecular size, considering both the footprint and the final thickness of the adsorbed protein. The structural implications of the final adsorption geometry for surface aggregation and nanoscale structural organization are also pointed out. Further MD runs are carried out in explicit water for the native structure and the most stable adsorption state to assess the local stability of the geometry obtained in implicit solvent, and to calculate the statistical distribution of the water molecules around the whole lysozyme and its backbone.

  20. Observation of adsorption behavior of biomolecules on ferroelectric crystal surfaces with polarization domain patterns

    NASA Astrophysics Data System (ADS)

    Nakayama, Tomoaki; Isobe, Akiko; Ogino, Toshio

    2016-08-01

    Lithium tantalate (LiTaO3) is one of the ferroelectric crystals that exhibit spontaneous polarization domain patterns on its surface. We observed the polarization-dependent adsorption of avidin molecules, which are positively charged in a buffer solution at pH 7.0, on LiTaO3 surfaces caused by electrostatic interaction at an electrostatic double layer using atomic force microscopy (AFM). Avidin adsorption in the buffer solution was confirmed by scratching the substrate surfaces using the AFM cantilever, and the adsorption patterns were found to depend on the avidin concentration. When KCl was added to the buffer solution to weaken the electrostatic double layer interaction between avidin molecules and LiTaO3 surfaces, adsorption domain patterns disappeared. From the comparison between the adsorption and chemically etched domain patterns, it was found that avidin molecule adsorption is enhanced on negatively polarized domains, indicating that surface polarization should be taken into account in observing biomolecule behaviors on ferroelectric crystals.

  1. Polyelectrolyte adsorption onto like-charged surfaces mediated by trivalent counterions: a Monte Carlo simulation study.

    PubMed

    Luque-Caballero, Germán; Martín-Molina, Alberto; Quesada-Pérez, Manuel

    2014-05-01

    Both experiments and theory have evidenced that multivalent cations can mediate the interaction between negatively charged polyelectrolytes and like-charged objects, such as anionic lipoplexes (DNA-cation-anionic liposome complexes). In this paper, we use Monte Carlo simulations to study the electrostatic interaction responsible for the trivalent-counterion-mediated adsorption of polyelectrolytes onto a like-charged planar surface. The evaluation of the Helmholtz free energy allows us to characterize both the magnitude and the range of the interaction as a function of the polyelectrolyte charge, surface charge density, [3:1] electrolyte concentration, and cation size. Both polyelectrolyte and surface charge favor the adsorption. It should be stressed, however, that the adsorption will be negligible if the surface charge density does not exceed a threshold value. The effect of the [3:1] electrolyte concentration has also been analyzed. In certain range of concentrations, the counterion-mediated attraction seems to be independent of this parameter, whereas very high concentrations of salt weaken the adsorption. If the trivalent cation diameter is doubled the adsorption moderates due to the excluded volume effects. The analysis of the integrated charge density and ionic distributions suggests that a delicate balance between charge inversion and screening effects governs the polyelectrolyte adsorption onto like-charged surfaces mediated by trivalent cations.

  2. Polyelectrolyte adsorption onto like-charged surfaces mediated by trivalent counterions: A Monte Carlo simulation study

    NASA Astrophysics Data System (ADS)

    Luque-Caballero, Germán; Martín-Molina, Alberto; Quesada-Pérez, Manuel

    2014-05-01

    Both experiments and theory have evidenced that multivalent cations can mediate the interaction between negatively charged polyelectrolytes and like-charged objects, such as anionic lipoplexes (DNA-cation-anionic liposome complexes). In this paper, we use Monte Carlo simulations to study the electrostatic interaction responsible for the trivalent-counterion-mediated adsorption of polyelectrolytes onto a like-charged planar surface. The evaluation of the Helmholtz free energy allows us to characterize both the magnitude and the range of the interaction as a function of the polyelectrolyte charge, surface charge density, [3:1] electrolyte concentration, and cation size. Both polyelectrolyte and surface charge favor the adsorption. It should be stressed, however, that the adsorption will be negligible if the surface charge density does not exceed a threshold value. The effect of the [3:1] electrolyte concentration has also been analyzed. In certain range of concentrations, the counterion-mediated attraction seems to be independent of this parameter, whereas very high concentrations of salt weaken the adsorption. If the trivalent cation diameter is doubled the adsorption moderates due to the excluded volume effects. The analysis of the integrated charge density and ionic distributions suggests that a delicate balance between charge inversion and screening effects governs the polyelectrolyte adsorption onto like-charged surfaces mediated by trivalent cations.

  3. First-principles study toward CO adsorption on Au/Ni surface alloys.

    PubMed

    Huang, Yu Cheng; Du, Jin Yan; Zhou, Tao; Wang, Su Fan

    2012-12-01

    The introduction of a second metal, gold, into a nickel matrix can effectively improve the catalytic performance and thermal stability of the catalysts toward steam reforming of methane. To investigate the effect of Au on the adsorption properties and electronic structure of the Ni(111) surface, we chose CO as a probe molecule and examined CO adsorption on various Au/Ni surfaces. It was revealed that Au addition weakened the absorbate-substrate interactions on the Ni(111) surface. With increasing gold concentration, the binding energy declines further. The variation of the binding energies has been interpreted by exploring the electronic structure of surface nickel atoms. The effect of gold can be quantitatively characterized by the slopes of the fitting equations between the binding energy and the number of gold atoms surrounding the adsorption site. Our results show that the binding energy at top sites can be approximately estimated by counting the number of surrounding gold atoms. On one specific surface, the relative magnitude of the binding energy can be simply judged by the distance between gold and the geometrical center of the adsorption site. This empirical rule holds true for C, H, and O adsorption on the Au/Ni surface. It may be applicable to a system in which a doped atom of larger atomic size is incorporated into the host metal surface by forming a surface alloy. PMID:23047643

  4. Human plasma protein adsorption onto dextranized surfaces: a two-dimensional electrophoresis and mass spectrometry study.

    PubMed

    Tsai, Irene Y; Tomczyk, Nancy; Eckmann, Joshua I; Composto, Russell J; Eckmann, David M

    2011-05-01

    Protein adsorption is fundamental to thrombosis and to the design of biocompatible materials. We report a two-dimensional electrophoresis and mass spectrometry study to characterize multiple human plasma proteins adsorbed onto four different types of model surfaces: silicon oxide, dextranized silicon, polyurethane and dextranized polyurethane. Dextran was grafted onto the surfaces of silicon and polyurethane to mimic the blood-contacting endothelial cell glycocalyx surface. Surface topography and hydrophobicity/hydrophilicity were determined and analyzed using atomic force microscopy and water contact angle measurements, respectively. Using two-dimensional electrophoresis, we show that, relative to the unmodified surfaces, dextranization significantly inhibits the adsorption of several human plasma proteins including IGHG1 protein, fibrinogen, haptoglobin, Apo A-IV, Apo A-I, immunoglobulin, serum retinal-binding protein and truncated serum albumin. We further demonstrate the selectivity of plasma protein adsorbed onto the different functionalized surfaces and the potential to control and manipulate proteins adsorption on the surfaces of medical devices, implants and microfluidic devices. This result shows that adsorption experiments using a single protein or a binary mixture of proteins are consistent with competitive protein adsorption studies. In summary, these studies indicate that coating blood-contacting biomedical applications with dextran is an effective route to reduce thrombo-inflammatory responses and to surface-direct biological activities. PMID:21277175

  5. Adsorption of a cell-adhesive oligopeptide on polymer surfaces irradiated by ion beams.

    PubMed

    Satriano, C; Manso, M; Gambino, G L; Rossi, F; Marletta, G

    2005-01-01

    The adsorption behavior of H-Arg-Gly-Asp-OH (RGD) oligopeptide on ion-irradiated polymer surfaces has been studied. The RGD-incubated surfaces of poly(ethylene terephtalate) (PET) and poly(hydroxymethylsiloxane) (PHMS) thin films, before and after irradiation with 50 keV Ar+ to 1x10(15) ions/cm2, were investigated by X-Ray Photoelectron Spectroscopy and Atomic Force Microscopy. It was found that no significant adsorption occurs on PET, while a measurable amount of RGD is preferentially adsorbed onto irradiated PHMS surfaces. The evaluated surface coverage was found to range between 5 and 12%. In situ adsorption measurements performed by using the Quartz Crystal Microbalance with Dissipation monitoring technique showed that the irradiation induced remarkable changes of mass uptake with respect to the unirradiated surfaces, mostly attributed to the change in the water adsorption capability of the irradiated surfaces. The adsorption results are discussed in terms of the ion-induced changes on the morphology, chemical structure and composition, surface free energy and surface charge. PMID:15623933

  6. Dissociative adsorption of O2 on unreconstructed metal (100) surfaces: Pathways, energetics, and sticking kinetics

    NASA Astrophysics Data System (ADS)

    Liu, Da-Jiang; Evans, James W.

    2014-05-01

    An accurate description of oxygen dissociation pathways and kinetics for various local adlayer environments is key for an understanding not just of the coverage dependence of oxygen sticking, but also of reactive steady states in oxidation reactions. Density functional theory analysis for M(100) surfaces with M =Pd, Rh, and Ni, where O prefers the fourfold hollow adsorption site, does not support the traditional Brundle-Behm-Barker picture of dissociative adsorption onto second-nearest-neighbor hollow sites with an additional blocking constraint. Rather adsorption via neighboring vicinal bridge sites dominates, although other pathways can be active. The same conclusion also applies for M =Pt and Ir, where oxygen prefers the bridge adsorption site. Statistical mechanical analysis is performed based on kinetic Monte Carlo simulation of a multisite lattice-gas model consistent with our revised picture of adsorption. This analysis determines the coverage and temperature dependence of sticking for a realistic treatment of the oxygen adlayer structure.

  7. Dissociative adsorption of O2 on unreconstructed metal (100) surfaces: Pathways, energetics, and sticking kinetics

    SciTech Connect

    Liu, Da-Jiang; Evans, James W.

    2014-05-06

    An accurate description of oxygen dissociation pathways and kinetics for various local adlayer environments is key for an understanding not just of the coverage dependence of oxygen sticking, but also of reactive steady states in oxidation reactions. Density functional theory analysis for M(100) surfaces with M=Pd, Rh, and Ni, where O prefers the fourfold hollow adsorption site, does not support the traditional Brundle-Behm-Barker picture of dissociative adsorption onto second-nearest-neighbor hollow sites with an additional blocking constraint. Rather adsorption via neighboring vicinal bridge sites dominates, although other pathways can be active. The same conclusion also applies for M=Pt and Ir, where oxygen prefers the bridge adsorption site. Statistical mechanical analysis is performed based on kinetic Monte Carlo simulation of a multisite lattice-gas model consistent with our revised picture of adsorption. This analysis determines the coverage and temperature dependence of sticking for a realistic treatment of the oxygen adlayer structure.

  8. SERS, XPS, and DFT Study of Adenine Adsorption on Silver and Gold Surfaces.

    PubMed

    Pagliai, Marco; Caporali, Stefano; Muniz-Miranda, Maurizio; Pratesi, Giovanni; Schettino, Vincenzo

    2012-01-19

    The adsorption of adenine on silver and gold surfaces has been investigated combining density functional theory calculations with surface-enhanced Raman scattering and angle-resolved X-ray photoelectron spectroscopy measurements, obtaining useful insight into the orientation and interaction of the nucleobase with the metal surfaces.

  9. Effect of natural organic substances on the surface and adsorptive properties of environmental black carbon (char): attenuation of surface activity by humic and fulvic acids.

    PubMed

    Pignatello, Joseph J; Kwon, Seokjoon; Lu, Yufeung

    2006-12-15

    Black carbon (BC) plays a potentially important role in the availability of pollutants in soils and sediments. Recent evidence points to the possible attenuation of the high surface activity of raw BC by natural substances. We studied the effects of soil humic (HA) and fulvic (FA) acids on the surface properties and affinity for organic compounds of synthesized wood charcoal. Char powder suspended in a solution of HA or FA was loaded with organic matter via adsorption, evaporation of the water, or coflocculation with Al3+. These treatments were chosen to simulate initial and more advanced stages of environmental exposure. Coevaporation dramatically reduced the N2 Brunauer-Emmett-Teller total surface area of the char, but only moderately the CO2 cumulative surface area up to 1.4 nm. Organic compound adsorption was suppressed in proportion to molecular size, benzene < naphthalene < phenanthrene and 1,2,4-trichlorobenzene < phenanthrene, for humics in the adsorbed and coflocculated states, respectively. Humic substances also increased the linearity of the isotherms. The model we propose assumes that humic substances are restricted to the external surface where they act as pore blocking agents or competitive adsorbates, depending on the temperature and adsorbate size. Nitrogen is blocked from the internal pore space due to stiffness at 77 K of humic strands extending into pore throats, giving an artificially low surface area. Together with previous results, this finding indicates that N2 may not detect BC microporosity in geosorbents. At higher temperatures (CO2, 273 K; organics, 293 K), humic strands are more flexible, allowing access to interior pores. The counterintuitive molecular size dependence of adsorption suppression by humics is due to a molecular sieving effect in pores in which the adsorption space available to the organic compound is more and more restricted to external sites. PMID:17256524

  10. Effect of biomass addition on the surface and adsorption characterization of carbon-based adsorbents from sewage sludge.

    PubMed

    Wu, Changzi; Song, Min; Jin, Baosheng; Wu, Yimin; Huang, Yaji

    2013-02-01

    Sewage sludge with the additive corn cob was used as prescusor to prepare sludge-based carbon adsorbents by pyrolysis method. And then, the carbonizated products were activated with potassium hydroxide. The mixing ratio of the corn cob to sewage sludge was investigated. The surface area and pore size distribution, elemental composition, surface chemistry structure and the surface physical morphology were determined and compared. The results demonstrated that the addition of corn cob into the sewage sludge sample could effectively improve the surface area (from 287 to 591 m2/g) and the microporosity (from 5% to 48%) of the carbon based adsorbent, thus enhancing the adsorption behavior. The sulfur dioxide adsorption capacity was measured according to breakthrough test. It was found that the sulfur dioxide adsorption capacity of the adsorbents was obviously enhanced after the addition of the corn cob. It is presumed that not only highly porous adsorbents, but also a high metallic content of these materials are required to achieve good performances. PMID:23596963

  11. Preparation of alumina-supported ceria. II. Measurement of ceria surface area after impregnation with platinum or rhodium

    SciTech Connect

    Rogemond, E.; Frety, R.; Perrichon, V.; Primet, M. |

    1997-07-01

    The surface area of cerium oxide was evaluated in an aluminium oxide supported catalyst. The catalyst were impregnated with rhodium chlorides and platinum chlorides. The adsorption of carbon dioxide is discussed.

  12. Selective adsorption of bovine hemoglobin on functional TiO2 nano-adsorbents: surface physic-chemical properties determined adsorption activity

    NASA Astrophysics Data System (ADS)

    Guo, Shiguang; Zhang, Jianghua; Shao, Mingxue; Zhang, Xia; Liu, Yufeng; Xu, Junli; Meng, Hao; Han, Yide

    2015-04-01

    Surface functionalized nanoparticles are efficient adsorbents which have shown good potential for protein separation. In this work, we chose two different types of organic molecules, oleic acid (OA) and 3-glycidoxypropyltrimethoxy silane (GPTMS), to functionalize the surface of TiO2 nanoparticles, and we studied the effects of this modification on their surface physicochemical properties in correlation with their selective adsorption of proteins. The results showed that the surface zeta potential and the surface water wettability of the modified TiO2 were significantly changed in comparison with the original TiO2 nanoparticles. The adsorption activities of bovine hemoglobin (BHb) and bovine serum albumin (BSA) on these functionalized TiO2 samples were investigated under different conditions, including pH values, contact time, ion strength, and initial protein concentration. In comparison with the non-specific adsorption of original TiO2, however, both the OA-TiO2 and GPTMS-TiO2 exhibited increased BHb adsorption and decreased BSA adsorption at the same time. Using a binary protein mixture as the adsorption object, a higher separation factor (SF) was obtained for OA-TiO2 under optimum conditions. The different adsorption activities of BHb and BSA on the modified TiO2 were correlated with different interactions at the protein/solid interface, and the chemical force as well as the electrostatic force played an important role in the selective adsorption process.

  13. Density functional theory calculations and molecular dynamics simulations of the adsorption of biomolecules on graphene surfaces.

    PubMed

    Qin, Wu; Li, Xin; Bian, Wen-Wen; Fan, Xiu-Juan; Qi, Jing-Yao

    2010-02-01

    There is increasing attention in the unique biological and medical properties of graphene, and it is expected that biomaterials incorporating graphene will be developed for the graphene-based drug delivery systems and biomedical devices. Despite the importance of biomolecules-graphene interactions, a detailed understanding of the adsorption mechanism and features of biomolecules onto the surfaces of graphene is lacking. To address this, we have performed density functional theory (DFT) and molecular dynamics (MD) methods exploring the adsorption geometries, adsorption energies, electronic band structures, adsorption isotherms, and adsorption dynamics of l-leucine (model biomolecule)/graphene composite system. DFT calculations confirmed the energetic stability of adsorption model and revealed that electronic structure of graphene can be controlled by the adsorption direction of l-leucine. MD simulations further investigate the potential energy and van der Waals energy for the interaction processes of l-leucine/graphene system at different temperatures and pressures. We find that the van der Waals interaction between the l-leucine and the graphene play a dominant role in the adsorption process under a certain range of temperature and pressure, and the l-leucine molecule could be adsorbed onto graphene spontaneously in aqueous solution. PMID:19880174

  14. Adsorption behavior of antimony(III) oxyanions on magnetite surface in aqueous organic acid environment

    NASA Astrophysics Data System (ADS)

    Mittal, Vinit K.; Bera, Santanu; Narasimhan, S. V.; Velmurugan, S.

    2013-02-01

    Antimony(III) adsorption is observed on magnetite (Fe3O4) surface under acidic and reducing condition through surface hydroxyl (SOH) groups bonding on Fe3O4 surface. Desorption of adsorbed Sb(III) is observed from Fe3O4 surface along with iron release in organic acid at 85 °C after 5 h of experiment. Tartaric acid (TA) shows minimum Sb(III) adsorption on Fe3O4 among the organic acid studied. The reason is TA having two sets of adjacent functional groups viz. Odbnd Csbnd OH and Csbnd OH which are responsible for the formation of five-membered bidendate chelate with Sb(III). Other oxyanions, cations or complexing agents along with TA influences the Sb(III) adsorption on Fe3O4. The surface of magnetite is modified by the addition of fatty acids viz. Lauric acid, benzoic acid to bind the Ssbnd OH groups present on the surface. This results in delaying the process of adsorption without changing the quantity of saturation adsorption of Sb(III) on Fe3O4 surface.

  15. How to determine the adsorption energy of the surfactant's hydrophilic head? How to estimate easily the surface activity of every simple surfactant?

    PubMed

    Karakashev, Stoyan I

    2014-10-15

    A definite way to determine the adsorption energy of the surfactant's hydrophilic head on the air water interface is presented. For this purpose, the Davies adsorption theory and the most advanced version of Helfand-Frish-Lebowitz adsorption theory were applied to the surface tension isotherms of homologous series of sodium alkyl sulfate (CnH2n+1SO4Na, n=7-12), thus deriving the equilibrium adsorption constant, the cross-sectional area of the surfactant molecule, the interaction coefficient and the cohesion constant versus the number of the carbon atoms into the alkyl sulfate molecule. Thus, the total adsorption energy of each particular homolog was calculated in line with the latest development of the adsorption theory, thus calculating the dimensionless adsorption energy of the hydrophilic head Ehead/kBT. In our particular case (SO4(-)) we calculated Ehead/kBT=-2.79, which indicates the strong propensity of the SO4(-) to be surrounded by water molecules. The procedure for calculation Ehead/kBT does not depend on the charge of the hydrophilic head. Similarly, we calculated Ehead/kBT of another six well known in the literature hydrophilic heads (COOH, OH, DMPO, DEPO, N(CH3)3(+), and NH3(+)), indicating that the adsorption energy of the CH2 group depends slightly on the type of the hydrophilic head, but it affects substantially the adsorption energy of the whole surfactant molecule. Finally, we defined and validated a parameter called adsorption capacity of surfactants with simple molecular structure, for easy estimation of their surface activity. Linear dependence between the CMC of ionic surfactants and their adsorption capacity was established.

  16. [Preparation of surface molecularly imprinted polymers for penicilloic acid, and its adsorption properties].

    PubMed

    Zheng, Penglei; Luo, Zhimin; Chang, Ruimiao; Ge, Yanhui; Du, Wei; Chang, Chun; Fu, Qiang

    2015-09-01

    On account of the specificity and reproducibility for the determination of penicilloic acid in penicillin, this study aims to prepare penicilloic acid imprinted polymers (PEOA-MIPs) by surface polymerization method at the surface of modified silica particles by using penicilloic acid (PEOA) as the template molecule, methacrylic acid (MAA) as the functional monomer, ethylene glycol dimethacrylate ( EGDMA) as the cross linker, and methanol/acetonitrile as the solvents. The synthesis conditions were optimized, and PEOA-MIPs had the best adsorption capacity when the molar ratio of template molecule/functional monomer was 1 :4, cross linking degree was 85% and the solvent ratio of methanol/acetonitrile was 1 :1 (v/v). The adsorption properties were evaluated by adsorption experiments, including the adsorption isotherms, kinetics and selectivity. The adsorption process between PEOA-MIPs and PEOA fitted the Langmuir adsorption isotherm with the maximum adsorption capacity of 122. 78 mg/g and the pseudo-second-order reaction kinetics with fast adsorption kinetics (the equilibrium time of 45 min). The as-synthesized PEOA-MIPs were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and thermal gravimetric analysis (TGA). The results indicated that the MIPs layer has been successfully grafted on the surface of SiO2 microparticles and the PEOA-MIPs had the excellent thermal stability. The PEOA-MIPs showed the highest selective recognition for PEOA. The PEOA-MIPs possess a high adsorption capacity, rapid mass-transfer rate and high selectivity to PEOA when compared with non-imprinted polymers (PEOA-NIPs). The PEOA-MIPs was expected to be used as the solid phase extraction medium and this study provides the potential applications for fast recognition and analysis of the penicilloic acid in penicillin. PMID:26753284

  17. Chemistry-specific surface adsorption of the barnacle settlement-inducing protein complex

    PubMed Central

    Petrone, Luigi; Aldred, Nick; Emami, Kaveh; Enander, Karin; Ederth, Thomas; Clare, Anthony S.

    2015-01-01

    Gregarious settlement in barnacle larvae (cyprids) is induced by a contact pheromone, the settlement-inducing protein complex (SIPC). The SIPC has been identified both in the cuticle of adult barnacles and in the temporary adhesive secretion (footprint) of cyprids. Besides acting as a settlement inducer, the presence of the SIPC in footprints points to its additional involvement in the adhesion process. SIPC adsorption behaviour was therefore investigated on a series of self-assembled monolayers (SAMs) by surface plasmon resonance at the pH of seawater (8.3). Fibrinogen and α2-macroglobulin (A2M) (blood complement protease inhibitors with which the SIPC shares 29% sequence homology) were used in the adsorption experiments as positive and negative standards, respectively. The mass uptake of the SIPC was comparable to that of fibrinogen, with adsorption observed even on the protein-resistant oligo(ethylene glycol) surface. Notably, on the positively charged SAM the SIPC showed a kinetic overshoot, indicating a metastable configuration causing the amount of adsorbed protein to temporarily exceed its equilibrium value. A2M adsorption was low or negligible on all SAMs tested, except for the positively charged surface, indicating that A2M adsorption is mainly driven by electrostatics. Evaluation of SIPC non-specific adsorption kinetics revealed that it adsorbed irreversibly and non-cooperatively on all surfaces tested. PMID:25657832

  18. Theoretical Study of Trimethylacetic Acid Adsorption on CeO 2 (111) Surface

    DOE PAGES

    Wang, Weina; Thevuthasan, S.; Wang, Wenliang; Yang, Ping

    2016-01-11

    We investigated trimethylacetic acid (TMAA) adsorption on stoichiometric and oxygen-deficient CeO2(111) surfaces using density functional theory that accounts for the on-site Coulomb interaction via a Hubbard term (DFT+U) and long-range dispersion correction. Both the molecular state and dissociative state (TMAA → TMA– + H+) were identified on stoichiometric and oxygen-deficient CeO2(111) surfaces. For the stoichiometric surface, two thermodynamically favorable configurations with adsorption energies of the order of -30 kcal/mol are identified; one is a molecule adsorption state, and the other one is a dissociative state. For the oxygen-deficient surface, dissociative states are more favorable than molecular states. Moreover, the mostmore » favorable configuration is the dissociative adsorption of TMAA with the adsorption energy of the order of -77 kcal/mol. The dissociated TMA moiety takes the position of oxygen vacancy, forming three Ce–O bonds. The signature vibrational frequencies for these thermodynamically stable structures are reported as well as their electronic structures. The effects of long-range dispersion interactions are found to be negligible for geometries but important for adsorption energies.« less

  19. Chemistry-specific surface adsorption of the barnacle settlement-inducing protein complex.

    PubMed

    Petrone, Luigi; Aldred, Nick; Emami, Kaveh; Enander, Karin; Ederth, Thomas; Clare, Anthony S

    2015-02-01

    Gregarious settlement in barnacle larvae (cyprids) is induced by a contact pheromone, the settlement-inducing protein complex (SIPC). The SIPC has been identified both in the cuticle of adult barnacles and in the temporary adhesive secretion (footprint) of cyprids. Besides acting as a settlement inducer, the presence of the SIPC in footprints points to its additional involvement in the adhesion process. SIPC adsorption behaviour was therefore investigated on a series of self-assembled monolayers (SAMs) by surface plasmon resonance at the pH of seawater (8.3). Fibrinogen and α2-macroglobulin (A2M) (blood complement protease inhibitors with which the SIPC shares 29% sequence homology) were used in the adsorption experiments as positive and negative standards, respectively. The mass uptake of the SIPC was comparable to that of fibrinogen, with adsorption observed even on the protein-resistant oligo(ethylene glycol) surface. Notably, on the positively charged SAM the SIPC showed a kinetic overshoot, indicating a metastable configuration causing the amount of adsorbed protein to temporarily exceed its equilibrium value. A2M adsorption was low or negligible on all SAMs tested, except for the positively charged surface, indicating that A2M adsorption is mainly driven by electrostatics. Evaluation of SIPC non-specific adsorption kinetics revealed that it adsorbed irreversibly and non-cooperatively on all surfaces tested. PMID:25657832

  20. First principles investigation of Ti adsorption and migration on Si(100) surfaces

    SciTech Connect

    Briquet, Ludovic G. V.; Wirtz, Tom; Philipp, Patrick

    2013-12-28

    The titanium adsorption on Si(100) is investigated using first principles computer modelling methods. Two new subsurface adsorption sites are described. They are located at the edge of the cavity topped by a surface silicon dimer. The migration of the titanium from the surface to the subsurface sites is facilitated when occurring via one of these sites. The ejection of one of the silicon atoms forming the surface dimer is also investigated. The actual step of the ejection requires more energy than previously thought although, when considering the global picture of a titanium atom on the surface leading to the ejection of a silicon atom, the overall rate is compensated by the facilitated migration of the titanium to the subsurface sites. The consecutive adsorption of a second and third titanium atom is also investigated. It is shown that titanium grows evenly on the surface in normal condition, showing no intermixing of the titanium and silicon beyond the silicon layer.

  1. The adsorption of ethylene on Au/Pd(100) alloy surfaces

    NASA Astrophysics Data System (ADS)

    Li, Zhenjun; Thuening, Theodore; Tysoe, Wilfred T.

    2016-04-01

    The surface chemistry of ethylene is explored on model Au/Pd(100) alloy surfaces using a combination of temperature-programmed desorption and reflection-absorption infrared spectroscopy. The heat of adsorption of ethylene on the model alloy surface is found to increase monotonically with increasing palladium coverage in the alloy, from ~ 33 kJ/mol for a completely gold-covered surface to ~ 80 kJ/mol as the gold coverage decreases to zero. A large change in heat of adsorption is found for palladium coverages between 0 and ~ 0.35 monolayers, where previous studies have shown that the surface comprises exclusively isolated palladium sites. The heat of adsorption changes more slowly for higher palladium coverages, when palladium-palladium bridge sites appear. Vinyl species are identified for palladium coverages above ~ 0.8 ML from a vibrational mode at ~ 1120 cm- 1, which disappears when the sample is heated to ~ 250 K, due to vinyl decomposition.

  2. Tunable and sizable band gap in silicene by surface adsorption

    PubMed Central

    Quhe, Ruge; Fei, Ruixiang; Liu, Qihang; Zheng, Jiaxin; Li, Hong; Xu, Chengyong; Ni, Zeyuan; Wang, Yangyang; Yu, Dapeng; Gao, Zhengxiang; Lu, Jing

    2012-01-01

    Opening a sizable band gap without degrading its high carrier mobility is as vital for silicene as for graphene to its application as a high-performance field effect transistor (FET). Our density functional theory calculations predict that a band gap is opened in silicene by single-side adsorption of alkali atom as a result of sublattice or bond symmetry breaking. The band gap size is controllable by changing the adsorption coverage, with an impressive maximum band gap up to 0.50 eV. The ab initio quantum transport simulation of a bottom-gated FET based on a sodium-covered silicene reveals a transport gap, which is consistent with the band gap, and the resulting on/off current ratio is up to 108. Therefore, a way is paved for silicene as the channel of a high-performance FET. PMID:23152944

  3. Distribution and factors affecting adsorption of sterols in the surface sediments of Bosten Lake and Manas Lake, Xinjiang.

    PubMed

    Liu, Jiang; Yao, Xiaorui; Lu, Jianjiang; Qiao, Xiuwen; Liu, Zilong; Li, Shanman

    2016-03-01

    This study investigated the concentrations and distribution of eight sterol compounds in the surface sediments of Bosten Lake and Manas Lake, Xinjiang, China. The ratios of sterols as diagnostic indices were used to identify pollution sources. The sediment of the two lakes was selected as an adsorbent to investigate the adsorption behaviour of sterols. Results showed that the sterols were widely distributed in the sediments of the lakes in the study areas. The total concentrations of the detected sterols in Bosten Lake and in Manas Lake were 1.584-27.897 and 2.048-18.373 μg g(-1)∙dw, respectively. In all of the sampling sites, the amount of faecal sterols was less than that of plant sterols. β-sitosterol was the dominant plant sterol with a mean concentration of 2.378 ± 2.234 μg g(-1)∙dw; cholesterol was the most abundant faecal sterol with a mean concentration of 1.060 ± 1.402 μg g(-1)∙dw. The pollution level was higher in Bosten Lake than in Manas Lake. Majority of the ratios clearly demonstrated that the contamination by human faecal sources was occurring at stations which are adjacent to residential areas and water inlets. The adsorption behaviour of sterols to sediment suggested that the sterol adsorption coefficients were reduced as temperature increased. As salinity increased, the adsorption quantity also increased. As pH increased, the sediment adsorption of sterol slightly increased because the strong alkaline solution is not conducive to the adsorption of sterols. The ratios between sterols did not change largely with the change in external factors.

  4. Adsorption of cadmium ions on oxygen surface sites in activated carbon

    SciTech Connect

    Jia, Y.F.; Thomas, K.M.

    2000-02-08

    Various types of oxygen functional groups were introduced onto the surface of coconut shell derived activated carbon by oxidation using nitric acid. Fourier-transform infrared spectroscopy (FTIR), temperature-programmed desorption (TPD), and selective neutralization were used to characterize the surface oxygen functional groups. The oxidized carbons were also heat treated to provide a suite of carbons where the oxygen functional groups of various thermal stabilities were varied progressively. The adsorption of cadmium ions was enhanced dramatically by oxidation of the carbon. The ratio of released protons to adsorbed cadmium ions on oxidized carbon was approximately 2, indicating cation exchange was involved in the process of adsorption. Na{sup +} exchange studies with the oxidized carbon gave a similar ratio. After heat treatment of the oxidized carbons to remove oxygen functional groups, the ratio of H{sup +} released to Cd{sup 2+} adsorbed and the adsorption capacity decreased significantly. Both reversible and irreversible processes were involved in cadmium ion adsorption with reversible adsorption having higher enthalpy. The irreversible adsorption resulted from cation exchange with carboxylic acid groups, whereas the reversible adsorption probably involved physisorption of the partially hydrated cadmium ion.

  5. Adsorption of plasmid DNA to mineral surfaces and protection against DNase I.

    PubMed Central

    Romanowski, G; Lorenz, M G; Wackernagel, W

    1991-01-01

    The adsorption of [3H]thymidine-labeled plasmid DNA (pHC314; 2.4 kb) of different conformations to chemically pure sand was studied in a flowthrough microenvironment. The extent of adsorption was affected by the concentration and valency of cations, indicating a charge-dependent process. Bivalent cations (Mg2+, Ca2+) were 100-fold more effective than monovalent cations (Na+, K+, NH4+). Quantitative adsorption of up to 1 microgram of negatively supercoiled or linearized plasmid DNA to 0.7 g of sand was observed in the presence of 5 mM MgCl2 at pH 7. Under these conditions, more than 85% of DNA adsorbed within 60 s. Maximum adsorption was 4 micrograms of DNA to 0.7 g of sand. Supercoil molecules adsorbed slightly less than linearized or open circular plasmids. An increase of the pH from 5 to 9 decreased adsorption at 0.5 mM MgCl2 about eightfold. It is concluded that adsorption of plasmid DNA to sand depends on the neutralization of negative charges on the DNA molecules and the mineral surfaces by cations. The results are discussed on the grounds of the polyelectrolyte adsorption model. Sand-adsorbed DNA was 100 times more resistant against DNase I than was DNA free in solution. The data support the idea that plasmid DNA can enter the extracellular bacterial gene pool which is located at mineral surfaces in natural bacterial habitats. PMID:1647748

  6. p-Chlorophenol adsorption on activated carbons with basic surface properties

    NASA Astrophysics Data System (ADS)

    Lorenc-Grabowska, Ewa; Gryglewicz, Grażyna; Machnikowski, Jacek

    2010-05-01

    The adsorption of p-chlorophenol (PCP) from aqueous solution on activated carbons (ACs) with basic surface properties has been studied. The ACs were prepared by two methods. The first method was based on the modification of a commercial CWZ AC by high temperature treatment in an atmosphere of ammonia, nitrogen and hydrogen. The second approach comprised the carbonization followed by activation of N-enriched polymers and coal tar pitch using CO 2 and steam as activation agent. The resultant ACs were characterized in terms of porous structure, elemental composition and surface chemistry (pH PZC, acid/base titration, XPS). The adsorption of PCP was carried out from an aqueous solution in static conditions. Equilibrium adsorption isotherm was of L2 type for polymer-based ACs, whereas L3-type isotherm was observed for CWZ ACs series. The Langmuir monolayer adsorption capacity was related to the porous structure and the amount of basic sites. A good correlation was found between the adsorption capacity and the volume of micropores with a width < 1.4 nm for polymer-based ACs. Higher nitrogen content, including that in basic form, did not correspond to the enhanced adsorption of PCP from aqueous solution. The competitive effect of water molecule adsorption on the PCP uptake is discussed.

  7. The influence of the surface properties of silicon-fluorine hydrogel on protein adsorption.

    PubMed

    Xie, Haijiao; Zhao, Zhengbai; An, Shuangshuang; Jiang, Yong

    2015-12-01

    A range of fluorinated hydrogels were synthesized using the copolymerization of 1, 1, 1, 3, 3, 3-hexafluoroisopropyl methacrylate (HFMA) or 1H, 1H, 7H-dodecafluoroheptyl methacrylate (DFMA) with hydrophilic monomers. Bovine serum albumin (BSA) and Lysozyme (LZM) were chosen as model proteins to investigate the performance of protein adsorption on the surface of these fluorinated hydrogels. It was found that the performance of the fluorinated hydrogels toward protein adsorption was different for different proteins; simultaneously, the amount of protein adsorption was related to but not linear with the fluorine content on the hydrogel surface. With increasing HFMA content, the mass of BSA adsorption increased in the first stage and then decreased, meanwhile the mass of LZM adsorption exhibited an upward trend in general. In addition, the amount of protein adsorption was also related to the type and length of the fluorinated groups. The hydrogels made from DFMA behaved better than HFMA hydrogels in terms of reducing protein adsorption. This study might provide further reference in choosing fluorine monomer to prepare protein-repelling hydrogels.

  8. Optical reflectivity changes induced by adsorption on metal surfaces: The origin and applications to monitoring adsorption kinetics

    NASA Astrophysics Data System (ADS)

    Dvorak, Joseph; Dai, Hai-Lung

    2000-01-01

    It is observed that when a monolayer of CO and acetylene is chemisorbed on the Cu(100) surface, the reflectivity of the metal surface at the He-Ne laser wavelength of 632 nm is reduced on the order of 1%, while the physisorption of water, methanol, and acetone induces a reflectivity change on the order of 0.01%. The small reflectivity change induced by physisorption can be described by a three-layer model taking into account the molecular layer refractive index. The much bigger reflectivity change induced by the chemisorbed adsorbates, on the other hand, is a result of bonding perturbations to the electronic structure of the metal surface layer. The latter is supported by an electron scattering model description of the reflectivity change up to 1.96 eV on Cu. For both CO and acetylene, the optical reflectivity change is found to be linearly proportional to the submonolayer coverage. The phenomenon thus offers an excellent method to measure surface kinetics. It is found from the reflectivity change measurements that the initial sticking coefficient for both adsorbates is nearly unity at 110 K; 0.85 for CO and 1.0 for acetylene. The temperature and coverage dependence of the sticking coefficient shows that the adsorption behavior of both molecules is well described as direct adsorption mediated with an extrinsic precursor. For acetylene adsorption, the sticking coefficient shows little dependence on the substrate temperature suggesting that the "extrinsic precursor" is not a thermally equilibrated species. For CO, the transition into a compression phase beyond 0.5 ML results in a corresponding change in the sticking coefficient deduced from the reflectivity data.

