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Sample records for adsorption studies revealed

  1. New insights into the dynamics of adsorption equilibria of humic matter as revealed by radiotracer studies

    NASA Astrophysics Data System (ADS)

    Lippold, Holger; Lippmann-Pipke, Johanna

    2014-05-01

    The mobility of contaminants in the subsurface hydrosphere can be governed by their interaction with aquatic humic substances, which may act as carriers. For modelling migration processes, retardation of humic molecules at mineral surfaces must be considered. There is, however, a lack of clarity concerning the reversibility of adsorption of these natural polyelectrolytes. In this work, evidence was provided that a dynamic adsorption equilibrium exists. For this purpose, adsorption of humic substances (purified Aldrich humic acid and an aquatic fulvic acid) onto kaolinite was examined in tracer exchange studies by means of 14C-labelled humic material. In addition, the kinetics of adsorption and desorption were investigated in batch experiments.

  2. Kinetic and thermodynamic studies of sulforaphane adsorption on macroporous resin.

    PubMed

    Yuanfeng, Wu; Lei, Zhang; Jianwei, Mao; Shiwang, Liu; Jun, Huang; Yuru, You; Lehe, Mei

    2016-08-15

    The adsorption equilibrium, kinetic and thermodynamic of sulforaphane (SF) adsorption onto macroporous resin in aqueous phase were studied. The SP850 resin was screened as the appropriate resin for SF purification. From the equilibrium studies, the Redlich-Peterson model was found to be the best for description of the adsorption behavior of SF onto SP850 resin, followed by the Freundlich model and the Langmuir model. Batch equilibrium experiments demonstrated that, in the examined temperature range, the equilibrium adsorption capacity of SP850 resin decreased with increasing adsorption temperature. Thermodynamics studies indicated that the adsorption of SF was a physical, exothermic, and spontaneous process. The adsorption kinetics revealed that the pseudo-second-order kinetic model was suitable to characterize the kinetics of adsorption of SF onto SP850. Finally, the intra-particle diffusion model demonstrated that SF diffused quickly into macropores, and that diffusion slowed down in the meso- and micropores.

  3. Fibrinogen adsorption mechanisms at the gold substrate revealed by QCM-D measurements and RSA modeling.

    PubMed

    Kubiak, Katarzyna; Adamczyk, Zbigniew; Cieśla, Michał

    2016-03-01

    Adsorption kinetics of fibrinogen at a gold substrate at various pHs was thoroughly studied using the QCM-D method. The experimental were interpreted in terms of theoretical calculations performed according to the random sequential adsorption model (RSA). In this way, the hydration functions and water factors of fibrinogen monolayers were quantitatively evaluated at various pHs. It was revealed that for the lower range of fibrinogen coverage the hydration function were considerably lower than previously obtained for the silica sensor [33]. The lower hydration of fibrinogen monolayers on the gold sensor was attributed to its higher roughness. However, for higher fibrinogen coverage the hydration functions for both sensors became identical exhibiting an universal behavior. By using the hydration functions, the fibrinogen adsorption/desorption runs derived from QCM-D measurements were converted to the Γd vs. the time relationships. This allowed to precisely determine the maximum coverage that varied between 1.6mgm(-2) at pH 3.5 and 4.5mgm(-2) at pH 7.4 (for ionic strength of 0.15M). These results agree with theoretical eRSA modeling and previous experimental data derived by using ellipsometry, OWLS and TIRF. Various fibrinogen adsorption mechanisms were revealed by exploiting the maximum coverage data. These results allow one to develop a method for preparing fibrinogen monolayers of well-controlled coverage and molecule orientation.

  4. Apparatus for the study of macromolecular adsorption

    NASA Astrophysics Data System (ADS)

    Mayo, C. S.; Hallock, R. B.

    1989-04-01

    A surface plasmon adsorbate monitor (SPAM) is described which allows the adsorption of macromolecules or other adsorbates to a metal surface to be monitored. Surface plasmons are employed and the apparatus has no moving parts. The kinetics of adsorption may be studied on a time scale of seconds rather than the more common time scale of minutes; a simple improvement in computer memory access should allow temporal studies in the millisecond range. As an illustration, the adsorption of carboxyl-terminated polystyrene from a solution with acetone onto a silver surface is measured.

  5. Study of cetyltrimethylammonium and cetylpyridinium adsorption on montmorillonite.

    PubMed

    Praus, Petr; Turicová, Martina; Studentová, Sona; Ritz, Michal

    2006-12-01

    Adsorption of cetyltrimethylammonium (CTA) and cetylpyridinium (CP) onto Na-rich montmorillonite (MMT) was studied. For this purpose, the adsorption isotherms of CTA and CP, along with desorption curves of metal cations (Na+, K+, Ca2+, Mg2+), were obtained by means of capillary isotachophoresis and atomic absorption spectrometry. Infrared, X-ray diffraction pattern, specific surface area, porosity, and moisture adsorption measurements of montmorillonite revealed that CTA and CP were adsorbed in monolayer arrangements. CTA is assumed to be attached to the negatively charged MMT surface mainly by electrostatic forces. On the other hand, CP, adsorbed in higher amounts, can be additionally bound via other interactions of pyridinium rings, such as induced and pi-pi interactions. By the surfactant adsorption, the montmorillonite surface became hydrophobic and its micro- and mesopores were significantly diminished. Using scanning electron microscopy, aggregation of such organically modified MMT particles was observed.

  6. Studies on Vapor Adsorption Systems

    NASA Technical Reports Server (NTRS)

    Shamsundar, N.; Ramotowski, M.

    1998-01-01

    The project consisted of performing experiments on single and dual bed vapor adsorption systems, thermodynamic cycle optimization, and thermal modeling. The work was described in a technical paper that appeared in conference proceedings and a Master's thesis, which were previously submitted to NASA. The present report describes some additional thermal modeling work done subsequently, and includes listings of computer codes developed during the project. Recommendations for future work are provided.

  7. Mechanism of Cr(VI) adsorption by coir pith studied by ESR and adsorption kinetic.

    PubMed

    Suksabye, Parinda; Nakajima, Akira; Thiravetyan, Paitip; Baba, Yoshinari; Nakbanpote, Woranan

    2009-01-30

    The oxidation state of chromium in coir pith after Cr(VI) adsorption from aqueous solution was investigated using electron spin resonance (ESR). To elucidate the mechanism of chromium adsorption on coir pith, the adsorption studies of Cr(VI) onto lignin, alpha-cellulose and holocellulose extracted from coir pith were also studied. ESR signals of Cr(V) and Cr(III) were observed in coir pith adsorbed Cr(VI) at solution pH 2, while ESR spectra of lignin extracted from coir pith revealed only the Cr(III) signal. In addition, ESR signal of Cr(V) was observed in alpha-cellulose and holocellulose extracted from coir pith adsorbed Cr(VI). These results confirmed that lignin in coir pith reduced Cr(VI) to Cr(III) while alpha-cellulose and holocellulose extracted from coir pith reduced Cr(VI) to Cr(V). The Cr(V) signal exhibited in ESR of alpha-cellulose and holocellulose might be bound with glucose in cellulose part of coir pith. In addition, xylose which is main in pentosan part of coir pith, indicated that it is involved in form complex with Cr(V) on coir pith. The adsorption kinetic of Cr(VI) from aqueous solution on coir pith was also investigated and described well with pseudo second order model. ESR and desorption experiments confirmed that Cr(VI), Cr(V) and Cr(III), exist in coir pith after Cr(VI) adsorption. The desorption data indicated that the percentage of Cr(VI), Cr(V) and Cr(III) in coir pith were 15.63%, 12.89% and 71.48%, respectively.

  8. Study on the methylene blue adsorption from wastewaters by pore-expanded calcium fluoride sludge adsorbent.

    PubMed

    Hong, Junming; Lin, Bing; Hong, Gui-Bing; Chang, Chang-Tang

    2014-04-01

    The adsorption of methylene blue (MB) onto pore-expanded calcium fluoride sludge (ECF) by the batch adsorption technique was investigated. The results showed that the adsorption capacity increased with increasing MB concentration but decreased as pH was increased. In order to investigate the adsorption mechanisms, three simplified isotherm models and kinetic models were used in this study. The best-fit adsorption isotherm was achieved with the Temkin model. Furthermore, the pseudo-second-order kinetic model agreed very well with the dynamical behavior for the adsorption of MB onto ECF. Thermodynamic studies revealed that the adsorption process of MB onto ECF was spontaneous and exothermic. The results indicated that ECF adsorbed MB efficiently and could be used as a waste adsorbent for the removal of cationic dyes in wastewater treatment.

  9. Studies on adsorption of phenol from wastewater by agricultural waste.

    PubMed

    Girish, C R; Ramachandramurty, V

    2013-07-01

    In this paper, preliminary investigation of various agricultural wastes-Rice mill residue (RM), Wheat mill reside (WM), Dall mill residue (DM) and the Banana peels (BM) was carried out to study their ability to be used as adsorbents for phenol-removal from wastewater. This study reports the feasibility of employing dal mill residue waste (DM) as an adsorbent for removing phenol from wastewater. The performance of DM was compared with the commercially available activated carbon (CAC). Batch mode experiments were conducted with activated DM to study the effects of initial concentration of phenol, pH and the temperature of aqueous solution on adsorption. Equilibrium adsorption isotherms and kinetics were investigated. The experimental data were analyzed by the Langmuir, Freundlich and Temkin models and the isotherm data fitted well to the Freundlich isotherm with monolayer adsorption capacity of 6.189 mg/g. The kinetic data obtained at different concentrations were analyzed using a pseudo-first order and pseudo-second- order equation. The experimental data fitted very well with the pseudo-first-order kinetic model. The FTIR analysis revealed that carboxyl and hydroxyl functional groups were mainly responsible for the sorption of phenol. Finally, the DM was found to be a promising adsorbent for phenol adsorption as compared to activated carbon.

  10. Kinetic and Conformational Insights of Protein Adsorption onto Montmorillonite Revealed Using in Situ ATR-FTIR/2D-COS.

    PubMed

    Schmidt, Michael P; Martínez, Carmen Enid

    2016-08-09

    Protein adsorption onto clay minerals is a process with wide-ranging impacts on the environmental cycling of nutrients and contaminants. This process is influenced by kinetic and conformational factors that are often challenging to probe in situ. This study represents an in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic investigation of the adsorption of a model protein (bovine serum albumin (BSA)) onto a clay mineral (montmorillonite) at four concentrations (1.50, 3.75, 7.50, and 15.0 μM) under environmentally relevant conditions. At all concentrations probed, FTIR spectra show that BSA readily adsorbs onto montmorillonite. Adsorption kinetics follow an Elovich model, suggesting that primary limitations on adsorption rates are surface-related heterogeneous energetic restrictions associated with protein rearrangement and lateral protein-protein interaction. BSA adsorption onto montmorillonite fits the Langmuir model, yielding K = 5.97 × 10(5) M(-1). Deconvolution and curve fitting of the amide I band at the end of the adsorption process (∼120 min) shows a large extent of BSA unfolding upon adsorption at 1.50 μM, with extended chains and turns increasing at the expense of α-helices. At higher concentrations/surface coverages, BSA unfolding is less pronounced and a more compact structure is assumed. Two-dimensional correlation spectroscopic (2D-COS) analysis reveals three different pathways corresponding to adsorbed conformations. At 1.50 μM, adsorption increases extended chains, followed by a loss in α-helices and a subsequent increase in turns. At 3.75 μM, extended chains decrease and then aggregated strands increase and side chains decrease, followed by a decrease in turns. With 7.50 and 15.0 μM BSA, the loss of side-chain vibrations is followed by an increase in aggregated strands and a subsequent decrease in turns and extended chains. Overall, the BSA concentration and resultant surface coverage have a profound

  11. Adsorption isotherm special study. Final report

    SciTech Connect

    1993-05-01

    The study was designed to identify methods to determine adsorption applicable to Uranium Mill Tailings Remedial Action (UMTRA) Project sites, and to determine how changes in aquifer conditions affect metal adsorption, resulting retardation factors, and estimated contaminant migration rates. EPA and ASTM procedures were used to estimate sediment sorption of U, As, and Mo under varying groundwater geochemical conditions. Aquifer matrix materials from three distinct locations at the DOE UMTRA Project site in Rifle, CO, were used as the adsorbents under different pH conditions; these conditions stimulated geochemical environments under the tailings, near the tailings, and downgradient from the tailings. Grain size, total surface area, bulk and clay mineralogy, and petrography of the sediments were characterized. U and Mo yielded linear isotherms, while As had nonlinear ones. U and Mo were adsorbed strongly on sediments acidified to levels similar to tailings leachate. Changes in pH had much less effect on As adsorption. Mo was adsorbed very little at pH 7-7.3, U was weakly sorbed, and As was moderately sorbed. Velocities were estimated for metal transport at different pHs. Results show that the aquifer materials must be characterized to estimate metal transport velocities in aquifers and to develop groundwater restoration strategies for the UMTRA project.

  12. Enhanced fluoride adsorption by nano crystalline γ-alumina: adsorption kinetics, isotherm modeling and thermodynamic studies

    NASA Astrophysics Data System (ADS)

    Chinnakoti, Prathibha; Chunduri, Avinash L. A.; Vankayala, Ranganayakulu K.; Patnaik, Sandeep; Kamisetti, Venkataramaniah

    2016-06-01

    Nano materials in particular nano oxides with enhanced surface area and an excellent catalytic surface serve as potential adsorbents for defluoridation of water. In the present study nano γ-alumina was synthesized through a simple and low cost, surfactant assisted solution combustion method. As synthesized material was characterized by XRD and FESEM for its phase, size and morphological characteristics. Surface properties have been investigated by BET method. Nano γ-alumina was further used for a detailed adsorption study to remove fluoride from water. Batches of experiments were performed at various experimental conditions such as solution pH, adsorbent dose, initial fluoride concentration and contact time to test the defluoridation ability of γ-alumina. Fluoride Adsorption by nano sized γ-alumina was rapid and reached equilibrium within two hours. The adsorption worked well at pH 4.0, where ˜96 % of fluoride was found to be adsorbed on adsorbent. It was possible to reduce fluoride levels to as low as 0.3 mg/L (within the safe limit of WHO: ≤1.5 mg/L) from an initial fluoride levels of 10 mg/L. This could be achieved using a very small quantity, 1 g/L of γ-alumina at pH 4 within 1 h of contact time. Defluoridation capacity of nano γ-alumina was further investigated by fitting the equilibrium data to various isotherm as well as kinetic models. The present study revealed that γ-alumina could be an efficient adsorbent for treating fluoride contaminated water.

  13. Heterogeneous adsorption behavior of landfill leachate on granular activated carbon revealed by fluorescence excitation emission matrix (EEM)-parallel factor analysis (PARAFAC).

    PubMed

    Lee, Sonmin; Hur, Jin

    2016-04-01

    Heterogeneous adsorption behavior of landfill leachate on granular activated carbon (GAC) was investigated by fluorescence excitation-emission matrix (EEM) combined with parallel factor analysis (PARAFAC). The equilibrium adsorption of two leachates on GAC was well described by simple Langmuir and Freundlich isotherm models. More nonlinear isotherm and a slower adsorption rate were found for the leachate with the higher values of specific UV absorbance and humification index, suggesting that the leachate containing more aromatic content and condensed structures might have less accessible sites of GAC surface and a lower degree of diffusive adsorption. Such differences in the adsorption behavior were found even within the bulk leachate as revealed by the dissimilarity in the isotherm and kinetic model parameters between two identified PARAFAC components. For both leachates, terrestrial humic-like fluorescence (C1) component, which is likely associated with relatively large sized and condensed aromatic structures, exhibited a higher isotherm nonlinearity and a slower kinetic rate for GAC adsorption than microbial humic-like (C2) component. Our results were consistent with size exclusion effects, a well-known GAC adsorption mechanism. This study demonstrated the promising benefit of using EEM-PARAFAC for GAC adsorption processes of landfill leachate through fast monitoring of the influent and treated leachate, which can provide valuable information on optimizing treatment processes and predicting further environmental impacts of the treated effluent.

  14. Adsorption-desorption studies of indigocarmine from industrial effluents by using deoiled mustard and its comparison with charcoal.

    PubMed

    Gupta, Vinod K; Jain, Rajeev; Malathi, S; Nayak, Arunima

    2010-08-15

    Deoiled mustard obtained from local oil mills has been used as an inexpensive and effective adsorbent for the removal of indigocarmine dye from industrial effluents. The influence of various factors on the adsorption capacity has been studied by batch experiments. The adsorption studies validate both Langmuir and Freundlich adsorption isotherms. Thermodynamic parameters such as DeltaG degrees, DeltaH degrees, and DeltaS degrees for the adsorption process were calculated, which indicated the feasibility of the adsorption process. Desorption profiles revealed that a significant portion (85%) could be desorbed from deoiled mustard by using 30% glycerol as eluting agent.

  15. Eriobotrya japonica seed biocomposite efficiency for copper adsorption: Isotherms, kinetics, thermodynamic and desorption studies.

    PubMed

    Mushtaq, Mehwish; Bhatti, Haq Nawaz; Iqbal, Munawar; Noreen, Saima

    2016-07-01

    Adsorption techniques are widely used to remove pollutants from wastewater; however, composites are gaining more importance due to their excellent adsorption properties. Bentonite composite with Eriobotrya japonica seed was prepared and used for the adsorption of copper (Cu) metal from aqueous media. The process variables such as pH, Cu(II) ions initial concentration, adsorbent dose, contact time and temperature were optimized for maximum Cu(II) adsorption. At pH 5, adsorbent dose 0.1 g, contact time 45 min, Cu(II) ions initial concentration 75 mg/L and temperature 45 °C, maximum Cu(II) adsorption was achieved. Desorption studies revealed that biocomposite is recyclable. Langmuir, Freundlich and Harkins-Jura isotherms as well as pseudo-first and pseudo-second-order kinetics models were applied to understand the adsorption mechanism. Thermodynamic parameters (ΔG(0), ΔH(0) and ΔS(0)) suggest that the adsorption process was spontaneous and endothermic in nature. The pseudo-second-order kinetic model and Langmuir isotherm fitted well to the adsorption data. Results showed that biocomposite was more efficient for Cu(II) adsorption in comparison to individuals native Eriobotrya japonica seed biomass and Na-bentonite.

  16. Adsorption studies of methylene blue dye on tunisian activated lignin

    NASA Astrophysics Data System (ADS)

    Kriaa, A.; Hamdi, N.; Srasra, E.

    2011-02-01

    Activated carbon prepared from natural lignin, providing from a geological deposit, was used as the adsorbent for the removal of methylene blue (MB) dye from aqueous solutions. Batch adsorption studies were conducted to evaluate various experimental parameters like pH and contact time for the removal of this dye. Effective pH for MB removal was 11. Kinetic study showed that the adsorption of dye was gradual process. Quasi equilibrium reached in 4 h. Pseudo-first-order, pseudo-second-order were used to fit the experimental data. Pseudo-second-order rate equation was able to provide realistic description of adsorption kinetics. The experimental isotherms data were also modelled by the Langmuir and Freundlich equation of adsorption. Equilibrium data fitted well with the Langmuir model with maximum monolayer adsorption capacity of 147 mg/g. Activated lignin was shown to be a promising material for adsorption of MB from aqueous solutions.

  17. 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.

  18. Self-consistent van der Waals density functional study of benzene adsorption on Si(100)

    NASA Astrophysics Data System (ADS)

    Hamamoto, Yuji; Hamada, Ikutaro; Inagaki, Kouji; Morikawa, Yoshitada

    2016-06-01

    The adsorption of benzene on the Si(100) surface is studied theoretically using the self-consistent van der Waals density functional (vdW-DF) method. The adsorption energies of two competing adsorption structures, butterfly (BF) and tight-bridge (TB) structures, are calculated with several vdW-DFs at saturation coverage. Our results show that recently proposed vdW-DFs with high accuracy all prefer TB to BF, in accord with more accurate calculations based on exact exchange and correlation within the random-phase approximation. Detailed analyses reveal the important roles played by the molecule-surface interaction and molecular deformation upon adsorption, and we suggest that their precise description is a prerequisite for accurate prediction of the most stable adsorption structure of organic molecules on semiconductor surfaces.

  19. Revealing the Adsorption Mechanisms of Nitroxides on Ultrapure, Metallicity-Sorted Carbon Nanotubes

    PubMed Central

    2014-01-01

    Carbon nanotubes are a natural choice as gas sensor components given their high surface to volume ratio, electronic properties, and capability to mediate chemical reactions. However, a realistic assessment of the interaction of the tube wall and the adsorption processes during gas phase reactions has always been elusive. Making use of ultraclean single-walled carbon nanotubes, we have followed the adsorption kinetics of NO2 and found a physisorption mechanism. Additionally, the adsorption reaction directly depends on the metallic character of the samples. Franck–Condon satellites, hitherto undetected in nanotube–NOx systems, were resolved in the N 1s X-ray absorption signal, revealing a weak chemisorption, which is intrinsically related to NO dimer molecules. This has allowed us to identify that an additional signal observed in the higher binding energy region of the core level C 1s photoemission signal is due to the C=O species of ketene groups formed as reaction byproducts . This has been supported by density functional theory calculations. These results pave the way toward the optimization of nanotube-based sensors with tailored sensitivity and selectivity to different species at room temperature. PMID:24404865

  20. Studies on adsorption of formaldehyde in zirconium phosphate-glyphosates

    NASA Astrophysics Data System (ADS)

    Zhang, Yuejuan; Yi, Jianjun; Xu, Qinghong

    2011-01-01

    In our previous work [22], a kind of layered compound of zirconium phosphate-glyphosate (ZrGP) was synthesized. Its large surface area (445 m 2/g) indicates this compound has possible application in adsorptions. In this paper, adsorption to formaldehyde in ZrGP and mechanisms of the adsorption were studied carefully. Balance time of adsorption (about 6 h) and largest adsorbed amount (7.8%) were found when adsorption temperature was at 40 °C and pH value of adsorption environment was about 3.0. H-bonds were found existing between molecules of formaldehyde and ZrGP, and formaldehyde molecules could exist in ZrGP stably.

  1. Spectroscopic study of amino acids adsorption on pyrite surface: From vacuum to solution conditions.

    NASA Astrophysics Data System (ADS)

    Mateo-Marti, E.; Sanchez-Arenillas, M.

    2015-10-01

    We characterized the adsorption of cystine molecules among other amino acids on pyrite surface via X-ray photoelectron spectroscopy. A novel comparative analysis revealed remarkable differences with respect to molecular adsorption and surface chemistry induced by environmental conditions. Pyrite is a highly reactive surface and contains two crucial types of surface functional groups that drive molecular chemistry on the surface depending on the surrounding conditions. Therefore, the systems explored in this study hold interesting implications for supporting catalyzed prebiotic chemistry reactions.

  2. Kinetic studies of elemental mercury adsorption in activated carbon fixed bed reactor.

    PubMed

    Skodras, G; Diamantopoulou, Ir; Pantoleontos, G; Sakellaropoulos, G P

    2008-10-01

    Activated carbons are suitable materials for Hg(0) adsorption in fixed bed operation or in injection process. The fixed bed tests provide good indication of activated carbons effectiveness and service lives, which depend on the rates of Hg(0) adsorption. In order to correlate fixed bed properties and operation conditions, with their adsorptive capacity and saturation time, Hg(0) adsorption tests were realized in a bench-scale unit, consisted of F400 activated carbon fixed bed reactor. Hg(0) adsorption tests were conducted at 50 degrees C, under 0.1 and 0.35 ng/cm(3) Hg(0) initial concentrations and with carbon particle sizes ranging between 75-106 and 150-250 microm. Based on the experimental breakthrough data, kinetic studies were performed to investigate the mechanism of adsorption and the rate controlling steps. Kinetic models evaluated include the Fick's intraparticle diffusion equation, the pseudo-first order model, the pseudo-second order model and Elovich kinetic equation. The obtained experimental results revealed that the increase in particle size resulted in significant decrease of breakthrough time and mercury adsorptive capacity, due to the enhanced internal diffusion limitations and smaller external mass transfer coefficients. Additionally, higher initial mercury concentrations resulted in increased breakthrough time and mercury uptake. From the kinetic studies results it was observed that all the examined models describes efficiently Hg(0) breakthrough curves, from breakpoint up to equilibrium time. The most accurate prediction of the experimental data was achieved by second order model, indicating that the chemisorption rate seems to be the controlling step in the procedure. However, the successful attempt to describe mercury uptake with Fick's diffusion model and the first order kinetic model, reveals that the adsorption mechanism studied was complex and followed both surface adsorption and particle diffusion.

  3. Functionalized mesoporous silica materials for molsidomine adsorption: Thermodynamic study

    SciTech Connect

    Alyoshina, Nonna A.; Parfenyuk, Elena V.

    2013-09-15

    A series of unmodified and organically modified mesoporous silica materials was prepared. The unmodified mesoporous silica was synthesized via sol–gel synthesis in the presence of D-glucose as pore-forming agent. The functionalized by phenyl, aminopropyl and mercaptopropyl groups silica materials were prepared via grafting. The fabricated adsorbent materials were characterized by Fourier transform infrared spectroscopy (FTIR) analysis, N{sub 2} adsorption/desorption and elemental analysis methods. Then their adsorption properties for mesoionic dug molsidomine were investigated at 290–313 K and physiological pH value. Thermodynamic parameters of molsidomine adsorption on the synthesized materials have been calculated. The obtained results showed that the adsorption process of molsidomine on the phenyl modified silica is the most quantitatively and energetically favorable. The unmodified and mercaptopropyl modified silica materials exhibit significantly higher adsorption capacities and energies for molsidomine than the aminopropyl modified sample. The effects are discussed from the viewpoint of nature of specific interactions responsible for the adsorption. - Graphical abstract: Comparative analysis of the thermodynamic characteristics of molsidomine adsorption showed that the adsorption process on mesoporous silica materials is controlled by chemical nature of surface functional groups. Molsidomine adsorption on the phenyl modified silica is the most quantitatively and energetically favorable. Taking into account ambiguous nature of mesoionic compounds, it was found that molsidomine is rather aromatic than dipolar. Display Omitted - Highlights: • Unmodified and organically modified mesoporous silica materials were prepared. • Molsidomine adsorption on the silica materials was studied. • Phenyl modified silica shows the highest adsorption capacity and favorable energy. • Molsidomine exhibits the lowest affinity to aminopropyl modified silica.

  4. EXAFS Reveals the Mechanism of U Isotope Fractionation During Adsorption to Mn Oxyhydroxide

    NASA Astrophysics Data System (ADS)

    Wasylenki, L. E.; Brennecka, G.; Bargar, J.; Weyer, S.; Anbar, A. D.

    2010-12-01

    Natural variations in the ratio of 238U/235U due to “stable” isotope fractionation have now been reported for a range of geological samples [1-3]. Among the observed variations are a small difference in 238U/235U between seawater and ferromanganese sediments (seawater slightly heavier) and a larger difference, with opposite sense, between seawater and black shales (seawater lighter). These variations suggest that long-term changes in the proportions of oxic and anoxic/sulfidic sinks for U in the ocean over Earth’s history may be recorded as shifts in the isotopic compositions of marine sediments. Thus U isotopes are a potential paleoredox proxy for the oceans, as suggested by [4]. In order to investigate the mechanism behind fractionation of U isotopes in oxidizing marine environments, we previously conducted simple adsorption experiments in which an isotopically known pool of dissolved U partly adsorbed onto synthetic birnessite, a common Mn oxyhydroxide in hydrogenetic ferromanganese crusts. Our experimental result agreed very well with that observed between seawater and natural ferromanganese sediments: δ238U/235U of adsorbed U was 0.2‰ lighter than δ238U/235U of dissolved U [5]. The magnitude of fractionation is constant as a function of experimental duration and fraction of U adsorbed, suggesting an equilibrium isotope effect. Many metal isotope effects are driven by changes in oxidation state for the metal of interest. Because both dissolved and adsorbed U are hexavalent in this system, a redox reaction cannot be causing isotope fractionation. We therefore hypothesized that a difference in uranium’s coordination environment between dissolved and adsorbed U is likely responsible for the isotope effect. We analyzed a sample from our experimental study with extended X-ray absorption fine structure (EXAFS) spectroscopy. Comparison of the EXAFS spectrum of U adsorbed on birnessite with the spectra of aqueous U species (UO22+ and UO2(CO3)34-) reveals

  5. Adsorption edge study about cadmium, copper, nickel and zinc adsorption by variable charge soils

    NASA Astrophysics Data System (ADS)

    Casagrande, J. C.; Mouta, E. R.; Soares, M. R.

    2009-04-01

    The improper discharge of industrial and urban residues and the inadvertent use of fertilizers and pesticides can result in soil and water pollution and improve the potential of trace metals to enter in the human food chain. Adsorption reactions occur at the solid/liquid interface and are the most important mechanisms for controlling the activity of metal ions in soil solution. In a complex system with amphoteric behavior, the comprehension of the mobility, availability and fate of pollutants in the soil system is crucial for the prediction of the environmental consequences and for development of prevention/remediation strategies. A comparative study of cadmium (Cd), copper (Cu), nickel (Ni) and zinc (Zn) adsorption by highly weathered soils was carried out. Surface (0-0.2m) and subsoil (B horizon) samples were taken from a Rhodic Kandiudalf (RH), an Anionic "Xanthic" Acrudox (XA) and an Anionic "Rhodic" Acrudox (RA), located in brazilian humid tropical area. As the pH and the ionic strength are important environmental factors influencing the solution chemistry of heavy metals in variable charge systems, adsorption envelopes, in a batch adsorption experiment, were elaborated by reacting, for 24 h, soil samples with individual 0.01, 0.1 and 1.0 mol L-1 Ca(NO3)2 aqueous solutions containing nitrate salts of the adsorptive heavy metal (Cd, Cu, Ni and Zn) at the initial concentration of 5 mg L-1, with an increasing pH value from 3.0 to 8.0. pH50-100%, the difference between the pH of 100 and 50 percent metal adsorption was determined. A sharp increase of adsorption density (adsorption edge) was observed within a very narrow pH range, usually less than two pH units. Commonly, the relative affinity of a soil for a metal cation increases with the tendency of the cation to form inner-sphere surface complexes. This may be caused by differences in extent of hydrolysis of Cu ions and in affinity of adsorption sites for Cu. In general, subsurface samples showed low pH50

  6. Kinetics and thermodynamic study of aniline adsorption by multi-walled carbon nanotubes from aqueous solution.

    PubMed

    Al-Johani, Hind; Abdel Salam, Mohamed

    2011-08-15

    Multi-walled carbon nanotubes (MWCNTs) were used in the adsorptive removal of aniline, an organic pollutant, from an aqueous solution. It was found that carbon nanotubes with a higher specific surface area adsorbed and removed more aniline from an aqueous solution. The adsorption was dependent on factors, such as MWCNTs dosage, contact time, aniline concentration, solution pH and temperature. The adsorption study was analyzed kinetically, and the results revealed that the adsorption followed pseudo-second order kinetics with good correlation coefficients. In addition, it was found that the adsorption of aniline occurred in two consecutive steps, including the slow intra-particle diffusion of aniline molecules through the nanotubes. Various thermodynamic parameters, including the Gibbs free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°), were calculated. The results indicated that the spontaneity of the adsorption, exothermic nature of the adsorption and the decrease in the randomness reported as ΔG°, ΔH° and ΔS°, respectively, were all negative.

  7. Adsorption thermodynamic and kinetic studies of trihalomethanes on multiwalled carbon nanotubes.

    PubMed

    Lu, Chungsying; Chung, Yao-Lei; Chang, Kuan-Foo

    2006-11-16

    Multiwalled carbon nanotubes (MWCNTs) were purified by mixed HNO3/H2SO4 solution and were employed as adsorbents to study adsorption kinetics and thermodynamics of trihalomethanes (THMs) from chlorinated drinking water. The amount of THMs adsorbed onto CNTs decreased with a rise in temperature and high adsorption capacities were found at 5 and 15 degrees C. Under the same conditions, the purified CNTs possess two to three times more adsorption capacities of CHCl3, which accounts for a major portion of THMs in the chlorinated drinking water, than the commercially available PAC suggesting that CNTs are efficient adsorbents. The thermodynamic analysis revealed that the adsorption of THMs onto CNTs is exothermic and spontaneous.

  8. Spectroscopic study of cystine adsorption on pyrite surface: From vacuum to solution conditions

    NASA Astrophysics Data System (ADS)

    Sanchez-Arenillas, M.; Mateo-Marti, E.

    2015-09-01

    We characterized the adsorption of cystine molecules on pyrite surface via X-ray photoelectron spectroscopy. Anoxic conditions were simulated under ultra-high-vacuum conditions. In contrast, to simulate oxidation conditions, the molecules were adsorbed on pyrite surface from solution. A novel comparative analysis revealed remarkable differences with respect to molecular adsorption and surface chemistry induced by environmental conditions. Molecular adsorption under anoxic conditions was observed to be more favorable, concentrating a large number of molecules on the surface and two different chemical species. In contrast, the presence of oxygen induced an autocatalytic oxidation process on the pyrite surface, which facilitated water binding on pyrite surface and partially blocked molecular adsorption. Pyrite is a highly reactive surface and contains two crucial types of surface functional groups that drive molecular chemistry on the surface depending on the surrounding conditions. Therefore, the system explored in this study holds interesting implications for supporting catalyzed prebiotic chemistry reactions.

  9. Coulometric Study of Ethanol Adsorption at a Polycrystalline Platinum Electrode

    DTIC Science & Technology

    2011-07-01

    value of the ratio Ian/Icalc: 1. The minimal ratio would be 1, corresponding to a one- electron oxidation of one-site attached CH3CH2O surface...Coulometric Study of Ethanol Adsorption at a Polycrystalline Platinum Electrode Sol Gilman Sensors and Electron Devices Directorate, ARL...noble metals and noble metal alloys that can provide what amounts to an adsorbed oxygen “valve” for initiating adsorption/reaction on a clean and

  10. An Infrared Spectroelectrochemical Study of Cyanide Adsorption on Palladium Surfaces

    DTIC Science & Technology

    1987-01-01

    NUMBER(s) Kevin Ashley, Frederick Weinert, Mahesh G. Samant, H. Seki and M. R. Philpott N00014-82-C-0583 ) PERFORMING ORGANIZATION NAME AND ADDRESS...8217TROELECTROCHEMICAL STUD 01)’ OCY(ANID)E ADSORPTION ON PAL.LADIUMN SUJRFACES hy Kevin Ashley, Frederick WVeinert, Mahiesh C. Simint, Ff. Seki. NI. R...SPECTROELECTROCHEMICAL STUDY OF CYANIDE ADSORPTION ON PALLADIUM SURFACES Kevin Ashley* and Frederick Weinert Department of Chemistry San Jose State

  11. Equilibrium and kinetic adsorption study of the adsorptive removal of Cr(VI) using modified wheat residue.

    PubMed

    Chen, Suhong; Yue, Qinyan; Gao, Baoyu; Xu, Xing

    2010-09-01

    A new adsorbent modified from wheat residue was synthesized after reaction with epichlorohydrin and triethylamine by using the modifying agents of diethylenetriamine in the presence of organic medium of N,N-dimethylformamide. The performance of the modified wheat straw (MWS) was characterized by Fourier transform infrared spectroscopy and point of zero charge analysis. The adsorption was investigated in a batch adsorption system, including both equilibrium adsorption isotherms and kinetics. Results showed that MWR had great anion-adsorbing capacity, due to the existence of a large number of introduced amino groups, and the value of pH(PZC) was around 5.0. Equilibrium data were analyzed using the Langmuir, Freundlich, and Temkin isotherm models and were found to be best represented by the Freundlich isotherm model. Evaluation of the adsorption process identified its endothermic nature. The maximum adsorption capacity of MWS for the removal of Cr(VI) was 322.58mg/g at 328K, indicating that MWS has high chromium removal efficiency, compared to other adsorbents reported. The kinetics of adsorption followed the pseudo-second-order kinetic equation. The mechanism of adsorption was investigated using the intraparticle diffusion model. Thermodynamic parameters (free energy change, enthalpy change, and entropy change) revealed that the adsorption of Cr(VI) onto MWS was endothermic and spontaneous; additionally, the adsorption can be characterized as an ion-exchange process. The results suggest that MWS is an inexpensive and efficient adsorbent for removing Cr(VI) ions from aqueous solution.

  12. Adsorption study of Ammonia Nitrogen by watermelon rind

    NASA Astrophysics Data System (ADS)

    Ibrahim, A.; Yusof, L.; Beddu, N. S.; Galasin, N.; Lee, P. Y.; Lee, R. N. S.; Zahrim, A. Y.

    2016-06-01

    The utilization of fruit waste for low-cost adsorbents as a replacement for costly conventional methods of removing ammonia nitrogen from wastewater has been reviewed. The adsorption studies were conducted as a function of contact time and adsorbent dosage and it were carried out on four different adsorbents; fresh watermelon rind and modified watermelon rind with sodium hydroxide (NaOH), potassium hydroxide (KOH) and sulphuric acid (H2SO4). Adsorbents were tested for characterization by using zeta potential test and all samples shows negative values thus makes it favourable for the adsorption process. The batch experimental result showed that adsorption process is rapid and equilibrium was established within 40 minutes of contact time. The ammonia nitrogen removal rate amounted in range of 96% to 99%, and the adsorption capacities were in range of 1.21 to 1.24 mg/g for all four different types of adsorbents used.

  13. Adsorption of chromium onto activated alumina: kinetics and thermodynamics studies.

    PubMed

    Marzouk, Ikhlass; Dammak, Lassaad; Hamrouni, Béchir

    2013-02-01

    In this study, the removal of chromium (VI) by adsorption on activated alumina was investigated and the results were fitted to Langmuir, Freundlich, Dubinin-Redushkevich, and Temkin adsorption models at various temperatures. The constants of each model were evaluated depending on temperature. Thermodynamic parameters for the adsorption system were determined at 10, 25 and 40 degrees C. (deltaH degrees = -21.18 kJ x mol(-1); deltaG degrees = -8.75 to -7.43 kJ x mol(-1) and deltaS degrees = -0.043 kJ x K(-1) x mol(-1)). The obtained values showed that chromium (VI) adsorption is a spontaneous and exothermic process. The kinetic process was evaluated by first-order, second-order and Elovich kinetic models.

  14. Studies on adsorption characteristics and mechanism of adsorption of chlorhexidine mainly by carbon black.

    PubMed

    Akaho, E; Fukumori, Y

    2001-09-01

    The extent of adsorption of chlorhexidine to carbon black and sanitary cotton was determined by measuring the amounts of chlorhexidine adsorbed to carbon black or sanitary cotton from the chlorhexidine solution containing specific amount of carbon black or sanitary cotton. As another comparative antiseptic example of adsorption phenomena, adsorption of acrinol to sanitary cotton was also studied. The specific surface area of carbon black was measured by the BET method of adsorption isotherm. The pattern of adsorption of chlorhexidine to carbon black was temperature-dependent Langmuir isotherms, and the amounts adsorbed increased as the temperature was raised. Since chlorhexidine, whose pKa's are 2.2 and 10.3, is considered to exist in aqueous solution as the di-cation, an ion-ion interaction should be formed between protonated biguanide and anionic portions of carbon black or sanitary cotton. The chlorophenyl and hexane moieties interact with hydrophobic portions of carbon black or sanitary cotton. The perturbation experiment conducted on this interaction system showed that the nature of interaction was irreversible. The enthalpy change calculated from Langmuir constants was small, indicating the existence of ion-ion interaction. The entropy values, 27.4 to 28.2 e.u. obtained in this system, suggested that the hydration shells of the ions were rather tightly bound. The area occupied by a chlorhexidine molecule, 548 (A)(2), was twice greater than the projection area, 276 (A)(2), suggesting that chlorhexidine was adsorbed in such a way that each molecule is sufficiently well spaced.

  15. A study on the adsorption of methylene blue onto gum ghatti/TiO2 nanoparticles-based hydrogel nanocomposite.

    PubMed

    Mittal, Hemant; Ray, Suprakas Sinha

    2016-07-01

    The objective of this work was to study the isotherm and kinetic models for the adsorption of methylene blue (MB) onto a TiO2 nanoparticle (TiO2NP)-containing hydrogel nanocomposite (HNC) of polyacrylamide-grafted gum ghatti (PAAm-g-Gg). The grafting of PAAm onto Gg was conducted using N,N'-methylene-bis-acrylamide (MBA) as a crosslinker, and different weight percentages of TiO2NPs were incorporated into the hydrogel matrix during the grafting reaction. The graft co-polymerization and the formation of the HNC were confirmed using FTIR, XRD, BET, SEM, TEM and EDS analyses. The adsorption of MB was studied in batch mode and it was found to be highly dependent on solution pH, ionic strength temperature and adsorbent loading. The MB-adsorption process followed the pseudo-second-order rate model and Langmuir adsorption isotherm with a maximum adsorption capacity of 1305.5mgg(-1). Thermodynamic studies revealed that the adsorption of MB onto the HNC surface was spontaneous, endothermic and through a process of physisorption. The results also showed that the HNC was much more effective for the adsorption of cationic dyes than anionic dyes, and it retained its original adsorption capacity for five successive cycles of adsorption-desorption. In conclusion, the hydrogel nanocomposite showed huge potential for remediating industrial wastewater polluted by toxic cationic dyes.

  16. Adsorption of mercury on lignin: combined surface complexation modeling and X-ray absorption spectroscopy studies.

    PubMed

    Lv, Jitao; Luo, Lei; Zhang, Jing; Christie, Peter; Zhang, Shuzhen

    2012-03-01

    Adsorption of mercury (Hg) on lignin was studied at a range of pH values using a combination of batch adsorption experiments, a surface complexation model (SCM) and synchrotron X-ray absorption spectroscopy (XAS). Surface complexation modeling indicates that three types of acid sites on lignin surfaces, namely aliphatic carboxylic-, aromatic carboxylic- and phenolic-type surface groups, contributed to Hg(II) adsorption. The bond distance and coordination number of Hg(II) adsorption samples at pH 3.0, 4.0 and 5.5 were obtained from extended X-ray absorption fine structure (EXAFS) spectroscopy analysis. The results of SCM and XAS combined reveal that the predominant adsorption species of Hg(II) on lignin changes from HgCl(2)(0) to monodentate complex -C-O-HgCl and then bidentate complex -C-O-Hg-O-C- with increasing pH value from 2.0 to 6.0. The good agreement between SCM and XAS results provides new insight into understanding the mechanisms of Hg(II) adsorption on lignin.

  17. Adsorption of cadmium on husk of Lathyrus sativus: physico-chemical study.

    PubMed

    Panda, G C; Das, S K; Chatterjee, S; Maity, P B; Bandopadhyay, T S; Guha, A K

    2006-06-01

    Adsorption of cadmium (II) from aqueous solution by low-cost biosorbents was investigated. Husk of Lathyrus sativus (HLS) was found to be the most efficient in this respect and removed approximately 95% of the metal. The influence of pH, temperature, contact time and metal ion concentration on the adsorption process by HLS was studied. Hydrogen ion concentration of the solution greatly influenced the process with an optimum at pH 5.0-6.0, whereas temperature had no significant effect. The process was very fast and more than 90% of the total adsorption took place within the first 5 min and was found to follow pseudo-second order rate kinetics. The adsorption data can better be explained by Langmuir isotherm model and the calculated maximum adsorption capacity was 35 mg/g of HLS at pH 5.0 and 30 degrees C. Scanning electron micrographs showed that cadmium was present as micro precipitate on the surface of the adsorbent. Cadmium replaced calcium of the biomass as revealed from the EDX analysis indicating that the adsorption proceeds through ion exchange mechanism. Cadmium could be desorbed from the loaded biomass by lowering pH approximately 1.0 with mineral acid.

  18. Surface plasmon resonance studies of pullulan and pullulan cinnamate adsorption onto cellulose.

    PubMed

    Kaya, Abdulaziz; Du, Xiaosong; Liu, Zelin; Lu, Jessica W; Morris, John R; Glasser, Wolfgang G; Heinze, Thomas; Esker, Alan R

    2009-09-14

    Surface plasmon resonance studies showed pullulan cinnamates (PCs) with varying degrees of substitution (DS) adsorbed onto regenerated cellulose surfaces from aqueous solutions below their critical aggregation concentrations. Results on cellulose were compared to PC adsorption onto hydrophilic and hydrophobic self-assembled thiol monolayers (SAMs) on gold to probe how different interactions affected PC adsorption. PC adsorbed onto methyl-terminated SAMs (SAM-CH(3)) > cellulose > hydroxyl-terminated SAMs (SAM-OH) for high DS and increased with DS for each surface. Data for PC adsorption onto cellulose and SAM-OH surfaces were effectively fit by Langmuir isotherms; however, Freundlich isotherms were required to fit PC adsorption isotherms for SAM-CH(3) surfaces. Atomic force microscopy images from the solid/liquid interfaces revealed PC coatings were uniform with surface roughnesses <2 nm for all surfaces. This study revealed hydrogen bonding alone could not explain PC adsorption onto cellulose and hydrophobic modification of water-soluble polysaccharides was a facile strategy for their conversion into surface modifying agents.

  19. A Study of Adsorptive Characteristics of Australian Coals

    NASA Astrophysics Data System (ADS)

    Lan, Y. P.; Tsai, L. L.

    2012-04-01

    Ever since the Kyoto Protocol, controlling carbon dioxide emission and reducing its content in atmosphere are very important environmental issues up to today. One of the effective methods for permanent sequestration of anthropogenic CO2 is to inject CO2 into deep, unminable coal seams and recover coal bed methane at the same time. CO2-ECBM technology had been proved to be very promising to meet the needs of both environment and energy. Beside other external environment factors, capacity of CO2 adsorption and CH4 desorption are the most influencing factors in selection of sites for the geological storage of CO2. Therefore, the objective of this study is to understand the relationship between gas adsorption and CO2 sequestration, by various experiments for the characterization of Australian of coals. Generally speaking, coal seam gas comprises mostly of CH4, CO2, C2H6, and N2. However, some of the Australian coals were reported with significant amount of CO2 up to 90%, which might strongly affect their capacity of CO2 capture and storage (CCS). High to medium volatile bituminous coals from Sydney Basin and Bowen Basin, southeast Australia were selected in this study. Experiments include maceral composition and vitrinite reflectance measurements, petrographic analysis, Proximate analysis, Ultimate analysis, specific surface area analysis as well as CO2 and CH4 adsorption experiments were performed. Parameters for difference adsorption functions (Langmuir, BET, D-R and D-A) were then calculated to fit their adsorption isotherms the best fitting curve can then be found. Among these adsorption functions, Langmuir is the most basic and commonly used function theory. The results of all experiments were synthesized to discuss the relations among each other, so as to establish the relationship between gas adsorption and coal characteristics.

  20. Adsorption studies of chromium (VI) removal from water by lanthanum diethanolamine hybrid material.

    PubMed

    Mandal, Sandip; Sahu, Manoj Kumar; Giri, Anil Kumar; Patel, Raj Kishore

    2014-01-01

    In the present research work, lanthanum diethanolamine hybrid material is synthesized by co-precipitation method and used for the removal of Cr(VI) from synthetic dichromate solution and hand pump water sample. The sorption experiments were carried out in batch mode to optimize various influencing parameters such as adsorbent dose, contact time, pH, competitive anions and temperature. The characterization of the material and mechanism of Cr(VI) adsorption on the material was studied by using scanning electron microscope, Fourier transform infrared, X-ray diffraction, Brunauer-Emmett-Teller and thermogravimetric analysis-differential thermal analysis. Adsorption kinetics studies reveal that the adsorption process followed first-order kinetics and intraparticle diffusion model with correlation coefficients (R2) of 0.96 and 0.97, respectively. The adsorption data were best fitted to linearly transformed Langmuir isotherm with correlation coefficient (R2) of 0.997. The maximum removal of Cr(VI) is found to be 99.31% at optimal condition: pH = 5.6 of the solution, adsorbent dose of 8 g L(-1) with initial concentration of 10mgL(-1) of Cr(VI) solution and an equilibrium time of 50 min. The maximum adsorption capacity of the material is 357.1 mg g(-1). Thermodynamic parameters were evaluated to study the effect of temperature on the removal process. The study shows that the adsorption process is feasible and endothermic in nature. The value of E (260.6 kJ mol(-1)) indicates the chemisorption nature of the adsorption process. The material is difficult to be regenerated. The above studies indicate that the hybrid material is capable of removing Cr(VI) from water.

  1. Arsenic Removal: Adsorptive Media and Coagulation/Filtration Case Studies

    EPA Science Inventory

    This presentation provides information on the results of three case studies from USEPA arsenic demonstration program. The first case study presented is on the Rimrock, AZ project that used an adsorptive media technology (E33 media) to remove arsenic. The second case study is on...

  2. Adsorption of two sodium atoms on graphene -- A first principles study

    SciTech Connect

    Kaur, Gagandeep; Rani, Babita; Gupta, Shuchi; Dharamvir, Keya

    2015-08-28

    We perform a systematic density functional theory (DFT) study of the adsorption of two sodium atoms on graphene using the SIESTA package, in the generalized gradient approximation (GGA). The adsorption energy, geometry, magnetic moment and charge transfer of the Na{sub n}-graphene (n=1, 2) system are calculated. Three initial horizontal orientations of the pair of sodium atoms on graphene are studied. Our calculations reveal that sodium atoms bind weakly to the graphene surface which is in agreement with previous results. We also notice a charge transfer of 0.288e from a sodium adatom to the graphene sheet altering its magnetic moment (−0.318 µ{sub B}) that is reduced from the gas phase value of the isolated atom (1 µ{sub B}). The calculated adsorption energies suggest that clustering of Na atoms on graphene is energetically favorable.

  3. 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.

  4. Kinetic studies of microfabricated biosensors using local adsorption strategy.

    PubMed

    Zhang, Menglun; Huang, Jingze; Cui, Weiwei; Pang, Wei; Zhang, Hao; Zhang, Daihua; Duan, Xuexin

    2015-12-15

    Micro/nano scale biosensors integrated with the local adsorption mask have been demonstrated to have a better limit of detection (LOD) and less sample consumptions. However, the molecular diffusions and binding kinetics in such confined droplet have been less studied which limited further development and application of the local adsorption method and imposed restrictions on discovery of new signal amplification strategies. In this work, we studied the kinetic issues via experimental investigations and theoretical analysis on microfabricated biosensors. Mass sensitive film bulk acoustic resonator (FBAR) sensors with hydrophobic Teflon film covering the non-sensing area as the mask were introduced. The fabricated masking sensors were characterized with physical adsorption of bovine serum albumin (BSA) and specific binding of antibody and antigen. Over an order of magnitude improvement on LOD was experimentally monitored. An analytical model was introduced to discuss the target molecule diffusion and binding kinetics in droplet environment, especially the crucial effects of incubation time, which has been less covered in previous local adsorption related literatures. An incubation time accumulated signal amplification effect was theoretically predicted, experimentally monitored and carefully explained. In addition, device optimization was explored based on the analytical model to fully utilize the merits of local adsorption. The discussions on the kinetic issues are believed to have wide implications for other types of micro/nano fabricated biosensors with potentially improved LOD.

  5. Study of char gasification in a reaction/adsorption apparatus

    SciTech Connect

    Sotirchos, S.V.; Crowley, J.A.

    1987-09-01

    The reaction of an activated carbon (coconut char) with CO/sub 2/ was studied in a reaction/adsorption apparatus which allows successive reactivity and physical adsorption measurements to be made on the same solid sample. Reaction and surface area evolution data were obtained in the temperature range from 800 to 900/sup 0/C. All reaction rate trajectories obtained in this study showed a maximum in the reaction rate, 2-3 times higher than the initial rate, at about 85% conversion. There was no correlation between these results and the evolution of the internal surface area although the reaction appeared to take place initially in the kinetically controlled regime.

  6. Chemical modification of chitosan by tetraethylenepentamine and adsorption study for anionic dye removal.

    PubMed

    Huang, Xiao-Yi; Mao, Xiao-Yun; Bu, Huai-Tian; Yu, Xiao-Yuan; Jiang, Gang-Biao; Zeng, Ming-Hua

    2011-07-15

    To utilize the contribution of introduced amino groups to the adsorption of an anionic dye (eosin Y), a batch adsorption system was applied to study the adsorption of eosin Y from aqueous solution by tetraethylenepentamine (TEPA) modified chitosan (TEPA-CS). Experiments were carried out as a function of particle size, initial pH, agitation rate, adsorbent dosage, agitation period, temperature and initial concentration of eosin Y. The Langmuir and Freundlich models were used to fit the adsorption isotherms. From the values of correlation coefficients (R2), it was observed that the experimental data fit very well to the Langmuir model, giving a maximum sorption capacity of 292.4mg/g at 298K. Kinetic studies showed that the kinetic data were well described by the pseudo-second-order kinetic model. The thermodynamic study revealed negative value of enthalpy change (ΔH°) and free energy change (ΔG°), indicating spontaneous and endothermic nature of the adsorption of eosin Y on to TEPA-CS.

  7. First-principle study of atomic oxygen and nitrogen adsorption on (1 1 1) β-cristobalite as a model of thermal protection coverage

    NASA Astrophysics Data System (ADS)

    Buchachenko, A. A.; Kroupnov, A. A.; Kovalev, V. L.

    2014-07-01

    Atomic oxygen and nitrogen adsorption on the Si site of the (1 1 1) face of ideal β-cristobalite is studied within the cluster model using the density functional approach. The M06 and B3LYP functionals are found to be the most appropriate for studying atomic adsorption on silica. The calculations show significant difference in adsorption properties with respect to previously studied (1 0 0) β-cristobalite face, but do not reveal remarkable effect of the surface relaxation.