  9. Evolution of the surface area of a snow layer

    SciTech Connect

    Hanot, L.; Domine, F.

    1999-12-01

    Atmospheric trace gases can partition between the atmosphere and the snow surface. Because snow has a large surface-to-volume ratio, an important interaction potential between ice and atmospheric trace gases exists. Quantifying this partitioning requires the knowledge of the surface area (SA) of snow. Eleven samples were taken from a 50 cm thick snow fall at Col de Porte, near Grenoble (French Alps) between January 20 and February 4, 1998. Fresh snow and 3, 8, and 15-day-old snow were sampled at three different depths. Surface hoar, formed after the fall, was also sampled. Air and surface snow temperature, snow density, and snow fall rate were measured. Snow temperature always remained below freezing. Snow SA was measured using methane adsorption at 77.15 K. Values ranged from 2.25 m{sup 2}/g for fresh snow to 0.25 m{sup 2}/g for surface hoar and surface snow after 15 days. These values are much too high to be explained by the macroscopic aspect of snow crystals, and microstructures such as small rime droplets must have been present. Large decrease in SA with time were observed. The first meter of snowpack had a total surface area of about 50,000 m{sup 2} per m{sup 2} of ground. Reduction in SA will lead to the emission of adsorbed species by the snowpack, with possible considerable increase in atmospheric concentrations.

  10. Adsorption and Pattern Recognition of Polymers at Complex Surfaces with Attractive Stripelike Motifs

    NASA Astrophysics Data System (ADS)

    Möddel, Monika; Janke, Wolfhard; Bachmann, Michael

    2014-04-01

    We construct the complete structural phase diagram of polymer adsorption at substrates with attractive stripelike patterns in the parameter space spanned by the adsorption affinity of the stripes and temperature. Results were obtained by extensive generalized-ensemble Monte Carlo simulations of a generic model for the hybrid organic-inorganic system. By comparing with adhesion properties at homogeneous substrates, we find substantial differences in the formation of adsorbed polymer structures if translational invariance at the surface is broken by a regular pattern. Beside a more specific understanding of polymer adsorption processes, our results are potentially relevant for the design of macromolecular pattern recognition devices such as sensors.

  11. Scaling Properties of Adsorption Energies for Hydrogen-Containing Molecules on Transition-Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Abild-Pedersen, F.; Greeley, J.; Studt, F.; Rossmeisl, J.; Munter, T. R.; Moses, P. G.; Skúlason, E.; Bligaard, T.; Nørskov, J. K.

    2007-07-01

    Density functional theory calculations are presented for CHx, x=0,1,2,3, NHx, x=0,1,2, OHx, x=0,1, and SHx, x=0,1 adsorption on a range of close-packed and stepped transition-metal surfaces. We find that the adsorption energy of any of the molecules considered scales approximately with the adsorption energy of the central, C, N, O, or S atom, the scaling constant depending only on x. A model is proposed to understand this behavior. The scaling model is developed into a general framework for estimating the reaction energies for hydrogenation and dehydrogenation reactions.

  12. Oxalate adsorption at a plagioclase (An47) surface and models for ligand-promoted dissolution

    USGS Publications Warehouse

    Stillings, L.L.; Drever, J.I.; Poulson, S.R.

    1998-01-01

    Previous work on adsorption of oxalate at aluminosilicate surfaces suggests that maximum adsorption occurs through a bidentate attachment of the organic ligand, at near-neutral pH. Rates of ligand-promoted dissolution are expected to be greatest at this pH as well. We tested this model by measuring oxalate adsorption on the surface of andesine (An47), in solutions of pH 3- 5 and total oxalate concentrations of 0-8 mM. Contrary to expectation, the greatest adsorption density of 24 ??mol m-2 total oxalate was observed at pH 3 and 8 mM total oxalate. Adsorption is dependent upon the activities of both oxalate (C2O42-) and bioxalate (HC2O4-) in solution and can be modeled with either a two-term Langmuir or a two-term Freundlich isotherm. A Freundlich adsorption model provided the best fit to rate data because it was not constrained to a finite number of adsorption sites, as was the Langmuir model. The two-term ligand adsorption model was incorporated into a rate model: R(tot) = k(H-)[H(ads)/+](L) + k(HOx-)[HOx(ads)/-] + k(Ox2- )[Ox2(ads)/-] where R(tot) is the net dissolution rate of the feldspar, [i(ads)] is the concentration of species i adsorbed to the surface, and k(i) is the rate constant for release of the surface complex. The model was fit to data for oxalate-promoted dissolution of andesine, resulting in estimates for the rate constants of k(HOx-) = 1.16 x 10-12, k(Ox2-) = 1.05 x 10-12, and k(H-) = 9.61 x 10-13 mol of feldspar (??mol of i) (??mol of i)-1 s-1.Previous work on adsorption of oxalate at aluminosilicate surfaces suggests that maximum adsorption occurs through a bidentate attachment of the organic ligand, at near-neutral pH. Rates of ligand-promoted dissolution are expected to be greatest at this pH as well. We tested this model by measuring oxalate adsorption on the surface of andesine (An47), in solutions of pH 3-5 and total oxalate concentrations of 0-8 mM. Contrary to expectation, the greatest adsorption density of 24 ??mol m-2 total oxalate was

  13. Adsorption and recognition characteristics of surface molecularly imprinted polymethacrylic acid/silica toward genistein.

    PubMed

    Zhang, Yanyan; Gao, Baojiao; An, Fuqiang; Xu, Zeqing; Zhang, Tingting

    2014-09-12

    In this paper, on the basis of surface-initiated graft polymerization, a new surface molecular imprinting technique is established by molecular design. And molecularly imprinted polymer MIP-PMAA/SiO2 is successfully prepared with genistein as template. The adsorption and recognition characteristics of MIP-PMAA/SiO2 for genistein are studied in depth by using static method, dynamic method and competitive adsorption experiment. The experimental results show that MIP-PMAA/SiO2 possesses very strong adsorption affinity and specific recognition for genistein. The saturated adsorption capacity could reach to 0.36mmolg(-1). The selectivity coefficients relative to quercetin and rutin are 5.4 and 11.8, respectively. Besides, MIP-PMAA/SiO2 is regenerated easily and exhibits excellent reusability. PMID:25085816

  14. Tailoring band gaps of insulators by adsorption at surface defects: Benzoic acids on NaCl surfaces

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Tegenkamp, Christoph; Pfnür, Herbert; Bredow, Thomas

    2009-06-01

    The adsorption of benzoic acid and its OH-substituted derivatives, namely, salicylic acid (SA) and parasalicylic acid on various NaCl surfaces has been investigated by density-functional theory with hybrid exchange-correlation functional. The ideal NaCl(100) surface is chemically inert as evidenced by the low binding energies. The molecular adsorption can be enhanced by both an anion vacancy and a surface step site. The bonding between the surface Na and the carboxylic O atom is of covalent character for all adsorption geometries. Our calculations show that the adsorption of SA has the largest binding energy of all three acids due to the additional interaction between Na and the phenolic O atom. Charge transfer between the molecule and the surface is generally very small, except in the presence of an anion vacancy where the unpaired electron is mostly transferred to the adsorbate. Surface defects generally have a strong influence on the electronic structure of the adsorbed molecules. Specifically, the adsorption of SA at [011]-oriented steps can significantly reduce the effective band gap to 1.6 eV due to the up shift of the Cl3p levels at the undercoordinated step edge. Implications of these results to the contact charging effect between wide-band-gap insulators will be discussed.

  15. Uranium(VI) adsorption to ferrihydrite: Application of a surface complexation model

    USGS Publications Warehouse

    Waite, T.D.; Davis, J.A.; Payne, T.E.; Waychunas, G.A.; Xu, N.

    1994-01-01

    A study of U(VI) adsorption by ferrihydrite was conducted over a wide range of U(VI) concentrations, pH, and at two partial pressures of carbon dioxide. A two-site (strong- and weak-affinity sites, FesOH and FewOH, respectively) surface complexation model was able to describe the experimental data well over a wide range of conditions, with only one species formed with each site type: an inner-sphere, mononuclear, bidentate complex of the type (FeO2)UO2. The existence of such a surface species was supported by results of uranium EXAFS spectroscopy performed on two samples with U(VI) adsorption density in the upper range observed in this study (10 and 18% occupancy of total surface sites). Adsorption data in the alkaline pH range suggested the existence of a second surface species, modeled as a ternary surface complex with UO2CO30 binding to a bidentate surface site. Previous surface complexation models for U(VI) adsorption have proposed surface species that are identical to the predominant aqueous species, e.g., multinuclear hydrolysis complexes or several U(VI)-carbonate complexes. The results demonstrate that the speciation of adsorbed U(VI) may be constrained by the coordination environment at the surface, giving rise to surface speciation for U(VI) that is significantly less complex than aqueous speciation. ?? 1994.

  16. Role of proton ordering in adsorption preference of polar molecule on ice surface.

    PubMed

    Sun, Zhaoru; Pan, Ding; Xu, Limei; Wang, Enge

    2012-08-14

    Adsorption of polar monomers on ice surface, relevant to the physical/chemical reaction in ice clouds as well as growth of ice, remains an open issue partially due to the unusual surface characteristics with protons at the top layer of ice. Using first-principle calculations, we explore the adsorption properties of ice surface in terms of a surface proton order parameter, which characterizes the inhomogeneity of the dangling atoms on ice surface. We show that, due to an effective electric field created by dangling OH bonds and lone pairs of water molecules not only directly neighboring but also further away from the adsorbed polar molecule on the ice surface, the adsorption energy of polar monomer on ice surface exhibits large variance and a strong correlation with the proton order parameter of ice surface. Our results about the positive correlation between the inhomogeneity of ice surface and adsorption energies suggest that the physical/chemical reactions as well as the growth of ice may prefer to occur firstly on surfaces with larger proton order parameter.

  17. Influence of Vacancy Defect on Surface Feature and Adsorption of Cs on GaN(0001) Surface

    PubMed Central

    Ji, Yanjun; Du, Yujie; Wang, Meishan

    2014-01-01

    The effects of Ga and N vacancy defect on the change in surface feature, work function, and characteristic of Cs adsorption on a (2 × 2) GaN(0001) surface have been investigated using density functional theory with a plane-wave ultrasoft pseudopotential method based on first-principles calculations. The covalent bonds gain strength for Ga vacancy defect, whereas they grow weak for N vacancy defect. The lower work function is achieved for Ga and N vacancy defect surfaces than intact surface. The most stable position of Cs adatom on Ga vacancy defect surface is at T1 site, whereas it is at BGa site on N vacancy defect surface. The Eads of Cs on GaN(0001) vacancy defect surface increases compared with that of intact surface; this illustrates that the adsorption of Cs on intact surface is more stable. PMID:25126599

  18. Influence of vacancy defect on surface feature and adsorption of Cs on GaN(0001) surface.

    PubMed

    Ji, Yanjun; Du, Yujie; Wang, Meishan

    2014-01-01

    The effects of Ga and N vacancy defect on the change in surface feature, work function, and characteristic of Cs adsorption on a (2 × 2) GaN(0001) surface have been investigated using density functional theory with a plane-wave ultrasoft pseudopotential method based on first-principles calculations. The covalent bonds gain strength for Ga vacancy defect, whereas they grow weak for N vacancy defect. The lower work function is achieved for Ga and N vacancy defect surfaces than intact surface. The most stable position of Cs adatom on Ga vacancy defect surface is at T1 site, whereas it is at B(Ga) site on N vacancy defect surface. The E(ads) of Cs on GaN(0001) vacancy defect surface increases compared with that of intact surface; this illustrates that the adsorption of Cs on intact surface is more stable.

  19. Adsorption of a biosurfactant on surfaces to enhance the disinfection of surfaces contaminated with Listeria monocytogenes.

    PubMed

    Meylheuc, T; Renault, M; Bellon-Fontaine, M N

    2006-05-25

    The effects of sodium hypochlorite (NaOCl) and peracetic acid/hydrogen peroxide (PAH) on the inactivation of adherent Listeria monocytogenes LO28 cells were examined. The surfaces tested were stainless steel and polytetrafluoroethylene (PTFE) conditioned or not with an anionic biosurfactant produced by Pseudomonas fluorescens. Dilution-neutralization methods were used to assess the effectiveness of sanitizer solutions on planktonic and adherent cells. Tests were performed on L. monocytogenes cultivated at 37 degrees Celsius (body temperature) or 20 degrees Celsius (ambient temperature). The results demonstrated that i) a total deficiency in nutrients induced by the incubation of cells in 0.15 M NaCl favored the action of NaOCl and PAH on planktonic cells; ii) by reducing the number of cells adhering to stainless steel, pre-conditioning of the surface with the biosurfactant reduced the level of contamination of the surface and thus favored the bactericidal activities of the disinfectants; and iii) the weak binding energies involved in the adsorption of the biosurfactant on PTFE surfaces resulted in there being no reduction by the polymer of the surface contamination. Furthermore, this study confirmed that adherent cells exhibited increased resistance to the actions of the disinfectants when compared to the resistance of planktonic cells. PMID:16488496

  20. Methane adsorption on the surface of a model of shale: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Zhu, Yuan-qiang; Su, Hong; Jing, Ya; Guo, Jianchun; Tang, Junlei

    2016-11-01

    As a model of shale, one part of polycyclic aromatic ring was used to represent the kerogen surface with the structural heterogeneity. The adsorption mechanisms of methane on the surface of the kerogen were investigated by M06-2× functional with D3 dispersion correction. Nine stable adsorption sites and the orientations of methane (CH4) on the surface of the kerogen were systematically considered. Information from different methods lead to the same conclusion that methane prefers to be adsorbed on the sites directly above the carbon atoms of the kerogen rather than above the center of the six-membered rings. The interactions between methane and the surface of the kerogen are the van der Waals interactions. The interaction energies with the basis set superposition error (BSSE) corrections are around 14 kJ mol-1 at the M06-2×-D3/Jun-cc-pVDZ level. The RDG scatter graphs and the RDG gradient isosurface further illustrate that the interactions between methane and the surface of the kerogen belong to the van der Waals interactions. The weak interactions indicate that the adsorption of methane on the surface of the kerogen is physical adsorption and it slightly depends upon the adsorption sites on kerogen as well as the orientations of methane. These results are helpful for the understanding of the microcosmic mechanism of methane-shale interactions and for the exploitation of shale gas.

  1. Quartz Crystal Microbalance Study of Kinetics and Thermodynamics of IgG Adsorption on the Polystyrene Surface

    NASA Astrophysics Data System (ADS)

    Feng, Bo; Feng, Xi; Xie, Xiaomei; Wang, Caiyun; Zhang, Mengxue; Zhang, Xiaoyun

    2015-03-01

    Polystyrene (PS) is a common substrate material for protein adsorption on biosensors and bioassays. By employing a quartz crystal microbalance (QCM) technique, we studied the kinetics and thermodynamics of anti-HBeAg adsorption on this substrate in situ. First, a thin PS film was deposited on the interface between the liquid and the quartz crystal wafer. Second, a solution containing anti-HBeAg was introduced into the holding tank. Third, we measured the change in the oscillation frequency of the quartz that was induced by the antibody-PS binding, which in turn depended on macroscopic parameters, such as antibody concentration and solution temperature, as well as on microscopic parameters, such as the diffusion type and the change in Gibb's free energy. The adsorption rate and capacity of anti-HBeAg on the PS surface were quantified and fitted using the conventional Langmuir model. It was shown that this model was applicable to protein-PS interface system. Approximately 250 nm2 of the surface area was occupied by a single antibody molecule at 298 K when the concentration was 90 μg/mL. The adsorption process might have been controlled by both liquid film and particle diffusions.

  2. Adsorption of surfactants on sand surface in enhanced oil recovery: Isotherms, kinetics and thermodynamic studies

    NASA Astrophysics Data System (ADS)

    Bera, Achinta; Kumar, T.; Ojha, Keka; Mandal, Ajay

    2013-11-01

    Adsorption of surfactants onto reservoir rock surface may result in the loss and reduction of their concentrations in surfactant flooding, which may render them less efficient or ineffective in practical applications of enhanced oil recovery (EOR) techniques. Surfactant flooding for EOR received attraction due to its ability to increase the displacement efficiency by lowering the interfacial tension between oil and water and mobilizing the residual oil. This article highlights the adsorption of surfactants onto sand surface with variation of different influencing factors. It has been experimentally found that adsorption of cationic surfactant on sand surface is more and less for anionic surfactant, while non-ionic surfactant shows intermediate behaviour. X-ray diffraction (XRD) study of clean sand particles has been made to determine the main component present in the sand particles. The interaction between sand particles and surfactant has been studied by Fourier Transform Infrared (FTIR) Spectroscopy of the sand particles before and after aging with surfactant. Salinity plays an important role in adsorption of anionic surfactant. Batch experiments were also performed to understand the effects of pH and adsorbent dose on the sorption efficiency. The sand particles exhibited high adsorption efficiency at low pH for anionic and nonionic surfactants. But opposite trend was found for cationic surfactant. Adsorption data were analyzed by fitting with Langmuir, Freundlich, Redlich-Peterson, and Sips isotherm models. Results show that the Langmuir isotherm and pseudo-second order kinetics models suit the equilibrium and kinetics of adsorption on sand surface. Thermodynamics feasibility of the adsorption process was also studied to verify the spontaneity of the process.

  3. Preferential adsorption behavior of methylene blue dye onto surface hydroxyl group enriched TiO2 nanotube and its photocatalytic regeneration.

    PubMed

    Natarajan, Thillai Sivakumar; Bajaj, Hari C; Tayade, Rajesh J

    2014-11-01

    The present manuscript focus on the synthesis of surface hydroxyl group enriched titanium dioxide nanotube (TNT) by hydrothermal method for preferential adsorption of methylene blue (MB) dye. The mixture of methylene blue (MB) and rhodamine B (RhB) dye was used to study the preferential adsorption nature of TNT. The synthesized TNT were characterized by various techniques such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption, and ammonia-temperature programmed desorption (NH3-TPD) analysis. Result demonstrated that enhancement in the surface area of TNT and higher number of hydroxyl group on the surface of TNT. In the binary mixture, the adsorption of MB dye was 12.9 times higher as compared to RhB dye, which clearly indicated the preferential adsorption of MB dye on TNT surface. The preferential interaction of MB on TNT is due to the electrostatic interaction between the cationic MB and negatively charged TNT surface. The preferential adsorption of MB dye was studied by applying Langmuir, Freundlich and Sips isotherm; pseudo-first and second-order kinetic model. Furthermore, the regeneration of dye adsorbed TNT was carried out by eco-friendly photocatalytic process under the irradiation of ultraviolet light.

  4. Adsorption and Distribution of Fluorescent Solutes near the Articular Surface of Mechanically Injured Cartilage

    PubMed Central

    Decker, Sarah G.A.; Moeini, Mohammad; Chin, Hooi Chuan; Rosenzweig, Derek H.; Quinn, Thomas M.

    2013-01-01

    The development of cartilage-specific imaging agents supports the improvement of tissue assessment by minimally invasive means. Techniques for highlighting cartilage surface damage in clinical images could provide for sensitive indications of posttraumatic injury and early stage osteoarthritis. Previous studies in our laboratory have demonstrated that fluorescent solutes interact with cartilage surfaces strongly enough to affect measurement of their partition coefficients within the tissue bulk. In this study, these findings were extended by examining solute adsorption and distribution near the articular surface of mechanically injured cartilage. Using viable cartilage explants injured by an established protocol, solute distributions near the articular surface of three commonly used fluorophores (fluorescein isothiocyanate (FITC), tetramethylrhodamine isothiocyanate (TRITC), and carboxytetramethylrhodamine (TAMRA)) were observed after absorption and subsequent desorption to assess solute-specific matrix interactions and reversibility. Both absorption and desorption processes demonstrated a trend of significantly less solute adsorption at surfaces of fissures compared to adjacent intact surfaces of damaged explants or surfaces of uninjured explants. After adsorption, normalized mean surface intensities of fissured surfaces of injured explants were 6%, 40%, and 32% for FITC, TRITC, and TAMRA, respectively, compared to uninjured surfaces. Similar values were found for sliced explants and after a desorption process. After desorption, a trend of increased solute adsorption at the site of intact damaged surfaces was noted (316% and 238% for injured and sliced explants exposed to FITC). Surface adsorption of solute was strongest for FITC and weakest for TAMRA; no solutes negatively affected cell viability. Results support the development of imaging agents that highlight distinct differences between fissured and intact cartilage surfaces. PMID:24268155

  5. Unravelling nonspecific adsorption of complex protein mixture on surfaces with SPR and MS.

    PubMed

    Breault-Turcot, Julien; Chaurand, Pierre; Masson, Jean-Francois

    2014-10-01

    Characterization of protein adsorption to surfaces has implications from biosensing to protective biocoatings. While research studies have principally focused on determining the magnitude of protein adsorption to surfaces, the proteins involved in the process remains only broadly identified and has not been investigated on several surfaces. To further elucidate the nonspecific adsorption process of serum to surfaces, surface plasmon resonance (SPR) and matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) were used in combination to obtain quantitative and qualitative information about the process of protein adsorption to surfaces. To validate the technique, crude serum was nonspecifically adsorbed on four self-assembled monolayer (SAM) on gold: 16-mercaptohexadecanoic acid (16-MHA), 11-mercaptoundecane(ethylene glycol)3-COOH (PEG), 3-MPA-LHDLHD-OH, and 3-MPA-HHHDD-OH. Direct MS analysis of the nonspecifically adsorbed proteins suggested the presence of a variety of protein (BSA, IgG, and apolipoprotein A-1). Performing a trypsin digestion of the nonspecifically adsorbed proteins confirmed the presence of BSA and apolipoprotein A-1 and further revealed the complexity of the process by detecting the presence of complement C3, SHC-transforming protein 1, and kininogen 2. The level of nonspecific adsorption on different surfaces measured by SPR sensing directly correlated with the intensity of the serum protein and indirectly with the tryptic peptides measured by MS. Detailed analysis of the BSA peptides digested on 16-MHA and for BSA digested in solution was used to investigate the orientation of BSA on this surface. The combination of SPR and MS allows the quantitative and qualitative understanding of protein adsorption processes to surfaces. PMID:25287274

  6. Electrochemistry of ferrocene derivatives on highly oriented pyrolytic graphite (HOPG): quantification and impacts of surface adsorption.

    PubMed

    Cuharuc, Anatolii S; Zhang, Guohui; Unwin, Patrick R

    2016-02-14

    Cyclic voltammetry of three ferrocene derivatives - (ferrocenylmethyl)trimethylammonium (FcTMA(+)), ferrocenecarboxylic acid (FcCOOH), and ferrocenemethanol (FcCH2OH) - in aqueous solutions shows that the reduced form of the first two redox species weakly adsorbs onto freshly cleaved surfaces of highly oriented pyrolytic graphite (HOPG), with the fractional surface coverage being in excess of 10% of a monolayer at a bulk concentration level of 0.25 mM for both compounds. FcCH2OH was found to exhibit greater and stronger adsorption (up to a monolayer) for the same bulk concentration. The adsorption of FcTMA(+) on freshly cleaved surfaces of high quality (low step edge density) and low quality (high step edge density) HOPG is the same within experimental error, suggesting that the amount of step edges has no influence on the adsorption process. The amount of adsorption of FcTMA(+) is the same (within error) for low quality HOPG, irrespective of whether the surface is freshly cleaved or left in air for up to 12 hours, while - with aging - high quality HOPG adsorbs notably more FcTMA(+). The formation of an airborne contaminating film is proposed to be responsible for the enhanced entrapment of FcTMA(+) on aged high quality HOPG surfaces, while low quality surfaces appear less prone to the accumulation of such films. The impact of the adsorption of ferrocene derivatives on graphite for voltammetric studies is discussed. Adsorption is quantified by developing a theory and methodology to process cyclic voltammetry data from peak current measurements. The accuracy and applicability, as well as limits of the approach, are demonstrated for various adsorption isotherms.

  7. Molecular Dynamics Modeling of Ion Adsorption to the Basal Surfaces of Kaolinite

    SciTech Connect

    Vasconcelos, Igor F.; Bunker, Bruce A.; Cygan, Randall T.

    2008-06-06

    Molecular dynamics simulation is used to study the mechanisms involved in the adsorption of various ions to the basal surfaces of kaolinite. Analysis of simulation data indicates that cations and anions adsorb preferably on the siloxane and gibbsite surfaces of kaolinite, respectively. Strong inner-sphere adsorption of chlorine at aluminum vacancies on the gibbsite surface and the occurrence of chlorine-driven inner-sphere adsorption of cesium and sodium on the gibbsite surface for high ionic strengths are observed. Cesium ions form strong inner-sphere complexes at ditrigonal cavities on the siloxane surface. Outer-sphere cesium is highly mobile and only weak adsorption may occur. A small amount of sodium adsorbs on the siloxane surface as inner-sphere complexes at less clearly defined sites. Like cesium, sodium only forms very weak outer-sphere complexes on this surface. Inner-sphere complexes of cadmium and lead do not occur on either surface. Relatively strong outer-sphere cadmium and lead complexes are present on the siloxane surface at ditrigonal cavities.

  8. A Modular Approach To Study Protein Adsorption on Surface Modified Hydroxyapatite.

    PubMed

    Ozhukil Kollath, Vinayaraj; Van den Broeck, Freya; Fehér, Krisztina; Martins, José C; Luyten, Jan; Traina, Karl; Mullens, Steven; Cloots, Rudi

    2015-07-13

    Biocompatible inorganic nano- and microcarriers can be suitable candidates for protein delivery. This study demonstrates facile methods of functionalization by using nanoscale linker molecules to change the protein adsorption capacity of hydroxyapatite (HA) powder. The adsorption capacity of bovine serum albumin as a model protein has been studied with respect to the surface modifications. The selected linker molecules (lysine, arginine, and phosphoserine) can influence the adsorption capacity by changing the electrostatic nature of the HA surface. Qualitative and quantitative analyses of linker-molecule interactions with the HA surface have been performed by using NMR spectroscopy, zeta-potential measurements, X-ray photoelectron spectroscopy, and thermogravimetric analyses. Additionally, correlations to theoretical isotherm models have been calculated with respect to Langmuir and Freundlich isotherms. Lysine and arginine increased the protein adsorption, whereas phosphoserine reduced the protein adsorption. The results show that the adsorption capacity can be controlled with different functionalization, depending on the protein-carrier selections under consideration. The scientific knowledge acquired from this study can be applied in various biotechnological applications that involve biomolecule-inorganic material interfaces. PMID:26096378

  9. A Modular Approach To Study Protein Adsorption on Surface Modified Hydroxyapatite.

    PubMed

    Ozhukil Kollath, Vinayaraj; Van den Broeck, Freya; Fehér, Krisztina; Martins, José C; Luyten, Jan; Traina, Karl; Mullens, Steven; Cloots, Rudi

    2015-07-13

    Biocompatible inorganic nano- and microcarriers can be suitable candidates for protein delivery. This study demonstrates facile methods of functionalization by using nanoscale linker molecules to change the protein adsorption capacity of hydroxyapatite (HA) powder. The adsorption capacity of bovine serum albumin as a model protein has been studied with respect to the surface modifications. The selected linker molecules (lysine, arginine, and phosphoserine) can influence the adsorption capacity by changing the electrostatic nature of the HA surface. Qualitative and quantitative analyses of linker-molecule interactions with the HA surface have been performed by using NMR spectroscopy, zeta-potential measurements, X-ray photoelectron spectroscopy, and thermogravimetric analyses. Additionally, correlations to theoretical isotherm models have been calculated with respect to Langmuir and Freundlich isotherms. Lysine and arginine increased the protein adsorption, whereas phosphoserine reduced the protein adsorption. The results show that the adsorption capacity can be controlled with different functionalization, depending on the protein-carrier selections under consideration. The scientific knowledge acquired from this study can be applied in various biotechnological applications that involve biomolecule-inorganic material interfaces.

  10. Fluoride adsorption onto amorphous aluminum hydroxide: Roles of the surface acetate anions.

    PubMed

    Zhang, Yong-Xing; Jia, Yong

    2016-12-01

    Amorphous aluminum hydroxide with hydroxyl groups, acetate anions and chlorine anions enriched surface was synthesized, and was characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption isotherms. Batch experiments were performed to study the influence of various experimental parameters such as contact time, initial fluoride concentration, temperature, pH value and the presence of competing anions on the adsorption of fluoride on amorphous aluminum hydroxide. The kinetic data was well fitted to pseudo-second-order model. The fluoride adsorption on the amorphous aluminum hydroxide can be well described by the Langmuir model, and the maximum adsorption capacity was 63.94mgg(-1) at pH 7.0. Thermodynamic parameters including the Gibbs free energy, standard enthalpy and standard entropy were calculated, and the results suggested that the adsorption of fluoride on the amorphous aluminum hydroxide was a feasible, spontaneous and exothermic process. The adsorption mechanism was revealed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis. The results suggested that the surface acetate anions and surface chlorine anions played important roles in the fluoride removal process. PMID:27565961

  11. On the role of long range interactions for the adsorption of sexithiophene on Ag(110) surface

    SciTech Connect

    Matos, Jeronimo; Rojas, Tomas; Yildirim, Handan E-mail: Abdelkader.Kara@ucf.edu; Kara, Abdelkader E-mail: Abdelkader.Kara@ucf.edu

    2014-04-14

    The adsorption characteristics of the sexithiophene (6T) molecule on Ag(110) are studied using density functional theory with the inclusion of van der Waals (vdW) interactions. The stable adsorption configurations on 6T on Ag(110) as well as the nature of bonding the Ag substrate are evaluated. We also assess the performance of the vdW-DF method in describing the adsorption, energetics, heights, as well as the interface characteristics with the Ag(110) surface. We find two lowest adsorption energy configurations, at which the 6T molecule aligns with its molecular long axis parallel and perpendicular to the [001] direction, to be energetically close to each other, suggesting that they may coexist. Our findings indicate a significant increase in the 6T adsorption energies upon the inclusion of vdW interactions with the highest increase obtained using the opt-type functionals, in particular with the optB86b-vdW functional. The revPBE-vdW and rPW86-vdW2 functionals lead to less enhancement in adsorption energies that is attributed to the strong repulsive nature of these functionals, in agreement with earlier predictions. Upon adsorption of the 6T molecule, the changes in the atomic and electronic structures of the 6T molecule and Ag surface are found to be negligible; there is no charge transfer, and no interface state is observed. The work function is reduced upon adsorption with the largest change is ∼0.6 eV obtained using the optB88-vdW functional. The results are in good agreement with the available experimental observations of the adsorption configurations and the work function changes. Based on our results, we conclude that the nature of bonding for 6T on Ag(110) can be classified as strong physisorption.

  12. Apparatus to measure adsorption of condensable solvents on technical surfaces by photothermal deflection

    NASA Astrophysics Data System (ADS)

    Plimmer, M. D.; du Colombier, D.; Iraqi Houssaini, N.; Silvestri, Z.; Pinot, P.; Hannachi, R.

    2012-11-01

    This article describes an instrument for the measurement of the mirage effect as a tool to determine the molar adsorption per unit surface area Y1 of condensable solvents in the presence of a non-condensable carrier gas. The present apparatus is a much improved version of previous prototypes developed in our laboratory and elsewhere with a higher surface bake-out temperature (150 °C rather than 40 °C), lower residual vacuum (3 Pa versus 100 Pa), greater sample surface (40 mm diameter instead of 10 mm), more powerful optical pump beam (150 W cf. 50 W), and larger saturated vapour preparation volume (4 L instead of 1 L). The new set-up also includes the in situ monitoring of the surface via a reflected HeNe laser beam for the real-time detection of the onset of condensation. Here, we give a detailed description of the various components, outline the experimental procedure, show typical results, and suggest some straightforward improvements.

  13. Apparatus to measure adsorption of condensable solvents on technical surfaces by photothermal deflection.

    PubMed

    Plimmer, M D; du Colombier, D; Iraqi Houssaini, N; Silvestri, Z; Pinot, P; Hannachi, R

    2012-11-01

    This article describes an instrument for the measurement of the mirage effect as a tool to determine the molar adsorption per unit surface area Y(1) of condensable solvents in the presence of a non-condensable carrier gas. The present apparatus is a much improved version of previous prototypes developed in our laboratory and elsewhere with a higher surface bake-out temperature (150 °C rather than 40 °C), lower residual vacuum (3 Pa versus 100 Pa), greater sample surface (40 mm diameter instead of 10 mm), more powerful optical pump beam (150 W cf. 50 W), and larger saturated vapour preparation volume (4 L instead of 1 L). The new set-up also includes the in situ monitoring of the surface via a reflected HeNe laser beam for the real-time detection of the onset of condensation. Here, we give a detailed description of the various components, outline the experimental procedure, show typical results, and suggest some straightforward improvements. PMID:23206087

  14. The adsorption of methyl methacrylate and vinyl acetate polymers on α-quartz surface: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Yan, Lijing; Yang, Yan; Jiang, Hui; Zhang, Bingjian; Zhang, Hui

    2016-01-01

    The molecular dynamics simulation was used to investigate the adsorption of polymethyl methacrylate (PMMA) and polyvinyl acetate (PVA), the commonly used surface coating materials, on α-quartz surface. The objective is to understand the interactions between quartz surface and polymers. The results clearly show adsorption of both polymers onto the quartz surface. Carbonyl group plays a significant role in the adsorption process. The adsorption energies of PMMA and PVA on α-quartz surface did not show significant difference, however, more hydrogen bonds were observed on the PVA/quartz system than PMMA/quartz. These observations might offer some insights on the polymer-quartz adhesion and its failure mechanism.

  15. The Effect of 200 MPa Pressure on Specific Surface Area of Clay

    NASA Astrophysics Data System (ADS)

    Koszela-Marek, Ewa

    2015-02-01

    The paper presents the results of laboratory studies of the 200 MPa pressure effect on specific surface area of clay. The original high-pressure investigation stand was used for the pressure tests. Determination of the specific surface area was performed by the methylene blue adsorption method. The results of the specific surface area test were compared for non-pressurized clays and for clays pressured in a high-pressure chamber. It was found that the specific surface area of pressurized soil clearly increased. This shows that some microstructural changes take place in the soil skeleton of clays.

  16. Adsorption of phthalic acid and its esters onto high-area activated carbon-cloth studied by in situ UV-spectroscopy.

    PubMed

    Ayranci, Erol; Bayram, Edip

    2005-06-30

    The adsorption behavior of phthalic acid and its three esters dimethyl phthalate, diethyl phthalate and diallyl phthalate onto high-area activated carbon-cloth was studied by in situ UV-spectroscopic technique. The effect of ionization of phthalic acid on its adsorption was examined by carrying out the adsorption process in three media; water, 1 M H(2)SO(4) and 0.005 M NaOH. Maximum adsorption was observed in 1 M H(2)SO(4) and almost no adsorption in 0.005 M NaOH. These results were discussed in terms of electrostatic and dispersion interactions between the adsorbate species and the carbon-cloth surface taking the point of zero charge (pH(pzc)) of the carbon-cloth into account. The adsorption process for the phthalate species studied was found to follow the first-order rate law, and the rate constants were determined. The isotherm data for the adsorption of phthalic acid and its esters were derived experimentally and fitted to Langmuir and Freundlich isotherm equations. Both equations were found to represent the experimental isotherm data almost equally well. PMID:15943937

  17. Theory of polyelectrolyte adsorption on heterogeneously charged surfaces applied to soluble protein-polyelectrolyte complexes

    NASA Astrophysics Data System (ADS)

    de Vries, R.; Weinbreck, F.; de Kruif, C. G.

    2003-03-01

    Existing theoretical approaches to polymer adsorption on heterogeneous surfaces are applied to the problems of polyelectrolyte and polyampholyte adsorption on randomly charged surfaces. Also, analytical estimates are developed for the critical pH at which weakly charged polyelectrolytes and globular proteins start forming soluble complexes. Below a critical salt concentration, soluble complexes form "on the wrong side" of the protein isoelectric point due to the heterogeneity of the protein surface charge distribution. The analytical estimates are consistent with experimental data on soluble complexes in mixtures of gum arabic and whey protein isolate.

  18. Effect of zeta potentials on bovine serum albumin adsorption to hydroxyapatite surfaces.

    PubMed

    Miyake, Nahoko; Sato, Toru; Maki, Yoshinobu

    2013-01-01

    The aim of the present study was to examine the adsorption of bovine serum albumin (BSA) to hydroxyapatite surfaces by means of zeta potential. The electrophoretic mobility of both hydroxyapatite and BSA were negative, with BSA itself less negative than hydroxyapatite. The zeta potential of the surface of BSA-adsorbed hydroxyapatite was significantly more negative than that of hydroxyapatite alone (p<0.0001). The BSA histogram indicated two negative peaks, and the zeta potential of BSA-adsorbed hydroxyapatite also showed two similar negative peaks. These results suggest that BSA adsorption to hydroxyapatite surfaces is related to electrostatic interaction. PMID:23903580

  19. Surface complexation modeling of U(VI) adsorption by aquifer sediments from a former mill tailings site at Rifle, Colorado

    USGS Publications Warehouse

    Hyun, S.P.; Fox, P.M.; Davis, J.A.; Campbell, K.M.; Hayes, K.F.; Long, P.E.

    2009-01-01

    A study of U(VI) adsorption by aquifer sediment samples from a former uranium mill tailings site at Rifle, Colorado, was conducted under oxic conditions as a function of pH, U(VI), Ca, and dissolved carbonate concentration. Batch adsorption experiments were performed using <2mm size sediment fractions, a sand-sized fraction, and artificial groundwater solutions prepared to simulate the field groundwater composition. To encompass the geochemical conditions of the alluvial aquifer at the site, the experimental conditions ranged from 6.8 ?? 10-8 to 10-5 M in [U(VI)]tot, 7.2 to 8.0 in pH, 3.0 ?? 10-3 to 6.0 ?? 10 -3 M in [Ca2+], and 0.05 to 2.6% in partial pressure of carbon dioxide. Surface area normalized U(VI) adsorption Kd values for the sand and <2 mm sediment fraction were similar, suggesting a similar reactive surface coating on both fractions. A two-site two-reaction, nonelectrostatic generalized composite surface complexation model was developed and successfully simulated the U(VI) adsorption data. The model successfully predicted U(VI) adsorption observed from a multilevel sampling well installed at the site. A comparison of the model with the one developed previously for a uranium mill tailings site at Naturita, Colorado, indicated that possible calcite nonequilibrium of dissolved calcium concentration should be evaluated. The modeling results also illustrate the importance of the range of data used in deriving the best fit model parameters. ?? 2009 American Chemical Society.

  20. Surface properties and adsorption characteristics to methylene blue and iodine of adsorbents from sludge.

    PubMed

    Deng, L Y; Xu, G R; Li, G B

    2010-01-01

    Adsorbent materials created from wastewater sludge have unique surface characteristics and could be effective in adsorption applications. In this research, the sludge-adsorbents were generated by pyrolyzing mixtures of sewage sludge and H(2)SO(4). Scanning electron microscope (SEM), thermal analysis, X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS) were used to analyze the properties of sludge-adsorbent. XPS results show that the adsorbent surface functional groups with high contents of oxygen-containing groups serve as active sites for the adsorption and affect the surface characteristics; the adsorption mechanism of methylene blue (MB) is mainly Brönsted acid-base reaction between the adsorbent surface and MB; and iodine atoms are bonded to the surface of the adsorbent mainly by dispersive interactions rather than by electrostatic interactions. The results also show that H(2)SO(4) level, pyrolysis temperature and sulfuric acid/sludge weight ratio actually affected the adsorption characteristics. Using the conditions (H(2)SO(4) level of 1-18 M, pyrolysis temperature of 650°C, and weight ratio of 0.8), the adsorption capacities for MB and iodine were 74.7-62.3 mg g(-1) and 169.5-209.3 mg g(-1), respectively.

  1. The role of van der Waals interactions in the adsorption of noble gases on metal surfaces

    SciTech Connect

    Chen, De-Li; Al-Saidi, W A; Johnson, J Karl

    2012-10-03

    Adsorption of noble gases on metal surfaces is determined by weak interactions. We applied two versions of the nonlocal van der Waals density functional (vdW-DF) to compute adsorption energies of Ar, Kr, and Xe on Pt(111), Pd(111), Cu(111), and Cu(110) metal surfaces. We have compared our results with data obtained using other density functional approaches, including the semiempirical vdW corrected DFT-D2. The vdW-DF results show considerable improvements in the description of adsorption energies and equilibrium distances over other DFTbased methods, giving good agreement with experiments. We have also calculated perpendicular vibrational energies for noble gases on the metal surfaces using vdWDF data and found excellent agreement with available experimental results. Our vdW-DF calculations show that adsorption of noble gases on low-coordination sites is energetically favored over high-coordination sites, but only by a few meV. Analysis of the 2-dimensional potential energy surface shows that the high-coordination sites are local maxima on the 2-dimensional potential energy surface and therefore unlikely to be observed in experiments, which provides an explanation of the experimental observations. The DFT-D2 approach with the standard parameterization was found to overestimate the dispersion interactions, and to give the wrong adsorption site preference for four of the nine systems we studied.

  2. DFT simulation of the adsorption of sodium silicate species on kaolinite surfaces

    NASA Astrophysics Data System (ADS)

    Han, Yonghua; Liu, Wenli; Chen, Jianhua

    2016-05-01

    The adsorption of Si(OH)4 molecules and the SiO(OH)3- anion on kaolinite surfaces was studied using density functional theory (DFT) calculations to investigate the dispersion mechanism of sodium silicate on kaolinite particles. The calculated results demonstrate that Si(OH)4 and SiO(OH)3- primarily adsorb on kaolinite Al-terminated (0 0 1) surfaces. Both Si(OH)4 and SiO(OH)3- bond with the Al-terminated surface by hybridization of the O2p orbital and H1s orbital. The unbonded O atom of SiO(OH)3- is notably active. The SiO(OH)3- anion can add more electrons and form a stronger electrostatic interaction with the Al surface. The adsorption of SiO(OH)3- is more stable than the adsorption of Si(OH)4. After adsorption of sodium silicate, the surfaces of kaolinite can become more hydrophilic and carry more negative charge. Therefore, the adsorption of silicate species makes the fine particles of kaolinite disperse in aqueous solution more easily.

  3. Surface Reactivity of Iron Oxide Pigmentary Powders toward Atmospheric Components: XPS and Gravimetry of Oxygen and Water Vapor Adsorption

    PubMed

    Ismail; Cadenhead; Zaki

    1996-11-10

    The adsorption of oxygen and water vapor on a number of specially prepared alpha-Fe2O3 samples was measured gravimetrically at 25°C. The samples themselves were prepared from a steel-pickling chemical waste (97 wt% FeSO4·7H2O) by roasting the original material at 700°C for 5 h in air, oxygen, and nitrogen. Estimated surface coverages by the adsorbed oxygen and water vapor were made on the basis of nitrogen-adsorption-based surface areas, while the nature of the sample surfaces was investigated by both X-ray photoelectron spectroscopy (XPS) and field emission SEM (FESEM) techniques. In addition a depth profiling study utilizing a sputtering argon beam and XPS was undertaken. Morphological studies using FESEM showed that, while the surface areas were essentially the same (27-29 m2/g) for all three samples, the sample prepared in nitrogen had a significantly larger particle size than the other two. These studies also indicated that neither oxygen nor water vapor adsorption caused any significant structural changes. The differing sample preparations resulted in differing oxygenated surfaces for the alpha-Fe2O3 samples, with the degree of oxygenation decreasing in the order of preparatory gases: oxygen, (wet) air, nitrogen. The amounts of both oxygen and water vapor adsorbed were in inverse proportion to the original degree of surface oxygenation, though the amounts of both represented fractional coverage at best. While the water vapor adsorption was always greater than that of oxygen, the former was more weakly adsorbed, as was indicated by the ease of desorption. Depth profiling failed to indicate any bulk diffusion of oxygen but could not be considered reliable since even the attenuated argon beam used here still brought about reduction of surface iron. Both oxygen and dissociative water adsorption are thought to involve surface sites of high coordination unsaturation. Oxygen is postulated to adsorb on such poorly oxygenated sites primarily as O-2; however, O2

  4. Surface Plasmon Resonance Analysis of Histidine-Tagged F1-ATPase Surface Adsorption

    NASA Astrophysics Data System (ADS)

    Tucker, Jenifer K.; Richter, Mark L.; Berrie, Cindy L.

    2015-11-01

    Studies of the rotational activity of the enzymatic core (α3β3γ) of the F1-ATPase motor protein have relied on binding the enzyme to NTA-coated glass surfaces via polyhistidine tags engineered into the C-termini of each of the three α or β subunits. Those studies revealed the rotational motion of the central γ subunit by monitoring the motion of attached micron-long actin filaments or spherical nanoparticles. However, only a small percentage of the attached filaments or particles were observed to rotate, likely due, at least in part, to non-uniform surface attachment of the motor proteins. In this study, we have applied surface plasmon resonance to monitor the kinetics and affinity of binding of the His-tagged motor protein to NTA-coated gold sensor surfaces. The binding data, when fit to a heterogeneous binding model, exhibit two sets of adsorption-desorption rate constants with two dissociation constants of 4.0 × 10-9 M and 8.6 × 10-11 M for 6His-α3β3γ binding to the nickel ion-activated NTA surface. The data are consistent with mixed attachment of the protein via two (bimodal) and three (trimodal) NTA/Ni2+-His-tag interactions, respectively, with the less stable bimodal interaction dominating. The results provide a partial explanation for the low number of surface-attached F1 motors previously observed in rotation studies and suggest alternative approaches to uniform F1 motor surface attachment for future fabrication of motor-based nanobiodevices and materials.

  5. Investigations of adsorption sites on oxide surfaces using solid-state NMR and TPD-IGC

    NASA Astrophysics Data System (ADS)

    Golombeck, Rebecca A.

    The number and chemical identity of reactive sites on surfaces of glass affects the processing, reliability, and lifetime of a number of important commercial products. Surface site densities, distributions, and structural identities are closely tied to the formation and processing of the glass surface, and exert a direct influence on strength and coating performance. The surface of a glass sample may vary markedly from the composition and chemistry of the bulk glass. We are taking a physicochemical approach to understanding adsorption sites on pristine multicomponent glass fibers surfaces, directly addressing the effect of processing on surface reactivity. This project aimed to understand the energy distributions of surface adsorption sites, the chemical/structural identity of those sites, and the relationship of these glasses to glass composition, thermal history, and in future work, surface coatings. We have studied the bulk and surface structure as well as the surface reactivity of the glass fibers with solid-state nuclear magnetic resonance (NMR) spectroscopy, inverse gas chromatography (IGC), and computational chemistry methods. These methods, solid-state NMR and IGC, typically require high surface area materials; however, by using probe molecules for NMR experiments or packing a column at high density for IGC measurements, lower surface area materials, such as glass fibers, can be investigated. The glasses used within this study were chosen as representative specimens of fibers with potentially different reactive sites on their surfaces. The two glass compositions were centered around a nominal E-glass, which contains very little alkali cations and mainly alkaline earth cations, and wool glass, which contains an abundance of alkali cations. The concentration of boron was varied from 0 to 8 mole % in both fiber compositions. Fibers were drawn from each composition at a variety of temperatures and draw speeds to provide a range of glass samples with varying

  6. Adsorption of malachite green by magnetic litchi pericarps: A response surface methodology investigation.

    PubMed

    Zheng, Hao; Qi, Jinqiu; Jiang, Ruixue; Gao, Yan; Li, Xiaochen

    2015-10-01

    In this work, we synthesized a novel magnetic adsorbent containing litchi pericarps, denoted as MLP, for the removal of malachite green (MG) from solution. The factors influencing MG adsorption, such as contact time, adsorbent dosage, and initial dye concentration, were optimized using the Box-Behnken response surface methodology (RSM). The adsorption isotherms as well as the kinetics and thermodynamics of the adsorption of MG onto MLP are discussed. The results showed that MLP has a maximum adsorption efficiency of 99.5% when the temperature, pH, contact time, adsorbent dosage, and initial MG concentration were optimally set as 25 °C, 6.0, 66.69 min, 5.14 g/L, and 150 mg/L, respectively. The best model to describe this process is the Langmuir isotherm, with the maximum adsorption capacity being 70.42 mg/g. In addition, the kinetics of MG adsorption onto MLP followed a pseudo-second-order model; moreover, thermodynamic analysis suggested that MG adsorption onto MLP is spontaneous and endothermic. Finally, it was found that the new magnetic adsorbent can be separated easily and rapidly from mixed solutions in the presence of an external magnetic field. PMID:26254991

  7. Adsorption of malachite green by magnetic litchi pericarps: A response surface methodology investigation.

    PubMed

    Zheng, Hao; Qi, Jinqiu; Jiang, Ruixue; Gao, Yan; Li, Xiaochen

    2015-10-01

    In this work, we synthesized a novel magnetic adsorbent containing litchi pericarps, denoted as MLP, for the removal of malachite green (MG) from solution. The factors influencing MG adsorption, such as contact time, adsorbent dosage, and initial dye concentration, were optimized using the Box-Behnken response surface methodology (RSM). The adsorption isotherms as well as the kinetics and thermodynamics of the adsorption of MG onto MLP are discussed. The results showed that MLP has a maximum adsorption efficiency of 99.5% when the temperature, pH, contact time, adsorbent dosage, and initial MG concentration were optimally set as 25 °C, 6.0, 66.69 min, 5.14 g/L, and 150 mg/L, respectively. The best model to describe this process is the Langmuir isotherm, with the maximum adsorption capacity being 70.42 mg/g. In addition, the kinetics of MG adsorption onto MLP followed a pseudo-second-order model; moreover, thermodynamic analysis suggested that MG adsorption onto MLP is spontaneous and endothermic. Finally, it was found that the new magnetic adsorbent can be separated easily and rapidly from mixed solutions in the presence of an external magnetic field.

  8. Surface-Bound Casein Modulates the Adsorption and Activity of Kinesin on SiO2 Surfaces

    PubMed Central

    Ozeki, Tomomitsu; Verma, Vivek; Uppalapati, Maruti; Suzuki, Yukiko; Nakamura, Mikihiko; Catchmark, Jeffrey M.; Hancock, William O.

    2009-01-01

    Abstract Conventional kinesin is routinely adsorbed to hydrophilic surfaces such as SiO2. Pretreatment of surfaces with casein has become the standard protocol for achieving optimal kinesin activity, but the mechanism by which casein enhances kinesin surface adsorption and function is poorly understood. We used quartz crystal microbalance measurements and microtubule gliding assays to uncover the role that casein plays in enhancing the activity of surface-adsorbed kinesin. On SiO2 surfaces, casein adsorbs as both a tightly bound monolayer and a reversibly bound second layer that has a dissociation constant of 500 nM and can be desorbed by washing with casein-free buffer. Experiments using truncated kinesins demonstrate that in the presence of soluble casein, kinesin tails bind well to the surface, whereas kinesin head binding is blocked. Removing soluble casein reverses these binding profiles. Surprisingly, reversibly bound casein plays only a moderate role during kinesin adsorption, but it significantly enhances kinesin activity when surface-adsorbed motors are interacting with microtubules. These results point to a model in which a dynamic casein bilayer prevents reversible association of the heads with the surface and enhances association of the kinesin tail with the surface. Understanding protein-surface interactions in this model system should provide a framework for engineering surfaces for functional adsorption of other motor proteins and surface-active enzymes. PMID:19383474

  9. Water adsorption behavior on metal surfaces and its influence on surface potential studied by in situ SPM

    NASA Astrophysics Data System (ADS)

    Guo, L. Q.; Zhao, X. M.; Bai, Y.; Qiao, L. J.

    2012-09-01

    The water adsorption behavior on the surfaces of chromium, copper and gold and its effect on the surface potential at various relative humidity were studied by in situ scanning Kelvin probe force microscopy (SKPFM) combined with force calibration. The thickness of water layer on different surfaces was obtained from the force-distance curve. It increases with the rise of humidity. The Volta potential map was measured using SKPFM within a wide humidity range of 20-100% as a function of the thickness of water layers. The surface potential decreases with the increasing thickness of water layers on the metal surfaces. The difference in the water adsorption behavior and its effect on surface potential originates from the different surface properties of three metals, such as the roughness and contact angle.

  10. On modeling biomolecular-surface nonbonded interactions: application to nucleobase adsorption on single-wall carbon nanotube surfaces.

    PubMed

    Akdim, B; Pachter, R; Day, P N; Kim, S S; Naik, R R

    2012-04-27

    In this work we explored the selectivity of single nucleobases towards adsorption on chiral single-wall carbon nanotubes (SWCNTs) by density functional theory calculations. Specifically, the adsorption of molecular models of guanine (G), adenine (A), thymine (T), and cytosine (C), as well as of AT and GC Watson-Crick (WC) base pairs on chiral SWCNT C(6, 5), C(9, 1) and C(8, 3) model structures, was analyzed in detail. The importance of correcting the exchange-correlation functional for London dispersion was clearly demonstrated, yet limitations in modeling such interactions by considering the SWCNT as a molecular model may mask subtle effects in a molecular-macroscopic material system. The trend in the calculated adsorption energies of the nucleobases on same diameter C(6, 5) and C(9, 1) SWCNT surfaces, i.e., G > A > T > C, was consistent with related computations and experimental work on graphitic surfaces, however contradicting experimental data on the adsorption of single-strand short homo-oligonucleotides on SWCNTs that demonstrated a trend of G > C > A > T (Albertorio et al 2009 Nanotechnology 20 395101). A possible role of electrostatic interactions in this case was partially captured by applying the effective fragment potential method, emphasizing that the interplay of the various contributions in modeling nonbonded interactions is complicated by theoretical limitations. Finally, because the calculated adsorption energies for Watson-Crick base pairs have shown little effect upon adsorption of the base pair farther from the surface, the results on SWCNT sorting by salmon genomic DNA could be indicative of partial unfolding of the double helix upon adsorption on the SWCNT surface.

  11. Theory of quasicrystal surfaces: Probing the chemical reactivity by atomic and molecular adsorption

    NASA Astrophysics Data System (ADS)

    Krajčí, M.; Hafner, J.

    The adsorption of oxygen and carbon atoms and of carbon monoxide molecules on a fivefold surface of icosahedral Al-Pd-Mn quasicrystals has been investigated using ab initio density-functional calculations. The quasicrystalline surface has been modeled by periodically repeated slabs cut from rational approximants to the quasicrystalline structure. Atomic and molecular adsorption have been studied for a large number of possible adsorption sites by performing three-dimensional static relaxations of the adsorbate/substrate complex. Four different scenarios for the dissociative adsorption of the CO molecule have been investigated via nudged-elastic band calculations of the transition states. Al and Mn-metal atoms present at the surface bind C and O atoms rather strongly, while Pd atoms are unstable adsorption sites: during relaxation, the adsorbate drifts to the nearest strong-binding site. The chemical reactivity with respect to a CO molecule varies very strongly across the surface. The adsorption close to Mn sites is promoted by rather strong covalent effects, but CO is only physisorbed at Al sites via weak polarization forces. On the basis of the observed local variations of the adsorption strength, we develop scenarios for dissociation and determine the potential energy barriers for this processes. We find that CO adsorbed close to a transition-metal atom can dissociate via an activated process, but the dissociation rate is expected to be rather low because of a high dissociation barrier and a "late" transition state. CO adsorbed close to Al atoms will desorb before dissociation. Surface vacancies present as a consequence of the irregular coordination of the Mackay cluster in the quasiperiodic structure will act as strongly attractive traps for diffusing molecules. Mn surface atoms are located in the center of truncated Mackay clusters. In scanning tunneling electron microscopy (STM) these truncated clusters are imaged as "white flowers". Surface vacancies are

  12. Adsorption of uranium by amidoximated chitosan-grafted polyacrylonitrile, using response surface methodology.

    PubMed

    Xu, Chao; Wang, Jingjing; Yang, Tilong; Chen, Xia; Liu, Xunyue; Ding, Xingcheng

    2015-05-01

    The amidoximated chitosan-grafted polyacrylonitrile (CTS-g-PAO) was prepared for the adsorption of uranium from water. The effects of pH, concentration of uranium and the solid-liquid ratio on the adsorption of uranium by CTS-g-PAO were optimized using Doehlert design of response surface methodology (RSM). The adsorption capacity and removal efficiency achieved 312.06 mg/g and 86.02%, respectively. The adsorption process attained equilibrium only in 120 min. More than 80% of the absorbed uranium could be desorbed by 0.1 mol/l HCl or EDTA-Na, and CTS-g-PAO could be reused at least 3 times. The CTS-g-PAO and U(VI) ions formed a chelate complex due to FTIR spectral analysis. The surface morphology of CTS-g-PAO was also investigated by SEM. The adsorption process was better described by Langmuir isotherm and pseudo second order kinetic model. Results obtained indicated that CTS-g-PAO was very promising in adsorption of uranium from water.

  13. Self-Catalyzed Carbon Dioxide Adsorption by Metal-Organic Chains on Gold Surfaces

    SciTech Connect

    Feng, Min; Sun, Hao; Zhao, Jin; Petek, Hrvoje

    2014-08-26

    Efficient capture of CO2 by chemical means requires a microscopic understanding of the interactions of the molecule-substrate bonding and adsorption-induced collective phenomena. By molecule-resolved imaging with scanning tunneling microscopy (STM), we investigate self-catalyzed CO2 adsorption on one-dimensional (1D) substrates composed of self-assembled metal-organic chains (MOCs) supported on gold surfaces. CO2 adsorption turns on attractive interchain interactions, which induce pronounced surface structural changes; the initially uniformly dispersed chains gather into close packed bundles, which are held together by highly ordered, single molecule wide CO2 ranks. CO2 molecules create more favorable adsorption sites for further CO2 adsorption by mediating the interchain attraction, thereby self-catalyzing their capture. The release of CO2 molecules by thermal desorption returns the MOCs to their original structure, indicating that the CO2 capture and release are reversible processes. The real space microscopic characterization of the self-catalyzed CO2 adsorption on 1D substrates could be exploited as platform for design of molecular materials for CO2 capture and reduction.

  14. Adsorption of uranium by amidoximated chitosan-grafted polyacrylonitrile, using response surface methodology.

    PubMed

    Xu, Chao; Wang, Jingjing; Yang, Tilong; Chen, Xia; Liu, Xunyue; Ding, Xingcheng

    2015-05-01

    The amidoximated chitosan-grafted polyacrylonitrile (CTS-g-PAO) was prepared for the adsorption of uranium from water. The effects of pH, concentration of uranium and the solid-liquid ratio on the adsorption of uranium by CTS-g-PAO were optimized using Doehlert design of response surface methodology (RSM). The adsorption capacity and removal efficiency achieved 312.06 mg/g and 86.02%, respectively. The adsorption process attained equilibrium only in 120 min. More than 80% of the absorbed uranium could be desorbed by 0.1 mol/l HCl or EDTA-Na, and CTS-g-PAO could be reused at least 3 times. The CTS-g-PAO and U(VI) ions formed a chelate complex due to FTIR spectral analysis. The surface morphology of CTS-g-PAO was also investigated by SEM. The adsorption process was better described by Langmuir isotherm and pseudo second order kinetic model. Results obtained indicated that CTS-g-PAO was very promising in adsorption of uranium from water. PMID:25659674

  15. Ice-surface adsorption enhanced colligative effect of antifreeze proteins in ice growth inhibition.

    PubMed

    Mao, Yougang; Ba, Yong

    2006-09-01

    This Communication describes a mechanism to explain antifreeze protein's function to inhibit the growth of ice crystals. We propose that the adsorption of antifreeze protein (AFP) molecules on an ice surface induces a dense AFP-water layer, which can significantly decrease the mole fraction of the interfacial water and, thus, lower the temperature for a seed ice crystal to grow in a super-cooled AFP solution. This mechanism can also explain the nearly unchanged melting point for the ice crystal due to the AFP's ice-surface adsorption. A mathematical model combining the Langmuir theory of adsorption and the colligative effect of thermodynamics has been proposed to find the equilibrium constants of the ice-surface adsorptions, and the interfacial concentrations of AFPs through fitting the theoretical curves to the experimental thermal hysteresis data. This model has been demonstrated by using the experimental data of serial size-mutated beetle Tenebrio molitor (Tm) AFPs. It was found that the AFP's ice-surface adsorptions could increase the interfacial AFP's concentrations by 3 to 4 orders compared with those in the bulk AFP solutions.

  16. Ice-surface adsorption enhanced colligative effect of antifreeze proteins in ice growth inhibition

    NASA Astrophysics Data System (ADS)

    Mao, Yougang; Ba, Yong

    2006-09-01

    This Communication describes a mechanism to explain antifreeze protein's function to inhibit the growth of ice crystals. We propose that the adsorption of antifreeze protein (AFP) molecules on an ice surface induces a dense AFP-water layer, which can significantly decrease the mole fraction of the interfacial water and, thus, lower the temperature for a seed ice crystal to grow in a super-cooled AFP solution. This mechanism can also explain the nearly unchanged melting point for the ice crystal due to the AFP's ice-surface adsorption. A mathematical model combining the Langmuir theory of adsorption and the colligative effect of thermodynamics has been proposed to find the equilibrium constants of the ice-surface adsorptions, and the interfacial concentrations of AFPs through fitting the theoretical curves to the experimental thermal hysteresis data. This model has been demonstrated by using the experimental data of serial size-mutated beetle Tenebrio molitor (Tm) AFPs. It was found that the AFP's ice-surface adsorptions could increase the interfacial AFP's concentrations by 3 to 4 orders compared with those in the bulk AFP solutions.

  17. Effects of topology on the adsorption of singly tethered ring polymers to attractive surfaces.

    PubMed

    Li, Bing; Sun, Zhao-Yan; An, Li-Jia

    2015-07-14

    We investigate the effect of topology on the equilibrium behavior of singly tethered ring polymers adsorbed on an attractive surface. We focus on the change of square radius of gyration Rg(2), the perpendicular component Rg⊥(2) and the parallel component Rg‖(2) to the adsorbing surface, the mean contacting number of monomers with the surface , and the monomer distribution along z-direction during transition from desorption to adsorption. We find that both of the critical point of adsorption εc and the crossover exponent ϕ depend on the knot type when the chain length of ring ranges from 48 to 400. The behaviors of Rg(2), Rg⊥(2), and Rg‖(2) are found to be dependent on the topology and the monomer-surface attractive strength. At weak adsorption, the polymer chains with more complex topology are more adsorbable than those with simple topology. However, at strong adsorption, the polymer chains with complex topology are less adsorbable. By analyzing the distribution of monomer along z-direction, we give a possible mechanism for the effect of topology on the adsorption behavior.

  18. Adsorption and decomposition of H2O on cobalt surfaces: A DFT study

    NASA Astrophysics Data System (ADS)

    Ma, F. F.; Ma, S. H.; Jiao, Z. Y.; Dai, X. Q.

    2016-10-01

    Water adsorption and dissociation on clean and O-covered Co(100), Co(110) and Co(111) surfaces are studied using the density functional theory calculations. The results indicate that molecular water weakly binds to the surfaces and is feasible to desorption from the clean surfaces. Moreover, the pre-adsorption of O atom increases the binding of water to the surfaces, and prominently decreases the activation barriers of water dissociation into OH, especially on Co(110) surface. In contrast, the activation barrier for OH dissociation is slightly affected in the presence of O atom. Overall, this study reveals that O-assisted H2O favorably adsorbs dissociatively, forming OH chemisorbed on the surfaces, which further hinders H2O dissociation, and also illustrates the fact that molecular water dissociation is structure-sensitive on metal surfaces.

  19. Krypton Adsorption on Zeolite-Templated Carbon and Anomalous Surface Thermodynamics.

    PubMed

    Murialdo, Maxwell; Stadie, Nicholas P; Ahn, Channing C; Fultz, Brent

    2015-07-28

    Krypton adsorption was measured at eight temperatures between 253 and 433 K on a zeolite-templated carbon and two commercial carbons. The data were fitted using a generalized Langmuir isotherm model and thermodynamic properties were extracted. Differing from that on commercial carbons, krypton adsorption on the zeolite-templated carbon is accompanied by an increasing isosteric enthalpy of adsorption, rising by up to 1.4 kJ mol(-1) as a function of coverage. This increase is a result of enhanced adsorbate-adsorbate interactions promoted by the ordered, nanostructured surface of the adsorbent. An assessment of the strength and nature of these adsorbate-adsorbate interactions is made by comparing the measured isosteric enthalpies of adsorption (and other thermodynamic quantities) to fundamental metrics of intermolecular interactions of krypton and other common gases.

  20. Krypton Adsorption on Zeolite-Templated Carbon and Anomalous Surface Thermodynamics.

    PubMed

    Murialdo, Maxwell; Stadie, Nicholas P; Ahn, Channing C; Fultz, Brent

    2015-07-28

    Krypton adsorption was measured at eight temperatures between 253 and 433 K on a zeolite-templated carbon and two commercial carbons. The data were fitted using a generalized Langmuir isotherm model and thermodynamic properties were extracted. Differing from that on commercial carbons, krypton adsorption on the zeolite-templated carbon is accompanied by an increasing isosteric enthalpy of adsorption, rising by up to 1.4 kJ mol(-1) as a function of coverage. This increase is a result of enhanced adsorbate-adsorbate interactions promoted by the ordered, nanostructured surface of the adsorbent. An assessment of the strength and nature of these adsorbate-adsorbate interactions is made by comparing the measured isosteric enthalpies of adsorption (and other thermodynamic quantities) to fundamental metrics of intermolecular interactions of krypton and other common gases. PMID:26136159

  1. Adsorption and desorption of NO and CO on a Pt(111)Ge surface alloy

    NASA Astrophysics Data System (ADS)

    Fukutani, K.; Magkoev, T. T.; Murata, Y.; Terakura, K.

    1996-08-01

    Adsorption of NO and CO on Pt(111) alloyed with a few per cent of Ge is investigated by reflection—absorption infrared spectroscopy and thermal desorption spectroscopy. Both molecules exclusively occupy the on-top site in contrast to bridge and on-top adsorption on clean Pt(111). The adsorption energy of NO is dramatically reduced compared with that on clean Pt(111). Photodesorption of CO observed on the clean Pt(111) is noticeably suppressed on the Pt(111)Ge surface alloy, while NO desorption is induced by photon irradiation. The rotational and translational temperatures of photodesorbed No are similar to those on clean Pt(111). The change in chemical properties of Pt(111) for molecular adsorption is discussed in terms of d-band filling of the substrate.

  2. Nisin adsorption on hydrophilic and hydrophobic surfaces: evidence of its interactions and antibacterial activity.

    PubMed

    Karam, Layal; Jama, Charafeddine; Nuns, Nicolas; Mamede, Anne-Sophie; Dhulster, Pascal; Chihib, Nour-Eddine

    2013-06-01

    Study of peptides adsorption on surfaces remains a current challenge in literature. A complementary approach, combining X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to investigate the antimicrobial peptide nisin adsorption on hydrophilic and hydrophobic surfaces. The native low density polyethylene was used as hydrophobic support and it was grafted with acrylic acid to render it hydrophilic. XPS permitted to confirm nisin adsorption and to determine its amount on the surfaces. ToF-SIMS permitted to identify the adsorbed bacteriocin type and to observe its distribution and orientation behavior on both types of surfaces. Nisin was more oriented by its hydrophobic side to the hydrophobic substrate and by its hydrophilic side to the outer layers of the adsorbed peptide, in contrast to what was observed on the hydrophilic substrate. A correlation was found between XPS and ToF-SIMS results, the types of interactions on both surfaces and the observed antibacterial activity. Such interfacial studies are crucial for better understanding the peptides interactions and adsorption on surfaces and must be considered when setting up antimicrobial surfaces.

  3. First-principles study of oxygen adsorption and diffusion on the UN(001) surface

    NASA Astrophysics Data System (ADS)

    Nie, J. L.; Ao, L.; Zu, X. T.; Huang, H.; Liu, K. Z.

    2015-12-01

    First-principles calculations have been performed to study the interaction of oxygen with UN(001) surface. The molecule oxygen was found to dissociate spontaneously on all considered adsorption sites on the surface. Atomic oxygen (O) preferred to adsorb on a hollow site or the top of uranium ions, which were energetically degenerate. Adsorption on top of nitrogen (N) ion was found to be unstable which may be attributed to the repulsion of negatively charged O with the N anions. In comparison with those on α-U(001)surface at the same coverage, the adsorption of O on UN(001) surface was found to be less stable, being about 0.7 eV higher in adsorption energy. The diffusion barrier for O on the surface was found to be ∼0.5 eV, similar to those of α-U(001)surface. The penetration of O into the substrate was difficult with a high barrier of 2.86 eV. Analysis on the density of states (DOS) has shown that the adsorbed oxygen has strong chemical interaction with surface ions, characterized by the hybridization of O 2p states with N 2p and U 6d, U 5f states.

  4. Nisin adsorption on hydrophilic and hydrophobic surfaces: evidence of its interactions and antibacterial activity.

    PubMed

    Karam, Layal; Jama, Charafeddine; Nuns, Nicolas; Mamede, Anne-Sophie; Dhulster, Pascal; Chihib, Nour-Eddine

    2013-06-01

    Study of peptides adsorption on surfaces remains a current challenge in literature. A complementary approach, combining X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to investigate the antimicrobial peptide nisin adsorption on hydrophilic and hydrophobic surfaces. The native low density polyethylene was used as hydrophobic support and it was grafted with acrylic acid to render it hydrophilic. XPS permitted to confirm nisin adsorption and to determine its amount on the surfaces. ToF-SIMS permitted to identify the adsorbed bacteriocin type and to observe its distribution and orientation behavior on both types of surfaces. Nisin was more oriented by its hydrophobic side to the hydrophobic substrate and by its hydrophilic side to the outer layers of the adsorbed peptide, in contrast to what was observed on the hydrophilic substrate. A correlation was found between XPS and ToF-SIMS results, the types of interactions on both surfaces and the observed antibacterial activity. Such interfacial studies are crucial for better understanding the peptides interactions and adsorption on surfaces and must be considered when setting up antimicrobial surfaces. PMID:23625525

  5. X-ray Absorption Spectroscopic Quantification and Speciation Modeling of Sulfate Adsorption on Ferrihydrite Surfaces.

    PubMed

    Gu, Chunhao; Wang, Zimeng; Kubicki, James D; Wang, Xiaoming; Zhu, Mengqiang

    2016-08-01

    Sulfate adsorption on mineral surfaces is an important environmental chemical process, but the structures and respective contribution of different adsorption complexes under various environmental conditions are unclear. By combining sulfur K-edge XANES and EXAFS spectroscopy, quantum chemical calculations, and surface complexation modeling (SCM), we have shown that sulfate forms both outer-sphere complexes and bidentate-binuclear inner-sphere complexes on ferrihydrite surfaces. The relative fractions of the complexes vary with pH, ionic strength (I), and sample hydration degree (wet versus air-dried), but their structures remained the same. The inner-sphere complex adsorption loading decreases with increasing pH while remaining unchanged with I. At both I = 0.02 and 0.1 M, the outer-sphere complex loading reaches maximum at pH ∼5 and then decreases with pH, whereas it monotonically decreases with pH at I = 0.5 M. These observations result from a combination of the ionic-strength effect, the pH dependence of anion adsorption, and the competition between inner- and outer-sphere complexation. Air-drying drastically converts the outer-sphere complexes to the inner-sphere complexes. The respective contributions to the overall adsorption loading of the two complexes were directly modeled with the extended triple layer SCM by implementing the bidentate-binuclear inner-sphere complexation identified in the present study. These findings improve our understanding of sulfate adsorption and its effects on other environmental chemical processes and have important implications for generalizing the adsorption behavior of anions forming both inner- and outer-sphere complexes on mineral surfaces. PMID:27377619

  6. A combined streaming-potential optical reflectometer for studying adsorption at the water/solid surface.

    PubMed

    Theodoly, O; Cascão-Pereira, L; Bergeron, V; Radke, C J

    2005-10-25

    A novel in-situ streaming-potential optical reflectometry apparatus (SPOR) was constructed and utilized to probe the molecular architecture of aqueous adsorbates on a negatively charged silica surface. By combining optical reflectometry and electrokinetic streaming potentials, we measure simultaneously the adsorption density, gamma, and zeta potential, zeta, in a rectangular flow cell constructed with one transparent wall. Both dynamic and equilibrium measurements are possible, allowing the study of sorption kinetics and reversibility. Using SPOR, we investigate the adsorption of a classic nonionic surfactant (pentaethylene glycol monododecyl ether, C12E5), a simple cationic surfactant (hexadecyl trimethylammonium bromide, CTAB) of opposite charge to that of the substrate surface, and two cationic polyelectrolytes (poly(2-(dimethylamino)ethyl methacrylate), PDAEMA; (poly(propyl methacrylate) trimethylammonium chloride, MAPTAC). For the polyethylene oxide nonionic surfactant, bilayer adsorption is established above the critical micelle concentration (cmc) both from the adsorption amounts and from the interpretation of the observed zeta potentials. Near adsorption saturation, CTAB also forms bilayer structures on silica. Here, however, we observe a strong charge reversal of the surface. The SPOR data, along with Gouy-Chapman theory, permit assessment of the net ionization fraction of the CTAB bilayer at 10% so that most of the adsorbed CTAB molecules are counterion complexed. The adsorption of both C12E5 and CTAB is reversible. The adsorption of the cationic polymers, however, is completely irreversible to a solvent wash. As with CTAB, both PDAEMA and MAPTAC demonstrate strong charge reversal. For the polyelectrolyte molecules, however, the adsorbed layer is thin and flat. Here also, a Gouy-Chapman analysis shows that less than 20% of the adsorbed layer is ionized. Furthermore, the amount of charge reversal is inversely proportional to the Debye length in agreement

  7. Vacuum ultraviolet treatment of polyethylene to change surface properties and characteristics of protein adsorption.

    PubMed

    Vasilets, Viktor N; Kuznetsov, Artem V; Sevastianov, Viktor I

    2004-06-01

    The effects of vacuum ultraviolet (VUV) treatment on surface chemical composition morphology and albumin adsorption for low-density polyethylene (LDPE) and high-density polyethylene (HDPE) were investigated. The attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectra and contact angle measurements indicated the formation of oxygen-containing polar groups and double bonds under VUV photooxidation in the presence of air or under VUV irradiation in vacuum. Scanning electron microscopy revealed the development of regular structure with the period about 1 microm on the surface of LDPE and HDPE during VUV photooxidation. The correlation between amount of tightly adsorbed albumin and surface concentration of carboxyl groups generated by VUV irradiation was found. The aging effect for protein adsorption during long storage of VUV irradiated samples in air or phosphate-buffered saline (PBS) was studied. The obtained results prove the VUV irradiation provides a high potential to regulate protein adsorption on polymers for biomedical applications.

  8. Adsorption of V on a Hematite (0001) Surface and its Oxidation: Monolayer Coverage

    SciTech Connect

    Jin, J.; Ma, X.; Kim, C.-Y.; Ellis, D.E.; Bedzyk, M.J.

    2008-10-06

    The adsorption of a monolayer of V on idealized Fe- and oxygen-terminated hematite (0 0 0 1) surfaces and subsequent oxidation under atomic O adsorption are studied by density functional theory. Theoretical results are compared with X-ray surface standing wave and X-ray photoelectron spectroscopic measurements, and interpreted in the light of data on sub-monolayer coverages. Near-surface Fe reduction under V adsorption and accompanying structural relaxation are examined. These effects and subsequent response to oxidation, are found to be highly site specific. A full monolayer of oxygen leads to a V{sup 5+} state and reoxidation of subsurface Fe to the trivalent state, seen in both theory and experiment.