  8. Surface study of gallium- and aluminum- doped graphenes upon adsorption of cytosine: DFT calculations

    NASA Astrophysics Data System (ADS)

    Shokuhi Rad, Ali; Zareyee, Daryoush; Peyravi, Majid; Jahanshahi, Mohsen

    2016-12-01

    The adsorption of cytosine molecule on Al- and Ga- doped graphenes is studied using first-principles density functional theory (DFT) calculations. The energetically most stable geometries of cytosine on both Al- and Ga- doped graphenes are determined and the adsorption energies are calculated. The net charge of transfer as well as local charge of doped atoms upon adsorption of cytosine are studied by natural bond orbitals (NBO) analysis. Orbital hybridizing of complexes was searched by frontier molecular orbital theory (FMO), and density of states (DOS). Depending on the side of cytosine, there are four possible sites for its adsorption on doped graphene; denoted as P1, P2, P3, and P4, respectively. The order of binding energy in the case of Al-doped graphene is found as P1 ˃ P4 ˃ P3 ˃ P2. Interestingly, the order in the case of Ga-doped graphene changes to: P4 ∼ P1˃ P3˃ P2. Both surfaces show superior adsorbent property, resulting chemisorption of cytosine, especially at P1 and P4 position configurations. The NBO charge analysis reveals that the charge transfers from Al- and Ga- doped graphene sheets to cytosine. The electronic properties of both surfaces undertake important changes after cytosine adsorption, which indicates notable change in its electrical conductivity.

  9. Adsorption of silver dimer on graphene - A DFT study

    SciTech Connect

    Kaur, Gagandeep; Gupta, Shuchi; Rani, Pooja; Dharamvir, Keya

    2014-04-24

    We performed a systematic density functional theory (DFT) study of the adsorption of silver dimer (Ag{sub 2}) on graphene using SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms) package, in the generalized gradient approximation (GGA). The adsorption energy, geometry, and charge transfer of Ag2-graphene system are calculated. The minimum energy configuration for a silver dimer is parallel to the graphene sheet with its two atoms directly above the centre of carbon-carbon bond. The negligible charge transfer between the dimer and the surface is also indicative of a weak bond. The methodology demonstrated in this paper may be applied to larger silver clusters on graphene sheet.

  10. Adsorption study of low-cost and locally available organic substances and a soil to remove pesticides from aqueous solutions

    NASA Astrophysics Data System (ADS)

    Rojas, Raquel; Morillo, José; Usero, José; Vanderlinden, Eva; El Bakouri, Hicham

    2015-01-01

    Sorption and desorption of chlorfenvinphos, chlorpyrifos, simazine and trifluralin on sunflower seed shells, rice husk, composted sewage sludge and an agricultural soil was studied. Film diffusion and sorption pointed to be related with pesticide physicochemical characteristics. Trifluralin and chlorpyrifos were the pesticides which showed the fastest sorption kinetics and the best sorption capacities when sorbed on all organic wastes. Rice husk revealed as the best adsorbent for simazine. Chlorfenvinphos showed comparable adsorption levels for all sorbents. Koc and Kf values suggested that not only the organic matter content but also the nature of the organic matter and other factors, such as physicochemical characteristics of the surface could be play a significant role in pesticide adsorption. Low desorption percentages were detected; nevertheless Kfd and H values reveal a weak and reversible adsorption. The studied organic residues can be used as an effective and alternative adsorbent for removing pesticides, because of their high adsorption capacity, being natural and economic.

  11. Stepwise adsorption of phenanthrene at the fly ash-water interface as affected by solution chemistry: experimental and modeling studies.

    PubMed

    An, Chunjiang; Huang, Guohe

    2012-11-20

    Fly ash (FA) is predominantly generated from coal-fired power plants. Contamination during disposal of FA can cause significant environmental problems. Knowledge about the interaction of FA and hydrophobic organic pollutants in the environment is very limited. This study investigated the adsorption of phenanthrene at the interface of FA and water. The performance of phenanthrene adsorption on FA and the effects of various aqueous chemistry conditions were evaluated. The adsorption isotherms exhibited an increasing trend in the adsorbed amounts of phenanthrene, while a stepwise pattern was apparent. A stepwise multisite Langmuir model was developed to simulate the stepwise adsorption process. The adsorption of phenanthrene onto FA was noted to be spontaneous at all temperatures. The thermodynamic results indicated that the adsorption was an exothermic process. The adsorption capacity gradually decreased as pH increased from 4 to 8; however, this trend became less significant when pH was changed from 8 to 10. The binding affinity of phenanthrene to FA increased after the addition of humic acid (HA). The pH variation was also responsible for the changes of phenanthrene adsorption on FA in the presence of HA. High ionic strength corresponded to low mobility of phenanthrene in the FA-water system. Results of this study can help reveal the migration patterns of organic contaminants in the FA-water system and facilitate environmental risk assessment at FA disposal sites.

  12. Mechanism of Arsenic Adsorption on Magnetite Nanoparticles from Water: Thermodynamic and Spectroscopic Studies.

    PubMed

    Liu, Cheng-Hua; Chuang, Ya-Hui; Chen, Tsan-Yao; Tian, Yuan; Li, Hui; Wang, Ming-Kuang; Zhang, Wei

    2015-07-07

    Removal of arsenic (As) from water supplies is needed to reduce As exposure through drinking water and food consumption in many regions of the world. Magnetite nanoparticles (MNPs) are promising and novel adsorbents for As removal because of their great adsorption capacity for As and easy separation. This study aimed to investigate the adsorption mechanism of arsenate, As(V), and arsenite, As(III), on MNPs by macroscopic adsorption experiments in combination with thermodynamic calculation and microspectroscopic characterization using synchrotron-radiation-based X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). Adsorption reactions are favorable endothermic processes as evidenced by increased adsorption with increasing temperatures, and high positive enthalpy change. EXAFS spectra suggested predominant formation of bidentate binuclear corner-sharing complexes ((2)C) for As(V), and tridentate hexanuclear corner-sharing ((3)C) complexes for As(III) on MNP surfaces. The macroscopic and microscopic data conclusively identified the formation of inner-sphere complexes between As and MNP surfaces. More intriguingly, XANES and XPS results revealed complex redox transformation of the adsorbed As on MNPs exposed to air: Concomitant with the oxidation of MNPs, the oxidation of As(III) and MNPs was expected, but the observed As(V) reduction was surprising because of the role played by the reactive Fe(II).

  13. Nanoscopic characterization of the water vapor-salt interfacial layer reveals a unique biphasic adsorption process

    PubMed Central

    Yang, Liu; He, Jianfeng; Shen, Yi; Li, Xiaowei; Sun, Jielin; Czajkowsky, Daniel M.; Shao, Zhifeng

    2016-01-01

    Our quantitative understanding of water adsorption onto salt surfaces under ambient conditions is presently quite poor owing to the difficulties in directly characterizing this interfacial layer under these conditions. Here we determine the thickness of the interfacial layer on NaCl at different relative humidities (RH) based on a novel application of atomic force spectroscopy and capillary condensation theory. In particular, we take advantage of the microsecond-timescale of the capillary condensation process to directly resolve the magnitude of its contribution in the tip-sample interaction, from which the interfacial water thickness is determined. Further, to correlate this thickness with salt dissolution, we also measure surface conductance under similar conditions. We find that below 30% RH, there is essentially only the deposition of water molecules onto this surface, typical of conventional adsorption onto solid surfaces. However, above 30% RH, adsorption is simultaneous with the dissolution of ions, unlike conventional adsorption, leading to a rapid increase of surface conductance. Thus, water adsorption on NaCl is an unconventional biphasic process in which the interfacial layer not only exhibits quantitative differences in thickness but also qualitative differences in composition. PMID:27527905

  14. 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.

  15. Modeling of boldine alkaloid adsorption onto pure and propyl-sulfonic acid-modified mesoporous silicas. A comparative study.

    PubMed

    Geszke-Moritz, Małgorzata; Moritz, Michał

    2016-12-01

    The present study deals with the adsorption of boldine onto pure and propyl-sulfonic acid-functionalized SBA-15, SBA-16 and mesocellular foam (MCF) materials. Siliceous adsorbents were characterized by nitrogen sorption analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared (FT-IR) spectroscopy and thermogravimetric analysis. The equilibrium adsorption data were analyzed using the Langmuir, Freundlich, Redlich-Peterson, and Temkin isotherms. Moreover, the Dubinin-Radushkevich and Dubinin-Astakhov isotherm models based on the Polanyi adsorption potential were employed. The latter was calculated using two alternative formulas including solubility-normalized (S-model) and empirical C-model. In order to find the best-fit isotherm, both linear regression and nonlinear fitting analysis were carried out. The Dubinin-Astakhov (S-model) isotherm revealed the best fit to the experimental points for adsorption of boldine onto pure mesoporous materials using both linear and nonlinear fitting analysis. Meanwhile, the process of boldine sorption onto modified silicas was described the best by the Langmuir and Temkin isotherms using linear regression and nonlinear fitting analysis, respectively. The values of adsorption energy (below 8kJ/mol) indicate the physical nature of boldine adsorption onto unmodified silicas whereas the ionic interactions seem to be the main force of alkaloid adsorption onto functionalized sorbents (energy of adsorption above 8kJ/mol).

  16. Kinetic and isotherms studies of phosphorus adsorption onto natural riparian wetland sediments: linear and non-linear methods.

    PubMed

    Zhang, Liang; Du, Chao; Du, Yun; Xu, Meng; Chen, Shijian; Liu, Hongbin

    2015-06-01

    Riparian wetlands provide critical functions for the improvement of surface water quality and storage of nutrients. Correspondingly, investigation of the adsorption characteristic and capacity of nutrients onto its sediments is benefit for utilizing and protecting the ecosystem services provided by riparian areas. The Langmuir and Freundlich isotherms and pseudo-second-order kinetic model were applied by using both linear least-squares and trial-and-error non-linear regression methods based on the batch experiments data. The results indicated that the transformations of non-linear isotherms to linear forms would affect the determination process significantly, but the non-linear regression method could prevent such errors. Non-linear Langmuir and Freundlich isotherms both fitted well with the phosphorus adsorption process (r (2) > 0.94). Moreover, the influences of temperature and ionic strength on the adsorption of phosphorus onto natural riparian wetland sediments were also studied. Higher temperatures were suitable for phosphorus uptake from aqueous solution using the present riparian wetland sediments. The adsorption capacity increased with the enhancement of ionic strength in agreement with the formation of inner-sphere complexes. The quick adsorption of phosphorus by the sediments mainly occurred within 10 min. The adsorption kinetic was well-fitted by pseudo-second-order kinetic model (r (2) > 0.99). The scanning electron microscopy (SEM) and Fourier transformation infrared (FT-IR) spectra analyses before and after phosphorus adsorption revealed the main adsorption mechanisms in the present system.

  17. Kinetic Batch Soil Adsorption Studies of 2, 4-dinitroanisole (DNAN)

    NASA Astrophysics Data System (ADS)

    Arthur, J.; Mark, N. W.; Taylor, S.; Brusseau, M. L.; Dontsova, K.

    2014-12-01

    Currently the explosive 2, 4, 6- trinitrotoluene (TNT) is used as a main ingredient in munitions; however the compound has failed to meet sensitivity requirements. The replacement compound being tested is 2, 4-dinitroanisole (DNAN). DNAN is less sensitive to shock, high temperatures, and has good detonation characteristics. However, DNAN is more soluble than TNT, which can influence transport and fate behavior and thus bioavailability and exposure potential. DNAN has been shown to have some human and environmental toxicity. The objective of this study was to investigate the environmental fate of DNAN in soil, with a specific focus on sorption processes. Batch experiments were conducted using 11 soils collected from military installations located across the United States. The soils were characterized for pH, specific surface area, electrical conductivity, cation exchange capacity, and organic carbon content. Adsorption kinetic data determined at room temperature were fitted using the first order kinetic equation. Adsorption isotherms were fitted with linear and Freundlich isotherm equations. The magnitudes of the linear adsorption coefficients ranged from 0.6 to 6 cm3/g. Results indicated that the adsorption of DNAN is strongly dependent on the amount of organic carbon present in the soil.

  18. The study of adsorption characteristics of electrospun polymer nanofibers for benzenes in water.

    PubMed

    Sun, Jing; Kang, Xue-Jun; Ma, Yu-Qin; Chen, Li-Qin; Wang, Yu; Gu, Zhong-Ze

    2011-01-01

    The adsorption properties of benzene, p-dichlorobenzene and nitrobenzene on polymer nanofibers were studied. Compared with polyacrylonitrile nanofiber, polystyrene (PS) nanofiber presented better adsorption performance. Langmuir and Freundlich adsorption models were used for the mathematical description of adsorption equilibria, and Freundlich isotherms fitted better. Kinetic studies showed that the adsorption of PS nanofiber followed pseudo first-order model. Various thermodynamic parameters such as standard free energy (delta G), enthalpy (delta H) and entropy (delta S) were calculated for predicting the adsorption nature of PS nanofiber for three benzenes, which indicated that the adsorption was spontaneous and a physical process. The regeneration efficiency maintains over 80% after five cycles of adsorption/desorption tests. It showed that PS nanofibers are promising candidates for adsorption and removal of aromatic hydrocarbons from water.

  19. Interfacial Adsorption of Antifreeze Proteins: A Neutron Reflection Study

    PubMed Central

    Xu, Hai; Perumal, Shiamalee; Zhao, Xiubo; Du, Ning; Liu, Xiang-Yang; Jia, Zongchao; Lu, Jian R.

    2008-01-01

    Interfacial adsorption from two antifreeze proteins (AFP) from ocean pout (Macrozoarces americanus, type III AFP, AFP III, or maAFP) and spruce budworm (Choristoneura fumiferana, isoform 501, or cfAFP) were studied by neutron reflection. Hydrophilic silicon oxide was used as model substrate to facilitate the solid/liquid interfacial measurement so that the structural features from AFP adsorption can be examined. All adsorbed layers from AFP III could be modeled into uniform layer distribution assuming that the protein molecules were adsorbed with their ice-binding surface in direct contact with the SiO2 substrate. The layer thickness of 32 Å was consistent with the height of the molecule in its crystalline form. With the concentration decreasing from 2 mg/ml to 0.01 mg/ml, the volume fraction of the protein packed in the monolayer decreased steadily from 0.4 to 0.1, consistent with the concentration-dependent inhibition of ice growth observed over the range. In comparison, insect cfAFP showed stronger adsorption over the same concentration range. Below 0.1 mg/ml, uniform layers were formed. But above 1 mg/ml, the adsorbed layers were characterized by a dense middle layer and two outer diffuse layers, with a total thickness around 100 Å. The structural transition indicated the responsive changes of conformational orientation to increasing surface packing density. As the higher interfacial adsorption of cfAFP was strongly correlated with the greater thermal hysteresis of spruce budworm, our results indicated the important relation between protein adsorption and antifreeze activity. PMID:18234809

  20. Kinetic study of aluminum adsorption by aluminosilicate clay minerals

    SciTech Connect

    Walker, W.J.; Cronan, C.S.; Patterson, H.H.

    1988-01-01

    The adsorption kinetics of Al/sup 3 +/ by montmorillonite, kaolinite, and vermiculite were investigated as a function of the initial Al concentration, the surface area of the clay, and H/sup +/ concentration, at 25/sup 0/, 18/sup 0/, and 10/sup 0/C. In order to minimize complicated side reactions the pH range was kept between 3.0 and 4.1. Results showed that the adsorption rate was first order with respect to both the initial Al concentration and the clay surface area. Changes in pH within this narrow range had virtually no effect on adsorption rate. This zero order reaction dependence suggested that the H/sup +/, compared to Al, has a weak affinity for the surface. The rates of adsorption decreased in the order of montmorillonite > kaolinite > vermiculite when compared on the basis of equal surface areas, but changed to kaolinite > montmorillonite > vermiculite when the clays were compared on an equal exchange capacity basis. The calculated apparent activation energies were < 32 kJ mol/sup -1/, indicating that over the temperature range of the study the adsorption process is only marginally temperature sensitive. The mechanism is governed by a simple electrostatic cation exchange involving outer sphere complexes between adsorbed Al and the clay surface. Vermiculite, may have a second reaction step governed by both electrostatic attraction and internal ion diffusion. Equilibrium constants for the formation of an adsorbed Al clay complex were also estimated and are 10/sup 5.34/, 10/sup 5.18/, and 10/sup 4.94/ for kaolinite, montmorillonite, and vermiculite, respectively, suggesting that these clays could play a significant role in controlling soil solutions Al concentrations.

  1. Adsorption of Roxarsone onto Drinking Water Treatment Residuals: Preliminary Studies

    NASA Astrophysics Data System (ADS)

    Salazar, J.; Sarkar, D.; Datta, R.; Sharma, S.

    2006-05-01

    Roxarsone (3-nitro-4-hydroxyphenyl-arsonic acid) is an organo-arsenical compound, commonly used as a feed additive in the broiler poultry industry to control coccidial intestinal parasites. Roxarsone is not toxic to the birds not only because of the low dose, and also because it most likely does not convert to toxic inorganic arsenic (As) in their systems. However, upon excretion, roxarsone may undergo transformation to inorganic As, posing a serious risk of contaminating the agricultural land and water bodies via surface runoff or leaching. The use of poultry litter as fertilizer results in As accumulation rates of up to 50 metric tons per year in agricultural lands. The immediate challenge, as identified by the various regulatory bodies in recent years is to develop an efficient, yet cost-effective and environmentally sound approach to cleaning up such As- contaminated soils. Recent studies conducted by our group have suggested that the drinking water treatment residuals (WTRs) can effectively retain As, thereby decreasing its mobility in the environment. The WTRs are byproducts of drinking water treatment processes and are typically composed of amorphous Fe/Al oxides, activated C and cationic polymers. They can be obtained free-of-cost from water treatment plants. It is well demonstrated that the environmental mobility of As is controlled by adsorption/desorption reactions onto mineral surfaces. Hence, knowledge of adsorption and desorption of As onto the WTRs is of environmental relevance. The reported study examined the adsorption and desorption characteristics of As using two types of WTRs, namely the Fe-WTRs (byproduct of Fe salt treatment), and the Al-WTRs (byproduct of Al salt treatment). All adsorption experiments were carried out in batch and As retention on the WTRs was investigated as a function of solid/solution ratio (1:5, 1:10, 1:25 and 1:50), equilibration time (10 min - 48 hr), pH (2 - 10) and initial As load (100, 500, 1000 and 2000 mg As/L). The

  2. Theoretical study of the adsorption of histidine amino acid on graphene

    NASA Astrophysics Data System (ADS)

    Rodríguez, S. J.; Makinistian, L.; Albanesi, E.

    2016-04-01

    Previous studies have demonstrated how the interactions between biomolecules and graphene play a crucial role in the characterization and functionalization of biosensors. In this paper we present a theoretical study of the adsorption of histidine on graphene using density functional theory (DFT). In order to evaluate the relevance of including the carboxyl (-COOH) and amino (-NH2) groups in the calculations, we considered i) the histidine complete (i.e., with its carboxyl and its amino groups included), and ii) the histidine’s imidazole ring alone. We calculated the density of states for the two systems before and after adsorption. Furthermore, we compared the results of three approximations of the exchange and correlation interactions: local density (LDA), the generalized gradients by Perdew, Burke and Ernzerhof (GGA-PBE), and one including van der Waals forces (DFT-D2). We found that the adsorption energy calculated by DFT-D2 is higher than the other two: Eads-DFT-D2 >E ads-LDA >E ads-GGA . We report the existence of charge transfer from graphene to the molecule when the adsorption occurs; this charge transfer turns up to be greater for the complete histidine than for the imidazole ring alone. Our results revealed that including the carboxyl and amino groups generates a shift in the states of imidazole ring towards EF .

  3. Adsorption of dyes using peat: equilibrium and kinetic studies.

    PubMed

    Sepúlveda, L; Fernández, K; Contreras, E; Palma, C

    2004-09-01

    In recent years, adsorption has been accepted as one of the most appropriate processes for decolorization of wastewaters. This paper presents experimental results on application of peat for removal of structurally diverse dyes (azo, oxazine, triphenylmethane, thiazine and others) with emphasis on relevant factors such as the adsorbate-adsorbent chemical properties and chemical interaction as well as adsorption conditions. The equilibrium experimental results were fitted to Langmuir and Freundlich isotherms to obtain the characteristic parameters of each model. According to the evaluation using the Langmuir equation, the maximum sorption capacity of basic dyes at 22 degrees C was 667 (mg g(-1)) for Basic Blue 24, 526 (mg g(-1)) for Basic Green 4 and 714 (mg g(-1)) for Basic Violet 4. On the other hand for Acid Black 1 it was only 25 (mg g(-1)). Batch kinetics studies were undertaken and the data evaluated in compliance with chemical sorption mechanisms. For all of the systems studied the pseudo-second order model provided the best correlation of the kinetic experimental data. A film-pore double resistance diffusion model for mass transfer has also been used in this study to determine the effective diffusivity, Deff, for the adsorption of basic dyes in to peat.

  4. Nitrotyrosine adsorption on defective graphene: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Majidi, R.; Karami, A. R.

    2015-06-01

    We have applied density functional theory to study adsorption of nitrotyrosine on perfect and defective graphene sheets. The graphene sheets with Stone-Wales (SW) defect, pentagon-nonagon (5-9) single vacancy, and pentagon-octagon-pentagon (5-8-5) double vacancy were considered. The calculations of adsorption energy showed that nitrotyrosine presents a more strong interaction with defective graphene rather than with perfect graphene sheet. The order of interaction strength is: SW>5-9>5-8-5>perfect graphene. It is found that the electronic properties of perfect and defective graphene are sensitive to the presence of nitrotyrosine. Hence, graphene sheets can be considered as a good sensor for detection of nitrotyrosine molecule which is observed in connection with several human disorders, such as Parkinson's and Alzheimer's disease.

  5. Equilibrium, kinetic and thermodynamic studies on the adsorption of 2-nitroaniline onto activated carbon prepared from cotton stalk fibre.

    PubMed

    Li, Kunquan; Zheng, Zheng; Huang, Xingfa; Zhao, Guohua; Feng, Jingwei; Zhang, Jibiao

    2009-07-15

    Activated carbon prepared from cotton stalk fibre has been utilized as an adsorbent for the removal of 2-nitroaniline from aqueous solutions. The influence of adsorbent mass, contact time and temperature on the adsorption was investigated by conducting a series of batch adsorption experiments. The equilibrium data at different temperatures were fitted with the Langmuir, Freundlich, Tempkin, Redlich-Peterson and Langmuir-Freundlich models. The Langmuir-Freundlich isotherm was found to best describe the experimental data. The adsorption amount increased with increasing temperature. The maximum adsorption capacity of 2-nitroaniline was found to be 383 mg/g for initial 2-nitroaniline concentration of 200mg/L at 45 degrees C. The kinetic rates were modeled by using the Lagergren-first-order, pseudo-second-order and Elovich models. The pseudo-second-order model was found to explain the adsorption kinetics most effectively. It was also found that the pore diffusion played an important role in the adsorption, and intraparticle diffusion was the rate-limiting step at the first 30 min for the temperatures of 25, 35 and 45 degrees C. FTIR and (13)C NMR study revealed that the amino and isocyanate groups present on the surface of the adsorbent were involved in chemical interaction with 2-nitroaniline. The negative change in free energy (Delta G degrees) and positive change in enthalpy (Delta H degrees) indicated that the adsorption was a spontaneous and endothermic process.

  6. Graphene oxide and adsorption of chloroform: A density functional study

    NASA Astrophysics Data System (ADS)

    Kuisma, Elena; Hansson, C. Fredrik; Lindberg, Th. Benjamin; Gillberg, Christoffer A.; Idh, Sebastian; Schröder, Elsebeth

    2016-05-01

    Chlorinated hydrocarbon compounds are of environmental concerns, since they are toxic to humans and other mammals, and are widespread, and exposure is hard to avoid. Understanding and improving methods to reduce the amount of the substances are important. We present an atomic-scale calculational study of the adsorption of chlorine-based substance chloroform (CHCl3) on graphene oxide, as a step in estimating the capacity of graphene oxide for filtering out such substances, e.g., from drinking water. The calculations are based on density functional theory, and the recently developed consistent-exchange functional for the van der Waals density-functional method is employed. We obtain values of the chloroform adsorption energy varying from roughly 0.2 to 0.4 eV per molecule. This is comparable to previously found results for chloroform adsorbed directly on clean graphene, using similar calculations. In a wet environment, like filters for drinking water, the graphene will not stay clean and will likely oxidize, and thus adsorption onto graphene oxide, rather than clean graphene, is a more relevant process to study.

  7. Equilibrium and kinetics study on hexavalent chromium adsorption onto diethylene triamine grafted glycidyl methacrylate based copolymers.

    PubMed

    Maksin, Danijela D; Nastasović, Aleksandra B; Milutinović-Nikolić, Aleksandra D; Suručić, Ljiljana T; Sandić, Zvjezdana P; Hercigonja, Radmila V; Onjia, Antonije E

    2012-03-30

    Two porous and one non-porous crosslinked poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) [abbreviated PGME] were prepared by suspension copolymerization and functionalized with diethylene triamine [abbreviated PGME-deta]. Samples were characterized by elemental analysis, mercury porosimetry, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and transmission electron microscopy. Kinetics of Cr(VI) sorption by PGME-deta were investigated in batch static experiments, in the temperature range 25-70°C. Sorption was rapid, with the uptake capacity higher than 80% after 30 min. Sorption behavior and rate-controlling mechanisms were analyzed using five kinetic models (pseudo-first order, pseudo-second order, Elovich, intraparticle diffusion and Bangham model). Kinetic studies showed that Cr(VI) adsorption adhered to the pseudo-second-order model, with definite influence of pore diffusion. Equilibrium data was tested with Langmuir, Freundlich and Tempkin adsorption isotherm models. Langmuir model was the most suitable indicating homogeneous distribution of active sites on PGME-deta and monolayer sorption. The maximum adsorption capacity from the Langmuir model, Q(max), at pH 1.8 and 25°C was 143 mg g(-1) for PGME2-deta (sample with the highest amino group concentration) while at 70°C Q(max) reached the high value of 198 mg g(-1). Thermodynamic parameters revealed spontaneous and endothermic nature of Cr(VI) adsorption onto PGME-deta.

  8. Phosphate adsorption from wastewater using zirconium (IV) hydroxide: Kinetics, thermodynamics and membrane filtration adsorption hybrid system studies.

    PubMed

    Johir, M A H; Pradhan, M; Loganathan, P; Kandasamy, J; Vigneswaran, S

    2016-02-01

    Excessive phosphate in wastewater should be removed to control eutrophication of water bodies. The potential of employing amorphous zirconium (Zr) hydroxide to remove phosphate from synthetic wastewater was studied in batch adsorption experiments and in a submerged membrane filtration adsorption hybrid (MFAH) reactor. The adsorption data satisfactorily fitted to Langmuir, pseudo-first order and pseudo-second order models. Langmuir adsorption maxima at 22 °C and pHs of 4.0, 7.1, and 10.0 were 30.40, 18.50, and 19.60 mg P/g, respectively. At pH 7.1 and temperatures of 40 °C and 60 °C, they were 43.80 and 54.60 mg P/g, respectively. The thermodynamic parameters, ΔG° and ΔS° were negative and ΔH° was positive. FTIR, zeta potential and competitive phosphate, sulphate and nitrate adsorption data showed that the mechanism of phosphate adsorption was inner-sphere complexation. In the submerged MFAH reactor experiment, when Zr hydroxide was added at doses of 1-5 g/L once only at the start of the experiment, the removal of phosphate from 3 L of wastewater containing 10 mg P/L declined after 5 h of operation. However, when Zr hydroxide was repeatedly added at 5 g/L dose every 24 h, satisfactory removal of phosphate was maintained for 3 days.

  9. Study on the adsorption feature of rutin aqueous solution on macroporous adsorption resins.

    PubMed

    Chen, Zhenbin; Zhang, Anjie; Li, Jie; Dong, Fang; Di, Duolong; Wu, Youzhi

    2010-04-15

    The adsorption feature of different kinds of polystyrene-based macroporous adsorption resins (MARs) was investigated systemically at constant temperature employing Rutin as the adsorbate. Different from traditional adsorption patterns, Langmuir and Freundlich adsorption, and the results showed interesting aspects: (1) With the increase of the volume of the initial solution, the adsorption capacity increased to the maximum, and then decreased gradually. (2) Experimental results clearly verified the opinion that the adsorption process of MARs could be divided into three stages-macropores, mesopores, and micropores-by the capillary effects occurring at the two intersections, and the adsorption feature for every stage could be described well by the fourth type of Brunauer model. (3) The model that the inductive effect transmitted to the first layer could not interpret our experimental results reasonably. Thus, the model that the inductive effect passed on to a higher layer was proposed by investigating regression of the experimental results and the conclusion that the inductive effect transmitted to the third layer was drawn.

  10. Antibody adsorption on the surface of water studied by neutron reflection.

    PubMed

    Smith, Charles; Li, Zongyi; Holman, Robert; Pan, Fang; Campbell, Richard A; Campana, Mario; Li, Peixun; Webster, John R P; Bishop, Steven; Narwal, Rojaramani; Uddin, Shahid; van der Walle, Christopher F; Lu, Jian R

    2017-04-01

    Surface and interfacial adsorption of antibody molecules could cause structural unfolding and desorbed molecules could trigger solution aggregation, resulting in the compromise of physical stability. Although antibody adsorption is important and its relevance to many mechanistic processes has been proposed, few techniques can offer direct structural information about antibody adsorption under different conditions. The main aim of this study was to demonstrate the power of neutron reflection to unravel the amount and structural conformation of the adsorbed antibody layers at the air/water interface with and without surfactant, using a monoclonal antibody 'COE-3' as the model. By selecting isotopic contrasts from different ratios of H2O and D2O, the adsorbed amount, thickness and extent of the immersion of the antibody layer could be determined unambiguously. Upon mixing with the commonly-used non-ionic surfactant Polysorbate 80 (Tween 80), the surfactant in the mixed layer could be distinguished from antibody by using both hydrogenated and deuterated surfactants. Neutron reflection measurements from the co-adsorbed layers in null reflecting water revealed that, although the surfactant started to remove antibody from the surface at 1/100 critical micelle concentration (CMC) of the surfactant, complete removal was not achieved until above 1/10 CMC. The neutron study also revealed that antibody molecules retained their globular structure when either adsorbed by themselves or co-adsorbed with the surfactant under the conditions studied.

  11. Adsorption of Zn2+ ions onto NaA and NaX zeolites: kinetic, equilibrium and thermodynamic studies.

    PubMed

    Nibou, D; Mekatel, H; Amokrane, S; Barkat, M; Trari, M

    2010-01-15

    The adsorption of Zn(2+) onto NaA and NaX zeolites was investigated. The samples were synthesized according to a hydrothermal crystallization using aluminium isopropoxide (Al[OCH(CH(3))(2)](3)) as a new alumina source. The effects of pH, initial concentration, solid/liquid ratio and temperature were studied in batch experiments. The Freundlich and the Langmuir models were applied and the adsorption equilibrium followed Langmuir adsorption isotherm. The uptake distribution coefficient (K(d)) indicated that the Zn(2+) removal was the highest at minimum concentration. Thermodynamic parameters were calculated. The negative values of standard enthalpy of adsorption revealed the exothermic nature of the adsorption process whereas the negative activation entropies reflected that no significant change occurs in the internal structure of the zeolites solid matrix during the sorption of Zn(2+). The negative values of Gibbs free energy were indicative of the spontaneity of the adsorption process. Analysis of the kinetic and rate data revealed that the pseudo second-order sorption mechanism is predominant and the intra particle diffusion was the determining step for the sorption of zinc ions. The obtained optimal parameters have been applied to wastewater from the industrial zone (Algeria) in order to remove the contained zinc effluents.

  12. Case Studies Reveal Camper Growth.

    ERIC Educational Resources Information Center

    Brannan, Steve; Fullerton, Ann

    1999-01-01

    Case studies in the National Camp Evaluation Project and National Inclusive Camp Practices project used interviews with counselors and parents about camper's growth to yield qualitative data for camp program evaluation. The importance, methods, and benefits of case studies are described. Sidebars give examples of comments on perceived camper…

  13. Theoretical study of adsorption of tabun on calcium oxide clusters

    NASA Astrophysics Data System (ADS)

    Michalkova, A.; Paukku, Y.; Majumdar, D.; Leszczynski, J.

    2007-04-01

    Interactions of tabun (GA) with non-hydroxylated and hydroxylated CaO clusters have been studied using density functional (DFT) and Møller-Plesset second order perturbation (MP2) levels of theory. The nature of interactions has been further investigated from the topology of charge distribution (using Atoms in Molecules formalism) and molecular electrostatic potential (MEP) surfaces. These adsorption studies indicate that GA adsorbs strongly on the non-hydroxylated CaO cluster through its P dbnd O bond, while interactions of GA on the hydroxylated cluster are weak. These model studies could thus be useful to characterize inorganic oxides for efficient detection and disposal of GA.

  14. A DFT study of volatile organic compounds adsorption on transition metal deposited graphene

    NASA Astrophysics Data System (ADS)

    Kunaseth, Manaschai; Poldorn, Preeyaporn; Junkeaw, Anchalee; Meeprasert, Jittima; Rungnim, Chompoonut; Namuangruk, Supawadee; Kungwan, Nawee; Inntam, Chan; Jungsuttiwong, Siriporn

    2017-02-01

    Recently, elevated global emission of volatile organic compounds (VOCs) was associated to the acceleration and increasing severity of climate change worldwide. In this work, we investigated the performance of VOCs removal via modified carbon-based adsorbent using density functional theory. Here, four transition metals (TMs) including Pd, Pt, Ag, and Au were deposited onto single-vacancy defective graphene (SDG) surface to increase the adsorption efficiency. Five prototypical VOCs including benzene, furan, pyrrole, pyridine, and thiophene were used to study the adsorption capability of metal-deposited graphene adsorbent. Calculation results revealed that Pd, Pt, Au, and Ag atoms and nanoclusters bind strongly onto the SDG surface. In this study, benzene, furan and pyrrole bind in the π-interaction mode using delocalized π-electron in aromatic ring, while pyridine and thiophene favor X- interaction mode, donating lone pair electron from heteroatom. In terms of adsorption, pyridine VOC adsorption strengths to the TM-cluster doped SDG surfaces are Pt4 (-2.11 eV) > Pd4 (-2.05 eV) > Ag4 (-1.53 eV) > Au4 (-1.87 eV). Our findings indicate that TM-doped SDG is a suitable adsorbent material for VOC removal. In addition, partial density of states analysis suggests that benzene, furan, and pyrrole interactions with TM cluster are based on p-orbitals of carbon atoms, while pyridine and thiophene interactions are facilitated by hybridized sp2-orbitals of heteroatoms. This work provides a key insight into the fundamentals of VOCs adsorption on carbon-based adsorbent.

  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. A quantum chemistry study of curvature effects on boron nitride nanotubes/nanosheets for gas adsorption.

    PubMed

    Sha, Haoyan; Faller, Roland

    2016-07-20

    Quantum chemistry calculations were performed to investigate the effect of the surface curvature of a Boron Nitride (BN) nanotube/nanosheet on gas adsorption. Curved boron nitride layers with different curvatures interacting with a number of different gases including noble gases, oxygen, and water on both their convex and concave sides of the surface were studied using density functional theory (DFT) with a high level dispersion corrected functional. Potential energy surfaces of the gas molecules interacting with the selected BN surfaces were investigated. In addition, the charge distribution and electrostatic potential contour of the selected BN surfaces are discussed. The results reveal how the curvature of the BN surfaces affects gas adsorption. In particular, small curvatures lead to a slight difference in the physisorption energy, while large curvatures present distinct potential energy surfaces, especially for the short-range repulsion.

  17. Electrochemical study on the adsorption of carbon oxides and oxidation of their adsorption products on platinum group metals and alloys.

    PubMed

    Siwek, Hanna; Lukaszewski, Mariusz; Czerwiński, Andrzej

    2008-07-07

    CO(2) reduction and CO adsorption on noble metals (Pt, Rh, Pd) and their alloys (Pt-Rh, Pd-Pt, Pd-Rh, Pd-Pt-Rh) prepared as thin rough deposits have been studied by chronoamperometry (CA), cyclic voltammetry (CV) and the electrochemical quartz crystal microbalance (EQCM). The influence of alloy surface composition on the values of surface coverage, eps (electron per site) and potential of the oxidation of CO(2) reduction and CO adsorption products is shown. The oxidation of the adsorbate on Pt-Rh alloys proceeds more easily (at lower potentials) than on pure metals. On the other hand, in the case of Pd-Pt and Pd-Rh alloys the adsorbate oxidation is more difficult and requires higher potentials than on Pt or Rh. The analysis of the EQCM signal is presented for the case of adsorption and oxidation of carbon oxide adsorption products on the electrodes studied. The comparison of adsorption parameters and the EQCM response obtained for platinum group metals and alloys leads to the conclusion that reduced CO(2) cannot be totally identified with adsorbed CO.

  18. Equilibrium, kinetic and thermodynamic studies on the adsorption of phenol onto graphene

    SciTech Connect

    Li, Yanhui; Du, Qiuju; Liu, Tonghao; Sun, Jiankun; Jiao, Yuqin; Xia, Yanzhi; Xia, Linhua; Wang, Zonghua; Zhang, Wei; Wang, Kunlin; Zhu, Hongwei; Wu, Dehai

    2012-08-15

    Graphical abstract: The effect of temperature on phenol adsorbed by graphene shows that the equilibrium adsorption capacity of phenol increases with the increase in temperature from 285 to 333 K. Increasing adsorption capacities with temperature indicates that the adsorption of phenol is controlled by an endothermic reaction. Highlights: ► The graphene has high phenol adsorption capacity. ► The graphene has a high specific surface area of 305 m{sup 2}/g. ► The adsorption capacity is high at acidic pH range. ► The graphene has rapid phenol adsorption rate. ► Phenol adsorption is a spontaneous and endothermic process. -- Abstract: Graphene, a new member of carbon family, has been prepared, characterized and used as adsorbent to remove phenol from aqueous solution. The effect parameters including pH, dosage, contact time, and temperature on the adsorption properties of phenol onto graphene were investigated. The results showed that the maximum adsorption capacity can reach 28.26 mg/g at the conditions of initial phenol concentration of 50 mg/L, pH 6.3 and 285 K. Adsorption data were well described by both Freundlich and Langmuir models. The kinetic study illustrated that the adsorption of phenol onto graphene fit the pseudo second-order model. The thermodynamic parameters indicated that the adsorption of phenol onto graphene was endothermic and spontaneous.

  19. First-principles study of cesium adsorption to weathered micaceous clay minerals

    NASA Astrophysics Data System (ADS)

    Okumura, Masahiko; Nakamura, Hiroki; Machida, Masahiko

    2014-05-01

    A large amount of radioactive nuclides was produced into environment due to the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Residents near FDNPP were suffering from radioactive cesium and then evacuated, because which has long half-life and is retained by surface soil for long time. The Japanese government has been decontaminating the cesium by removing the surface soil in order to return them to their home. This decontamination method is very effective, but which produces huge amount of waste soil. This becomes another big problem in Fukushima, because it is not easy to find large storage sites. Then effective and economical methods to reduce the volume of the waste soil are needed. However, it has not been invented yet. One of the reasons is lack of knowledge about microscopic process of adsorption/desorption of cesium to/from soil. It is known that weathered micaceous clay minerals play crucial role on adsorption and retention of cesium. They are expected to have special sorption sites, called frayed edge sites (FESs), which adsorb cesium selectively and irreversibly. Properties of FES have been intensely investigated by experiments. But microscopic details of the adsorption process on FES are still unclear. Because direct observation of the process with current experimental techniques is quite difficult. We investigated the adsorption of cesium to FES in muscovite, which is a typical micaceous clay mineral, via first-principles calculations (density functional theory). We made a minimal model of FES and evaluate the energy difference before and after cesium adsorption to FES. This is the first numerical modeling of FES. It was shown that FES does adsorb cesium if the weathering of muscovite has been weathered. In addition, we revealed the mechanism of cesium adsorption to FES, which is competition between ion radius of cesium and the degree of weathering. I plan to discuss volume reduction of the waste soil based on our result. Reference M. Okumura

  20. Simultaneous adsorption of Cd2+ and phenol on modified N-doped carbon nanotubes: experimental and DFT studies.

    PubMed

    Diaz-Flores, Paola E; López-Urías, Florentino; Terrones, Mauricio; Rangel-Mendez, J Rene

    2009-06-15

    Carbon nanotubes are novel materials that have been investigated for diverse applications, but only a few studies have been focused on environmental issues. In this work, we report on the efficient adsorption of phenol and cadmium ions on N-doped carbon nanotubes (CNx), which have been modified in air at different temperatures. The pristine and modified CNx nanotubes were characterized by SEM, TGA, elemental analysis and their surface areas were also determined. The adsorption experiments of toxic pollutants were carried out in batch reactors at 25 degrees C. The characterization of modified CNx by these techniques showed an increase in oxygen content and surface area in comparison with the pristine CNx tubes. The individual adsorption capacity was 0.10 and 0.07 mmol/g for phenol and Cd(2+), respectively. The experimental data of the competitive adsorption of phenol and Cd(2+) revealed that the cadmium removal was favored as the phenol concentration increased, whereas the phenol adsorption capacity was slightly affected at any cadmium concentration. These results suggest that modified CNx tubes have a great potential in environmental applications as adsorbents of organic and inorganic compounds in aqueous phases. In addition, first-principles calculations were carried out in order to elucidate the mechanism of Cd(2+) adsorption on CNx.

  1. Diblock copolymer adsorption onto a solid surface as revealed by evanescent wave ellipsometry

    SciTech Connect

    Kim, M.W. ); Russell, T.P. . Almaden Research Center); Moses, T.; Chen, W.; Shen, Y.R. . Center for Advanced Materials Univ. of California, Berkeley, CA . Dept. of Physics)

    1994-12-05

    The interfacial behavior of diblock copolymers play an important role in many practical applications, for example, polymer compatibilization, adhesion, and colloid stabilization. There has been considerable theoretical and experimental effort to understand the adsorption behavior of diblock copolymers from a solution onto a solid surface. Recent neutron reflectivity measurements on solutions of symmetric diblock copolymers of polystyrene and poly(methyl methacrylate), denoted P(S-b-MMA), near a quartz wall have shown that the PMMA segments adsorb preferentially onto the quartz forming a dense layer. However, the segmental concentration of polystyrene (PS) was too low to be observable. Evanescent wave ellipsometry, EWE, on the other hand, allows one to determine the density of molecules adsorbed onto a surface without labeling the segments with deuterium. Here, EWE results on P(S-b-MMA) adsorbed onto a solid substrate are presented as a function of molecular weight. It is shown that the adsorbed amount of copolymer is maximized for a particular molecular weight. This result contradicts theoretical predictions, and a possible origin of this discrepancy is provided.

  2. Adsorptive desulphurization study of liquid fuels using Tin (Sn) impregnated activated charcoal.

    PubMed

    Shah, Syed Sikandar; Ahmad, Imtiaz; Ahmad, Waqas

    2016-03-05

    Keeping in view the growing concern regarding desulphurization of petroleum products, the present study was under taken to investigate the efficiency of tin impregnated activated charcoal (Sn-AC) as a potential adsorbent for the desulphurization of model and real commercial straight run kerosene and diesel oil samples. The adsorbent Sn-AC was prepared by wet impregnation process in the laboratory and characterized by SEM, EDX and surface area analysis. Initial experiments were carried out using model oil, which was prepared by dissolving dibenzothiophene (DBT) in cyclohexane, the optimum conditions for desulfurization were found to be, 60°C temperature, 1h contact time and adsorbent dosage of 0.8g, under which about 99.4% of DBT removal was attained. Under optimized conditions the desulfurization of real oil i.e., kerosene and diesel oil was also investigated. Kinetic studies revealed that DBT adsorption followed pseudo second order kinetics and the data best fits in the Langmuir adsorption isotherm as compared to Freundlich adsorption isotherm model. The adsorbent could be easily regenerated simply by washing with toluene for a multiple cycles and reused without losing its efficiency.

  3. Interactions between sparfloxacin and antacids - dissolution and adsorption studies.

    PubMed

    Hussain, Fida; Arayne, M Saeed; Sultana, Najma

    2006-01-01

    Sparfloxacin is a broad-spectrum oral fluoroquinolone antimicrobial agent with a long elimination half-life, extensively used against both Gram-positive as well as Gram-negative microorganism. Concurrent administration of antacids and sparfloxacin decreases the gastrointestinal absorption of sparfloxacin and therapeutic failure may result. The present study was designed to evaluate the influence of some antacids on the availability of sparfloxacin. The release of sparfloxacin from tablets in the presence of antacids like sodium bicarbonate, calcium hydroxide, calcium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium carbonate, magnesium trisilicate and magaldrate has been studied on BP 2003 dissolution test apparatus. These studies were carried out in simulated gastric and intestinal juices for three hours at 37 degrees C. The results confirmed that the dissolution rate of tablets was markedly retarded in the presence all of antacids studied, whereas magaldrate and calcium carbonate exhibited relatively higher adsorption capacities in simulated gastric juice and magnesium trisilicate and calcium hydroxide in simulated intestinal juice.

  4. Interactions between ciprofloxacin and antacids--dissolution and adsorption studies.

    PubMed

    Arayne, M Saeed; Sultana, Najma; Hussain, Fida

    2005-01-01

    Ciprofloxacin is a fluorinated quinolone antibacterial agent extensively used against both Gram-positive and Gram-negative microorganisms. In certain polytherapy programs, ciprofloxacin can be administered with some antacids that could modify its dissolution rate and reduce its absorption leading to therapeutic failure. The aim of this study was to evaluate the influence of some antacids on the availability of ciprofloxacin. The release of ciprofloxacin from tablets in the presence of antacids, such as sodium bicarbonate, calcium hydroxide, calcium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium carbonate, magnesium trisilicate and magaldrate was studied on BP 2002 dissolution test apparatus. These studies were carried out in simulated gastric and intestinal juices for 3 hours at 37 degrees C. The results confirmed that the dissolution rate of tablets was markedly retarded in the presence of all the antacids studied. Magaldrate and calcium carbonate in simulated gastric juice exhibited relatively higher adsorption capacities, as did magnesium trisilicate and calcium hydroxide in simulated intestinal juice.

  5. Study of the adsorption of aromatic hydrocarbons by marine sediments. Final report

    SciTech Connect

    Henrichs, S.M.; Luoma, M.; Smith, S.

    1997-08-01

    Three aromatic hydrocarbons--benzene, naphthalene, and phenanthrene--were rapidly and strongly adsorbed by intertidal sediments from Jakolof Bay, lower Cook Inlet. Adsorption of phenanthrene was more than twice that of naphthalene and benzene. Adsorption was not completely, rapidly reversible by suspension of the sediment in clean seawater. Longer adsorption reaction times led to decreased desorption, except for benzene. All sites for adsorption on the sediment surface appeared to be equivalent, and availability of adsorption sites did not limit adsorption over the concentration range studied. Adsorption coefficients for phenanthrene varied among sediment samples by as much as a factor of 3. This variability was not correlated with sediment organic carbon content, indicating that organic matter was not solely responsible for the adsorption properties of these sediments. The bioavailability of phenanthrene was decreased by adsorption to sediment. Combined with the finding that adsorption is not completely reversible, these results indicate that adsorption could contribute to the persistence of aromatic hydrocarbons in lower Cook Inlet sediments.

  6. MALDI-TOF mass spectrometry imaging reveals molecular level changes in ultrahigh molecular weight polyethylene joint implants in correlation with lipid adsorption.

    PubMed

    Fröhlich, Sophie M; Archodoulaki, Vasiliki-Maria; Allmaier, Günter; Marchetti-Deschmann, Martina

    2014-10-07

    Ultrahigh molecular weight polyethylene (PE-UHMW), a material with high biocompatibility and excellent mechanical properties, is among the most commonly used materials for acetabular cup replacement in artificial joint systems. It is assumed that the interaction with synovial fluid in the biocompartment leads to significant changes relevant to material failure. In addition to hyaluronic acid, lipids are particularly relevant for lubrication in an articulating process. This study investigates synovial lipid adsorption on two different PE-UHMW materials (GUR-1050 and vitamin E-doped) in an in vitro model system by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry imaging (MSI). Lipids were identified by high performance thin layer chromatography (HP-TLC) and tandem mass spectrometry (MS/MS) analysis, with an analytical focus on phospholipids and cholesterol, both being species of high importance for lubrication. Scanning electron microscopy (SEM) analysis was applied in the study to correlate molecular information with PE-UHMW material qualities. It is demonstrated that lipid adsorption preferentially occurs in rough or oxidized polymer regions. Polymer modifications were colocalized with adsorbed lipids and found with high density in regions identified by SEM. Explanted, the in vivo polymer material showed comparable and even more obvious polymer damage and lipid adsorption when compared with the static in vitro model. A three-dimensional reconstruction of MSI data from consecutive PE-UHMW slices reveals detailed information about the diffusion process of lipids in the acetabular cup and provides, for the first time, a promising starting point for future studies correlating molecular information with commonly used techniques for material analysis (e.g., Fourier-transform infrared spectroscopy, nanoindentation).

  7. Batch study of liquid-phase adsorption of methylene blue using cedar sawdust and crushed brick.

    PubMed

    Hamdaoui, Oualid

    2006-07-31

    This paper presents a study on the batch adsorption of basic dye, methylene blue, from aqueous solution (40 mg L(-1)) onto cedar sawdust and crushed brick in order to explore their potential use as low-cost adsorbents for wastewater dye removal. Adsorption isotherms were determined at 20 degrees C and the experimental data obtained were modelled with the Langmuir, Freundlich, Elovich and Temkin isotherm equations. Adsorption kinetic data determined at a temperature of 20 degrees C were modelled using the pseudo-first and pseudo-second-order kinetic equations, liquid-film mass transfer and intra-particle diffusion models. By considering the experimental results and adsorption models applied in this study, it can be concluded that equilibrium data were represented well by a Langmuir isotherm equation with maximum adsorption capacities of 142.36 and 96.61 mg g(-1) for cedar sawdust and crushed brick, respectively. The second-order model best describes adsorption kinetic data. Analysis of adsorption kinetic results indicated that both film- and particle-diffusion are effective adsorption mechanisms. The Influence of temperature and pH of the solution on adsorption process were also studied. The extent of the dye removal decreased with increasing the solution temperature and optimum pH value for dye adsorption was observed at pH 7 for both adsorbents. The results indicate that cedar sawdust and crushed brick can be attractive options for dye removal from dilute industrial effluents.

  8. Degradation and adsorption characteristics of PHB depolymerase as revealed by kinetics of mutant enzymes with amino acid substitution in substrate-binding domain.

    PubMed

    Hiraishi, Tomohiro; Komiya, Naoya; Matsumoto, Nobuhiko; Abe, Hideki; Fujita, Masahiro; Maeda, Mizuo

    2010-01-11

    Extracelluar Poly[(R)-3-hydroxybutyrate] (PHB) depolymerase (PhaZ(RpiT1)) from Ralstonia pickettii T1 adsorbs to PHB surface via its substrate-binding domain (SBD) to enhance PHB degradation. Our previous study combining PCR random mutagenesis with the determination of PHB degradation levels of mutant enzymes suggested that Ser, Tyr, Val, Ala, and Leu residues in SBD are probably involved in the enzymatic adsorption to and degradation of PHB. In the present study, the effects of mutations at Leu441, Tyr443, and Ser445 on PHB degradation were investigated because these residues were predicted to form a beta-sheet structure and orient in the same direction to interact possibly directly with the PHB surface. Purified L441H, Y443H, and S445C mutant enzymes were prepared, and their CD spectra and hydrolytic activities for water-soluble substrates were found to be identical to those of wild-type enzyme, indicating that these mutations have no influence on their structures and their ability to cleave the ester bond. In contrast, the PHB-degrading activity of these mutants differed from that of the wild type: L441H and Y443H enzymes had lower PHB-degrading activity than their wild-type counterpart, whereas S445C had higher activity. Kinetic analysis of PHB degradation by the mutants suggested that the hydrophobic residues at these positions are important for the enzyme adsorption to the PHB surface, and such substitutions as Y443H and S445C may more effectively disrupt the PHB surface to enhance the hydrolysis of PHB polymer chains than the wild-type enzyme. Surface plasmon resonance (SPR) analysis revealed that the three substitutions mentioned above altered the association phase rather than the dissociation phase in the enzyme adsorption to the polymer surface.

  9. Adsorptive removal of phthalate ester (Di-ethyl phthalate) from aqueous phase by activated carbon: a kinetic study.

    PubMed

    Venkata Mohan, S; Shailaja, S; Rama Krishna, M; Sarma, P N

    2007-07-19

    Adsorptive studies were carried out on Di-ethyl phthalate (DEP) removal from aqueous phase onto activated carbon. Batch sorption studies were performed and the results revealed that activated carbon demonstrated ability to adsorb DEP. Influence of varying experimental conditions such as DEP concentration, pH of aqueous solution, and dosage of adsorbent were investigated on the adsorption process. Sorption interaction of DEP onto activated carbon obeyed the pseudo second order rate equation. Experimental data showed good fit with both the Langmuir and Freundlich adsorption isotherm models. DEP sorption was found to be dependent on the aqueous phase pH and the uptake was observed to be greater at acidic pH.

  10. A computational study of surface adsorption and desorption

    NASA Astrophysics Data System (ADS)

    Wang, Lin-Lin

    In this work, the phenomena of surface adsorption and desorption have been studied by various computational methods. Large-scale density functional calculations with the local density approximation have been applied to investigate the energetics and electronic structure of a C60 monolayer adsorbed on noble metal (111) surfaces. In all cases, the most energetically preferred adsorption configuration corresponds to a hexagon of C60 adsorbing on an hcp site. A small amount of electronic charge transfer of 0.8, 0.5 and 0.2 electrons per molecule from the Cu(111), Ag(111) and Au(111) surfaces to C60 has been found. We also find that the work function decreases by 0.1 eV on Cu(111) surface, increases by 0.1 eV on Ag(111) surface and decreases by 0.6 eV on Au(111) surface upon the adsorption of a C60 monolayer. The puzzling work function change is well explained by a close examination of the surface dipole formation due to electron density redistribution in the interface region. Potential sputtering on the lithium fluoride (LiF) (100) surface by slow highly charged ions has been studied via molecular dynamics (MD) simulations. A model that is different from the conventional MD is formulated to allow electrons to be in the ground state as well as the low-lying excited states. The interatomic potential energy functions are obtained by a high-level quantum chemistry method. The results from MD simulations demonstrate that the so-called defect-mediated sputtering model provides a qualitatively correct picture. The simulations provide quantitative descriptions in which neutral particles dominate the sputtering yield by 99%, in agreement with experiments. An embedding atom-jellium model has been formulated into a multiscale simulation scheme to treat only the top metal surface layers in atomistic pseudopotential and the rest of the surface in a jellium model. The calculated work functions of Al and Cu clean surfaces agree well with the all-atomistic calculations. The multiscale

  11. A study of metal ion adsorption at low suspended-solid concentrations

    USGS Publications Warehouse

    Chang, Cecily C.Y.; Davis, J.A.; Kuwabara, J.S.