  9. Adsorption of ethanol on V2O5 (010) surface for gas-sensing applications: Ab initio investigation

    NASA Astrophysics Data System (ADS)

    Qin, Yuxiang; Cui, Mengyang; Ye, Zhenhua

    2016-08-01

    The adsorption of ethanol on V2O5 (010) surface was investigated by means of density functional theory (DFT) with a combined generalized gradient approximation (GGA) plus Hubbard U approach to exploit the potential sensing applications. The adsorption configurations were first constructed by considering different orientations of ethanol molecule to V and O sites on the "Hill"- and "Valley"-like regions of corrugated (010) surface. It is found that ethanol molecule can adsorb on whole surface in multiple stable configurations. Nevertheless the molecular adsorption on the "Hill"-like surface is calculated to occur preferentially, and the single coordinated oxygen on "Hill"-like surface (O1(H)) acting as the most energetically favorable adsorption site shows the strongest adsorption ability to ethanol molecule. Surface adsorption of ethanol tunes the electronic structure of V2O5 and cause an n-doping effect. As a consequence, the Fermi levels shift toward the conductive bond increasing the charge carrier concentration of electrons in adsorbed V2O5. The sensitive electronic structure and the multiple stable configurations to ethanol adsorption highlight the high adsorption activity and then the potential of V2O5 (010) surface applied to high sensitive sensor for ethanol vapor detection. Further Mulliken population and Natural bond orbital (NBO) calculations quantify the electron transfer from the adsorbed ethanol to the surface, and correlates the adsorption ability of surface sites with the charge donation and dispersion.

  10. Surface Characterization and in situ Protein Adsorption Studies on Carbene-Modified Polymers.

    PubMed

    Nelson, Geoffrey W; Parker, Emily M; Singh, Kulveer; Blanford, Christopher F; Moloney, Mark G; Foord, John S

    2015-10-13

    Polystyrene thin films were functionalized using a facile two-step chemical protocol involving carbene insertion followed by azo-coupling, permitting the introduction of a range of chemical functional groups, including aniline, hexyl, amine, carboxyl, phenyl, phosphonate diester, and ethylene glycol. X-ray photoelectron spectroscopy (XPS) confirmed the success of the two-step chemical modification with a grafting density of at least 1/10th of the typical loading density (10(14)-10(15)) of a self-assembled monolayer (SAM). In situ, real-time quartz crystal microbalance with dissipation (QCM-D) studies show that the dynamics of binding of bovine serum albumin (BSA) are different at each modified surface. Mass, viscoelastic, and kinetic data were analyzed, and compared to cheminformatic descriptors (i.e., c log P, polar surface area) typically used for drug discovery. Results show that functionalities may either resist or adsorb BSA, and uniquely influence its adsorption dynamics. It is concluded that carbene-based surface modification can usefully influence BSA binding dynamics in a manner consistent with, and more robust than, traditional systems based on SAM chemistry. PMID:26391812

  11. Effect of biochar aging on surface characteristics and adsorption behavior of dialkyl phthalates.

    PubMed

    Ghaffar, Abdul; Ghosh, Saikat; Li, Fangfang; Dong, Xudong; Zhang, Di; Wu, Min; Li, Hao; Pan, Bo

    2015-11-01

    The implications of biochar aging regarding their material properties as well as their interactions with other contaminants are not vivid. We report the role of biochar aging on sorption behavior of di-alkyl phthalates (PAEs). Biochars used in this study were produced from peanut-shell and their aging was simulated by chemical oxidation. The structural composition and morphology of the obtained biochars, before and after oxidation with HNO3/H2SO4, were analyzed by element composition, XPS, DRIFT, and SEM/EDX. Several experimental results unequivocally showed oxygen enrichment in the mixed acid treated samples compared to their precursors. Despite surface area reduction and pore destruction, increased PAEs sorption on oxidized biochar surfaces portrayed existence of strong PAEs binding sites. The adsorption of PAEs on oxidized biochar surface is a cumulative influence of hydrophobic interactions and pi-pi electron donor-acceptor interactions. Our results suggest that imminent aging of biochar upon environmental exposure may change their sorbent properties. PMID:26281762

  12. Adsorption of Xyloglucan onto Cellulose Surfaces of Different Morphologies: An Entropy-Driven Process.

    PubMed

    Benselfelt, Tobias; Cranston, Emily D; Ondaral, Sedat; Johansson, Erik; Brumer, Harry; Rutland, Mark W; Wågberg, Lars

    2016-09-12

    The temperature-dependence of xyloglucan (XG) adsorption onto smooth cellulose model films regenerated from N-methylmorpholine N-oxide (NMMO) was investigated using surface plasmon resonance spectroscopy, and it was found that the adsorbed amount increased with increasing temperature. This implies that the adsorption of XG to NMMO-regenerated cellulose is endothermic and supports the hypothesis that the adsorption of XG onto cellulose is an entropy-driven process. We suggest that XG adsorption is mainly driven by the release of water molecules from the highly hydrated cellulose surfaces and from the XG molecules, rather than through hydrogen bonding and van der Waals forces as previously suggested. To test this hypothesis, the adsorption of XG onto cellulose was studied using cellulose films with different morphologies prepared from cellulose nanocrystals (CNC), semicrystalline NMMO-regenerated cellulose, and amorphous cellulose regenerated from lithium chloride/dimethylacetamide. The total amount of high molecular weight xyloglucan (XGHMW) adsorbed was studied by quartz crystal microbalance and reflectometry measurements, and it was found that the adsorption was greatest on the amorphous cellulose followed by the CNC and NMMO-regenerated cellulose films. There was a significant correlation between the cellulose dry film thickness and the adsorbed XG amount, indicating that XG penetrated into the films. There was also a correlation between the swelling of the films and the adsorbed amounts and conformation of XG, which further strengthened the conclusion that the water content and the subsequent release of the water upon adsorption are important components of the adsorption process. PMID:27476615

  13. Surface complexation modeling calculation of Pb(II) adsorption onto the calcined diatomite

    NASA Astrophysics Data System (ADS)

    Ma, Shu-Cui; Zhang, Ji-Lin; Sun, De-Hui; Liu, Gui-Xia

    2015-12-01

    Removal of noxious heavy metal ions (e.g. Pb(II)) by surface adsorption of minerals (e.g. diatomite) is an important means in the environmental aqueous pollution control. Thus, it is very essential to understand the surface adsorptive behavior and mechanism. In this work, the Pb(II) apparent surface complexation reaction equilibrium constants on the calcined diatomite and distributions of Pb(II) surface species were investigated through modeling calculations of Pb(II) based on diffuse double layer model (DLM) with three amphoteric sites. Batch experiments were used to study the adsorption of Pb(II) onto the calcined diatomite as a function of pH (3.0-7.0) and different ionic strengths (0.05 and 0.1 mol L-1 NaCl) under ambient atmosphere. Adsorption of Pb(II) can be well described by Freundlich isotherm models. The apparent surface complexation equilibrium constants (log K) were obtained by fitting the batch experimental data using the PEST 13.0 together with PHREEQC 3.1.2 codes and there is good agreement between measured and predicted data. Distribution of Pb(II) surface species on the diatomite calculated by PHREEQC 3.1.2 program indicates that the impurity cations (e.g. Al3+, Fe3+, etc.) in the diatomite play a leading role in the Pb(II) adsorption and dominant formation of complexes and additional electrostatic interaction are the main adsorption mechanism of Pb(II) on the diatomite under weak acidic conditions.

  14. Surface area coefficients for airship envelopes

    NASA Technical Reports Server (NTRS)

    Diehl, W S

    1922-01-01

    In naval architecture, it is customary to determine the wetted surface of a ship by means of some formula which involves the principal dimensions of the design and suitable constants. These formulas of naval architecture may be extended and applied to the calculation of the surface area of airship envelopes by the use of new values of the constants determined for this purpose. Surface area coefficients were calculated from the actual dimensions, surfaces, and volumes of 52 streamline bodies, which form a series covering the entire range of shapes used in the present aeronautical practice.

  15. Defatted algal biomass as a non-conventional low-cost adsorbent: surface characterization and methylene blue adsorption characteristics.

    PubMed

    Sarat Chandra, T; Mudliar, S N; Vidyashankar, S; Mukherji, S; Sarada, R; Krishnamurthi, K; Chauhan, V S

    2015-05-01

    The present study investigates the use of defatted algal biomass (DAB) as a non-conventional low cost adsorbent. The maximum adsorption capacity of biomass (raw, defatted and sulfuric acid pretreated DAB) was determined by liquid phase adsorption studies in batch mode for the removal of methylene blue present at various concentrations (1, 2, 3, 4, and 5 mg L(-1)) from aqueous solutions. The data was well fitted with Langmuir and Freundlich isotherms. The maximum adsorption capacity for raw, defatted and sulfuric acid pretreated DAB was found to be 6.0, 7.73 and 7.80 mg g(-1), respectively. The specific surface area of raw, defatted and sulfuric acid pretreated DAB was estimated to be 14.70, 18.94, and 19.10 m(2) g(-1), respectively. To evaluate the kinetic mechanism that controls the adsorption process, pseudo-first order, pseudo-second order, intraparticle diffusion and particle diffusion has been tested. The data fitted quite well with pseudo-second order kinetic model.

  16. Scaling Relationships for Adsorption Energies of C2 Hydrocarbons on Transition Metal Surfaces

    SciTech Connect

    Jones, G

    2011-08-18

    Using density functional theory calculations we show that the adsorption energies for C{sub 2}H{sub x}-type adsorbates on transition metal surfaces scale with each other according to a simple bond order conservation model. This observation generalizes some recently recognized adsorption energy scaling laws for AH{sub x}-type adsorbates to unsaturated hydrocarbons and establishes a coherent simplified description of saturated as well as unsaturated hydrocarbons adsorbed on transition metal surfaces. A number of potential applications are discussed. We apply the model to the dehydrogenation of ethane over pure transition metal catalysts. Comparison with the corresponding full density functional theory calculations shows excellent agreement.

  17. Ethylene adsorption on regularly stepped copper surface: C 2H 4 on Cu(210)

    NASA Astrophysics Data System (ADS)

    Yamazaki, Daichi; Okada, Michio; Franco, Francisco C., Jr.; Kasai, Toshio

    2011-05-01

    Ethylene adsorption on regularly stepped Cu(210) surface was investigated with infrared reflection-adsorption spectroscopy and temperature programmed desorption. At 90 K, π-bonded ethylene was adsorbed on Cu(210) molecularly and all species were desorbed below 160 K. There were three types of π-bonded ethylene on the surface. Recent experimental studies have suggested that ethylene is dehydrogenated on Cu(410) due to the regular step [Kravchuk et al ., J. Phys. Chem. C, 113 (2009) 20881]. However, neither the formation of di-σ-bonded ethylene nor dehydrogenation occurred on Cu(210).

  18. Surface status and size influences of nickel nanoparticles on sulfur compound adsorption

    NASA Astrophysics Data System (ADS)

    Ko, Chang Hyun; Park, Jung Geun; Park, Ji Chan; Song, Hyunjoon; Han, Sang-Sup; Kim, Jong-Nam

    2007-04-01

    Metallic nickel nanoparticles were incorporated on mesoporous silica to remove sulfur compounds in diesel selectively. In the first method, nickel nanoparticles were formed on mesoporous silica SBA-15 by impregnation and subsequent reduction of nickel nitrate. The sulfur adsorption capacity was strongly dependent on the nickel loading and the average nickel particle size. In the second method, nickel nanoparticles were synthesized in solution in the presence of a capping agent and then incorporated in mesoporous silica MCF by sonication. Although these particles maintain their sizes on the MCF surface after heat treatment, capping agent remaining on the Ni particle surface might interfere the adsorption of sulfur compounds.

  19. Molecular adsorption and methanol synthesis on the oxidized Cu/ZnO(0001) surface

    NASA Astrophysics Data System (ADS)

    Lyle, Matthew J.; Warschkow, Oliver; Delley, Bernard; Stampfl, Catherine

    2015-11-01

    Cu/ZnO is an important catalyst used in the industrial synthesis of methanol from syngas. Many aspects of the functional synergy between the Cu and ZnO components in this system require further understanding. This work uses density functional theory calculations to examine the adsorption of various reactants of methanol synthesis to a recently proposed copper-oxide overlayer reconstruction on the ZnO(0001) surface. We identify the preferred binding configurations as a function of adsorbate coverage and compare the energetics of adsorption to that on the clean ZnO(0001) surface. The relevance of our results to methanol synthesis is discussed.

  20. Adsorption of a binary gas mixture which laterally interacts on a random heterogeneous surface

    SciTech Connect

    Ritter, J.A.

    1992-10-01

    Analytical expressions for the adsorption of a binary gas mixture which laterally interacts on a heterogeneous surface are developed. The lateral interactions are of the Bragg-Williams type and the surface heterogeneity is modeled via a random distribution of sites described by a uniform distribution of Henry`s Law constants. The parametric study shows that complex phase behavior can be predicted, including azeotropes and sigmoidal shaped X-Y diagrams. Also, this model may be useful for modeling and designing adsorption processes as it requires few iterations to simultaneously solve the implicit and coupled algebraic expressions.

  1. Adsorption of a binary gas mixture which laterally interacts on a random heterogeneous surface

    SciTech Connect

    Ritter, J.A.

    1992-01-01

    Analytical expressions for the adsorption of a binary gas mixture which laterally interacts on a heterogeneous surface are developed. The lateral interactions are of the Bragg-Williams type and the surface heterogeneity is modeled via a random distribution of sites described by a uniform distribution of Henry's Law constants. The parametric study shows that complex phase behavior can be predicted, including azeotropes and sigmoidal shaped X-Y diagrams. Also, this model may be useful for modeling and designing adsorption processes as it requires few iterations to simultaneously solve the implicit and coupled algebraic expressions.

  2. First principles study of nanoscale mechanism of oxygen adsorption on lanthanum zirconate surfaces

    NASA Astrophysics Data System (ADS)

    Guo, Xingye; Wu, Linmin; Zhang, Yi; Jung, Yeon-Gil; Li, Li; Knapp, James; Zhang, Jing

    2016-09-01

    Lanthanum zirconate (La2Zr2O7) is a rare-earth pyrochlore material, which has been proposed as a promising thermal barrier coating (TBC) material due to its low thermal conductivity and high temperature phase stability. At elevated temperatures, degradation of La2Zr2O7 may occur due to adsorption of oxygen (O2) on La2Zr2O7 surfaces. This paper investigates nanoscale mechanism of O2 adsorption on La2Zr2O7 coating surfaces using the density functional theory (DFT) calculations. La2Zr2O7 surface energies on (001), (011) and (111) planes are calculated. The surface free energy of (011) plane is lower than those of (001) and (111) planes. On (001), (011) and (111) planes of La2Zr2O7, the lowest adsorption energy occurs at 4-fold site, bridge site, and 3-fold-FCC site, respectively. Among all calculated cases, the lowest adsorption energy site is 3-fold-FCC on (111) plane, which is confirmed by the Bader charge transfer analyses. Charge density difference analyses show that the 3-fold-FCC site on (111) surface has the largest charge density, suggesting the strongest interaction between O2 and La2Zr2O7 surface.

  3. Electrochemical Characterization of Protein Adsorption onto YNGRT-Au and VLGXE-Au Surfaces

    PubMed Central

    Trzeciakiewicz, Hanna; Esteves-Villanueva, Jose; Soudy, Rania; Kaur, Kamaljit; Martic-Milne, Sanela

    2015-01-01

    The adsorption of the proteins CD13, mucin and bovine serum albumin on VLGXE-Au and YNGRT-Au interfaces was monitored by electrochemical impedance spectroscopy in the presence of [Fe(CN)6]3−/4−. The hydrophobicity of the Au surface was tailored using specific peptides, blocking agents and diluents. The combination of blocking agents (ethanolamine or n-butylamine) and diluents (hexanethiol or 2-mercaptoethanol) was used to prepare various peptide-modified Au surfaces. Protein adsorption onto the peptide-Au surfaces modified with the combination of n-butylamine and hexanethiol produced a dramatic decrease in the charge transfer resistance, Rct, for all three proteins. In contrast, polar peptide-surfaces induced a minimal change in Rct for all three proteins. Furthermore, an increase in Rct was observed with CD13 (an aminopeptidase overexpressed in certain cancers) in comparison to the other proteins when the VLGXE-Au surface was modified with n-butylamine as a blocking agent. The electrochemical data indicated that protein adsorption may be modulated by tailoring the peptide sequence on Au surfaces and that blocking agents and diluents play a key role in promoting or preventing protein adsorption. The peptide-Au platform may also be used for targeting cancer biomarkers with designer peptides. PMID:26262621

  4. Surface Areas and Morphology of Thin Ice Films

    NASA Technical Reports Server (NTRS)

    Leu, Ming-Taun; Keyser, Leon F.; Timonen, Raimo S.

    1996-01-01

    Thin ice films formed by deposition from the vapor phase in a fast flow-tube reactor have been used to simulate polar stratospheric cloud surfaces in order to obtain laboratory data on uptake and heterogeneous reaction rates. Surface areas are determined from BET (Brunauer, Emmett, and Teller) analysis of gas adsorption isotherms. The results for ices prepared at 196 K or 77 K are consistent with previous data on thicker ice films. Environmental scanning electron microscopy is used to obtain particle sizes and shapes, and to investigate the morphology of the ices on borosilicate or silicon windows. In addition, the uptake of HCI on ice films prepared at 196 K is investigated. The results suggest that the layer model we have previously developed for analysis of uptake and heterogeneous reaction rates on ice films is valid. Detailed information will be presented at the conference.

  5. Water adsorption induced in-plane domain switching on BaTiO{sub 3} surface

    SciTech Connect

    Li, X.; Bai, Y.; Su, Y. J.; Wang, B. C.

    2015-09-07

    In this study, the influences of the adsorption of water molecules on the changes in the atomic and electric structures of BaTiO{sub 3} surface were investigated using ab initio calculation. Water molecules are molecularly and dissociatively adsorbed on the BaTiO{sub 3} surface, which makes electrons transfer from water molecules to the BaTiO{sub 3} surface. The redistribution of electrons in the BaTiO{sub 3} surface layers weakens the Ba-O interactions and strengthens the Ti-O interactions, so that the Ti atom shifts in TiO{sub 2} plane, i.e., an in-plane domain switching. The adsorption of water molecules on BaTiO{sub 3} surfaces also results in a reduction in the surface rumpling.

  6. Deposition at glancing angle, surface roughness, and protein adsorption: Monte Carlo simulations.

    PubMed

    Zhdanov, Vladimir P; Rechendorff, Kristian; Hovgaard, Mads B; Besenbacher, Flemming

    2008-06-19

    To generate rough surfaces in Monte Carlo simulations, we use the 2 + 1 solid-on-solid model of deposition with rapid transient diffusion of newly arrived atoms supplied at glancing angle. The surfaces generated are employed to scrutinize the effect of surface roughness on adsorption of globular and anisotropic rodlike proteins. The obtained results are compared with the available experimental data for Ta deposition at glancing angle and for the bovine serum albumin and fibrinogen uptake on the corresponding Ta films.

  7. Effects of solution conditions and surface chemistry on the adsorption of three recombinant botulinum neurotoxin antigens to aluminum salt adjuvants.

    PubMed

    Vessely, Christina; Estey, Tia; Randolph, Theodore W; Henderson, Ian; Nayar, Rajiv; Carpenter, John F

    2007-09-01

    Botulinum neurotoxin (BoNT) is a biological warfare threat. Protein antigens have been developed against the seven major BoNT serotypes for the development of a recombinant protein vaccine. This study is an evaluation of adsorption profiles for three of the recombinant protein antigens to aluminum salt adjuvants in the development of a trivalent vaccine against BoNT. Adsorption profiles were obtained over a range of protein concentrations. The results document that charge-charge interactions dominate the adsorption of antigen to adjuvant. Optimal conditions for adsorption were determined. However, potency studies and solution stability studies indicated the necessity of using aluminum hydroxide adjuvant at low pH. To improve the adsorption profiles to AlOH adjuvant, phosphate ions were introduced into the adsorption buffers. The resulting change in the adjuvant chemistry led to an improvement of adsorption of the BoNT antigens to aluminum hydroxide adjuvant while maintaining potency. Competitive adsorption profiles were also determined, and showed changes in maximum adsorption from mixed solutions compared to adsorption from individual protein solutions. The adsorption profiles for each protein varied due to differences in adsorption mechanism and affinity for the adjuvant surface. These results emphasize the importance of evaluating competitive adsorption in the development of multivalent vaccine products. PMID:17518359

  8. Study of adsorption of bovine serum albumin to Langmuir Blodgett film coated surfaces using work of adhesion as a tool

    NASA Astrophysics Data System (ADS)

    Sandhya, S.; Lakshmanan, Muthuselvi; Dhathathreyan, A.

    2008-08-01

    This work reports on the use of rate of change of work of adhesion (Δ W) as a tool to study adsorption of bovine serum albumin (BSA) to glass and Langmuir-Blodgett film of dihexadecyl phosphate (DHP) and dioctadecyl dimethyl ammonium bromide (DOMA) coated surfaces. Pure BSA and BSA with additives - sorbitol and urea - have been adsorbed to bare glass surfaces and DHP and DOMA coated surfaces. The results suggest that an increase in Δ W with time indicates promotion of adsorption while a decrease indicates hindered adsorption. Further adsorption of BSA was most effective on DHP coated surface compared with bare glass and DOMA coated glass. In case of mixtures of BSA with urea and sorbitol, BSA + urea showed hindered adsorption while adsorption of BSA + sorbitol was efficient for all substrates.

  9. Oriented adsorption of purple membrane to cationic surfaces.

    PubMed

    Fisher, K A; Yanagimoto, K; Stoeckenius, W

    1978-05-01

    We have investigated the orientation of isolated fragments of Halobacterium halobium purple membrane (PM) adsorbed to poly-L-lysine-treated glass (PL-glass), by quanitative electron microscopy. Three lines of evidence support the conclusion that the cytoplasmic side of the membrane is preferentially absorbed. First, monolayer freeze-fracture reveals nonrandom orientation; more fracture faces (89%) are particulate than smooth. Second, the amount of each membrane surface present can be assayed using polycationic ferritin; 90% of all adsorbed membrane fragments are labeled. Third, it is possible to distinguish two surfaces, "cracked" (the extracellular surface) and "pitted" (the cytoplasmic surface) , in slowly air-dried, platinum-carbon-shadowed membranes. When applied under standard conditions, more than 80% appear cracked. Selection for the cytoplasmic by the cationic substrate suggests that the isolated PM, buffered at pH 7.4 and in the light, has a higher negative charge on its cytoplasmic surface than on its extracellular surface. Nevertheless, cationic ferritin (CF) preferentially adsorbs to the extracellular surface. Orientation provides a striking example of biomembrane surface asymmetry as well as the means to examine the chemical reactivity and physical properties of surfaces of a purified, nonvesicular membrane fragment. PMID:649662

  10. Study on Super-Hydrophobic and Oleophobic Surfaces Prepared by Chemical Adsorption Technique

    NASA Astrophysics Data System (ADS)

    Tsuji, Issei; Ohkubo, Yuji; Ogawa, Kazufumi

    2009-04-01

    Preparation techniques for super-hydrophobic and oleophobic surfaces were studied by forming a fractally roughened surface and preparing a hydrophobic monolayer. In this study, the fractal structure on the surface of an aluminum substrate was formed by combining sand-blasting with electrolytical etching. Then, a hydrophobic monolayer was prepared on the roughened surface, without decreasing roughness. The surface of the treated substrate can be evaluated by contact angle measurement and field emission scanning electron microscopy (FE-SEM). The surface treated by a technique combining chemical adsorption, sandblasting, and electrolytical etching was super-hydrophobic and highly oleophobic.

  11. Surface modification influencing adsorption of red wine constituents: The role of functional groups

    NASA Astrophysics Data System (ADS)

    Mierczynska-Vasilev, Agnieszka; Smith, Paul A.

    2016-11-01

    The adsorption of wine constituents at solid surfaces is important in applications such as filtration and membrane fouling, binding to tanks and fittings and interactions with processing aids such as bentonite. The interaction of wine constituents with surfaces is mediated through adsorbed wine components, where the type of constituents, amount, orientation, and conformation are of consequence for the surface response. This study examines the effect of surface chemical functionalities on the adsorption of red wine constituents. Plasma-polymerized films rich in amine, carboxyl, hydroxyl, formyl and methyl functional groups were generated on solid substrates whereas, glycidyltrimethylammonium chloride was covalently attached to allylamine plasma-polymer modified surface and poly(sodium styrenesulfonate) was electrostatically adsorbed to an amine plasma-polymerized surface. The surface chemical functionalities were characterized by X-ray photoelectron spectroscopy. The ability of different substrates to adsorb red wine constituents was evaluated by quartz crystal microbalance and atomic force microscopy. The results showed that substrates modified with -SO3H and -COOH groups can adsorb more of the wine nitrogen-containing compounds whereas -NH2 and -NR3 groups encourage carbon-containing compounds adsorption. Red wine constituents after filtration were adsorbed in higher extend on -NR3 and -CHO surfaces. The -OH modified surfaces had the lowest ability to absorb wine components.

  12. Protein adsorption and cell adhesion on polyurethane/Pluronic surface with lotus leaf-like topography.

    PubMed

    Zheng, Jun; Song, Wei; Huang, He; Chen, Hong

    2010-06-01

    Lotus leaf-like polyurethane/Pluronic F-127 surface was fabricated via replica molding using a natural lotus leaf as the template. Water contact angle measurements showed that both the hydrophobicity of the unmodified polyurethane (PU) surface and the hydrophilicity of the PU/Pluronic surface were enhanced by the construction of lotus leaf-like topography. Protein adsorption on the PU/Pluronic surface without topographic modification was significantly lower than on the PU surface. Adsorption was further reduced when lotus leaf-like topography was constructed on the PU/Pluronic surface. Cell culture experiments with L929 cells showed that adhesion on the PU/Pluronic surface with lotus leaf-like topography was low and adherent cells were spherical and of low viability. The PU/Pluronic surface with lotus leaf-like topography thus appears to be resistant to nonspecific protein adsorption and to cell adhesion, and these effects derive from the both chemical composition and topography. The results suggest a new strategy based on surface topography for the design of antifouling materials.

  13. Density functional study of H2O molecule adsorption on α-U(001) surface.

    PubMed

    Huang, Shanqisong; Zeng, Xiu-Lin; Zhao, Feng-Qi; Ju, Xuehai

    2016-04-01

    Periodic density functional theory (DFT) calculations were performed to investigate the adsorption of H2O on U(001) surface. The metallic nature of uranium atom and different adsorption sites of U(001) surface play key roles in the H2O molecular dissociate reaction. The long-bridge site is the most favorable site of H2O-U(001) adsorption configuration. The triangle-center site of the H atom is the most favorable site of HOH-U(001) adsorption configuration. The interaction between H2O and U surface is more evident on the first layer than that on any other two sub-layers. The dissociation energy of one hydrogen atom from H2O is -1.994 to -2.215 eV on U(001) surface, while the dissociating energy decreases to -3.351 to -3.394 eV with two hydrogen atoms dissociating from H2O. These phenomena also indicate that the Oads can promote the dehydrogenation of H2O. A significant charge transfer from the first layer of the uranium surface to the H and O atoms is also found to occur, making the bonding partly ionic. PMID:26994022

  14. DNA adsorption to and elution from silica surfaces: influence of amino acid buffers.

    PubMed

    Vandeventer, Peter E; Mejia, Jorge; Nadim, Ali; Johal, Malkiat S; Niemz, Angelika

    2013-09-19

    Solid phase extraction and purification of DNA from complex samples typically requires chaotropic salts that can inhibit downstream polymerase amplification if carried into the elution buffer. Amino acid buffers may serve as a more compatible alternative for modulating the interaction between DNA and silica surfaces. We characterized DNA binding to silica surfaces, facilitated by representative amino acid buffers, and the subsequent elution of DNA from the silica surfaces. Through bulk depletion experiments, we found that more DNA adsorbs to silica particles out of positively compared to negatively charged amino acid buffers. Additionally, the type of the silica surface greatly influences the amount of DNA adsorbed and the final elution yield. Quartz crystal microbalance experiments with dissipation monitoring (QCM-D) revealed multiphasic DNA adsorption out of stronger adsorbing conditions such as arginine, glycine, and glutamine, with DNA more rigidly bound during the early stages of the adsorption process. The DNA film adsorbed out of glutamate was more flexible and uniform throughout the adsorption process. QCM-D characterization of DNA elution from the silica surface indicates an uptake in water mass during the initial stage of DNA elution for the stronger adsorbing conditions, which suggests that for these conditions the DNA film is partly dehydrated during the prior adsorption process. Overall, several positively charged and polar neutral amino acid buffers show promise as an alternative to methods based on chaotropic salts for solid phase DNA extraction.

  15. A DFT study of adsorption of glycine onto the surface of BC2N nanotube

    NASA Astrophysics Data System (ADS)

    Soltani, Alireza; Azmoodeh, Zivar; Javan, Masoud Bezi; Lemeski, E. Tazikeh; Karami, Leila

    2016-10-01

    A theoretical study of structure and the energy interaction of amino acid glycine (NH2CH2COOH) with BC2N nanotube is crucial for apperception behavior occurring at the nanobiointerface. Herein, we studied the adsorption of glycine in their radical and zwitterionic forms upon the surface of BC2N nanotube using M06 functional and 6-311G** standard basis set. We also considered the different orientations of the glycine amino acid on the surface of adsorbent. Further, we found out that the stability of glycine from its carbonyl group is higher than hydroxyl and amine groups. Our results also indicated that the electronic structure of BC2N nanotube on the adsorption of glycine from its amine group is more altered than the other groups. Our study exhibits that opto-electronic property of adsorbent is changed after the glycine adsorption.

  16. Glutathione-Coated Luminescent Gold Nanoparticles: A Surface Ligand for Minimizing Serum Protein Adsorption

    PubMed Central

    2015-01-01

    Ultrasmall glutathione-coated luminescent gold nanoparticles (GS-AuNPs) are known for their high resistance to serum protein adsorption. Our studies show that these NPs can serve as surface ligands to significantly enhance the physiological stability and lower the serum protein adsorption of superparamagnetic iron oxide nanoparticles (SPIONs), in addition to rendering the NPs the luminescence property. After the incorporation of GS-AuNPs onto the surface of SPIONs to form the hybrid nanoparticles (HBNPs), these SPIONs’ protein adsorption was about 10-fold lower than those of the pure glutathione-coated SPIONs suggesting that GS-AuNPs are capable of providing a stealth effect against serum proteins. PMID:25029478

  17. Flexible star polymer chain adsorption by a flat surface: a molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Zenak, Siham; Guenachi, Aicha; Sabeur, Sid Ahmed

    2016-08-01

    In this work, we have studied the adsorption of a single flexible star polymer chain by a flat surface. The molecular dynamics simulation has been validated for the case of a free star polymer chain using the diffusion experiment. The scaling laws found are in agreement with the Flory theory predictions and the Rouse model. For the adsorption, preliminary results were obtained for chains of different sizes N=31 to N=199 and different functionalities (f=3,4,6,8,10). For the case of semi-flexible star polymer chains, further investigation is needed to locate the critical point of adsorption when varying the potential interaction strength between the chain and the surface.

  18. Glutathione-coated luminescent gold nanoparticles: a surface ligand for minimizing serum protein adsorption.

    PubMed

    Vinluan, Rodrigo D; Liu, Jinbin; Zhou, Chen; Yu, Mengxiao; Yang, Shengyang; Kumar, Amit; Sun, Shasha; Dean, Andrew; Sun, Xiankai; Zheng, Jie

    2014-08-13

    Ultrasmall glutathione-coated luminescent gold nanoparticles (GS-AuNPs) are known for their high resistance to serum protein adsorption. Our studies show that these NPs can serve as surface ligands to significantly enhance the physiological stability and lower the serum protein adsorption of superparamagnetic iron oxide nanoparticles (SPIONs), in addition to rendering the NPs the luminescence property. After the incorporation of GS-AuNPs onto the surface of SPIONs to form the hybrid nanoparticles (HBNPs), these SPIONs' protein adsorption was about 10-fold lower than those of the pure glutathione-coated SPIONs suggesting that GS-AuNPs are capable of providing a stealth effect against serum proteins. PMID:25029478

  19. Preparation of surface-functionalized porous clay heterostructures via carbonization of soft-template and their adsorption performance for toluene

    NASA Astrophysics Data System (ADS)

    Wang, Yuebo; Su, Xiaoli; Xu, Zhen; Wen, Ke; Zhang, Ping; Zhu, Jianxi; He, Hongping

    2016-02-01

    A new type of surface-functionalized porous clay heterostructures (SF-PCH) was synthesized via carbonization of the template agents with sulfuric acid. The converted carbons deposited on the porous surface of the SF-PCH samples and changed their surface chemical properties. The composites possessed a maximum carbon content of 5.35%, a large specific surface area of 428 m2/g and micropore volume of approximately 0.2 cm3/g. The layered and porous structure of SF-PCH was retained after carbonization and calcination when sulfuric acid solution with a mild concentration was used. Analysis by XPS confirmed that the carbonaceous matter in the pore channels was functionalized with various organic groups, including carbonaceous, nitrogenous, and sulfated groups. Both the surface chemical property and structural characteristic of adsorbents have effects on the adsorption properties of SF-PCH for toluene. The SF-PCH samples exhibited a stronger adsorption affinity to toluene compared with untreated PCH in the low pressure region, which is more valuable in the practical applications. These results demonstrate that carbonization of soft-template is a feasible process for the surface modification of PCH, enabling the resulting composites to become promising candidates for application in toluene emission control.

  20. Uncovering surface area and micropores in almond shell biochars by rainwater wash

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Biochars have been considered for adsorption of contaminants in soil and water, as well as conditioning and improving soil quality. One important property of the biochar is surface area in the pores of the biochar. Biochars were created from almond shells from two almond varieties with different ash...

  1. Oxalic acid adsorption states on the clean Cu(110) surface

    NASA Astrophysics Data System (ADS)

    Fortuna, Sara

    2016-11-01

    Carboxylic acids are known to assume a variety of configurations on metallic surfaces. In particular oxalic acid on the Cu(110) surface has been proposed to assume a number of upright configurations. Here we explore with DFT calculations the possible structures that oxalic acid can form on copper 110 at different protonation states, with particular attention at the possibility of forming structures composed of vertically standing molecules. In its fully protonated form it is capable of anchoring itself on the surface thanks to one of its hydrogen-free oxygens. We show the monodeprotonated upright molecule with two oxygens anchoring it on the surface to be the lowest energy conformation of a single oxalic molecules on the Cu(110) surface. We further show that it is possible for this configuration to form dense hexagonally arranged patterns in the unlikely scenario in which adatoms are not involved.

  2. Thiol Adsorption on and Reduction of Copper Oxide Particles and Surfaces.

    PubMed

    Wang, Yiwen; Im, Jisun; Soares, Jason W; Steeves, Diane M; Whitten, James E

    2016-04-26

    The adsorption of 1-dodecanethiol at room temperature and at 75 °C on submicron cuprous and cupric oxide particles suspended in ethanol has been investigated by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy. Thiol adsorption occurs in all cases via Cu-S bond formation, with partial dissolution of CuO at 75 °C and formation of a copper-thiolate complex replacement layer. Regardless of temperature, the surface of the CuO particles is essentially completely reduced to either Cu2O or metallic copper, as evidenced by loss of the characteristic Cu(2+) XPS features of dried powder samples. Companion ultrahigh-vacuum studies have been performed by dosing clean, oxygen-dosed, and ozone-treated single crystal Cu(111) with methanethiol (MT) gas at room temperature. In the latter case, the surface corresponds to CuO/Cu(111). XPS confirms MT adsorption in all cases, with an S 2p peak binding energy of 162.9 ± 0.1 eV, consistent with methanethiolate adsorption. Heating of MT-covered Cu(111) and oxygen-dosed Cu(111) leads to decomposition/desorption of the MT by 100 °C and formation of copper sulfide with an S 2p binding energy of 161.8 eV. Dosing CuO/Cu(111) with 50-200 L of MT leads to only partial reduction/removal of the CuO surface layers prior to methanethiolate adsorption. This is confirmed by ultraviolet photoelectron spectroscopy (UPS), which measures the occupied states near the Fermi level. For both the colloidal CuO and single crystal CuO/Cu(111) studies, the reduction of the Cu(2+) surface is believed to occur by formation and desorption of the corresponding dithiol prior to thiolate adsorption. PMID:27036074

  3. Thiol Adsorption on and Reduction of Copper Oxide Particles and Surfaces.

    PubMed

    Wang, Yiwen; Im, Jisun; Soares, Jason W; Steeves, Diane M; Whitten, James E

    2016-04-26

    The adsorption of 1-dodecanethiol at room temperature and at 75 °C on submicron cuprous and cupric oxide particles suspended in ethanol has been investigated by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy. Thiol adsorption occurs in all cases via Cu-S bond formation, with partial dissolution of CuO at 75 °C and formation of a copper-thiolate complex replacement layer. Regardless of temperature, the surface of the CuO particles is essentially completely reduced to either Cu2O or metallic copper, as evidenced by loss of the characteristic Cu(2+) XPS features of dried powder samples. Companion ultrahigh-vacuum studies have been performed by dosing clean, oxygen-dosed, and ozone-treated single crystal Cu(111) with methanethiol (MT) gas at room temperature. In the latter case, the surface corresponds to CuO/Cu(111). XPS confirms MT adsorption in all cases, with an S 2p peak binding energy of 162.9 ± 0.1 eV, consistent with methanethiolate adsorption. Heating of MT-covered Cu(111) and oxygen-dosed Cu(111) leads to decomposition/desorption of the MT by 100 °C and formation of copper sulfide with an S 2p binding energy of 161.8 eV. Dosing CuO/Cu(111) with 50-200 L of MT leads to only partial reduction/removal of the CuO surface layers prior to methanethiolate adsorption. This is confirmed by ultraviolet photoelectron spectroscopy (UPS), which measures the occupied states near the Fermi level. For both the colloidal CuO and single crystal CuO/Cu(111) studies, the reduction of the Cu(2+) surface is believed to occur by formation and desorption of the corresponding dithiol prior to thiolate adsorption.

  4. Evaluation of various substances to prevent adsorption of tuberculin purified protein derivative (PPD) to glass surfaces*

    PubMed Central

    Landi, S.; Held, H. R.; Tseng, M. C.

    1970-01-01

    It is well known that a dilute tuberculin PPD solution (1 IU or 5 IU per dose) very rapidly loses its potency owing to adsorption of tuberculoprotein to the wall of the container into which it is dispensed. The amount of tuberculoprotein adsorbed per cm2 of glass surface has been measured for phosphate-buffered saline over a wide pH range (pH 1 to pH 10). The maximum adsorption was found at pH 4 (0.31 μg/cm2) and the least at between pH 6 and pH 10 (0.15 μg/cm2). The rate of adsorption of tuberculoprotein to glass was not changed when the phosphate-buffered saline was replaced by borate-buffered saline. Tuberculin PPD prepared by the ammonium sulfate precipitation method, by the trichloroacetic acid precipitation method and by a combination of both methods adsorbed equally well to glass and no difference in the rate of adsorption for these tuberculoproteins was found. Forty-two substances in addition to Tween 80 were tested for their property to prevent adsorption of tuberculoprotein to glass in dilute tuberculin PPD solutions (50 IU/ml of 14C-labelled PPD). The most efficient anti-adsorption agents were found to be nonionic surfactants, some ionic surfactants and some colloidal substances; polypeptides and non-surface-active substances of low molecular weight showed little or no anti-adsorption property. The labelling of PPD with 14C has proved to be a valuable tool, particularly for long-term adsorption studies and for screening substances to be used as efficient anti-adsorption agents. These studies have permitted the selection of agents which could be added to dilute solutions of tuberculin PPD (10 IU/ml to 500 IU/ml or 0.2 μg/ml to 10 μg/ml respectively) in order to avoid loss of potency due to adsorption. PMID:5312323

  5. Surface morphology of orthorhombic Mo2C catalyst and high coverage hydrogen adsorption

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Tian, Xinxin; Yang, Yong; Li, Yong-Wang; Wang, Jianguo; Beller, Matthias; Jiao, Haijun

    2016-09-01

    High coverage hydrogen adsorption on twenty two terminations of orthorhombic Mo2C has been systematically studied by using density functional theory and ab initio thermodynamics. Hydrogen stable coverage on the surfaces highly depends on temperatures and H2 partial pressure. The estimated hydrogen desorption temperatures under ultra-high vacuum condition on Mo2C are in reasonable agreement with the available temperature-programmed desorption data. Obviously, hydrogen adsorption can affect the surface stability and therefore modify the surface morphology of Mo2C. Upon increasing the chemical potential of hydrogen which can be achieved by increasing the H2 partial pressure and/or decreasing the temperature, the proportions of the (001), (010), (011) and (100) surfaces increase, while those of the (101), (110) and (111) surfaces decrease. Among these surfaces, the (100) surface is most sensitive upon hydrogen adsorption and the (111) surface is most exposed under a wide range of conditions. Our study clearly reveals the role of hydrogen on the morphology of orthorhombic Mo2C catalyst in conjugation with hydro-treating activity.

  6. Synthesis and adsorption of polymers: Control of polymer and surface structure

    SciTech Connect

    Stoichet, M.S.

    1992-01-01

    A simple and versatile technique to introduce carboxylic acid functionality to the surfaces of three fluoropolymer film samples is described. The adsorption of neutral poly(L-lysine) (PLL) from solution to the water-fluoropolymer interface is described. The methods of surface modification are combined and the adsorption of charged PLL to carboxylic acid-functionalized fluoropolymer film surface is discussed. The hydrophobic interaction as a driving force for adsorption is further studied where the synthesis and adsorption of poly(ethylene oxide) (PEO) and its derivatives are discussed. The synthesis of carboxylic acid-functionalized fluoropolymer films rely upon a two step mechanism where unsaturation is oxidatively removed. Contact angles of the acid-functionalized fluoropolymer films decrease with increasing pH. The adsorption of poly(L-lysine) (PLL) to the water-FEP interface was controlled by pH of the aqueous solution and PLL solution conformation. Only neutral [alpha]-helical PLL adsorbed to FEP (FEP-PLL). The adsorption of PLL to FEP-CO[sub 2]H was controlled by an electrostatic interaction. Both FEP-PLL and FEP-CO[sub 2]H-PLL are more hydrophilic than FEP. FEP-PLL-[epsilon]-amine reacts with 3,5-dinitrobenzoyl chloride in 65% yield whereas FEP-CO[sub 2]H-PLL-[epsilon]-amine reacts in 100% yield. Adsorption of PLL to FEP and FEP-CO[sub 2]H improves the peel strength of adhesive joints prepared with these substrates and the adhesion and growth of biological cells on these film samples. PEO was synthesized by anionic ring opening polymerization of ethylene oxide and was end-capped (PEO-R) by reaction with a (perfluoro)alkyl acid chloride. A polar interaction between substrate and segment controlled adsorption at the fluoropolymer-water interface. PEO and PEO-R adsorbed to the polystyrene latex-water interface. PEO-R showed increase surface activity over PEO at the air-water interface; PEO-perfluorodecanoate decreased the surface tension of water to 35 dyn/cm.

  7. Computer simulations for the adsorption of polymers onto surfaces

    SciTech Connect

    Balazs, A.C.

    1993-01-01

    Polymer-surface interactions are important in every stage of oil and coal production, production of new energy-efficient composite materials, and in medicine. Therefore, it is important to isolate the factors that influence the interfacial activity of polymer chains. We developed theoretical models and computer simulations to determine effects of polymer architecture, solvent quality, and surface morphology on properties of chains at penetrable and impenetrable interfaces. 7 figs, 27 refs.

  8. Adsorption of protein-coated lipid droplets to mixed biopolymer hydrogel surfaces: role of biopolymer diffusion.

    PubMed

    Vargas, Maria; Weiss, Jochen; McClements, D Julian

    2007-12-18

    The adsorption of charged particles to hydrogel surfaces is important in a number of natural and industrial processes. In this study, the adsorption of cationic lipid droplets to the surfaces of anionic hydrogels was examined. An oil-in-water emulsion containing cationic beta-lactoglobulin-coated lipid droplets was prepared (d32=0.24 microm, zeta=+74 mV, pH 3.0). An anionic hydrogel containing 0.1 wt % beet pectin and 1.5 wt % agar (pH 3.0) was prepared. Emulsions containing different lipid droplet concentrations (0.3-5 wt %) were brought into contact with the hydrogel surfaces for different times (0-24 h). The adsorption of lipid droplets to the hydrogel surfaces could not be explained by a typical adsorption isotherm. We found that the electrical charge on the nonadsorbed lipid droplets became less positive or even became negative in the presence of the hydrogel and that extensive droplet aggregation occurred, which was attributed to the ability of pectin molecules to diffuse through the hydrogels and interact with the lipid droplets. These results may have important consequences for understanding certain industrial and biological processes, as well as for the design of controlled or triggered release systems.

  9. THE EFFECT OF ACTIVATED CARBON SURFACE MOISTURE ON LOW TEMPERATURE MERCURY ADSORPTION

    EPA Science Inventory

    Experiments with elemental mercury (Hg0) adsorption by activated carbons were performed using a bench-scale fixed-bed reactor at room temperature (27 degrees C) to determine the role of surface moisture in capturing Hg0. A bituminous-coal-based activated carbon (BPL) and an activ...

  10. The adsorption, reaction and decomposition of propylene on a clean Mo(100) surface

    NASA Astrophysics Data System (ADS)

    Wang, Luping; Tysoe, W. T.

    1991-04-01

    Propylene adsorbs onto Mo(100) at 110 K via precursor-state kinetics to saturate at a coverage, θ sat(C 3H 6) = 0.63 ± 0.05. Adsorption at lower temperatures results in multilayer adsorption. In contrast to ethylene, which rehybridizes to ~ sp 3 following adsorption at 80 K on Mo(100), propylene adsorbs molecularly at this temperature, rehybridizing only after heating to between 100 and 140 K. Further heating to between 180 and 200 K results in loss of hydrogen from the surface propylenic species and the formation of an aliene- or methylacetylene-like adsorbate which appears to be oriented so that the C-C-C axis is essentially parallel to the surface. Photoelectron spectroscopic data suggests significant carbon-carbon bond cleavage in the adsorbed C 3 species is underway by ~ 270 K. on Mo(100), resulting finally in the formation of adsorbed CH x species on heating the Mo(100) surface to room temperature. This chemistry is closely analogous to that observed following ethylene adsorption onto Mo(100) where a similar carbon-carbon bond cleavage was noted, and is in accord with the catalytic chemistry of molybdenum which catalyzes both olefin metathesis and hydrogenolysis. Further heating to above 400 K completely dehydrogenates the surface leaving chemisorbed, atomic carbon.

  11. IMPORTANCE OF ACTIVATED CARBON'S OXYGEN SURFACE FUNCTIONAL GROUPS ON ELEMENTAL MERCURY ADSORPTION

    EPA Science Inventory

    The effect of varying physical and chemical properties of activated carbons on adsorption of elemental mercury [Hg(0)] was studied by treating two activated carbons to modify their surface functional groups and pore structures. Heat treatment (1200 K) in nitrogen (N2), air oxidat...

  12. Dynamic technique for measuring adsorption in a gas chromatograph

    NASA Technical Reports Server (NTRS)

    Deuel, C. L.; Hultgren, N. W.; Mobert, M. L.

    1973-01-01

    Gas-chromatographic procedure, together with mathematical analysis of adsorption isotherm, allows relative surface areas and adsorptive powers for trace concentrations to be determined in a few minutes. Technique may be used to evaluate relative surface areas of different adsorbates, expressed as volume of adsorbent/gram of adsorbate, and to evaluate their relative adsorptive power.

  13. Surface fractal dimension, water adsorption efficiency, and cloud nucleation activity of insoluble aerosol

    PubMed Central

    Laaksonen, Ari; Malila, Jussi; Nenes, Athanasios; Hung, Hui-Ming; Chen, Jen-Ping

    2016-01-01

    Surface porosity affects the ability of a substance to adsorb gases. The surface fractal dimension D is a measure that indicates the amount that a surface fills a space, and can thereby be used to characterize the surface porosity. Here we propose a new method for determining D, based on measuring both the water vapour adsorption isotherm of a given substance, and its ability to act as a cloud condensation nucleus when introduced to humidified air in aerosol form. We show that our method agrees well with previous methods based on measurement of nitrogen adsorption. Besides proving the usefulness of the new method for general surface characterization of materials, our results show that the surface fractal dimension is an important determinant in cloud drop formation on water insoluble particles. We suggest that a closure can be obtained between experimental critical supersaturation for cloud drop activation and that calculated based on water adsorption data, if the latter is corrected using the surface fractal dimension of the insoluble cloud nucleus. PMID:27138171

  14. Surface fractal dimension, water adsorption efficiency, and cloud nucleation activity of insoluble aerosol

    NASA Astrophysics Data System (ADS)

    Laaksonen, Ari; Malila, Jussi; Nenes, Athanasios; Hung, Hui-Ming; Chen, Jen-Ping

    2016-05-01

    Surface porosity affects the ability of a substance to adsorb gases. The surface fractal dimension D is a measure that indicates the amount that a surface fills a space, and can thereby be used to characterize the surface porosity. Here we propose a new method for determining D, based on measuring both the water vapour adsorption isotherm of a given substance, and its ability to act as a cloud condensation nucleus when introduced to humidified air in aerosol form. We show that our method agrees well with previous methods based on measurement of nitrogen adsorption. Besides proving the usefulness of the new method for general surface characterization of materials, our results show that the surface fractal dimension is an important determinant in cloud drop formation on water insoluble particles. We suggest that a closure can be obtained between experimental critical supersaturation for cloud drop activation and that calculated based on water adsorption data, if the latter is corrected using the surface fractal dimension of the insoluble cloud nucleus.

  15. Surface fractal dimension, water adsorption efficiency, and cloud nucleation activity of insoluble aerosol.

    PubMed

    Laaksonen, Ari; Malila, Jussi; Nenes, Athanasios; Hung, Hui-Ming; Chen, Jen-Ping

    2016-01-01

    Surface porosity affects the ability of a substance to adsorb gases. The surface fractal dimension D is a measure that indicates the amount that a surface fills a space, and can thereby be used to characterize the surface porosity. Here we propose a new method for determining D, based on measuring both the water vapour adsorption isotherm of a given substance, and its ability to act as a cloud condensation nucleus when introduced to humidified air in aerosol form. We show that our method agrees well with previous methods based on measurement of nitrogen adsorption. Besides proving the usefulness of the new method for general surface characterization of materials, our results show that the surface fractal dimension is an important determinant in cloud drop formation on water insoluble particles. We suggest that a closure can be obtained between experimental critical supersaturation for cloud drop activation and that calculated based on water adsorption data, if the latter is corrected using the surface fractal dimension of the insoluble cloud nucleus. PMID:27138171

  16. Surface fractal dimension, water adsorption efficiency, and cloud nucleation activity of insoluble aerosol.

    PubMed

    Laaksonen, Ari; Malila, Jussi; Nenes, Athanasios; Hung, Hui-Ming; Chen, Jen-Ping

    2016-05-03

    Surface porosity affects the ability of a substance to adsorb gases. The surface fractal dimension D is a measure that indicates the amount that a surface fills a space, and can thereby be used to characterize the surface porosity. Here we propose a new method for determining D, based on measuring both the water vapour adsorption isotherm of a given substance, and its ability to act as a cloud condensation nucleus when introduced to humidified air in aerosol form. We show that our method agrees well with previous methods based on measurement of nitrogen adsorption. Besides proving the usefulness of the new method for general surface characterization of materials, our results show that the surface fractal dimension is an important determinant in cloud drop formation on water insoluble particles. We suggest that a closure can be obtained between experimental critical supersaturation for cloud drop activation and that calculated based on water adsorption data, if the latter is corrected using the surface fractal dimension of the insoluble cloud nucleus.

  17. Impact of surface steps and oxygen pre-coverage on the adsorption of methylamine on gold.

    PubMed

    Lewoczko, April D; BelBruno, Joseph J

    2013-04-01

    Using density functional theory calculations, we report on the adsorption of methylamine on gold and compare its adsorption to a selection of alkylamines, methanol and methanethiol. On the (111) surface, the amines, thiol and alcohol bind in the ontop site with a preference over hollow and bridge sites of 0.3 eV, 0.2 eV and 0.1 eV for methylamine, methanethiol and methanol, respectively. The effect of steps is considered on the (211) surface of gold and we find that methylamine adsorbs 0.2 eV more strongly in the step ontop site of the surface than on the (111) surface. For oxygen atom pre-coverages of 0.04-0.25 ML on the (111) surface, we find cooperative adsorption of amines and oxygen atoms. The energetic costs of adsorbate tilt from the surface normal and of rotation about the gold-heteroatom bond are compared among the studied surfaces and conditions.

  18. Surface-Energetic Heterogeneity of Nanoporous Solids for CO2 and CO Adsorption: The Key to an Adsorption Capacity and Selectivity at Low Pressures.

    PubMed

    Kim, Moon Hyeon; Cho, Il Hum; Choi, Sang Ok; Lee, In Soo

    2016-05-01

    This study has been focused on surface energetic heterogeneity of zeolite (H-mordenite, "HM"), activated carbon ("RB2") and metal-organic framework family ("Z1200") materials and their isotherm features in adsorption of CO2 and CO at 25 degrees C and low pressures ≤ 850 Torr. The nanoporous solids showed not only distinctive shape of adsorption isotherms for CO2 with relatively high polarizability and quadrupole moment but also different capacities in the CO2 adsorption. These differences between the adsorbents could be well correlated with their surface nonuniformity. The most heterogeneous surfaces were found with the HM that gave the highest CO2 uptake at all pressures allowed, while the Z1200 consisted of completely homogeneous surfaces and even CO2 adsorption linearly increased with pressure. An intermediate character was indicated on the surface of RB2 and thus this sorbent possessed isotherm features between the HM and Z1200 in CO2 adsorption. Such different surface energetics was fairly consistent with changes in CO2/CO selectivity on the nanoporous adsorbents up to equilibrated pressures near 850 Torr. PMID:27483776

  19. Adsorption of a PEO-PPO-PEO triblock copolymer on metal oxide surfaces with a view to reducing protein adsorption and further biofouling.

    PubMed

    Yang, Y; Poleunis, C; Románszki, L; Telegdi, J; Dupont-Gillain, C C

    2013-01-01

    Abstract Biomolecule adsorption is the first stage of biofouling. The aim of this work was to reduce the adsorption of proteins on stainless steel (SS) and titanium surfaces by modifying them with a poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-PEO triblock copolymer. Anchoring of the central PPO block of the copolymer is known to be favoured by hydrophobic interaction with the substratum. Therefore, the surfaces of metal oxides were first modified by self-assembly of octadecylphosphonic acid. PEO-PPO-PEO preadsorbed on the hydrophobized surfaces of titanium or SS was shown to prevent the adsorption of bovine serum albumin (BSA), fibrinogen and cytochrome C, as monitored by quartz crystal microbalance (QCM). Moreover, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry were used to characterize the surfaces of the SS and titanium after competitive adsorption of PEO-PPO-PEO and BSA. The results show that the adsorption of BSA is well prevented on hydrophobized surfaces, in contrast to the surfaces of native metal oxides.

  20. Importance of structural and chemical heterogeneity of activated carbon surfaces for adsorption of dibenzothiophene

    SciTech Connect

    Ania, C.O.; Bandosz, T.J.

    2005-08-16

    The performance of various activated carbons obtained from different carbon precursors (i.e., plastic waste, coal, and wood) as adsorbents for the desulfurization of liquid hydrocarbon fuels was evaluated. To increase surface heterogeneity, the carbon surface was modified by oxidation with ammonium persulfate. The results showed the importance of activated carbon pore sizes and surface chemistry for the adsorption of dibenzothiophene (DBT) from liquid phase. Adsorption of DBT on activated carbons is governed by two types of contributions: physical and chemical interactions. The former include dispersive interactions in the microporous network of the carbons. While the volume of micropores governs the amount physisorbed, mesopores control the kinetics of the process. On the other hand, introduction of surface functional groups enhances the performance of the activated carbons as a result of specific interactions between the acidic centers of the carbon and the basic structure of DBT molecule as well as sulfur-sulfur interactions.

  1. Density functional study of the adsorption of aspirin on the hydroxylated (0 0 1) α-quartz surface

    NASA Astrophysics Data System (ADS)

    Abbasi, A.; Nadimi, E.; Plänitz, P.; Radehaus, C.

    2009-08-01

    In this study the adsorption geometry of aspirin molecule on a hydroxylated (0 0 1) α-quartz surface has been investigated using DFT calculations. The optimized adsorption geometry indicates that both, adsorbed molecule and substrate are strongly deformed. Strong hydrogen bonding between aspirin and surface hydroxyls, leads to the breaking of the original hydroxyl-hydroxyl hydrogen bonds (Hydrogenbridges) on the surface. In this case new hydrogen bonds on the hydroxylated (0 0 1) α-quartz surface appear which significantly differ from those at the clean surface. The 1.11 eV adsorption energy reveals that the interaction of aspirin with α-quartz is an exothermic chemical interaction.

  2. Protein adsorption on surfaces: dynamic contact-angle (DCA) and quartz-crystal microbalance (QCM) measurements.

    PubMed

    Stadler, H; Mondon, M; Ziegler, C

    2003-01-01

    Adsorption of the protein bovine serum albumin (BSA) on gold has been tested at various concentrations in aqueous solution by dynamic contact-angle analysis (DCA) and quartz-crystal microbalance (QCM) measurements. With the Wilhelmy plate technique advancing and receding contact angles and the corresponding hysteresis were measured and correlated with the hydrophilicity and the homogeneity of the surface. With electrical admittance measurements of a gold-coated piezoelectrical quartz crystal, layer mass and viscoelastic contributions to the resonator's frequency shift during adsorption could be separated. A correlation was found between the adsorbed mass and the homogeneity and hydrophilicity of the adsorbed film.

  3. Continuum random sequential adsorption of polymer on a flat and homogeneous surface

    NASA Astrophysics Data System (ADS)

    Cieśla, Michał

    2013-05-01

    Random sequential adsorption (RSA) of polymer, modeled as a chain of identical spheres, is systematically studied. In order to control precisely anisotropy and number of degrees of freedom, two different kinds of polymers are used. In the first one, monomers are placed along a straight line, whereas in the second, relative orientations of particles are random. Such polymers fill a flat homogeneous surface randomly. The paper focuses on maximal random coverage ratio and adsorption kinetics dependence on polymer size, shape anisotropy, and numbers of degrees of freedom. Obtained results were discussed and compared with other numerical experiments and theoretical predictions.

  4. Adsorption of vapreotide on gold colloids studied by surface enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Gómez, J. A.; Cabanzo, R.; Mejia Ospino, E.

    2016-02-01

    Surface Enhanced Raman Spectroscopy (SERS) has been used to investigate the somatostatin (SST) analogue Vapreotide (VAP) in gold colloids. The optimum conditions to detect SERS signals of VAP have been studied. The observed SERS bands correspond to different vibrational modes of the peptide; being the most dominant SERS signals the ones derived from the aromatic amino acids Tryptophan (Trp), Phenylalanine (Phe) and Tyrosine (Tyr). Changes in enhancement and wavenumber of the proper bands upon adsorption on gold colloid are consistent with VAP adsorption, primarily through Tryptophan residues.

  5. Distinct binding states in adsorption on a homogeneous surface: Te on W(100)

    NASA Astrophysics Data System (ADS)

    Park, C.; Kramer, H. M.; Bauer, E.

    1982-05-01

    The adsorption of Te on a W(100) surface is studied by thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and work function change (Δϕ) measurements. Three distinct binding states are observed in the first monolayer corresponding the coverages from 0 to {1}/{2} monolayers (ML), {1}/{2} to {2}/{3} ML and {2}/{3} to 1 ML. Within each state a coverage dependence of the desorption parameters is found. The three binding states are discussed in terms of heterogeneity induced by lateral interactions and in terms of inherently different adsorption sites.

  6. Peptide adsorption on a hydrophobic surface results from an interplay of solvation, surface, and intrapeptide forces.

    PubMed

    Horinek, D; Serr, A; Geisler, M; Pirzer, T; Slotta, U; Lud, S Q; Garrido, J A; Scheibel, T; Hugel, T; Netz, R R

    2008-02-26

    The hydrophobic effect, i.e., the poor solvation of nonpolar parts of molecules, plays a key role in protein folding and more generally for molecular self-assembly and aggregation in aqueous media. The perturbation of the water structure accounts for many aspects of protein hydrophobicity. However, to what extent the dispersion interaction between molecular entities themselves contributes has remained unclear. This is so because in peptide folding interactions and structural changes occur on all length scales and make disentangling various contributions impossible. We address this issue both experimentally and theoretically by looking at the force necessary to peel a mildly hydrophobic single peptide molecule from a flat hydrophobic diamond surface in the presence of water. This setup avoids problems caused by bubble adsorption, cavitation, and slow equilibration that complicate the much-studied geometry with two macroscopic surfaces. Using atomic-force spectroscopy, we determine the mean desorption force of a single spider-silk peptide chain as F = 58 +/- 8 pN, which corresponds to a desorption free energy of approximately 5 k(B)T per amino acid. Our all-atomistic molecular dynamics simulation including explicit water correspondingly yields the desorption force F = 54 +/- 15 pN. This observation demonstrates that standard nonpolarizable force fields used in classical simulations are capable of resolving the fine details of the hydrophobic attraction of peptides. The analysis of the involved energetics shows that water-structure effects and dispersive interactions give contributions of comparable magnitude that largely cancel out. It follows that the correct modeling of peptide hydrophobicity must take the intimate coupling of solvation and dispersive effects into account.

  7. Carbonaceous materials for adsorptive refrigerators

    NASA Astrophysics Data System (ADS)

    Buczek, B.; Wolak, E.

    2012-06-01

    Carbon monoliths prepared from hard coal precursors were obtained. The porous structure of the monoliths was evaluated on the basis of nitrogen adsorption — desorption equilibrium data. The investigated monoliths have a well-developed microporous structure with significant specific surface area (S BET ). Equilibrium studies of methanol vapour adsorption were used to characterize the methanol adsorptive capacity that was determined using a volumetric method. The heat of wetting by methanol was determined in order to estimate the energetic effects of the adsorption process. The results of the investigations show that all monoliths exhibit high adsorption capacity and high heat of wetting with methanol.

  8. Adsorption of Polyethylene from Solution onto Starch Film Surfaces

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Starch films were prepared by jet cooking aqueous dispersions of high-amylose starch and then allowing the jet cooked dispersions to air-dry on Teflon surfaces. When the starch films were immersed in 1 % solutions of PE in 1-dodecanol, dodecane and xylene at 120º C and the solutions were allowed to...

  9. Influence of self-assembled monolayer surface chemistry on Candida antarctica lipase B adsorption and specific activity

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Immobilization of Candida antarctica B lipase was examined on gold surfaces modified with either methyl- or hydroxyl-terminated self-assembled alkylthiol monolayers (SAMs), representing hydrophobic and hydrophilic surfaces, respectively. Lipase adsorption was monitored gravimetrically using a quart...

  10. A first-principles study of ZnO polar surface growth: adsorption of Zn(x)O(y) clusters.

    PubMed

    Wang, Zhunzhun; Pan, Nan; Li, Zhenyu; Yang, Jinlong

    2013-09-28

    Adsorption of Zn(x)O(y) (x + y = 1-6) clusters on ZnO (000 ± 1) polar surfaces is studied systematically via density function theory (DFT) calculations. Different adsorption behaviors are predicted for these two surfaces. On the (0001)-Zn surface, O atoms adsorb on hollow sites at the initial stage. Then Zn atoms come in, and the stable structure becomes bulk-like for some specific clusters. On the (0001)-O surface, Zn cluster adsorption leads to stable cage structures formed by pulling substrate O out. In clusters with both Zn and O, O atoms avoid directly bonding with the surface, and no energetically favorable bulk-like structure is found. On the basis of the prediction of these surface adsorption behaviors, experimentally observed growth rate and surface roughness differences on these two polar surfaces can be understood. PMID:24089792

  11. A first-principles study of ZnO polar surface growth: Adsorption of ZnxOy clusters

    NASA Astrophysics Data System (ADS)

    Wang, Zhunzhun; Pan, Nan; Li, Zhenyu; Yang, Jinlong

    2013-09-01

    Adsorption of ZnxOy (x + y = 1-6) clusters on ZnO (000 ± 1) polar surfaces is studied systematically via density function theory (DFT) calculations. Different adsorption behaviors are predicted for these two surfaces. On the (0001)-Zn surface, O atoms adsorb on hollow sites at the initial stage. Then Zn atoms come in, and the stable structure becomes bulk-like for some specific clusters. On the (000overline 1)-O surface, Zn cluster adsorption leads to stable cage structures formed by pulling substrate O out. In clusters with both Zn and O, O atoms avoid directly bonding with the surface, and no energetically favorable bulk-like structure is found. On the basis of the prediction of these surface adsorption behaviors, experimentally observed growth rate and surface roughness differences on these two polar surfaces can be understood.

  12. Chromate adsorption on selected soil minerals: Surface complexation modeling coupled with spectroscopic investigation.

    PubMed

    Veselská, Veronika; Fajgar, Radek; Číhalová, Sylva; Bolanz, Ralph M; Göttlicher, Jörg; Steininger, Ralph; Siddique, Jamal A; Komárek, Michael

    2016-11-15

    This study investigates the mechanisms of Cr(VI) adsorption on natural clay (illite and kaolinite) and synthetic (birnessite and ferrihydrite) minerals, including its speciation changes, and combining quantitative thermodynamically based mechanistic surface complexation models (SCMs) with spectroscopic measurements. Series of adsorption experiments have been performed at different pH values (3-10), ionic strengths (0.001-0.1M KNO3), sorbate concentrations (10(-4), 10(-5), and 10(-6)M Cr(VI)), and sorbate/sorbent ratios (50-500). Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy were used to determine the surface complexes, including surface reactions. Adsorption of Cr(VI) is strongly ionic strength dependent. For ferrihydrite at pH <7, a simple diffuse-layer model provides a reasonable prediction of adsorption. For birnessite, bidentate inner-sphere complexes of chromate and dichromate resulted in a better diffuse-layer model fit. For kaolinite, outer-sphere complexation prevails mainly at lower Cr(VI) loadings. Dissolution of solid phases needs to be considered for better SCMs fits. The coupled SCM and spectroscopic approach is thus useful for investigating individual minerals responsible for Cr(VI) retention in soils, and improving the handling and remediation processes.

  13. Chromate adsorption on selected soil minerals: Surface complexation modeling coupled with spectroscopic investigation.

    PubMed

    Veselská, Veronika; Fajgar, Radek; Číhalová, Sylva; Bolanz, Ralph M; Göttlicher, Jörg; Steininger, Ralph; Siddique, Jamal A; Komárek, Michael

    2016-11-15

    This study investigates the mechanisms of Cr(VI) adsorption on natural clay (illite and kaolinite) and synthetic (birnessite and ferrihydrite) minerals, including its speciation changes, and combining quantitative thermodynamically based mechanistic surface complexation models (SCMs) with spectroscopic measurements. Series of adsorption experiments have been performed at different pH values (3-10), ionic strengths (0.001-0.1M KNO3), sorbate concentrations (10(-4), 10(-5), and 10(-6)M Cr(VI)), and sorbate/sorbent ratios (50-500). Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy were used to determine the surface complexes, including surface reactions. Adsorption of Cr(VI) is strongly ionic strength dependent. For ferrihydrite at pH <7, a simple diffuse-layer model provides a reasonable prediction of adsorption. For birnessite, bidentate inner-sphere complexes of chromate and dichromate resulted in a better diffuse-layer model fit. For kaolinite, outer-sphere complexation prevails mainly at lower Cr(VI) loadings. Dissolution of solid phases needs to be considered for better SCMs fits. The coupled SCM and spectroscopic approach is thus useful for investigating individual minerals responsible for Cr(VI) retention in soils, and improving the handling and remediation processes. PMID:27450335

  14. Scattering, Adsorption, and Langmuir-Hinshelwood Desorption Models for Physisorptive and Chemisorptive Gas-Surface Systems

    NASA Astrophysics Data System (ADS)

    Bentley, Brook I.

    Surface effects limit the performance of hypersonic vehicles, micro-electro-mechanical devices, and directed energy systems. This research develops methods to predict adsorption, scattering, and thermal desorption of molecules on a surface. These methods apply to physisorptive (adsorption and scattering) and chemisorptive (thermal desorption) gas-surface systems. Engineering and design applications will benefit from these methods, hence they are developed under the Direct Simulation Monte Carlo construct. The novel adsorption and scattering contribution, the Modified Kisliuk with Scattering method, predicts angular and energy distributions, and adsorption probabilities. These results agree more closely with experiment than the state-of-the-art Cercignani-Lampis-Lord scattering kernel. Super-elastic scattering is predicted. Gas-adlayer interactions are included for the first time. Accommodation coefficents can be determined by fitting simulations to experimental data. The new thermal desorption model accurately calculates angular, translational, rotational, and vibrational distributions, and the rotational alignment parameter. The model is validated by comparing with experiments. Multiple transition states are considered in a set of non-dimensionalized equations of motion, linked with temporally-accurate event timing. Initial conditions are chosen from a new truncated Maxwell-Boltzmann distribution. Run times are improved by eliminating the Gaussian Weighting of desorbing products. The absorption energy barrier is shown to significantly contribute only to the translational energy of desorbing molecules by contributing energy to each adatom in a similar manner.

  15. Adsorption of glycosaminoglycans to the cell surface is responsible for cellular donnan effects.

    PubMed

    Hagenfeld, Daniel; Kathagen, Nadine; Prehm, Peter

    2014-07-01

    In previous publications, we showed that extracellular glycosaminoglycans reduced the membrane potential, caused cell blebbing and swelling and decreased the intracellular pH independently of cell surface receptors. These phenomena were explained by Donnan effects. The effects were so large that they could not be attributed to glycosaminoglycans in solution. Therefore, we tested the hypothesis that glycosaminoglycans were concentrated on the cell membrane and analysed the mechanism of adsorption by fluorescent hyaluronan, chondroitin sulphate and heparin. The influence of the CD44 receptor was evaluated by comparing CD44 expressing human fibroblasts with CD44 deficient HEK cells. Higher amounts of glycosaminoglycans adsorbed to fibroblasts than to HEK cells. When the membrane potential was annihilated by substituting NaCl by KCl in the medium, adsorption was reduced and intracellular pH decrease was abolished. To eliminate other cellular interfering factors, potential-dependent adsorption was demonstrated for hyaluronan which adsorbed to inert gold foils in physiological salt concentrations at pH 7.2 and surface potentials up to 120 mV. From these results, we conclude that large cellular Donnan effects of glycosaminoglycans results from receptor mediated, hydrophobic and ionic adsorption to cell surfaces.

  16. Effects of surface heterogeneity on the adsorption of CO₂ in microporous carbons.

    PubMed

    Liu, Yangyang; Wilcox, Jennifer

    2012-02-01

    Carbon capture combined with utilization and storage has the potential to serve as a near-term option for CO(2) emissions reduction. CO(2) capture by carbon-based sorbents and CO(2) storage in geologic formations such as coal and shale both require a thorough understanding of the CO(2) adsorption properties in microporous carbon-based materials. Complex pore structures for natural organic materials, such as coal and gas shale, in addition to general carbon-based porous materials are modeled as a collection of independent, noninterconnected, functionalized graphitic slit pores with surface heterogeneities. Electronic structure calculations coupled with van der Waals-inclusive corrections have been performed to investigate the electronic properties of functionalized graphitic surfaces. With Bader charge analysis, electronic structure calculations can provide the initial framework comprising both the geometry and corresponding charge information required to carry out statistical modeling. Grand canonical Monte Carlo simulations were carried out to determine the adsorption isotherms for a given adsorbent-adsorbate interaction at temperature/pressure conditions relevant to carbon capture applications to focus on the effect of the surface functionalities. On the basis of the current work, oxygen-containing functional groups were predicted to enhance CO(2) adsorption in microporous carbon materials in the absence of water vapor, and the hydrated graphite was found to hinder CO(2) adsorption. PMID:22216997

  17. Effect of surface adsorption and non-stoichiometry on the workfunction of ZnO surfaces: A first principles study

    SciTech Connect

    Sun, Wei; Li, Yun; Jha, Jitendra Kumar; Shepherd, Nigel D.; Du, Jincheng

    2015-04-28

    ZnO has been actively studied for potential usage as a transparent conducting oxide (TCO) for a variety of applications including organic light emitting diodes and solar cells. In these applications, fine-tuning the workfunction of ZnO is critical for controlling interfacial barriers and improving the charge injection (or outcoupling) efficiencies. We have performed plane wave periodic density functional theory calculations to investigate the effect of different surface absorbents and surface defects (including surface non-stoichiometry) on the workfunction of ZnO. The aim was to understand the underlying mechanism of workfunction changes, in order to engineer specific workfunction modifications. Accurate calculations of workfunctions of polar surfaces were achieved by introducing balancing pseudo charges on one side of the surface to remove the dipolar effect. It was found that increasing the surface coverage of hydrocarbons (-CH{sub 3}) decreased the workfunction, while adsorption of highly electronegative-F and -CF{sub 3} groups and increases in surface O/Zn ratio increased the workfunction of ZnO. The increase of workfunction was found to be directly correlated to the enhancement variation of surface dipole moment due to adsorptions or other surface modifications. Introducing surface absorbents that increase surface dipole moment can be an effective way to increase workfunction in ZnO TCOs.

  18. Effect of surface charge distribution on the adsorption orientation of proteins to lipid monolayers.

    PubMed

    Tiemeyer, Sebastian; Paulus, Michael; Tolan, Metin

    2010-09-01

    The adsorption orientation of the proteins lysozyme and ribonuclease A (RNase A) to a neutral 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and a negatively charged stearic acid lipid film was investigated by means of X-ray reflectivity. Both proteins adsorbed to the negatively charged lipid monolayer, whereas at the neutral monolayer, no adsorption was observed. For acquiring comprehensive information on the proteins' adsorption, X-ray reflectivity data were combined with electron densities obtained from crystallographic data. With this method, it is possible to determine the orientation of adsorbed proteins in solution underneath lipid monolayers. While RNase A specifically coupled with its positively charged active site to the negatively charged lipid monolayer, lysozyme prefers an orientation with its long axis parallel to the Langmuir film. In comparison to the electrostatic maps of the proteins, our results can be explained by the discriminative surface charge distribution of lysozyme and RNase A.

  19. Effect of surface charge distribution on the adsorption orientation of proteins to lipid monolayers.

    PubMed

    Tiemeyer, Sebastian; Paulus, Michael; Tolan, Metin

    2010-09-01

    The adsorption orientation of the proteins lysozyme and ribonuclease A (RNase A) to a neutral 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and a negatively charged stearic acid lipid film was investigated by means of X-ray reflectivity. Both proteins adsorbed to the negatively charged lipid monolayer, whereas at the neutral monolayer, no adsorption was observed. For acquiring comprehensive information on the proteins' adsorption, X-ray reflectivity data were combined with electron densities obtained from crystallographic data. With this method, it is possible to determine the orientation of adsorbed proteins in solution underneath lipid monolayers. While RNase A specifically coupled with its positively charged active site to the negatively charged lipid monolayer, lysozyme prefers an orientation with its long axis parallel to the Langmuir film. In comparison to the electrostatic maps of the proteins, our results can be explained by the discriminative surface charge distribution of lysozyme and RNase A. PMID:20707324

  20. Theoretical Simulation of isocyanate (NCO) adsorption on the Ag(001) surface

    NASA Astrophysics Data System (ADS)

    Boungou, C. C.; N'dollo, M.; Malonda-Boungou, B. R.; Moussounda, P. S.; Dintzer, T.