    1987-01-01

    A procedure for conducting adsorption studies at low suspended solid concentrations in natural waters (<50 mg l-1) is described. Methodological complications previously associated with such experiments have been overcome. Adsorption of zinc ion onto synthetic colloidal titania (TiO2) was studied as a function of pH, supporting electrolyte (NaCl) concentration (0??1-0??002 m) and particle concentration (2-50 mg l-1). The lack of success of the Davis Leckie site bonding model in describing Zn(II) adsorption emphasizes the need for further studies of adsorption at low suspended-solid concentrations. ?? 1987.

  12. A computational study of carbon dioxide adsorption on solid boron.

    PubMed

    Sun, Qiao; Wang, Meng; Li, Zhen; Du, Aijun; Searles, Debra J

    2014-07-07

    Capturing and sequestering carbon dioxide (CO2) can provide a route to partial mitigation of climate change associated with anthropogenic CO2 emissions. Here we report a comprehensive theoretical study of CO2 adsorption on two phases of boron, α-B12 and γ-B28. The theoretical results demonstrate that the electron deficient boron materials, such as α-B12 and γ-B28, can bond strongly with CO2 due to Lewis acid-base interactions because the electron density is higher on their surfaces. In order to evaluate the capacity of these boron materials for CO2 capture, we also performed calculations with various degrees of CO2 coverage. The computational results indicate CO2 capture on the boron phases is a kinetically and thermodynamically feasible process, and therefore from this perspective these boron materials are predicted to be good candidates for CO2 capture.

  13. XPS study of protein adsorption onto nanocrystalline aluminosilicate microparticles

    NASA Astrophysics Data System (ADS)

    Vanea, E.; Simon, V.

    2011-01-01

    X-ray photoelectron spectroscopy (XPS) was used to study the interaction of two different sized proteins, bovine serum albumin (BSA) and fibrinogen, with an aluminosilicate system containing yttrium and iron that is a potential biomaterial. Serum albumin and fibrinogen are two major plasma proteins and the most relevant proteins adsorbed on the surface of biomaterials in blood contact. The aluminosilicate samples were incubated for several exposure times, up to 24 h, in simulated body fluid enriched with BSA, and in buffered fibrinogen solution. Time dependence of proteins adsorption onto surface of the investigated samples is reflected by the evolution of the new N 1s photoelectron peak and by the modification of C 1s core-level spectra recorded from the samples immersed in protein solution.

  14. Study of Methylene Blue adsorption on keratin nanofibrous membranes.

    PubMed

    Aluigi, A; Rombaldoni, F; Tonetti, C; Jannoke, L

    2014-03-15

    In this work, keratin nanofibrous membranes (mean diameter of about 220nm) were prepared by electrospinning and tested as adsorbents for Methylene Blue through batch adsorption tests. The adsorption capacity of the membranes was evaluated as a function of initial dye concentration, pH, adsorbent dosage, time and temperature. The adsorption capacity increased with increasing the initial dye concentration and pH, while it decreased with increasing the adsorbent dosage and temperature, indicating an exothermic process. The adsorption results indicated that the Langmuir isotherm fitted the experimental data better than the Freundlich and Temkin isotherm models. A mean free energy evaluated through the Dubinin-Radushkevich model of about 16kJmol(-1), indicated a chemisorption process which occurred by ion exchange. The kinetic data were found to fit the pseudo-second-order model better than the pseudo-first-order model. The obtained results suggest that keratin nanofibrous membranes could be promising candidates as dye adsorption filters.

  15. Comparison of batch, stirred flow chamber, and column experiments to study adsorption, desorption and transport of carbofuran within two acidic soils.

    PubMed

    Bermúdez-Couso, Alipio; Fernández-Calviño, David; Rodríguez-Salgado, Isabel; Nóvoa-Muñoz, Juan Carlos; Arias-Estévez, Manuel

    2012-06-01

    Different methods (batch, column and stirred flow chamber experiments) used for adsorption and desorption of carbofuran studies were compared. All tested methods showed that the carbofuran adsorption was higher in the soil with the higher organic matter content, whereas the opposite behaviour was observed for the percentage of carbofuran desorbed. However, different methods have revealed some discrepancies in carbofuran adsorption/desorption kinetics. Although batch method showed interesting data on equilibrium experiments, such as a low heterogeneity for the carbofuran adsorption sites independent of soil organic matter content, it had some disadvantages for carbofuran adsorption/desorption kinetic studies. The disadvantages were related with the excessive limitations of this method on kinetics, i.e., no difference could be detected between different soils. However, with column and stirred flow chamber methods the carbofuran adsorption/desorption kinetics of different soils could be compared. Moreover, the absolute values of carbofuran adsorption/desorption and its rate were higher in the stirred flow chamber than in the batch and column experiments. Using stirred flow chamber experiments the carbofuran desorption was significantly faster than its adsorption, whereas carbofuran using column experiments they were similar. These discrepancies should be considered when the results obtained only with one method is discussed.

  16. Study on the adsorption of DNA on the layered double hydroxides (LDHs).

    PubMed

    Li, Bin; Wu, Pingxiao; Ruan, Bo; Liu, Paiyu; Zhu, Nengwu

    2014-01-01

    Four kinds of layered double hydroxides (LDHs) were prepared by chemical coprecipitation method and used as DNA adsorbents. Multiple characterization tools such as power X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Standard electronic modules (SEM) were employed to characterize the LDHs. By examining the effect of initial concentration, solution pH, adsorption experiments were carried out to investigate the adsorption capacities of LDHs for DNA. The results revealed that the LDHs with Mg/Al=3 had higher ability on adsorbing the DNA and were not affected by pH values. The LDHs exhibited excellent adsorption properties and completely adsorbed DNA within 2h. The adsorption equilibrium data were fitted to the Langmuir and Freundlich models, showing that the Langmuir model which represented monolayer adsorption had better correlation with the adsorption linear equation. In addition, Circular dichroism (CD) spectrum, UV-vis spectorscopy and agarose gel electrophoresis revealed the integrity of DNA structure, suggesting that there had no damage on the DNA structure during the adsorption process.

  17. Study on the adsorption of DNA on the layered double hydroxides (LDHs)

    NASA Astrophysics Data System (ADS)

    Li, Bin; Wu, Pingxiao; Ruan, Bo; Liu, Paiyu; Zhu, Nengwu

    2014-03-01

    Four kinds of layered double hydroxides (LDHs) were prepared by chemical coprecipitation method and used as DNA adsorbents. Multiple characterization tools such as power X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Standard electronic modules (SEM) were employed to characterize the LDHs. By examining the effect of initial concentration, solution pH, adsorption experiments were carried out to investigate the adsorption capacities of LDHs for DNA. The results revealed that the LDHs with Mg/Al = 3 had higher ability on adsorbing the DNA and were not affected by pH values. The LDHs exhibited excellent adsorption properties and completely adsorbed DNA within 2 h. The adsorption equilibrium data were fitted to the Langmuir and Freundlich models, showing that the Langmuir model which represented monolayer adsorption had better correlation with the adsorption linear equation. In addition, Circular dichroism (CD) spectrum, UV-vis spectorscopy and agarose gel electrophoresis revealed the integrity of DNA structure, suggesting that there had no damage on the DNA structure during the adsorption process.

  18. Studies on Thorium Adsorption Characteristics upon Activated Titanium Hydroxide Prepared from Rosetta Ilmenite Concentrate

    SciTech Connect

    Gado, M Zaki, S

    2016-01-01

    The titanium hydroxide prepared from Rosetta ilmenite concentrate has been applied for Th (IV) adsorption from its acid aqueous solutions. The prepared hydroxide is first characterized by both Fourier transform infrared (FT-IR) spectrum and thermogravimetric analysis. The relevant factors affecting the adsorption process have been studied. The obtained equilibrium data fits well with the Langmuir isotherm rather than Freundlich isotherm, while the adsorption kinetic data follow the pseudo-second order model. The different thermodynamic parameters have also been calculated and indicate that the adsorption process is spontaneous.

  19. Temperature-dependent infrared and calorimetric studies on arsenicals adsorption from solution to hematite nanoparticles

    Technology Transfer Automated Retrieval System (TEKTRAN)

    To address the lack of systematic and surface sensitive studies on the adsorption energetics of arsenic compounds on metal (oxyhydr)oxides, we conducted temperature-dependent ATR-FTIR studies for the adsorption of arsenate, monomethylarsonic acid, and dimethylarsinic acid on hematite nanoparticles a...

  20. Experimental and molecular dynamic simulation study of perfluorooctane sulfonate adsorption on soil and sediment components.

    PubMed

    Zhang, Ruiming; Yan, Wei; Jing, Chuanyong

    2015-03-01

    Soil and sediment play a crucial role in the fate and transport of perfluorooctane sulfonate (PFOS) in the environment. However, the molecular mechanisms of major soil/sediment components on PFOS adsorption remain unclear. This study experimentally isolated three major components in soil/sediment: humin/kerogen, humic/fulvic acid (HA/FA), and inorganic component after removing organics, and explored their contributions to PFOS adsorption using batch adsorption experiments and molecular dynamic simulations. The results suggest that the humin/kerogen component dominated the PFOS adsorption due to its aliphatic features where hydrophobic effect and phase transfer are the primary adsorption mechanism. Compared with the humin/kerogen, the HA/FA component contributed less to the PFOS adsorption because of its hydrophilic and polar characteristics. The electrostatic repulsion between the polar groups of HA/FA and PFOS anions was attributable to the reduced PFOS adsorption. When the soil organic matter was extracted, the inorganic component also plays a non-negligible role because PFOS molecules might form surface complexes on SiO2 surface. The findings obtained in this study illustrate the contribution of organic matters in soils and sediments to PFOS adsorption and provided new perspective to understanding the adsorption process of PFOS on micro-interface in the environment.

  1. Adsorption and reactions of atmospheric constituents and pollutants on ice particles: an FTIR study

    NASA Astrophysics Data System (ADS)

    Rudakova, A. V.; Marinov, I. L.; Poretskiy, M. S.; Tsyganenko, A. A.

    2009-04-01

    Processes on icy particles attract much attention due to their importance for atmospheric science, ecology and astrophysics. In this work, adsorption and ecologically important reactions of some molecules on pure and mixed water icy films by means of FTIR spectroscopy have been investigated. The cell for spectral studies of adsorbed molecules at variable temperatures (55-370 K), described elsewhere1, enables one to run the spectra in the presence of gaseous adsorbate, and even to perform adsorption from the solution in some cryogenic solvents. For the studies of ice films, it was equipped with a device for water vapour sputtering from the heated capillaries and deposition onto the inner BaF2 or ZnSe windows of the cell, cooled by liquid nitrogen. Lower temperatures were obtained by pumping off evaporating nitrogen from the coolant volume. The estimated specific surface area of freshly deposited at 77 K water ice film was about 160 m2/g and decreases on raising the temperature together with the diminishing intensity of the bands of dangling OH (OD) groups at 3696 (2727) cm-1 until the latter disappear at 130 - 160 K when the changes of bulk absorption provide evidence for a phase transition from amorphous to polycrystalline ice. CO adsorption at 77 K results in two bands at 2153 and 2137 cm-1 assigned to molecules forming weak H-bond with the dangling hydroxyl groups and bound to unsaturated surface oxygen atoms, respectively2. The band of dangling hydroxyl groups moves to lower wavenumbers on adsorption of different molecules (hydrogen, nitrogen, methane, ozone, NO, ethane or chlorinated ethenes, etc.). The shift value depends on the nature of adsorbate. Besides this shift, spectra of adsorbed nitrogen and methane registered at 55 K reveal the adsorption intensity decrease at ~ 2650 cm-1 at the high-frequency slope of bulk adsorption, and increase at about 25 cm-1 below. We interpret this perturbation as a strengthening of H-bonds between surface water molecules

  2. [Study on treatment of methylene blue wastewater by fly ash adsorption-Fenton and thermal regeneration].

    PubMed

    Bai, Yu-Jie; Zhang, Ai-Li; Zhou, Ji-Ti

    2012-07-01

    The physicochemical properties of water-washed fly ash (FA) and acid modified fly ash (M-FA) were investigated. The adsorption of methylene blue by FA and M-FA were studied by batch experiments. Two methods, Fenton-drive oxidation regeneration and thermal regeneration, were used for regeneration of the used FA and M-FA. The result showed that the rate of adsorption process followed the second order kinetics and the adsorption followed Langmuir isotherms. The adsorption equilibrium time was 30 min, and the equilibrium adsorption capacity of FA and M-FA were 4.22 mg x g(-1) and 5.98 mg x g(-1) respectively. The adsorption capability of M-FA was higher than that of FA. In the range of pH 2-12, the adsorption capacity of M-FA increased with the increase of pH, whereas the adsorption capacity of FA decreased slowly until the pH 8 and then increased. Electrostatic adsorption was the major factor on the adsorption capacity. Around 61% and 55% percentage regeneration (PR) were obtained for FA and M-FA respectively when 78.4 mmol x L(-1) H2O2 and 0.72 mmol x L(-1) Fe2+ were used. When the condition of thermal regeneration was 400 degrees C and 2 h, a positive correlation can be found between the PRs of FA and regeneration times, the PRs were 102%, 104% and 107% in three cycles of adsorption-thermal regeneration process. However a negative correlation can be found between the PRs of M-FA and regeneration times, the PRs were 82%, 75% and 74% in three cycles of adsorption-thermal regeneration process. The PR of FA was higher than that of M-FA, and thermal regeneration was superior to Fenton-drive regeneration.

  3. Study of Adsorption of Copper Species onto Multiwall Carbon Nanotubes

    EPA Science Inventory

    Functionalized CNTs have improved adsorptive capacities over pristine CNTs. These can be used for sensors, membranes, filters and matrix composite enhancements made possible because of their nano-size.

  4. Isotherm, thermodynamic, kinetics and adsorption mechanism studies of methyl orange by surfactant modified silkworm exuviae.

    PubMed

    Chen, Hao; Zhao, Jie; Wu, Junyong; Dai, Guoliang

    2011-08-15

    This paper reports on the development of organo-modified silkworm exuviae (MSE) adsorbent prepared by using hexadecyltrimethylammonium bromide (HDTMAB) for removing methyl orange (MO), a model anionic dye, from aqueous solution. The natural and modified samples were characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FT-IR). Batch adsorption experiments were carried out to remove MO from its aqueous solutions using SE and MSE. It was observed that the adsorption capacity of MSE is 5-6 times of SE. The different parameters effecting on the adsorption capacity such as pH of the solution, initial dye concentration, temperature and contact time have been investigated. Analysis of adsorption results obtained at different temperatures showed that the adsorption pattern on the MSE can be described perfectly with Langmuir isotherm model compared with Freundlich and Dubinin-Radushkevich (D-R) isotherm models, and the characteristic parameters for each adsorption isotherm were also determined. The adsorption process has been found exothermic in nature and thermodynamic parameters have been calculated. The adsorption kinetic followed the pseudo-second order kinetic model. The results of FT-IR, EDS and desorption studies all suggest that methyl orange adsorption onto the MSE should be mainly controlled by the hydrophobic interaction mechanism, along with a considerable contribution of the anionic exchange mechanism. The results indicate that HDTMAB-modified silkworm exuviae could be employed as low-cost material for the removal of methyl orange anionic dye from wastewater.

  5. Adsorption studies of azotetrazolate and 3,6-dihydrazinotetrazine on peat.

    PubMed

    Borkowski, Andrzej; Rydelek, Paweł; Szala, Mateusz

    2013-01-01

    The objective of our studies was the evaluation of the adsorption process of two high-nitrogen compounds-dihydrazinotetrazine (DHTz) and azotetrazolate ion (AZ)-on a chosen peat. The experiments were performed using a static method at three different temperatures (283, 298, and 333 K). The adsorption process of DHTz and AZ on peat was characterized by isotherms according to the Freundlich and Langmuir models. The obtained correlations between adsorption and equilibrium concentration were in good accordance with the Freundlich and Langmuir models, as confirmed by high values of the correlation coefficients (0.97-0.99). Adsorption of AZ on peat was less efficient than that of DHTz, and this inference was experimentally proven. The maximum surface coverages of peat particles with adsorbate according to the Langmuir model were calculated as 0.02 and 0.17 mol kg(-1) (at 298 K) for AZ and DHTz, respectively. The determined adsorption equilibrium constants confirmed greater adsorption of DHTz on the investigated peat. It can be concluded that adsorption of AZ occurred to a much lesser extent compared to that of DHTz, pointing to a potentially greater threat of migration of soluble azotetrazolates in soil. Standard enthalpies of adsorption estimated for AZ and DHTz were -11.1 and -23.7 kJ mol(-1), respectively. Based on these adsorption enthalpy values, it can be stated that both investigated compounds are adsorbed on peat by a physisorption process.

  6. Kinetic and thermodynamic studies on the adsorption of anionic surfactant on quaternary ammonium cationic cellulose.

    PubMed

    Zhang, Yuanzhang; Shi, Wenjian; Zhou, Hualan; Fu, Xing; Chen, Xuan

    2010-06-01

    Removal of anionic surfactants from aqueous solutions by adsorption onto quaternary ammonium cationic cellulose (QACC) was investigated. The effects of solution acidity, initial concentration, adsorption time, and temperature on the adsorption of sodium dodecyl-benzene sulfonate (SDBS), sodium lauryl sulfate (SLS), and sodium dodecyl sulfonate (SDS) were studied. The kinetic experimental data fit well with the pseudo-second-order model; the rate constant of the adsorption increased with temperature. The values of apparent activation energy for the adsorption were calculated as ranging from 10.2 to 17.4 kJ/ mol. The adsorption isotherm can be described by the Langmuir isotherm. The values of thermodynamic parameters (deltaH0, deltaS0, and deltaG0) for the adsorption indicated that this process was spontaneous and endothermic. At 318 K, the saturated adsorption capacities of QACC for SDBS, SLS, and SDS were 1.75, 1.53, and 1.39 mmol/g, respectively. The adsorption process was mainly chemisorption and partially physisorption. The results show that QACC is effective for the removal of anionic surfactants.

  7. Adsorption on vicinal surfaces: {Pb}/{Cu(1,1,11) } — a TEAS study

    NASA Astrophysics Data System (ADS)

    Goapper, S.; Barbier, L.; Salanon, B.

    1996-08-01

    Pb adsorption on Cu(1,1,11) has been studied by He diffraction. Measurements of Pb cross-sections for He scattering as a function of coverage and temperature indicate a complex behavior of the absorbate. Dense island formation, preferential adsorption at steps and surface alloying effects were found.

  8. Adsorption studies of Cu(II) on Boston fern (Nephrolepis exaltata Schott cv. Bostoniensis) leaves

    NASA Astrophysics Data System (ADS)

    Rao, Rifaqat Ali Khan; Khan, Umra

    2016-02-01

    Adsorption studies were done on Boston fern leaves for the effective removal of Cu(II) ions from aqueous solution. It has been tested for the first time for heavy metal adsorption from aqueous solution. This promising material has shown remarkable adsorption capacity towards Cu(II) ions which confirm its novelty, ease of availability, non-toxic nature, cheapness, etc., and give the main innovation to the present study. The adsorbent was analyzed by FT-IR, SEM and EDS. The effect of pH, contact time, initial metal ion concentration and temperature on the adsorption was investigated using batch process to optimize conditions for maximum adsorption. The adsorption of Cu(II) was maximum (96 %) at pH 4. The experimental data were analyzed by Langmuir, Freundlich and Tempkin isotherms. The kinetic studies of Cu(II)were carried out at room temperature (30 °C) in the concentration range 10-100 mg L-1. The data obtained fitted well with the Langmuir isotherm and pseudo-second-order kinetics model. The maximum adsorption capacity (q m) obtained from Langmuir adsorption isotherm was found to be 27.027 mg g-1 at 30 °C. The process was found to be exothermic and spontaneous in nature. The breakthrough and exhaustive capacities were found to be 12.5 and 37.5 mg g-1, respectively. Desorption studies showed that 93.3 % Cu(II) could be desorbed with 0.1 M HCl by continuous mode.

  9. Kinetics adsorption study of the ethidium bromide by graphene oxide as adsorbent from aqueous matrices

    NASA Astrophysics Data System (ADS)

    Rajabi, M.; Moradi, O.; Zare, K.

    2017-01-01

    In this study of ethidium bromide, adsorption from aqueous matrices by graphene oxide as adsorbent was investigated. Influencing parameters in the adsorption study included contact time, temperature, and pH. The optimum time was selected 17 min, and the best value of pH was determined at 8. All adsorption experiments were performed at 298 K temperature. The maximum wavelength of ethidium bromide was 475 nm. The Elovich, four types of the pseudo-second-order, the pseudo-first-order, and intra-particle diffusion kinetic adsorption models were used for kinetic study, and the results show that adsorption of ethidium bromide on graphene oxide surface best complied with type (I) of the pseudo-second-order kinetic model.

  10. Photocatalytic degradation of phenol and phenolic compounds Part I. Adsorption and FTIR study.

    PubMed

    Araña, J; Pulido Melián, E; Rodríguez López, V M; Peña Alonso, A; Doña Rodríguez, J M; González Díaz, O; Pérez Peña, J

    2007-07-31

    With the goal of predicting the photocatalytic behaviour of different phenolic compounds (catechol, resorcinol, phenol, m-cresol and o-cresol), their adsorption and interaction types with the TiO(2) Degussa P-25 surface were studied. Langmuir and Freundlich isotherms were applied in the adsorption studies. The obtained results indicated that catechol adsorption is much higher than those of the other phenolics and its interaction occurs preferentially through the formation of a catecholate monodentate. Resorcinol and the cresols interact by means of hydrogen bonds through the hydroxyl group, and their adsorption is much lower than that of catechol. Finally, phenol showed an intermediate behaviour, with a Langmuir adsorption constant, K(L), much lower than that of catechol, but a similar interaction. The interaction of the selected molecules with the catalyst surface was evaluated by means of FTIR experiments, which allowed us to determine the probability of OH radical attack to the aromatic ring.

  11. Initial stages of CO2 adsorption on CaO: a combined experimental and computational study.

    PubMed

    Solis, Brian H; Cui, Yi; Weng, Xuefei; Seifert, Jan; Schauermann, Swetlana; Sauer, Joachim; Shaikhutdinov, Shamil; Freund, Hans-Joachim

    2017-02-08

    Room temperature adsorption of carbon dioxide (CO2) on monocrystalline CaO(001) thin films grown on a Mo(001) substrate was studied by infrared reflection-absorption spectroscopy (IRAS) and quantum chemical calculations. For comparison, CO2 adsorption was examined on poorly ordered, nanoparticulate CaO films prepared on Ru(0001). For both systems, CO2 readily adsorbs on the clean CaO surface. However, additional bands were observable on the CaO/Ru(0001) films compared with CaO/Mo(001), because the stricter IRAS surface selection rules do not apply to adsorption on the disordered thin films grown on Ru(0001). Spectral evolution with increasing exposure of the IRA bands suggested the presence of several adsorption sites which are consecutively populated by CO2. Density functional calculations showed that CO2 adsorption occurs as monodentate surface carbonate (CO3(2-)) species at monatomic step sites and other low-coordinated sites, followed by formation of carbonates on terraces, which dominate at increasing CO2 exposure. To explain the coverage-dependent IRAS results, we propose CO2 surface islanding from the onset, most likely in the form of pairs and other chain-like species, which were calculated as thermodynamically favorable. The calculated adsorption energy for isolated CO2 on the terrace sites (184 ± 10 kJ mol(-1)) is larger than the adsorption energy obtained by temperature programmed desorption (∼120-140 kJ mol(-1)) and heat of adsorption taken from microcalorimetry measurements at low coverage (∼125 kJ mol(-1)). However, the calculated adsorption energies become less favorable when carbonate chains intersect on CaO terraces, forming kinks. Furthermore, our assignments of the initial stages of CO2 adsorption are consistent with the observed coverage effect on the CO2 adsorption energy measured by microcalorimetry and the IRAS results.

  12. First Principles Study of HCN Adsorption on Graphene Doped with 5d Transition Metal

    NASA Astrophysics Data System (ADS)

    Dong, Hai-Kuan; Wang, Yong-Ping; Shi, Li Bin

    2016-11-01

    Hydrogen cyanide (HCN) adsorption on graphene doped with 5d transition metal (TM) is investigated by the first principles based on density functional theory. It is observed that Hg atom cannot be doped into graphene due to saturated valence electron configurations of 5d106s2. Three kinds of HCN adsorption configurations are investigated, in which H, C and N in HCN are close to the adsorption site, respectively. The most stable adsorption configuration is obtained by total energy optimization. HCN adsorption can be studied by adsorption energy and electron density difference. HCN can only be physisorbed on Ir, Pt and Au-doped graphenes, while chemisorption is observed for Lu, Hf, Ta, W, Re and Os-doped graphenes. The band structure is calculated by B3LYP and Generalized gradient approximation (GGA) functionals. It is observed from B3LYP method that the conductivity of Lu, Hf, Re and Os-doped graphenes does not obviously change before and after HCN adsorption. Ta and W-doped graphenes change from semiconductor to metal after adsorption of HCN molecule. The results indicate that Ta and W-doped graphenes may be a promising sensor for detecting HCN. This study provides a useful basis for understanding of a wide variety of physical properties on graphene.

  13. Equilibrium, kinetic and thermodynamic study of cesium adsorption onto nanocrystalline mordenite from high-salt solution.

    PubMed

    Lee, Keun-Young; Park, Minsung; Kim, Jimin; Oh, Maengkyo; Lee, Eil-Hee; Kim, Kwang-Wook; Chung, Dong-Yong; Moon, Jei-Kwon

    2016-05-01

    In this study, the equilibrium, kinetics and thermodynamics of cesium adsorption by nanocrystalline mordenite were investigated under cesium contamination with high-salt solution, simulating the case of an operation and decommissioning of nuclear facilities or an accident during the processes. The adsorption rate constants were determined using a pseudo second-order kinetic model. The kinetic results strongly demonstrated that the cesium adsorption rate of nano mordenite is extremely fast, even in a high-salt solution, and much faster than that of micro mordenite. In the equilibrium study, the Langmuir isotherm model fit the cesium adsorption data of nano mordenite better than the Freundlich model, which suggests that cesium adsorption onto nano mordenite is a monolayer homogeneous adsorption process. The obtained thermodynamic parameters indicated that the adsorption involved a very stable chemical reaction. In particular, the combination of rapid particle dispersion and rapid cesium adsorption of the nano mordenite in the solution resulted in a rapid and effective process for cesium removal without stirring, which may offer great advantages for low energy consumption and simple operation.

  14. Adsorption of uranyl species on hydroxylated titanium carbide nanosheet: A first-principles study.

    PubMed

    Zhang, Yu-Juan; Lan, Jian-Hui; Wang, Lin; Wu, Qun-Yan; Wang, Cong-Zhi; Bo, Tao; Chai, Zhi-Fang; Shi, Wei-Qun

    2016-05-05

    In this work, hydroxylated titanium carbide Ti3C2(OH)2, a representative of the two-dimensional transition metal carbides, has been predicted to be an effective adsorbent for uranyl ions in aqueous environments for the first time using density functional theory simulations. The calculations revealed that the uranyl ion can strongly bind with Ti3C2(OH)2 nanosheet in aqueous solution regardless of the presence of anionic ligands such as OH(-), Cl(-) and NO3(-). The bidentate coordination of uranyl to the surface is energetically more favorable than other adsorption configurations, and the uranyl ion prefers to bind with the deprotonated O adsorption site rather than the protonated one on the hydroxylated surface. During the adsorption process, the chemical adsorption as well as the formation of hydrogen bonds is the dominant factor.

  15. Barium adsorption on Si(100)-(2×1) at room temperature: a bi-polar scanning tunneling microscopy study

    NASA Astrophysics Data System (ADS)

    Hu, X.; Yao, X.; Peterson, C. A.; Sarid, D.; Yu, Z.; Wang, J.; Marshall, D. S.; Curless, J. A.; Ramdani, J.; Droopad, R.; Hallmark, J. A.; Ooms, W. J.

    2000-06-01

    The initial stages of barium adsorption on Si(100)-(2×1) at room temperature has been studied by ultrahigh vacuum scanning tunneling microscopy (STM) under both positive and negative sample-bias imaging conditions. Two distinct adsorption sites have been identified by the high-resolution STM images. It was found that, with the substrate held at room temperature, barium atoms can occupy both valley-bridge sites in the trough between silicon dimers and silicon-vacancy sites. It is possible to image the barium atoms at valley-bridge sites with both negative and positive sample bias, revealing filled and empty surface states, respectively. For barium atoms adsorbed at vacancy sites, however, it is only possible to obtain filled-state images, and imaging with positive sample bias will induce the removal of the atom, possibly transferred to the tip, revealing a missing silicon dimer below.

  16. Revealing the Effect of Protein Weak Adsorption to Nanoparticles on the Interaction between the Desorbed Protein and its Binding Partner by Surface-Enhanced Infrared Spectroelectrochemistry.

    PubMed

    Liu, Li; Zeng, Li; Wu, Lie; Jiang, Xiue

    2017-03-07

    In recent years, the properties of protein corona have attracted intense interest in the field of nanobio interface, but a long-ignored research issue is how the desorbed proteins suffering from conformational change upon weak association with nanoparticles affect their functional properties when further interacting with their downstream protein partners. In this Article, surface-enhanced infrared absorption spectroscopy (SEIRAS) and electrochemical cyclic voltammetry were used to study the adsorption and redox properties of the soluble cytochrome c (cyt c) on 11-mercaptoundecanoic acid (MUA) self-assembled monolayer (SAM) after weakly binding to and then desorbed from nano-TiO2. For the first time, our study reveals that the weak interaction between cyt c and nano-TiO2 induces the protein to undergo a heterogeneous conformational change. More importantly, the cyt c with a largely unfolded conformation exhibits a weaker interaction with its binding partner mimics than the native-like cyt c but a faster adsorption rate even at a concentration that is much lower than that of native-like cyt c. Correspondingly, the cyt c with a large unfolding shows a greatly positive-shifted formal potential (Ef) relative to the native-like protein possibly due to the disruption of the pocket structure of heme in the vicinity of Met80. These properties could enable the largely unfolded cyt c to undergo a favorable binding but an unavailable electron transfer to cytochrome c oxidase even in the presence of high-concentration native cyt c, probably causing the disruption of electron flow.

  17. Adsorption of methyl tertiary butyl ether on granular zeolites: Batch and column studies.

    PubMed

    Abu-Lail, Laila; Bergendahl, John A; Thompson, Robert W

    2010-06-15

    Methyl tertiary butyl ether (MTBE) has been shown to be readily removed from water with powdered zeolites, but the passage of water through fixed-beds of very small powdered zeolites produces high friction losses not encountered in flow through larger sized granular materials. In this study, equilibrium and kinetic adsorption of MTBE onto granular zeolites, a coconut shell granular activated carbon (CS-1240), and a commercial carbon adsorbent (CCA) sample was evaluated. In addition, the effect of natural organic matter (NOM) on MTBE adsorption was evaluated. Batch adsorption experiments determined that ZSM-5 was the most effective granular zeolite for MTBE adsorption. Further equilibrium and kinetic experiments verified that granular ZSM-5 is superior to CS-1240 and CCA in removing MTBE from water. No competitive adsorption effects between NOM and MTBE were observed for adsorption to granular ZSM-5 or CS-1240, however there was competition between NOM and MTBE for adsorption onto the CCA granules. Fixed-bed adsorption experiments for longer run times were performed using granular ZSM-5. The bed depth service time model (BDST) was used to analyze the breakthrough data.

  18. Adsorption of Methyl Tertiary Butyl Ether on Granular Zeolites: Batch and Column Studies

    PubMed Central

    Abu-Lail, Laila; Bergendahl, John A.; Thompson, Robert W.

    2010-01-01

    Methyl tertiary butyl ether (MTBE) has been shown to be readily removed from water with powdered zeolites, but the passage of water through fixed beds of very small powdered zeolites produces high friction losses not encountered in flow through larger sized granular materials. In this study, equilibrium and kinetic adsorption of MTBE onto granular zeolites, a coconut shell granular activated carbon (CS-1240), and a commercial carbon adsorbent (CCA) sample was evaluated. In addition, the effect of natural organic matter (NOM) on MTBE adsorption was evaluated. Batch adsorption experiments determined that ZSM-5 was the most effective granular zeolite for MTBE adsorption. Further equilibrium and kinetic experiments verified that granular ZSM-5 is superior to CS-1240 and CCA in removing MTBE from water. No competitive-adsorption effects between NOM and MTBE were observed for adsorption to granular ZSM-5 or CS-1240, however there was competition between NOM and MTBE for adsorption onto the CCA granules. Fixed-bed adsorption experiments for longer run times were performed using granular ZSM-5. The bed depth service time model (BDST) was used to analyze the breakthrough data. PMID:20153106

  19. A comparative study of fibrinogen adsorption onto metal oxide thin films

    NASA Astrophysics Data System (ADS)

    Silva-Bermudez, P.; Muhl, S.; Rodil, S. E.

    2013-10-01

    One of the first events occurring upon foreign material-biological medium contact is the adsorption of proteins, which evolution greatly determines the cells response to the material. Protein-surface interactions are a complex phenomenon driven by the physicochemical properties of the surface, protein(s) and liquid medium involve in the interaction. In this article the adsorption of fibrinogen (Fbg) onto Ta2O5, Nb2O5, TiO2 and ZrO2 thin films is reported. The adsorption kinetics and characteristics of the adsorbed fibrinogen layer were studied in situ using dynamic and spectroscopic ellipsometry. The films wettability, surface energy (γLW/AB) and roughness were characterized aiming to elucidate their correlations with Fbg adsorption. The adsorption rate changed accordingly to the film; the fastest adsorption rate and highest Fbg surface mass concentration (Γ) was observed on ZrO2. The hydrophobic/hydrophilic character of the oxide highly influenced Fbg adsorption. On Ta2O5, Nb2O5 and TiO2, which were either hydrophilic or in the breaking-point between hydrophilicity and hydrophobicity, Γ was correlated to the polar component of γLW/AB and roughness of the surface. On ZrO2, clearly hydrophobic, Γ increased significantly off the correlation observed for the other films. The results indicated different adsorption dynamics and orientations of the Fbg molecules dependent on the surface hydrophobic/hydrophilic character.

  20. 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

    2013-09-04

    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).

  1. Comparative study of calcium alginate, activated carbon, and their composite beads on methylene blue adsorption.

    PubMed

    Hassan, A F; Abdel-Mohsen, A M; Fouda, Moustafa M G

    2014-02-15

    Three adsorbents, calcium alginate beads (AB), sodium hydroxide activated carbon based coconut shells (C), and calcium alginate/activated carbon composite beads (ACB) were prepared. Their textural properties were characterized by N2-adsorption at -196°C and scanning electron microscopy. The porosity, surface area and total pore volume of C>ACB>AB, but AB adsorbent was more acidic function groups more than the other adsorbents. Adsorption experiments were conducted to examine the effects of adsorbent dosage, pH, time, temperature and initial concentration of methylene blue. Methylene blue adsorption on C, AB and ACB was observed at pH>6 to avoid the competition of H(+). The amount of dye adsorbed increases as the adsorbent dosage increase. Adsorption of dye follows pseudo-second order mechanism. Thermodynamic studies show spontaneous and endothermic nature of the overall adsorption process.

  2. Adsorption of large hydrocarbons on coinage metals: a van der Waals density functional study.

    PubMed

    Björk, Jonas; Stafström, Sven

    2014-09-15

    The adsorption of organic molecules onto the close-packed facets of coinage metals is studied, and how accurately adsorption heights can be described by using recent advances of the van der Waals density functional (vdWDF), with optPBE/vdWDF, optB86b/vdWDF, vdWDF2, and rev/vdWDF2 functionals is illustrated. The adsorption of two prototypical aromatic hydrocarbons is investigated, and the calculated adsorption heights are compared to experimental literature values from normal incident X-ray standing wave absorption and a state-of-the-art semi-empirical method. It is shown that both the optB86b/vdWDF and rev/vdWDF2 functionals describe adsorption heights with an accuracy of 0.1 Å, compared to experimental values, and are concluded as reliable methods of choice for related systems.

  3. A Comparative Study of the Adsorption of Water and Methanol in Zeolite BEA: A Molecular Simulation Study

    SciTech Connect

    Nguyen, Van T.; Nguyen, Phuong T.; Dang, Liem X.; Mei, Donghai; Wick, Collin D.; Do, Duong D.

    2014-09-15

    Grand Canonical Monte Carlo (GCMC) simulations were carried out to study the equilibrium adsorption concentration of methanol and water in all-silica zeolite BEA over the wide temperature and pressure ranges. For both water and methanol, their adsorptive capacity increases with increasing pressure and decreasing temperature. The onset of methanol adsorption occurs at much lower pressures than water adsorption at all temperatures. Our GCMC simulation results also indicate that the adsorption isotherms of methanol exhibit a gradual change with pressure while water adsorption shows a sharp first-order phase transition at low temperatures. To explore the effects of Si/Al ratio on adsorption, a series of GCMC simulations of water and methanol adsorption in zeolites HBEA with Si/Al=7, 15, 31, 63 were performed. As the Si/Al ratio decreases, the onsets of both water and methanol adsorption dramatically shift to lower pressures. The type V isotherm obtained for water adsorption in hydrophobic BEA progressively changes to type I isotherm with decreasing Si/Al ratio in hydrophilic HBEA. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle.

  4. A spectroscopic study on the adsorption of cationic dyes into mesoporous AlMCM-41 materials

    NASA Astrophysics Data System (ADS)

    Zanjanchi, M. A.; Ebrahimian, A.; Alimohammadi, Z.

    2007-03-01

    Mesoporous materials loaded with dyes are of interest with respect to novel optical applications. The spectral behaviors of some dyes in these materials are considerably affected by the presence of surfactants. A comparative study has been carried out on the adsorption of the methylene blue, rhodamine 6G and thionine dyes into a surfactant-free and surfactant-containing mesoporous AlMCM-41. The ion exchange method has been employed for incorporation of the dye molecules into the structure of MCM-41. The exchangeable sites in the MCM-41 were generated prior to dye loading by isomorphous substitution of aluminum for silicon in the structure of the mesoporous material during the synthesis procedure. Diffuse reflectance measurements indicate adsorption of methylene blue and rhodamine 6G dye molecules into AlMCM-41 taken place via ion exchange at room temperature. The spectra show presence of monomer and dimer aggregates of the dyes established into the pores and surface of AlMCM-41. The ratio of dimer to monomer forms of rhodamine 6G incorporated in the surfactant-free and surfactant-containing AlMCM-41 is about one which is higher than those observed in aqueous solutions. The surfactant-containing AlMCM-41 induced destabilization and decomposition of methylene blue while uploading the dye. Degradation of this dye produces intermediate species identified as demethylated forms of methylene blue adsorbed on AlMCM-41. Our experiments revealed that kinetics of ion exchange for thionine dye is very slow at room temperature, but it become faster at higher temperatures. The spectral properties of thionine in AlMCM-41 are close to that of thionine in an aqueous solution, possibly due to high pore space in a mesoporous molecular sieve. No adsorption of thionine was observed for surfactant-containing AlMCM-41 even at higher temperatures.

  5. Recovery of polyphenols from rose oil distillation wastewater using adsorption resins--a pilot study.

    PubMed

    Rusanov, Krasimir; Garo, Eliane; Rusanova, Mila; Fertig, Orlando; Hamburger, Matthias; Atanassov, Ivan; Butterweck, Veronika

    2014-11-01

    The production of rose oil from rose flowers by water steam distillation leaves a water fraction of the distillate as main part of the waste. Therefore, the rose oil distillation wastewater represents a serious environmental problem due to the high content of polyphenols which are difficult to decompose and have to be considered as biopollutants when discarded into the drainage system and rivers. On the other hand, natural polyphenols are valuable compounds with useful properties as bioactive substances. Until now there is no established practice for processing of rose oil distillation wastewater and utilization of contained substances. Thus, it was the aim of this study to develop a strategy to separate this wastewater into a polyphenol depleted water fraction and a polyphenol enriched fraction which could be developed into innovative value-added products. In a first step, the phytochemical profile of rose oil distillation wastewater was determined. Its HPLC-PDA-MS analysis revealed the presence of flavan-3-ols, flavanones, flavonols and flavones. In a second step, the development of a stepwise concentration of rose oil distillation wastewater was performed. The concentration process includes a filtration process to eliminate suspended solids in the wastewater, followed by adsorption of the contained phenolic compounds onto adsorption resins (XAD and SP). Finally, desorption of the polyphenol fraction from the resin matrix was achieved using ethanol and/or aqueous ethanol. The result of the process was a wastewater low in soluble organic compounds and an enriched polyphenol fraction (RF20 SP-207). The profile of this fraction was similar to that of rose oil distillation wastewater and showed the presence of flavonols such as quercetin and kaempferol glycosides as major metabolites. These compounds were isolated from the enriched polyphenol fraction and their structures confirmed by NMR. In summary, a pilot medium scale system was developed using adsorption resins

  6. Vibrational Spectroscopic Studies of Hydrogen, Carbon-Monoxide and Thiophene Adsorption on Ruthenium-Sulfide and Sulfided Ruthenium Catalysts.

    NASA Astrophysics Data System (ADS)

    Heise, William Herbert

    The "working surface" of ruthenium hydrodesulfurization (HDS) catalysts has been modeled by preadsorption of sulfur, carbon and carbon plus sulfur on Ru(0001). Adsorption and decomposition of thiophene over these surfaces have been investigated using TDS/TPRS, XPS and EELS. Thiophene is proposed to decompose via a three-step mechanism involving: (i) initial thiophene cracking at 120 K yielding surface sulfur and hydrocarbon species, (ii) hydrogen desorption near 230 K providing additional decomposition ensembles and (iii) continued decomposition to form "metallocycle -like" intermediates which retain EELS features similar to thiophene. Preadsorbed carbon or carbon plus sulfur are not as effective for passivation of the surface toward metallocycle formation as preadsorbed sulfur alone. This result is attributed to the fact that carbon deposited from butadiene annealed and decomposed at 700 K forms islands, while sulfur establishes a well-ordered superlattice on the surface. The decrease in metallocycle formation with increasing poison levels appears to explain HDS selectivity and specific activity trends observed in our laboratory from mildly sulfided (10% H_2S/H_2 , 673 K, 2h) ruthenium catalysts retaining submonolayers of sulfur. Incoherent inelastic neutron scattering (IINS) has been used to characterize hydrogen adsorption sites on ruthenium sulfide. Hydrogen resides on sulfur anions to form SH groups, yielding two non-degenerate bending modes at 600 and 710 cm^{-1}. Complementary hydrogen adsorption and H_2/D _2 exchange data suggest that the active sites for hydrogen adsorption may be coordinatively unsaturated S-S anion pairs. Comparison of CO adsorption on sulfided Ru/Al _2O_3 to sulfur precovered Ru(0001) reveals an adsorption site related to edge/corner atoms directly perturbed by sulfur, consistent with previous kinetic studies demonstrating higher specific activity for thiophene HDS over smaller ruthenium crystallites.

  7. ADSORPTION STUDIES IN A SYNTHETIC RUBBER LATEX-OVALBUMIN SYSTEM

    PubMed Central

    Williams, H. B.; Choppin, A. R.

    1950-01-01

    1. Adsorption of ovalbumin on the latex surface was in excess of the quantity required to produce coverage of the surface over most of the protein concentrations range which was investigated. 2. "S" shaped isothermals which probably indicated multilayer adsorption were obtained. 3. The quantity of ovalbumin required to produce a constant surface charge density on the latex particle surface was a function of the pH, and a theory of active centers on the latex particles has been suggested. 4. A shift in the isoelectric point from that of native ovalbumin has been observed for the protein when adsorbed on a synthetic latex. PMID:14824490

  8. Lead adsorption, anticoagulation and in vivo toxicity studies on the new magnetic nanomaterial Fe3O4@SiO2@DMSA as a hemoperfusion adsorbent.

    PubMed

    Xiang, Yang; Bai, Zhiming; Zhang, Shufang; Sun, Yan; Wang, Shunlan; Wei, Xiaobin; Mo, Wenshi; Long, Jiale; Liu, Zhenxiang; Yang, Chao; Zheng, Linlin; Guo, Xueyi; Xiaoyang, Wang; Mao, Fangfang; Feng, Ningchuan

    2017-01-20

    This project aimed to develop and characterize a new nanoadsorbent for hemoperfusion. Fe3O4 nanoparticles synthesized by a facile solvothermal method were coated with SiO2 and further modified by DMSA. TEM, XRD, FTIR, XPS and SEM were performed before and after lead adsorption to reveal the general performance and adsorption mechanism. Rabbit lead poisoning models were established to study the adsorption rate; then, a pig hemoperfusion experiment was used for further validation. In addition, coagulation, liver, kidney and heart function, blood lipids, electrolytes and the immune inflammatory system were studied before and after hemoperfusion. The results indicated that the materials had a high adsorption rate and chemisorbed lead mainly in the plasma. No obvious coagulation-fibrinolysis, organ toxicity, electrolyte disturbances, inflammatory reactions or immunosuppression was observed. The excellent blood compatibility and high biosafety of this material demonstrate its potential as a new type of hemoperfusion adsorbent.

  9. An Adsorptive Transfer Technique Coupled with Brdicka Reaction to Reveal the Importance of Metallothionein in Chemotherapy with Platinum Based Cytostatics

    PubMed Central

    Krizkova, Sona; Fabrik, Ivo; Huska, Dalibor; Adam, Vojtech; Babula, Petr; Hrabeta, Jan; Eckschlager, Tomas; Pochop, Pavel; Darsova, Denisa; Kukacka, Jiri; Prusa, Richard; Trnkova, Libuse; Kizek, Rene

    2010-01-01

    The drugs based on platinum metals represent one of the oldest, but also one of the most effective groups of chemotherapeutic agents. Thanks to many clinical studies it is known that resistance of tumor cells to drugs is a frequent cause of chemotherapy failure. With regard to platinum based drugs, multidrug resistance can also be connected with increased expression of low-molecular weight protein metallothionein (MT). This study aimed at investigating the interactions of MT with cisplatin or carboplatin, using the adsorptive transfer technique coupled with differential pulse voltammetry Brdicka reaction (AdTS DPV Brdicka reaction), and a comparison of in vitro results with results obtained in vivo. The results obtained from the in vitro study show a strong affinity between platinum based drugs and MT. Further, we analyzed extracts of neuroblastoma cell lines treated with cisplatin or carboplatin. It is clear that neuroblastoma UKF-NB-4 cisplatin-resistant and cisplatin-sensitive cell lines unlikely respond to the presence of the platinum-based cytostatics cisplatin and carboplatin. Finally, we determined the level of MT in samples from rabbits treated with carboplatin and patients with retinoblastoma treated with the same drug. PMID:21614176

  10. The adsorption of basic dye (Astrazon Blue FGRL) from aqueous solutions onto sepiolite, fly ash and apricot shell activated carbon: kinetic and equilibrium studies.

    PubMed

    Karagozoglu, B; Tasdemir, M; Demirbas, E; Kobya, M

    2007-08-17

    In this study, sepiolite, fly ash and apricot stone activated carbon (ASAC) were used as adsorbents for the investigation of the adsorption kinetics, isotherms and thermodynamic parameters of the basic dye (Astrazon Blue FGRL) from aqueous solutions at various concentrations (100-300 mg/L), adsorbent doses (3-12 g/L) and temperatures (303-323 K). The result showed that the adsorption capacity of the dye increased with increasing initial dye concentration, adsorbent dose and temperature. Three kinetic models, the pseudo-first-order, second-order, intraparticle diffusion, were used to predict the adsorption rate constants. The kinetics of adsorption of the basic dye followed pseudo-second-order kinetics. Equations were developed using the pseudo-second-order model which predicts the amount of the basic dye adsorbed at any contact time, initial dye concentration and adsorbent dose within the given range accurately. The adsorption equilibrium data obeyed Langmuir isotherm. The adsorption capacities (Q0) calculated from the Langmuir isotherm were 181.5 mg/g for ASAC, 155.5 mg/g for sepiolite and 128.2 mg/g for fly ash at 303 K. Thermodynamical parameters were also evaluated for the dye-adsorbent systems and revealed that the adsorption process was endothermic in nature.

  11. In situ infrared study of adsorbed species during catalytic oxidation and carbon dioxide adsorption

    NASA Astrophysics Data System (ADS)

    Khatri, Rajesh A.

    2005-11-01

    Hydrogen is considered to be the fuel of the next century. Hydrogen can be produced by either water splitting using the solar or nuclear energy or by catalytic cracking and reforming of the fossil fuels. The water splitting process using solar energy and photovoltaics is a clean way to produce hydrogen, but it suffers from very low efficiency. A promising scheme to produce H 2 from natural gas involves following steps: (i) partial oxidation and reforming of natural gas to syngas, (ii) water-gas shift reaction to convert CO in the syngas to additional H2, (iii) separation of the H2 from CO2, and (iv) CO2 sequestration. The requirements for the above scheme are (i) a highly active coke resistant catalyst for generation of syngas by direct partial oxidation, (ii) a highly active sulfur tolerant catalyst for the water-gas shift reaction, and (iii) a low cost sorbent with high CO2 adsorption capacity for CO2 sequestration. This dissertation will address the mechanisms of partial oxidation, CO2 adsorption, and water-gas shift catalysis using in situ IR spectroscopy coupled with mass spectrometry (MS). The results from these studies will lead to a better understanding of the reaction mechanism and design of both the catalyst and sorbent for production of hydrogen with zero emissions. Partial oxidation of methane is studied over Rh/Al2O 3 catalyst to elucidate the reaction mechanism for synthesis gas formation. The product lead-lag relationship observed with in situ IR and MS results revealed that syngas is produced via a two-step reforming mechanism: the first step involving total oxidation of CH4 to CO2 and H 2O and the second step involving the reforming of unconverted methane with CO2 and H2O to form syngas. Furthermore, the Rh on the catalyst surface remains predominantly in the partially oxidized state (Rhdelta+ and Rh0). For the water-gas shift reaction, addition of Re to the Ni/CeO2 catalyst enhanced the water gas shift activity by a factor of three. The activity

  12. Effect of hydrophilicity of end-grafted polymers on protein adsorption behavior: A Monte Carlo study.

    PubMed

    Han, Yuanyuan; Jin, Jing; Cui, Jie; Jiang, Wei

    2016-06-01

    Monte Carlo simulation is employed to investigate protein adsorption behavior on end-grafted polymers. The effect of hydrophilicity of end-grafted polymers on protein adsorption behavior is investigated in detail. The simulation results indicate that the hydrophilicity of the end-grafted polymers can affect both the amount and speed of protein adsorption. An increase in the hydrophilicity of the end-grafted polymers can significantly decrease the amount and speed of protein adsorption first. However, a further increase in the hydrophilicity of the end-grafted polymers results in the increase in the amount and speed of protein adsorption. This phenomenon is easier to be observed in the end-grafted polymer systems with lower grafting density and longer chain length. In addition, the investigation of the chain conformation of the end-grafted polymers reveals that the end-grafted polymers with mediate hydrophilicity have relatively small size difference along the parallel and perpendicular directions to the substrate, and these end-grafted polymers have relatively wide height distribution. Such characteristics favor covering the space above the hydrophobic substrate and thus can effectively resist protein adsorption.

  13. Equilibrium and dynamic study on hexavalent chromium adsorption onto activated carbon.

    PubMed

    Di Natale, F; Erto, A; Lancia, A; Musmarra, D

    2015-01-08

    In this work, the results of equilibrium and dynamic adsorption tests of hexavalent chromium, Cr (VI), on activated carbon are presented. Adsorption isotherms were determined at different levels of pH and temperature. Dynamic tests were carried out in terms of breakthrough curves of lab-scale fixed bed column at different pH, inlet concentration and flow rate. Both the adsorption isotherms and the breakthrough curves showed non-linear and unconventional trends. The experimental results revealed that chromium speciation played a key role in the adsorption process, also for the occurrence of Cr(VI)-to-Cr(III) reduction reactions. Equilibrium tests were interpreted in light of a multi-component Langmuir model supported by ion speciation analysis. For the interpretation of the adsorption dynamic tests, a mass transfer model was proposed. Dynamic tests at pH 11 were well described considering the external mass transfer as the rate controlling step. Differently, for dynamic tests at pH 6 the same model provided a satisfying description of the experimental breakthrough curves only until a sorbent coverage around 1.6mgg(-1). Above this level, a marked reduction of the breakthrough curve slope was observed in response to a transition to an inter-particle adsorption mechanism.

  14. Adsorption kinetics and equilibrium study of nitrogen species onto radiata pine (Pinus radiata) sawdust.

    PubMed

    Harmayani, Kadek D; Faisal Anwar, A H M

    Nitrogen species (NH3-N, NO3-N, and NO2-N) are found as one of the major dissolved constituents in wastewater or stormwater runoff. In this research, laboratory experiments were conducted to remove these pollutants from the water environment using radiata pine (Pinus radiata) sawdust. A series of batch tests was conducted by varying initial concentration, dosage, particle size, pH, and contact time to check the removal performance. Test results confirmed the effectiveness of radiata pine sawdust for removing these contaminants from the aqueous phase (100% removal of NO3-N, and NO2-N; 55% removal of NH3-N). The adsorbent dosage and initial concentration showed a significantly greater effect on the removal process over pH or particle sizes. The optimum dosage for contaminant removal on a laboratory scale was found to be 12 g. Next, the adsorption kinetics were studied using intraparticle diffusion, liquid-film diffusion, and a pseudo-first order and pseudo-second order model. The adsorption of all species followed a pseudo-second order model but NO2-N adsorption followed both models. In addition, the kinetics of NO2-N adsorption showed two-step adsorption following intraparticle diffusion and liquid-film diffusion. The isotherm study showed that NO3-N and NO2-N adsorption fitted slightly better with the Freundlich model but that NH3-N adsorption followed both Freundlich and Langmuir models.

  15. Polyelectrolyte adsorption on thin cellulose films studied with reflectometry and quartz crystal microgravimetry with dissipation.

    PubMed

    Enarsson, Lars-Erik; Wågberg, Lars

    2009-01-12

    Thin cellulose films were prepared by dissolving carboxymethylated cellulose fibers in N-methyl morpholine oxide and forming thin films on silicon wafers by spin-coating. The adsorption of cationic polyacrylamides and polydiallyldimethylammonium chloride onto these films was studied by stagnation point adsorption reflectometry (SPAR) and by quartz crystal microgravimetry with dissipation (QCM-D). The polyelectrolyte adsorption was studied by SPAR as a function of salt concentration, and it was found that the adsorption maximum was located at 1 mM NaCl for polyelectrolytes of low charge density and at 10 mM NaCl for polyelectrolytes of high charge density. Electrostatic screening led to complete elimination of the polyelectrolyte adsorption at salt concentrations of 300 mM NaCl. According to the QCM-D analysis, the cellulose films showed a pronounced swelling in water that took several hours to complete. Subsequent adsorption of polyelectrolytes onto the cellulose films led to a release of water from the cellulose, an effect that was substantial for polyelectrolytes of high charge density at low salt concentrations. The total mass change including water could therefore show either an increase or a decrease during adsorption onto the cellulose films, depending on the experimental conditions.

  16. 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.

  17. Equilibrium and kinetic adsorption study of a cationic dye by a natural adsorbent--silkworm pupa.

    PubMed

    Noroozi, B; Sorial, G A; Bahrami, H; Arami, M

    2007-01-02

    In this work the use of silkworm pupa, which is the waste of silk spinning industries has been investigated as an adsorbent for the removal of C.I. Basic Blue 41. The amino acid nature of the pupa provided a reasonable capability for dye removal. Equilibrium adsorption isotherms and kinetics were investigated. The adsorption equilibrium data were analyzed by using various adsorption isotherm models and the results have shown that adsorption behavior of the dye could be described reasonably well by either Langmuir or Freundlich models. The characteristic parameters for each isotherm have been determined. The monolayer adsorption capacity was determined to be 555 mg/g. Kinetic studies indicated that the adsorption follows pseudo-second-order kinetics with a rate constant of 0.0434 and 0.0572 g/min mg for initial dye concentration of 200 mg/l at 20 and 40 degrees C, respectively. Kinetic studies showed that film diffusion and intra-particle diffusion were simultaneously operating during the adsorption process. The rate constant for intra-particle diffusion was estimated to be 1.985 mg/g min(0.5).

  18. 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.

  19. 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.

    2015-12-01

    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-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.

  20. 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.

  1. An experimental-computer modeling study of inorganic phosphates surface adsorption on hydroxyapatite particles.

    PubMed

    Rivas, Manuel; Casanovas, Jordi; del Valle, Luis J; Bertran, Oscar; Revilla-López, Guillermo; Turon, Pau; Puiggalí, Jordi; Alemán, Carlos

    2015-06-07

    The adsorption of orthophosphate, pyrophosphate, triphosphate and a trisphosphonate onto hydroxyapatite has been examined using experiments and quantum mechanical calculations. Adsorption studies with FTIR and X-ray photoelectron spectroscopies have been performed considering both crystalline hydroxyapatite (HAp) and amorphous calcium phosphate particles, which were specifically prepared and characterized for this purpose. Density functional theory (DFT) calculations have been carried out considering the (100) and (001) surfaces of HAp, which were represented using 1 × 2 × 2 and 3 × 3 × 1 slab models, respectively. The adsorption of phosphate onto the two crystallographic surfaces is very much favored from an energetic point of view, which is fully consistent with current interpretations of the HAp growing process. The structures calculated for the adsorption of pyrophosphate and triphosphate evidence that this process is easier for the latter than for the former. Thus, the adsorption of pyrophosphate is severely limited by the surface geometry while the flexibility of triphosphate allows transforming repulsive electrostatic interactions into molecular strain. On the other hand, calculations predict that the trisphosphonate only adsorbs onto the (001) surface of HAp. Theoretical predictions are fully consistent with experimental data. Thus, comparison of DFT results and spectroscopic data suggests that the experimental conditions used to prepare HAp particles promote the predominance of the (100) surface. Accordingly, experimental identification of the adsorption of trisphosphonate onto such crystalline particles is unclear while the adsorption of pyrophosphate and triphosphate is clearly observed.

  2. Studies on the adsorption of Brij-35 and CTAB at the coal-water interface.

    PubMed

    Mishra, S K; Panda, D

    2005-03-15

    The adsorption behavior of polyoxyethylene (23) lauryl ether (Brij-35) and cetyl trimethyl ammonium bromide (CTAB) on coal sample has been studied. The adsorption process is found to be sensitive to pH, temperature, electrolyte concentration, and the amount of surface active agent. An attempt has been made to explain the adsorption behavior of the surfactants using the Langmuir equation. The extent of adsorption of Brij-35 on coal is found to be the highest at pH 2, which decreases with increase in pH and remains constant in the neutral and alkaline pH regions. But, the adsorption of CTAB exhibits the opposite behavior of that of Brij-35. Adsorption of any of the surfactant at the coal/water interface sharply decreases the apparent viscosity of 55 wt% coal-water slurry (CWS) at a shear rate of 100 s(-1). Electrostatic adsorption of the surfactants on the coal surface decreases the surface charge and renders the coal surface hydrophobic which is manifested in the form of high apparent viscosity of the coal-water slurry under the test conditions.

  3. Study on the adsorption of chromium (VI) by hydrolyzed keratin/polyamide 6 blend nanofibres.

    PubMed

    Aluigi, Annalisa; Tonetti, Cinzia; Vineis, Claudia; Varesano, Alessio; Tonin, Claudio; Casasola, Raffaella

    2012-09-01

    In this study, nanofibre mats for chemical adsorption of heavy metals were prepared by electrospinning blends of hydrolyzed keratin (HK) and polyamide 6 (PA6) in formic acid. Viscosity measurements of the spinning solutions and morphological analyses of the fracture sections of the same polymer blends cast into films, suggested intermolecular interactions and good compatibility between HK and PA6. The mats made of continuous randomly oriented blend nanofilaments of HK/PA6 50/50 wt, with a mean diameter of about 200 nm, were tested as chromium (VI) ion adsorbents. The parameters investigated included initial chromium ion concentration, pH, contact time and adsorbent dosage. The maximum adsorption capacity occurred at acidic pH. The pseudo-first order, the pseudo-second order and the intraparticle diffusion models were used to describe the kinetics of adsorption process. It was found that kinetic data fit the pseudo-second order model and follow the intraparticle diffusion model, although diffusion is not the only rate control step. Adsorption data fit well the Freundlich isotherm model and the maximum adsorption capacity was found 55.9 mg/g. Moreover, the mean free energy (E) of adsorption ranges between 8 and 16 kJ/mol, so that the adsorption mechanism for HK-based nanofibres was explained as an ion-exchange process.

  4. Adsorption studies of the gram-negative bacteria onto nanostructured silicon carbide.

    PubMed

    Borkowski, Andrzej; Szala, Mateusz; Cłapa, Tomasz

    2015-02-01

    In this study, we demonstrated a significant adsorption of Pseudomonas putida bacteria onto aggregates of nanofibers (NFSiC) and nanorods (NRSiC) of silicon carbide (SiC) in aqueous suspensions. Langmuir and Freundlich isotherms were used to quantify adsorption affinities. It was found that adsorption of the bacteria strongly depended on the structure of the silicon carbide and the pH of the aqueous solution, which affected the isoelectric point of both the silicon carbide and the bacterial cells. The strongest affinity of bacteria was noted in the case of NRSiC aggregates. Affinity was inversely proportional to pH. Similarly, the adsorption of bacteria to the surface of the aggregates increased with decreasing pH. For NFSiC, the affinity of the bacteria for the surface of the aggregates was also inversely proportional to pH. However, adsorption increased at higher pH values. This discrepancy was explained by microscopic analysis, which showed that the bacterial cells were both adsorbed onto and trapped by NFSiC. The adsorption of bacteria onto a micrometric silicon carbide reference material was significantly smaller than adsorption onto nanostructured SiC.

  5. First principles study of halogens adsorption on intermetallic surfaces

    NASA Astrophysics Data System (ADS)

    Zhu, Quanxi; Wang, Shao-qing

    2016-02-01

    Halides are often present at electrochemical environment, they can directly influence the electrode potential or zero charge potential through the induced work-function change. In this work, we focused in particular on the halogen-induced work function change as a function of the coverage of fluorine, chlorine, bromine and iodine on Al2Au and Al2Pt (110) surfaces. Results show that the real relation between work function change and dipole moment change for halogens adsorption on intermetallic surfaces is just a common linear relationship rather than a directly proportion. Besides, the different slopes between fitted lines and the theoretical slope employed in pure metal surfaces demonstrating that the halogens adsorption on intermetallic surfaces are more complicated. We also present a weight parameter β to describe different factors effect on work function shift and finally qualify which factor dominates the shift direction.

  6. Hydrogen Adsorption in Zeolite Studied with Sievert and Thermogravimetric Methods

    NASA Astrophysics Data System (ADS)

    Lesnicenoks, P.; Sivars, A.; Grinberga, L.; Kleperis, J.

    2012-08-01

    Natural clinoptilolite (mixture from clinoptilolite, quartz and muscovite) is activated with palladium and tested for hydrogen adsorption capability at temperatures RT - 200°C. Thermogravimetric and volumetric methods showed that zeolite activated with palladium (1.25%wt) shows markedly high hydrogen adsorption capacity - up to 3 wt%. Lower amount of adsorbed hydrogen (~1.5 wt%) was found for raw zeolite and activated with higher amount of palladium sample. Hypothesis is proposed that the heating of zeolite in argon atmosphere forms and activates the pore structure in zeolite material, where hydrogen encapsulation (trapping) is believed to occur when cooling down to room temperature. An effect of catalyst (Pd) on hydrogen sorption capability is explained by spillover phenomena were less-porous fractions of natural clinoptilolite sample (quartz and muscovite) are involved.

  7. A study of boron adsorption onto activated sludge.

    PubMed

    Fujita, Yuichiro; Hata, Takayosi; Nakamaru, Makoto; Iyo, Toru; Yoshino, Tsuneo; Shimamura, Tadashi

    2005-08-01

    Boron adsorption onto activated sludge was investigated using bench-scale reactors under simulated wastewater treatment conditions. Two experiments, continuous flow and batch, were performed. Boron concentrations were determined by means of inductively coupled plasma mass spectrometry. The results of the continuous-flow experiment indicated that a small amount of boron accumulated on the activated sludge and its concentration in the sludge depended on the nature of the biota in the sludge. Freundlich and Langmuir isotherm plots generated using the data from the batch experiment indicated that boron was adsorbed onto rather than absorbed into the sludge. The Freundlich constants, k and 1/n, were determined to be 26 mg/kg and 0.87. These values indicate that activated sludge has a limited capacity for boron adsorption and thus utilization of the excess sludge for farmland may not be toxic to plant at least boron concern.

  8. Adsorption and desorption studies of lysozyme by Fe3O4-polymer nanocomposite via fluorescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Koc, Kenan; Alveroglu, Esra

    2015-06-01

    The work have been undertaken in this study is to synthesis and characterize Fe3O4-polymer nanocomposites which are having different morphological properties. Also, investigation of the adsorption and desorption behaviour of lysozyme onto Fe3O4-polymer nanocomposites have been studied. Fe3O4 nanoparticles, synthesized by in situ in polyacrylamide hydrogels, show super-paramagnetic behaviour and saturation magnetization of composite material have been tuned by changing the hydrogel conformation. Adsorption and desorption studies of lysozyme were followed by using pure water at room temperature via fluorescence measurements. Fluorescence measurements showed that, the composite materials adsorbed lysozyme molecules less than 20 s and higher monomer concentration of composite materials cause faster adsorption. Besides, structure of lysozyme molecules were not changed during the adsorption and desorption. As a result Fe3O4-polymer nanocomposites could be used for drug delivery, protein separation and PAAm gels could be used for synthesis of magnetic composites with varying magnetic properties.

  9. Simple approach to study biomolecule adsorption in polymeric microfluidic channels.

    PubMed

    Gubala, Vladimir; Siegrist, Jonathan; Monaghan, Ruairi; O'Reilly, Brian; Gandhiraman, Ram Prasad; Daniels, Stephen; Williams, David E; Ducrée, Jens

    2013-01-14

    Herein a simple analytical method is presented for the characterization of biomolecule adsorption on cyclo olefin polymer (COP, trade name: Zeonor(®)) substrates which are widely used in microfluidic lab-on-a-chip devices. These Zeonor(®) substrates do not possess native functional groups for specific reactions with biomolecules. Therefore, depending on the application, such substrates must be functionalized by surface chemistry methods to either enhance or suppress biomolecular adsorption. This work demonstrates a microfluidic method for evaluating the adsorption of antibodies and oligonucleotides surfaces. The method uses centrifugal microfluidic flow-through chips and can easily be implemented using common equipment such as a spin coater. The working principle is very simple. The user adds 40 L of the solution containing the sample to the starting side of a microfluidic channel, where it is moved through by centrifugal force. Some molecules are adsorbed in the channel. The sample is then collected at the other end in a small reservoir and the biomolecule concentration is measured. As a pilot application, we characterized the adsorption of goat anti-human IgG and a 20-mer DNA on Zeonor(®), and on three types of functionalized Zeonor: 3-aminopropyltriethoxysilane (APTES) modified surface with mainly positive charge, negatively charged surface with immobilized bovine serum albumin (BSA), and neutral, hydrogel-like film with polyethylene glycol (PEG) characteristics. This simple analytical approach adds to the fundamental understanding of the interaction forces in real, microfluidic systems. This method provides a straightforward and rapid way to screen surface compositions and chemistry, and relate these to their effects on the sensitivity and resistance to non-specific binding of bioassays using them. In an additional set of experiments, the surface area of the channels in this universal microfluidic chip was increased by precision milling of microscale

  10. Study on the preparation of straw activated carbon and its phenol adsorption properties

    NASA Astrophysics Data System (ADS)

    Chen, Liping

    2017-01-01

    Using sunflower straw as raw materials to manufacture straw activated carbon-modified by phosphoric acidand adsorption isotherm of phenol on straw activated carbon was studied in a batch reactor. The physical properties of the prepared straw activated carbons were characterized by scanning electron microscopy. The effect of various parameters, adsorbent dose, pH and temperature, were studied on optimum conditions. The results have shown that the absorbent was efficient, the removal ratio of phenol up to 99.36% with an adsorbent dosage of 16 g·L-1, a pH of 6.0-8.0, at 25 °C. The experimental adsorption data fitted reasonably well to the Langmuir isotherm, the maximum adsorption capacity was 109.89 mg/g. The process of adsorption is a exothermic process.

  11. Radiotracer study of the adsorption of organic compounds on gold. adsorption of chloroacetic and phenylacetic acid, and the effects of cadmium, copper, and silver adatoms on it

    SciTech Connect

    Horani, G.; Andreev, V.N.; Vazarinov, V.E.

    1986-04-01

    This paper studies the adsorption of monochloroacetic and phenylacetic acid (MA and PA, respectively) by the radiotracer technique on gold-plated gold electrodes in acidic solutions. The authors also study the effect of cadmium, copper, and silver adatoms on these processes. The adsorption of MA was measured as a function of potential of the electrode. Data from these measurements are presented. Data show that cadmium, copper, and silver ions present in the solution have no effect on the adsorption of PA at potentials where they are not adsorbed on the gold surface. It is confirmed that the radiotracer technique will be as effective in adsorption studies on the gold-plated gold electrode as it was in the case of the platinized platinum electrode.

  12. Adsorption of pyrantel pamoate on mercury from aqueous solutions: studies by stripping voltammetry.

    PubMed

    Gupta, Vinod K; Jain, Rajeev; Jadon, N; Radhapyari, K

    2010-10-01

    Adsorption and electrochemical reduction of pyrantel pamoate are studied in Britton Robinson buffer medium at hanging mercury drop electrode (HMDE) by Adsorptive Stripping Voltammetric technique. The peak current shows a linear dependence with the drug concentration over the range 250 ng mL(-1) to 64 microg mL(-1). Applicability to assay the drug in urine samples is illustrated in the concentration range 5-20 microg mL(-1).

  13. Surfactant loss control in chemical flooding spectroscopic and calorimetric study of adsorption and precipitation on reservoir minerals. Annual report, September 30, 1992--September 30 1995

    SciTech Connect

    Casteel, J.

    1996-07-01

    The aim of this research project was to investigate mechanisms governing adsorption and surface precipitation of flooding surfactants on reservoir minerals. Effects of surfactant structure, surfactant combinations, various inorganic and polymeric species, and solids mineralogy have been determined. A multi-pronged approach consisting of micro & nano spectroscopy, electrokinetics, surface tension and wettability is used in this study. The results obtained should help in controlling surfactant loss in chemical flooding and in developing optimum structures and conditions for efficient chemical flooding processes. During the three years contract period, adsorption of single surfactants and select surfactant mixtures was studied at the solid-liquid and gas-liquid interfaces. Alkyl xylene sulfonates, polyethoxylated alkyl phenols, octaethylene glycol mono n-decyl ether, and tetradecyl trimethyl ammonium chloride were the surfactants studied. Adsorption of surfactant mixtures of varying composition was also investigated. The microstructure of the adsorbed layer was characterized using fluorescence spectroscopy. Changes in interfacial properties such as wettability, electrokinetics and stability of reservoir minerals were correlated with the amounts of reagent adsorbed. Strong effects of the structure of the surfactant and position of functional groups were revealed. Changes of microstructure upon dilution (desorption) were also studied. Presence of the nonionic surfactants in mixed aggregate leads to shielding of the charge of ionic surfactants which in turn promotes aggregation but reduced electrostatic attraction between the charged surfactant and the mineral surface. Strong consequences of surfactant interactions in solution on adsorption as well as correlations between monomer concentration in mixtures and adsorption were revealed.

  14. 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.

  15. A first-principles study of oxygen adsorption on Ir(111) surface

    NASA Astrophysics Data System (ADS)

    Gao, Hengjiao; Xiong, Yuqing; Liu, Xiaoli; Zhao, Dongcai; Feng, Yudong; Wang, Lanxi; Wang, Jinxiao

    2016-12-01

    In order to understand deposition mechanism of iridium thin film by atomic layer deposition, the adsorption of oxygen on Ir(111) surface was studied by use of density functional theory and a periodical slab model. By calculating the adsorption energy and structure of oxygen at four adsorption sites (top, bridge, fcc-hollow and hcp-hollow) on Ir(111) surface, the most stable adsorption site was determined. On this basis, the banding mechanism of O and Ir atoms was studied by density of states of oxygen and iridium atoms. Oxygen adsorbed at hcp(parallel) site on Ir(111) surface was the most stable one according to the adsorption energy calculation results. Orbital charge analysis indicate that charge transferred from 5p and 5d orbit to 2p orbit of adsorbed O atoms, and 6s orbit of iridium atoms. Meanwhile, density of state study indicated that adsorption of oxygen on Ir(111) surface is mainly due to the interaction between 2p orbit of O atoms and 5d orbit of iridium atoms.

  16. Adsorption of molecular oxygen on VIIIB transition metal-doped graphene: A DFT study

    NASA Astrophysics Data System (ADS)

    Nasehnia, F.; Seifi, M.

    2014-12-01

    Adsorption of molecular oxygen with a triplet ground state on Fe-, Co-, Ni-, Ru-, Rh-, Pd-, OS-, Ir- and Pt-doped graphene is studied using density functional theory (DFT) calculations. The calculations show that O2 molecule is chemisorbed on the doped graphene sheets with large adsorption energies ranging from -0.653 eV to -1.851 eV and the adsorption process is irreversible. Mulliken atomic charge analysis of the structure shows that charge transfer from doped graphene sheets to O2 molecule. The amounts of transferred charge are between 0.375e- to 0.650e-, indicating a considerable change in the structures conductance. These results imply that the effect of O2 adsorption on transition metal-doped graphene structures can alter the possibility of using these materials as a toxic-gas (carbon monoxide, hydrogen fluoride, etc.) sensor.

  17. X-ray Spectromicroscopy Study of Protein Adsorption to a Polystyrene-Polylactide Blend

    SciTech Connect

    Leung, Bonnie; Hitchcock, Adam; Cornelius, Rena; Brash, John; Scholl, Andreas; Doran, Andrew

    2010-06-09

    Synchrotron-based X-ray photoemission electron microscopy (X-PEEM) was used to study the adsorption of human serum albumin (HSA) to polystyrene-polylactide (40:60 PS-PLA, 0.7 wt percent) thin films, annealed under various conditions. The rugosity of the substrate varied from 35 to 90 nm, depending on the annealing conditions. However, the characteristics of the protein adsorption (amounts and phase preference) were not affected by the changes in topography. The adsorption was also not changed by the phase inversion which occured when the PS-PLA substrate was annealed above Tg of the PLA. The amount of protein adsorbed depended on whether adsorption took place from distilled water or phosphate buffered saline solution. These differences are interpreted as a result of ionic strength induced changes in the protein conformation in solution.

  18. Kinetics and thermodynamics studies of silver ions adsorption onto coconut shell activated carbon.

    PubMed

    Silva-Medeiros, Flávia V; Consolin-Filho, Nelson; Xavier de Lima, Mateus; Bazzo, Fernando Previato; Barros, Maria Angélica S D; Bergamasco, Rosângela; Tavares, Célia R G

    2016-12-01

    The presence of silver in the natural water environment has been of great concern because of its toxicity, especially when it is in the free ion form (Ag(+)). This paper aims to study the adsorption kinetics of silver ions from an aqueous solution onto coconut shell activated carbon using batch methods. Batch kinetic data were fitted to the first-order model and the pseudo-second-order model, and this last equation fits correctly the experimental data. Equilibrium experiments were carried out at 30°C, 40°C, and 50°C. The adsorption isotherms were reasonably fit using Langmuir model, and the adsorption process was slightly influenced by changes in temperature. Thermodynamic parameters (ΔH°, ΔG°, and ΔS°) were determined. The adsorption process seems to be non-favorable, exothermic, and have an increase in the orderness.

  19. Optimization of conditions for Cu(II) adsorption on D151 resin from aqueous solutions using response surface methodology and its mechanism study.

    PubMed

    Zhang, Hao; Xiong, Chunhua; Liu, Fang; Zheng, Xuming; Jiang, Jianxiong; Zheng, Qunxiong; Yao, Caiping

    2014-01-01

    An experimental study on the removal of Cu(II) from aqueous solutions by D151 resin was carried out in a batch system. The response surface methodology (RSM)-guided optimization indicated that the optimal adsorption conditions are: temperature of 35 °C, pH of 5.38, and initial Cu(II) concentration of 0.36 mg/mL, and the predicted adsorption capacity from the model reached 328.3 mg/g. At optimum adsorption conditions, the adsorption capacity of Cu(II) was 321.6 mg/g, which obtained from real experiments what were in close agreement with the predicted value. The adsorption isotherms data fitted the Langmuir model well, and the correlation coefficient has been evaluated. The calculation data of thermodynamic parameters (ΔG, ΔS, and ΔH) confirmed that the adsorption process was endothermic and spontaneous in nature. The desorption study revealed that Cu(II) can be effectively eluted by 1 mol/l HCl solution, and the recovery was 100%. Moreover, the characterization was undertaken by infrared (IR) spectroscopy.

  20. Adsorption of Dimethyldodecylamine Oxide and Its Mixtures with Triton X-100 at the Hydrophilic Silica/Water Interface Studied Using Total Internal Reflection Raman Spectroscopy.

    PubMed

    Ngo, Dien; Baldelli, Steven

    2016-12-08

    Adsorption of dimethyldodecylamine oxide (DDAO) and its mixtures with Triton X-100 (TX-100) at the hydrophilic silica/water interface has been studied using total internal reflection (TIR) Raman spectroscopy and target factor analysis (TFA). The use of a linear vibrational spectroscopic technique helps obtain information on molecular behavior, adsorbed amount, and conformational order of surfactant molecules at the interface. The results obtained from polarized Raman measurements of pure DDAO show insignificant changes in the orientation and conformational order of surface molecules as a function of DDAO bulk concentrations. The adsorption isotherm of pure DDAO shows a change in the structure of the adsorbed layer at concentrations close to the critical micelle concentration (cmc). TFA reveals that, for a low concentration of DDAO (0.30 mM in this study), adsorption of both DDAO and TX-100 in the mixed surfactants was enhanced at low TX-100 concentrations. The synergistic effect is dominant at low concentrations of TX-100, with enhanced adsorption of both surfactants. Although competitive adsorption is effective at high concentrations of TX-100, the presence of a small amount of DDAO at the interface still enhances TX-100 adsorption. When DDAO concentrations are increased to 1.00 mM, TX-100 replaces DDAO molecules on the surface when TX-100 concentration is increased.

  1. Kafirin adsorption on ion-exchange resins: isotherm and kinetic studies.

    PubMed

    Kumar, Prashant; Lau, Pei Wen; Kale, Sandeep; Johnson, Stuart; Pareek, Vishnu; Utikar, Ranjeet; Lali, Arvind

    2014-08-22

    Kafirin is a natural, hydrophobic and celiac safe prolamin protein obtained from sorghum seeds. Today kafirin is found to be useful in designing delayed delivery systems and coatings of pharmaceuticals and nutraceuticals where its purity is important and this can be obtained by adsorptive chromatography. This study is the first scientific insight into the isotherm and kinetic studies of kafirin adsorption on anion- and cation-exchange resins for practical applications in preparative scale chromatography. Adsorption isotherms of kafirin were determined for five anion- and two cation-exchange resins in batch systems. Isotherm parameters such as maximum binding capacity and dissociation constant were determined from Langmuir isotherm, and adsorptive capacity and affinity constant from Freundlich isotherm. Langmuir isotherm was found to fit the adsorption equilibrium data well. Batch uptake kinetics for kafirin adsorption on these resins was also carried out and critical parameters including the diffusion coefficient, film mass transfer coefficient, and Biot number for film-pore diffusion model were calculated. Both the isotherm and the kinetic parameters were considered for selection of appropriate resin for kafirin purification. UNOsphere Q (78.26 mg/ml) and Toyopearl SP-650M (57.4 mg/ml) were found to offer better kafirin binding capacities and interaction strength with excellent uptake kinetics under moderate operating conditions. With these adsorbents, film diffusion resistance was found to be major governing factor for adsorption (Bi<10 and δ<1). Based on designer objective function, UNOsphere Q was found be best adsorbent for binding of kafirin. The data presented is valuable for designing large scale preparative adsorptive chromatographic kafirin purification systems.

  2. Functionalized mesoporous materials for adsorption and release of different drug molecules: A comparative study

    SciTech Connect

    Wang Gang; Otuonye, Amy N.; Blair, Elizabeth A.; Denton, Kelley; Tao Zhimin; Asefa, Tewodros

    2009-07-15

    The adsorption capacity and release properties of mesoporous materials for drug molecules can be improved by functionalizing their surfaces with judiciously chosen organic groups. Functionalized ordered mesoporous materials containing various types of organic groups via a co-condensation synthetic method from 15% organosilane and by post-grafting organosilanes onto a pre-made mesoporous silica were synthesized. Comparative studies of their adsorption and release properties for various model drug molecules were then conducted. Functional groups including 3-aminopropyl, 3-mercaptopropyl, vinyl, and secondary amine groups were used to functionalize the mesoporous materials while rhodamine 6G and ibuprofen were utilized to investigate the materials' relative adsorption and release properties. The self-assembly of the mesoporous materials was carried out in the presence of cetyltrimethylammonium bromide (CTAB) surfactant, which produced MCM-41 type materials with pore diameters of {approx}2.7-3.3 nm and moderate to high surface areas up to {approx}1000 m{sup 2}/g. The different functional groups introduced into the materials dictated their adsorption capacity and release properties. While mercaptopropyl and vinyl functionalized samples showed high adsorption capacity for rhodamine 6G, amine functionalized samples exhibited higher adsorption capacity for ibuprofen. While the diffusional release of ibuprofen was fitted on the Fickian diffusion model, the release of rhodamine 6G followed Super Case-II transport model. - Graphical abstract: The adsorption capacity and release properties of mesoporous materials for various drug molecules are tuned by functionalizing the surfaces of the materials with judiciously chosen organic groups. This work reports comparative studies of the adsorption and release properties of functionalized ordered mesoporous materials containing different hydrophobic and hydrophilic groups that are synthesized via a co-condensation and post

  3. Adsorption studies of Cu(II) onto biopolymer chitosan and its nanocomposite 5%bentonite/chitosan.

    PubMed

    Moussout, Hamou; Ahlafi, Hammou; Aazza, Mustapha; Zegaoui, Omar; El Akili, Charaf

    2016-01-01

    Chitosan (CS) and nanocomposite 5%bentonite/chitosan (5%Bt/CS) prepared from the natural biopolymer CS were tested to remove Cu(II) ions using a batch adsorption experiment at various temperatures (25, 35 and 45°C). X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis/differential thermal analysis (TGA/DTA) were used in CS and the nanocomposite characterisation. This confirmed the exfoliation of bentonite (Bt) to form the nanocomposite. The adsorption kinetics of copper on both solids was found to follow a pseudo-second-order law at each studied temperature. The Cu(II) adsorption capacity increased as the temperature increased from 25 to 45°C for nanocomposite adsorbent but slightly increased for CS. The data were confronted to the nonlinear Langmuir, Freundlich and Redlich-Peterson models. It was found that the experimental data fitted very well the Langmuir isotherm over the whole temperature and concentration ranges. The maximum monolayer adsorption capacity for the Cu(II) was 404-422 mg/g for CS and 282-337 mg/g for 5%Bt/CS at 25-45°C. The thermodynamic study showed that the adsorption process was spontaneous and endothermic. The complexation of Cu(II) with NH(2) and C = O groups as active sites was found to be the main mechanism in the adsorption processes.

  4. A DFT study of hydrogen adsorption on Be, Mg and Ca frameworks in erionite zeolite

    NASA Astrophysics Data System (ADS)

    Fellah, Mehmet Ferdi

    2017-02-01

    The molecular hydrogen adsorption was investigated on additional frameworks with earth alkaline metal atoms (Be, Mg and Ca) in 24T ERI zeolite cluster model by means of Density Functional Theory study. HOMO and LUMO energy values, chemical potential, chemical hardness, electronegativity, adsorption energy and adsorption enthalpy values have been calculated in this study. Mg-ERI and Ca-ERI clusters have much lower chemical potentials with much lower adsorption energy values when compared to the value of Be-ERI cluster. Additionally, they are softer than Be-ERI cluster with respect to their lower chemical hardness values. Hydrogen adsorption enthalpy values were computed as -3.6 and -3.9 kJ/mol on Mg-ERI and Ca-ERI clusters, respectively. These adsorption enthalpy values are significantly larger than the enthalpy value of liquefaction for hydrogen molecule. This consequently specifies that Mg-ERI and Ca-ERI zeolite structures which have higher chemical reactivity appear to be a promising candidate cryoadsorbent for hydrogen storage.

  5. Modification of bentonite with a cationic surfactant: An adsorption study of textile dye Reactive Blue 19.

    PubMed

    Ozcan, Adnan; Omeroğlu, Ciğdem; Erdoğan, Yunus; Ozcan, A Safa

    2007-02-09

    The utilization of modified bentonite with a cationic surfactant (dodecyltrimethylammonium (DTMA) bromide) as an adsorbent was successfully carried out to remove a synthetic textile dye (Reactive Blue 19 (RB19)) by adsorption, from aqueous solutions. Batch studies were carried out to address various experimental parameters such as pH, contact time and temperature. The surface modification of bentonite with a surfactant was examined using the FTIR spectroscopic technique and elemental analysis. Effective pH for the adsorption of RB19 onto DTMA-bentonite was around 1.5. The Langmuir isotherm model was found to be the best to represent the equilibrium with experimental data. The maximum adsorption capacity (q(max)) has been found to be 3.30x10(-4)molg(-1) or 206.58mgg(-1). The thermodynamic study indicated that the adsorption of RB19 onto DTMA-bentonite was favored with the negative Gibbs free energy values. The pseudo-second-order rate equation was able to provide the best description of adsorption kinetics and the intraparticle diffusion model was also applicable up to 40min for the adsorption of RB19 onto DTMA-bentonite.

  6. Study on the adsorption of Cu(II) by folic acid functionalized magnetic graphene oxide

    NASA Astrophysics Data System (ADS)

    Wang, Cuicui; Ge, Heyi; Zhao, Yueying; Liu, Shanshan; Zou, Yu; Zhang, Wenbo

    2017-02-01

    The folic acid functionalized magnetic graphene oxide (FA-mGO) as a new adsorbent has been synthesized in this work for the elimination of Cu(II) from waste water. The as-prepared FA-mGO was tested by SEM, TEM, particle size analyzer, FTIR, XRD, Roman spectrum, TGA and magnetic properties analyzer. Some factors, such as adsorbent dose, pH, contact time, initial concentration of adsorbate and temperature were explored. The results showed that the FA-mGO had the better adsorption performance than mGO. After 40 min, the adsorption equilibrium could be reached. Furthermore, the adsorption property obeyed the pseudo-second order kinetic model and the Temkin isotherms well. The maximum adsorption capacity was 283.29 mg/g for Cu(II) from Pseudo-second-order model at pH=5 and 318 K. The chelation action between FA and Cu(II) along with electrostatic incorporation between GO and Cu(II) determined the favourable adsorption property. Besides, thermodynamic studies results ∆G0<0, ∆H0>0, ∆S0>0 suggested that the adsorption mechanism was an endothermic and spontaneous process essentially. Finally, desorption and reusability studies imply FA-mGO has an excellent reproducibility and is benefit to environmental protection and resource conservation.

  7. Study of interaction and adsorption of aromatic amines by manganese oxides and their role in chemical evolution

    NASA Astrophysics Data System (ADS)

    Bhushan, Brij; Nayak, Arunima; Kamaluddin

    2017-04-01

    The role of manganese oxides in concentrating organic moieties and offering catalytic activity for prebiotic reactions is investigated by studying their interaction with different aromatic amines such as aniline, p-chloroaniline, p-toluidine and p-anisidine. For all amines, metal oxides showed highest adsorption at neutral pH. The order of their adsorption capacity and affinity as revealed by the Langmuir constants was found to be manganosite (MnO) > bixbyite (Mn2O3) > hausmannite (Mn3O4) > and pyrolusite (MnO2). At alkaline pH, these manganese oxides offered their surfaces for oxidation of amines to form coloured oligomers. Analysis of the oxidation products by gas chromatography-mass spectrometry showed the formation of a dimer from p-anisidine and p-chloroaniline, while a trimer and tetramer is formed from p-toluidine and aniline, respectively. A reaction mechanism is proposed for the formation of the oligomers. While field-emission scanning electron microscopic studies confirm the binding phenomenon, the Fourier transform infrared spectroscopy analysis suggests that the mechanism of binding of amines on the manganese oxides was primarily electrostatic. The adsorption behaviour of the studied aromatic amines followed the order: p-anisidine > p-toluidine > aniline > p-chloroaniline, which is related to the basicities and structure of the amines. Our studies confirmed the significance of the role of manganese oxides in prebiotic chemistry.

  8. Phosphate adsorption on lanthanum loaded biochar.

    PubMed

    Wang, Zhanghong; Shen, Dekui; Shen, Fei; Li, Tianyu

    2016-05-01

    To attain a low-cost and high-efficient phosphate adsorbent, lanthanum (La) loaded biochar (La-BC) prepared by a chemical precipitation method was developed. La-BC and its pristine biochar (CK-BC) were comparatively characterized using zeta potential, BET surface area, scanning electron microscopy/energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The adsorption ability and the mechanisms during adsorption process for the La-BC samples were also investigated. La loaded on the surface of biochar can be termed as La-composites (such as LaOOH, LaONO3 and La(OH)3), leading to the decrease of negative charge and surface area of biochar. La-BC exhibited the high adsorption capacity to phosphate compared to CK-BC. Adsorption isotherm and adsorption kinetic studies showed that the Langmuir isotherm and second order model could well describe the adsorption process of La-BC, indicating that the adsorption was dominated by a homogeneous and chemical process. The calculated maximum adsorption capacity was as high as 46.37 mg g(-1) (computed in P). Thermodynamic analysis revealed that the adsorption was spontaneous and endothermic. SEM, XRD, XPS and FT-IR analysis suggested that the multi-adsorption mechanisms including precipitation, ligand exchange and complexation interactions can be evidenced during the phosphate adsorption process by La-composites in La-BC.

  9. Adsorption behavior of mercury on functionalized aspergillus versicolor mycelia: atomic force microscopic study.

    PubMed

    Das, Sujoy K; Das, Akhil R; Guha, Arun K

    2009-01-06

    The adsorption characteristics of mercury on Aspergillus versicolor mycelia have been studied under varied environments. The mycelia are functionalized by carbon disulfide (CS(2)) treatment under alkaline conditions to examine the enhance uptake capacity and explore its potentiality in pollution control management. The functionalized A. versicolor mycelia have been characterized by scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDXA), attenuated total reflection infrared (ATR-IR), and atomic force microscopy (AFM) probing. SEM and AFM images exhibit the formation of nanoparticles on the mycelial surface. ATR-IR profile confirms the functionalization of the mycelia following chemical treatment. ATR-IR and EDXA results demonstrate the binding of the sulfur groups of the functionalized mycelia to the mercury and consequent formation metal sulfide. AFM study reveals that the mycelial surface is covered by a layer of densely packed domain like structures. Sectional analysis yields significant increase in average roughness (R(rms)) value (20.5 +/- 1.82 nm) compared to that of the pristine mycelia (4.56 +/- 0.82 nm). Surface rigidity (0.88 +/- 0.06 N/m) and elasticity (92.6 +/- 10.2 MPa) obtained from a force distance curve using finite element modeling are found to increase significantly with respect to the corresponding values of (0.65 +/- 0.05 N/m and 32.8 +/- 4.5 MPa) of the nonfunctionalized mycelia. The maximum mercury adsorption capacity of the functionalized mycelia is observed to be 256.5 mg/g in comparison to 80.71 mg/g for the pristine mycelia.

  10. Ionic adsorption of catalase on bioskin: kinetic and ultrastructural studies.

    PubMed

    Solas, M T; Vicente, C; Xavier, L; Legaz, M E

    1994-03-15

    Bioskin is a natural polymer produced by Acetobacter xylinum and several yeasts in culture. It contains glucosamine and N-acetyl galactosamine which promote ionic adsorption of catalase at the adequate pH value. High values of ionic strength are required to enzyme desorption. Adsorption of catalase on bioskin fibers has been visualized by scanning electron microscopy associated to a dispersion X-ray analyzer. At low enzyme density, the affinity of the immobilized catalase for hydrogen peroxide was 30% lower than that of the free enzyme. This affinity decreased dramatically at higher density of immobilized enzyme and could not be increased by agitation of the enzyme reaction mixture. Immobilized catalase retains about 70% of its initial activity after 16 d storage, whereas soluble enzyme is completely inactivated after 3 d at room temperature. The haeme group of catalase is not protected after immobilization since it is accessible to both EDTA and phloroglucinol, chelating agents which inactivate catalase by removing the iron atom from the haeme group.

  11. Fixed-bed adsorption study of methylene blue onto pyrolytic tire char

    NASA Astrophysics Data System (ADS)

    Makrigianni, Vassiliki; Giannakas, Aris; Papadaki, Maria; Albanis, Triantafyllos; Konstantinou, Ioannis

    2016-04-01

    In this work, the adsorption efficiency of acid treated pyrolytic tire char to cationic methylene blue (MB) dye adsorption from aqueous solutions was investigated by fixed-bed adsorption column experiments. The effects of the initial dye concentration (10 - 40 mg L-1) and feed flow rate (50 - 150 mL min -1) with a fixed bed height (15 cm) were studied in order to determine the breakthrough characteristics of the adsorption system. The Adams-Bohart, Yoon-Nelson and Thomas model were applied to the adsorption of MB onto char at different operational conditions to predict the breakthrough curves and to determine the characteristic parameters of the column. The results showed that the maximum adsorbed quantities decreased with increasing flow rate and increased with increasing initial MB concentration. Breakthrough time and exhaustion time increased with decreasing inlet dye concentration and flow rate. In contrast with Adams-Bohart model, Yoon-Nelson model followed by Thomas model were found more suitable to describe the fixed-bed adsorption of methylene blue by char. The correlation coefficient values R2 for both models at different operating conditions are higher than 0.9 and the low average relative error values provided very good fittings of experimental data at different operating conditions. Higher adsorption capacity of 3.85 mg g -1 was obtained at 15 cm of adsorbent bed height, flow rate of 100 mL min -1and initial MB concentration of 40 mg L-1. Although that activated carbons exhibited higher adsorption capacities in the literature, acid-treated pyrolytic tire char was found to be considerably efficient adsorbent for the removal of MB dye column taking into account the advantages of the simpler production process compared to activated carbons, as well as, the availability of waste tire feedstock and concurrent waste tire management.

  12. First-principles study of adsorption of methanethiol on Co(0001)

    NASA Astrophysics Data System (ADS)

    Wang, L. G.; Tsymbal, E. Y.; Jaswal, S. S.

    2004-08-01

    Investigation of the resident site and the adsorption phase structure of thiolates is of fundamental importance for understanding the formation of self-assembled organic monolayers on metal substrate surfaces. In the present study, we have investigated adsorption of methanethiol, CH3SH , on the ferromagnetic Co(0001) surface using density functional theory calculations. We find that the dissociative adsorption of CH3SH forming an adsorbed methylthiolate (CH3S) and an adsorbed H atom is energetically favorable, and that the CH3S molecule adsorbed at the threefold fcc and hcp hollow sites is most stable. The adsorption energy at the bridge site is only ˜0.2eV smaller than that at the threefold hollow site, and the adsorption of CH3S at the atop site is unstable. For the (3×3)R30° , (2×2) and (2×3) adsorptions, we find that the S-C bond tends to be normal to the surface, whereas for the (2×1) adsorption it tilts away from the surface normal direction by ˜40° . The (2×1) adsorption phase is much less stable. The reduction of the adsorption energy with the increasing coverage is attributed to the repulsive interaction between the adsorbates. Our calculations show that the (3×3)R30° structure may form in the process of methylthiolate adsorption on Co(0001) due to its adsorption energy being only 0.1eV lower than that for the (2×2) and (2×3) structures. We find that there is a charge transfer from the substrate surface atoms to the S atoms, and that the S-Co bond is strongly polar. The surface Co atoms bound to S have a magnetic moment of ˜1.66μB , while the surface Co atoms unbound to S have a larger magnetic moment of ˜1.85μB . The S atom in the adsorbed CH3S acquires a magnetic moment of ˜0.08μB .

  13. Flue gas adsorption by single-wall carbon nanotubes: A Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Romero-Hermida, M. I.; Romero-Enrique, J. M.; Morales-Flórez, V.; Esquivias, L.

    2016-08-01

    Adsorption of flue gases by single-wall carbon nanotubes (SWCNT) has been studied by means of Monte Carlo simulations. The flue gas is modeled as a ternary mixture of N2, CO2, and O2, emulating realistic compositions of the emissions from power plants. The adsorbed flue gas is in equilibrium with a bulk gas characterized by temperature T, pressure p, and mixture composition. We have considered different SWCNTs with different chiralities and diameters in a range between 7 and 20 Å. Our results show that the CO2 adsorption properties depend mainly on the bulk flue gas thermodynamic conditions and the SWCNT diameter. Narrow SWCNTs with diameter around 7 Å show high CO2 adsorption capacity and selectivity, but they decrease abruptly as the SWCNT diameter is increased. For wide SWCNT, CO2 adsorption capacity and selectivity, much smaller in value than for the narrow case, decrease mildly with the SWCNT diameter. In the intermediate range of SWCNT diameters, the CO2 adsorption properties may show a peculiar behavior, which depend strongly on the bulk flue gas conditions. Thus, for high bulk CO2 concentrations and low temperatures, the CO2 adsorption capacity remains high in a wide range of SWCNT diameters, although the corresponding selectivity is moderate. We correlate these findings with the microscopic structure of the adsorbed gas inside the SWCNTs.

  14. Kinetic study for copper adsorption onto soil minerals in the absence and presence of humic acid.

    PubMed

    Komy, Zanaty R; Shaker, Ali M; Heggy, Said E M; El-Sayed, Mohamed E A

    2014-03-01

    Equilibrium and kinetics of Cu(2+) adsorption onto soil minerals (kaolinite and hematite) in the absence and presence of humic acid have been investigated under various conditions. The influences of ionic strength, pH and solution cations on the rate of the adsorption have been studied. The rate and the amount of adsorbed Cu(2+) onto soil minerals in the absence or the presence of humic acid increased with decreasing ionic strength, increasing pH and in the presence of the background electrolyte K(+) rather than Ca(2+). Humic acid enhanced the rate and the amount of adsorbed Cu(2+) onto soil minerals. The adsorption equilibrium data showed that adsorption behavior of Cu(2+) could be described more reasonably by Langmiur adsorption isotherm than Freundlich isotherm in the absence or presence of humic acid. Pseudo first and pseudo second order models were used to evaluate the kinetic data and the rate constants. The results indicated that the adsorption of Cu(2+) onto hematite and kaolinite in the absence and presence of humic acid is more conforming to pseudo second order kinetics.

  15. 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

    2014-05-07

    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.

  16. 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.

  17. Adsorption of CO molecules on doped graphene: A first-principles study

    NASA Astrophysics Data System (ADS)

    Wang, Weidong; Zhang, Yuxiang; Shen, Cuili; Chai, Yang

    2016-02-01

    As a typical kinds of toxic gases, CO plays an important role in environmental monitoring, control of chemical processes, space missions, agricultural and medical applications. Graphene is considered a potential candidate of gases sensor, so the adsorption of CO molecules on various graphene, including pristine graphene, Nitrogen-doped graphene (N-doped graphene) and Aluminum-doped graphene (Al-doped graphene), are studied by using first-principles calculations. The optimal configurations, adsorption energies, charge transfer, and electronic properties including band structures, density of states and differential charge density are obtained. The adsorption energies of CO molecules on pristine graphene and N-doped graphene are -0.01 eV, and -0.03 eV, respectively. In comparison, the adsorption energy of CO on Al-doped graphene is much larger, -2.69 eV. Our results also show that there occurs a large amount of charge transfer between CO molecules and graphene sheet after the adsorption, which suggests Al-doped graphene is more sensitive to the adsorption of CO than pristine graphene and N-doped graphene. Therefore, the sensitivity of gases on graphene can be drastically improved by introducing the suitable dopants.

  18. Electrophoretic Mobility Study of the Adsorption of Alkyl Xanthate Ions on Galena and Sphalerite.

    PubMed

    Song, S.; Lopez-Valdivieso, A.; Ojeda-Escamilla, M. C.

    2001-05-01

    The adsorption of ethyl and amyl xanthate ions on galena and sphalerite fines has been studied using electrophoretic light-scattering (ELS) measurements. It was performed on galena and sphalerite (<2&mgr;m) in aqueous solution at different potassium ethyl xanthate (PEX) and potassium amyl xanthate (PAX) concentrations. It has been observed that the presence of PEX or PAX caused the isoelectric points (IEP) of galena and sphalerite fines to shift and the electrophoretic mobility to reverse in sign, indicating that the xanthate ions chemisorbed on galena and sphalerite surfaces. This adsorption markedly broadened the electrophoretic mobility distribution of the mineral fines, suggesting that the populations of the particles have quite different adsorption densities of xanthate ions, and therefore the particle hydrophobicity was different. This phenomenon might be attributable to the effect of the hemimicelle adsorption of the xanthate ions on the minerals, the nonuniform distribution of active sites and their degree of activity, the effect of particle size and shape, etc. The nonuniform adsorption has been found to increase with increasing PEX or PAX concentration, reaching a maximum at a medium concentration followed by a decline. Also, experimental results have demonstrated that the nonuniform adsorption of the xanthate ions is much stronger on sphalerite than on galena, which may explain why sphalerite has a worse flotation response than galena when alkyl xanthates are used as collectors in flotation systems. Copyright 2001 Academic Press.

  19. Adsorption of methylene blue onto activated carbon produced from tea (Camellia sinensis L.) seed shells: kinetics, equilibrium, and thermodynamics studies.

    PubMed

    Gao, Jun-Jie; Qin, Ye-Bo; Zhou, Tao; Cao, Dong-Dong; Xu, Ping; Hochstetter, Danielle; Wang, Yue-Fei

    2013-07-01

    Tea (Camellia sinensis L.) seed shells, the main byproduct of the manufacture of tea seed oil, were used as precursors for the preparation of tea activated carbon (TAC) in the present study. A high yield (44.1%) of TAC was obtained from tea seed shells via a one-step chemical method using ZnCl2 as an agent. The Brunauer-Emmett-Teller (BET) surface area and the total pore volumes of the obtained TAC were found to be 1530.67 mg(2)/g and 0.7826 cm(3)/g, respectively. The equilibrium adsorption results were complied with Langmuir isotherm model and its maximum monolayer adsorption capacity was 324.7 mg/g for methylene blue. Adsorption kinetics studies indicated that the pseudo-second-order model yielded the best fit for the kinetic data. An intraparticle diffusion model suggested that the intraparticle diffusion was not the only rate-controlling step. Thermodynamics studies revealed the spontaneous and exothermic nature of the sorption process. These results indicate that tea seed shells could be utilized as a renewable resource to develop activated carbon which is a potential adsorbent for methylene blue.

  20. Adsorption of methylene blue onto activated carbon produced from tea (Camellia sinensis L.) seed shells: kinetics, equilibrium, and thermodynamics studies*

    PubMed Central

    Gao, Jun-jie; Qin, Ye-bo; Zhou, Tao; Cao, Dong-dong; Xu, Ping; Hochstetter, Danielle; Wang, Yue-fei

    2013-01-01

    Tea (Camellia sinensis L.) seed shells, the main byproduct of the manufacture of tea seed oil, were used as precursors for the preparation of tea activated carbon (TAC) in the present study. A high yield (44.1%) of TAC was obtained from tea seed shells via a one-step chemical method using ZnCl2 as an agent. The Brunauer-Emmett-Teller (BET) surface area and the total pore volumes of the obtained TAC were found to be 1 530.67 mg2/g and 0.782 6 cm3/g, respectively. The equilibrium adsorption results were complied with Langmuir isotherm model and its maximum monolayer adsorption capacity was 324.7 mg/g for methylene blue. Adsorption kinetics studies indicated that the pseudo-second-order model yielded the best fit for the kinetic data. An intraparticle diffusion model suggested that the intraparticle diffusion was not the only rate-controlling step. Thermodynamics studies revealed the spontaneous and exothermic nature of the sorption process. These results indicate that tea seed shells could be utilized as a renewable resource to develop activated carbon which is a potential adsorbent for methylene blue. PMID:23825151

  1. Activated carbon from vetiver roots: gas and liquid adsorption studies.

    PubMed

    Gaspard, S; Altenor, S; Dawson, E A; Barnes, P A; Ouensanga, A

    2007-06-01

    Large quantities of lignocellulosic residues result from the industrial production of essential oil from vetiver grass (Vetiveria zizanioides) roots. These residues could be used for the production of activated carbon. The yield of char obtained after vetiver roots pyrolysis follows an equation recently developed [A. Ouensanga, L. Largitte, M.A. Arsene, The dependence of char yield on the amounts of components in precursors for pyrolysed tropical fruit stones and seeds, Micropor. Mesopor. Mater. 59 (2003) 85-91]. The N(2) adsorption isotherm follows either the Freundlich law K(F)P(alpha) which is the small alpha equation limit of a Weibull shaped isotherm or the classical BET isotherm. The surface area of the activated carbons are determined using the BET method. The K(F) value is proportional to the BET surface area. The alpha value increases slightly when the burn-off increases and also when there is a clear increase in the micropore distribution width.