    2016-05-01

    The adsorption of isocyanate (NCO) on a Ag (001) surface with different coverages [θ = 0.25, 0.50, 0.75 and 1.00 monolayer (ML)] is studied by using density functional theory and the periodic slab model. Adsorption energies, geometrical parameters and work function changes are calculated. We found that the most energetic sites are the bridge for 0.25 ML and the hollow for 0.50, 0.75 and 1.00 ML. The change in the work function depends on both the adsorption site and the NCO coverage. A detailed analysis of the computed local density of states shows that the NCO π and σ states strongly interact with the Ag (pz, dz2) bands.

  1. Theoretical studies of arsenite adsorption and its oxidation mechanism on a perfect TiO 2 anatase (1 0 1) surface

    NASA Astrophysics Data System (ADS)

    Wei, Zhigang; Zhang, Shaowen; Pan, Zhanchang; Liu, Yue

    2011-11-01

    There are many areas in the world where the ground water has been contaminated by arsenic. TiO2 is one of the most promising materials that can remove arsenic from groundwater supplies by the adsorption-based processes. The TiO2 surface is capable of photo-catalytic oxidation (PCO) changing the arsenite [As(III)] to arsenate [As(V)] which is more easily absorbed by the surface, increasing the efficiency of the process. In this paper, a density functional theory calculation has been performed to investigate the adsorption of As(III) on a perfect TiO2 anatase (1 0 1) surface. All the As(III) solution species such as H3AsO3, H2AsO3-, HAsO32- and AsO33- are put onto the surface with many different possible attitudes to obtain the adsorption energy. Based on the adsorption energy and the concentration of H3AsO3, H2AsO3-, HAsO32- and AsO33- in an aqueous solution, the bidentate binuclear (BB) adsorption configurations of H2AsO3- on the surface are more favorable at low As(III) concentrations, whereas BB form and monodentate mononuclear (MM) form may coexist at higher concentrations. By calculating H2AsO3- co-adsorption with water and oxygen, we can confirm the deep acceptor character of an adsorbed O2 molecule which implies that surface superoxide (or hydroperoxyl radical) plays an important role during the PCO process of As(III) on TiO2 surface.

  2. Adsorption of gold subnano-structures on a magnetite(111) surface and their interaction with CO.

    PubMed

    Pabisiak, Tomasz; Winiarski, Maciej J; Ossowski, Tomasz; Kiejna, Adam

    2016-07-21

    Gold deposited on iron oxide surfaces can catalyze the oxidation of carbon monoxide. The adsorption of gold subnano-structures on the Fe-rich termination of the magnetite(111) surface has been investigated using density functional theory. The structural, energetic, and electronic properties of gold/magnetite systems have been examined for vertical and flattened configurations of adsorbed Aun (n = 1-4) species. Single gold adatoms strongly bonded to the iron atoms of the Fe3O4(111) surface appear to be negatively charged, and consequently increase the work function. For a more stable class of larger, flattened Aun structures the adsorption binding energy per adatom is substantially increased. The structures exhibit a net positive charge, with the Au atoms binding with the oxide having distinctly cationic character. A charge transfer from the larger gold structures to the substrate is consistent with the lowering of the work function. The bonding of a CO molecule to a Au monomer on the Fe3O4(111) surface has been found nearly as strong as that to the iron site of the bare Fe-terminated surface. However, CO bonding to larger, oxide supported Aun structures is distinctly stronger than that to the bare oxide surface. Upon CO adsorption all Aun structures are cationic and CO shows a tendency to bind to the most cationic atom of the Aun cluster.

  3. Surface Modification of a Perfluorinated Ionomer Using a Glow Discharge Deposition Method to Control Protein Adsorption

    PubMed Central

    Valdes, T.I.; Ciridon, W.; Ratner, B.D.; Bryers, J.D.

    2008-01-01

    Nafion™ is the membrane material preferred for in situ glucose sensors. Unfortunately, surface properties of Nafion promote random protein adsorption and eventual foreign body encapsulation thus leading to loss if glucose signal over time. Here we detail surface modifications made by RF plasma deposition to Nafion with the intent to prevent random protein adsorption while providing enough functional sites (hydroxyl groups) to bind a biologically active peptide known to induce cellular adhesion (YRGDS). Nafion surfaces were modified by RF plasma polymerizing five different combinations of (1) tetraethylene glycol dimethyl ether (tetraglyme) and (2) 2-hydroxyethyl methacrylate (HEMA): pure tetraglyme, 2.5% HEMA/97.5% tetraglyme; 5% HEMA/95% tetraglyme, 10% HEMA/90% tetraglyme; and pure HEMA. Resultant surfaces were characterized by XPS (low and high resolution), dynamic contact angle, and atomic force microscopy. Protein adsorption and retention was determined and correlated to surface layer composition. The ability to bind a cell adhesion peptide was also determined and correlated well with surface layer composition. PMID:18155292

  4. Adsorption of gold subnano-structures on a magnetite(111) surface and their interaction with CO.

    PubMed

    Pabisiak, Tomasz; Winiarski, Maciej J; Ossowski, Tomasz; Kiejna, Adam

    2016-07-21

    Gold deposited on iron oxide surfaces can catalyze the oxidation of carbon monoxide. The adsorption of gold subnano-structures on the Fe-rich termination of the magnetite(111) surface has been investigated using density functional theory. The structural, energetic, and electronic properties of gold/magnetite systems have been examined for vertical and flattened configurations of adsorbed Aun (n = 1-4) species. Single gold adatoms strongly bonded to the iron atoms of the Fe3O4(111) surface appear to be negatively charged, and consequently increase the work function. For a more stable class of larger, flattened Aun structures the adsorption binding energy per adatom is substantially increased. The structures exhibit a net positive charge, with the Au atoms binding with the oxide having distinctly cationic character. A charge transfer from the larger gold structures to the substrate is consistent with the lowering of the work function. The bonding of a CO molecule to a Au monomer on the Fe3O4(111) surface has been found nearly as strong as that to the iron site of the bare Fe-terminated surface. However, CO bonding to larger, oxide supported Aun structures is distinctly stronger than that to the bare oxide surface. Upon CO adsorption all Aun structures are cationic and CO shows a tendency to bind to the most cationic atom of the Aun cluster. PMID:27332962

  5. Measurements of water sorption enthalpy on polymer surfaces and its effect on protein adsorption

    NASA Astrophysics Data System (ADS)

    Kim, Joonyeong; Qian, Wei; Al-Saigh, Zeki Y.

    2011-02-01

    The molar enthalpy of sorption ( ΔHms`) of water vapor onto three polymer surfaces and its effect on nonspecific protein adsorption were investigated by inverse gas chromatography (IGC). The values of ΔHms measured by IGC were found to be -16.9 ± 1.2, -18.6 ± 1.3, and -29.9 ± 2.4 kJ/mole for polystyrene (PS), polymethylmethacrylate (PMMA), and poly(2-hydroxyethyl methacrylate) (PHEMA), respectively, over a temperature range of 333-423 K. Protein adsorption to three polymer-coated substrates was conducted as a function of the bulk protein concentration using lysozyme, fibrinogen, and bovine serum albumin (BSA), and the amount of adsorbed protein was measured by the solution depletion method. For a given bulk protein concentration, a larger amount of protein is adsorbed on PS and PMMA surfaces which have greater ΔHms than that of PHEMA surfaces. Although ΔHms for PS and PMMA are close to each other, PS surfaces were found to exhibit a higher adsorption affinity than PMMA surfaces over the proteins and concentrations investigated. Our results indicate that the strength of water-polymer interactions and the functional groups on the polymer surface are important factors for controlling the amount of nonspecifically adsorbed protein.

  6. Adsorption of protein streptavidin to the plasma treated surface of polystyrene

    NASA Astrophysics Data System (ADS)

    Vesel, Alenka; Elersic, Kristina

    2012-05-01

    Immobilization of protein streptavidin to the surface of polystyrene (PS) polymer was studied by X-ray photoelectron spectroscopy (XPS). Two different protocols were used to attach streptavidin to the PS surface: physical adsorption and chemical coupling. In both cases the surface properties of PS samples were modified by exposure to cold oxygen plasma for 10 s. Plasma was created in oxygen at 75 Pa by en electrode-less RF discharge. The RF generator operated at 27.12 MHz and the nominal power was about 120 W. The electron temperature was about 3 eV, the plasma density was about 3 × 1015 m-3 and the neutral oxygen atom density was about 3 × 1021 m-3. Oxygen plasma treatment caused formation of O-rich functional groups on the surface of PS. The concentration of oxygen was determined by XPS and was about 28 at.%. A thin film of streptavidin was deposited by physical adsorption and chemical bonding. The appearance of streptavidin on the surface was determined from XPS spectra measuring the ratio between N and C peaks. The plasma treatment caused poor adsorption and but strong chemisorption of streptavidin. The results were explained by specific interaction of protein with polar functional groups on the surface of PS after plasma treatment.

  7. Uncovering surface area and micropores in almond shell biochars by rainwater wash.

    PubMed

    Thomas Klasson, K; Uchimiya, Minori; Lima, Isabel M

    2014-09-01

    Biochars have been considered for adsorption of contaminants in soil and water, as well as conditioning and improving soil quality. Pore surface area is an important property of biochar. Biochars were created from shells of two almond varieties with different ash content. The pyrolysis was performed at 650 and 800°C for 40-240min. Significant surface areas developed at the higher temperature and at pyrolysis times of 120min and longer. Washing the materials in synthetic rainwater removed ash and exposed additional surface area, particularly in small-diameter pores. When results from low-ash almond shell biochars were compared with high-ash almond shell biochars, it was found that the pore distribution was more uniform for the high-ash starting material and almost independent of pyrolysis time or washing. The result from the washing study is important as it suggested that adsorptive properties may change once biochars are exposed to rainwater. PMID:24997909

  8. Insights into the superhydrophobicity of metallic surfaces prepared by electrodeposition involving spontaneous adsorption of airborne hydrocarbons

    NASA Astrophysics Data System (ADS)

    Liu, Peng; Cao, Ling; Zhao, Wei; Xia, Yue; Huang, Wei; Li, Zelin

    2015-01-01

    Electrochemical fabrication of micro/nanostructured metallic surfaces with superhydrophobicity has recently aroused great attention. However, the origin still remains unclear why smooth hydrophilic metal surfaces become superhydrophobic by making micro/nanostructures without additional surface modifications. In this work, several superhydrophobic micro/nanostructured metal surfaces were prepared by a facile one-step electrodeposition process, including non-noble and noble metals such as copper, nickel, cadmium, zinc, gold, and palladium with (e.g. Cu) or without (e.g. Au) surface oxide films. We demonstrated by SEM and XPS that both hierarchical micro/nanostructures and spontaneous adsorption of airborne hydrocarbons endowed these surfaces with excellent superhydrophobicity. We revealed by XPS that the adsorption of airborne hydrocarbons at the Ar+-etched clean Au surface was rather quick, such that organic contamination can hardly be prevented in practical operation of surface wetting investigation. We also confirmed by XPS that ultraviolet-O3 treatment of the superhydrophobic metal surfaces did not remove the adsorbed hydrocarbons completely, but mainly oxidized them into hydrophilic oxygen-containing organic substances. We hope our findings here shed new light on deeper understanding of superhydrophobicity for micro/nanostructured metal surfaces with and without surface oxide films.

  9. Surface silylation of natural mesoporous/macroporous diatomite for adsorption of benzene.

    PubMed

    Yu, Wenbin; Deng, Liangliang; Yuan, Peng; Liu, Dong; Yuan, Weiwei; Liu, Peng; He, Hongping; Li, Zhaohui; Chen, Fanrong

    2015-06-15

    Naturally occurring porous diatomite (Dt) was functionalized with phenyltriethoxysilane (PTES), and the PTES-modified diatomite (PTES-Dt) was characterized using diffuse reflectance Fourier transform infrared spectroscopy, nitrogen adsorption, nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. After silylation, a functional group (-C6H5, phenyl) was successfully introduced onto the surface of Dt. PTES-Dt exhibited hydrophobic properties with a water contact angle (WCA) as high as 120°±1°, whereas Dt was superhydrophilic with a WCA of 0°. The benzene adsorption data on both Dt and PTES-Dt fit well with the Langmuir isotherm equation. The Langmuir adsorption capacity of benzene on PTES-Dt is 28.1 mg/g, more than 4-fold greater than that on Dt. Moreover, the adsorption kinetics results show that equilibrium was achieved faster for PTES-Dt than for Dt, over the relative pressure range of 0.118-0.157. The excellent benzene adsorption performance of PTES-Dt is attributed to strong π-system interactions between the phenyl groups and the benzene molecules as well as to the macroporosity of the PTES-Dt. These results show that the silylated diatomite could be a new and inexpensive adsorbent suitable for use in benzene emission control. PMID:25792477

  10. Surface silylation of natural mesoporous/macroporous diatomite for adsorption of benzene.

    PubMed

    Yu, Wenbin; Deng, Liangliang; Yuan, Peng; Liu, Dong; Yuan, Weiwei; Liu, Peng; He, Hongping; Li, Zhaohui; Chen, Fanrong

    2015-06-15

    Naturally occurring porous diatomite (Dt) was functionalized with phenyltriethoxysilane (PTES), and the PTES-modified diatomite (PTES-Dt) was characterized using diffuse reflectance Fourier transform infrared spectroscopy, nitrogen adsorption, nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. After silylation, a functional group (-C6H5, phenyl) was successfully introduced onto the surface of Dt. PTES-Dt exhibited hydrophobic properties with a water contact angle (WCA) as high as 120°±1°, whereas Dt was superhydrophilic with a WCA of 0°. The benzene adsorption data on both Dt and PTES-Dt fit well with the Langmuir isotherm equation. The Langmuir adsorption capacity of benzene on PTES-Dt is 28.1 mg/g, more than 4-fold greater than that on Dt. Moreover, the adsorption kinetics results show that equilibrium was achieved faster for PTES-Dt than for Dt, over the relative pressure range of 0.118-0.157. The excellent benzene adsorption performance of PTES-Dt is attributed to strong π-system interactions between the phenyl groups and the benzene molecules as well as to the macroporosity of the PTES-Dt. These results show that the silylated diatomite could be a new and inexpensive adsorbent suitable for use in benzene emission control.

  11. Protein adsorption at calcium oxalate monohydrate crystal surfaces.

    NASA Astrophysics Data System (ADS)

    Wesson, J.; Sheng, X.; Rimer, J.; Jung, T.; Ward, M.

    2008-03-01

    Calcium oxalate monohydrate (COM) crystals are the dominant inorganic phase in most kidney stones, and kidney stones form as aggregates of COM crystals and organic material, principally proteins, but little is known about the molecular level events at COM surfaces that regulate COM aggregation. We have examined the influence of polyelectrolytes on the force of adhesion between chemically modified atomic force microscopy (AFM) tips and selected COM crystal faces in saturated solution. In general, we found that polyanions bind to COM surfaces and block adhesion of a carboxylate functionalized AFM tip, while polycations had no measureable effect on adhesion force under the same conditions. We did observe a unique absence of interaction between poly(glutamic acid) and the COM (100) face compared to other synthetic polyanions, and some native urinary protein structures also exhibited unique face selective interactions, suggesting that simple electrostatic models will not completely explain the data.

  12. Uranyl adsorption and surface speciation at the imogolite-water interface: Self-consistent spectroscopic and surface complexation models

    USGS Publications Warehouse

    Arai, Y.; McBeath, M.; Bargar, J.R.; Joye, J.; Davis, J.A.

    2006-01-01

    Macro- and molecular-scale knowledge of uranyl (U(VI)) partitioning reactions with soil/sediment mineral components is important in predicting U(VI) transport processes in the vadose zone and aquifers. In this study, U(VI) reactivity and surface speciation on a poorly crystalline aluminosilicate mineral, synthetic imogolite, were investigated using batch adsorption experiments, X-ray absorption spectroscopy (XAS), and surface complexation modeling. U(VI) uptake on imogolite surfaces was greatest at pH ???7-8 (I = 0.1 M NaNO3 solution, suspension density = 0.4 g/L [U(VI)]i = 0.01-30 ??M, equilibration with air). Uranyl uptake decreased with increasing sodium nitrate concentration in the range from 0.02 to 0.5 M. XAS analyses show that two U(VI) inner-sphere (bidentate mononuclear coordination on outer-wall aluminol groups) and one outer-sphere surface species are present on the imogolite surface, and the distribution of the surface species is pH dependent. At pH 8.8, bis-carbonato inner-sphere and tris-carbonato outer-sphere surface species are present. At pH 7, bis- and non-carbonato inner-sphere surface species co-exist, and the fraction of bis-carbonato species increases slightly with increasing I (0.1-0.5 M). At pH 5.3, U(VI) non-carbonato bidentate mononuclear surface species predominate (69%). A triple layer surface complexation model was developed with surface species that are consistent with the XAS analyses and macroscopic adsorption data. The proton stoichiometry of surface reactions was determined from both the pH dependence of U(VI) adsorption data in pH regions of surface species predominance and from bond-valence calculations. The bis-carbonato species required a distribution of surface charge between the surface and ?? charge planes in order to be consistent with both the spectroscopic and macroscopic adsorption data. This research indicates that U(VI)-carbonato ternary species on poorly crystalline aluminosilicate mineral surfaces may be important in

  13. First-principles Analysis of NOx Adsorption on Anhydrous γ-Al2O3 Surfaces

    SciTech Connect

    Mei, Donghai; Ge, Qingfeng; Szanyi, Janos; Peden, Charles HF

    2009-04-09

    The interaction of nitrogen oxides NOx (x=1-3) with gamma Al2O3 has been investigated using first-principles density functional theory calculations. NO and NO2 weakly physisorb on the clean, dehydrated (100) and (110) surfaces of gamma Al2O3, whereas the adsorption of the NO3 radical is rather strong. Only the basic-like O-down adsorption configurations were found to be stable. The interaction between NOx and gamma Al2O3 can be described as a surface mediated electron transfer process. For single NOx adsorption, greater electron transfer from the surface to the adsorbate (negatively charged) yields stronger interactions between NOx and the surface. The adsorption of four combinations of NOx+NOy (x=1-3, y=2, 3) pairs on the (100) and the (110) facets of gamma Al2O3 were investigated. Except for the NO2+NO2 pair, a strong cooperative effect that substantially enhances the stability of NOx on both gamma Al2O3 surfaces was found. This cooperative effect consists of surface-mediated electron transfer processes resulting in a favorable electrostatic interaction between two adsorbed NOx species. The pair was found to be the thermodynamically most stable state among the co-adsorbed NOx+NOy pairs on both gamma Al2O3 surfaces. The results are used to analyze the experimentally observed NOx evolution during temperature programmed desorption from NO2-saturated gamma Al2O3 substrates. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  14. Atomic-scale surface roughness of rutile and implications for organic molecule adsorption.

    PubMed

    Livi, Kenneth J T; Schaffer, Bernhard; Azzolini, David; Seabourne, Che R; Hardcastle, Trevor P; Scott, Andrew J; Hazen, Robert M; Erlebacher, Jonah D; Brydson, Rik; Sverjensky, Dimitri A

    2013-06-11

    Crystal surfaces provide physical interfaces between the geosphere and biosphere. It follows that the arrangement of atoms at the surfaces of crystals profoundly influences biological components at many levels, from cells through biopolymers to single organic molecules. Many studies have focused on the crystal-molecule interface in water using large, flat single crystals. However, little is known about atomic-scale surface structures of the nanometer- to micrometer-sized crystals of simple metal oxides typically used in batch adsorption experiments under conditions relevant to biogeochemistry and the origins of life. Here, we present atomic-resolution microscopy data with unprecedented detail of the circumferences of nanosized rutile (α-TiO2) crystals previously used in studies of the adsorption of protons, cations, and amino acids. The data suggest that one-third of the {110} faces, the largest faces on individual crystals, consist of steps at the atomic scale. The steps have the orientation to provide undercoordinated Ti atoms of the type and abundance for adsorption of amino acids as inferred from previous surface complexation modeling of batch adsorption data. A remarkably uniform pattern of step proportions emerges: the step proportions are independent of surface roughness and reflect their relative surface energies. Consequently, the external morphology of rutile nanometer- to micrometer-sized crystals imaged at the coarse scale of scanning electron microscope images is not an accurate indicator of the atomic smoothness or of the proportions of the steps present. Overall, our data strongly suggest that amino acids attach at these steps on the {110} surfaces of rutile. PMID:23675906

  15. Physical and chemical nature of the scaling relations between adsorption energies of atoms on metal surfaces.

    PubMed

    Calle-Vallejo, F; Martínez, J I; García-Lastra, J M; Rossmeisl, J; Koper, M T M

    2012-03-16

    Despite their importance in physics and chemistry, the origin and extent of the scaling relations between the energetics of adsorbed species on surfaces remain elusive. We demonstrate here that scalability is not exclusive to adsorbed atoms and their hydrogenated species but rather a general phenomenon between any set of adsorbates bound similarly to the surface. On the example of the near-surface alloys of Pt, we show that scalability is a result of identical variations of adsorption energies with respect to the valence configuration of both the surface components and the adsorbates. PMID:22540492

  16. Computer simulation of argon adsorption on graphite surface from subcritical to supercritical conditions: the behavior of differential and integral molar enthalpies of adsorption.

    PubMed

    Fan, Chunyan; Do, D D; Li, Zili; Nicholson, D

    2010-10-19

    We investigate in detail the computer simulation of argon adsorption on a graphite surface over a very wide range of temperature, from below the triple point to well above the critical point. Adsorption over such a wide temperature range has not been reported previously in the form of adsorption isotherms and enthalpy change during adsorption. The adsorption isotherms can be classified broadly into four categories: below the triple point, the isotherms show stepwise character (a strict layering mechanism) with 2D condensation; type II (according to the IUPAC classification) is followed by isotherms at temperatures above the triple point and below the critical point and a sharp spike is seen for isotherms in the neighborhood of the critical point; and finally the typical behavior of a maximum is observed for isotherms above the critical point. For the isosteric heat, the heat curve (plotted against loading) remains finite for subcritical conditions but is infinite (singularity) at the maximum in excess loading for supercritical adsorption. For the latter case, a better representation of the energy change is the use of the integral molecular enthalpy because this does not exhibit a singularity as in the case of isosteric heat. We compare the differential and integral molecular enthalpies for the subcritical and supercritical adsorptions.

  17. Relating material surface heterogeneity to protein adsorption: the effect of annealing of micro-contact-printed OTS patterns

    PubMed Central

    HODGKINSON, GERALD; HLADY, VLADIMIR

    2009-01-01

    We have investigated the influence of micrometer- and sub-micrometer-scale surface heterogeneities in patterned octadecyltrichlorosilane (OTS) films on human serum albumin (HSA) adsorption and its spatial distribution. 5-μm-wide OTS patterns were created on glass substrates by micro-contact printing and in some instances subsequent annealing was used to alter OTS molecule distribution within the patterns. Scanning force microscopy (SFM), advancing water contact angles and water vapor condensation figures were used to characterize the OTS films and to assess the nature of the heterogeneities within the various surface areas. High-resolution fluorescence microscopy was used to record images of fluorescently labeled albumin on OTS patterned films and fluorescence intensity was quantified and converted into the adsorbed amount. Adsorbed albumin was also characterized through SFM measurements. Combined SFM topography and lateral force microscopy (LFM) imaging revealed that micro-contact printing of OTS onto glass both replicated the stamp pattern and created small islands within the non-stamped regions between the patterns. The OTS coverage within stamped regions was not fully continuous but improved with subsequent annealing. Annealing also resulted in OTS island growth within the non-stamped regions and decreased average wettability on both the stamped and non-stamped areas. The extent of albumin adsorption was not proportional to OTS coverage, but correlated with the sub-μm distribution of OTS chains. We inferred that the surface distribution of ligands such as OTS on a sub-μm length scale determines the nature of albumin adsorption and its kinetics. PMID:19693285

  18. Modeling the Adsorption of Hydrophobic Ethoxylated Urethane (HEUR) Thickeners onto Latex Surfaces using Self-Consistent Field Theory

    NASA Astrophysics Data System (ADS)

    Ginzburg, Valeriy; van Dyk, Antony; Chatterjee, Tirtha; Wang, Shihu; Larson, Ronald

    2015-03-01

    Hydrophobic Ethoxylated Urethane (HEUR) polymers are widely used as rheology modifiers (thickeners) in waterborne latex paints. Recently, it has been shown that the thickening effect of HEURs in paints is largely determined by their adsorption onto latex surfaces, this adsorption being a function of polymer structure, latex surface chemistry, and total available latex surface. Here, we describe the application of Self-Consistent Field Theory (SCFT) to calculate adsorption isotherms of several model HEURs onto ideal hydrophobic latex surfaces. Unlike earlier SCFT studies of adsorption, we explicitly take into account the role of HEUR micelles and competition between adsorption and micellization. The results are compared with experimental data and coarse-grained molecular dynamic (CG-MD) simulations, and good qualitative and semi-quantitative agreement is found. This work was supported by The Dow Chemical Company.

  19. The dynamics of adsorption on clean and adsorbate-modified transition metal surfaces. [Progress report, 1989--1991

    SciTech Connect

    Madix, R.J.

    1991-06-01

    Research is being carried out on both nondissociative and dissociative adsorption of gases on transition metal surfaces, with emphasis on alkanes. Particular attention is be placed on understanding the effects of adsorbed species on adsorption probabilities and on clarifying the role of energy exchange processes at the surface in both dissociative and nondissociative adsorption. Molecular beam methods are coupled with methods of surface science to gain the greatest control of the variables of the problem, including the incident kinetic energy, vibrational energy and angle of incidence of the incoming molecules. The dynamics of both direct and precursor-influenced dissociative adsorption routes are examined. Surface intermediates formed by activated adsorption are identified by vibrational spectroscopy and temperature programmed reaction. Emphasis is on comparative studies of low molecular weight alkanes in order to understand the origin of the differences in their reactivities on different metals.

  20. Determining the association constant and adsorption properties of ion pairs in water by fitting surface tension data.

    PubMed

    Pradines, Vincent; Lavabre, Dominique; Micheau, Jean-Claude; Pimienta, Véronique

    2005-11-22

    Association constants and adsorption parameters of tetraalkylammoniumdodecyl sulfate (TAADS) ion pairs in water were determined. We have analyzed water/air surface tension measurements obtained for mixtures of sodium dodecyl sulfate (SDS) and tetraalkylammonium bromide of increasing chain lengths (TMAB, TEAB, TPAB, and TBAB). To reproduce the experimental isotherms, we coupled the association equilibrium of the ion pairs to the equations proposed by Fainerman and co-workers to model the adsorption of binary mixtures of surfactants (SDS and TAADS) with different molar areas at a nonideal surface layer. The parameters found showed that the model is not convenient to describe the effect of the addition of TMAB but a clear coherency was obtained for the three longer compounds. Ranging from TEADS to TBADS increasing hydrophobic interactions give rise to a higher associability but to a lower surface activity. Self-interactions coefficients extracted by the fitting procedure confirmed the importance of attractive interactions between the ion pairs. The calculated surface coverage showed that in every case the compound mainly adsorbed at the interface was the ion pair. For TBADS strong attractive interactions result in a phase transition at very low concentration.

  1. Specific ion adsorption and surface forces in colloid science.

    PubMed

    Lima, E R A; Horinek, D; Netz, R R; Biscaia, E C; Tavares, F W; Kunz, W; Boström, M

    2008-02-14

    Mean-field theories that include nonelectrostatic interactions acting on ions near interfaces have been found to accommodate many experimentally observed ion specific effects. However, it is clear that this approach does not fully account for the liquid molecular structure and hydration effects. This is now improved by using parametrized ionic potentials deduced from recent nonprimitive model molecular dynamics (MD) simulations in a generalized Poisson-Boltzmann equation. We investigate how ion distributions and double layer forces depend on the choice of background salt. There is a strong ion specific double layer force set up due to unequal ion specific short-range potentials acting between ions and surfaces. PMID:18205350

  2. Hydrogen Adsorption Studies Using Surface Acoustic Waves on Nanoparticles

    SciTech Connect

    A.B. Phillips; G. Myneni; B.S. Shivaram

    2005-06-13

    Vanadium nanoparticles, on the order of 20 nm, were deposited on a quartz crystal surface acoustic wave resonator (SAW) using a Nd:YAG pulsed laser deposition system. Due to the high Q and resonant frequency of the SAW, mass changes on the order of 0.1 nanogram can be quantitatively measured. Roughly 60 nanogram of V was deposited on the SAW for these experiments. The SAW was then moved into a hydrogen high pressure cell.At room temperature and 1 atmosphere of hydrogen pressure, 1 wt% H, or H/V {approx} 0.5 (atomic ratio) absorption was measured.

  3. Adsorption of Ar on planar surfaces studied with a density functional theory.

    PubMed

    Sartarelli, Salvador A; Szybisz, Leszek

    2009-11-01

    The adsorption of Ar on planar structureless substrates of alkali metals, alkaline-earth metal Mg, CO2 , and Au was analyzed by applying a density functional formalism which includes a recently proposed effective attractive pair potential conditioned to Ar. It is shown that this approach reproduces the experimental surface tension of the liquid-vapor interface over the entire bulk coexistence curve for temperatures T spanning from the triple point Tt up to the critical point Tc. The wetting properties were studied over the entire range temperatures Tt<-->Tc. It was found that Ar wets all the investigated surfaces. The adsorption isotherms for alkali metals exhibit first-order phase transitions. Prewetting lines were resolved even for the less attractive surfaces. In the cases of Mg, CO2 , and Au a continuous growth for T> or =Tt was obtained. A comparison with experimental data and other microscopic calculations is reported.

  4. The adsorption of a hydrogen atom on the two types of boron sheets surface

    NASA Astrophysics Data System (ADS)

    Boroznina, E. V.; Borkhoeva, N. N.; Boroznin, S. V.

    2015-01-01

    The possible connection between the atom of hydrogen and the surface of twodimensional boron sheets have been investigated. The calculations were carried out within the model of molecular cluster with the use of quantum chemical MNDO scheme. Two types of BS were studied: triangular BS (TBS) and α-sheet of boron atoms (αBS). The hydrogen atoms attacking BS have been simulated by a step-by-step approach for all atom locations. The surface patterns of potential energy for these processes were built. The analysis of curves showed that the active atom of hydrogen is adsorbed on the surface of BS. The adsorption distances (Rad) and the adsorption energy (Ead) were calculated. We have proved that αBS has a greater sorption capacity than hydrogen TBS.

  5. Adsorption of humic acid onto carbonaceous surfaces: atomic force microscopy study.

    PubMed

    Liu, Zhiguo; Zu, Yuangang; Meng, Ronghua; Xing, Zhimin; Tan, Shengnan; Zhao, Lin; Sun, Tongze; Zhou, Zhen

    2011-12-01

    The adsorption of humic acid (HA) onto highly ordered pyrolytic graphite (HOPG) surfaces at different concentrations has been studied by atomic force microscopy. When HA concentration was increased from 10 to 1,000 mg/L, HA can sequentially form spherical particles, layered structures, and connected blocks on HOPG surfaces. The findings of the layer structures and small amount of fine chains have been verified and discussed. When HA was acidified by addition of acetic acid, it changed into small rigid particles. These results indicated that HA can be considered as supramolecular associations of self-assembling heterogeneous and relatively small molecules, and a small amount of polymers. The present results are important for understanding HA molecular structures and their adsorption characteristic on carbonaceous surfaces. PMID:22047766

  6. Surface Treatment for Effective Dye Adsorption on Nanocrystalline TiO2

    NASA Astrophysics Data System (ADS)

    Yanagida, Masatoshi; Han, Chen; Han, Liyuan

    2012-10-01

    To improve the efficiency of dye-sensitized solar cells (DSCs) by controlling dye adsorption on TiO2 surface, the effect of surface treatments on the properties of [NBu4]2[Ru(Htcterpy)(NCS)3] (black dye; [NBu4]: tetrabutylammonium cation; H3tcterpy: 4,4',4''-tricarboxy-2,2':6',2''-terpyridine) on nanocrystalline TiO2 films was investigated by analysis of the photovoltaic performance and the electron transport properties. Although the surface treatments do not affect on the condition band edge of TiO2, the amount of dye on TiO2 increases. The enhancement of dye adsorption by treatment of TiO2 in HCl solution is more effective than that by dipping the dye solution containing deoxycholic acid (DCA) as additive. But the charge recombination between an electron in TiO2 and I3- in the electrolyte can be reduced by the DCA treatment.

  7. In vitro investigation of protein adsorption and platelet adhesion on inorganic biomaterial surfaces

    NASA Astrophysics Data System (ADS)

    Huang, Yan; Lü, Xiaoying; Jingwu, Ma; Huang, Nan

    2008-11-01

    The aim of this paper was to study the surface properties, protein adsorption and platelet adhesion behaviors of diamond-like carbon (DLC) and titanium (Ti) films. The surface energy and microstructures of these films were characterized by contact angle measurement and atomic force microscopy (AFM). A modified Coomassie brilliant blue (CBB) protein assay was used to study the amount of adsorbed proteins. Platelet adhesion was assessed by scanning electron microscopy (SEM). The AFM results show that the DLC film is smoother than Ti. Protein adsorption results from CBB protein assay show that the ratio of adsorbed albumin (Alb) to IgG ( RA/I) on DLC is larger than Ti, which coincide with the sequence of the ratio of interfacial tension between solid surface and Alb ( γS,Alb) to interfacial tension between surface and IgG ( γS,IgG) ( γS,Alb/ γS,IgG). The DLC film has a preferential adsorption for Alb. The results suggest that the ratio of γS,Alb/ γS,IgG may indicate an Alb/IgG affinity ratio of materials. More platelets adhere on Ti film than on DLC, which may correspond to the surface roughness of materials. The conclusion is the blood compatibility of DLC seems to be better than Ti.

  8. Influence of alkane chain length on adsorption on an α-alumina surface by MD simulations

    NASA Astrophysics Data System (ADS)

    Turgut, C.; Pandiyan, S.; Mether, L.; Belmahi, M.; Nordlund, K.; Philipp, P.

    2015-06-01

    Plasma surface techniques provide both an efficient and ecological tool for the functionalization of surfaces. Hence, a proper understanding of the plasma-surface interactions of precursors and radicals during the deposition process is of great importance. Especially during the initial deposition process, the deposition of molecules and fragments is difficult to investigate by experimental techniques and import insights can be obtained by molecular dynamics simulations. In this work, the reactive force field developed by the group of Kieffer at the University of Michigan was used to study the adsorption of single linear alkane chains on an α-alumina surface. The chain length was changed from 6 backbone carbon atoms to 16 carbon atoms, the deposition energy from 0.01 to 10 eV and the incidence angle from 0° to 60° with respect to the surface normal. Results show that the adsorption depends a lot on the ratio of deposition energy to alkane chain length and the incidence angle. More grazing incidence reduces the adsorption probability and a low ratio of energy to chain length increases it.

  9. The adsorption and photo-degradation of oxalic acid at the TiO2 surface.

    NASA Astrophysics Data System (ADS)

    Mendive, Cecilia; Blesa, Miguel; Bahnemann, Detlef

    2006-03-01

    Oxalic acid is the simplest model compound to study the heterogeneous photocatalytic oxidation of pollutants on TiO2 containing more than one carboxylate group. We have carried out a study of a system of an oxalic acid solution in contact with a thin film of TiO2 particles employing ATR - FTIR in combination with quantum chemical calculations. Thus, possible adsorption structures have been identified and molecular dynamic simulations have been used to compare their predictions with the experimental data. It was found that the adsorption of oxalic acid on TiO2 in the dark can be explained in terms of two surface complexation modes for the anatase phase and only one surface complexation mode for the rutile phase. We have found that under illumination one of the complexes on the anatase phase preferably undergoes photo-degradation. At the same time water molecules are desorbed from the TiO2 surface by a thermal mechanism induced by the absorption of photons. Both processes favor the adsorption of more molecules of oxalic acid at the TiO2 surface which is thus enriched in the second complexation mode. A similar mechanism was found to occur on the rutile phase. The only complexation mode appears not to be photo-sensitive but the TiO2 surface is enriched in oxalic acid under illumination due to the replacement of photo-desorbed water molecules.

  10. Risedronate adsorption on bioactive glass surface for applications as bone biomaterial

    NASA Astrophysics Data System (ADS)

    Mosbahi, Siwar; Oudadesse, Hassane; Lefeuvre, Bertand; Barroug, Allal; Elfeki, Hafed; Elfeki, Abdelfattah; Roiland, Claire; Keskes, Hassib

    2016-03-01

    The aim of the current work is to study the physicochemical interactions between bisphosphonates molecules, risedronate (RIS) and bioactive glass (46S6) after their association by adsorption phenomenon. To more understand the interaction processes of RIS with the 46S6 surface we have used complementary physicochemical techniques such as infrared (FTIR), Raman and nuclear magnetic resonance (NMR) spectroscopy. The obtained results suggest that risedronate adsorption corresponds to an ion substitution reaction with silicon ions occurring at the bioactive glass surface. Thus, a pure bioactive glass was synthesized and fully characterized comparing the solids after adsorption (46S6-XRIS obtained after the interaction of 46S6 and X% risedronate). Therefore, based on the spectroscopic results FTIR, Raman and MAS-NMR, it can be concluded that strong interactions have been established between RIS ions and 46S6 surface. In fact, FTIR and Raman spectroscopy illustrate the fixation of risedronate on the bioactive glass surface by the appearance of several bands characterizing risedronate. The 31P MAS-NMR of the composite 46S6-XRIS show the presence of two species at a chemical shift of 15 and 19 ppm demonstrating thus the fixation of the RIS on 46S6 surface.

  11. Bacterial Cell Surface Adsorption of Rare Earth Elements

    NASA Astrophysics Data System (ADS)

    Jiao, Y.; Park, D.; Reed, D.; Fujita, Y.; Yung, M.; Anderko, A.; Eslamimanesh, A.