  2. Tetracycline-loaded biomimetic apatite: an adsorption study.

    PubMed

    Cazalbou, Sophie; Bertrand, Ghislaine; Drouet, Christophe

    2015-02-19

    Biomimetic apatites are appealing compounds for the elaboration of bioactive bone-repair scaffolds due to their intrinsic similarity to bone mineral. Bone surgeries are however often heavy procedures, and the infiltration of pathogens may not be totally avoided. To prevent their development, systemic antibiotic prophylaxis is widespread but does not specifically target surgical sites and involves doses not always optimized. A relevant alternative is a preliminary functionalization by an infection-fighting agent. In this work, we investigated from a physicochemical viewpoint the association of a wide-spectrum antibiotic, tetracycline (TC), and a biomimetic nanocrystalline apatite previously characterized. TC adsorption kinetics and isotherm were thoroughly explored. Kinetic data were fitted to various models (pseudo-first-order, pseudo-second-order, general kinetic model of order n, Elovich, double-exponential, and purely diffusive models). The best fit was found for a double-exponential kinetic model or with a decimal reaction order of 1.4, highlighting a complex process with such TC molecules which do not expose high-affinity end groups for the surface of apatite. The adsorption isotherm was perfectly fitted to the Sips (Langmuir-Freundlich) model, while other models failed to describe it, and the Sips exponent greater than unity (1.08) suggested a joint impact of surface heterogeneity and positive cooperativity between adsorbed molecules. Finally, preliminary insights on TC release from pelletized nanocrystalline apatite, in aqueous medium and neutral pH, were obtained using a recirculation cell, indicating a release profile mainly following a Higuchi-like diffusion-limited rate. This work is intended to shed more light on the interaction between polar molecules not exhibiting high-affinity end groups and biomimetic apatites and is a starting point in view of the elaboration of biomimetic apatite-based bone scaffolds functionalized with polar organic drugs for a

  3. Adsorption Properties of Tetracycline onto Graphene Oxide: Equilibrium, Kinetic and Thermodynamic Studies

    PubMed Central

    Ghadim, Ehsan Ezzatpour; Manouchehri, Firouzeh; Soleimani, Gholamreza; Hosseini, Hadi; Kimiagar, Salimeh; Nafisi, Shohreh

    2013-01-01

    Graphene oxide (GO) nanoparticle is a high potential effective absorbent. Tetracycline (TC) is a broad-spectrum antibiotic produced, indicated for use against many bacterial infections. In the present research, a systematic study of the adsorption and release process of tetracycline on GO was performed by varying pH, sorption time and temperature. The results of our studies showed that tetracycline strongly loads on the GO surface via π–π interaction and cation–π bonding. Investigation of TC adsorption kinetics showed that the equilibrium was reached within 15 min following the pseudo-second-order model with observed rate constants of k2 = 0.2742–0.5362 g/mg min (at different temperatures). The sorption data has interpreted by the Langmuir model with the maximum adsorption of 323 mg/g (298 K). The mean energy of adsorption was determined 1.83 kJ/mol (298 K) based on the Dubinin–Radushkevich (D–R) adsorption isotherm. Moreover, the thermodynamic parameters such as ΔH°, ΔS° and ΔG° values for the adsorption were estimated which indicated the endothermic and spontaneous nature of the sorption process. The electrochemistry approved an ideal reaction for the adsorption under electrodic process. Simulation of GO and TC was done by LAMMPS. Force studies in z direction showed that tetracycline comes close to GO sheet by C8 direction. Then it goes far and turns and again comes close from amine group to the GO sheet. PMID:24302989

  4. [Study on the co-adsorption mechanism of Pb (II) and chlorpyrifos on arid loess in northwestern China].

    PubMed

    Fan, Chun-Hui; Zhang, Ying-Chao; Wang, Jia-Hong

    2013-08-01

    The co-adsorption characteristics of Pb(II) and chlorpyrifos on arid loess were investigated with batch adsorption procedures, and the co-adsorption mechanism was studied with approaches of SEM, FT-IR, XRD and theoretical analysis. The experimental results indicated that the adsorption process of Pb(II) and chlorpyrifos on loess fit better the Langmuir isotherm, the maximum adsorption capacity of q(m) is 12.5 and 0.64 mg x g(-1) for Pb(II) and chlorpyrifos on loess, respectively, and the reaction could be illustrated with pseudo-second order kinetic equation. The SEM micrograph of loess surface varies little after the adsorption process of Pb(II) and chlorpyrifos, and certain wave peaks of FTIR spectra red-shift, disappears or intensity-decrease, with the XRD pattern and theoretical analysis, the adsorption mechanism is described as follows: the adsorption of Pb (II) on arid loess is the chemical-effect of coordination-complexation and Van der Waals force; the physical-adsorption on chlorpyrifos involves the interception function, hydrogen bonds and Van der Waals force, and chemical adsorption effect to some extent. The organic matter in arid loess plays an important role in Pb(II) and chlorpyrifos adsorption.

  5. Adsorption studies of cadmium ions on alginate-calcium carbonate composite beads

    NASA Astrophysics Data System (ADS)

    Mahmood, Zahid; Amin, Athar; Zafar, Uzma; Raza, Muhammad Amir; Hafeez, Irfan; Akram, Adnan

    2015-07-01

    Alginate-calcium carbonate composite material was prepared in the form of beads and characterized using Fourier transform infra red (FT-IR) spectroscopy and scanning electron microscope (SEM) techniques. The adsorption of Cd2+ ions was studied through batch experiments. The adsorption parameters such as contact time (120 min), adsorbent dose (1.5 g), initial metal ion concentration(10 mg/L), pH (6) and agitation speed (150 rpm) were optimized at room temperature. Langmuir and Freundlich isotherms were applied to the data and it was noted that the adsorption of Cd2+ ions is better explained by Freundlich model. The kinetic studies showed that the adsorption of Cd2+ ions followed pseudo-first order kinetics. Thermodynamic parameters like ∆G 0, ∆H 0 and ∆S 0 were calculated and on the basis of these values it was established that the adsorption process is feasible and endothermic in nature. It was concluded from the study that the composite material of alginate and calcium carbonate can effectively be used to recover Cd2+ ions from wastewater.

  6. Kinetic study of brilliant green adsorption from aqueous solution onto white rice husk ash.

    PubMed

    Tavlieva, Mariana P; Genieva, Svetlana D; Georgieva, Velyana G; Vlaev, Lyubomir T

    2013-11-01

    The present research was focused on the study of adsorption kinetics of brilliant green (BG) onto white rice husk ash from aqueous solutions. The research was performed in the temperature interval 290-320 K in 10° steps and in the concentration range of 3-100 mg L(-1). Batch studies were conducted in order to determine the optimal adsorbent dose, and the time required to reach the adsorption equilibrium at each temperature. The effect of the initial concentration of brilliant green was studied (pH not adjusted), as well as the effect of temperature. The maximum adsorption capacity of the WRHA for BG at 320 K was determined to be 85.56 mg g(-1). The adsorption kinetic data were analyzed employing several kinetic models: pseudo-first-order equation, pseudo-second-order equation, Elovichequation, Banghman's equation, Diffusion-chemisorption model, and Boyd kinetic expression. It was established that the adsorption process obeyed the pseudo-second-order kinetic model. Based on the rate constants obtained by this kinetic model using Arrhenius and Eyring equations, the activation parameters were determined, namely the activation energy (50.04 kJ mol(-1)), the change of entropy (-318.31 J mol(-1) K(-1)), enthalpy (-47.50 kJ mol(-1)), and Gibbs free energy (range 44.81-54.36 kJ mol(-1)) for the formation of activated complex from the reagents.

  7. 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.

  8. Arsenic Removal - Adsorptive Media and Coagulation/Filtration Case Studies - Slides

    EPA Science Inventory

    This presentation provides information on the results of three case studies from USEPA arsenic demonstration program. The first case study presented is on the Rimrock, AZ project that used an adsorptive media technology (E33 media) to remove arsenic. The second case study is o...

  9. Dynamic behaviour of Cd2+ adsorption in equilibrium batch studies by CaCO3(-)-rich Corbicula fluminea shell.

    PubMed

    Ismail, Farhah Amalya; Aris, Ahmad Zaharin; Latif, Puziah Abdul

    2014-01-01

    This work presents the structural and adsorption properties of the CaCO3(-)-rich Corbicula fluminea shell as a natural and economic adsorbent to remove Cd ions from aqueous solutions under batch studies. Experiments were conducted with different contact times, various initial concentrations, initial solution pH and serial biosorbent dosage to examine the dynamic characterization of the adsorption and its influence on Cd uptake capacity. The characterization of the C. fluminea shell using SEM/EDX revealed that the adsorbent surface is mostly impregnated by small particles of potentially calcium salts. The dominant Cd adsorption mechanism is strongly pH and concentration dependent. A maximum Cd removal efficiency of 96.20% was obtained at pH 7 while the optimum adsorbent dosage was observed as 5 g/L. The Langmuir isotherm was discovered to be more suitable to represent the experimental equilibrium isotherm results with higher correlation coefficients (R(2) > 0.98) than Freundlich (R(2) < 0.97).The correlation coefficient values (p < 0.01) indicated the superiority of the Langmuir isotherm over the Freundlich isotherm.

  10. Density functional theory study of the adsorption and incorporation of Sc and Y on the AlN(0001) surface

    NASA Astrophysics Data System (ADS)

    González-Hernández, Rafael; González-Garcia, Alvaro; López-Perez, William

    2016-06-01

    Density functional theory (DFT) calculations were carried out in order to study the adsorption and incorporation of scandium and yttrium atoms on the AlN(0001) surface aiming to gain insight into epitaxial growth of ScxAl1-x N and YxAl1-x N layers on AlN. The adsorption energy, geometry, formation energy, band structure and density of states of Sc (and Y) adatom/AlN(0001) systems are calculated. The calculations showed that the interaction between Sc (and Y) adatom and the AlN(0001) surface is strong (~ 3.9 eV) and it prefers to adsorb on N-top site (T4). However, formation energy calculations reveal that the incorporation of Sc and Y atoms in the Al-substitutional site is energetically more favorable compared with the adsorption on the top layers, which can be attributed to the lower enthalpy of formation of ScN and YN with respect to that of AlN. The results also suggest that the Sc and Y atoms prefer to incorporate in top AlN surface layers. At full coverage, calculations show the formation of metallic ScxN and YxAl1-x N layers on the AlN polar surface over the entire range of Al chemical potentials, in agreement with experimental observations. In addition, we found that for high coverage Sc atoms couple ferromagnetically in the Al-substitutional sites on the AlN(0001) surface.

  11. Adsorption of crystal violet onto functionalised multi-walled carbon nanotubes: Equilibrium and kinetic studies.

    PubMed

    Sabna, V; Thampi, Santosh G; Chandrakaran, S

    2016-12-01

    Synthetic dyes present in effluent from textile, paper and paint industries contain crystal violet (CV), a known carcinogenic agent. This study investigates the modification of multiwalled carbon nanotubes by acid reflux method and equilibrium and kinetic behaviour of adsorption of CV onto functionalized multi-walled carbon nanotubes (fMWNTs) in batch system. High stability of the fMWNTs suspension in water indicates the hydrophilicity of fMWNTs induced due to the formation of functional groups that make hydrogen bonds with water molecules. fMWNTs were characterized by Fourier Transform Infra Red (FTIR) spectroscopy and the functional groups present on the fMWNTs were confirmed. Characteristic variation was observed in the FTIR spectra of fMWNTs after adsorption of crystal violet onto it. Adsorption characteristics were evaluated as a function of system variables such as contact time, dosage of fMWNTs and initial concentration and pH of the crystal violet solution. Adsorption capacity of fMWNTs and percentage removal of the dye increased with increase in contact time, adsorbent dosage and pH but declined with increase in initial concentration of the dye. fMWNTs showed higher adsorption capacity compared to that of pristine MWNTs. Data showed good fit with the Langmuir and Freundlich isotherm models and the pseudo-second order kinetic model; the maximum adsorption capacity was 90.52mg/g. Kinetic parameters such as rate constants, equilibrium adsorption capacities and regression coefficients were estimated. Results indicate that fMWNTs are an effective adsorbent for the removal of crystal violet from aqueous solution.

  12. First-principles study on hydrogen adsorption on nitrogen doped graphene

    NASA Astrophysics Data System (ADS)

    Muhammad, Rafique; Shuai, Yong; Tan, He-Ping

    2017-04-01

    In this paper we have investigated the adsorption of Hydrogen on Nitrogen doped graphene in detail by means of first-principles calculations. A comprehensive study is performed of the structural, electronic and optical properties of hydrogen atoms adsorbed on dopant atoms sites and on carbon atoms neighboring dopant atoms. The effect of doping has been investigated by varying the concentration of doping atoms from 3.125%(one atom of nitrogen in 32 host atoms) to 6.25% (two nitrogen atoms in 32 host atoms). Similarly the effect of adsorption has been investigated by varying the concentration of hydrogen atoms and also varying the adsorption sites. Band structure, partial density of states (PDOS) and optical properties of pure, nitrogen doped and hydrogen adsorbed graphene sheet were calculated using VASP (Vienna ab-initio Simulation Package). The calculated results for pure graphene sheet were then compared with nitrogen doped graphene and Hydrogen adsorbed graphene sheet. It is found that upon nitrogen doping the Dirac point in the graphene band structure shifts below the Fermi Energy level and energy gap appears at the high symmetric K-point. On the other hand, by adsorption of Hydrogen atom, there is further change in the band structure near the Fermi level and also the energy gap at the high symmetric K-point is increased. There is change in the dielectric function and refractive index of the graphene after H atoms adsorption on N-doped graphene. The overall absorption spectra is decreased in case of nitrogen doping and after adsorption process of Hydrogen atoms. However a significant red shift in absorption towards visible range of radiation is found to occur for hydrogen atoms adsorbed on nitrogen doped graphene sheet. The reflectivity peak of graphene increases in low energy region after H adsorption on N-doped graphene. The results can be used to tune the Fermi Energy level and to tailor the optical properties of graphene sheet in visible region.

  13. Equilibrium studies of copper ion adsorption onto palm kernel fibre.

    PubMed

    Ofomaja, Augustine E

    2010-07-01

    The equilibrium sorption of copper ions from aqueous solution using a new adsorbent, palm kernel fibre, has been studied. Palm kernel fibre is obtained in large amounts as a waste product of palm oil production. Batch equilibrium studies were carried out and system variables such as solution pH, sorbent dose, and sorption temperature were varied. The equilibrium sorption data was then analyzed using the Langmuir, Freundlich, Dubinin-Radushkevich (D-R) and Temkin isotherms. The fit of these isotherm models to the equilibrium sorption data was determined, using the linear coefficient of determination, r(2), and the non-linear Chi-square, chi(2) error analysis. The results revealed that sorption was pH dependent and increased with increasing solution pH above the pH(PZC) of the palm kernel fibre with an optimum dose of 10g/dm(3). The equilibrium data were found to fit the Langmuir isotherm model best, with a monolayer capacity of 3.17 x 10(-4)mol/g at 339K. The sorption equilibrium constant, K(a), increased with increasing temperature, indicating that bond strength between sorbate and sorbent increased with temperature and sorption was endothermic. This was confirmed by the increase in the values of the Temkin isotherm constant, B(1), with increasing temperature. The Dubinin-Radushkevich (D-R) isotherm parameter, free energy, E, was in the range of 15.7-16.7kJ/mol suggesting that the sorption mechanism was ion exchange. Desorption studies showed that a high percentage of the copper was desorbed from the adsorbent using acid solutions (HCl, HNO(3) and CH(3)COOH) and the desorption percentage increased with acid concentration. The thermodynamics of the copper ions/palm kernel fibre system indicate that the process is spontaneous and endothermic.

  14. A comparison between dual polarization interferometry (DPI) and surface plasmon resonance (SPR) for protein adsorption studies.

    PubMed

    Sonesson, Andreas W; Callisen, Thomas H; Brismar, Hjalmar; Elofsson, Ulla M

    2007-02-15

    This work was performed with the aim of comparing protein adsorption results obtained from the recently developed dual polarization interferometry (DPI) with the well-established surface plasmon resonance (SPR) technique. Both techniques use an evanescent field as the sensing element but completely different methods to calculate the adsorbed mass. As a test system we used adsorption of the lipase from Thermomyces lanuginosus (TLL) on C18 surfaces. The adsorbed amount calculated with both techniques is in good agreement, with both adsorption isotherms saturating at 1.30-1.35 mg/m(2) at TLL concentrations of 1000 nM and above. Therefore, this supports the use of both SPR and DPI as tools for studying protein adsorption, which is very important when comparing adsorption data obtained from the use different techniques. Due to the spot sensing in SPR, this technique is recommended for initial kinetic studies, whereas DPI is more accurate when the refractive index and thickness of the adsorbed layer is of more interest.

  15. DFT study of gases adsorption on sharp tip nano-catalysts surface for green fertilizer synthesis

    NASA Astrophysics Data System (ADS)

    Yahya, Noorhana; Irfan, Muhammad; Shafie, Afza; Soleimani, Hassan; Alqasem, Bilal; Rehman, Zia Ur; Qureshi, Saima

    2016-11-01

    The energy minimization and spin modifications of sorbates with sorbents in magnetic induction method (MIM) play a vital role in yield of fertilizer. Hence, in this article the focus of study is the interaction of sorbates/reactants (H2, N2 and CO2) in term of average total adsorption energies, average isosteric heats of adsorption energies, magnetic moments, band gaps energies and spin modifications over identical cone tips nanocatalyst (sorbents) of Fe2O3, Fe3O4 (magnetic), CuO and Al2O3 (non-magnetic) for green nano-fertilizer synthesis. Study of adsorption energy, band structures and density of states of reactants with sorbents are purely classical and quantum mechanical based concepts that are vividly illustrated and supported by ADSORPTION LOCATOR and Cambridge Seriel Total Energy Package (CASTEP) modules following classical and first principle DFT simulation study respectively. Maximum values of total average energies, total average adsorption energies and average adsorption energies of H2, N2 and CO2 molecules are reported as -14.688 kcal/mol, -13.444 kcal/mol, -3.130 kcal/mol, - kcal/mol and -6.348 kcal/mol over Al2O3 cone tips respectively and minimum over magnetic cone tips. Whereas, the maximum and average minimum values of average isosteric heats of adsorption energies of H2, N2 and CO2 molecules are figured out to be 3.081 kcal/mol, 4.842 kcal/mol and 6.848 kcal/mol, 0.988 kcal/mol, 1.554 kcal/mol and 2.236 kcal/mol over aluminum oxide and Fe3O4 cone tips respectively. In addition to the adsorption of reactants over identical cone sorbents the maximum and minimum values of net spin, electrons and number of bands for magnetite and aluminum oxide cone structures are attributed to 82 and zero, 260 and 196, 206 and 118 for Fe3O4 and Al2O3 cones respectively. Maximum and least observed values of band gap energies are figured out to be 0.188 eV and 0.018 eV with Al2O3 and Fe3O4 cone structures respectively. Ultimately, with the adsorption of reactants an

  16. In situ chitin isolation from body parts of a centipede and lysozyme adsorption studies.

    PubMed

    Bulut, Esra; Sargin, Idris; Arslan, Ozlem; Odabasi, Mehmet; Akyuz, Bahar; Kaya, Murat

    2017-01-01

    Isolation of structurally intact chitin samples for biotechnological applications has gained much recent attention. So far, three-dimensional chitin isolates have been obtained from only diplopods and sponges. In this study, three-dimensional chitin isolates were obtained from the body parts of centipede Scolopendra sp. (antennae, head, forcipule, collum, trunk, trunk legs and last pair of legs) without leading to structural failure. FT-IR spectra of chitin isolates confirmed that chitin samples are in α allomorph. TGA, XRD and SEM analyses and lysozyme adsorption studies revealed that each chitin isolate had different thermal stability, crystallinity and surface characteristics. Among the chitin isolates, Cu(II)-immobilized forcipule chitin showed the highest affinity for lysozyme (54.1mg/g), whereas chitin from last pair of legs exhibited the lowest affinity (3.7mg/g). This study demonstrated that structurally intact chitin isolates can be obtained from the body parts of centipede Scolopendra sp. (antennae, head, forcipule, collum, trunk, trunk legs and last pair of legs) by using a simple chemical procedure. Also, it gives a biotechnological perspective to the organisms in the group of Chilipoda.

  17. Adsorption of ammonium ion by coconut shell-activated carbon from aqueous solution: kinetic, isotherm, and thermodynamic studies.

    PubMed

    Boopathy, Ramasamy; Karthikeyan, Sekar; Mandal, Asit Baran; Sekaran, Ganesan

    2013-01-01

    Ammonium ions are one of the most encountered nitrogen species in polluted water bodies. High level of ammonium ion in aqueous solution imparts unpleasant taste and odor problems, which can interfere with the life of aquatics and human population when discharged. Many chemical methods are developed and being used for removal of ammonium ion from aqueous solution. Among various techniques, adsorption was found to be the most feasible and environmentally friendly with the use of natural-activated adsorbents. Hence, in this study, coconut shell-activated carbon (CSAC) was prepared and used for the removal of ammonium ion by adsorption techniques. Ammonium chloride (analytical grade) was purchased from Merck Chemicals for adsorption studies. The CSAC was used to adsorb ammonium ions under stirring at 100 rpm, using orbital shaker in batch experiments. The concentration of ammonium ion was estimated by ammonia distillate, using a Buchi distillation unit. The influence of process parameters such as pH, temperature, and contact time was studied for adsorption of ammonium ion, and kinetic, isotherm models were validated to understand the mechanism of adsorption of ammonium ion by CSAC. Thermodynamic properties such as ∆G, ∆H, and ∆S were determined for the ammonium adsorption, using van't Hoff equation. Further, the adsorption of ammonium ion was confirmed through instrumental analyses such as SEM, XRD, and FTIR. The optimum conditions for the effective adsorption of ammonium ion onto CSAC were found to be pH 9.0, temperature 283 K, and contact time 120 min. The experimental data was best followed by pseudosecond order equation, and the adsorption isotherm model obeyed the Freundlich isotherm. This explains the ammonium ion adsorption onto CSAC which was a multilayer adsorption with intraparticle diffusion. Negative enthalpy confirmed that this adsorption process was exothermic. The instrumental analyses confirmed the adsorption of ammonium ion onto CSAC.

  18. Comparison study of phosphorus adsorption on different waste solids: Fly ash, red mud and ferric-alum water treatment residues.

    PubMed

    Wang, Ying; Yu, Yange; Li, Haiyan; Shen, Chanchan

    2016-12-01

    The adsorption of phosphorus (P) onto three industrial solid wastes (fly ash, red mud and ferric-alum water treatment residual (FAR)) and their modified materials was studied systematically via batch experiments. Compared with two natural adsorbents (zeolite and diatomite), three solid wastes possessed a higher adsorption capacity for P because of the higher Fe, Al and Ca contents. After modification (i.e., the fly ash and red mud modified by FeCl3 and FARs modified by HCl), the adsorption capacity increased, especially for the modified red mud, where more Fe bonded P was observed. The P adsorption kinetics can be satisfactorily fitted using the pseudo-second-order model. The Langmuir model can describe well the P adsorption on all of the samples in our study. pH and dissolved organic matter (DOM) are two important factors for P adsorption. Under neutral conditions, the maximum adsorption amount on the modified materials was observed. With the deviation from pH7, the adsorption amount decreased, which resulted from the change of P species in water and surface charges of the adsorbents. The DOM in water can promote P adsorption, which may be due to the promotion effects of humic-Fe(Al) complexes and the pH buffer function exceeds the depression of competitive adsorption.

  19. An In Situ Surface Fourier Transform Infrared Study of the Adsorption of Isoquinoline at a Stationary Mercury Electrode

    DTIC Science & Technology

    1988-07-15

    Infrared Study of the Adsorption of Isoquinoline at a Stationary Mercury Electrode by DJ. Blackwood and S. Pons Prepared for publication in J...Secunt ClaMwfkation) An in situ Surface Fourier Transform Infrared Study of the Adsorption of Isoquinoline at a Stationary Mercury Electrode D.lc...SUBJECT TERMS (Continue on roverse if necessary and identify by block ’e’ 9ELD I GROUP I SUB-GROUP infrared spectroelectrochemistry ,adsorption, mercury I

  20. A study on the adsorption mechanism of mercury on Aspergillus versicolor biomass.

    PubMed

    Das, Sujoy K; Das, Akhil R; Guha, Arun K

    2007-12-15

    The adsorption behavior of mercury on Aspergillus versicolor biomass (AVB) has been investigated in aqueous solution to understand the physicochemical process involved and to explore the potentiality of AVB in pollution control management. This biomass has been successfully used for reducing the mercury concentration level in the effluent of chloralkali and battery industries to a permissible limit. The results establish that 75.6 mg of mercury is adsorbed per gram of biomass. The adsorption process is found to be a function of pH of the solution, with the optimum range being pH 5.0-6.0. The process obeys the Langmuir-Freundlich isotherm model. Scanning electron microscopic analysis demonstrates a conspicuous surface morphology change of the mercury-adsorbed biomass. A nearly uniform distribution of metal ions on the mycelial surface excepting a few aggregation points is revealed by X-ray elemental mapping profiles. The results of zeta potential measurement, Fourier transform infrared (FTIR) spectroscopy, and blocking of the functional groups by chemical modification reflect the binding of mercury on the biomass occurs through electrostatic and complexation reactions. The accumulation of mercury on the cell wall associated with negligible diffusion and or transportation into cytoplasm finds support from the results of adsorption kinetics and transmission electron micrographs. Mercury adsorption on biomass also leads to elongation of cells and cytoplasmic aggregation of spheroplast/protoplasts, indicating that the cell wall acts as a permeation barrier against this toxic metal.

  1. NMR study of small molecule adsorption in MOF-74-Mg

    NASA Astrophysics Data System (ADS)

    Lopez, M. G.; Canepa, Pieremanuele; Thonhauser, T.

    2013-04-01

    We calculate the carbon nuclear magnetic resonance (NMR) shielding for CO2 and the hydrogen shieldings for both H2 and H2O inside the metal organic framework MOF-74-Mg. Our ab initio calculations are at the density functional theory level using the van der Waals including density functional vdW-DF. The shieldings are obtained while placing the small molecules throughout the structure, including the calculated adsorption site for various loading scenarios. We then explore relationships between loading, rotational and positional characteristics, and the NMR shieldings for each adsorbate. Our NMR calculations show a change in the shielding depending on adsorbate, position, and loading in a range that is experimentally observable. We further provide a simple model for the energy and the NMR shieldings throughout the cavity of the MOF. By providing this mapping of shielding to position and loading for these adsorbates, we argue that NMR probes could be used to provide additional information about the position at which these small molecules bind within the MOF, as well as the loading of the adsorbed molecule.

  2. Adsorption studies of methylene blue and phenol onto vetiver roots activated carbon prepared by chemical activation.

    PubMed

    Altenor, Sandro; Carene, Betty; Emmanuel, Evens; Lambert, Jacques; Ehrhardt, Jean-Jacques; Gaspard, Sarra

    2009-06-15

    Vetiver roots have been utilized for the preparation of activated carbon (AC) by chemical activation with different impregnation ratios of phosphoric acid, X(P) (gH(3)PO(4)/g precursor): 0.5:1; 1:1 and 1.5:1. Textural characterization, determined by nitrogen adsorption at 77K shows that mixed microporous and mesoporous structures activated carbons (ACs) with high surface area (>1000 m(2)/g) and high pore volume (up to 1.19 cm(3)/g) can be obtained. The surface chemical properties of these ACs were investigated by X-ray photoelectron spectroscopy (XPS) and Boehm titration. Their textural and chemical characteristics were compared to those of an AC sample obtained by steam activation of vetiver roots. Classical molecules used for characterizing liquid phase adsorption, phenol and methylene blue (MB), were used. Adsorption kinetics of MB and phenol have been studied using commonly used kinetic models, i.e., the pseudo-first-order model, the pseudo-second-order model, the intraparticle diffusion model and as well the fractal, BWS (Brouers, Weron and Sotolongo) kinetic equation. The correlation coefficients (R(2)) and the normalized standard deviation Deltaq (%) were determined showing globally, that the recently derived fractal kinetic equation could best describe the adsorption kinetics for the adsorbates tested here, indicating a complex adsorption mechanism. The experimental adsorption isotherms of these molecules on the activated carbon were as well analysed using four isotherms: the classical Freundlich, Langmuir, Redlich-Peterson equations, but as well the newly published deformed Weibull Brouers-Sotolongo isotherm. The results obtained from the application of the equations show that the best fits were achieved with the Brouers-Sotolongo equation and with the Redlich-Peterson equation. Influence of surface functional groups towards MB adsorption is as well studied using various ACs prepared from vetiver roots and sugar cane bagasse. Opposite effects governing MB

  3. Modeling and Experimental Studies of Mercury Oxidation and Adsorption in a Fixed-Bed Reactor

    SciTech Connect

    Buitrago, Paula A.; Morrill, Mike; Lighty, JoAnn S.; Silcox, Geoffrey D.

    2009-06-15

    This report presents experimental and modeling mercury oxidation and adsorption data. Fixed-bed and single-particle models of mercury adsorption were developed. The experimental data were obtained with two reactors: a 300-W, methane-fired, tubular, quartz-lined reactor for studying homogeneous oxidation reactions and a fixed-bed reactor, also of quartz, for studying heterogeneous reactions. The latter was attached to the exit of the former to provide realistic combustion gases. The fixed-bed reactor contained one gram of coconut-shell carbon and remained at a temperature of 150°C. All methane, air, SO2, and halogen species were introduced through the burner to produce a radical pool representative of real combustion systems. A Tekran 2537A Analyzer coupled with a wet conditioning system provided speciated mercury concentrations. At 150°C and in the absence of HCl or HBr, the mercury uptake was about 20%. The addition of 50 ppm HCl caused complete capture of all elemental and oxidized mercury species. In the absence of halogens, SO2 increased the mercury adsorption efficiency to up to 30 percent. The extent of adsorption decreased with increasing SO2 concentration when halogens were present. Increasing the HCl concentration to 100 ppm lessened the effect of SO2. The fixed-bed model incorporates Langmuir adsorption kinetics and was developed to predict adsorption of elemental mercury and the effect of multiple flue gas components. This model neglects intraparticle diffusional resistances and is only applicable to pulverized carbon sorbents. It roughly describes experimental data from the literature. The current version includes the ability to account for competitive adsorption between mercury, SO2, and NO2. The single particle model simulates in-flight sorbent capture of elemental mercury. This model was developed to include Langmuir and Freundlich isotherms, rate equations, sorbent feed rate, and

  4. Adsorption studies of etherdiamine onto modified sugarcane bagasses in aqueous solution.

    PubMed

    Gusmão, Karla Aparecida Guimarães; Gurgel, Leandro Vinícius Alves; Melo, Tânia Márcia Sacramento; Carvalho, Cornélio de Freitas; Gil, Laurent Frédéric

    2014-01-15

    In this study sugarcane bagasse was modified with succinic anhydride and EDTA dianhydride to obtain SCB 2 and EB adsorbents, respectively. These adsorbents were used to remove etherdiamine, which is used for iron ore flotation from single aqueous solutions. The removal and recovery of etherdiamine is important for environmental and economic reasons due to its toxicity and high cost. The results demonstrated that adsorption of etherdiamine by SCB 2 and EB was better fitted by a pseudo-second-order kinetic model than pseudo-first-order and Elovich models. Adsorption isotherms were better fitted by the Langmuir model rather than the Freundlich, Sips, and Temkin models. The maximum adsorption capacities (Qmax) of SCB 2 and EB for etherdiamine adsorption were found to be 869.6 and 1203.5 mg/g, respectively. The calculated ΔG° values for adsorption of etherdiamine on SCB 2 (-22.70 kJ/mol) and EB (-19.10 kJ/mol) suggested that chemisorption is the main mechanism by which etherdiamine is removed from the aqueous solution for both adsorbents. The high Qmax values showed that SCB 2 and EB are potential adsorbents for recovering the etherdiamine and treating effluents produced from iron ore flotation.

  5. Dye adsorption of cotton fabric grafted with PPI dendrimers: Isotherm and kinetic studies.

    PubMed

    Salimpour Abkenar, Samera; Malek, Reza Mohammad Ali; Mazaheri, Firouzmehr

    2015-11-01

    In this research, the cotton fabrics grafted with two generations of the poly(propylene imine) dendrimers were applied to adsorb textile dyes from aqueous solutions. Direct Red 80 (anionic dye), Disperse Yellow 42 (nonionic dye) and Basic Blue 9 (cationic dye) were selected as model dyes. The effect of various experimental parameters such as initial concentration of dyes, charge of dyes molecule, salt and pH was investigated on the adsorption process. Furthermore, kinetics and equilibrium of the adsorption process on the grafted samples were studied. It was found that maximum adsorption of anionic and disperse dyes took place at around pH 3, while cationic dye could be adsorbed at around pH 11. The Langmuir equation was able to describe the mechanism of dyes adsorption. In addition, the second-order equation was found to be fit with the kinetics data. Interestingly, it seems that the dye adsorption of the grafted fabrics is strongly pH dependent.

  6. Equilibrium, kinetic and thermodynamic studies of mercury adsorption on almond shell.

    PubMed

    Khaloo, Shokooh Sadat; Matin, Amir Hossein; Sharifi, Sahar; Fadaeinia, Masoumeh; Kazempour, Narges; Mirzadeh, Shaghayegh

    2012-01-01

    The application of almond shell as a low cost natural adsorbent to remove Hg(2+) from aqueous solution was investigated. Batch experiments were carried out to evaluate the adsorption capacity of the material. The chemical and physical parameters such as pH, sorbent amount, initial ion concentration, and contact time were optimized for the maximum uptake of mercury onto the solid surface. Adsorption isotherms were expressed by Langmuir and Freundlich adsorption models, and the experimental data were found to fit the Langmuir model rather than the Freundlich. The maximum adsorption capacity obtained from the Langmuir isotherm was 135.13 mg/g. A kinetic study was carried out with pseudo-first-order and pseudo-second-order reaction equations and it was found that the Hg(2+) uptake process followed the pseudo-second-order rate expression. The thermodynamic values, ΔG(0), ΔH(0) and ΔS(0), indicated that adsorption was an endothermic and spontaneous process. The potential of this material for mercury elimination was demonstrated by efficient Hg(2+) removal from a synthetic effluent.

  7. Adsorption from black tea and red wine onto in vitro salivary pellicles studied by ellipsometry.

    PubMed

    Joiner, Andrew; Muller, Dries; Elofsson, Ulla M; Malmsten, Martin; Arnebrant, Thomas

    2003-10-01

    The adsorption of black tea and red wine components onto a pellicle-like protein layer formed in vitro by adsorption from whole unstimulated saliva on hydroxyapatite discs were studied by in situ ellipsometry. It was found that components from black tea readily adsorbed to the pellicle. Subsequent exposure to saliva led to further adsorption of salivary components to give an overall increase in the amounts adsorbed. The amounts adsorbed increased still further following a third tea and saliva exposure. Components of red wine gave significantly greater amounts of adsorption to the pellicle than black tea. The adsorption of components of black tea gave a concomitant increase in colour or stain as measured by a reflectance chromameter. In all cases, the black tea- and red wine-modified pellicles were not eluted by either phosphate buffer or sodium dodecyl sulphate (SDS) rinses. Thus, black tea and red wine components have been shown to have a profound effect on in vitro pellicle maturation, causing thickened layers of stained material to build up, which are not readily removed.

  8. Spontaneous Membrane-Translocating Peptide Adsorption at Silica Surfaces: A Molecular Dynamics Study

    PubMed Central

    2013-01-01

    Spontaneous membrane-translocating peptides (SMTPs) have recently been shown to directly penetrate cell membranes. Adsorption of a SMTP, and some engineered extensions, at model silica surfaces is studied herein using fully atomistic molecular dynamics simulations in order to assess their potential to construct novel drug delivery systems. The simulations are designed to reproduce the electric fields above single, siloxide-rich charged surfaces, and the trajectories indicate that the main driving force for adsorption is electrostatic. An increase in the salt concentration slows down but does not prevent adsorption of the SMTP to the surface; it also does not result in peptide desorption, suggesting additional binding via hydrophobic forces. The results are used to design extensions to the peptide sequence which we find enhance adsorption but do not affect the adsorbed conformation. We also investigate the effect of surface hydroxylation on the peptide adsorption. In all cases, the final adsorbed conformations are with the peptide flattened to the surface with arginine residues, which are key to the peptide’s function, anchoring it to the surface so that they are not exposed to solution. This conformation could impact their role in membrane translocation and thus has important implications for the design of future drug delivery vehicles. PMID:24176015

  9. Modeling water adsorption in carbon micropores: study of water in carbon molecular sieves.

    PubMed

    Rutherford, S W

    2006-01-17

    Measurements of water adsorption equilibrium in a carbon molecular sieve are undertaken in order to gain insight into the nature of water adsorption in carbon micropores. The measurements are taken at low concentrations to emphasize the role of oxygen-containing functional groups in the adsorption of water. Comparisons are made with previously published water adsorption data at higher concentrations to provide a data set spanning a wide range of loading. The assembled data set provides an opportunity for comparison of various theories for prediction of water adsorption in carbon micropores. Shortcomings of current theories are outlined, and an analytical theory that is free of these deficiencies is proposed in this investigation. With the consideration of micropore volume and pore size distribution, the experimental data and proposed isotherm model are consistent with previous studies of Takeda carbon molecular sieves. Also investigated is the uptake kinetics of water, which is characterized by a Fickian diffusion mechanism. The Maxwell-Stefan formulation is applied to characterize the dependence of the diffusional mobility upon loading.

  10. Experimental study on asphaltene adsorption onto formation rock: An approach to asphaltene formation damage prevention

    SciTech Connect

    Piro, G.; Barberis Canonica, L.; Galbariggi, G.; Bertero, L.; Carniani, C.

    1995-12-31

    In this paper, through a comparative study on Static vs Dynamic adsorption of asphaltene onto formation rock, it is reported how, for the particular asphaltene/formation rock system here considered, the Dynamic asphaltene adsorption onto formation rock is a continuous phenomenon by which the quantity of adsorbed asphaltene increases continuously. In the authors` opinion this rather remarkable adsorption behavior may contribute to asphaltene formation damage. In the hypothesis that prevention may represent a more economical approach than removal, in this work is also reported a possible prevention approach based on formation rock treatment by means of specific chemicals more apt than asphaltenes to be adsorbed onto rock. As preliminary demonstration, with the aim at assessing qualitatively the potential of their approach, the authors have pre-treated the rock by means of commercially available asphaltene dispersant and flocculation inhibitors. Albeit the chosen additives are not commercialized on the base of their specific adsorption feature, a prevention effect has been effectively found. Experimental set ups and procedures used as a base for a test able to rank chemicals with respect to their asphaltene adsorption inhibitive effects are also reported.

  11. Butanethiol adsorption and dissociation on Ag (111): A periodic DFT study

    NASA Astrophysics Data System (ADS)

    Li, Aixiao; Piquemal, Jean-Philip; Richardi, Johannes; Calatayud, Monica

    2016-04-01

    The molecular and dissociative adsorption of butanethiol (C4H9SH) on regular Ag (111) surfaces has been studied by means of periodic ab initio density functional techniques. In molecular form, butanethiol is bound to the surface only by weak polarization-induced forces with the C-S axis tilted by 38° relative to the normal surface. The S atom occupies a position between a hollow fcc and a bridge site. In the dissociative adsorption process, the S-H bond breaks leading to butanethiolate. The S atom of the thiolate also occupies a threefold position, slightly displaced to a hollow fcc site compared to the thiol adsorption case. The C-S axis of the thiolate is tilted by about 37°. The calculated adsorption energies show that the butanethiol and butanethiolate have similar adsorption ability. The computed reaction pathway for the S-H dissociation gives an activation energy of 0.98 eV indicating that the thiolate formation from thiol, although not spontaneous at room temperature, might be feasible on silver surfaces. The dissociation process induces both adsorbate and surface polarization with a significant charge transfer from the substrate to the adsorbate.

  12. Equilibrium isotherms, kinetics and thermodynamics studies of phenolic compounds adsorption on palm-tree fruit stones.

    PubMed

    Ahmed, Muthanna J; Theydan, Samar K

    2012-10-01

    Adsorption capacity of an agricultural waste, palm-tree fruit stones (date stones), for phenolic compounds such as phenol (Ph) and p-nitro phenol (PNPh) at different temperatures was investigated. The characteristics of such waste biomass were determined and found to have a surface area and iodine number of 495.71 m2/g and 475.88 mg/g, respectively. The effects of pH (2-12), adsorbent dose (0.6-0.8 g/L) and contact time (0-150 min) on the adsorptive removal process were studied. Maximum removal percentages of 89.95% and 92.11% were achieved for Ph and PNPh, respectively. Experimental equilibrium data for adsorption of both components were analyzed by the Langmuir, Freundlich and Tempkin isotherm models. The results show that the best fit was achieved with the Langmuir isotherm equation with maximum adsorption capacities of 132.37 and 161.44 mg/g for Ph and PNPh, respectively. The kinetic data were fitted to pseudo-first order, pseudo-second order and intraparticle diffusion models, and was found to follow closely the pseudo-second order model for both components. The calculated thermodynamic parameters, namely ΔG, ΔH, and ΔS showed that adsorption of Ph and PNPh was spontaneous and endothermic under examined conditions.

  13. Adsorption of methyl orange from aqueous solution by aminated pumpkin seed powder: Kinetics, isotherms, and thermodynamic studies.

    PubMed

    Subbaiah, Munagapati Venkata; Kim, Dong-Su

    2016-06-01

    Present research discussed the utilization of aminated pumpkin seed powder (APSP) as an adsorbent for methyl orange (MO) removal from aqueous solution. Batch sorption experiments were carried to evaluate the influence of pH, initial dye concentration, contact time, and temperature. The APSP was characterized by using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The experimental equilibrium adsorption data were fitted using two two-parameter models (Langmuir and Freundlich) and two three-parameter models (Sips and Toth). Langmuir and Sips isotherms provided the best model for MO adsorption data. The maximum monolayer sorption capacity was found to be 200.3mg/g based on the Langmuir isotherm model. The pseudo-first-order and pseudo-second-order model equations were used to analyze the kinetic data of the adsorption process and the data was fitted well with the pseudo-second-order kinetic model (R(2)>0.97). The calculated thermodynamic parameters such as ΔG(0), ΔH(0) and ΔS(0) from experimental data showed that the sorption of MO onto APSP was feasible, spontaneous and endothermic in the temperature range 298-318 K. The FTIR results revealed that amine and carboxyl functional groups present on the surface of APSP. The SEM results show that APSP has an irregular and porous surface which is adequate morphology for dye adsorption. Desorption experiments were carried to explore the feasibility of adsorbent regeneration and the adsorbed MO from APSP was desorbed using 0.1M NaOH with an efficiency of 93.5%. Findings of the present study indicated that APSP can be successfully used for removal of MO from aqueous solution.

  14. Infrared studies of propene and propene oxide adsorption on nanoparticulate Au/TiO2

    NASA Astrophysics Data System (ADS)

    Panayotov, Dimitar; McEntee, Monica; Burrows, Steve; Driscoll, Darren; Tang, Wenjie; Neurock, Matthew; Morris, John

    2016-10-01

    Direct gas-phase epoxidation of propene to propene oxide over a heterogeneous catalyst holds the potential to revolutionize production of one of the world's major commodity chemicals. New research into fundamental aspects of propene chemistry on nanoparticulate catalysts will help guide strategies for materials development. In the current study, Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) have been employed to explore the molecular-level details of propene and propene oxide binding at a Au/TiO2 catalyst. Competitive binding studies for propene and carbon monoxide reveal that propene readily displaces CO from: first, interfacial Au ||TiO2 sites, then low coordinated Au sites at particulate corners and edges, and finally terrace regions of the particles. DFT calculations show that the Cdbnd C bond of propene weakens upon coordination to Au, which suggests that these sites may activate the molecule for epoxidation. Like propene, propene oxide adsorbs on both Au sites and Ti sites. In addition, Ti-OH sites also readily bind the oxide. However, competitive binding experiments show that the propene oxide adsorption is favored relative to propene on all sites, which would likely passivate the catalyst at room temperature.

  15. Direct coupling between stress, strain and adsorption reactions - A study on coal-CO2 systems

    NASA Astrophysics Data System (ADS)

    Hol, S.; Peach, C. J.; Spiers, C. J.

    2012-12-01

    ) and sorption, and was found to be consistent with experimental data. Third, it was observed that microfractures form in coal due to exposure to CO2 under unconfined conditions, which illustrates the potentially high forces and the large thermodynamic work term involved in adsorption reactions. The findings of this study all lead to the conclusion that direct effects of stress can have a considerable impact on adsorption processes. If this is the case for coal, also other adsorbate-rock interactions (e.g. clay-fluids in shale formations and deep fault rocks) may be subject to such a coupling. We believe that this topic deserved attention in future research.

  16. Equilibrium and kinetic studies of adsorption of phosphate onto ZnCl2 activated coir pith carbon.

    PubMed

    Namasivayam, C; Sangeetha, D

    2004-12-15

    Phosphate removal from aqueous solution was investigated using ZnCl(2)-activated carbon developed from coir pith, an agricultural solid waste. Studies were conducted to delineate the effect of contact time, adsorbent dose, phosphate concentration, pH, and temperature. The adsorption equilibrium data followed both Langmuir and Freundlich isotherms. Langmuir adsorption capacity was found to be 5.1 mg/g. Adsorption followed second-order kinetics. The removal was maximum in the pH range 3-10. pH effect and desorption studies showed that adsorption occurred by both ion exchange and chemisorption mechanisms. Adsorption was found to be spontaneous and endothermic. Effect of foreign ions on adsorption shows that perchlorate, sulfate, and selenite decreased the percent removal of phosphate.

  17. Driving force behind adsorption-induced protein unfolding: a time-resolved X-ray reflectivity study on lysozyme adsorbed at an air/water interface.

    PubMed

    Yano, Yohko F; Uruga, Tomoya; Tanida, Hajime; Toyokawa, Hidenori; Terada, Yasuko; Takagaki, Masafumi; Yamada, Hironari

    2009-01-06

    Time-resolved X-ray reflectivity measurements for lysozyme (LSZ) adsorbed at an air/water interface were performed to study the mechanism of adsorption-induced protein unfolding. The time dependence of the density profile at the air/water interface revealed that the molecular conformation changed significantly during adsorption. Taking into account previous work using Fourier transform infrared (FTIR) spectroscopy, we propose that the LSZ molecules initially adsorbed on the air/water interface have a flat unfolded structure, forming antiparallel beta-sheets as a result of hydrophobic interactions with the gas phase. In contrast, as adsorption continues, a second layer forms in which the molecules have a very loose structure having random coils as a result of hydrophilic interactions with the hydrophilic groups that protrude from the first layer.

  18. Adsorption of trihalomethanes by humin: Batch and fixed bed column studies.

    PubMed

    Cunha, G da C; Romão, L P C; Santos, M C; Araújo, B R; Navickiene, S; de Pádua, V L

    2010-05-01

    The objective of the present work was to assess the performance of batch and fixed bed column systems, using humin in natura and immobilized on sodium silicate, respectively, for the adsorption of the principal trihalomethanes (THMs) found in water supply systems. Kinetically, adsorption of THMs by humin follows a pseudo-second order reaction, with more than 50% removal in the first 5min for all compounds studied, and equilibrium described by the Freundlich model reached in 240min. The THM adsorption results were significant at p<0.05 for both batch (74.6-83.2% removal) and column (99.7% removal in optimized tests) experiments, and were significantly (p<0.05) influenced by flow rate and bed height. The work demonstrates the potential of humin for removal of THMs.

  19. Study of malachite green adsorption by organically modified clay using a batch method

    NASA Astrophysics Data System (ADS)

    Arellano-Cárdenas, Sofía; López-Cortez, Socorro; Cornejo-Mazón, Maribel; Mares-Gutiérrez, Juan Carlos

    2013-09-01

    The adsorption of toxic dye malachite green from aqueous effluents by organically modified clay was studied in a batch system. The organoclay (OC) used was prepared by the intercalation of cationic surfactant hexadecyltrimethylammonium bromide in a Mexican montmorillonite. The effects of initial dye concentration, temperature, pH, and contact time were investigated. The OC showed a high dye removal (99.6%) from an initial dye concentration of 60 mg L-1 at pH 6 and 25 °C. The adsorption capacity was independent of pH and increased with the temperature. Equilibrium data were well fitted by Langmuir adsorption model. The rate of sorption was adjusted to a pseudo second-order kinetic model.

  20. Study of Solar Driven Silica gel-Water based Adsorption Chiller

    NASA Astrophysics Data System (ADS)

    Habib, K.; Assadi, M. K.; Zainudin, M. H. B.

    2015-09-01

    In this study, a dynamic behaviour of a solar powered single stage four bed adsorption chiller has been analysed designed for Malaysian climate. Silica gel and water have been used as adsorbent-refrigerant pair. A simulation program has been developed for modeling and performance evaluation of the chiller using the meteorological data of Kuala Lumpur. The optimum cooling capacity and coefficient of performance (COP) are calculated in terms of adsorption/desorption cycle time and regeneration temperature. Results indicate that the chiller is feasible even when low temperature heat source is available. Results also show that the adsorption cycle can achieve a cooling capacity of 14 kW when the heat source temperature is about 85°C.

  1. Breakthrough adsorption study of migratory nickel in fine-grained soil.

    PubMed

    Ghosh, S; Mukherjee, S N; Kumar, Sunil; Chakraborty, P; Fan, Maohong

    2007-09-01

    The present study was conducted to evaluate the breakthrough curve for nickel adsorption in fine-grained soil from a nearby ash pond site of a thermal power plant. Nickel was found to be the major polluting solute in the ash sluicing wastewater. The adsorption of nickel by vertical soil column batch test and horizontal migration test was carried out in the laboratory. Field investigation was conducted also, by installing test wells around the ash pond site. Experimental results showed a good adsorptive capacity of soil for nickel ions. The breakthrough curves showed a reasonable fitting with a one-dimensional mathematical model. The breakthrough curves yielded from field test results showed good agreement with a two-dimensional mathematical model.

  2. Kinetic studies of competitive adsorption processes related to automobile catalytic converters

    SciTech Connect

    Zaera, F.; Paffett, M.T.

    1998-12-31

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The goal of this project was to study the microscopic details for the adsorption of CO, NO, and O{sub 2} on transition metal surfaces under conditions resembling those present in automobile catalytic converters. Initial sticking coefficients were measured as a function of temperature on transition metal single crystals by using a method originally developed by King and Wells. These measurements were performed under conditions emulating those typical of competitive adsorption, namely, where the substrate is exposed to a mixture of two or more gases simultaneously, or where one molecule is adsorbed on the surface prior to exposure to the second gas. The experimental results were then analyzed by using Monte Carlo computer simulation algorithm in an attempt to better understand the relevant aspects of the adsorption process.

  3. Density function theory study of the adsorption and dissociation of carbon monoxide on tungsten nanoparticles.

    PubMed

    Weng, Meng-Hsiung; Ju, Shin-Pon; Chen, Hsin-Tsung; Chen, Hui-Lung; Lu, Jian-Ming; Lin, Ken-Huang; Lin, Jenn-Sen; Hsieh, Jin-Yuan; Yang, Hsi-Wen

    2013-02-01

    The adsorption and dissociation properties of carbon monoxide (CO) molecule on tungsten W(n) (n = 10-15) nanoparticles have been investigated by density-functional theory (DFT) calculations. The lowest-energy structures for W(n) (n = 10-15) nanoparticles are found by the basin-hopping method and big-bang method with the modified tight-binding many-body potential. We calculated the corresponding adsorption energies, C-O bond lengths and dissociation barriers for adsorption of CO on nanoparticles. The electronic properties of CO on nanoparticles are studied by the analysis of density of state and charge density. The characteristic of CO on W(n) nanoparticles are also compared with that of W bulk.

  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. Adsorption of BMP-2 on a hydrophobic graphite surface: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Mücksch, Christian; Urbassek, Herbert M.

    2011-07-01

    Using classical molecular-dynamics simulations based on the OPLS-AA force field we study the adsorption of a BMP-2 molecule to a hydrophobic graphite surface. Using an implicit inviscid water model, the adsorption dynamics and energetics are monitored for four different initial protein orientations towards the surface. In all cases we find that the protein partially unfolds and spreads on the surface. We conclude that due to the substantially denatured protein structure, interactions of the adsorbed BMP-2 with cell receptors might be unlikely.

  6. An experimental study of adsorption in vapor-dominated geothermal systems

    SciTech Connect

    Satik, Cengiz; Horne, Roland N.

    1995-01-26

    We report results of steam adsorption experiments conducted for rock samples from vapor-dominated geothermal reservoirs. We examine the effect of the temperature on the adsorption/desorption isotherms. We find that the temperature effect is only important on the desorption such that the hysteresis becomes more pronounced as the temperature increases. The scanning behavior within the steam sorption hysteresis loop is also studied to investigate the behavior during repressurization. Collection of sets of data on the sorption behavior of The Geysers geothermal field in California is presented.

  7. Study of methane adsorption on nickel films by Raman effect method

    SciTech Connect

    Plato, S.E.; Bobrov, A.V.; Kadushin, A.A.; Kimmel'feld, Y.M.

    1986-10-01

    The adsorption of methane on nickel films, deposited by the resistivity method in vacuo on a quartz support cooled to 77/sup 0/K, was studied by SERS method (Raman-effect, surface-reinforced). The analysis of the spectrum showed that the adsorption of methane is dissociative in character and CH/sub 2/ and CH/sub 3/ groups are present on the surface, and that the formation of groups containing C-C and C=C bonds is also possible.

  8. Rapid adsorption of copper(II) and lead(II) by rice straw/Fe₃O₄ nanocomposite: optimization, equilibrium isotherms, and adsorption kinetics study.

    PubMed

    Khandanlou, Roshanak; Ahmad, Mansor B; Fard Masoumi, Hamid Reza; Shameli, Kamyar; Basri, Mahiran; Kalantari, Katayoon

    2015-01-01

    Rice straw/magnetic nanocomposites (RS/Fe3O4-NCs) were prepared via co-precipitation method for removal of Pb(II) and Cu(II) from aqueous solutions. Response surface methodology (RSM) was utilized to find the optimum conditions for removal of ions. The effects of three independent variables including initial ion concentration, removal time, and adsorbent dosage were investigated on the maximum adsorption of Pb (II) and Cu (II). The optimum conditions for the adsorption of Pb(II) and Cu(II) were obtained (100 and 60 mg/L) of initial ion concentration, (41.96 and 59.35 s) of removal time and 0.13 g of adsorbent for both ions, respectively. The maximum removal efficiencies of Pb(II) and Cu(II) were obtained 96.25% and 75.54%, respectively. In the equilibrium isotherm study, the adsorption data fitted well with the Langmuir isotherm model. The adsorption kinetics was best depicted by the pseudo-second order model. Desorption experiments showed adsorbent can be reused successfully for three adsorption-desorption cycles.

  9. Infrared Spectroscopic Study of the Adsorption of HCN by gamma-Al2O3: Competition with Triethylenediamine for Adsorption Sites

    SciTech Connect

    Kim, S.; Sorescu, D.C.; Yates, J.T., Jr.

    2007-04-12

    The adsorption and vibrational properties of chemisorbed HCN on Lewis acid sites, Lewis base sites, and Brønsted Al-OH acid sites on a partially hydroxylated [gamma]-Al2O3 surface have been obtained by a combination of FTIR and density functional theory studies. The vibrational modes from the molecular and dissociative adsorption of HCN were assigned by using deuterium and 13C-labeled D13CN molecules at 170 K. In addition, [eta]2(C, N)-HCN bonding is also found from the [nu](CdN) vibrational spectra. Good correlation of the calculated vibrational frequencies for the adsorbed species with experimental data is found. The effect of triethylenediamine (TEDA) (also called 1, 4-diazabicyclo [2.2.2]octane, DABCO) on the adsorption of hydrogen cyanide (HCN) on the high area [gamma]-Al2O3 surface has been investigated using transmission FTIR spectroscopy. During HCN adsorption on TEDA-functionalized surfaces, there is no spectral change or emerging feature in either the TEDA or HCN spectral regions, indicating that no direct interaction occurs between these two molecules. Instead, we found that TEDA competes with HCN for the active sites on [gamma]-Al2O3. The observed [nu](C [identical with] N) mode on a TEDA-precovered surface is due to the HCN adsorption on Lewis base sites (Al-O-Al) which are less affected by TEDA preadsorption.

  10. Rapid Adsorption of Copper(II) and Lead(II) by Rice Straw/Fe3O4 Nanocomposite: Optimization, Equilibrium Isotherms, and Adsorption Kinetics Study

    PubMed Central

    Khandanlou, Roshanak; Ahmad, Mansor B.; Fard Masoumi, Hamid Reza; Shameli, Kamyar; Basri, Mahiran; Kalantari, Katayoon

    2015-01-01

    Rice straw/magnetic nanocomposites (RS/Fe3O4-NCs) were prepared via co-precipitation method for removal of Pb(II) and Cu(II) from aqueous solutions. Response surface methodology (RSM) was utilized to find the optimum conditions for removal of ions. The effects of three independent variables including initial ion concentration, removal time, and adsorbent dosage were investigated on the maximum adsorption of Pb (II) and Cu (II). The optimum conditions for the adsorption of Pb(II) and Cu(II) were obtained (100 and 60 mg/L) of initial ion concentration, (41.96 and 59.35 s) of removal time and 0.13 g of adsorbent for both ions, respectively. The maximum removal efficiencies of Pb(II) and Cu(II) were obtained 96.25% and 75.54%, respectively. In the equilibrium isotherm study, the adsorption data fitted well with the Langmuir isotherm model. The adsorption kinetics was best depicted by the pseudo-second order model. Desorption experiments showed adsorbent can be reused successfully for three adsorption-desorption cycles. PMID:25815470

  11. Equilibrium and kinetics study on the adsorption of perfluorooctanoic acid from aqueous solution onto powdered activated carbon.

    PubMed

    Qu, Yan; Zhang, Chaojie; Li, Fei; Bo, Xiaowen; Liu, Guangfu; Zhou, Qi

    2009-09-30

    Powdered activated carbon (PAC) was applied to remove perfluorooctanoic acid (PFOA) from the aqueous PFOA solution in this study. Contact time, adsorbent dose and temperature were analyzed as the effect factors in the adsorption reaction. The contact time of maximum PFOA uptake was around 1h while the sorption removal efficiency increased with the PAC concentrations. And the process of adsorption increased from 303 K to 313 K and then decreased from 313 K to 323 K. Among four applied models, the experimental isotherm data were discovered to follow Langmuir isotherm model more closely. Thermodynamically, adsorption was endothermic because enthalpy, entropy and Gibbs constants were 198.5 kJ/mol, 0.709 kJ/mol/K and negative, respectively, which also indicated that the adsorption process was spontaneous and feasible. From kinetic analysis, the adsorption was suggested to be pseudo-second-order model. The adsorption of PFOA on the PAC was mainly controlled by particle diffusion.

  12. A van der Waals density functional study of adenine on graphene: Single molecular adsorption and overlayer binding

    SciTech Connect

    Berland, Kristian; Cooper, Valentino R; Langreth, David C.; Schroder, Prof. Elsebeth; Chakarova-Kack, Svetla

    2011-01-01

    The adsorption of an adenine molecule on graphene is studied using a first-principles van der Waals functional (vdW-DF) [Dion et al., Phys. Rev. Lett. 92, 246401 (2004)]. The cohesive energy of an ordered adenine overlayer is also estimated. For the adsorption of a single molecule, we determine the optimal binding configuration and adsorption energy by translating and rotating the molecule. The adsorption energy for a single molecule of adenine is found to be 711 meV, which is close to the calculated adsorption energy of the similar-sized naphthalene. Based on the single molecular binding configuration, we estimate the cohesive energy of a two-dimensional ordered overlayer. We find a significantly stronger binding energy for the ordered overlayer than for single-molecule adsorption.

  13. Adsorption of humic acid from aqueous solutions on crosslinked chitosan-epichlorohydrin beads: kinetics and isotherm studies.

    PubMed

    Wan Ngah, W S; Hanafiah, M A K M; Yong, S S

    2008-08-01

    The adsorption of humic acid on crosslinked chitosan-epichlorohydrin (chitosan-ECH) beads was investigated. Chitosan-ECH beads were characterized by Fourier transform infrared spectroscopy (FTIR), surface area and pore size analyses, and scanning electron microscopy (SEM). Batch adsorption experiments were carried out and optimum humic acid adsorption on chitosan-ECH beads occurred at pH 6.0, agitation rate of 300 rpm and contact time of 50 min. Adsorption equilibrium isotherms were analyzed by Langmuir and Freundlich models. Freundlich model was found to show the best fit for experimental data while the maximum adsorption capacity determined from Langmuir model was 44.84 mg g(-1). The adsorption of humic acid on chitosan-ECH beads was best described with pseudo-first-order kinetic model. For desorption study, more than 60% of humic acid could be desorbed from the adsorbent using 1.0M HCl for 180 min.

  14. Theoretical and experimental studies of hydrogen adsorption and desorption on Ir surfaces

    DOE PAGES

    Kaghazchi, Payam; Jacob, Timo; Chen, Wenhua; ...

    2013-06-03

    Here, we report adsorption and desorption of hydrogen on planar Ir(210) and faceted Ir(210), consisting of nanoscale {311} and (110) facets, by means of temperature programmed desorption (TPD) and density functional theory (DFT) in combination with the ab initio atomistic thermodynamics approach. TPD spectra show that only one H2 peak is seen from planar Ir(210) at all coverages whereas a single H2 peak is observed at around 440 K (F1) at fractional monolayer (ML) coverage and an additional H2 peak appears at around 360 K (F2) at 1 ML coverage on faceted Ir(210), implying structure sensitivity in recombination and desorptionmore » of hydrogen on faceted Ir(210) versus planar Ir(210), but no evidence is found for size effects in recombination and desorption of hydrogen on faceted Ir(210) for average facet sizes of 5-14 nm. Calculations indicate that H prefers to bind at the two-fold short-bridge sites of the Ir surfaces. In addition, we studied the stability of the Ir surfaces in the presence of hydrogen at different H coverages through surface free energy plots as a function of the chemical potential, which is also converted to a temperature scale. Moreover, the calculations revealed the origin of the two TPD peaks of H2 from faceted Ir(210): F1 from desorption of H2 on {311} facets while F2 from desorption of H2 on (110) facets.« less

  15. A comparative study for adsorption of lysozyme from aqueous samples onto Fe3O4 magnetic nanoparticles using different ionic liquids as modifier.

    PubMed

    Kamran, Sedigheh; Absalan, Ghodratollah; Asadi, Mozaffar

    2015-12-01

    In this paper, nanoparticles of Fe3O4 as well as their modified forms with different ionic liquids (IL-Fe3O4) were prepared and used for adsorption of lysozyme. The mean size and the surface morphology of the nanoparticles were characterized by TEM, XRD and FTIR techniques. Adsorption studies of lysozyme were performed under different experimental conditions in batch system on different modified magnetic nanoparticles such as, lysozyme concentration, pH of the solution, and contact time. Experimental results were obtained under the optimum operational conditions of pH 9.0 and a contact time of 10 min when initial protein concentrations of 0.05-2.0 mg mL(-1) were used. The isotherm evaluations revealed that the Langmuir model attained better fits to the equilibrium data than the Freundlich model. The maximum obtained adsorption capacities were 370.4, 400.0 500.0 and 526.3 mg of lysozyme for adsorption onto Fe3O4 and modified magnetic nanoparticles by [C4MIM][Br], [C6MIM][Br] and [C8MIM][Br] per gram of adsorbent, respectively. The Langmuir adsorption constants were 0.004, 0.019, 0.024 and 0.012 L mg(-1) for adsorptions of lysozyme onto Fe3O4 and modified magnetic nanoparticles by [C4MIM][Br], [C6MIM][Br] and [C8MIM][Br], respectively. The adsorption capacity of lysozyme was found to be dependent on its chemical structure, pH of the solution, temperature and type of ionic liquid as modifier. The applicability of two kinetic models including pseudo-first order and pseudo-second order model was estimated. Furthermore, the thermodynamic parameters were calculated. Protein could desorb from IL-Fe3O4 nanoparticles by using NaCl solution at pH 9.5 and was reused.

  16. A spectroscopic study of the effects of a microbial siderophore on Pb adsorption to kaolinite

    SciTech Connect

    Mishra, Bhoopesh; Haack, Elizabeth A.; Maurice, Patricia A.; Bunker, Bruce A.

    2010-11-12

    Batch adsorption experiments were combined with X-ray Absorption Spectroscopy (XAS) analysis to determine the mechanism(s) whereby the microbial trihydroxamate siderophore ligand desferrioxamine-B (DFO-B) affects Pb sorption to kaolinite at pH 4, 6, and 7.5 (in 0.1 M NaClO{sub 4}, 22 C; Pb:DFO-B ratio 120:240 {micro}M). In the absence of DFO-B, Pb adsorbs only slightly to kaolinite at pH 4, by a combination of inner- and outer-sphere complexation. Adsorption increases at pH 6, and sorption (adsorption/surface precipitation) further increases at pH 7.5. At pH 4, DFO-B does not bind Pb in solution appreciably, and the Pb adsorption mechanism(s) is unchanged by the presence of DFO-B. At pH 6, DFO-B slightly enhances Pb adsorption, due at least in part to formation of a DFO-B-Pb-kaolinite type A ternary surface complex. At pH 7.5, DFO-B decreases Pb sorption and Pb adsorption is dominated by a DFO-B-Pb-kaolinite type A ternary surface complex. Although XAS and thermodynamic speciation modeling indicate that Pb is bound by multiple DFO-B functional groups in solution at pH 7.5, the DFO-B-Pb-kaolinite surface complex appears to involve only a single hydroxamate group. This study thus demonstrates that the detailed structure of a ternary surface complex cannot necessarily be predicted from the structure of the solution organic-metal complex.

  17. Water adsorption on charcoal: New approach in experimental studies and data representation

    SciTech Connect

    Geynisman, M.; Walker, R.

    1991-08-01

    The experimental apparatus was built to study the H{sub 2}O adsorption on charcoal at very low concentrations and collect the data in the form of isosteres. Experimental method is discussed and the global three-dimensional fit is constructed to predict the post-regeneration conditions of charcoal absorbers. 11 refs.

  18. Adsorption studies of molasse's wastewaters on activated carbon: modelling with a new fractal kinetic equation and evaluation of kinetic models.

    PubMed

    Figaro, S; Avril, J P; Brouers, F; Ouensanga, A; Gaspard, S

    2009-01-30

    Adsorption kinetic of molasses wastewaters after anaerobic digestion (MSWD) and melanoidin respectively on activated carbon was studied at different pH. The kinetic parameters could be determined using classical kinetic equations and a recently published fractal kinetic equation. A linear form of this equation can also be used to fit adsorption data. Even with lower correlation coefficients the fractal kinetic equation gives lower normalized standard deviation values than the pseudo-second order model generally used to fit adsorption kinetic data, indicating that the fractal kinetic model is much more accurate for describing the kinetic adsorption data than the pseudo-second order kinetic model.

  19. Density functional theory based-study of 5-fluorouracil adsorption on β-cristobalite (1 1 1) hydroxylated surface: The importance of H-bonding interactions

    NASA Astrophysics Data System (ADS)

    Simonetti, S.; Compañy, A. Díaz; Pronsato, E.; Juan, A.; Brizuela, G.; Lam, A.

    2015-12-01

    Silica-based mesoporous materials have been recently proposed as an efficient support for the controlled release of a popular anticancer drug, 5-fluorouracil (5-FU). Although the relevance of this topic, the atomistic details about the specific surface-drug interactions and the energy of adsorption are almost unknown. In this work, theoretical calculations using the Vienna Ab-initio Simulation Package (VASP) applying Grimme's-D2 correction were performed to elucidate the drug-silica interactions and the host properties that control 5-FU drug adsorption on β-cristobalite (1 1 1) hydroxylated surface. This study shows that hydrogen bonding, electron exchange, and dispersion forces are mainly involved to perform the 5-FU adsorption onto silica. This phenomenon, revealed by favorable energies, results in optimum four adsorption geometries that can be adopted for 5-FU on the hydroxylated silica surface. Silanols are weakening in response to the molecule approach and establish H-bonds with polar groups of 5-FU drug. The final geometry of 5-FU adopted on hydroxylated silica surface is the results of H-bonding interactions which stabilize and fix the molecule to the surface and dispersion forces which approach it toward silica (1 1 1) plane. The level of hydroxylation of the SiO2 (1 1 1) surface is reflected by the elevated number of hydrogen bonds that play a significant role in the adsorption mechanisms.

  20. In situ ATR FTIR studies of SO4 adsorption on goethite in the presence of copper ions.

    PubMed

    Beattie, D A; Chapelet, J K; Gräfe, M; Skinner, W M; Smith, E

    2008-12-15

    Despite the existence of many single ion sorption studies on iron and aluminum oxides, fewer studies have been reported that describe cosorption reactions. In this work, we present an in situ ATR FTIR study of synergistic adsorption of sulfate (SO4) and copper (Cu) on goethite, which is representative of the minerals and ions present in mine wastes, acid sulfate soils, and other industrial and agricultural settings. Sulfate adsorption was studied as a function of varying pH, and as a function of increasing concentration in the absence and presence of Cu. The presence of Cu ions in solution had a complex effect on the ability of SO4 ions to be retained on the goethite surface with increasing pH, with complete desorption occurring near pH 7 and 9 in the absence and presence of Cu, respectively. In addition, Cu ions altered the balance of inner vs outer sphere adsorbed SO4. The solid phase partitioning of SO4 at pH 3 and pH 5 was elevated by the presence of Cu; in both cases Cu increased the affinity of SO4 for the goethite surface. Complementary ex situ sorption edge studies of Cu on goethite in the absence and presence of SO4 revealed that the Cu adsorption edge shifted to lower pH (6.3 --> 5.6) in the presence of SO4, consistent with a decrease of the electrostatic repulsion between the goethite surface and adsorbing Cu. Based on the ATR FTIR and bulk sorption data we surmise that the cosorption products of SO4 and Cu at the goethite-water interface were not in the nature of ternary complexes under the conditions studied here. This information is critical for the evaluation of the onset of surface precipitates of copper-hydroxy sulfates as a function of pH and solution concentration.

  1. Kinetic studies of adsorption of thiocyanate onto ZnCl2 activated carbon from coir pith, an agricultural solid waste.

    PubMed

    Namasivayam, C; Sangeetha, D

    2005-09-01

    The adsorption of thiocyanate onto ZnCl2 activated carbon developed from coir pith was investigated to assess the possible use of this adsorbent. The influence of various parameters such as agitation time, thiocyanate concentration, adsorbent dose, pH and temperature has been studied. Adsorption followed second-order rate kinetics. Two theoretical adsorption isotherms, namely, Langmuir and Freundlich were used to describe the experimental results. The Langmuir adsorption capacity (Q0) was found to be 16.2 mg g(-1) of the adsorbent. The per cent adsorption was maximum in the pH range 3.0-7.0. pH effect and desorption studies showed that ion exchange and chemisorption mechanism are involved in the adsorption process. Thermodynamic parameters such as DeltaG0, DeltaH0 and DeltaS0 for the adsorption were evaluated. The negative values of DeltaH0 confirm the exothermic nature of adsorption. Effects of foreign ions on the adsorption of thiocyanate have been investigated. Removal of thiocyanate from ground water was also tested.

  2. Adsorption isotherm of non-azeotropic solution onto porous adsorbents

    NASA Astrophysics Data System (ADS)

    Bono, A.; Ramlan, N. A.; Anisuzzaman, S. M.; Chu, C. M.; Farm, Y. Y.

    2016-06-01

    Adsorption isotherm is essential component in the understanding of the adsorption process. Several methods of the measurements, analysis and interpretation of adsorption from solution have been reported in the literature. Most of the measurements of adsorption isotherm from solution were involved the measurement of excess isotherm conducted at low region of sorbates concentration. Direct interpretation of excess adsorption isotherm as adsorption isotherm is always been practice. Therefore, in this work a study on the measurement of the adsorption isotherm from solution of non-azeotropic organic solvent mixture onto porous adsorbents for whole range of liquid concentration was conducted. The study included the measurement of excess adsorption isotherm using conventional technique. Theoretical analysis and interpretation of adsorption isotherm from the excess isotherm were conducted using Pseudo Ideal Adsorption, Gibbs Dividing Plane Model and Langmuir-Fruendlich binary isotherm model. For organic solvents, acetone and propanol were chosen as the adsorbates due to the non-azeotropic properties in the mixture. Activated carbon and silicalite were chosen as adsorbents due to the different in their porosity such as macro porous and micro porous structure. The result of the study has revealed that the adsorption isotherm of non-azeotropic mixture onto activated carbon and silicalite can be interpreted as monolayer type of adsorption.

  3. A study of competitive adsorption of organic molecules onto mineral oxides using DRIFTS

    SciTech Connect

    Joan E. Thomas; Kelley, Michael J.

    2009-10-20

    In this study, analysis of DRIFTS spectra was used for a quantitative study of competitive adsorption of myristic and salicylic acids onto kaolinite or γ-alumina. Peaks unique to the ring or the chain were selected and single molecule studies used as calibration. Samples were exposed to hexane solution containing equal molecular quantities of each acid. The surface loading of salicylic acid was not influenced by the presence of myristic acid on either mineral but the maximum loading of myristic acid was decreased (46-50%) by salicylic acid. Displacement of myristic acid from {gamma}-alumina, but not kaolinite, was observed when excess salicylic acid remained in solution. A 25% increase in the maximum loading was observed for kaolinite, but not for{gamma}-alumina. On {gamma}-alumina, after a loading of 1 molecule per nm2, increased exposure resulted in salicylic acid adsorption only, this value is approximately the same for salicylic acid adsorption from aqueous solution or for water washed hexane treated samples. Thus a set of sites for adsorption of either acid is indicated together with other energetically less favorable sites, which can be occupied by salicylic, but not by myristic, acid.

  4. A study of competitive adsorption of organic molecules onto mineral oxides using DRIFTS

    DOE PAGES

    Joan E. Thomas; Kelley, Michael J.

    2009-10-20

    In this study, analysis of DRIFTS spectra was used for a quantitative study of competitive adsorption of myristic and salicylic acids onto kaolinite or γ-alumina. Peaks unique to the ring or the chain were selected and single molecule studies used as calibration. Samples were exposed to hexane solution containing equal molecular quantities of each acid. The surface loading of salicylic acid was not influenced by the presence of myristic acid on either mineral but the maximum loading of myristic acid was decreased (46-50%) by salicylic acid. Displacement of myristic acid from {gamma}-alumina, but not kaolinite, was observed when excess salicylicmore » acid remained in solution. A 25% increase in the maximum loading was observed for kaolinite, but not for{gamma}-alumina. On {gamma}-alumina, after a loading of 1 molecule per nm2, increased exposure resulted in salicylic acid adsorption only, this value is approximately the same for salicylic acid adsorption from aqueous solution or for water washed hexane treated samples. Thus a set of sites for adsorption of either acid is indicated together with other energetically less favorable sites, which can be occupied by salicylic, but not by myristic, acid.« less

  5. Sytematic Study of the Adsorption of Thiol Molecules on Noble-Metal Nanoparticles

    NASA Astrophysics Data System (ADS)

    Barron, H.; Hidalgo, F.; Fernandez-Seivane, L.; Noguez, C.; Lopez-Lozano, X.

    2012-03-01

    The study of the interaction between nanoparticles and different types of ligands has been intensively investigated in the last years due to the potential contribution of their properties to the nanotechnology device design. These properties have opened new research fields like plasmonics, with interesting applications in optics, electronics, biophysics, medicine, pharmacology and materials science. Self-assembly monolayers have been thoroughly studied at experimental and theoretical level on extended (111) gold and silver surfaces. However, nanoparticle and molecule properties after the adsorption are still not well understood due to the different factors involved in this process such as the adsorption sites, size and element type of the nanoparticle. In this work we have performed a systematic study of the adsorption of methyl-thiol molecules on Au55 and Ag55 clusters through density functional theory calculations with the SIESTA code. Different adsorption modes of the methyl-thiol molecule on Au55 and Ag55 were considered. In general, for both type of nanoparticles, the methyl-thiol molecule prefers to be adsorbed on the Bridge sites. These results provide valuable information of the structural and electronic properties of methyl-thiol passivated Au and Ag nanoparticles.

  6. Noble gas adsorption in two-dimensional zeolites: a combined experimental and density functional theory study

    NASA Astrophysics Data System (ADS)

    Wang, Mengen; Zhong, Jianqiang; Boscoboinik, Jorge Anibal; Lu, Deyu

    Zeolites are important industrial catalysts with porous three-dimensional structures. The catalytically active sites are located inside the pores, thus rendering them inaccessible for surface science measurements. We synthesized a two-dimensional (2D) zeolite model system, consisting of an (alumino)silicate bilayer weakly bound to a Ru (0001) surface. The 2D zeolite is suitable for surface science studies; it allows a detailed characterization of the atomic structure of the active site and interrogation of the model system during the catalytic reaction. As an initial step, we use Ar adsorption to obtain a better understanding of the atomic structure of the 2D zeolite. In addition, atomic level studies of rare gas adsorption and separation by zeolite are important for its potential application in nuclear waste sequestration. Experimental studies found that Ar atoms can be trapped inside the 2D-zeolite, raising an interesting question on whether Ar atoms are trapped inside the hexagonal prism nano-cages or at the interface between the (alumino)silicate bilayer and Ru(0001), or both. DFT calculations using van der Waals density functionals were carried out to determine the preferred Ar adsorption sites and the corresponding adsorption energies. This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704.

  7. Sum Frequency Generation Spectroscopy and Molecular Dynamics Simulations Reveal a Rotationally Fluid Adsorption State of α-Pinene on Silica

    SciTech Connect

    Ho, Junming; Psciuk, Brian T.; Chase, Hilary M.; Rudshteyn, Benjamin; Upshur, Mary Alice; Fu, Li; Thomson, Regan J.; Wang, Hong-Fei; Geiger, Franz M.; Batista, Victor S.

    2016-06-16

    A rotationally fluid state of α-pinene at fused silica/vapor interfaces is revealed by computational and experimental vibrational sum frequency generation (SFG) studies. We report the first assignment of the vibrational modes in the notoriously congested C-H stretching region of α-pinene and identify its bridge methylene group on the four-membered ring ("βCH2") as the origin of its dominant spectral feature. We find that the spectra are perfused with Fermi resonances that need to be accounted for explicitly in the computation of vibrational spectra of strained hydrocarbons such α-pinene. The preferred orientations of α-pinene are consistent with optimization of van der Waals contacts with the silica surface that results in a bimodal distribution of highly fluxional orientations in which the βCH2 group points "towards" or "away from” the surface. The reported findings are particularly relevant to the exposure of α-pinene to primary oxidants in heterogeneous catalytic pathways that exploit α-pinene as a sustainable feedstock for fine chemicals and polymers.

  8. Equilibrium, kinetic and thermodynamic studies on the adsorption of the toxins of Bacillus thuringiensis subsp. kurstaki by clay minerals

    NASA Astrophysics Data System (ADS)

    Fu, Qingling; Deng, Yali; Li, Huishu; Liu, Jie; Hu, Hongqing; Chen, Shouwen; Sa, Tongmin

    2009-02-01

    The persistence of Bacillus thuringiensis ( Bt) toxins in soil is further enhanced through association with soil particles. Such persistence may improve the effectiveness of controlling target pests, but impose a hazard to non-target organisms in soil ecosystems. In this study, the equilibrium adsorption of the Bt toxin by four clay minerals (montmorillonite, kaolinite, goethite, and silicon dioxide) was investigated, and the kinetic and thermodynamic parameters were calculated. The results showed that Bt toxin could be adsorbed easily by minerals, and the adsorption was much easier at low temperature than at high temperature at the initial concentration varying from 0 to 1000 mg L -1. The adsorption fitted well to both Langmuir and Freundlich isotherm models, but the Freundlich equation was more suitable. The pseudo-second-order (PSO) was the best application model to describe the adsorption kinetic. The adsorption process appeared to be controlled by chemical process, and the intra-particle diffusion was not the only rate-controlling step. The negative standard free energy ( ΔGmθr) values of the adsorption indicated that the adsorption of the Bt toxin by the minerals was spontaneous, and the changes of the standard enthalpy ( ΔHmθr) showed that the adsorption of the Bt toxin by montmorillonite was endothermic while the adsorption by the other three minerals was exothermic.

  9. Influence of pH on cephalexin adsorption onto SBA-15 mesoporous silica: Theoretical and experimental study

    NASA Astrophysics Data System (ADS)

    Legnoverde, María S.; Simonetti, Sandra; Basaldella, Elena I.

    2014-05-01

    Cephalexin adsorption from aqueous solutions using SBA-15 mesoporous silica as adsorbent and the influence of pH solution on drug adsorption were studied. In order to have a better knowledge about the way the drug molecules interact with the inorganic matrix, the adsorption process was estimated by applying the computational chemistry software YAeHMOP (Yet Another extended Hückel Molecular Orbital Package). A strong correlation between the theoretical calculations and the experimental results was established, showing that the adsorbate-adsorbent interaction is pH dependent. Calculated cephalexin horizontal adsorption energy was almost 9 eV more stable than the one corresponding to vertical adsorption, and also the lowest enthalpy of contact and the maximum adsorption percent were found for the cationic cephalexin-silica system. Cephalexin adsorption through the NH3+ group is 8 eV stronger than the molecule adsorption through the COO- group. In agreement with these theoretical predictions, experimental results indicate that the electrostatic attraction between CPX ions and the surface of mesoporous silica is favored at pH values between 2 and 2.56, the maximum being for cephalexin adsorption obtained at pH 2.3.

  10. Adsorption kinetic and equilibrium study for removal of mercuric chloride by CuCl2-impregnated activated carbon sorbent.

    PubMed

    Li, Xin; Liu, Zhouyang; Lee, Joo-Youp

    2013-05-15

    The intrinsic adsorption kinetics of mercuric chloride (HgCl2) was studied for raw, 4% and 10% CuCl2-impregnated activated carbon (CuCl2-AC) sorbents in a fixed-bed system. An HgCl2 adsorption kinetic model was developed for the AC sorbents by taking into account the adsorption kinetics, equilibrium, and internal and external mass transfer. The adsorption kinetic constants determined from the comparisons between the simulation and experimental results were 0.2, 0.3, and 0.5m(3)/(gs) for DARCO-HG, 4%(wt), and 10%(wt) CuCl2-AC sorbents, respectively, at 140 °C. CuCl2 loading was found to slightly increase the adsorption kinetic constant or at least not to decrease it. The HgCl2 equilibrium adsorption data based on the Langmuir isotherm show that high CuCl2 loading can result in high binding energy of the HgCl2 adsorption onto the carbon surface. The adsorption equilibrium constant was found to increase by ~10 times when CuCl2 loading varied from 0 to 10%(wt), which led to a decrease in the desorption kinetic constant (k2) by ~10 times and subsequently the desorption rate by ~50 times. Intraparticle pore diffusion considered in the model showed good accuracy, allowing for the determination of intrinsic HgCl2 adsorption kinetics.

  11. Adsorption of albumin and sodium hyaluronate on UHMWPE: a QCM-D and AFM study.

    PubMed

    Serro, A P; Degiampietro, K; Colaço, R; Saramago, B

    2010-06-15

    The biotribological properties of artificial joints, in particular the efficiency of the lubrication, strongly determine their lifetime. The most commonly used artificial joints combine a metallic or ceramic part articulating against a ultra high molecular weight polyethylene (UHMWPE) counterface, and are lubricated by the periprosthetic fluid. This fluid contains several macromolecules, namely albumin and sodium hyaluronate (NaHA), that are known to be involved in the lubrication process. There are several studies in the literature concerning the interaction of the referred macromolecules with ceramic or metallic prosthetic materials. However, to our knowledge, information about their binding to the polymeric surface is practically inexistent. The objective of this work is to contribute to clarify the role played by albumin and NaHA on the biolubrication process, through the investigation of their interaction with the UHMWPE surface. The study involves adsorption measurements using a quartz crystal microbalance with dissipation (QCM-D), the characterization of the adsorbed films by atomic force microscopy (AFM) and wettability determinations. Albumin was found to adsorb strongly and extensively to the polymer, while NaHA led to a very low adsorption. In both cases rigid films were obtained, but with different morphology and porosity. The high binding affinity of the protein to the polymer was demonstrated both by the results of the fittings to Langmuir and Freundlich models and by the values of the adhesion forces determined by AFM. In the simultaneous adsorption of albumin and NaHA, protein adsorption is predominant and determines the surface properties.

  12. Adsorption of malachite green by polyaniline-nickel ferrite magnetic nanocomposite: an isotherm and kinetic study

    NASA Astrophysics Data System (ADS)

    Patil, Manohar R.; Shrivastava, V. S.

    2014-11-01

    This work deals with the development of an efficient method for the removal of a MG (malachite green) dye from aqueous solution using polyaniline (PANI)-Nickel ferrite (NiFe2O4) magnetic nanocomposite. It is successfully synthesised in situ through self polymerisation of monomer aniline. Adsorptive removal studies are carried out for water soluble MG dye using PANI-Nickel ferrite magnetic nanocomposite in aqueous solution. Different parameters like dose of adsorbent, contact time, different initial conc., and pH have been studied to optimise reaction condition. It is concluded that adsorptive removal by PANI-Nickel ferrite magnetic nanocomposite is an efficient method for removing a MG dye from aqueous solution than work done before. The optimum conditions for the removal of the dye are initial concentration 30 mg l-1, adsorbent dose 5gm l-1 and pH 7. The adsorption capacity is found 4.09 mg g-1 at optimum condition 30 mg l-1. The adsorption followed pseudo-second-order kinetics. The experimental isotherm is found to fit with Langmuir equation. The prepared adsorbent is characterised by techniques SEM, EDS, XRD and VSM.

  13. Microcalorimetric study of adsorption of glycomacropeptide on anion-exchange chromatography adsorbent.

    PubMed

    Lira, Rafael A; Minim, Luis A; Bonomo, Renata C F; Minim, Valéria P R; da Silva, Luis H M; da Silva, Maria C H

    2009-05-15

    The adsorption of glycomacropeptide (GMP) from cheese whey on an anion-exchange adsorbent was investigated using isothermal titration microcalorimetry to measure thermodynamic information regarding such processes. Isotherms data were measured at temperatures of 25 and 45 degrees C, pH 8.2 and various ionic strengths (0-0.08 molL(-1) NaCl). The equilibrium data were fit using the Langmuir model and the process was observed to be reversible. Temperature was observed to positively affect the interaction of the protein and adsorbent. Microcalorimetric studies indicated endothermic adsorption enthalpy in all cases, except at 45 degrees C and 0.0 molL(-1) NaCl. The adsorption process was observed to be entropically driven at all conditions studied. It was concluded that the increase in entropy, attributed to the release of hydration waters as well as bounded ions from the adsorbent and protein surface due to interactions of the protein and adsorbent, was a major driving force for the adsorption of GMP on the anion-exchange adsorbent. These results could allow for design of more effective ion-exchange separation processes for proteins.

  14. Computational study of hydrocarbon adsorption in metal-organic framework Ni2(dhtp)

    SciTech Connect

    Sun, Xiuquan; Wick, Collin D.; Thallapally, Praveen K.; McGrail, B. Peter; Dang, Liem X.

    2011-03-31

    Molecular dynamic simulations were carried out to study the sorption, structural properties, and diffusivities of n-hexane and cyclohexane adsorbed in Ni2(dhtp). The results indicated strong interactions between the alkanes and the host material. The free energy perturbation method was employed to investigate the adsorption free energies of methane, ethane, n-butane, n-hexane and cyclohexane. For linear alkanes, the free energy lowered as the length of the carbon chain increased. Also, the adsorption of n-hexane was preferred over cyclohexane, due to its ability to rearrange its structure to maximize contacts with the host. Furthermore, due to the large pore size of Ni2(dhtp), higher loadings of alkanes did not significantly affect the alkane structure, and enhanced the free energy of adsorption for subsequent alkanes being loaded. According to our studies, Ni2(dhtp) has a very promising potential for adsorption and storage of alkanes. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  15. DFT study of the adsorption of D-(L-)cysteine on flat and chiral stepped gold surfaces.

    PubMed

    Fajín, José L C; Gomes, José R B; Cordeiro, M Natália D S

    2013-07-16

    The adsorption of cysteine onto the intrinsically chiral gold surface, Au(321)(R,S), was investigated by means of a periodic supercell density functional theory approach. The results are compared to those obtained at the same level of theory with a nonchiral surface having the same terrace orientation, the Au(111) surface. Neutral and zwitterionic cysteine forms of the L and D enantiomers are considered, as are surface coverage effects. It was found that at high coverage the zwitterionic forms of L- and D-cysteine are more stable on the Au(321)(R,S) faces of the stepped surface and also on the flat Au(111) surface, leading to highly organized cysteine monolayers. However, at low coverage the adsorption of cysteine dimers, with the pairs interacting through their carbonyl groups, is more favorable than or at least equally favorable to the adsorption of single cysteine molecules on both surfaces. A comparison between the cysteine adsorption on the two different surface structures shows that the adsorption on the stepped surface is clearly more favorable than on the flat surface, revealing the importance of the low-coordinated gold atoms in the adsorption of these species. Furthermore, non-negligible differences between the adsorption energy of the enantiomers of cysteine were found both at high and low coverage, thus showing the enantiospecificity of this intrinsically chiral surface regarding cysteine adsorption. This adsorption occurs with the cysteine binding the surface through only one contact point (by its sulfur atom), in contrast to previous work where the enantiospecific adsorption of cysteine has been related to two nonequivalent binding sites of the cysteine enantiomers with the surface.

  16. Effects of Adsorption Constant Uncertainty on Contaminant Plume Migration: One and Two Dimensional Numerical Studies

    NASA Astrophysics Data System (ADS)

    Eliassi, M.

    2002-12-01

    In this study, we use one- and two-dimensional (1D and 2D) reactive-transport models to numerically examine variations in predictions due to uncertainty in the adsorption constants. The study specifically focuses on the hydrogeology and mineralogy of the Naturita uranium mill tailings site in Colorado. This work demonstrates the importance of selecting the appropriate adsorption constants when using reactive-transport models to evaluate risk and pollution attenuation at contaminated sites. In our model, uranium is removed from mill tailings leachate through adsorption onto smectite, an abundant clay mineral at the Naturita site. Uranium adsorbs to specific surface sites on both the basal planes and edges of the smectite. Because uranium adsorbs predominantly to the aluminum edge surface sites [>(e)AlOH], we chose to examine uncertainty only in the equilibrium constants associated with these sites. Using the Latin Hypercube Sampling method, one-hundred pairs of adsorption constant (log K) values are selected for the surface species >(e)AlO- and >(e)AlOUO2+, from normal distributions of each log K. Following a grid convergence study, 1D simulation results can be identified by two distinct groups of uranium breakthrough curves. In the first group, the breakthrough curves exhibit a classical sigmoidal shape whereas in the second group the breakthrough curves display higher uranium concentrations in solution over greater distances and times. These two groups are clearly separated by two different ranges of log K >(e)AlO- values or two different ranges for the smectite point of zero charge. Preliminary 2D simulations, in both homogeneous and randomly heterogeneous aquifers demonstrate that plume geometry and migration in longitudinal and transverse directions are also influenced by the choice of adsorption constants.

  17. Synthesis and gas adsorption study of porous metal-organic framework materials

    NASA Astrophysics Data System (ADS)

    Mu, Bin

    Metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) have become the focus of intense study over the past decade due to their potential for advancing a variety of applications including air purification, gas storage, adsorption separations, catalysis, gas sensing, drug delivery, and so on. These materials have some distinct advantages over traditional porous materials such as the well-defined structures, uniform pore sizes, chemically functionalized sorption sites, and potential for postsynthetic modification, etc. Thus, synthesis and adsorption studies of porous MOFs have increased substantially in recent years. Among various prospective applications, air purification is one of the most immediate concerns, which has urgent requirements to improve current nuclear, biological, and chemical (NBC) filters involving commercial and military purposes. Thus, the major goal of this funded project is to search, synthesize, and test these novel hybrid porous materials for adsorptive removal of toxic industrial chemicals (TICs) and chemical warfare agents (CWAs), and to install the benchmark for new-generation NBC filters. The objective of this study is three-fold: (i) Advance our understanding of coordination chemistry by synthesizing novel MOFs and characterizing these porous coordination polymers; (ii) Evaluate porous MOF materials for gasadsorption applications including CO2 capture, CH4 storage, other light gas adsorption and separations, and examine the chemical and physical properties of these solid adsorbents including thermal stability and heat capacity of MOFs; (iii) Evaluate porous MOF materials for next-generation NBC filter media by adsorption breakthrough measurements of TICs on MOFs, and advance our understanding about structureproperty relationships of these novel adsorbents.

  18. Adsorption of heavy metal cations by Na-clinoptilolite: equilibrium and selectivity studies.

    PubMed

    Mihaly-Cozmuta, L; Mihaly-Cozmuta, A; Peter, A; Nicula, C; Tutu, H; Silipas, Dan; Indrea, Emil

    2014-05-01

    This paper summarizes the conclusions of experiments conducted on the adsorption of Cd(2+), Co(2+), Cu(2+), Mn(2+), Ni(2+), Pb(2+) and Zn(2+) onto zeolite. The focus of the experiments was to establish the influence of the initial pH of the contact solution as well as the selectivity of zeolite on the efficiency of the adsorption process. To this end, experimental adsorption isotherms were established for the pH values ranging from 1 to 4 by using the Na-form of clinoptilolite (particle size range 0.5-1 mm) as an adsorbent. Langmuir, Freundlich and Dubinin-Raduschkevich isotherm models were used to validate the experimental data and the Gibbs free energy was calculated based on the distribution coefficient. From the Langmuir model, correlations between the maximum adsorption capacity and selected physical-chemical parameters of the cations studied were established. The results of the experiments suggest that the selectivity of zeolite is strongly influenced by the pH of the contact solution, dehydration energy of cations, diffusion coefficient and the pH at which the precipitation of hydroxides occurs.

  19. Comparative study of adsorption of Pb(II) on native garlic peel and mercerized garlic peel.

    PubMed

    Liu, Wei; Liu, Yifeng; Tao, Yaqi; Yu, Youjie; Jiang, Hongmei; Lian, Hongzhen

    2014-02-01

    A comparative study using native garlic peel and mercerized garlic peel as adsorbents for the removal of Pb(2+) has been proposed. Under the optimized pH, contact time, and adsorbent dosage, the adsorption capacity of garlic peel after mercerization was increased 2.1 times and up to 109.05 mg g(-1). The equilibrium sorption data for both garlic peels fitted well with Langmuir adsorption isotherm, and the adsorbent-adsorbate kinetics followed pseudo-second-order model. These both garlic peels were characterized by elemental analysis, Fourier transform infrared spectrometry (FT-IR), and scanning electron microscopy, and the results indicated that mercerized garlic peel offers more little pores acted as adsorption sites than native garlic peel and has lower polymerization and crystalline and more accessible functional hydroxyl groups, which resulted in higher adsorption capacity than native garlic peel. The FT-IR and X-ray photoelectron spectroscopy analyses of both garlic peels before and after loaded with Pb(2+) further illustrated that lead was adsorbed on the through chelation between Pb(2+) and O atom existed on the surface of garlic peels. These results described above showed that garlic peel after mercerization can be a more attractive adsorbent due to its faster sorption uptake and higher capacity.

  20. Uranyl adsorption at the muscovite (mica)/water interface studied by second harmonic generation.

    PubMed

    Saslow Gomez, Sarah A; Jordan, David S; Troiano, Julianne M; Geiger, Franz M

    2012-10-16

    Uranyl adsorption at the muscovite (mica)/water interface was studied by second harmonic generation (SHG). Using the nonresonant χ(3) technique and the Gouy-Chapman model, the initial surface charge density of the mica surface was determined to be -0.022(1) C/m(2) at pH 6 and in the presence of dissolved carbonate. Under these same conditions, uranyl adsorption isotherms collected using nonresonant χ(3) experiments and resonantly enhanced SHG experiments that probe the ligand-to-metal charge transfer bands of the uranyl cation yielded a uranyl binding constant of 3(1) × 10(7) M(-1), corresponding to a Gibbs free energy of adsorption of -52.6(8) kJ/mol, and a maximum surface charge density at monolayer uranyl coverage of 0.028(3) C/m(2). These results suggest favorable adsorption of uranyl ions to the mica interface through strong ion-dipole or hydrogen interactions, with a 1:1 uranyl ion to surface site ratio that is indicative of monovalent cations ((UO(2))(3)(OH)(5)(+), (UO(2))(4)(OH)(7)(+), UO(2)OH(+), UO(2)Cl(+), UO(2)(CH(3)COO(-))(+)) binding at the interface, in addition to neutral uranyl species (UO(2)(OH)(2) and UO(2)CO(3)). This work provides benchmark measurements to be used in the improvement of contaminant transport modeling.

  1. Adsorption Studies of Chromium(VI) on Activated Carbon Derived from Mangifera indica (Mango) Seed Shell

    NASA Astrophysics Data System (ADS)

    Mise, Shashikant; Patil, Trupti Nagendra

    2015-09-01

    The removal of chromium(VI) from synthetic sample by adsorption on activated carbon prepared from Mangifera indica (mango) seed shell have been carried out at room temperature 32 ± 1 °C. The removal of chromium(VI) from synthetic sample by adsorption on two types of activated carbon, physical activation and chemical activation (Calcium chloride and Sodium chloride), Impregnation Ratio's (IR) 0.25, 0.50, 0.75 for optimum time, optimum dosages and variation of pH were studied. It is observed that contact time differs for different carbons i.e. for physically and chemically activated carbons. The contact time decreases for chemically activated carbon compared to the physically activated carbon. It was observed that as dosage increases the adsorption increased along with the increase in impregnation ratio. It was also noted that as I.R. increases the surface area of Mangifera indica shell carbon increased. These dosage data were considered in the construction of isotherms and it was found that adsorption obeys Freundlich Isotherm and does not obey Langmuir Isotherm. The maximum removal of chromium (VI) was obtained in highly acidic medium at a pH of 1.50.

  2. N2 adsorption study on quartz, silver, and carbon nanotube by inductive pulse quartz crystal microbalance

    NASA Astrophysics Data System (ADS)

    Park, Jang-ik; Yu, Insuk; Seo, Yongho

    2007-03-01

    We utilize an "inductive pulse" quartz crystal microbalance method to study N2 adsorption on quartz, silver, and a single wall carbon nanotube at 77 K. This method is based on radio frequency electric pulse excitation and ring-down signal measurements of quartz crystal resonators located in an induction coil. The surface areas and adsorption strength c are estimated by the Brunauer-Emmett-Teller (BET) model. The estimated c for quartz and silver surface are about 1/5 times smaller than that measured by the conventional method. This is explained as suppression of the self-heating effect, by using our inductive pulse method. We suggest a simple theoretical estimation of self-heating effects on conventional and inductive pulse methods. For the intermediate adsorption range, we analyze our data using the generalized Frenkel-Hasley-Hill (FHH) model with fractal dimension. While the quartz and silver have fractal dimensions of about 2.2±0.1, single wall carbon nanotube has 1.2±0.1, which are explained by its strong adsorptive force.

  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. A robust approach to studying the adsorption of Pluronic F108 on nonporous membranes.

    PubMed

    Govender, S; Jacobs, E P; Bredenkamp, M W; Swart, P

    2005-02-15

    A method for poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) desorption from synthetic nonporous polymeric membranes, using hexane:isopropanol treatment and subsequent colorimetric quantification, is described. The polymers polysulfone, poly(vinyldiene fluoride), and poly(ether imide) were used to fabricate solid adsorption matrices. The desorbed Pluronic F108 forms a color complex with ammonium ferrothiocyanate (NH4FeSCN) and is based on partitioning of a chromophore present in NH4FeSCN from an aqueous phase to a chloroform phase in the presence of Pluronic. The protocols for Pluronic desorption and detection are simple, sensitive, inexpensive, rapid, and reproducible over a wide range of Pluronic coating concentrations and membrane surface chemistries. A linear response over the concentration range from 3 to 130 microg ml(-1) is obtained. The adsorption isotherms for flat sheet membranes are also described and the Langmuir equation provides the best fit for the adsorption data obtained within the concentration range studied. The absence of any significant interference from certain proteins, vitamins, carbohydrates, plasma, and halogenated derivatives makes the assay equally suitable for the estimation of Pluronic F108 in the attendant Pluronic conjugates or in biomedical applications. Using nonporous hollow fine fibers and capillary membranes as model curved substrates we were also able to correlate an increase in the radius of curvature with a corresponding increase in the surface interfacial adsorption of Pluronic F108.

  5. Monoclonal Antibody Interactions with Micro- and Nanoparticles: Adsorption, Aggregation and Accelerated Stress Studies

    PubMed Central

    Bee, Jared S.; Chiu, David; Sawicki, Suzanne; Stevenson, Jennifer L.; Chatterjee, Koustuv; Freund, Erwin; Carpenter, John F.; Randolph, Theodore W.

    2009-01-01

    Therapeutic proteins are exposed to various wetted surfaces that could shed sub-visible particles. In this work we measured the adsorption of a monoclonal antibody (mAb) to various microparticles, characterized the adsorbed mAb secondary structure, and determined the reversibility of adsorption. We also developed and used a front-face fluorescence quenching method to determine that the mAb tertiary structure was near-native when adsorbed to glass, cellulose and silica. Initial adsorption to each of the materials tested was rapid. During incubation studies, exposure to the air-water interface was a significant cause of aggregation but acted independently of the effects of microparticles. Incubations with glass, cellulose, stainless steel or Fe2O3 microparticles gave very different results. Cellulose preferentially adsorbed aggregates from solution. Glass and Fe2O3 adsorbed the mAb but did not cause aggregation. Adsorption to stainless steel microparticles was irreversible, and caused appearance of soluble aggregates upon incubation. The secondary structure of mAb adsorbed to glass and cellulose was near-native. We suggest that the protocol described in this work could be a useful preformulation stress screening tool to determine the sensitivity of a therapeutic protein to exposure to common surfaces encountered during processing and storage. PMID:19492408

  6. Adsorption of carbon on Pd clusters of nanometer size: a first-principles theoretical study.

    PubMed

    Neyman, Konstantin M; Inntam, Chan; Gordienko, Alexei B; Yudanov, Ilya V; Rösch, Notker

    2005-05-01

    Adsorbed atomic C species can be formed in the course of surface reactions and commonly decorate metal catalysts. We studied computationally C adsorption on Pd nanoclusters using an all-electron scalar relativistic density functional method. The metal particles under investigation, Pd(55), Pd(79), Pd(85), Pd(116), Pd(140), and Pd(146), were chosen as fragments of bulk Pd in the form of three-dimensional octahedral or cuboctahedral crystallites, exposing (111) and (100) facets as well as edge sites. These cluster models are shown to yield size-converged adsorption energies. We examined which surface sites of these clusters are preferentially occupied by adsorbed C. According to calculations, surface C atoms form strongly adsorbed carbide species (with adsorption energies of more than 600 kJ mol(-1)) bearing a significant negative charge. Surface sites allowing high, fourfold coordination of carbon are overall favored. To avoid effects of adsorbate-adsorbate interaction in the cluster models for carbon species in the vicinity of cluster edges, we reduced the local symmetry of selected adsorption complexes on the nanoclusters by lowering the global symmetry of the nanocluster models from point group O(h) to D(4h). On (111) facets, threefold hollow sites in the center are energetically preferred; adsorbed C is calculated to be slightly less stable when displaced to the facet borders.

  7. Theoretical study of adsorption of nitrogen-containing environmental contaminants on kaolinite surfaces.

    PubMed

    Scott, Andrea Michalkova; Burns, Elizabeth A; Hill, Frances C

    2014-08-01

    The adsorption of nitrogen-containing compounds (NCCs) including 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), 2,4-dinitroanisole (DNAN), and 3-nitro-1,2,4-triazol-5-one (NTO) on kaolinite surfaces was investigated. The M06-2X and M06-2X-D3 density functionals were applied with the cluster approximation. Several different positions of NCCs relative to the adsorption sites of kaolinite were examined, including NCCs in perpendicular and parallel orientation toward both surface models of kaolinite. The binding between the target molecules and kaolinite surfaces was analyzed and bond energies were calculated applying the atoms in molecules (AIM) method. All NCCs were found to prefer a parallel orientation toward both kaolinite surfaces, and were bound more strongly to the octahedral than to the tetrahedral site. TNT exhibited the strongest interaction with the octahedral surface and DNAN with the tetrahedral surface of kaolinite. Hydrogen bonding was shown to be the dominant non-covalent interaction for NCCs interacting with the octahedral surface of kaolinite with a small stabilizing effect of dispersion interactions. In the case of adsorption on the tetrahedral surface, kaolonite-NCC binding was shown to be governed by the balance between hydrogen bonds and dispersion forces. The presence of water as a solvent leads to a significant decrease in the adsorption strength for all studied NCCs interacting with both kaolinite surfaces.

  8. Design of a hybrid advective-diffusive microfluidic system with ellipsometric detection for studying adsorption.

    PubMed

    Wang, Lei; Zhao, Cunlu; Wijnperlé, Daniel; Duits, Michel H G; Mugele, Frieder

    2016-05-01

    Establishing and maintaining concentration gradients that are stable in space and time is critical for applications that require screening the adsorption behavior of organic or inorganic species onto solid surfaces for wide ranges of fluid compositions. In this work, we present a design of a simple and compact microfluidic device based on steady-state diffusion of the analyte, between two control channels where liquid is pumped through. The device generates a near-linear distribution of concentrations. We demonstrate this via experiments with dye solutions and comparison to finite-element numerical simulations. In a subsequent step, the device is combined with total internal reflection ellipsometry to study the adsorption of (cat)ions on silica surfaces from CsCl solutions at variable pH. Such a combined setup permits a fast determination of an adsorption isotherm. The measured optical thickness is compared to calculations from a triple layer model for the ion distribution, where surface complexation reactions of the silica are taken into account. Our results show a clear enhancement of the ion adsorption with increasing pH, which can be well described with reasonable values for the equilibrium constants of the surface reactions.

  9. Surfactant loss control in chemical flooding spectroscopic and calorimetric study of adsorption and precipitation on reservoir minerals. Annual report, September 30, 1993--September 30, 1994

    SciTech Connect

    Somasundaran, P.

    1995-06-01

    The aim of this project is to elucidate the mechanisms underlying adsorption and surface precipitation of flooding surfactants on reservoir minerals. Effect of surfactant structure, surfactant combinations, other inorganic and polymeric species is being studied. A multi-pronged approach consisting of micro and nano spectroscopy, microcalorimetry, electrokinetics, surface tension and wettability is used to achieve the goals. The results of this study should help in controlling surfactant loss in chemical flooding and also in developing optimum structures and conditions for efficient chemical flooding processes. During the second year of this three year contract, adsorption/desorption of single surfactants and select surfactant mixtures on alumina and silica was studied. Surfactants studied include the anionic sodium dodecyl sulfate (SDS), cationic tetradecyl trimethyl ammonium chloride (TTAC), nonionic pentadecylethoxylated nonyl phenol (NP-15) and the nonionic octaethylene glycol n-dodecyl ether (C{sub 12}EO{sub 8}) of varying hydrocarbon chain length. The microstructure of the adsorbed layer in terms of micropolarity and aggregation numbers was probed using fluorescence spectroscopy. Changes of microstructure upon dilution (desorption) were also studied. Presence of the nonionic surfactant in the mixed aggregate led to shielding of the charge of the ionic surfactant which in-turn promoted aggregation but reduced electrostatic attraction between the charged surfactant and the mineral surface. Strong consequences of surfactant interactions in solution upon adsorption as well as correlations between monomer concentrations in mixtures and adsorption were revealed.

  10. [Study of the adsorption behaviors of plasma proteins on the single-walled carbon nanotubes nonwoven].

    PubMed

    Meng, Jie; Song, Li; Meng, Jie; Kong, Hua; Wang, Chaoying; Guo, Xiaotian; Xu, Haiyan; Xie, Sishen

    2007-02-01

    Single walled carbon nanotubes (SWNT) have attracted increasing research interests for the purpose of biomedical application because they provide not only nanostructured topography, but also chemical composition of pure carbon atoms, as well as ultra high strength and excellent flexibility. Regarding the interactions of nanomaterials to biological systems, non-specific adsorption of plasma proteins is one of the most important issues to be concerned, which plays a crucial role that would determine how biological systems response to the biomaterials. Motivated by application of SWNT materials in biomedical fields, in this study, the adsorption behaviors of plasma proteins on the surface of SWNT nonwoven, prepared directly by floating chemical vapor observation and energy deposition method were investigated by means of scanning electron microscope (SEM), dispersive X-ray (EDX) analysis and ELISA. Results indicated the SWNT non-woven showed a clear adsorption preference of fibrinogen over albumin. There was no human serum albumin detected using above analysis methods on the SWNT nonwoven even incubated in the albumin solution of 4 mg/ml. While more than 0.15 microg of human fibrinogen was detected by ELISA on the SWNT nonwoven with area of 40 mm x 40 mm incubated in the fibrinogen solution of 5 microg/ml. In addition, IgG of sheep-anti-human serum fibrinogen exhibited strong nonspecific adsorption on the surface of SWNT nonwoven. The adsorption behaviors are different significantly from those of other carbon materials and conventional biomaterials. The unique interaction of SWNT nonwoven to plasma proteins is of significance to further studies of blood cells responses.