    2015-12-01

    Rare earth elements (REE) play a critical role in many emerging clean energy technologies, including high-power magnets, wind turbines, solar panels, hybrid/electric vehicle batteries and lamp phosphors. In order to sustain demand for such technologies given current domestic REE shortages, there is a need to develop new approaches for ore processing/refining and recycling of REE-containing materials. To this end, we have developed a microbially-mediated bioadsorption strategy with application towards enrichment of REE from complex mixtures. Specifically, the bacterium Caulobacter crescentus was genetically engineered to display lanthanide binding tags (LBTs), short peptides that possess high affinity and specificity for rare earth elements, on its cell surface S-layer protein. Under optimal conditions, LBT-displayed cells adsorbed greater than 5-fold more REE than control cells lacking LBTs. Competition binding experiments with a selection of REEs demonstrated that our engineered cells could facilitate separation of light- from heavy- REE. Importantly, binding of REE onto our engineered strains was much more favorable compared to non-REE metals. Finally, REE bound to the cell surface could be stripped off using citrate, providing an effective and non-toxic REE recovery method. Together, this data highlights the potential of our approach for selective REE enrichment from REE containing mixtures.

  12. Effects of dissolved carbonate on arsenate adsorption and surface speciation at the hematite--water interface.

    PubMed

    Arai, Yuji; Sparks, D L; Davis, J A

    2004-02-01

    Effects of dissolved carbonate on arsenate [As(V)] reactivity and surface speciation at the hematite-water interface were studied as a function of pH and two different partial pressures of carbon dioxide gas [P(CO2) = 10(-3.5) atm and approximately 0; CO2-free argon (Ar)] using adsorption kinetics, pseudo-equilibrium adsorption/titration experiments, extended X-ray absorption fine structure spectroscopic (EXAFS) analyses, and surface complexation modeling. Different adsorbed carbonate concentrations, due to the two different atmospheric systems, resulted in an enhanced and/or suppressed extent of As(V) adsorption. As(V) adsorption kinetics [4 g L(-1), [As(V)]0 = 1.5 mM and I = 0.01 M NaCl] showed carbonate-enhanced As(V) uptake in the air-equilibrated systems at pH 4 and 6 and at pH 8 after 3 h of reaction. Suppressed As(V) adsorption was observed in the air-equilibrated system in the early stages of the reaction at pH 8. In the pseudo-equilibrium adsorption experiments [1 g L(-1), [As(V)]0 = 0.5 mM and I = 0.01 M NaCI], in which each pH value was held constant by a pH-stat apparatus, effects of dissolved carbonate on As(V) uptake were almost negligible at equilibrium, but titrant (0.1 M HCl) consumption was greater in the air-equilibrated systems (P(CO2) = 10(-3.5) atm) than in the CO2-free argon system at pH 4-7.75. The EXAFS analyses indicated that As(V) tetrahedral molecules were coordinated on iron octahedral via bidentate mononuclear ( 2.8 A) and bidentate binuclear (approximately equal to 3.3 A) bonding at pH 4.5-8 and loading levels of 0.46-3.10 microM m(-2). Using the results of the pseudo-equilibrium adsorption data and the XAS analyses, the pH-dependent As(V) adsorption under the P(CO2) = 10(-3.5) atm and the CO2-free argon system was modeled using surface complexation modeling, and the results are consistent with the formation of nonprotonated bidentate surface species at the hematite surfaces. The results also suggest that the acid titrant consumption

  13. Effects of Dissolved Carbonate on Arsenate Adsorption and Surface Speciation at the Hematite-Water Interface

    USGS Publications Warehouse

    Arai, Y.; Sparks, D.L.; Davis, J.A.

    2004-01-01

    Effects of dissolved carbonate on arsenate [As(V)] reactivity and surface speciation at the hematite-water interface were studied as a function of pH and two different partial pressures of carbon dioxide gas [PCO2 = 10 -3.5 atm and ???0; CO2-free argon (Ar)] using adsorption kinetics, pseudo-equilibrium adsorption/titration experiments, extended X-ray absorption fine structure spectroscopic (EXAFS) analyses, and surface complexation modeling. Different adsorbed carbonate concentrations, due to the two different atmospheric systems, resulted in an enhanced and/or suppressed extent of As(V) adsorption. As(V) adsorption kinetics [4 g L -1, [As(V)]0 = 1.5 mM and / = 0.01 M NaCl] showed carbonate-enhanced As(V) uptake in the air-equilibrated systems at pH 4 and 6 and at pH 8 after 3 h of reaction. Suppressed As(V) adsorption was observed in the air-equilibrated system in the early stages of the reaction at pH 8. In the pseudo-equilibrium adsorption experiments [1 g L-1, [As(V)] 0 = 0.5 mM and / = 0.01 M NaCl], in which each pH value was held constant by a pH-stat apparatus, effects of dissolved carbonate on As(V) uptake were almost negligible at equilibrium, but titrant (0.1 M HCl) consumption was greater in the air-equilibrated systems (PCO2 = 10-3.5 atm)than in the CO2-free argon system at pH 4-7.75. The EXAFS analyses indicated that As(V) tetrahedral molecules were coordinated on iron octahedral via bidentate mononuclear (???2.8 A??) and bidentate binuclear (???3.3 A??) bonding at pH 4.5-8 and loading levels of 0.46-3.10 ??M m-2. Using the results of the pseudoequilibrium adsorption data and the XAS analyses, the pH-dependent As(V) adsorption under the PCO2 = 10-3.5 atm and the CO2-free argon system was modeled using surface complexation modeling, and the results are consistent with the formation of nonprotonated bidentate surface species at the hematite surfaces. The results also suggest that the acid titrant consumption was strongly affected by changes to

  14. Adsorption of Amorphous Silica Nanoparticles onto Hydroxyapatite Surfaces Differentially Alters Surfaces Properties and Adhesion of Human Osteoblast Cells.

    PubMed

    Kalia, Priya; Brooks, Roger A; Kinrade, Stephen D; Morgan, David J; Brown, Andrew P; Rushton, Neil; Jugdaohsingh, Ravin

    2016-01-01

    Silicon (Si) is suggested to be an important/essential nutrient for bone and connective tissue health. Silicon-substituted hydroxyapatite (Si-HA) has silicate ions incorporated into its lattice structure and was developed to improve attachment to bone and increase new bone formation. Here we investigated the direct adsorption of silicate species onto an HA coated surface as a cost effective method of incorporating silicon on to HA surfaces for improved implant osseointegration, and determined changes in surface characteristics and osteoblast cell adhesion. Plasma-sprayed HA-coated stainless steel discs were incubated in silica dispersions of different concentrations (0-42 mM Si), at neutral pH for 12 h. Adsorbed Si was confirmed by XPS analysis and quantified by ICP-OES analysis following release from the HA surface. Changes in surface characteristics were determined by AFM and measurement of surface wettability. Osteoblast cell adhesion was determined by vinculin plaque staining. Maximum Si adsorption to the HA coated disc occurred after incubation in the 6 mM silica dispersion and decreased progressively with higher silica concentrations, while no adsorption was observed with dispersions below 6 mM Si. Comparison of the Si dispersions that produced the highest and lowest Si adsorption to the HA surface, by TEM-based analysis, revealed an abundance of small amorphous nanosilica species (NSP) of ~1.5 nm in diameter in the 6 mM Si dispersion, with much fewer and larger NSP in the 42 mM Si dispersions. 29Si-NMR confirmed that the NSPs in the 6 mM silica dispersion were polymeric and similar in composition to the larger NSPs in the 42 mM Si dispersion, suggesting that the latter were aggregates of the former. Amorphous NSP adsorbed from the 6 mM dispersion on to a HA-coated disc surface increased the surface's water contact angle by 53°, whereas that adsorbed from the 42 mM dispersion decreased the contact angle by 18°, indicating increased and decreased

  15. Fabrication and oil adsorption of carbon nanotube/polyvinylpyrrolidone surface composite.

    PubMed

    Nan, Dou; Wei, Jinquan; Guo, Fengmei; Fan, Guozhong; Xu, Fu; Li, Luming; Zhu, Hongwei; Wang, Kunlin; Wu, Dehai

    2014-08-01

    It needs to assemble the industrial CNT powders into macroscopic porous surface composite to utilize the surface properties of CNTs, as well as to prevent them entering into environments. We demonstrate a method to fabricate the surface composites from CNTs and polyvinylpyrrolidone (PVP) by electrospinning, where CNTs distribute firmly and mainly on the surface PVP nanofibers. The CNTs/PVP surface composites have high pore volume of 10 cc/g and remarkable CNTs load of 98%. Thus the surface composites show high oil adsorption capacity of 0.9~1.1 g/cm3. It can absorb more oil than commercial sponges due to the surface composite swells after absorbing oil. It shows attractive potential application of the CNT/PVP surface composite in oil spill cleanup.

  16. Osmosis and Surface Area to Volume Ratio.

    ERIC Educational Resources Information Center

    Barrett, D. R. B.

    1984-01-01

    Describes an experiment designed to help students understand the concepts of osmosis and surface area to volume ratio (SA:VOL). The task for students is to compare water uptake in different sizes of potato cubes and relate differences to their SA:VOL ratios. (JN)

  17. Volumes and surface areas of pendular rings

    USGS Publications Warehouse

    Rose, W.

    1958-01-01

    A packing of spheres is taken as a suitable model of porous media. The packing may be regular and the sphere size may be uniform, but in general, both should be random. Approximations are developed to give the volumes and surface areas of pendular rings that exist at points of sphere contact. From these, the total free volume and interfacial specific surface area are derived as expressive of the textural character of the packing. It was found that the log-log plot of volumes and surface areas of pendular rings vary linearly with the angle made by the line joining the sphere centers and the line from the center of the largest sphere to the closest edge of the pendular ring. The relationship, moreover, was found not to be very sensitive to variation in the size ratio of the spheres in contact. It also was found that the addition of pendular ring material to various sphere packings results in an unexpected decrease in the surface area of the boundaries that confine the resulting pore space. ?? 1958 The American Institute of Physics.

  18. Hydrophilic crosslinked-polymeric surface capable of effective suppression of protein adsorption

    NASA Astrophysics Data System (ADS)

    Kamon, Yuri; Inoue, Naoko; Mihara, Erika; Kitayama, Yukiya; Ooya, Tooru; Takeuchi, Toshifumi

    2016-08-01

    We investigated the nonspecific adsorption of proteins towards three hydrophilic crosslinked-polymeric thin layers prepared by surface-initiated atom transfer radical polymerization using N,N‧-methylenebisacrylamide, 2-(methacryloyloxy)ethyl-[N-(2-methacryloyloxy)ethyl]phosphorylcholine (MMPC), or 6,6‧-diacryloyl-trehalose crosslinkers. Protein binding experiments were performed by surface plasmon resonance with six proteins of different pI values including α-lactalbumin, bovine serum albumin (BSA), myoglobin, ribonuclease A, cytochrome C, and lysozyme in buffer solution at pH 7.4. All of the obtained crosslinked-polymeric thin layers showed low nonspecific adsorption of negatively charged proteins at pH 7.4 such as α-lactalbumin, BSA, and myoglobin. Nonspecific adsorption of positively charged proteins including ribonuclease A, cytochrome C, and lysozyme was the lowest for poly(MMPC). These results suggest poly(MMPC) can effectively reduce nonspecific adsorption of a wide range of proteins that are negatively or positively charged at pH 7.4. MMPC is a promising crosslinker for a wide range of polymeric materials requiring low nonspecific protein binding.

  19. Effect of complexing ligands on the adsorption of Cu(II) onto the silica gel surface. 1: Adsorption of ligands

    SciTech Connect

    Park, Y.J.; Jung, K.H.; Park, K.K.; Park, K.K.

    1995-04-01

    The adsorption of several ligands on silica gel was investigated in aqueous solutions. The ligands used were 2,2{prime},6{prime},2{double_prime}-terpyridine, pyridine, 3,4-lutidine, 2-aminomethyl pyridine, 2-pyridine methanol, picolinic acid, salicylic acid, and 5-sulfosalicylic acid. The adsorption behaviors of these ligands were interpreted by means of three adsorption modes: ion exchange, hydrogen bonding, and hydrophobic interaction. For 2,2{prime},6{prime},2{double_prime}-terpyridine, pyridine, and 3,4-lutidine, the adsorption maxima appeared near their respective pK{sub a} values and were found to be due mainly to ion exchange, whereas the adsorption of these ligands at low pH was strongly attributed to hydrophobic interaction. The adsorption of 2-aminomethyl pyridine increased with increasing pH over the entire pH range investigated and was due mainly to ion exchange. Picolinic acid was adsorbed mainly by hydrogen bonding either via pyridine N atoms at low pH or via carboxylic O atoms at high pH. 2-Pyridine methanol was adsorbed by hydrophobic interaction at low pH and by hydrogen bonding at high pH. The adsorptions of salicylic and 5-sulfosalicylic acid were very small over the entire pH ranges investigated. For the adsorption mechanism, the Stern model was used to fit adsorption data.

  20. Conformational mechanics, adsorption, and normal force interactions of lubricin and hyaluronic acid on model surfaces.

    PubMed

    Chang, Debby P; Abu-Lail, Nehal I; Guilak, Farshid; Jay, Gregory D; Zauscher, Stefan

    2008-02-19

    Glycoproteins, such as lubricin, and hyaluronic acid (HA) play a prominent role in the boundary lubrication mechanism in diarthrodial joints. Although many studies have tried to elucidate the lubrication mechanisms of articular cartilage, the molecular details of how lubricin and HA interact with cartilage surfaces and mediate their interaction still remain poorly understood. Here we used model substrates, functionalized with self-assembled monolayers terminating in hydroxyl or methyl groups, (1) to determine the effect of surface chemistry on lubricin and HA adsorption using surface plasmon resonance (SPR) and (2) to study normal force interactions between these surfaces as a function of lubricin and HA concentration using colloidal probe microscopy. We found that lubricin is amphiphilic and adsorbed strongly onto both methyl- and hydroxyl-terminated surfaces. On hydrophobic surfaces, lubricin likely adopts a compact, looplike conformation in which its hydrophobic domains at the N and C termini serve as surface anchors. On hydrophilic surfaces, lubricin likely adsorbs anywhere along its hydrophilic central domain and adopts, with increasing solution concentration, an extended tail-like conformation. Overall, lubricin develops strong repulsive interactions when compressing two surfaces into contact. Furthermore, upon surface separation, adhesion occurs between the surfaces as a result of molecular bridging and chain disentanglement. This behavior is in contrast to that of HA, which does not adsorb appreciably on either of the model surfaces and does not develop significant repulsive interactions. Adhesive forces, particularly between the hydrophobic surfaces, are large and not appreciably affected by HA. For a mixture of lubricin and HA, we observed slightly larger adsorptions and repulsions than those found for lubricin alone. Our experiments suggest that this interaction depends on unspecific physical rather than chemical interactions between lubricin and HA. We

  1. Adsorption of Amorphous Silica Nanoparticles onto Hydroxyapatite Surfaces Differentially Alters Surfaces Properties and Adhesion of Human Osteoblast Cells

    PubMed Central

    Kalia, Priya; Brooks, Roger A.; Kinrade, Stephen D.; Morgan, David J.; Brown, Andrew P.; Rushton, Neil; Jugdaohsingh, Ravin

    2016-01-01

    Silicon (Si) is suggested to be an important/essential nutrient for bone and connective tissue health. Silicon-substituted hydroxyapatite (Si-HA) has silicate ions incorporated into its lattice structure and was developed to improve attachment to bone and increase new bone formation. Here we investigated the direct adsorption of silicate species onto an HA coated surface as a cost effective method of incorporating silicon on to HA surfaces for improved implant osseointegration, and determined changes in surface characteristics and osteoblast cell adhesion. Plasma-sprayed HA-coated stainless steel discs were incubated in silica dispersions of different concentrations (0–42 mM Si), at neutral pH for 12 h. Adsorbed Si was confirmed by XPS analysis and quantified by ICP-OES analysis following release from the HA surface. Changes in surface characteristics were determined by AFM and measurement of surface wettability. Osteoblast cell adhesion was determined by vinculin plaque staining. Maximum Si adsorption to the HA coated disc occurred after incubation in the 6 mM silica dispersion and decreased progressively with higher silica concentrations, while no adsorption was observed with dispersions below 6 mM Si. Comparison of the Si dispersions that produced the highest and lowest Si adsorption to the HA surface, by TEM-based analysis, revealed an abundance of small amorphous nanosilica species (NSP) of ~1.5 nm in diameter in the 6 mM Si dispersion, with much fewer and larger NSP in the 42 mM Si dispersions. 29Si-NMR confirmed that the NSPs in the 6 mM silica dispersion were polymeric and similar in composition to the larger NSPs in the 42 mM Si dispersion, suggesting that the latter were aggregates of the former. Amorphous NSP adsorbed from the 6 mM dispersion on to a HA-coated disc surface increased the surface’s water contact angle by 53°, whereas that adsorbed from the 42 mM dispersion decreased the contact angle by 18°, indicating increased and decreased

  2. Effective decolorization and adsorption of contaminant from industrial dye effluents using spherical surfaced magnetic (Fe3O4) nanoparticles

    NASA Astrophysics Data System (ADS)

    Suriyaprabha, R.; Khan, Samreen Heena; Pathak, Bhawana; Fulekar, M. H.

    2016-04-01

    Treatment of highly concentrated Industrial dye stuff effluents released in the environment is the major issue faced in the era of waste management as well as in water pollution. Though there is availability of conventional techniques in large numbers, there is a need of efficient and effective advance technologies. In account of that, Nanotechnology plays a prominent role to treat the heavy metals, organic and inorganic contaminants using smart materials in nano regime (1 -100 nm). Among these nanomaterials like Iron Oxide (Fe3O4, magnetic nanoparticle) is one of the most promising candidates to remove the heavy metals from the industrial effluent. Fe3O4 is the widely used smart material with magnetic property having high surface area; high surface to volume ratio provides more surface for the chemical reaction for the surface adsorption. Fe3O4 nanoparticles have been synthesized using sonochemical method using ultra frequency in aqueous solution under optimized conditions. The as-synthesized nanoparticle was analyzed using different characterization tool. The Transmission Electron microscope (TEM) images revealed 10-12 nm spherical shape nanoparticles; crystal phase and surface morphology was confirmed by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM), respectively. The functional group were identified by Fourier Transform-Infra Red Spectroscopy (FT-IR), revealed the bending and stretching vibrations associated with Iron Oxide nanoparticle. In present study, for the efficient removal of contaminants, different concentration (10-50 ppm) of dye stuff effluent has been prepared and subjected to adsorption and decolourization at definite time intervals with Fe3O4 nanoparticles. The concentration of Iron oxide and the time (45 mins) was kept fixed for the reaction whereas the concentration of dye stuff effluent was kept varying. It was found that the spherical shaped Fe3O4 proved to be the potential material for the adsorption of corresponding

  3. Effect of low-concentration rhamnolipid on adsorption of Pseudomonas aeruginosa ATCC 9027 on hydrophilic and hydrophobic surfaces.

    PubMed

    Zhong, Hua; Jiang, Yongbing; Zeng, Guangming; Liu, Zhifeng; Liu, Liuxia; Liu, Yang; Yang, Xin; Lai, Mingyong; He, Yibin

    2015-03-21

    The effects of low-concentration monorhamnolipid (monoRL) on the adsorption of Pseudomonas aeruginosa ATCC 9027 grown on glucose or hexadecane to glass beads with hydrophobic or hydrophilic surfaces was investigated using batch adsorption experiments. Results showed that adsorption isotherms of the cells on both types of glass beads fitted the Freundlich equation better than the Langmuir equation. The Kf of the Freundlich equation for adsorption of hexadecane-grown cell to glass beads with hydrophobic surface was remarkably higher than that for adsorption of hexadecane-grown cell to glass beads with hydrophilic surface, or glucose-grown cell to glass beads with either hydrophilic or hydrophobic surface. Furthermore, it decreased with the increasing monoRL concentration. For both groups of cells, the zeta potential was close to each other and stable with the increase of monoRL concentration. The surface hydrophobicity of hexadecane-grown cells, however, was significantly higher than that of the glucose-grown cells and it decreased with the increase of monoRL concentration. The results indicate the importance of hydrophobic interaction on adsorption of bacterial cells to surfaces and monoRL plays a role in reducing the bacterial adsorption by affecting cell surface hydrophobicity.

  4. Modified Surface Coatings and their Effect on Drug Adsorption within the Extracorporeal Life Support Circuit

    PubMed Central

    Preston, Thomas J.; Ratliff, Todd M.; Gomez, Daniel; Olshove, Vincent F.; Nicol, Kathleen K.; Sargel, Cheryl L.; Chicoine, Louis G.

    2010-01-01

    Abstract: A recently completed study quantified the percent of fentanyl or morphine sulfate lost to uncoated polyvinylchloride (PVC) tubing or to one of two hollow fiber oxygenators within the extracorporeal life support (ECLS) circuit. The results demonstrated the majority of drug loss was due to adsorption by the PVC tubing. The purpose of this study was to determine if a tubing coating process affects fentanyl or morphine Sulfate adsorption. The goal was to quantify fentanyl or morphine sulfate lost due to adhesion within surface modified tubing. The following surface modifications were studied: 1) Maquet Safeline® (synthetic immobilized albumin); 2) Maquet Softline® (a heparin free biopassive polymer); 3) Maquet Bioline® (recombinant human albumin + heparin) (Maquet Cardiopulmonary AG, Hirrlingen, Germany); 4) Terumo X Coating™ (poly2methoxylacrylate)) (Terumo Cardiovascular Systems Corporation, Ann Arbor, MI); 5) Medtronic Carmeda® (covalently bonded heparin); and 6) Medtronic Trillium® (covalently bonded heparin) (Medtronic, Minneapolis, MN). A total of 36 individual circuits were built from the above six available modified surface coatings, for a total of six individual circuits of each coating type. Blood samples were drawn at 5 minutes, 120 minutes, and 360 minutes followed by High-Performance Liquid Chromatography to determine available circulating levels of either fentanyl or morphine sulfate. Fentanyl concentrations decreased to an average final available concentration of 35% (±5%) within the 18 circuits. Morphine sulfate however, decreased to a final available concentration of 57% (±1%) in all Maquet tubing and the Medtronic Trillium tubing, while it decreased to a final concentration of 35% (±1%) in the Medtronic Carmeda coated tubing and in the Terumo X Coating tubing. Biocompatible ECLS circuit surface coatings affected drug-adsorption and availability. Further evaluation is necessary to understand the adsorptive loss of other drugs

  5. Probing the adsorption mechanism in thiamazole bound to the silver surface with Surface-enhanced Raman Scattering and DFT

    NASA Astrophysics Data System (ADS)

    Biswas, Nandita; Thomas, Susy; Sarkar, Anjana; Mukherjee, Tulsi; Kapoor, Sudhir

    2009-09-01

    Surface-enhanced Raman scattering (SERS) of thiamazole have been investigated in aqueous solution. Thiamazole is an important anti-thyroid drug that is used in the treatment of hyperthyroidism (over activity of the thyroid gland). Due to its medicinal importance, the surface adsorption properties of thiamazole have been studied. The experimental Raman and SERS data are supported with DFT calculations using B3LYP functional with LANL2DZ basis set. From the SERS spectra as well as theoretical calculations, it has been inferred that thiamazole is chemisorbed to the silver surface directly through the sulphur atom and the ring N atom, with a tilted orientation.

  6. Particle Size Controls on Water Adsorption and Condensation Regimes at Mineral Surfaces.

    PubMed

    Yeşilbaş, Merve; Boily, Jean-François

    2016-01-01

    Atmospheric water vapour interacting with hydrophilic mineral surfaces can produce water films of various thicknesses and structures. In this work we show that mineral particle size controls water loadings achieved by water vapour deposition on 21 contrasting mineral samples exposed to atmospheres of up to ~16 Torr water (70% relative humidity at 25 °C). Submicrometer-sized particles hosted up to ~5 monolayers of water, while micrometer-sized particles up to several thousand monolayers. All films exhibited vibrational spectroscopic signals akin to liquid water, yet with a disrupted network of hydrogen bonds. Water adsorption isotherms were predicted using models (1- or 2- term Freundlich and Do-Do models) describing an adsorption and a condensation regime, respectively pertaining to the binding of water onto mineral surfaces and water film growth by water-water interactions. The Hygroscopic Growth Theory could also account for the particle size dependence on condensable water loadings under the premise that larger particles have a greater propensity of exhibiting of surface regions and interparticle spacings facilitating water condensation reactions. Our work should impact our ability to predict water film formation at mineral surfaces of contrasting particle sizes, and should thus contribute to our understanding of water adsorption and condensation reactions occuring in nature. PMID:27561325

  7. Particle Size Controls on Water Adsorption and Condensation Regimes at Mineral Surfaces

    PubMed Central

    Yeşilbaş, Merve; Boily, Jean-François

    2016-01-01

    Atmospheric water vapour interacting with hydrophilic mineral surfaces can produce water films of various thicknesses and structures. In this work we show that mineral particle size controls water loadings achieved by water vapour deposition on 21 contrasting mineral samples exposed to atmospheres of up to ~16 Torr water (70% relative humidity at 25 °C). Submicrometer-sized particles hosted up to ~5 monolayers of water, while micrometer-sized particles up to several thousand monolayers. All films exhibited vibrational spectroscopic signals akin to liquid water, yet with a disrupted network of hydrogen bonds. Water adsorption isotherms were predicted using models (1- or 2- term Freundlich and Do-Do models) describing an adsorption and a condensation regime, respectively pertaining to the binding of water onto mineral surfaces and water film growth by water-water interactions. The Hygroscopic Growth Theory could also account for the particle size dependence on condensable water loadings under the premise that larger particles have a greater propensity of exhibiting of surface regions and interparticle spacings facilitating water condensation reactions. Our work should impact our ability to predict water film formation at mineral surfaces of contrasting particle sizes, and should thus contribute to our understanding of water adsorption and condensation reactions occuring in nature. PMID:27561325

  8. Molecular dynamics simulations of uranyl adsorption and structure on the basal surface of muscovite

    DOE PAGES

    Teich-McGoldrick, Stephanie L.; Greathouse, Jeffery A.; Cygan, Randall T.

    2014-02-05

    Anthropogenic activities have led to an increased concentration of uranium on the Earth’s surface and potentially in the subsurface with the development of nuclear waste repositories. Uranium is soluble in groundwater, and its mobility is strongly affected by the presence of clay minerals in soils and in subsurface sediments. We use molecular dynamics simulations to probe the adsorption of aqueous uranyl (UO22+) ions onto the basal surface of muscovite, a suitable proxy for typically ultrafine-grained clay phases. Model systems include the competitive adsorption between potassium counterions and aqueous ions (0.1 M and 1.0 M UO2Cl2 , 0.1 M NaCl). Wemore » find that for systems with potassium and uranyl ions present, potassium ions dominate the adsorption phenomenon. Potassium ions adsorb entirely as inner-sphere complexes associated with the ditrigonal cavity of the basal surface. Uranyl ions adsorb in two configurations when it is the only ion species present, and in a single configuration in the presence of potassium. Finally, the majority of adsorbed uranyl ions are tilted less than 45° relative to the muscovite surface, and are associated with the Si4Al2 rings near aluminum substitution sites.« less

  9. Dissolved organic matter adsorption to model surfaces: adlayer formation, properties, and dynamics at the nanoscale.

    PubMed

    Armanious, Antonius; Aeppli, Meret; Sander, Michael

    2014-08-19

    Adlayers of dissolved organic matter (DOM) form on many surfaces in natural and engineered systems and affect a number of important processes in these systems. Yet, the nanoscalar properties and dynamics of DOM adlayers remain poorly investigated. This work provides a systematic analysis of the properties and dynamics of adlayers formed from a diverse set of eight humic and fulvic acids, used as DOM models, on surfaces of self-assembled monolayers (SAMs) of different alkylthiols covalently bound to gold supports. DOM adsorption to positively charged amine-terminated SAMs resulted in the formation of water-rich adlayers with nanometer thicknesses that were relatively rigid, irreversibly adsorbed, and collapsed upon air drying, as demonstrated by combined quartz crystal microbalance and ellipsometry measurements. DOM adlayer thicknesses varied only slightly with solution pH from 5 to 8 but increased markedly with increasing ionic strength. Contact angle measurements revealed that the DOM adlayers were relatively polar, likely due to the high water contents of the adlayers. Comparing DOM adsorption to SAM-coated sensors that systematically differed in surface charge and polarity characteristics showed that electrostatics dominated DOM-surface interactions. Laccase adsorption to DOM adlayers on amine-terminated SAMs served to demonstrate the applicability of the presented experimental approach to study the interactions of (bio)macromolecules and (nano)particles with DOM.

  10. Molecular dynamics simulations of uranyl adsorption and structure on the basal surface of muscovite

    SciTech Connect

    Teich-McGoldrick, Stephanie L.; Greathouse, Jeffery A.; Cygan, Randall T.

    2014-02-05

    Anthropogenic activities have led to an increased concentration of uranium on the Earth’s surface and potentially in the subsurface with the development of nuclear waste repositories. Uranium is soluble in groundwater, and its mobility is strongly affected by the presence of clay minerals in soils and in subsurface sediments. We use molecular dynamics simulations to probe the adsorption of aqueous uranyl (UO22+) ions onto the basal surface of muscovite, a suitable proxy for typically ultrafine-grained clay phases. Model systems include the competitive adsorption between potassium counterions and aqueous ions (0.1 M and 1.0 M UO2Cl2 , 0.1 M NaCl). We find that for systems with potassium and uranyl ions present, potassium ions dominate the adsorption phenomenon. Potassium ions adsorb entirely as inner-sphere complexes associated with the ditrigonal cavity of the basal surface. Uranyl ions adsorb in two configurations when it is the only ion species present, and in a single configuration in the presence of potassium. Finally, the majority of adsorbed uranyl ions are tilted less than 45° relative to the muscovite surface, and are associated with the Si4Al2 rings near aluminum substitution sites.

  11. Adsorption and characterization of MCPA on DDTMA- and raw-montmorillonite: Surface sites involved.

    PubMed

    Santiago, Cintia C; Fernández, Mariela A; Torres Sánchez, Rosa M

    2016-01-01

    The 4-chloro-2-methylphenoxy acid (MCPA) is an herbicide widely used in agriculture, which generates a great concern about contamination of surface water and serious consequences for human health and the environment. In this work, the adsorption of MCPA on an Argentine montmorillonite (MMT) and its organo-montmorillonite product (OMMT) with different dodecyl trimethyl ammonium loading was investigated. MCPA adsorption on OMMT increases at least 3 times, with respect to the amount determined for MMT. X-ray diffraction and zeta potential analyses indicated the inner (interlayer) and outer surface participate as adsorption sites. Changes in surface electric charge and also interlayer expansion suggest that dimethyl amine (MCPA counterion) was also surface-adsorbed. The larger aggregates of OMMT, without and with MCPA, obtained compared to those of MMT samples, generate an improvement in the coagulation efficiency. This property, particularly after MCPA retention, allows an easier separation of the solids from the solution and enables a simple technological process application. PMID:26786275

  12. Particle Size Controls on Water Adsorption and Condensation Regimes at Mineral Surfaces

    NASA Astrophysics Data System (ADS)

    Yeşilbaş, Merve; Boily, Jean-François

    2016-08-01

    Atmospheric water vapour interacting with hydrophilic mineral surfaces can produce water films of various thicknesses and structures. In this work we show that mineral particle size controls water loadings achieved by water vapour deposition on 21 contrasting mineral samples exposed to atmospheres of up to ~16 Torr water (70% relative humidity at 25 °C). Submicrometer-sized particles hosted up to ~5 monolayers of water, while micrometer-sized particles up to several thousand monolayers. All films exhibited vibrational spectroscopic signals akin to liquid water, yet with a disrupted network of hydrogen bonds. Water adsorption isotherms were predicted using models (1- or 2- term Freundlich and Do-Do models) describing an adsorption and a condensation regime, respectively pertaining to the binding of water onto mineral surfaces and water film growth by water-water interactions. The Hygroscopic Growth Theory could also account for the particle size dependence on condensable water loadings under the premise that larger particles have a greater propensity of exhibiting of surface regions and interparticle spacings facilitating water condensation reactions. Our work should impact our ability to predict water film formation at mineral surfaces of contrasting particle sizes, and should thus contribute to our understanding of water adsorption and condensation reactions occuring in nature.

  13. Sensitive detection and prevention of protein adsorption on biomaterial (lipid bilayer) surfaces

    NASA Astrophysics Data System (ADS)

    Xu, Zhong

    2000-10-01

    The adsorption of proteins on biomaterial surfaces is recognized as the first and the most important event that determines or directs consequent host responses. The amount, composition, conformation, and binding affinity of the adsorbed proteins are critical in determining events leading to blood coagulation, platelet adhesion and activation, mammalian and bacterial cell adhesion, and complement activation. This thesis is concerned with the non-specific adsorption of plasma proteins on self-assembled phospholipid surfaces. To examine molecular events in detail, adsorption of plasma proteins on lipid bilayers was studied on both supported planar bilayer and liposomes (phospholipid vesicles) systems. Monolayers of mixed distearoylphosphatidlcholine (DSPC) and PEO (MW. 2000)-grafted distearoylphosphatidylethanolanane (PEO2k-DSPE) were deposited on DSPE-coated quartz substrates by Langmuir-Blodgett (LB) deposition technique. A sensitive total internal reflection fluorescence (TIRF) method, capable of detecting the adsorption of <0.3 ng/cm2 of fluorescein-labeled fibrinogen at a temporal resolution of 0.2 sec, was utilized to study adsorption kinetics of plasma proteins on the supported lipid bilayers. All supported lipid bilayers exhibited over a magnitude reduction in adsorbed plasma proteins compared with the quartz substrate. The increase of PEO2k-DSPE density in the mixed bilayers slightly increased the amount of adsorbed proteins on the bilayers. Plasma proteins adsorbed on liposomes (composed of DSPC and cholesterol) were studied using a spin column procedure for liposome isolation, and SDS-polyacrylamide gel electrophoresis and immunoanalysis for protein separation, quantification and identification. Plasma proteins isolated from liposome surfaces showed distinct and complex profiles. Albumin and fibrinogen were identified as two major plasma proteins that undergo non-specific adsorption on liposomes. Incorporating (PEO2k-DSPE) into liposomes reduced the amount

  14. XPS study of nitrogen dioxide adsorption on metal oxide particle surfaces under different environmental conditions.

    PubMed

    Baltrusaitis, Jonas; Jayaweera, Pradeep M; Grassian, Vicki H

    2009-10-01

    The adsorption of nitrogen dioxide on gamma aluminium oxide (gamma-Al(2)O(3)) and alpha iron oxide (alpha-Fe(2)O(3)) particle surfaces under various conditions of relative humidity, presence of molecular oxygen and UV light has been investigated. X-Ray photoelectron spectroscopy (XPS) is used to monitor the different surface species that form under these environmental conditions. Adsorption of NO(2) on aluminum oxide particle surfaces results primarily in the formation of surface nitrate, NO(3)(-) with an oxidation state of +5, as indicated by a peak with binding energy of 407.3 eV in the N1s region. An additional minority species, sensitive to the presence of relative humidity and molecular oxygen, is also observed in the N1s region with lower binding energy of 405.9 eV. This peak is assigned to a surface species in the +4 oxidation state. When irradiated with UV light, other species form on the surface. These surface-bound photochemical products all have lower binding energy, between 400 and 402 eV, indicating reduced nitrogen species in the range of N oxidations states spanning +1 to -1. Co-adsorbed water decreases the amount of these reduced surface-bound products while the presence of molecular oxygen completely suppresses the formation of all reduced nitrogen species on aluminum oxide particle surfaces. For NO(2) on iron oxide particle surfaces, photoreduction is enhanced relative to gamma-Al(2)O(3) and surface bound photoreduced species are observed under all environmental conditions. Complementing the experimental data, N1s core electron binding energies (CEBEs) were calculated using DFT for a number of nitrogen-containing species in the gas phase and adsorbed on an Al(8)O(12) cluster. A range of CEBEs is calculated for various nitrogen species in different adsorption modes and oxidation states. These calculated values are discussed in light of the peaks observed in the XPS N1s region and the possible species that form following NO(2) adsorption and

  15. Fluoride Adsorption on Goethite in Relation to Different Types of Surface Sites.

    PubMed

    Hiemstra; Van Riemsdijk WH

    2000-05-01

    Metal (hydr)oxides have different types of surface groups. Fluoride ions have been used as a probe to assess the number of surface sites. We have studied the F(-) adsorption on goethite by measuring the F(-) and H(+) interaction and F(-) adsorption isotherms. Fluoride ions exchange against singly coordinated surface hydroxyls at low F(-) concentrations. At higher concentrations also the doubly coordinated OH groups are involved. The replacement of a surface OH(-) by F(-) suggests that all F charge (-1) is located at the surface in contrast to oxyanions which have a charge distribution in the interface due to the binding structure in which the anion only partially coordinates with the surface. Analysis of our F(-) data with the CD-MUSIC approach shows that the formation of the fluoride surface complex is accompanied by a redistribution of charge. This is supposed to be due to a net switch in the H bonding as a result of the change of the type of surface complex from donating (FeOH, FeOH(2)) to proton accepting (FeF). The modeled redistribution of charge is approximately equivalent with the change of a donating H bond into an accepting H bond. At high F(-) concentrations precipitation of F(-), as for instance FeF(3)(s), may occur. The rate of formation is catalyzed by the presence of high electrolyte concentrations. Copyright 2000 Academic Press. PMID:10767149

  16. Adsorption of methylamine on mackinawite (FES) surfaces: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Dzade, N. Y.; Roldan, A.; de Leeuw, N. H.

    2013-09-01

    We have used density functional theory calculations to investigate the interaction between methylamine (CH3NH2) and the dominant surfaces of mackinawite (FeS), where the surface and adsorption properties of mackinawite have been characterized using the DFT-D2 method of Grimme. Our calculations show that while the CH3NH2 molecule only interacts weakly with the most stable FeS(001), it adsorbs relatively strongly on the FeS(011) and FeS(100) surfaces releasing energies of 1.26 eV and 1.51 eV, respectively. Analysis of the nature of the bonding reveals that the CH3NH2 molecule interacts with the mackinawite surfaces through the lone-pair of electrons located on the N atom. The electron density built up in the bonding region between N and Fe is very much what one would expect of covalent type of bonding. We observe no significant adsorption-induced changes of the FeS surface structures, suggesting that amine capping agents would not distort the FeS nanoparticle surfaces required for active heterogeneous catalytic reactions. The vibrational frequencies and the infrared spectra of adsorbed methylamine have been calculated and assignments for vibrational modes are used to propose a kinetic model for the desorption process, yielding a simulated temperature programmed desorption with a relative desorption temperature of <140 K at the FeS(011) surface and <170 K at FeS(100) surface.