  11. Experimental and kinetic studies on methylene blue adsorption by coir pith carbon.

    PubMed

    Kavitha, D; Namasivayam, C

    2007-01-01

    Varying the parameters such as agitation time, dye concentration, adsorbent dose, pH and temperature carried out the potential feasibility of thermally activated coir pith carbon prepared from coconut husk for removal of methylene blue. Greater percentage of dye was removed with decrease in the initial concentration of dye and increase in amount of adsorbent used. Kinetic study showed that the adsorption of dye on coir pith carbon was a gradual process. Lagergren first-order, second-order, intra particle diffusion model and Bangham were used to fit the experimental data. Equilibrium isotherms were analysed by Langmuir, Freundlich, Dubnin-Radushkevich, and Tempkin isotherm. The adsorption capacity was found to be 5.87 mg/g by Langmuir isotherm for the particle size 250-500 microm. The equilibrium time was found to be 30 and 60 min for 10 and 20 mg/L and 100 min for 30, 40 mg/L dye concentrations, respectively. A maximum removal of 97% was obtained at natural pH 6.9 for an adsorbent dose of 100 mg/50 mL and 100% removal was obtained for an adsorbent dose of 600 mg/50 mL of 10 mg/L dye concentration. The pH effect and desorption studies suggest that chemisorption might be the major mode of the adsorption process. The change in entropy (DeltaS0) and heat of adsorption (DeltaH0) of coir pith carbon was estimated as 117.20 J/mol/K and 30.88 kJ/mol, respectively. The high negative value of change in Gibbs free energy indicates the feasible and spontaneous adsorption of methylene blue on coir pith carbon.

  12. The adsorption of H2 on Fe(111) studied by thermal energy atom scattering

    NASA Astrophysics Data System (ADS)

    Jiang, P.; Zappone, M.; Bernasek, S. L.

    1993-11-01

    The interaction of H2 with Fe(111) has been studied by thermal energy atom scattering (TEAS). The specularly scattered He intensity as a function of hydrogen coverage exhibits a concave drop in scattered He intensity up to 30% coverage, followed by a plateau and another drop in intensity at 80% coverage. A model has been developed to account for this data which assumes three adsorption sites for H on Fe(111), in analogy with the three desorption peaks seen in temperature-programmed desorption (TPD). The adsorption sites have not been definitely assigned, but are labeled ``deep-hollow,'' ``shallow-hollow,'' and ``on-top.'' Competitive adsorption into the deep-hollow and shallow-hollow sites is assumed to account for the initial concavity of the data. Adsorption into on-top sites only becomes significant at 80% coverage. Effective cross sections and reflectivities for the three sites have been obtained for θi=60° and 40°. When a H saturated surface is heated, the scattered He intensity decreases upon heating from 173 to 240 K, at which point desorption has already begun. This drop in intensity is not completely explicable by a Debye-Waller attenuation. It is proposed to be due to a shift in population of the adsorbed H to more exposed, on-top sites, in accord with a Boltzmann distribution of adsorption sites. The scattered He intensity increases upon further heating from 240 to 400 K, corresponding to the desorption of recombined H2 from the surface. Comparison of the He/H/Fe(111) system is made with the He/H/Pt(111) and He/H/Fe(110) systems.

  13. Adsorption of Bovine Serum Albumin (BSA) at the Oil/Water Interface: A Neutron Reflection Study.

    PubMed

    Campana, M; Hosking, S L; Petkov, J T; Tucker, I M; Webster, J R P; Zarbakhsh, A; Lu, J R

    2015-05-26

    The structure of the adsorbed protein layer at the oil/water interface is essential to the understanding of the role of proteins in emulsion stabilization, and it is important to glean the mechanistic events of protein adsorption at such buried interfaces. This article reports on a novel experimental methodology for probing protein adsorption at the buried oil/water interface. Neutron reflectivity was used with a carefully selected set of isotopic contrasts to study the adsorption of bovine serum albumin (BSA) at the hexadecane/water interface, and the results were compared to those for the air/water interface. The adsorption isotherm was determined at the isoelectric point, and the results showed that a higher degree of adsorption could be achieved at the more hydrophobic interface. The adsorbed BSA molecules formed a monolayer on the aqueous side of the interface. The molecules in this layer were partially denatured by the presence of oil, and once released from the spatial constraint by the globular framework they were free to establish more favorable interactions with the hydrophobic medium. Thus, a loose layer extending toward the oil phase was clearly observed, resulting in an overall broader interface. By analogy to the air/water interface, as the concentration of BSA increased to 1.0 mg mL(-1) a secondary layer extending toward the aqueous phase was observed, possibly resulting from the steric repulsion upon the saturation of the primary monolayer. Results clearly indicate a more compact arrangement of molecules at the oil/water interface: this must be caused by the loss of the globular structure as a consequence of the denaturing action of the hexadecane.

  14. Maghemite nanosorbcats for methylene blue adsorption and subsequent catalytic thermo-oxidative decomposition: Computational modeling and thermodynamics studies.

    PubMed

    El-Qanni, Amjad; Nassar, Nashaat N; Vitale, Gerardo; Hassan, Azfar

    2016-01-01

    In this study methylene blue (MB) has been investigated for its adsorption and subsequent catalytic thermo-oxidative decomposition on surface of maghemite (γ-Fe2O3) nanoparticles. The experimental adsorption isotherm fit well to the Freundlich model, indicating multi-sites adsorption. Computational modeling of the interaction between the MB molecule and γ-Fe2O3 nanoparticle surface was carried out to get more insights into its adsorption behavior. Adsorption energies of MB molecules on the surface indicated that there are different adsorption sites on the surface of γ-Fe2O3 confirming the findings regarding the adsorption isotherm. The catalytic activity of the γ-Fe2O3 nanoparticles toward MB thermo-oxidative decomposition has been confirmed by subjecting the adsorbed MB to a thermo oxidation process up to 600 °C in a thermogravimetric analyzer. The experimental results showed a catalytic activity for post adsorption oxidation. The oxidation kinetics were studied using the Ozawa-Flyn-Wall (OFW) corrected method. The most probable mechanism functions were fifth and third orders for virgin MB and MB adsorbed onto γ-Fe2O3 nanoparticles, respectively. Moreover, the results of thermodynamic transition state parameters, namely changes in Gibbs free energy of activation (ΔG(‡)), enthalpy of activation (ΔH(‡)), and entropy of activation (ΔS(‡)), emphasized the catalytic activity of γ-Fe2O3 nanoparticles toward MB oxidation.

  15. Application of AlMCM-41 for competitive adsorption of methylene blue and rhodamine B: Thermodynamic and kinetic studies.

    PubMed

    Eftekhari, S; Habibi-Yangjeh, A; Sohrabnezhad, Sh

    2010-06-15

    AlMCM-41 was applied for adsorption of methylene blue (MB) and rhodamine B (RB) in single and binary component systems. In the single component systems, AlMCM-41 represents higher adsorption capacity for MB than RB with the maximal adsorption capacity of 2.08x10(-4) and 8.74x10(-5)mol/g at 25 degrees C for MB and RB, respectively. In the binary component system, MB and RB exhibit competitive adsorption onto the adsorbent. The adsorption is approximately reduced to 94 and 79% of single component adsorption systems for MB and RB (initial concentration of 8x10(-6)M) at 25 degrees C. In single and binary component systems, kinetic and adsorption isotherm studies demonstrate that the data are following pseudo-second-order kinetic model and Langmuir isotherm. Effect of solution pH on the adsorption in single and binary component systems was studied and the results were described by electrostatic interactions.

  16. Modeling studies: Adsorption of aniline blue by using Prosopis Juliflora carbon/Ca/alginate polymer composite beads.

    PubMed

    Kumar, M; Tamilarasan, R

    2013-02-15

    The research article describes the experimental and modeling study for the adsorptive removal of aniline blue dye (AB dye) from aqueous matrices using a Prosopis Juliflora modified carbon/Ca/alginate polymer bead as a low cost and eco-friendly adsorbent. The rate of adsorption was investigated under various experimental parameters such as contact time, adsorbent dose, dye concentration, pH and temperature. The kinetics, equilibrium and thermodynamic studies were assessed to find out the efficiency of the adsorption process. The equilibrium uptake capacity of the adsorption process was found with Freundlich and Langmuir adsorption isotherm equations and it was evaluated by dimensionless separation factor (R(L)). The dynamics of adsorption was predicted by pseudo-first order, pseudo-second order Lagergren's equation and intra particle diffusion model. Adsorption feasibility was assessed with thermodynamic parameters such as isosteric heat of adsorption (ΔH°), standard entropy (ΔS°) and Gibbs free energy (ΔG°) using VantHoff plot. The alginate bead was characterized with FTIR spectroscopy and Scanning Electron Microscopy (SEM).

  17. Unprecedentedly high selective adsorption of gas mixtures in rho zeolite-like metal-organic framework: a molecular simulation study.

    PubMed

    Babarao, Ravichandar; Jiang, Jianwen

    2009-08-19

    We report a molecular simulation study for the separation of industrially important gas mixtures (CO(2)/H(2), CO(2)/CH(4), and CO(2)/N(2)) in rho zeolite-like metal-organic framework (rho-ZMOF). Rho-ZMOF contains a wide-open anionic framework and charge-balancing extraframework Na(+) ions. Two types of binding sites for Na(+) ions are identified in the framework. Site I is in the single eight-membered ring, whereas site II is in the alpha-cage. Na(+) ions at site I have a stronger affinity for the framework and thus a smaller mobility. The binding sites in rho-ZMOF resemble those in its inorganic counterpart rho-zeolite. CO(2) is adsorbed predominantly over other gases because of its strong electrostatic interactions with the charged framework and the presence of Na(+) ions acting as additional adsorption sites. At ambient temperature and pressure, the CO(2) selectivities are 1800 for the CO(2)/H(2) mixture, 80 for the CO(2)/CH(4) mixture, and 500 for the CO(2)/N(2) mixture. Compared with other MOFs and nanoporous materials reported to date, rho-ZMOF exhibits unprecedentedly high selective adsorption for these gas mixtures. This work represents the first simulation study to characterize extraframework ions and examine gas separation in a charged ZMOF. The simulation results reveal that rho-ZMOF is a promising candidate for the separation of syngas, natural gas, and flue gas.

  18. CO adsorption on W(100) during temperature-programmed desorption: A combined density functional theory and kinetic Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Albao, Marvin A.; Padama, Allan Abraham B.

    2017-02-01

    Using a combined density functional theory (DFT) and kinetic Monte Carlo (KMC) simulations, we study the adsorption at 800 K and subsequent desorption of CO on W(100) at higher temperatures. The resulting TPD profiles are known experimentally to exhibit three desorption peaks β1, β2, and β3 at 930 K, 1070 K, and 1375 K, respectively. Unlike more recent theoretical studies that propose that all three aforementioned peaks are molecularly rather than associatively desorbed, our KMC analyses are in support of the latter, since at 800 K dissociation is facile and that CO exists as dissociation fragments C and O. We show that these peaks arise from desorption from the same adsorption site but whose binding energy varies depending on local environment, that is, the presence of CO as well as dissociation fragments C and O nearby. Furthermore we show that several key parameters, such as desorption, dissociation and recombination barriers all play a key role in the TPD spectra-these parameter effectively controls not only the location of the TPD peaks but the shape and width of the desorption peaks as well. Moreover, our KMC simulations reveal that varying the heating rate shifts the peaks but leaves their shape intact.

  19. An investigative study of polymer adsorption onto montmorillonite clay

    SciTech Connect

    McConnell, C.L.; Lochhead, R.Y.

    1996-10-01

    Few studies have been geared towards the study of the mechanisms governing stabilization and flocculation of polymers and clay particles. The overall goal of this research is to relate these mechanisms to properties above and below the critical overlap concentration, c*, of the polymer/clay species. Initially, phase behavior and sedimentation studies were conducted to screen for anionic, cationic and nonionic polymers capable of both flocculation and restabilization. As a result three polymers were selected for further testing: polyacrylamide, poly(acrylamide-co-acrylic acid) and poly(acrylamide-co-diallyldimethylammonium chloride). Polyacrylamide and poly(acrylamide-co-acrylic acid) have been synthesized and characterized by viscometry and {sup 13}C NMR. C* of the polymers was determined by viscometry via Huggins` plots and dynamic light scattering measurements have shown variations in the mean particle size as a function of polymer concentration.

  20. Experimental study of albumin and lysozyme adsorption onto acrylic acid (AA) and 2-hydroxyethyl methacrylate (HEMA) surfaces.

    PubMed

    Moradi, Omid; Modarress, Hamid; Noroozi, Mehdi

    2004-03-01

    Many commercial soft contact lenses are based on poly-2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA) hydrogels. The adsorption of proteins, albumin and lysozyme, on such contact lens surfaces may cause problems in their applications. In this work the adsorption of proteins, albumin and lysozyme, on hydrogel surfaces, AA and HEMA, was investigated as a function of concentration of protein. Also the effects of pH and ionic strength of protein solution on the adsorption of protein were examined. The obtained results indicated that the degree of adsorption of protein increased with the concentration of protein, and the adsorption of albumin on HEMA surface at the studied pHs (6.2-8.6) was higher than AA surface, whereas the adsorption of lysozyme on AA surface at the same pHs was higher than HEMA. The change in ionic strength of protein solution affected the proteins adsorption on both AA and HEMA surfaces. Also, the amount of sodium ions deposited on the AA surface was much higher than HEMA surface. This effect can be related to the negative surface charge of AA and its higher tendency for adsorption of sodium ions compared to the HEMA surface.

  1. Effects of monovalent cations on the competitive adsorption of perfluoroalkyl acids by kaolinite: experimental studies and modeling.

    PubMed

    Xiao, Feng; Zhang, Xiangru; Penn, Lee; Gulliver, John S; Simcik, Matt F

    2011-12-01

    Our hypothesis that longer-chained perfluoroalkyl acids (PFAAs) outcompete shorter-chained PFAAs during adsorption was tested in this study, wherein the adsorption interactions of six frequently detected PFAAs with kaolinite clay were modeled and examined experimentally using various suspension compositions. Competitive adsorption of PFAAs on the kaolinite surface was observed for the first time, and longer-chained PFAAs outcompeted those with a shorter chain. The electrostatic repulsion between adsorbed PFAA molecules is a primary inhibitory factor in PFAA adsorption. An increase in aqueous sodium or hydrogen ion concentration weakened electrostatic repulsions and changed the adsorption free energy. Therefore, the adsorption of a shorter-chained PFAA with weaker hydrophobicity could occur at high sodium or hydrogen ion concentrations. The experimental and modeling data suggest that the adsorption of shorter-chained PFAAs (≤4 perfluorinated carbons) in freshwater with a typical ionic strength of 10(-2.5) is not thermodynamically favorable. Furthermore, by measuring the electrokinetic potential of kaolinite suspension in the presence of PFAAs, we found that the kaolinite surface became more negatively charged because of the adsorption of PFAAs. This observation indicates that the adsorbed PFAA molecules were within the electrical double layer of the kaolinite surface and that they contributed to the potential at the slipping plane. The possible alignments of adsorbed PFAA molecules on the kaolinite surface were then proposed.

  2. Studying the role of common membrane surface functionalities on adsorption and cleaning of organic foulants using QCM-D.

    PubMed

    Contreras, Alison E; Steiner, Zvi; Miao, Jing; Kasher, Roni; Li, Qilin

    2011-08-01

    Adsorption of organic foulants on nanofiltration (NF) and reverse osmosis (RO) membrane surfaces strongly affects subsequent fouling behavior by modifying the membrane surface. In this study, impact on organic foulant adsorption of specific chemistries including those in commercial thin-film composite membranes was investigated using self-assembled monolayers with seven different ending chemical functionalities (-CH(3), -O-phenyl, -NH(2), ethylene-glycol, -COOH, -CONH(2), and -OH). Adsorption and cleaning of protein (bovine serum albumin) and polysaccharide (sodium alginate) model foulants in two solution conditions were measured using quartz crystal microbalance with dissipation monitoring, and were found to strongly depend on surface functionality. Alginate adsorption correlated with surface hydrophobicity as measured by water contact angle in air; however, adsorption of BSA on hydrophilic -COOH, -NH(2), and -CONH(2) surfaces was high and dominated by hydrogen bond formation and electrostatic attraction. Adsorption of both BSA and alginate was the fastest on -COOH, and adsorption on -NH(2) and -CONH(2) was difficult to remove by surfactant cleaning. BSA adsorption kinetics was shown to be markedly faster than that of alginate, suggesting its importance in the formation of the conditioning layer. Surface modification to render -OH or ethylene-glycol functionalities are expected to reduce membrane fouling.

  3. Adsorption study for uranium in Rocky Flats groundwater

    SciTech Connect

    Laul, J.C.; Rupert, M.C.; Harris, M.J.; Duran, A.

    1995-01-01

    Six adsorbents were studied to determine their effectiveness in removing uranium in Rocky Flats groundwater. The bench column and batch (Kd) tests showed that uranium can be removed (>99.9%) by four adsorbents. Bone Charcoal (R1O22); F-1 Alumina (granular activated alumina); BIOFIX (immobilized biological agent); SOPBPLUS (mixed metal oxide); Filtrasorb 300 (granular activated carbon); and Zeolite (clinoptilolite).

  4. Optimization and adsorption kinetic studies of aqueous manganese ion removal using chitin extracted from shells of edible Philippine crabs

    NASA Astrophysics Data System (ADS)

    Quimque, Mark Tristan J.; Jimenez, Marvin C.; Acas, Meg Ina S.; Indoc, Danrelle Keth L.; Gomez, Enjelyn C.; Tabuñag, Jenny Syl D.

    2017-01-01

    Manganese is a common contaminant in drinking water along with other metal pollutants. This paper investigates the use of chitin, extracted from crab shells obtained as restaurant throwaway, as an adsorbent in removing manganese ions from aqueous medium. In particular, this aims to optimize the adsorption parameters and look into the kinetics of the process. The adsorption experiments done in this study employed the batch equilibration method. In the optimization, the following parameters were considered: pH and concentration of Mn (II) sorbate solution, particle size and dosage of adsorbent chitin, and adsorbent-adsorbate contact time. At the optimal condition, the order of the adsorption reaction was estimated using kinetic models which describes the process best. It was found out that the adsorption of aqueous Mn (II) ions onto chitin obeys the pseudo-second order model. This model assumes that the adsorption occurred via chemisorption

  5. Synthesized magnetic nanoparticles coated zeolite for the adsorption of pharmaceutical compounds from aqueous solution using batch and column studies.

    PubMed

    Salem Attia, Tamer Mohamed; Hu, Xia Lin; Yin, Da Qiang

    2013-11-01

    The contamination of fresh water with pharmaceutical and personal care products (PPCPs) has risen during the last few years. The adsorption of some PPCPs namely, Diclofenac-Na, Naproxen, Gemfibrozil and Ibuprofen from aqueous solution has been studied, magnetic nanoparticles coated zeolite (MNCZ) has been used as the adsorbent. Batch adsorption experiment was conducted to study the influences of different adsorption parameters such as contact time, solution pH and PPCPs concentrations in order to optimize the reaction conditions. The removal was favored at low pH values. Thus, as pH turns from acidic to basic conditions these compounds were less efficiently removed. The initial concentration does not appear to exert a noticeable effect on the removal efficiency of the studied PPCPs at low concentrations, but it showed less removal efficiency during high concentration of PPCPs especially for Ibuprofen. The removal of Diclofenac-Na was independent on time, while the contact time was of significant effect on the adsorption of Naproxen, Gemfibrozil and Ibuprofen even though these compounds were removed up to 95% during 10 min using MNCZ. From the isotherm adsorption study, the adsorption of PPCPs studied on MNCZ was best fitted with Freundlich isotherm equation. Pseudo-second order model providing the best fit model with the experimental data. Column adsorption study was conducted to compare the removal efficiency of MNCZ with other processes used at drinking water treatment plants (DWTPs), MNCZ showed high removal efficiency (>99%) than other used processes at DWTPs.

  6. Theoretical and experimental studies of hydrogen adsorption and desorption on Ir surfaces

    SciTech Connect

    Kaghazchi, Payam; Jacob, Timo; Chen, Wenhua; Bartynski, Robert A.

    2013-06-03

    Here, we report adsorption and desorption of hydrogen on planar Ir(210) and faceted Ir(210), consisting of nanoscale {311} and (110) facets, by means of temperature programmed desorption (TPD) and density functional theory (DFT) in combination with the ab initio atomistic thermodynamics approach. TPD spectra show that only one H2 peak is seen from planar Ir(210) at all coverages whereas a single H2 peak is observed at around 440 K (F1) at fractional monolayer (ML) coverage and an additional H2 peak appears at around 360 K (F2) at 1 ML coverage on faceted Ir(210), implying structure sensitivity in recombination and desorption of hydrogen on faceted Ir(210) versus planar Ir(210), but no evidence is found for size effects in recombination and desorption of hydrogen on faceted Ir(210) for average facet sizes of 5-14 nm. Calculations indicate that H prefers to bind at the two-fold short-bridge sites of the Ir surfaces. In addition, we studied the stability of the Ir surfaces in the presence of hydrogen at different H coverages through surface free energy plots as a function of the chemical potential, which is also converted to a temperature scale. Moreover, the calculations revealed the origin of the two TPD peaks of H2 from faceted Ir(210): F1 from desorption of H2 on {311} facets while F2 from desorption of H2 on (110) facets.

  7. Enantioselectivity of (321) chiral noble metal surfaces: A density functional theory study of lactate adsorption

    SciTech Connect

    Franke, J.-H.; Kosov, D. S.

    2013-12-14

    The adsorption of the chiral molecule lactate on the intrinsically chiral noble metal surfaces Pt(321), Au(321), and Ag(321) is studied by density functional theory calculations. We use the oPBE-vdW functional which includes van der Waals forces on an ab initio level. It is shown that the molecule binds via its carboxyl and the hydroxyl oxygen atoms to the surface. The binding energy is larger on Pt(321) and Ag(321) than on Au(321). An analysis of the contributions to the binding energy of the different molecular functional groups reveals that the deprotonated carboxyl group contributes most to the binding energy, with a much smaller contribution of the hydroxyl group. The Pt(321) surface shows considerable enantioselectivity of 0.06 eV. On Au(321) and Ag(321) it is much smaller if not vanishing. The chiral selectivity of the Pt(321) surface can be explained by two factors. First, it derives from the difference in van der Waals attraction of L- and D-lactate to the surface that we trace to differences in the binding energy of the methyl group. Second, the multi-point binding pattern for lactate on the Pt(321) surface is sterically more sensitive to surface chirality and also leads to large binding energy contributions of the hydroxyl group. We also calculate the charge transfer to the molecule and the work function to gauge changes in electronic structure of the adsorbed molecule. The work function is lowered by 0.8 eV on Pt(321) with much smaller changes on Au(321) and Ag(321)

  8. Synthesis evaluation and adsorption studies of anionic copolymeric surfactants based on fatty acrylate ester

    NASA Astrophysics Data System (ADS)

    El-Dougdoug, W. I. A.; El-Mossalamy, E. H.

    2006-12-01

    A series of anionic copolymeric surfactants based on n-dodecylacrylate ester (M 1) as hydrophobe, and oxypropylated acrylate ester (MA 4,6) as hydrophiles, were prepared by copolymerization of n-dodecylacrylate (M 1) and oxypropylated acrylate ester (MA 4,6) with molar ratio's (0.3:0.7, 0.4:0.6 and 0.5:0.5, respectively) in presence of benzoyl peroxide as initiator followed by sulfation and neutralization to afforded [(PAS 4), and (PAS 6)] a-c, as anionic copolymeric surfactant in suitable yield. These derivatives were purified and characterized by IR and 1H NMR spectral studies. Surface activity, and biodegradability were evaluated. Adsorption of some copolymeric surfactant on salary sand was investigated to assess possibility of treating waste water streams for removal of Pb 2+ and Hg 2+ toxic minerals. The effect of several factors governing the adsorption such as initial concentration, temperature, pH, have been studied.

  9. Phosphate mediated adsorption and electron transfer of cytochrome c. A time-resolved SERR spectroelectrochemical study.

    PubMed

    Capdevila, Daiana A; Marmisollé, Waldemar A; Williams, Federico J; Murgida, Daniel H

    2013-04-21

    The study of proteins immobilized on biomimetic or biocompatible electrodes represents an active field of research as it pursues both fundamental and technological interests. In this context, adsorption and redox properties of cytochrome c (Cyt) on different electrode surfaces have been extensively reported, although in some cases with contradictory results. Here we report a SERR spectroelectrochemical study of the adsorption and electron transfer behaviour of the basic protein Cyt on electrodes coated with amino-terminated monolayers. The obtained results show that inorganic phosphate (Pi) and ATP anions are able to mediate high affinity binding of the protein with preservation of the native structure and rendering an average orientation that guarantees efficient pathways for direct electron transfer. These findings aid the design of Cyt-based bioelectronic devices and understanding the modulation by Pi and ATP of physiological functions of Cyt.

  10. Computational studies of adsorption in metal organic frameworks and interaction of nanoparticles in condensed phases

    SciTech Connect

    Annapureddy, HVR; Motkuri, RK; Nguyen, PTM; Truong, TB; Thallapally, PK; McGrail, BP; Dang, LX

    2014-02-05

    In this review, we describe recent efforts to systematically study nano-structured metal organic frameworks (MOFs), also known as metal organic heat carriers, with particular emphasis on their application in heating and cooling processes. We used both molecular dynamics and grand canonical Monte Carlo simulation techniques to gain a molecular-level understanding of the adsorption mechanism of gases in these porous materials. We investigated the uptake of various gases such as refrigerants R12 and R143a. We also evaluated the effects of temperature and pressure on the uptake mechanism. Our computed results compared reasonably well with available measurements from experiments, thus validating our potential models and approaches. In addition, we investigated the structural, diffusive and adsorption properties of different hydrocarbons in Ni-2(dhtp). Finally, to elucidate the mechanism of nanoparticle dispersion in condensed phases, we studied the interactions among nanoparticles in various liquids, such as n-hexane, water and methanol.

  11. Adsorption of modified dextrins on molybdenite: AFM imaging, contact angle, and flotation studies.

    PubMed

    Beaussart, Audrey; Parkinson, Luke; Mierczynska-Vasilev, Agnieszka; Beattie, David A

    2012-02-15

    The adsorption of three dextrins (a regular wheat dextrin, Dextrin TY, carboxymethyl (CM) Dextrin, and hydroxypropyl (HP) Dextrin) on molybdenite has been investigated using adsorption isotherms, tapping mode atomic force microscopy (TMAFM), contact angle measurements, and dynamic bubble-surface collisions. In addition, the effect of the polymers on the flotation recovery of molybdenite has been determined. The isotherms revealed the importance of molecular weight in determining the adsorbed amounts of the polymers on molybdenite at plateau coverage. TMAFM revealed the morphology of the three polymers, which consisted of randomly dispersed domains with a higher area fraction of surface coverage for the substituted dextrins. The contact angle of polymer-treated molybdenite indicated that polymer layer coverage and hydration influenced the mineral surface hydrophobicity. Bubble-surface collisions indicated that the polymers affected thin film rupture and dewetting rate differently, correlating with differences in the adsorbed layer morphology. Direct correlations were found between the surface coverage of the adsorbed layers, their impact on thin film rupture time, and their impact on flotation recovery, highlighting the paramount role of the polymer morphology in the bubble/particle attachment process and subsequent flotation.

  12. A closer study of methanol adsorption and its impact on solute retentions in supercritical fluid chromatography.

    PubMed

    Glenne, Emelie; Öhlén, Kristina; Leek, Hanna; Klarqvist, Magnus; Samuelsson, Jörgen; Fornstedt, Torgny

    2016-04-15

    Surface excess adsorption isotherms of methanol on a diol silica adsorbent were measured in supercritical fluid chromatography (SFC) using a mixture of methanol and carbon dioxide as mobile phase. The tracer pulse method was used with deuterium labeled methanol as solute and the tracer peaks were detected using APCI-MS over the whole composition range from neat carbon dioxide to neat methanol. The results indicate that a monolayer (4Å) of methanol is formed on the stationary phase. Moreover, the importance of using the set or the actual methanol fractions and volumetric flows in SFC was investigated by measuring the mass flow respective pressure and by calculations of the actual volume fraction of methanol. The result revealed a significant difference between the value set and the actually delivered volumetric methanol flow rate, especially at low modifier fractions. If relying only on the set methanol fraction in the calculations, the methanol layer thickness should in this system be highly overestimated. Finally, retention times for a set of solutes were measured and related to the findings summarized above concerning methanol adsorption. A strongly non-linear relationship between the logarithms of the retention factors and the modifier fraction in the mobile phase was revealed, prior to the established monolayer. At modifier fractions above that required for establishment of the methanol monolayer, this relationship turns linear which explains why the solute retention factors are less sensitive to changes in modifier content in this region.

  13. Physico-chemical studies and CO adsorption on zeolite-encapsulated Mn II, Mn III-hydrazone complexes

    NASA Astrophysics Data System (ADS)

    Ahmed, Ayman H.

    2007-08-01

    Complexes of Mn(II) and Mn(III) with N 2O 3 hydrazone ligand derived from salicylaldehyde and benzenesulphonylhydrazide have been encapsulated in zeolite Y- supercages by a diffusion method. The synthesized new materials have been characterized by combination of elemental analysis, FT-IR, UV-vis., magnetic measurements, XRD, thermal analysis (TG, DTG and DTA), as well as surface area measurements and nitrogen adsorption studies. Investigation of the stereochemistry of these incorporated chelates pointed out that, Mn(II) complex is tetrahedral with involvement of zeolite oxygen in coordination meanwhile Mn(III) complex has octahedral configuration without contribution of the lattice oxygen. The intrazeolitic hydrazone complexes are thermally stable up to 1000 °C without decomposition. Catalytic activity towards CO adsorption for these zeolite encapsulated complexes has been investigated and compared with Mn II-Y using in situ FT-IR spectroscopy. The results revealed that, Mn II(SBSH)/Y and Mn III(SBSH)/Y give an elementary peak near 1728 cm -1 indicating a selectivity to form sbnd COOH species while Mn II-Y catalyst gives a broad band in the region of 1765-1560 cm -1 assigned to different ( sbnd COOH) and carbonates species. On the other hand, the in situ FT-IR data indicate that Mn II(SBSH)/Y and Mn III(SBSH)/Y can be used as reactive catalysts in water gas shift reaction (WGSR).

  14. An STM study of C 60 adsorption on Si(100)-(2 × 1) surfaces: from physisorption to chemisorption

    NASA Astrophysics Data System (ADS)

    Chen, Dong; Sarid, Dror

    1995-05-01

    The adsorption of C 60 molecules on Si(100)-(2 × 1) surfaces before and after annealing has been studied using scanning tunneling microscopy (STM). For room temperature deposition, the STM images reveal that the C 60 molecules adsorb predominantly at the four-dimer sites in the troughs between dimer rows. C 60 molecules bonded to two-dimer sites are also observed in small molecular clusters forming even at a low coverage. The nature of the interaction between the adsorbates and the Si(100)-(2 × 1) surface is explained in terms of a dipole-induced dipole interaction. Subsequent annealing of the samples to 600°C changes the adsorption characteristics of the C 60 molecules. First, the annealing causes a strong covalent bonding between the carbon atoms of the C 60 molecules and the silicon atoms of the substrate, and modifies the bonding sites of the adsorbates from locations in the troughs to locations on the dimer rows. Second, the annealing causes some initial surface diffusion and clustering of the C 60 molecules, which now tend to stick to the ends, rather than the sides, of the dimer rows. Furthermore, after the annealing process, it is observed that small silicon islands form on the substrate terraces along with isolated and clustered adsorbates.

  15. A fundamental study on analyte adsorption onto metallophthalocyanines

    NASA Astrophysics Data System (ADS)

    Tran, Ngoc L.

    A Web of Science search shows that the number of articles found in the literature pertaining to Phthalocyanines has doubled in the last eight years alone in comparison to all previous years. Based on the types of articles found, it is clear that the potential applications for Metal Phthalocyanines (MPcs) are multifaceted. Initially, MPcs were used as blue and green dye products. Subsequent interest in MPcs increased due to its similarities to the biologically relevant porphyrin. More recently, MPcs have been integrated into information storage systems, liquid crystal color displays and as the active material in semiconductor devices. Their diverse electronic properties, chemical and thermal robustness and ease of deposition (spin coating and organic molecular beam epitaxy) make them an attractive and economical candidate for use in chemical sensors. Although the literature contains many studies pertaining to MPcs, most are focused on the applications aspect of the material or on the fundamental understanding of the electronic properties of the Pcs in the absence of an analyte. This dissertation attempts to obtain an atomic level understanding of the fundamental mechanisms in which analytes interact with MPcs.

  16. Study of SF6 adsorption on graphite using infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Thomas, Petros; Xia, Yu; Boyd, David A.; Hopkins, Todd A.; Hess, George B.

    2009-09-01

    We report an experimental study of adsorbed monolayers of SF6 on graphite using infrared reflection absorption spectroscopy supplemented by ellipsometry. The asymmetric S-F stretch mode ν3 near 948 cm-1 in the gas is strongly blueshifted in the film by dynamic dipole coupling. This blueshift is very sensitive to the intermolecular spacing in the SF6 layer. We convert the measured frequency ν3 to a lattice spacing a, using a self-consistent field calculation, calibrated by the frequency in the commensurate phase. The resolution in lattice spacing is 0.002 Å, although there is a larger systematic uncertainty associated with nondynamic-dipole contributions to the frequency shift. We map the commensurate-incommensurate transition, a transition between two incommensurate phases, and the melting transition. These results are compared to previous x-ray data. We provide a new determination of the layer critical point (156 K), the layer condensation line down to 110 K, and the spreading pressure at saturation in this temperature range.

  17. Study of catalase adsorption on two mixed-mode ligands and the mechanism involved therein.

    PubMed

    Shiva Ranjini, S; Vijayalakshmi, M A

    2012-11-01

    Mixed-mode chromatography sorbents n-hexylamine HyperCel™ (HEA) and phenylpropylamine HyperCel™ (PPA) were evaluated for the study of adsorption of catalase from two different sources. Various parameters such as buffer composition, ionic strength and pH were investigated to study the mechanism of interaction of commercially available pre-purified catalase from Bovine liver, purified catalase from black gram (Vigna mungo) and crude extract of black gram containing catalase with these mixed-mode ligands. A simple and economical screening protocol for identifying optimal buffer conditions for adsorption and desorption of catalase was established with micro volumes of the sorbent in batch mode. With HEA HyperCel, it was observed that pre-purified catalase from both bovine liver and black gram was completely retained at pH 7.0, irrespective of the presence or absence of NaCl in the adsorption buffer, whereas the catalase from crude extract of black gram was completely retained only in the presence of 0.2 M salt in the adsorption buffer. The elution of catalase from both the sources was accomplished by lowering the pH to 4.5 in absence of salt. In case of PPA HyperCel, catalase from both the sources was very strongly adsorbed under different buffer conditions studied, and elution did not yield a significant catalase activity. From the screening experiments, it could be concluded that the interaction of catalase with HEA HyperCel could be dominated by hydrophobic forces with minor contributions from ionic interaction and with PPA HyperCel, it could be a combination of different non-covalent interactions acting on different loci on the surface of the protein.

  18. Batch soil adsorption and column transport studies of 2,4-dinitroanisole (DNAN) in soils.

    PubMed

    Arthur, Jennifer D; Mark, Noah W; Taylor, Susan; Šimunek, J; Brusseau, M L; Dontsova, Katerina M

    2017-04-01

    The explosive 2,4,6-trinitrotoluene (TNT) is currently a main ingredient in munitions; however the compound has failed to meet the new sensitivity requirements. The replacement compound being tested is 2,4-dinitroanisole (DNAN). DNAN is less sensitive to shock, high temperatures, and has good detonation characteristics. However, DNAN is more soluble than TNT, which can influence transport and fate behavior and thus bioavailability and human exposure potential. The objective of this study was to investigate the environmental fate and transport of DNAN in soil, with specific focus on sorption processes. Batch and column experiments were conducted using soils collected from military installations located across the United States. The soils were characterized for pH, electrical conductivity, specific surface area, cation exchange capacity, and organic carbon content. In the batch rate studies, change in DNAN concentration with time was evaluated using the first order equation, while adsorption isotherms were fitted using linear and Freundlich equations. Solution mass-loss rate coefficients ranged between 0.0002h(-1) and 0.0068h(-1). DNAN was strongly adsorbed by soils with linear adsorption coefficients ranging between 0.6 and 6.3Lg(-1), and Freundlich coefficients between 1.3 and 34mg(1)(-)(n)L(n)kg(-1). Both linear and Freundlich adsorption coefficients were positively correlated with the amount of organic carbon and cation exchange capacity of the soil, indicating that similar to TNT, organic matter and clay minerals may influence adsorption of DNAN. The results of the miscible-displacement column experiments confirmed the impact of sorption on retardation of DNAN during transport. It was also shown that under flow conditions DNAN transforms readily with formation of amino transformation products, 2-ANAN and 4-ANAN. The magnitudes of retardation and transformation observed in this study result in significant attenuation potential for DNAN, which would be anticipated

  19. Batch soil adsorption and column transport studies of 2,4-dinitroanisole (DNAN) in soils

    NASA Astrophysics Data System (ADS)

    Arthur, Jennifer D.; Mark, Noah W.; Taylor, Susan; Šimunek, J.; Brusseau, M. L.; Dontsova, Katerina M.

    2017-04-01

    The explosive 2,4,6-trinitrotoluene (TNT) is currently a main ingredient in munitions; however the compound has failed to meet the new sensitivity requirements. The replacement compound being tested is 2,4-dinitroanisole (DNAN). DNAN is less sensitive to shock, high temperatures, and has good detonation characteristics. However, DNAN is more soluble than TNT, which can influence transport and fate behavior and thus bioavailability and human exposure potential. The objective of this study was to investigate the environmental fate and transport of DNAN in soil, with specific focus on sorption processes. Batch and column experiments were conducted using soils collected from military installations located across the United States. The soils were characterized for pH, electrical conductivity, specific surface area, cation exchange capacity, and organic carbon content. In the batch rate studies, change in DNAN concentration with time was evaluated using the first order equation, while adsorption isotherms were fitted using linear and Freundlich equations. Solution mass-loss rate coefficients ranged between 0.0002 h- 1 and 0.0068 h- 1. DNAN was strongly adsorbed by soils with linear adsorption coefficients ranging between 0.6 and 6.3 L g- 1, and Freundlich coefficients between 1.3 and 34 mg1 - n Ln kg- 1. Both linear and Freundlich adsorption coefficients were positively correlated with the amount of organic carbon and cation exchange capacity of the soil, indicating that similar to TNT, organic matter and clay minerals may influence adsorption of DNAN. The results of the miscible-displacement column experiments confirmed the impact of sorption on retardation of DNAN during transport. It was also shown that under flow conditions DNAN transforms readily with formation of amino transformation products, 2-ANAN and 4-ANAN. The magnitudes of retardation and transformation observed in this study result in significant attenuation potential for DNAN, which would be anticipated to

  20. Interaction of Pseudomonas putida with kaolinite and montmorillonite: a combination study by equilibrium adsorption, ITC, SEM and FTIR.

    PubMed

    Rong, Xingmin; Huang, Qiaoyun; He, Xiaomin; Chen, Hao; Cai, Peng; Liang, Wei

    2008-06-15

    Equilibrium adsorption along with isothermal titration calorimetry (ITC), Fourier transform infrared spectra (FTIR) and scanning electron microscopy (SEM) techniques were employed to investigate the adsorption of Pseudomonas putida on kaolinite and montmorillonite. A higher affinity as well as larger amounts of adsorption of P. putida was found on kaolinite. The majority of sorbed bacterial cells (88.7%) could be released by water from montmorillonite, while only a small proportion (9.3%) of bacteria desorbed from kaolinite surface. More bacterial cells were observed to form aggregates with kaolinite, while fewer cells were within the larger bacteria-montmorillonite particles. The sorption of bacteria on kaolinite was enthalpically more favorable than that on montmorillonite. Based on our findings, it is proposed that the non-electrostatic forces other than electrostatic force play a more important role in bacterial adsorption by kaolinite and montmorillonite. Adsorption of bacteria on clay minerals resulted in obvious shifts of infrared absorption bands of water molecules, showing the importance of hydrogen bonding in bacteria-clay mineral adsorption. The enthalpies of -4.1+/-2.1 x 10(-8) and -2.5+/-1.4 x 10(-8)mJ cell(-1) for the adsorption of bacteria on kaolinite and montmorillonite, respectively, at 25 degrees C and pH 7.0 were firstly reported in this paper. The enthalpy of bacteria-mineral adsorption was higher than that reported previously for bacteria-biomolecule interaction but lower than that of bacterial coaggregation. The bacteria-mineral adsorption enthalpies increased at higher temperature, suggesting that the enthalpy-entropy compensation mechanism could be involved in the adsorption of P. putida on clay minerals. Data obtained in this study would provide valuable information for a better understanding of the mechanisms of mineral-microorganism interactions in soil and associated environments.

  1. Study on adsorption mechanism of proteins onto synthetic calcium hydroxyapatites through ionic concentration measurements.

    PubMed

    Kandori, K; Masunari, A; Ishikawa, T

    2005-03-01

    To clarify the adsorption mechanism of proteins onto calcium hydroxyapatite (Hap), the kinetic studies of dissolution and ion-exchange properties of synthetic Hap particles in the absence and presence of proteins were examined at 15 degrees C. In the absence of proteins, Hap particles slightly dissolved to give low amounts of calcium ([Ca(2+)] = 0.09-0.14 micromol m(-2)) and phosphate [PO(4) (3-)] = 0.01-0.08 micromol m(-2)) ions in KCl, CaCl(2), BaCl(2) and AlCl(3) solutions. The [Ca(2+)] increased with increase in the Ca/P ratio of Hap, while the [PO(4) (3-)] decreased. The[ Ca(2+)] and [ PO(4) (3-)] were independent of the ionic strength. Ba(2+) and AI(3+) ions were completely ion-exchanged with calcium ions in Hap lattice within 2 hr. The solution pH was increased by 1.1-1.8 after the dissolution of OH(-) ions on the Hap surface. In the presence of bovine serum albumin (BSA), the Hap particles dissolved slightly faster than the systems without protein. This fact was explained by a complexation of dissolved ions to functional groups of BSA. The adsorption of BSA induced a reduction of [Ca(2+)] and [ PO(4) (3-)] in the aqueous medium and minima appeared on [Ca(2+)] and [PO(4) (3-)] profiles before the BSA adsorption reached a saturation. This result suggests that the adsorption of BSA onto Hap is governed by [Ca(2+)] ions complexing to BSA molecules (binding effect) together with the operation of [Ca(2+)] ions exposing on the Hap surfaces by dissolution of OH(-) ions, so-called "C-sites". The addition of BaCl(2) and AlCl(3 )steeply increased the amounts of adsorbed BSA (n(BSA)) at the initial adsorption step by the strong binding effect of these di- and tri-valent cations between BSA and Hap. However, after eliminating these cations from the Hap surface by the ion-exchange reaction, the binding effects disappeared and n(BSA) decreased. Since the number of functional groups is small, the binding effect of the counter ions was only slightly detected for the systems

  2. [Infrared study on adsorption of O3 at SnO2 surface].

    PubMed

    Zeng, Yu-Feng; Liu, Zi-Li; Qin, Zu-Zeng; Liu, Hong-Wei

    2008-05-01

    SnO2 was prepared by precipitation method and mental oxides modified SnO2 catalysts were prepared by coprecipitation method. High concentration molasses fermentation wastewater degradation by SnO2 catalyzed ozonation was used as a probe reaction and IR spectra were used to study the adsorption of O3 at SnO2 and different metal oxides modification SnO2 surface. The results showed, that in the infrared absorption spectra of adsorption of O3 prepared by pure O2 at SnO2 catalyst surface, two obvious bidentate absorption double peaks were found at 1 027 and 1 055 cm(-1), and 2 099 and 2 122 cm(-1), respectively. However, there was competitive adsorption between O3 prepared by air, and CO and CO2. Then the O3 adsorption decreased, leading to the decrease in the degradation of molasses fermentation wastewater by SnO2 catalytic ozonation, and after 60 min reaction, the degradation rate by pure oxygen as oxygen source was 79.2%. It was 33.1% more by air as oxygen source. Similar strength adsorption peaks in the infrared spectra were found at 2 236, 2213 cm(-1) and 1 628, 1 599 cm (-1) with Fe2O3, NiO, CuO, ZnO, MgO, SrO and BaO modified SnO2. But the adsorption of CO2 and CO was different on modifier-SnO2, There was a wide absorption peak at 1 580-1 070 cm(-1) in the infrared spectra of transition metal modified SnO2, and two new peaks at 1 298 and 1 274 cm(-1) were found between 1 580 and 1 070 cm(-1) in the infrared spectra of alkaline-earth metals modified SnO2 catalysts. These changes leaded to a different catalytic ozonation activity of modifier-SnO2, the results of molasses fermentation wastewater degradation by ozone combined with alkaline-earth metal modified SnO2 was obviously better than ozone combined with transition metal modified SnO2. And among them, the ozonation catalytic activity of BaO-SnO2 was the best.

  3. In Situ Infrared Ellipsometry for Protein Adsorption Studies on Ultrathin Smart Polymer Brushes in Aqueous Environment

    SciTech Connect

    Kroning, Annika; Furchner, Andreas; Aulich, Dennis; Bittrich, Eva; Rauch, Sebastian; Uhlmann, Petra; Eichhorn, Klaus-Jochen; Seeber, Michael; Luzinov, Igor; Kilbey, S. Michael; Lokitz, Bradley S.; Minko, Sergiy; Hinrichs, Karsten

    2015-02-10

    The protein-adsorbing and -repelling properties of various smart nanometer-thin polymer brushes with high potential for biosensing and biomedical applications are studied by in-situ infrared-spectroscopic ellipsometry (IRSE). IRSE as a highly sensitive non-destructive technique allows us to investigate protein adsorption on polymer brushes in aqueous environment in dependence of external stimuli like temperature and pH. These stimuli are, for instance, relevant in switchable mixed brushes containing poly(N-isopropyl acrylamide) and poly(acrylic acid), respectively. We use such brushes as model surfaces for controlling protein adsorption of human serum albumin and human fibrinogen. IRSE can distinguish between polymer-specific vibrational bands, which yield insights into the hydration state of the brushes, and changes in the protein-specific amide bands, which are related to changes of the protein secondary structure.

  4. In Situ Infrared Ellipsometry for Protein Adsorption Studies on Ultrathin Smart Polymer Brushes in Aqueous Environment

    DOE PAGES

    Kroning, Annika; Furchner, Andreas; Aulich, Dennis; ...

    2015-02-10

    The protein-adsorbing and -repelling properties of various smart nanometer-thin polymer brushes with high potential for biosensing and biomedical applications are studied by in-situ infrared-spectroscopic ellipsometry (IRSE). IRSE as a highly sensitive non-destructive technique allows us to investigate protein adsorption on polymer brushes in aqueous environment in dependence of external stimuli like temperature and pH. These stimuli are, for instance, relevant in switchable mixed brushes containing poly(N-isopropyl acrylamide) and poly(acrylic acid), respectively. We use such brushes as model surfaces for controlling protein adsorption of human serum albumin and human fibrinogen. IRSE can distinguish between polymer-specific vibrational bands, which yield insights intomore » the hydration state of the brushes, and changes in the protein-specific amide bands, which are related to changes of the protein secondary structure.« less

  5. 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.

  6. Hydrogen adsorption on Ru(001) studied by Scanning TunnelingMicroscopy

    SciTech Connect

    Tatarkhanov, Mous; Rose, Franck; Fomin, Evgeny; Ogletree, D.Frank; Salmeron, Miquel

    2008-01-18

    The adsorption of hydrogen on Ru(001) was studied by scanning tunneling microscopy at temperatures around 50 K. Hydrogen was found to adsorb dissociatively forming different ordered structures as a function of coverage. In order of increasing coverage {theta} in monolayers (ML) these were ({radical}3 x {radical}3)r30{sup o} at {theta} = 0.3 ML; (2 x 1) at {theta} = 0.50 ML, (2 x 2)-3H at {theta} = 0.75, and (1 x 1) at {theta} = 1.00. Some of these structures were observed to coexist at intermediate coverage values. Close to saturation of 1 ML, H-vacancies (unoccupied three fold fcc hollow Ru sites) were observed either as single entities or forming transient aggregations. These vacancies diffuse and aggregate to form active sites for the dissociative adsorption of hydrogen.

  7. Immobilization of tryptophan hydroxylase by immune adsorption: a method to study regulation of catalytic activity.

    PubMed

    Johansen, P A; Jennings, I; Cotton, R G; Kuhn, D M

    1992-12-01

    Tryptophan hydroxylase (TPH) can be immobilized by adsorption to Pansorbin after binding to the monoclonal antibody PH8. This method yields recoveries of 35%-40% of total TPH activity in crude extracts and can be completed in 1.5 h. The immobilized form of TPH retains the essential kinetic properties of the native enzyme and responds to activators (phosphatidylserine) and inhibitors (catechol compounds) as does the native enzyme. Unlike TPH in brain extracts, immobilized TPH is not activated by calcium-stimulated phosphorylating conditions. When extracts from which TPH has been precipitated, and which contain calcium-calmodulin dependent protein kinase are added to immobilized TPH, the activation of TPH is restored. This method of immobilization of TPH via immune-adsorption allows for the highly specific and rapid preparation of affinity purified TPH that can be used to study the regulation of this enzyme by a variety of effectors, especially protein kinases.

  8. Adsorption of methylene blue onto jute fiber carbon: kinetics and equilibrium studies.

    PubMed

    Senthilkumaar, S; Varadarajan, P R; Porkodi, K; Subbhuraam, C V

    2005-04-01

    Jute fiber obtained from the stem of a plant was used to prepare activated carbon using phosphoric acid. Feasibility of employing this jute fiber activated carbon (JFC) for the removal of Methylene blue (MB) from aqueous solution was investigated. The adsorption of MB on JFC has found to dependent on contact time, MB concentration and pH. Experimental result follows Langmuir isotherm model and the capacity was found to be 225.64 mg/g. The optimum pH for the MB removal was found to be 5-10. The kinetic data obtained at different concentrations have been analyzed using a pseudo-first-order, pseudo-second-order equation, intraparticle diffusion and Elovich equation. Among the kinetic models studied, the intraparticle diffusion was the best applicable model to describe the adsorption of MB onto JFC.

  9. Experimental studies of the streaming flow due to the adsorption of particles at a liquid surface

    NASA Astrophysics Data System (ADS)

    Singh, Pushpendra; Musunuri, Naga; Fischer, Ian

    2016-11-01

    The particle image velocimetry (PIV) technique is used to study the streaming flow that is induced when particles are adsorbed at a liquid surface. The flow develops within a fraction of second after the adsorption of the particle and persists for several seconds. The fluid directly below the particle rises upward, and near the surface, it moves away from the particle. The flow causes powders sprinkled on a liquid surface to disperse on the surface. The flow strength, and the volume over which it extends, decreases with decreasing particle size. The streaming flow induced by the adsorption of two or more particles is a combination of the flows which they induce individually. The work was supported by National Science Foundation.

  10. Study of the behaviour of thorium adsorption on PAN/zeolite composite adsorbent.

    PubMed

    Kaygun, A Kilincarslan; Akyil, S

    2007-08-17

    The adsorption behaviour of thorium from aqueous solutions by a composite adsorbent has been investigated by a batch technique. The thorium adsorption on composite adsorbent was studied as a function of initial concentration, pH, shaking time and temperature. The sorption of thorium at the determined optimum conditions follows Langmuir, Freundlich and D-R type isotherms. Langmuir constants Q=0.04 mmol g(-1) and b=64.94 L mol(-1) and of D-R parameter Xm = 0.04, beta=0.79 and of sorption energy E=0.80 and Freundlich constants 1/n=3.12 and cm = 0.012 mmol g(-1) were evaluated. Thermodynamic parameters such as DeltaH and DeltaS were found to be 37.32 kJ mol(-1) and 206.17 J mol(-1)K(-1), respectively.

  11. A study of the adsorption of NH 3 and SO 2 on leaf surfaces

    NASA Astrophysics Data System (ADS)

    Van Hove, L. W. A.; Adema, E. H.; Vredenberg, W. J.; Pieters, G. A.

    The adsorption of NH 3 and SO 2 on the external leaf surface of bean ( Phaseolus vulgaris L.) and poplar ( Populus euramericana L.) was studied. The adsorbed quantities increased strongly with increasing air humidity, indicating that water on the leaf surface plays a major role in the interaction of these gases with the leaf surface. On the other hand temperature in the range between 15 and 26°C had no significant influence. The adsorbed quantities of NH 3 at a specific air humidity appeared to be proportional to NH 3 concentration. This proportionality was less clear for SO 2. The affinity of SO 2 for the leaf surface was found to be approximately twice that of NH 3. A mixture of these gases in the air mutually stimulated their adsorption on the leaf. No significant desorption or uptake of these gases through the cuticle could be detected, indicating that the bulk of the adsorbed gases remains associated with the cuticle.