  17. Adsorption of methylamine on mackinawite (FES) surfaces: a density functional theory study.

    PubMed

    Dzade, N Y; Roldan, A; de Leeuw, N H

    2013-09-28

    We have used density functional theory calculations to investigate the interaction between methylamine (CH3NH2) and the dominant surfaces of mackinawite (FeS), where the surface and adsorption properties of mackinawite have been characterized using the DFT-D2 method of Grimme. Our calculations show that while the CH3NH2 molecule only interacts weakly with the most stable FeS(001), it adsorbs relatively strongly on the FeS(011) and FeS(100) surfaces releasing energies of 1.26 eV and 1.51 eV, respectively. Analysis of the nature of the bonding reveals that the CH3NH2 molecule interacts with the mackinawite surfaces through the lone-pair of electrons located on the N atom. The electron density built up in the bonding region between N and Fe is very much what one would expect of covalent type of bonding. We observe no significant adsorption-induced changes of the FeS surface structures, suggesting that amine capping agents would not distort the FeS nanoparticle surfaces required for active heterogeneous catalytic reactions. The vibrational frequencies and the infrared spectra of adsorbed methylamine have been calculated and assignments for vibrational modes are used to propose a kinetic model for the desorption process, yielding a simulated temperature programmed desorption with a relative desorption temperature of <140 K at the FeS(011) surface and <170 K at FeS(100) surface.

  18. Effect of complexing ligands on the adsorption of Cu(II) onto the silica gel surface. 2: Adsorption of Cu(II)-ligand complexes

    SciTech Connect

    Park, Y.J.; Jung, K.H.; Park, K.K.

    1995-06-15

    The effect of complexing ligands on the adsorption of Cu(II) onto silica gel was investigated in aqueous solution. The adsorption was conspicuously enhanced by 2,2{prime},6{prime},2{double_prime}-terpyridine, 2-pyridine methanol and 2-aminomethyl pyridine, as compared to non-complexed Cu{sup 2+} ions. This enhancement was attributed to both hydrophobic interaction in the low pH region and the formation of ternary surface complexes in the high pH region. It was attenuated by picolinic acid, salicylic acid, and 5-sulfosalicylic acid due to the competition of dissolved ligands and silanol groups with Cu{sup 2+} ions. In the presence of pyridine or 3,4-lutidine, the adsorption was slightly increased, as compared to non-complexed Cu{sup 2+} ions. In both cases, the adsorption at low pH was interpreted in terms of the type B ternary surface complex formation. For 2-pyridine methanol, the formation of cyclic ternary surface complexes was proposed. The Stern model was adopted for the treatment of the adsorption data in the present study.

  19. Role of surface chemistry and morphology in the reactive adsorption of H₂S on iron (hydr)oxide/graphite oxide composites.

    PubMed

    Arcibar-Orozco, Javier A; Wallace, Rajiv; Mitchell, Joshua K; Bandosz, Teresa J

    2015-03-10

    Composites of magnetite and two-line ferrihydrite with graphite oxide (GO) were synthesized and tested as hydrogen sulfide adsorbents. Exhausted and initial composites were characterized by the adsorption of nitrogen, X-ray diffraction, potentiometric titration, thermal analysis, and FTIR. The addition of GO increased the surface area of the composites due to the formation of new micropores. The extent of the increase depended on the nature of the iron (hydr)oxide and the content of GO. The addition of GO did not considerably change the crystal structure but increased the number of acidic functional groups. While for the magnetite composites an increase in the H2S adsorption capacity after GO addition was found, the opposite effect was recorded for the ferrihydrite composites. That increase in the adsorption capacity was linked to the affinity of the composites to adsorb water in mesopores of specific sizes in which the reaction with basic surface groups takes place. Elemental sulfur and ferric and ferrous sulfates were detected on the surface of the exhausted samples. A redox reactive adsorption mechanism is proposed to govern the retention of hydrogen sulfide on the surface of the composites. The incorporation of GO enhances the chemical retention of H2S due to the incorporation of OH reactive groups and an increase in surface heterogeneity.

  20. Surface forces and protein adsorption on dextran- and polyethylene glycol-modified polydimethylsiloxane.

    PubMed

    Farrell, Megan; Beaudoin, Stephen

    2010-12-01

    Dextran and polyethylene glycol (PEG) are often covalently bound to the surface of polydimethylsiloxane (PDMS) for the purpose of modifying its hydrophilicity and biocompatibility. In this work, the effects of the dextran and PEG on the morphology, wetting, and surface charge of the resulting surfaces were quantified and correlated with changes in the amount of fibrinogen and albumin adsorbed from aqueous solution. PDMS films were functionalized in a microwave oxygen plasma to create surface hydroxyl groups that were subsequently aminated by incubation in a (3-aminopropyl)trimethoxysilane (APTES) solution. Oxidized dextran and PEG-aldehyde were linked to the surface amines via reductive amination. This process resulted in low surface coverage of immobilized PEG in the end-on conformation and a more uniform and dense distribution of side-on immobilized dextran. The immobilized dextran reduced the contact angle of the PDMS film from 109° to 80° and neutralized the zeta potential over the pH range from 3 to 11. An atomic force microscope was used to measure the interaction force between the modified PDMS and a model hydrophobic surface (polystyrene latex) and a model hydrophilic surface (silica) in aqueous solution to show that van der Waals and hydrophobic attractive forces are the dominant forces for protein adsorption in this system. The PEG- and dextran-modified PDMS were exposed to BSA and fibrinogen to test their resistance to protein adsorption. The coatings were ineffective at reducing the adsorption of either molecule, and the dextran-modification of the PDMS caused more BSA to adsorb than in the case of the unmodified PDMS. PMID:20801620

  1. In situ photoelectron spectroscopy study of water adsorption on model biomaterial surfaces

    SciTech Connect

    Salmeron, Miquel; Ketteler, Guido; Ashby, Paul; Mun, B.S.; Ratera, I.; Bluhm, Hendrik; Kasemo, B.; Salmeron, Miquel

    2007-07-10

    Using in situ photoelectron spectroscopy at near ambient conditions, we compare the interaction of water with four different model biomaterial surfaces: self-assembled thiol monolayers on Au(111) that are functionalized with methyl, hydroxyl, and carboxyl groups, and phosphatidylcholine (POPC) lipid films on Silicon. We show that the interaction of water with biomaterial surfaces is mediated by polar functional groups that interact strongly with water molecules through hydrogen bonding, resulting in adsorption of 0.2-0.3 ML water on the polar thiol films in 700 mTorr water pressure and resulting in characteristic N1s and P2p shifts for the POPC films. Provided that beam damage is carefully controlled, in situ electron spectroscopy can give valuable information about water adsorption which is not accessible under ultra-high vacuum conditions.

  2. Hydrogen Adsorption, Dissociation and Diffusion on the α-U(001) Surface

    SciTech Connect

    Nie, JL; Xiao, H. Y.; Zu, Xiaotao T.; Gao, Fei

    2008-11-05

    First-principles pseudopotential plane wave calculations based on density functional theory and the generalized gradient approximation have been used to study the adsorption, dissociation, and diffusion of hydrogen on the α-U(001) surface. Weak molecular chemisorption was observed for H2 approaching with its molecular axis parallel to the surface. The optimization of the adsorption geometries on the threefold hollow sites yields final configurations with H2 molecules move towards the top site at both coverages of 0.25 and 0.5 monolayer. A low dissociation barrier of 0.081 eV was determined for H2 dissociated from onefold top site with the H atoms falling into the two adjacent threefold hollow sites. The density of states analysis along the dissociation paths show that the hybridization of U 5f and H 1s states only occurs when H2 molecule is dissociated.

  3. Zr(IV) loaded cross-linked chitosan beads with enhanced surface area for the removal of nitrate and phosphate.

    PubMed

    Sowmya, Appunni; Meenakshi, Sankaran

    2014-08-01

    In this work, a new method namely silica dissolution method, has been adapted to increase the surface area of the cross-linked chitosan beads. Zr(IV) was loaded in the cross-linked chitosan beads in order to make it selective for the nitrate and phosphate anions from aqueous solutions. Zr(IV) loaded cross-linked chitosan beads prepared by normal method (ZrCB) and silica dissolution method (SD-ZrCB) were characterised using N2 adsorption/desorption studies, SEM, EDAX, XRD, FTIR, TGA, DTA and water regain property. The SD-ZrCB exhibited higher N2 adsorption, water regain property as well as anion adsorption capacity than ZrCB. Batch method was adapted for the adsorption studies. The nitrate and phosphate adsorbed SD-ZrCB was regenerated using 0.025M NaCl solution. There was not much drop in adsorption capacities up to 10th regeneration cycle. Freundlich adsorption isotherm was the best fit adsorption isotherm among Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms which have been used to fit the nitrate and phosphate adsorption data. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated in order to understand the nature of adsorption process.

  4. New findings on the influence of carbon surface curvature on energetics of benzene adsorption from gaseous phase

    NASA Astrophysics Data System (ADS)

    Terzyk, Artur P.; Furmaniak, Sylwester; Wiśniewski, Marek; Werengowska, Karolina; Gauden, Piotr A.; Kowalczyk, Piotr

    2016-02-01

    In this Letter, new results of calorimetric study on benzene adsorption from the gaseous phase are presented. According to some of recently published reports, the energy of solid-fluid, interactions increases with the rise in carbon nanotube curvature during adsorption. The recent considerations [Chem. Phys. Lett. 619 (2015) 219] on thermodynamics of adsorption from aqueous solutions on a series of carbon nanotubes have confirmed this observation. Although comparable 'energy-tube diameter' relations for benzene adsorption from the solution and from the gaseous phase are observed, remarkable differences between the mechanisms of the both processes caused by surface heterogeneity are noticeable.

  5. Shear rheology of mixed protein adsorption layers vs their structure studied by surface force measurements.

    PubMed

    Danov, Krassimir D; Kralchevsky, Peter A; Radulova, Gergana M; Basheva, Elka S; Stoyanov, Simeon D; Pelan, Eddie G

    2015-08-01

    The hydrophobins are proteins that form the most rigid adsorption layers at liquid interfaces in comparison with all other investigated proteins. The mixing of hydrophobin HFBII with other conventional proteins is expected to reduce the surface shear elasticity and viscosity, E(sh) and η(sh), proportional to the fraction of the conventional protein. However, the experiments show that the effect of mixing can be rather different depending on the nature of the additive. If the additive is a globular protein, like β-lactoglobulin and ovalbumin, the surface rigidity is preserved, and even enhanced. The experiments with separate foam films indicate that this is due to the formation of a bilayer structure at the air/water interface. The more hydrophobic HFBII forms the upper layer adjacent to the air phase, whereas the conventional globular protein forms the lower layer that faces the water phase. Thus, the elastic network formed by the adsorbed hydrophobin remains intact, and even reinforced by the adjacent layer of globular protein. In contrast, the addition of the disordered protein β-casein leads to softening of the HFBII adsorption layer. Similar (an even stronger) effect is produced by the nonionic surfactant Tween 20. This can be explained with the penetration of the hydrophobic tails of β-casein and Tween 20 between the HFBII molecules at the interface, which breaks the integrity of the hydrophobin interfacial elastic network. The analyzed experimental data for the surface shear rheology of various protein adsorption layers comply with a viscoelastic thixotropic model, which allows one to determine E(sh) and η(sh) from the measured storage and loss moduli, G' and G″. The results could contribute for quantitative characterization and deeper understanding of the factors that control the surface rigidity of protein adsorption layers with potential application for the creation of stable foams and emulsions with fine bubbles or droplets.

  6. Effects of surface features on sulfur dioxide adsorption on calcined NiAl hydrotalcite-like compounds.

    PubMed

    Zhao, Ling; Li, Xinyong; Quan, Xie; Chen, Guohua

    2011-06-15

    The hydrotalcite-based NiAl mixed oxides were synthesized by coprecipitation and urea hydrolysis approaches and employed for SO₂ removal. The samples were well characterized by inductively coupled plasma (ICP) elemental analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and N₂ adsorption/desorption isotherm analyses. The acid-base properties were characterized by pyridine chemisorption and CO₂ temperature-programmed desorption (TPD). The calcined NiAlO from the urea method showed excellent SO₂ adsorption and its adsorption equilibrium showed a type I isotherm, which significantly improved the adsorption performance for low-concentration SO₂. Both the physical structure and the acidic-basic sites were found to play important roles in the SO₂ adsorption process. In situ Fourier transform infrared spectroscopy (FTIR) investigation revealed that adsorbed SO₂ molecules formed surface bisulfite, sulfite, and bidentate binuclear sulfate. The mechanisms for SO₂ adsorption and transformation are discussed in detail. PMID:21609013

  7. Ozone treatment of coal- and coffee grounds-based active carbons: Water vapor adsorption and surface fractal micropores

    SciTech Connect

    Tsunoda, Ryoichi; Ozawa, Takayoshi; Ando, Junichi

    1998-09-15

    Characteristics of the adsorption iostherms of water vapor on active carbons from coal and coffee grounds and those ozonized ones from the surface fractal dimension analysis are discussed. The upswing of the adsorption isotherms in the low relative pressure of coffee grounds-based active carbon, of which isotherms were not scarcely affected on ozonization, was attributed to the adsorption of water molecules on the metallic oxides playing the role of oxygen-surface complexes, which formed the corrugated surfaces on the basal planes of micropore walls with the surface fractal dimension D{sub s} > 2. On the other hand, coal-based active carbon with D{sub s} < 2, which indicated the flat surfaces of micropore walls, showed little effect on the upswing even on ozonization, even though the adsorption amounts of water vapor were increased in the low relative pressure.

  8. Random heteropolymer adsorption on disordered multifunctional surfaces: Effect of specific intersegment interactions

    SciTech Connect

    Srebnik, S.; Chakraborty, A.K.; Bratko, D.

    1998-10-01

    Biopolymers adsorb on cell and virus surfaces with great specificity. Recently, theoretical and computational studies have inquired as to whether there are any universal design strategies that nature employs in order to affect such recognition. Specifically, the efficacy of multifunctionality and quenched disorder as essential design strategies has been explored. It has been found that when random heteropolymers interact with disordered multifunctional surfaces, a sharp transition from weak to strong adsorption occurs when the statistics characterizing the sequence and surface site distributions are related in a special way. The aforementioned studies consider the intersegment interactions to be much weaker than the surface site interactions. In this work we use nondynamic ensemble growth Monte Carlo simulations to study the effect of the competition between frustrating intersegment and segment{endash}surface interactions. We find that as the intersegment interactions become stronger, the transition from weak to strong adsorption occurs at higher surface disorder strengths. This trend is reversed beyond a threshold strength of the intersegment interactions because interactions with the surface are no longer able to {open_quotes}unravel{close_quotes} the dominant conformations favored by the intersegment interactions. {copyright} {ital 1998 American Institute of Physics.}

  9. Random heteropolymer adsorption on disordered multifunctional surfaces: Effect of specific intersegment interactions

    NASA Astrophysics Data System (ADS)

    Srebnik, Simcha; Chakraborty, Arup K.; Bratko, Dusan

    1998-10-01

    Biopolymers adsorb on cell and virus surfaces with great specificity. Recently, theoretical and computational studies have inquired as to whether there are any universal design strategies that nature employs in order to affect such recognition. Specifically, the efficacy of multifunctionality and quenched disorder as essential design strategies has been explored. It has been found that when random heteropolymers interact with disordered multifunctional surfaces, a sharp transition from weak to strong adsorption occurs when the statistics characterizing the sequence and surface site distributions are related in a special way. The aforementioned studies consider the intersegment interactions to be much weaker than the surface site interactions. In this work we use nondynamic ensemble growth Monte Carlo simulations to study the effect of the competition between frustrating intersegment and segment-surface interactions. We find that as the intersegment interactions become stronger, the transition from weak to strong adsorption occurs at higher surface disorder strengths. This trend is reversed beyond a threshold strength of the intersegment interactions because interactions with the surface are no longer able to "unravel" the dominant conformations favored by the intersegment interactions.

  10. NMR characterization of hydrocarbon adsorption on calcite surfaces: a first principles study.

    PubMed

    Bevilaqua, Rochele C A; Rigo, Vagner A; Veríssimo-Alves, Marcos; Miranda, Caetano R

    2014-11-28

    The electronic and coordination environment of minerals surfaces, as calcite, are very difficult to characterize experimentally. This is mainly due to the fact that there are relatively few spectroscopic techniques able to detect Ca(2+). Since calcite is a major constituent of sedimentary rocks in oil reservoir, a more detailed characterization of the interaction between hydrocarbon molecules and mineral surfaces is highly desirable. Here we perform a first principles study on the adsorption of hydrocarbon molecules on calcite surface (CaCO3 (101¯4)). The simulations were based on Density Functional Theory with Solid State Nuclear Magnetic Resonance (SS-NMR) calculations. The Gauge-Including Projector Augmented Wave method was used to compute mainly SS-NMR parameters for (43)Ca, (13)C, and (17)O in calcite surface. It was possible to assign the peaks in the theoretical NMR spectra for all structures studied. Besides showing different chemical shifts for atoms located on different environments (bulk and surface) for calcite, the results also display changes on the chemical shift, mainly for Ca sites, when the hydrocarbon molecules are present. Even though the interaction of the benzene molecule with the calcite surface is weak, there is a clearly distinguishable displacement of the signal of the Ca sites over which the hydrocarbon molecule is located. A similar effect is also observed for hexane adsorption. Through NMR spectroscopy, we show that aromatic and alkane hydrocarbon molecules adsorbed on carbonate surfaces can be differentiated.

  11. NMR characterization of hydrocarbon adsorption on calcite surfaces: A first principles study

    SciTech Connect

    Bevilaqua, Rochele C. A.; Miranda, Caetano R.; Rigo, Vagner A.; Veríssimo-Alves, Marcos

    2014-11-28

    The electronic and coordination environment of minerals surfaces, as calcite, are very difficult to characterize experimentally. This is mainly due to the fact that there are relatively few spectroscopic techniques able to detect Ca{sup 2+}. Since calcite is a major constituent of sedimentary rocks in oil reservoir, a more detailed characterization of the interaction between hydrocarbon molecules and mineral surfaces is highly desirable. Here we perform a first principles study on the adsorption of hydrocarbon molecules on calcite surface (CaCO{sub 3} (101{sup ¯}4)). The simulations were based on Density Functional Theory with Solid State Nuclear Magnetic Resonance (SS-NMR) calculations. The Gauge-Including Projector Augmented Wave method was used to compute mainly SS-NMR parameters for {sup 43}Ca, {sup 13}C, and {sup 17}O in calcite surface. It was possible to assign the peaks in the theoretical NMR spectra for all structures studied. Besides showing different chemical shifts for atoms located on different environments (bulk and surface) for calcite, the results also display changes on the chemical shift, mainly for Ca sites, when the hydrocarbon molecules are present. Even though the interaction of the benzene molecule with the calcite surface is weak, there is a clearly distinguishable displacement of the signal of the Ca sites over which the hydrocarbon molecule is located. A similar effect is also observed for hexane adsorption. Through NMR spectroscopy, we show that aromatic and alkane hydrocarbon molecules adsorbed on carbonate surfaces can be differentiated.

  12. NMR characterization of hydrocarbon adsorption on calcite surfaces: a first principles study.

    PubMed

    Bevilaqua, Rochele C A; Rigo, Vagner A; Veríssimo-Alves, Marcos; Miranda, Caetano R

    2014-11-28

    The electronic and coordination environment of minerals surfaces, as calcite, are very difficult to characterize experimentally. This is mainly due to the fact that there are relatively few spectroscopic techniques able to detect Ca(2+). Since calcite is a major constituent of sedimentary rocks in oil reservoir, a more detailed characterization of the interaction between hydrocarbon molecules and mineral surfaces is highly desirable. Here we perform a first principles study on the adsorption of hydrocarbon molecules on calcite surface (CaCO3 (101¯4)). The simulations were based on Density Functional Theory with Solid State Nuclear Magnetic Resonance (SS-NMR) calculations. The Gauge-Including Projector Augmented Wave method was used to compute mainly SS-NMR parameters for (43)Ca, (13)C, and (17)O in calcite surface. It was possible to assign the peaks in the theoretical NMR spectra for all structures studied. Besides showing different chemical shifts for atoms located on different environments (bulk and surface) for calcite, the results also display changes on the chemical shift, mainly for Ca sites, when the hydrocarbon molecules are present. Even though the interaction of the benzene molecule with the calcite surface is weak, there is a clearly distinguishable displacement of the signal of the Ca sites over which the hydrocarbon molecule is located. A similar effect is also observed for hexane adsorption. Through NMR spectroscopy, we show that aromatic and alkane hydrocarbon molecules adsorbed on carbonate surfaces can be differentiated. PMID:25429955

  13. Identical Binding Energies and Work Functions for Distinct Adsorption Structures: Olympicenes on the Cu(111) Surface.

    PubMed

    Liu, Wei; Schuler, Bruno; Xu, Yong; Moll, Nikolaj; Meyer, Gerhard; Gross, Leo; Tkatchenko, Alexandre

    2016-03-17

    Reliability is one of the major concerns and challenges in designing organic/inorganic interfaces for (opto)electronic applications. Even small structural differences for molecules on substrates can result in a significant variation in the interface functionality, due to the strong correlation between geometry, stability, and electronic structure. Here, we employed state-of-the-art first-principles calculations with van der Waals interactions, in combination with atomic force microscopy experiments, to explore the interaction mechanism for three structurally related olympicene molecules adsorbed on the Cu(111) surface. The substitution of a single atom in the olympicene molecule switches the nature of adsorption from predominantly physisorptive character [olympicene on Cu(111)], to an intermediate state [olympicene-derived ketone on Cu(111)], then to chemisorptive character [olympicene radical on Cu(111)]. Despite the remarkable difference in adsorption structures (by up to 0.9 Å in adsorption height) and different nature of bonding, the olympicene, its ketone, and its radical derivatives have essentially identical binding energies and work functions upon interaction with the metal substrate. Our findings suggest that the stability and work functions of molecular adsorbates could be rendered insensitive to their adsorption structures, which could be a useful property for (opto)electronic applications. PMID:26928143

  14. Molecular dynamics simulation of the adsorption of a fibronectin module on a graphite surface.

    PubMed

    Raffaini, Giuseppina; Ganazzoli, Fabio

    2004-04-13

    We report atomistic simulations of the adsorption of a fibronectin type I module on a hydrophobic graphite surface. This module comprises only beta-sheets, unlike the albumin fragments previously investigated by us which contained only alpha-helices (Raffaini, G.; Ganazzoli, F. Langmuir 2003, 19, 3403-3412). As done in the latter case, most simulations are carried out in an effective dielectric medium by energy minimizations and molecular dynamics (MD). Further optimizations and MD runs in the explicit presence of water are also performed to assess the stability of the geometries found and to describe the solvation of the adsorbed fibronectin module. The initial adsorption is accompanied by local rearrangements of the strands in contact with the surface, but the overall molecular structure is largely preserved. Much larger rearrangements take place at longer times as found through the MD runs, with the molecule spreading as much as possible so as to maximize the surface coverage, hence the interaction energy, despite a significant strain energy. Energetic aspects of adsorption together with the concomitant size change are discussed in comparison with our previous results for two albumin fragments.

  15. The role of beaded activated carbon's surface oxygen groups on irreversible adsorption of organic vapors.

    PubMed

    Jahandar Lashaki, Masoud; Atkinson, John D; Hashisho, Zaher; Phillips, John H; Anderson, James E; Nichols, Mark

    2016-11-01

    The objective of this study is to determine the contribution of surface oxygen groups to irreversible adsorption (aka heel formation) during cyclic adsorption/regeneration of organic vapors commonly found in industrial systems, including vehicle-painting operations. For this purpose, three chemically modified activated carbon samples, including two oxygen-deficient (hydrogen-treated and heat-treated) and one oxygen-rich sample (nitric acid-treated) were prepared. The samples were tested for 5 adsorption/regeneration cycles using a mixture of nine organic compounds. For the different samples, mass balance cumulative heel was 14 and 20% higher for oxygen functionalized and hydrogen-treated samples, respectively, relative to heat-treated sample. Thermal analysis results showed heel formation due to physisorption for the oxygen-deficient samples, and weakened physisorption combined with chemisorption for the oxygen-rich sample. Chemisorption was attributed to consumption of surface oxygen groups by adsorbed species, resulting in formation of high boiling point oxidation byproducts or bonding between the adsorbates and the surface groups. Pore size distributions indicated that different pore sizes contributed to heel formation - narrow micropores (<7Å) in the oxygen-deficient samples and midsize micropores (7-12Å) in the oxygen-rich sample. The results from this study help explain the heel formation mechanism and how it relates to chemically tailored adsorbent materials. PMID:27295065

  16. The process of dissociative adsorption of fluorine on Ge(001) surface

    NASA Astrophysics Data System (ADS)

    Stankiewicz, B.; Mikołajczyk, P.

    2016-10-01

    The process of dissociation of a fluorine molecule on the (001) surface of germanium has been analyzed using density functional theory. Initial orientations of the F2 molecule with respect to the substrate leading to its dissociative adsorption have been identified. Reaction paths at p(1 × 2) and c(2 × 4) reconstructed Ge(001) surfaces are different, but final configurations of the adsorbate/substrate system are found qualitatively the same. Adsorption energy of around 5 eV per molecule depends on the final arrangement of adatoms, being always higher for the p(1 × 2) substrate reconstruction. The energy barrier for dissociative adsorption of F2 on Ge(001) is always less than 0.2 eV. The structural and electronic properties of distinct final adsorbate configurations have been examined, indicating that the surface density of states is metallic at Ge dimers with one adsorbed F atom and non-metallic at Ge dimers with two F adatoms.

  17. Adsorption structures and energetics of molecules on metal surfaces: Bridging experiment and theory

    NASA Astrophysics Data System (ADS)

    Maurer, Reinhard J.; Ruiz, Victor G.; Camarillo-Cisneros, Javier; Liu, Wei; Ferri, Nicola; Reuter, Karsten; Tkatchenko, Alexandre

    2016-05-01

    Adsorption geometry and stability of organic molecules on surfaces are key parameters that determine the observable properties and functions of hybrid inorganic/organic systems (HIOSs). Despite many recent advances in precise experimental characterization and improvements in first-principles electronic structure methods, reliable databases of structures and energetics for large adsorbed molecules are largely amiss. In this review, we present such a database for a range of molecules adsorbed on metal single-crystal surfaces. The systems we analyze include noble-gas atoms, conjugated aromatic molecules, carbon nanostructures, and heteroaromatic compounds adsorbed on five different metal surfaces. The overall objective is to establish a diverse benchmark dataset that enables an assessment of current and future electronic structure methods, and motivates further experimental studies that provide ever more reliable data. Specifically, the benchmark structures and energetics from experiment are here compared with the recently developed van der Waals (vdW) inclusive density-functional theory (DFT) method, DFT + vdWsurf. In comparison to 23 adsorption heights and 17 adsorption energies from experiment we find a mean average deviation of 0.06 Å and 0.16 eV, respectively. This confirms the DFT + vdWsurf method as an accurate and efficient approach to treat HIOSs. A detailed discussion identifies remaining challenges to be addressed in future development of electronic structure methods, for which the here presented benchmark database may serve as an important reference.

  18. Fluoride removal by calcite: evidence for fluorite precipitation and surface adsorption.

    PubMed

    Turner, Brett D; Binning, Philip; Stipp, S L S

    2005-12-15

    Fluoride contamination of groundwater, both anthropogenic and natural, is a major problem worldwide. In this study, fluoride removal by crushed limestone (99% pure calcite) was investigated by batch studies and surface-sensitive techniques from solutions with fluoride concentrations from 150 micromol/L (3 mg/L) to 110 mM (approximately 2100 mg/L). Surface-sensitive techniques, including atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) as well as zeta potential measurements, confirm that, in addition to precipitation reactions, adsorption of fluoride also occurs. Results indicate that fluoride adsorption occurs immediately over the entire calcite surface with fluorite precipitating at step edges and kinks, where dissolved Ca2+ concentration is highest. The PHREEQ geochemical model was applied to the observed data and indicates that existing models, especially at low fluoride concentrations and high pH (>7.5) are not equipped to describe this complex system, largely because the PHREEQ model includes only precipitation reactions, whereas a combination of adsorption and precipitation parameters are required.

  19. Oxygen subsurface adsorption on the Cu(110)-c(6 × 2) surface

    NASA Astrophysics Data System (ADS)

    Li, Liang; Zhou, Guangwen

    2013-09-01

    To understand the initial steps of the oxidation of Cu(110), we applied density functional theory (DFT) calculations to study oxygen subsurface adsorption at the Cu(110)-c(6 × 2) reconstructed surface by increasing oxygen coverage. A transition from oxygen octahedral occupancy to tetrahedral preference occurs when the coverage reaches 1 monolayer, which may signal the onset of bulk oxidation that initially forms highly distorted Cusbnd O tetrahedrons by comparing the bond lengths and angles of the resulting Cusbnd O tetrahedron with the bulk Cu2O structure. These results suggest that a critical oxygen coverage is required for such a crossover from the oxygen chemisorption to bulk oxide formation. A comparison with the oxygen subsurface adsorption at Cu(100) suggests that the Cu(110) surface has a larger tendency to form Cusbnd O tetrahedrons. We model oxygen subsurface adsorption at the Cu(110)-c(6 × 2) reconstructed surface. Increasing O coverage leads to O tetrahedral preference over octahedral occupancy. The resulting Cusbnd O tetrahedrons show resemblance to that of the Cu2O structure. Cu(110) shows a stronger tendency than Cu(100) to form Cu2O-like tetrahedrons.

  20. Theoretical study of SO2 adsorption on goethite (1 1 0) surface

    NASA Astrophysics Data System (ADS)

    Zubieta, Carolina E.; Fortunato, Leandro F.; Belelli, Patricia G.; Ferullo, Ricardo M.

    2014-09-01

    Adsorption of SO2 on fully hydrated and partially dehydrated (1 1 0) surface of goethite (α-FeOOH) has been investigated using density functional theory (DFT) and periodic conditions. Different degrees of dehydration were modeled by eliminating one or two water molecules from the fully hydrated surface. Calculations indicate that SO2 shows preference to adsorb on dehydrated surface and the transformation to surface sulfite, bisulfite and sulfate was observed. In particular, surface sulfite can be formed over a variety of different dehydrated surfaces as monodentate and bidentate complexes. Theoretical vibrational frequencies of all the species have also been computed. Taking into account all the structures, we found frequency values within the 650-1030 cm-1 region due to Ssbnd OFe stretching, and between 1010 and 1190 cm-1 due to Ssbnd O stretching. Furthermore, monodentate mononuclear and bidentate binuclear sulfite complexes present distinctive features at low frequencies (600-700 cm-1).

  1. CO adsorption on small Aun (n = 1-4) structures supported on hematite. I. Adsorption on iron terminated α-Fe2O3 (0001) surface

    NASA Astrophysics Data System (ADS)

    Pabisiak, Tomasz; Winiarski, Maciej J.; Kiejna, Adam

    2016-01-01

    This is the first of two papers dealing with the adsorption of Au and formation of Aun nanostructures (n = 1-4) on hematite (0001) surface and adsorption of CO thereon. The stoichiometric Fe-terminated (0001) surface of hematite was investigated using density functional theory in the generalized gradient approximation of Perdew-Burke-Ernzerhof (PBE) form with Hubbard correction U, accounting for strong electron correlations (PBE+U). The structural, energetic, and electronic properties of the systems studied were examined for vertical and flattened configurations of Aun nanostructures adsorbed on the hematite surfaces. The flattened ones, which can be viewed as bilayer-like structures, were found energetically more favored than vertical ones. For both classes of structures the adsorption binding energy increases with the number of Au atoms in a structure. The adsorption of Aun induces charge rearrangement at the Aun/oxide contact which is reflected in work function changes. In most considered cases Aun adsorption increases the work function. A detailed analysis of the bonding electron charge is presented and the corresponding electron charge rearrangements at the contacts were quantified by a Bader charge analyses. The interaction of a CO molecule with the Aun nanostructures supported on α-Fe2O3 (0001) and the oxide support was studied. It is found that the CO adsorption binding to the hematite supported Aun structures is more than twice as strong as to the bare hematite surface. Analysis of the Bader charges on the atoms showed that in each case CO binds to the most positively charged (cationic) atom of the Aun structure. Changes in the electronic structure of the Aun species and of the oxide support, and their consequences for the interactions with CO, are discussed.

  2. Adsorption of some important tautomers of 5-amino tetrazole on the (001) and (101) surfaces of anatase: Theoretical study

    NASA Astrophysics Data System (ADS)

    Chermahini, Alireza Najafi; Farrokhpour, Hossein; Zeinodini, Abbas

    2016-10-01

    In the present work, the adsorption of some important tautomers of 5-amino tetrazole (5-AT) on the (101) and (001) surface of anatase have been studied, theoretically. The adsorption energies of the tautomers, with (Ead) and without (Ead-p) considering the deformation energy, were calculated for the different adsorption configurations. The calculations showed that the highest value of Ead-p on the (001) surface (-188.84 kcal/mol) is related to the chemical adsorption of the 1H tautomer from the Nsbnd N of the tetrazole ring (1HATc) accompanied with the cleavage of the Nsbnd H bond of the tautomer and forming O2csbnd H bond on the surface. It was found that the (101) surface is more active for the chemical adsorption of the tautomers compared to the (001) surface. The deformation of the surface and tautomer upon the adsorption were also studied and it was observed that the deformation of the (101) surface is more than that of (001) surface. The change in the energy band gap and density of states (DOS) of the selected TiO2 due to the adsorption of the tautomer were also studied. Finally, the effect of the solvent molecules (acetonitrile) on the chemical adsorption of the 1H tautomer on the (001) surface with the highest value of Ead-p (1HATc) were studied. It was observed that by increasing the number of solvent molecules the value of Ead-p become more negative and the reactivity of the surface increases.

  3. Adsorption and oxidation of oxalic acid on anatase TiO2 (001) surface: A density functional theory study.

    PubMed

    Sun, Tao; Wang, Yun; Zhang, Haimin; Liu, Porun; Zhao, Huijun

    2015-09-15

    Anatase TiO2 (001) surfaces have attracted great interest for photo-degradation of organic species recently due to their high reactivity. In this work, adsorption properties and oxidation mechanisms of oxalic acid on the anatase TiO2 (001) surface have been theoretically investigated using the first-principles density functional theory. Various possible adsorption configurations are considered by diversifying the connectivity of carboxylic groups with the surface. It is found that the adsorption of oxalic acid on the anatase (001) surface prefer the dissociative states. A novel double-bidentate configuration has been found due to the structural match between oxalic acid and the (001) surface. More charge is transferred from the adsorbed oxalic acid to the surface with the double-bidentate configuration when comparing with other adsorption structures. Thus, there is a positive correlation relationship between the transferred charge amount and the interfacial bond numbers when oxalic acid adsorbs on the anatase TiO2 (001) surface. The adsorption energies with dispersion corrections have demonstrated that the van der Waals interactions play an important role in the adsorption, especially when adsorbates are close to the surface.

  4. Adsorption behavior of hydrophobically modified polyelectrolytes onto amino- or methyl-terminated surfaces.

    PubMed

    Briones, Ximena G; Encinas, María V; Petri, Denise F S; Pavez, Jorge E; Tapia, Ricardo A; Yazdani-Pedram, M; Urzúa, Marcela D

    2011-11-15

    The adsorption of hydrophobically modified polyelectrolytes derived from poly(maleic anhydride-alt-styrene) (P(MA-alt-St)) containing in their side chain aryl-alkyl groups onto amino- or methyl-terminated silicon wafers was investigated. The effect of the spacer group, the chemical nature of the side chain, molecular weight of polyelectrolyte, and ionic strength of solution on the polyelectrolyte adsorbed amount was studied by null ellipsometry. The adsorbed amount of polyelectrolyte increased with increasing ionic strength, in agreement with the screening-enhanced adsorption regime, indicating that hydrophobic interactions with the surface play an important role in the adsorption process. At constant ionic strength, the adsorbed amount was slightly higher for polyelectrolytes with larger alkyl side chain and decreased with the hydrophobicity of aryl group. The adsorption behavior is discussed in terms of the side chain flexibility of the polymer. Characteristics of the adsorbed layer were studied by atomic force microscopy (AFM) and contact angle measurements. AFM images show the presence of aggregates and closed globular structure of polyelectrolyte onto the amino- or methyl-terminated surface, which agrees with a 3D and 2D growth mechanism, respectively. Fluorescence measurements showed that the aggregation of polyelectrolyte containing the hydrophobic naphthyl group occurs already in the solution. However, the aggregation of polyelectrolytes containing the phenyl group in its side chain is not observed in solution but is induced by the amino-terminated surface. This difference can be explained in terms of the higher flexibility of side chain bearing the phenyl group. The polyelectrolyte films showed a high chemical heterogeneity and moderate hydrophobicity.

  5. Behavior of aluminum adsorption and incorporation at GaN(0001) surface: First-principles study

    SciTech Connect

    Qin, Zhenzhen; Xiong, Zhihua Wan, Qixin; Qin, Guangzhao

    2013-11-21

    First-principles calculations are performed to study the energetics and atomic structures of aluminum adsorption and incorporation at clean and Ga-bilayer GaN(0001) surfaces. We find the favorable adsorption site changes from T4 to T1 as Al coverage increased to 1 monolayer on the clean GaN(0001) surface, and a two-dimensional hexagonal structure of Al overlayer appears. It is interesting the Al atoms both prefer to concentrate in one deeper Ga layer of clean and Ga-bilayer GaN(0001)