  12. Quantum Chemical Study of Water Adsorption on the Surfaces of SrTiO3 Nanotubes.

    PubMed

    Bandura, Andrei V; Kuruch, Dmitry D; Evarestov, Robert A

    2015-07-20

    We have studied the adsorption of water molecules on the inner and outer surfaces of nanotubes generated by rolling (001) layers of SrTiO3 cubic crystals. The stability and the atomic and electronic structures of the adsorbed layers are determined by using hybrid density functional theory. The absorption energy and the preferred adsorbate structure are essentially governed by the nature of the surface of the nanotube. Dissociative adsorption prevails on the outer nanotube surfaces. The stability of the adsorbed layers on the inner surfaces is related to the possibility of the formation of hydrogen bonds between water molecules and surface oxygen atoms, and depends on the surface curvature. The presence of water molecules on the inner surface of the nanotubes leads to an increase of the electronic band gap. Externally TiO2 -terminated nanotubes could be used for the photocatalytic decomposition of water by ultraviolet radiation.

  13. Adsorption and wettability study of methyl ester sulphonate on precipitated asphaltene

    NASA Astrophysics Data System (ADS)

    Okafor, H. E.; Sukirman, Y.; Gholami, R.

    2016-03-01

    Asphaltene precipitation from crude oil and its subsequent aggregation forms solid, which preferentially deposit on rock surfaces causing formation damage and wettability changes leading to loss of crude oil production. To resolve this problem, asphaltene inhibitor has been injected into the formation to prevent the precipitation of asphaltene. Asphaltene inhibitors that are usually employed are generally toxic and non-biodegradable. This paper presents a new environmentally friendly asphaltene inhibitor (methyl ester sulphonate), an anionic surfactant, which has excellent sorption on formation rock surfaces. Result from adsorption study validated by Langmuir and Freundlich models indicate a favourable adsorption. At low volumes injected, methyl ester sulphonate is capable of reverting oil-wet sandstone surface to water-wet surface. Biodegradability test profile shows that for concentrations of 100-5000ppm it is biodegradable by 65-80%.

  14. Adsorption of Ar on planar surfaces studied with a density functional theory

    NASA Astrophysics Data System (ADS)

    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≥Tt was obtained. A comparison with experimental data and other microscopic calculations is reported.

  15. Adsorption studies on wastewaters from cypermethrin manufacturing process using activated coconut shell carbon.

    PubMed

    Bhuvaneswari, K; Ravi Prasad, P; Sarma, P N

    2007-10-01

    Cypermethrin is a pyrethroid pesticide and is used in the control of a wide range of insects on crops like vegetables, cereals, maize etc. In the present study, the adsorption efficiency of coconut shell based activated carbon for the removal of color and organic matter from cypermethrin pesticide manufacturing industrial wastewater was investigated. Effect of carbon dosage, pH and contact time on the removal of COD was also studied. Equilibrium and kinetic studies were carried out and the data was fitted in Freundlich and Langmuir models. The study proved that activated coconut shell carbon (acc) is an efficient adsorbent for treatment of cypermethrin industrial wastewaters under study.

  16. Treatment of cyanide effluents by oxidation and adsorption in batch and column studies.

    PubMed

    Yazici, E Y; Deveci, H; Alp, I

    2009-07-30

    In this study the removal of free cyanide from aqueous solutions by air oxidation and adsorption was investigated. Effects of air and pure oxygen, and catalyst on the rate and extent of the removal of cyanide were studied. It was found that the oxidative removal of cyanide by air/oxygen was very limited although it tended to improve in the presence of pure oxygen and catalyst such as activated carbon (AC) and copper sulphate. In the presence of continuous aeration, the non-oxidative removal of cyanide was correlated with a decrease in pH effected apparently by the transfer of carbon dioxide from air phase into the medium. The removal of cyanide by adsorption on activated carbon, nut shell (NS) and rice husk (RH) was also examined. Adsorption capacity of activated carbon was shown to be significantly enhanced via impregnation of activated carbons with metals such as copper (AC-Cu) and silver (AC-Ag). In the column tests, the breakthrough capacity of adsorbents was found to be in an increasing order of RH

  17. Study of adsorption mechanism of heavy metals onto waste biomass (wheat bran).

    PubMed

    Ogata, Fumihiko; Kangawa, Moe; Tominaga, Hisato; Tanaka, Yuko; Ueda, Ayaka; Iwata, Yuka; Kawasaki, Naohito

    2013-01-01

    In this study, raw wheat bran (R-WB), a type of waste biomass (WB) was treated with Pectinase PL (P-WB), and the properties (yield percentage, carboxy group surface concentration, the solution pH, and specific surface area) of R-WB and P-WB were investigated. The surface concentration of carboxy groups on R-WB (3.56 mmol/g) was greater than that of P-WB (2.11 mmol/g). In contrast, the specific surface area of P-WB (24.98 m²/g) was greater than that of R-WB (3.25 m²/g). In addition, the adsorption of cadmium and lead ions to WB was evaluated. Adsorption of the heavy-metal ions reached equilibrium within 9 h, and the experimental data was fitted to a pseudo-second-order model. More heavy-metal ions were adsorbed onto R-WB than onto P-WB. The correlation coefficient between the amount of ions adsorbed and the number of carboxy groups or pectin exceeded 0.884 and 0.975, respectively. This study indicated that wheat bran was useful for the removal of cadmium or lead ions from aqueous solutions. The adsorption mechanism of cadmium and lead ions to WB was associated with presence of carboxy group in pectin.

  18. Adsorption kinetics and equilibrium studies for removal of acid azo dyes by aniline formaldehyde condensate

    NASA Astrophysics Data System (ADS)

    Terangpi, Praisy; Chakraborty, Saswati

    2016-12-01

    Adsorption of two acid dyes named Acid orange 8 (AO8) and Acid violet 7 (AV7) by amine based polymer aniline formaldehyde condensate (AFC) was studied. Adsorption of both dyes was favored at acidic pH. Electrostatic attraction between protonated amine group (NH3 +) of AFC and anionic sulfonate group (SO3 -) of dye molecule along with hydrogen bond formation and interaction between aromatic group of dye and AFC were responsible mechanisms for dye uptake. Isotherm of AO8 was Type I and followed Langmuir isotherm model. AV7 isotherm on AFC was of Type III and followed Freundlich model. Kinetics study showed that external mass transfer was the rate limiting step followed by intraparticle diffusion. Maximum adsorption capacities of AO8 and AV7 were observed as 164 and 68 mg/g. AO8 dye being smaller in molecular size was adsorbed more due to higher diffusion rate and higher dye: AFC ratio, which enhanced the interaction between dye and polymer.

  19. Adsorption of binary hydrocarbon mixtures in carbon slit pores: A density functional theory study

    SciTech Connect

    Bhatia, S.K.

    1998-10-13

    Adsorption of binary hydrocarbons mixtures involving methane in carbon slit pores is theoretically studied here from the viewpoints of separation and of the effect of impurities on methane storage. It is seen that even small amounts of ethane, propane, or butane can significantly reduce the methane capacity of carbons. Optimal pore sizes and pressures, depending on impurity concentration, are noted in the present work, suggesting that careful adsorbent and process design can lead to enhanced separation. These results are consistent with earlier literature studies for the infinite dilution limit. For methane storage applications a carbon micropore width of 11.4 {angstrom} (based on distance between centers of carbon atoms on opposing walls) is found to be the most suitable from the point of view of lower impurity uptake during high-pressure adsorption and greater impurity retention during low-pressure delivery. The results also theoretically confirm unusual recently reported observations of enhanced methane adsorption in the presence of a small amount of heavier hydrocarbon impurity.

  20. A GCMC simulation and experimental study of krypton adsorption/desorption hysteresis on a graphite surface.

    PubMed

    Prasetyo, Luisa; Horikawa, Toshihide; Phadungbut, Poomiwat; Johnathan Tan, Shiliang; Do, D D; Nicholson, D

    2016-09-15

    Adsorption isotherms and isosteric heats of krypton on a highly graphitized carbon black, Carbopack F, have been studied with a combination of Monte Carlo simulation and high-resolution experiments at 77K and 87K. Our investigation sheds light on the microscopic origin of the experimentally observed, horizontal hysteresis loop in the first layer, and the vertical hysteresis-loop in the second layer, and is found to be in agreement with our recent Monte Carlo simulation study (Diao et al., 2015). From detailed analysis of the adsorption isotherm, the latter is attributed to the compression of an imperfect solid-like state in the first layer, to form a hexagonally packed, solid-like state, immediately following the first order condensation of the second layer. To ensure that capillary condensation in the confined spaces between microcrystallites of Carbopack F does not interfere with these hysteresis loops, we carried out simulations of krypton adsorption in the confined space of a wedge-shaped pore that mimics the interstices between particles. These simulations show that, up to the third layer, any such interference is negligible.

  1. Studies on the batch adsorption of plasmid DNA onto anion-exchange chromatographic supports.

    PubMed

    Ferreira, G N; Cabral, J M; Prazeres, D M

    2000-01-01

    The adsorption of a supercoiled 4.8 kbp plasmid onto quaternary ammonium anion-exchangers was studied in a finite bath. Equilibrium experiments were performed with pure plasmid, at 25 degrees C, using commercial Q-Sepharose matrices differing in particle diameter (High Performance, 34 microm; Fast Flow, 90 microm; and Big Beads, 200 microm) and a recently commercialized ion-exchanger, Streamline QXL (d(p) = 200 microm) at different salt concentrations (0.5, 0.7, and 1 M NaCl). Plasmid adsorption was found to follow second-order kinetics (Langmuir isotherm) with average association constants K(A) = 0.32+/-0.12 mL microg(-)(1) and K(A) = 0.25+/-0.15 mL microg(-1) at 0.5 and 0.7 M Nacl, respectively. The maximum binding capacities were not dependent on the ionic strength in the range 0.5-0.7 M but decreased with increasing particle diameter, suggesting that adsorption mainly occurs at the surface of the particles. No adsorption was found at 1 M NaCl. A nonporous model was applied to describe the uptake rate of plasmid onto Streamline QXL at 0.5 M NaCl. The overall process rate was controlled by mass transfer in the regions of low relative amounts of adsorbent (initial stages) and kinetically controlled in the later stages of the process for high relative amounts of adsorbent. The forward reaction rate constant (k(1) = 0.09+/-0.01 mL mg(-1) s(-1)) and film mass transfer coefficient (K(f) = (6 +/- 2) x 10(-4) cm s(-1)) were calculated. Simulations were performed to study the effect of the relative amount of adsorbent on the overall process rate, yield, and media capacity utilization.

  2. Activated carbon adsorptive removal of azo dye and peroxydisulfate regeneration: from a batch study to continuous column operation.

    PubMed

    Li, Jing; Du, Yue; Deng, Bin; Zhu, Kangmeng; Zhang, Hui

    2016-12-17

    The performance of activated carbon (AC) for the adsorption of Acid Orange 7 (AO7) was investigated in both batch and column studies. The optimal conditions for adsorption process in batch study were found to be a stirring speed of 500 rpm, AC dosage of 5 g/L, and initial AO7 concentration of 100 mg/L. The spent AC was then treated with peroxydisulfate (PDS), and the regenerated AC was used again to adsorb AO7. Both pseudo-first-order and pseudo-second-order rate models for adsorption kinetics were investigated, and the results showed that the latter model was more appropriate. The effects of regeneration time, PDS concentration, and stirring speed on AO7-spent AC regeneration were investigated in batch studies, and the optimal conditions were time 2 h, stirring speed 700 rpm, and PDS concentration 10 g/L. Under the same adsorption conditions, 89% AO7 could be decolorized by adsorption using regenerated AC. In the column studies, the effect of flow rate was investigated and the adsorption capacity was nearly the same when the flow rate rose from 7.9 to 11.4 mL/min, but it decreased significantly when the flow rate was increased to 15.2 mL/min. The performance of regenerated AC in the column was also investigated, and a slight increase in the adsorption capacity was observed in the second adsorption cycle. However, the adsorption capacity decreased to some extent in the third cycle due to the consumption of C-OH group on the AC surface during PDS regeneration.

  3. Development of sustainable dye adsorption system using Nutraceutical Industrial Fennel Seed Spent - Studies with Congo Red dye.

    PubMed

    Taqui, Syed Noeman; Yahya, Rosiyah; Hassan, Aziz; Nayak, Nayan; Syed, Akheel Ahmed

    2017-01-25

    Fennel seed spent (FSS) - an inexpensive nutraceutical industrial spent has been used as an efficient biosorbent for the removal of Congo Red (CR) from aqueous media. Results show that pH of 2 - 4 and temperature of 30°C was ideal for maximum adsorption. Based on regression fitting of the data it was determined that the SIPS isotherm (R(2) = 0.994, χ(2) = 0.5) adequately described the mechanism of adsorption, suggesting that the adsorption occurs in a homogeneous layer by layer with favourable interaction between layers. Thermodynamic analysis showed that the adsorption is favourable (negative values for ΔG°) and endothermic (ΔH° = 12-20 kJ mol(-1)) for an initial dye concentration of 25, 50 and 100 ppm. The low ΔH° value indicates that the adsorption is a physical process involving weak chemical interactions like hydrogen bonds and van der Waals interactions. The kinetics revealed that the adsorption process showed pseudo second order tendencies with the equal influence of intra-particle as well as film diffusion. The SEM images of FSS show a highly fibrous matrix with a hierarchical porous structure. The FTIR analysis of the spent confirmed the presence of cellulosic and ligno-cellulosic matter giving it both hydrophilic and hydrophobic properties. The investigations indicate that FSS is a cost-effective and efficient biosorbent for the remediation of toxic Congo Red dye.

  4. Theoretical study of the adsorption of 3d- and 4d-metals on a WC(0001) surface

    SciTech Connect

    Bakulin, A. V.; Kulkova, S. E.

    2013-08-15

    The interaction of 3d- and 4d-metals with a WC(0001) surface has been studied theoretically by density-functional theory methods depending on surface termination and adsorbate position. The most stable sites of metal adsorption on the surface have been determined. The binding energy of d-metals with the surface is shown to be higher in the case of carbon terminated surface. This is explained by the predominant ionic-covalent contribution to the chemical bond at the interface, with the bond ionicity being determined by charge transfer from the metals to the electronegative carbon. Analysis of the electronic and structural characteristics has revealed the factors affecting the bonding energetics at the metal-carbide interface depending on the metal d-shell filling with electrons.

  5. Enhancement of the adsorption capacity of the light-weight expanded clay aggregate surface for the metronidazole antibiotic by coating with MgO nanoparticles: Studies on the kinetic, isotherm, and effects of environmental parameters.

    PubMed

    Kalhori, Ebrahim Mohammadi; Al-Musawi, Tariq J; Ghahramani, Esmaeil; Kazemian, Hossein; Zarrabi, Mansur

    2017-02-09

    The synthesized MgO nanoparticles were used to coat the light-weight expanded clay aggregates (LECA) and as a metronidazole (MNZ) adsorbent. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier-transformed infrared (FTIR) techniques were employed to study the surface morphology and characteristics of the adsorbents. MgO/LECA clearly revealed the advantages of the nanocomposite particles, showing high specific surface area (76.12 m(2)/g), significant adsorption sites and functional groups. Between pH 5 and 9, the MNZ sorption was not significantly affected. Kinetic studies revealed that the MNZ adsorption closely followed the Avrami model, with no dominant process controlling the sorption rate. The study of the effects of foreign ions revealed that the addition of carbonate raised the MNZ removal efficiency of LECA by 8% and the total removal of MNZ by MgO/LECA. Furthermore, nitrate and hardness only marginally influenced the MNZ removal efficiency and their effects can be ranked in the order of carbonate>nitrate>hardness. The isotherm adsorption of MNZ was best fitted with the Langmuir model enlighten the monolayer MNZ adsorption on the homogeneous LECA and MgO/LECA surfaces. The maximum adsorption capacity under optimum conditions was enhanced from 56.31 to 84.55 mg/g for LECA and MgO/LECA, respectively. These findings demonstrated that the MgO/LECA nanocomposite showed potential as an efficient adsorbent for MNZ removal.

  6. Adsorption of oxygen on W/100/ - Adsorption kinetics and structure

    NASA Technical Reports Server (NTRS)

    Bauer, E.; Poppa, H.; Viswanath, Y.

    1976-01-01

    The adsorption of oxygen on W(100) single-crystal surfaces is studied by Auger electron spectroscopy (AES), flash desorption, low-energy electron diffraction (LEED), and retarding-field work-function measurements. The AES results reveal stepwise changes in the sticking coefficients in the coverage range 0 to 1 and activated adsorption at higher coverages. Upon room-temperature adsorption, a series of complex LEED patterns is observed. In layers adsorbed at 1050 K and cooled to room temperature, the p(2 x 1) structure is the first ordered structure observed. This structure shows a reversible order-disorder transition between 700 and 1000 K and is characterized by a work function which is lower than that of the clean surface. Heating room-temperature adsorbates changes their structure irreversibly. At temperatures below 750 K, some new structures are observed.

  7. Adsorption mechanism of an antimicrobial peptide on carbonaceous surfaces: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Roccatano, Danilo; Sarukhanyan, Edita; Zangi, Ronen

    2017-02-01

    Peptides are versatile molecules with applications spanning from biotechnology to nanomedicine. They exhibit a good capability to unbundle carbon nanotubes (CNT) by improving their solubility in water. Furthermore, they are a powerful drug delivery system since they can easily be uptaken by living cells, and their high surface-to-volume ratio facilitates the adsorption of molecules of different natures. Therefore, understanding the interaction mechanism between peptides and CNT is important for designing novel therapeutical agents. In this paper, the mechanisms of the adsorption of antimicrobial peptide Cecropin A-Magainin 2 (CA-MA) on a graphene nanosheet (GNS) and on an ultra-short single-walled CNT are characterized using molecular dynamics simulations. The results show that the peptide coats both GNS and CNT surfaces through preferential contacts with aromatic side chains. The peptide packs compactly on the carbon surfaces where the polar and functionalizable Lys side chains protrude into the bulk solvent. It is shown that the adsorption is strongly correlated to the loss of the peptide helical structure. In the case of the CNT, the outer surface is significantly more accessible for adsorption. Nevertheless when the outer surface is already covered by other peptides, a spontaneous diffusion, via the amidated C-terminus into the interior of the CNT, was observed within 150 ns of simulation time. We found that this spontaneous insertion into the CNT interior can be controlled by the polarity of the entrance rim. For the positively charged CA-MA peptide studied, hydrogenated and fluorinated rims, respectively, hinder and promote the insertion.

  8. Adsorption mechanism of an antimicrobial peptide on carbonaceous surfaces: A molecular dynamics study.

    PubMed

    Roccatano, Danilo; Sarukhanyan, Edita; Zangi, Ronen

    2017-02-21

    Peptides are versatile molecules with applications spanning from biotechnology to nanomedicine. They exhibit a good capability to unbundle carbon nanotubes (CNT) by improving their solubility in water. Furthermore, they are a powerful drug delivery system since they can easily be uptaken by living cells, and their high surface-to-volume ratio facilitates the adsorption of molecules of different natures. Therefore, understanding the interaction mechanism between peptides and CNT is important for designing novel therapeutical agents. In this paper, the mechanisms of the adsorption of antimicrobial peptide Cecropin A-Magainin 2 (CA-MA) on a graphene nanosheet (GNS) and on an ultra-short single-walled CNT are characterized using molecular dynamics simulations. The results show that the peptide coats both GNS and CNT surfaces through preferential contacts with aromatic side chains. The peptide packs compactly on the carbon surfaces where the polar and functionalizable Lys side chains protrude into the bulk solvent. It is shown that the adsorption is strongly correlated to the loss of the peptide helical structure. In the case of the CNT, the outer surface is significantly more accessible for adsorption. Nevertheless when the outer surface is already covered by other peptides, a spontaneous diffusion, via the amidated C-terminus into the interior of the CNT, was observed within 150 ns of simulation time. We found that this spontaneous insertion into the CNT interior can be controlled by the polarity of the entrance rim. For the positively charged CA-MA peptide studied, hydrogenated and fluorinated rims, respectively, hinder and promote the insertion.

  9. Recombinant albumin adsorption on mica studied by AFM and streaming potential measurements.

    PubMed

    Kujda, Marta; Adamczyk, Zbigniew; Morga, Maria; Sofińska, Kamila

    2015-03-01

    Recombinant human serum albumin (rHSA) in monomeric state is widely used in pharmaceutical industry as a drug excipient and for preparing coatings for medical devices. In this work the adsorption process of rHSA on model mica surface at pH 3.5 was studied using the atomic force microscopy (AFM) and in situ streaming potential measurements. The kinetics of albumin adsorption was determined by a direct enumeration of single molecules over various substrate areas. These results were consistent with streaming potential measurements carried out for the parallel-plate channel flow and with theoretical predictions derived from the random sequential adsorption (RSA) model. Desorption kinetics of albumin under flow conditions was also evaluated via the streaming potential measurements. In this way, the amount of irreversibly bound albumin was quantitatively evaluated to be 0.64 and 1.2 mg m(-2) for ionic strength of 0.01 and 0.15 M, respectively. This agrees with previous results obtained for HSA and theoretical calculations derived from the RSA model. Additionally, it was demonstrated that there existed a fraction of reversibly bound albumin that can be fully eluted within a few hours. The binding energy of these fraction of molecules was -18 kT that is consistent with the electrostatic controlled adsorption mechanism of albumin at this pH. It was concluded that the rHSA monolayers of well-defined coverage can find applications for quantitatively analyzing ligand binding and for performing efficient biomaterials and immunological tests.

  10. Adsorption of Phenol from Aqueous Solution Using Lantana camara, Forest Waste: Kinetics, Isotherm, and Thermodynamic Studies

    PubMed Central

    Girish, C. R.; Ramachandra Murty, V.

    2014-01-01

    The present work investigates the potential of Lantana camara, a forest waste, as an adsorbent for the phenol reduction in wastewater. Batch studies were conducted with adsorbent treated with HCl and KOH to determine the influence of various experimental parameters such as pH, contact time, adsorbent dosage, and phenol concentration. The experimental conditions were optimized for the removal of phenol from wastewater. Equilibrium isotherms for the adsorption of phenol were analyzed by Freundlich, Langmuir, Temkin, and Dubinin-Radushkevich isotherm models. Thermodynamic parameters like the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were also determined and they showed that the adsorption process was feasible, spontaneous, and exothermic in the temperature range of 298–328 K. The kinetic data were fitted with pseudo-second-order model. The equilibrium data that followed Langmuir model with the monolayer adsorption capacity was found to be 112.5 mg/g and 91.07 mg/g for adsorbent treated with HCl and KOH, respectively, for the concentration of phenol ranging from 25 to 250 mg/L. This indicates that the Lantana camara was a promising adsorbent for the removal of phenol from aqueous solutions. PMID:27350997

  11. Adsorption of Phenol from Aqueous Solution Using Lantana camara, Forest Waste: Kinetics, Isotherm, and Thermodynamic Studies.

    PubMed

    Girish, C R; Ramachandra Murty, V

    2014-01-01

    The present work investigates the potential of Lantana camara, a forest waste, as an adsorbent for the phenol reduction in wastewater. Batch studies were conducted with adsorbent treated with HCl and KOH to determine the influence of various experimental parameters such as pH, contact time, adsorbent dosage, and phenol concentration. The experimental conditions were optimized for the removal of phenol from wastewater. Equilibrium isotherms for the adsorption of phenol were analyzed by Freundlich, Langmuir, Temkin, and Dubinin-Radushkevich isotherm models. Thermodynamic parameters like the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were also determined and they showed that the adsorption process was feasible, spontaneous, and exothermic in the temperature range of 298-328 K. The kinetic data were fitted with pseudo-second-order model. The equilibrium data that followed Langmuir model with the monolayer adsorption capacity was found to be 112.5 mg/g and 91.07 mg/g for adsorbent treated with HCl and KOH, respectively, for the concentration of phenol ranging from 25 to 250 mg/L. This indicates that the Lantana camara was a promising adsorbent for the removal of phenol from aqueous solutions.

  12. Adsorption of cationic polyacrylamide at the cellulose-liquid interface: a neutron reflectometry study.

    PubMed

    Su, Jielong; Garvey, Christopher J; Holt, Stephen; Tabor, Rico F; Winther-Jensen, Bjorn; Batchelor, Warren; Garnier, Gil

    2015-06-15

    The layer thickness and density of high molecular weight cationic polyacrylamide (CPAM) adsorbed at the cellulose-water interface was quantified by neutron reflectometry. The thickness of a full monolayer of CPAM of constant molecular weight (13 MD) but different charge densities, adsorbed with or without NaCl (10(-3) M), was studied. Thin cellulose films (40±7 Å) of roughness <10 Å were produced by spin coating a cellulose acetate-acetone solution and regenerating by alkaline hydrolysis. Film smoothness was greatly improved by controlling the concentration of cellulose acetate (0.13 wt%) and the hydrolysis time in sodium methoxide. The adsorption thickness of CPAM (40% charge 13 MD) at the solid-D2O interface was 43±4 Å on cellulose and 13±2 Å on silicon, an order of magnitude smaller than the CPAM radius of gyration. At constant molecular weight, the thickness of the CPAM layer adsorbed on cellulose increases with polymer charge density (10±1 Å at 5%). Addition of 10(-3) M NaCl decreased the thickness of CPAM layer already adsorbed on cellulose. However, the adsorption layer on cellulose of a CPAM solution equilibrated in 10(-3) M NaCl is much thicker (89±11 Å for 40% CPAM). For high molecular weight CPAMs adsorbed from solution under constant conditions, the adsorption layer can be varied by 1 order of magnitude via control of the variables affecting electrostatic intra- and inter-polymer chain interactions.

  13. Adsorption of alkenes on acidic zeolites. Theoretical study based on the electron charge density.

    PubMed

    Zalazar, M Fernanda; Duarte, Darío J R; Peruchena, Nélida M

    2009-12-10

    In the present work, experiments on electron density changes in the adsorption process of alkenes on acidic zeolites, in the framework of atoms in molecules theory (AIM), were carried out. Electron densities were obtained at MP2 and B3LYP levels using a 6-31++G(d,p) basis set. This study explores the energetic and the electron density redistributions associated with O-H...pi interactions. The main purpose of this work is to provide an answer to the following questions: (a) Which and how large are the changes induced on the molecular electron distribution by the formation of adsorbed alkenes? (b) Can a reasonable estimate of the adsorption energy of alkenes on the active site of zeolite be solely calculated from an analysis of the electron densities? We have used topological parameters to determine the strength and nature of the interactions in the active site of the zeolite. All the results derived from the electron density analysis show that the stabilization of the adsorbed alkenes follows the order isobutene > trans-2-butene congruent with 1-butene congruent with propene > ethene, reflecting the order of basicity of C=C bonds, i.e., (C(ter)=C(prim)) > (C(sec)=C(sec)) congruent with (C(prim)=C(sec)) > (C(prim)=C(prim)). In addition, we have found a useful set of topological parameters that are good for estimating the adsorption energy in adsorbed alkenes.

  14. Ionic adsorption on the brucite (0001) surface: A periodic electrostatic embedded cluster method study

    NASA Astrophysics Data System (ADS)

    Makkos, Eszter; Kerridge, Andrew; Austin, Jonathan; Kaltsoyannis, Nikolas

    2016-11-01

    Density functional theory (DFT) at the generalised gradient approximation level is employed within the periodic electrostatic embedded cluster method (PEECM) to model the brucite (0001) surface. Three representative studies are then used to demonstrate the reliability of the PEECM for the description of the interactions of various ionic species with the layered Mg(OH)2 structure, and its performance is compared with periodic DFT, an approach known to be challenging for the adsorption of charged species. The adsorption energies of a series of s block cations, including Sr2+ and Cs+ which are known to coexist with brucite in nuclear waste storage ponds, are well described by the embedded cluster model, provided that basis sets of triple-zeta quality are employed for the adsorbates. The substitution energies of Ca2+ and Sr2+ into brucite obtained with the PEECM are very similar to periodic DFT results, and comparison of the approaches indicates that two brucite layers in the quantum mechanical part of the PEECM are sufficient to describe the substitution. Finally, a detailed comparison of the periodic and PEECM DFT approaches to the energetic and geometric properties of differently coordinated Sr[(OH)2(H2O)4] complexes on brucite shows an excellent agreement in adsorption energies, Sr-O distances, and bond critical point electron densities (obtained via the quantum theory of atoms-in-molecules), demonstrating that the PEECM can be a useful alternative to periodic DFT in these situations.

  15. Separation of chiral nanotubes with an opposite handedness by chiral oligopeptide adsorption: A molecular dynamics study.

    PubMed

    Raffaini, Giuseppina; Ganazzoli, Fabio

    2015-12-18

    The separation of enantiomeric chiral nanotubes that can form non-covalent complexes with an unlike stability upon adsorption of chiral molecules is a process of potential interest in different fields and applications. Using fully atomistic molecular dynamics simulations, we report in this paper a theoretical study of the adsorption and denaturation of an oligopeptide formed by 16 chiral amino acids having a helical structure in the native state on both the inner and the outer surface of the chiral (10, 20) and (20, 10) single-walled carbon nanotubes having an opposite handedness, and of the armchair (16, 16) nanotube with a similar diameter for comparison. In the final adsorbed state, the oligopeptide loses in all cases its native helical conformation, assuming elongated geometries that maximize its contact with the surface through all the 16 amino acids. We find that the complexes formed by the two chiral nanotubes and the chosen oligopeptide have a strongly unlike stability both when adsorption takes place on the outer convex surface of the nanotube, and when it occurs on the inner concave surface. Thus, our molecular simulations indicate that separation of chiral, enantiomeric carbon nanotubes for instance by chromatographic methods can indeed be carried out using oligopeptides of a sufficient length.

  16. Scanning probe microscopy studies on the adsorption of selected molecular dyes on titania

    PubMed Central

    Zajac, Lukasz; Olszowski, Piotr; Jöhr, Res; Hinaut, Antoine; Glatzel, Thilo; Such, Bartosz; Meyer, Ernst; Szymonski, Marek

    2016-01-01

    Titanium dioxide, or titania, sensitized with organic dyes is a very attractive platform for photovoltaic applications. In this context, the knowledge of properties of the titania–sensitizer junction is essential for designing efficient devices. Consequently, studies on the adsorption of organic dyes on titania surfaces and on the influence of the adsorption geometry on the energy level alignment between the substrate and an organic adsorbate are necessary. The method of choice for investigating the local environment of a single dye molecule is high-resolution scanning probe microscopy. Microscopic results combined with the outcome of common spectroscopic methods provide a better understanding of the mechanism taking place at the titania–sensitizer interface. In the following paper, we review the recent scanning probe microscopic research of a certain group of molecular assemblies on rutile titania surfaces as it pertains to dye-sensitized solar cell applications. We focus on experiments on adsorption of three types of prototypical dye molecules, i.e., perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), phtalocyanines and porphyrins. Two interesting heteromolecular systems comprising molecules that are aligned with the given review are discussed as well. PMID:28144513

  17. SANS and UV-vis spectroscopy studies of resultant structure from lysozyme adsorption on silica nanoparticles.

    PubMed

    Kumar, Sugam; Aswal, Vinod K; Kohlbrecher, Joachim

    2011-08-16

    The interaction of lysozyme protein (M.W. 14.7 kD) with two sizes of silica nanoparticles (16 and 25 nm) has been examined in aqueous solution using UV-vis spectroscopy and small-angle neutron scattering (SANS). The measurements were performed on fixed concentration (1 wt %) of nanoparticles and varying concentration of protein in the range 0 to 2 wt %. The adsorption isotherm as obtained using UV-vis spectroscopy suggests strong interaction of the two components and shows an exponential behavior. The saturation values of adsorption are found to be around 90 and 270 protein molecules per particle for 16 and 25 nm sized nanoparticles, respectively. The adsorption of protein on nanoparticles leads to the aggregation of particles and these structures have been studied by SANS. The aggregates are characterized by fractal structure coexisting with unaggregated particles at low protein concentrations and free proteins at higher protein concentrations. Further, contrast variation SANS measurements have been carried out to differentiate the adsorbed and free protein in these systems.

  18. In Situ Infrared Ellipsometry for Protein Adsorption Studies on Ultrathin Smart Polymer Brushes in Aqueous Environment.

    PubMed

    Kroning, Annika; Furchner, Andreas; Aulich, Dennis; Bittrich, Eva; Rauch, Sebastian; Uhlmann, Petra; Eichhorn, Klaus-Jochen; Seeber, Michael; Luzinov, Igor; Kilbey, S Michael; Lokitz, Bradley S; Minko, Sergiy; Hinrichs, Karsten

    2015-06-17

    The protein-adsorbing and -repelling properties of various smart nanometer-thin polymer brushes containing poly(N-isopropylacrylamide) and poly(acrylic acid) with high potential for biosensing and biomedical applications are studied by in situ infrared-spectroscopic ellipsometry (IRSE). IRSE is a highly sensitive nondestructive technique that allows protein adsorption on polymer brushes to be investigated in an aqueous environment as external stimuli, such as temperature and pH, are varied. These changes are relevant to conditions for regulation of protein adsorption and desorption for biotechnology, biocatalysis, and bioanalytical applications. Here brushes are used as model surfaces for controlling protein adsorption of human serum albumin and human fibrinogen. The important finding of this work is that IRSE in the in situ experiments in protein solutions can distinguish between contributions of polymer brushes and proteins. The vibrational bands of the polymers provide insights into the hydration state of the brushes, whereas the protein-specific amide bands are related to changes of the protein secondary structure.

  19. Adsorption and kinetic studies of the intercalation of some organic compounds onto Na+-montmorillonite.

    PubMed

    Gemeay, A H; El-Sherbiny, A S; Zaki, A B

    2002-01-01

    The adsorption and the kinetics of the intercalation of metanil yellow dye, p-aminodiphenylamine (p-NH(2)-DPA), and benzidine by colloidally dispersed Na(+)-montmorillonte (Na(+)-MMT) have been studied. The adsorption isotherm parameters confirmed the occurrence of chemical adsorption that is based on the cation-exchange process. The selectivity of these compounds toward Na(+)-MMT follows the order metanil yellowp-NH(2)-DPA>benzidine. The rate of oxidation has been quantitatively measured using a stopped-flow spectrophotometer. The rate constant follows the order benzidine

  20. Experimental study on activated carbon-nitrogen pair in a prototype pressure swing adsorption refrigeration system

    NASA Astrophysics Data System (ADS)

    Anupam, Kumar; Palodkar, Avinash V.; Halder, G. N.

    2016-04-01

    Pressure swing adsorption of nitrogen onto granular activated carbon in the single-bed adsorber-desorber chamber has been studied at six different pressures 6-18 kgf/cm2 to evaluate their performance as an alternative refrigeration technique. Refrigerating effect showed a linear rise with an increase in the operating pressure. However, the heat of adsorption and COP exhibited initial rise with the increasing operating pressure but decreased later after reaching a maximum value. The COP initially increases with operating pressures however, with the further rise of operating pressure it steadily decreased. The highest average refrigeration, maximum heat of adsorption and optimum coefficient of performance was evaluated to be 415.38 W at 18 kgf/cm2, 92756.35 J at 15 kgf/cm2 and 1.32 at 12 kgf/cm2, respectively. The system successfully produced chilled water at 1.7 °C from ambient water at 28.2 °C.

  1. Scanning probe microscopy studies on the adsorption of selected molecular dyes on titania.

    PubMed

    Prauzner-Bechcicki, Jakub S; Zajac, Lukasz; Olszowski, Piotr; Jöhr, Res; Hinaut, Antoine; Glatzel, Thilo; Such, Bartosz; Meyer, Ernst; Szymonski, Marek

    2016-01-01

    Titanium dioxide, or titania, sensitized with organic dyes is a very attractive platform for photovoltaic applications. In this context, the knowledge of properties of the titania-sensitizer junction is essential for designing efficient devices. Consequently, studies on the adsorption of organic dyes on titania surfaces and on the influence of the adsorption geometry on the energy level alignment between the substrate and an organic adsorbate are necessary. The method of choice for investigating the local environment of a single dye molecule is high-resolution scanning probe microscopy. Microscopic results combined with the outcome of common spectroscopic methods provide a better understanding of the mechanism taking place at the titania-sensitizer interface. In the following paper, we review the recent scanning probe microscopic research of a certain group of molecular assemblies on rutile titania surfaces as it pertains to dye-sensitized solar cell applications. We focus on experiments on adsorption of three types of prototypical dye molecules, i.e., perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), phtalocyanines and porphyrins. Two interesting heteromolecular systems comprising molecules that are aligned with the given review are discussed as well.

  2. A study on adsorption mechanism of organoarsenic compounds on ferrihydrite by XAFS

    NASA Astrophysics Data System (ADS)

    Tanaka, M.; Takahashi, Y.; Yamaguchi, N.

    2013-04-01

    Anthropogenic organoarsenic compounds which were used such as agrochemicals, pesticides, and herbicides can have a potential as a source of arsenic pollution in water. In the process, the adsorption of arsenic onto mineral surface in soil may play an important role to affect arsenic distribution in solid-water interface. However, adsorption structures of organoarsenic compounds on the iron-(oxyhydr)oxides are not well known. In this study, extended X-ray absorption fine structure (EXAFS) spectroscopy was employed to know the adsorption structure of methyl- and phenyl-substituted organoarsenic compounds (methylarsonic acid (MMA), dimethylarsinic acid (DMA), phenylarsonic acid (PAA), and diphenylarsinic acid (DPAA) onto ferrihydrite which can be a strong adsorbent of arsenic. EXAFS analysis suggests that the formation of inner-sphere surface complex for all organoarsenic compounds with ferrihydrite regardless of the organic functional groups and the number of substitution. The As-Fe distances are around 3.27 , which suggests both mono-and bi-dentate inner-sphere complexes by DFT calculations. The corresponding coordination numbers (CNs) are less than two, suggesting that coexistence of both structures of inner-sphere complexes.

  3. Characteristics of Organobentonite and Study of Iodide Adsorption on Organobentonite using X-ray Absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

    Yoon, J.; Ha, J.; Hwang, B.; Hwang, J.; Brown, G. E.

    2008-12-01

    The adsorption of iodide on untreated bentonite and bentonites modified with organic cation (i.e., hexadecylpyridinium chloride monohydrate (HDP+)) was investigated, and the organobentonites were characterized using uptake measurements, micro X-ray diffraction (micro-XRD), and electrophoretic mobility measurements prior to reaction with KI solutions. Uptake measurements indicate that bentonite has a high affinity for HDP+. Increasing [HDP+](aq) results in an increase in HDP+ uptake on bentonite by up to 280% of the CEC equivalents of bentonite, and causes a concomitant increase in Na released as a result of the replacement of exchangeable inorganic cations in bentonite interlayers. Based micro-XRD, the d001 spacing of untreated bentonite was 1.22 nm whereas organobentonites modified with HDP+ at different equivalent amounts, corresponding to 100%, 200%, and 400% of the cation exchange capacity (CEC) of bentonite, showed d001 spacings of 1.96 nm, 3.77 nm, and 3.77 nm, respectively. Our micro-XRD study indicates that organobentonites significantly expanded in basal spacing and organic cations were substantially intercalated into the interlayer spaces of montmorillonite. The electrophoretic mobility indicates that the untreated bentonite had a negative surface charge over the entire pH range examined (pH 2-12) whereas the organobentonite at an equivalent amount corresponding to 200% of the CEC had a positive surface charge over this pH range. We found significant differences in adsorption capacities of iodide depending on the bentonite properties as follows: iodide adsorption capacities were 439 mmol/kg for the bentonite modified with HDP+ at an equivalent amount corresponding to 200% of the CEC of bentonite whereas no adsorption of iodide was observed for the untreated bentonite. The molecular environments of iodine adsorbed on organobentonites were further studied using I K-edge and LIII-edge x-ray absorption spectroscopy (XAS). The X-ray absorption near

  4. Microcalorimetric study of adsorption and disassembling of virus-like particles on anion exchange chromatography media.

    PubMed

    Yu, Mengran; Zhang, Songping; Zhang, Yan; Yang, Yanli; Ma, Guanghui; Su, Zhiguo

    2015-04-03

    Chromatographic purification of virus-like particles (VLPs) is important to the development of modern vaccines. However, disassembly of the VLPs on the solid-liquid interface during chromatography process could be a serious problem. In this study, isothermal titration calorimetric (ITC) measurements, together with chromatography experiments, were performed on the adsorption and disassembling of multi-subunits hepatitis B virus surface antigen virus-like particles (HB-VLPs). Two gigaporous ion-exchange chromatography (IEC) media, DEAE-AP-280 nm and DEAE-POROS, were used. The application of gigaporous media with high ligand density led to significantly increased irreversible disassembling of HB-VLPs and consequently low antigen activity recovery during IEC process. To elucidate the thermodynamic mechanism of the effect of ligand density on the adsorption and conformational change of VLPs, a thermodynamic model was proposed. With this model, one can obtain the intrinsic molar enthalpy changes related to the binding of VLPs and the accompanying conformational change on the liquid-solid interface during its adsorption. This model assumes that, when intact HB-VLPs interact with the IEC media, the total adsorbed proteins contain two states, the intact formation and the disassembled formation; accordingly, the apparent adsorption enthalpy, ΔappH, which can be directly measured from ITC experiments, presents the sum of three terms: (1) the intrinsic molar enthalpy change associated to the binding of intact HB-VLPs (ΔbindHintact), (2) the intrinsic molar enthalpy change associated to the binding of HB-VLPs disassembled formation (ΔbindHdis), and (3) the enthalpy change accompanying the disassembling of HB-VLPs (ΔconfHdis). The intrinsic binding of intact HB-VLPs and the disassembled HB-VLPs to both kinds of gigaporous media (each of which has three different ligand densities), were all observed to be entropically driven as indicated by positive values of

  5. Theoretical study of the adsorption of DOPA-quinone and DOPA-quinone chlorides on Cu (1 0 0) surface

    NASA Astrophysics Data System (ADS)

    Chen, Shuang-Kou; Wang, Bo-Chu; Zhou, Tai-Gang; Huang, Wen-Zhang

    2011-07-01

    The marine mussel secreted adhesive proteins and could bind strongly to all kinds of surfaces. Studies indicated that there was an unusual amino acid 3,4-dihydroxy-L-phenylanine (DOPA). DOPA could be oxidized to DOPA-quinone easily, which had a superior ability to on surface directly. The technology of electrolyzing seawater was employed to generate HOCl solution to react with DOPA-quinone and form DOPA-quinone chlorides (DOPA-quinone-Cl) to hinder the adhesion. However, the detailed hinder-mechanism remained unknown to be fully explained. Herein, using quantum chemical density functional theory methods, we have systematically studied three kinds of adsorption for DOPA-quinone and DOPA-quinone-Cl on Cu (1 0 0) surface: hydroxyl oxygen-side vertical, carbonyl oxygen-side vertical, amino N-terminal vertical adsorptions and carried out geometry optimization and energy calculation. The results showed that two molecules could absorb on the Cu (1 0 0) through hydroxyl oxygen-side vertical adsorption, while the other two kinds of adsorption could not form an effective adsorption. Calculations of adsorption energy for hydroxyl oxygen-side vertical adsorption indicated that: after HOCl modification, adsorption energy decreased from -247.2310 kJ/mol to -177.0579 kJ/mol for DOPA-quinone and DOPA-quinone-Cl; and the Mulliken Charges Populations showed that the electrons transferred from surface to DOPA-quinone-Cl was less than that to DOPA-quinone, namely, the fewer the number of electrons transferred, the weaker interaction between molecular and surface. After the theoretical calculation, we found that the anti-foul goal had been achieved by electrolysis of seawater to generate HOCl to modify DOPA-quinone, which led to the reduction of adsorption energy and transferred electrons.

  6. Investigation of dye adsorption onto activated carbon from the shells of Macoré fruit.

    PubMed

    Aboua, Kouassi Narcisse; Yobouet, Yao Augustin; Yao, Kouassi Benjamin; Goné, Droh Lanciné; Trokourey, Albert

    2015-06-01

    The activated carbon obtained from the shells of Macoré fruit was used as an adsorbent for the removal of dyes such as methylene blue (MB) and methyl orange (MO) from synthetic contaminated aqueous solutions. It holds that the adsorption is more favourable at acidic pH, with an optimum adsorption at pH = 2. At this pH, the adsorption rate is more than 98% for the two dyes. The sorption capacity was enhanced by increasing the amount of activated carbon. Above room temperature, the adsorption rates remain constant at a value of approximately 99%. The study of the adsorption kinetics indicates that the adsorption on the studied dyes follows second-order kinetics. The isotherm adsorption data were found to be described by both Langmuir and Freundlich. In addition, the thermodynamic studies revealed that the adsorption process is a favourable, endothermic and spontaneous phenomenon.

  7. Batch removal of malachite green from aqueous solutions by adsorption on oil palm trunk fibre: equilibrium isotherms and kinetic studies.

    PubMed

    Hameed, B H; El-Khaiary, M I

    2008-06-15

    Oil palm trunk fibre (OPTF)--an agricultural solid waste--was used as low-cost adsorbent to remove malachite green (MG) from aqueous solutions. The operating variables studied were contact time, initial dye concentration, and solution pH. Equilibrium adsorption data were analyzed by three isotherms, namely the Freundlich isotherm, the Langmuir isotherm, and the multilayer adsorption isotherm. The best fit to the data was obtained with the multilayer adsorption. The monolayer adsorption capacity of OPTF was found to be 149.35 mg/g at 30 degrees C. Adsorption kinetic data were modeled using the Lagergren pseudo-first-order, Ho's pseudo-second-order and Elovich models. It was found that the Lagergren's model could be used for the prediction of the system's kinetics. The overall rate of dye uptake was found to be controlled by external mass transfer at the beginning of adsorption, then for initial MG concentrations of 25, 50, 100, 150, and 300 mg/L the rate-control changed to intraparticle diffusion at a later stage, but for initial MG concentrations 200 and 250 mg/L no evidence was found of intraparticle diffusion at any period of adsorption. It was found that with increasing the initial concentration of MG, the pore-diffusion coefficient increased while the film-diffusion coefficient decreased.

  8. Experimental and theoretical study using DFT method for the competitive adsorption of two cationic dyes from wastewaters

    NASA Astrophysics Data System (ADS)

    Regti, Abdelmajid; Ayouchia, Hicham Ben El; Laamari, My Rachid; Stiriba, Salah Eddine; Anane, Hafid; Haddad, Mohammadine El

    2016-12-01

    The adsorption of cationic dyes, Basic Yellow (BY28) and Methylene Blue (MB) on a new activated carbon from medlar species were studied in both single and binary system. Some experimental parameters, namely, pH, amount of adsorbent and contact time are studied. Quantum chemical results indicate that the adsorption efficiency was directly related to the dye electrophilicity power. Some theorical parameters were calculated and proved that MB is more electrophilic than BY28, than greatest interaction with surface sites. Kinetic study showed that the adsorption follows the pseudo-second-order model and Freundlich was the best model to describe the phenomenon in the single and binary system. According to the local reactivity results using Parr functions, the sulphur and nitrogen atoms will be the main adsorption sites.

  9. Phenomenological study of monomer adsorption on fcc (335) surfaces with application to CO, O, and N(2) adsorption on Pt(335).

    PubMed

    Phares, Alain J; Grumbine, David W; Wunderlich, Francis J

    2009-01-20

    We extend our recent study of adsorption on fcc (112) to fcc (335) surfaces, still considering only first- and second-neighbor interactions with repulsive first-neighbors. We consider the adsorbate-substrate interaction on the step sites of one of the two edges of the infinitely long terraces to be different from that on the remaining sites. The adsorption features on fcc (335) surfaces are richer than those on fcc (112), which can be attributed to the fact that the equilateral triangular terraces are now four-atoms wide rather than three. Our approach is independent of the chemical composition of the substrate and adsorbates and consequently may be applied to a variety of adsorption systems on fcc (335) surfaces which satisfy the limitations of our model. The basic question that our phenomenological approach intends to answer is: what are the constraints that can be obtained on the interaction energies from the experimental observation of one or more phases? This question is answered in the cases of CO, O, and N(2) adsorbed on Pt(335).

  10. Microcalorimetry Study of the Adsorption of Asphaltenes and Asphaltene Model Compounds at the Liquid-Solid Surface.

    PubMed

    Pradilla, Diego; Subramanian, Sreedhar; Simon, Sébastien; Sjöblom, Johan; Beurroies, Isabelle; Denoyel, Renaud

    2016-07-26

    The adsorption of an acidic polyaromatic asphaltene model compound (C5PeC11) and indigenous C6-asphaltenes onto the liquid-solid surface is studied. Model compound C5PeC11 exhibits a similar type of adsorption with a plateau adsorbed amount as C6-asphaltenes onto three surfaces (silica, calcite, and stainless steel). Model compound BisAC11, with aliphatic end groups and no acidic functionality, does not adsorb at the liquid-silica surface, indicating the importance of polar interactions on adsorption. The values of the adsorption enthalpy characterized by the ΔHz parameter (the enthalpy at zero coverage) indicate that the type of adsorption and the driving force depend on the surface, a key feature when discussing asphaltene deposition. The adsorption of C5PeC11 onto silica is shown to be driven primarily by H bonding (ΔHz = -34.9 kJ/mol), unlike adsorption onto calcite where polar van der Waals and acidic/basic interactions are thought to be predominant (ΔHz = -23.5 kJ/mol). Interactions between C5PeC11 and stainless steel are found to be weak (ΔHz = -7.7 kJ/mol). Comparing C6-asphaltenes and their esterified counterpart shows that adsorption at the liquid-solid surface is not influenced by the formation of H bonds. This was evidenced by the similar adsorbed amounts obtained. Finally, C5PeC11 captures, to a certain extent, the adsorption interactions of asphaltenes present at the calcite-oil and stainless steel-oil surfaces.

  11. Synthesis, characterization and study of arsenate adsorption from aqueous solution by {alpha}- and {delta}-phase manganese dioxide nanoadsorbents

    SciTech Connect

    Singh, Mandeep; Thanh, Dong Nguyen; Ulbrich, Pavel; Strnadova, Nina; Stepanek, Frantisek

    2010-12-15

    Single-phase {alpha}-MnO{sub 2} nanorods and {delta}-MnO{sub 2} nano-fiber clumps were synthesized using manganese pentahydrate in an aqueous solution. These nanomaterials were characterized using the Transmission Electron Microscope (TEM), Field Emission Scanning Electron Microscope (FE-SEM), Powder X-ray diffraction (XRD) and the Brunauer-Elmet-Teller nitrogen adsorption technique (BET-N{sub 2} adsorption). The structural analysis shows that {alpha}-MnO{sub 2} (2x2 tunnel structure) has the form of needle-shaped nanorods and {delta}-MnO{sub 2} (2D-layered structure) consists of fine needle-like fibers arranged in ball-like aggregates. Batch adsorption experiments were carried out to determine the effect of pH on adsorption kinetics and adsorption capacity for the removal of As(V) from aqueous solution onto these two types of nanoadsorbents. The adsorption capacity of As(V) was found to be highly pH dependent. The adsorption of As(V) onto {alpha}-MnO{sub 2} reached equilibrium more rapidly with higher adsorption capacity compared to {delta}-MnO{sub 2}. -- Graphical abstract: {alpha}-MnO{sub 2} (2x2 tunnel structure) nanorods and {delta}-MnO{sub 2} (2-D layered structure) nano-fiber clumps were synthesized in a facile way in an aqueous solution and characterized by TEM, FE-SEM, XRD and BET-N{sub 2} adsorption techniques. The structural analysis shows that {alpha}-MnO{sub 2} is needle shaped nanorods and {delta}-MnO{sub 2} consists of 2-D platelets of fine needle-like fibers arranged in ball-like aggregates. Further batch experiments confirmed that both nanoadsorbents are potential candidates for the adsorption of As(V) with a capacity of 19.41 and 15.33 mg g{sup -1} for {alpha}-MnO{sub 2} and {delta}-MnO{sub 2}, respectively. The presence of As3d peak in XPS study indicates that arsenic on the surface of nanoadsorbents is in the stable form of As(V) with a percentage of arsenate onto {alpha}-MnO{sub 2} is 0.099% as compared to 0.021% onto {delta}-MnO{sub 2

  12. Preliminary study of phosphate adsorption onto cerium oxide nanoparticles for use in water purification; nanoparticles synthesis and characterization.

    PubMed

    Recillas, Sonia; García, Ana; González, Edgar; Casals, Eudald; Puntes, Victor; Sánchez, Antoni; Font, Xavier

    2012-01-01

    In this study, the synthesis and characterization of cerium oxide nanoparticles (CeO(2)-NPs) and their adsorption potential for removing phosphate from water was evaluated using a multi-factor experimental design to explore the effect of various factors on adsorption. The objective function selected was the percentage of phosphate removed from water, in which the phosphate concentration and the CeO(2)-NP concentration are quantitative variables (factors in the experimental design). A lineal polynomial fitted the experimental results well (R(2) = 0.9803). The nanostructure was studied by transmission electron microscopy (TEM) and high-resolution TEM techniques before and after the adsorption process. During the adsorption and desorption processes several changes in the morphology and surface chemistry of the CeO(2)-NPs were observed.

  13. DFT study of BaTiO3 (001) surface with O and O2 adsorption

    NASA Astrophysics Data System (ADS)

    Rakotovelo, G.; Moussounda, P. S.; Haroun, M. F.; Légaré, P.; Rakotomahevitra, A.; Parlebas, J. C.

    2007-06-01

    Progress of scanning tunneling microscopy (STM) allowed to handle various molecules adsorbed on a given surface. New concepts emerged with molecules on surfaces considered as nano machines by themselves. In this context, a thorough knowledge of surfaces and adsorbed molecules at an atomic scale is thus particularly invaluable. In this work, within the framework of density functional theory (DFT), we present an electronic and structural ab initio study of a BaTiO3 (001) surface (perovskite structure) in its paraelectric phase. As far as we know the atomic and molecular adsorption of oxygen at surface is then analyzed for the first time in the literature. Relaxation is taken into account for several layers. Its analysis for a depth of at least four layers enables us to conclude that a reasonable approximation for a BaTiO3 (001) surface is provided with a slab made up of nine plans. The relative stability of two possible terminations is considered. By using a kinetic energy cut off of 400 eV, we found that a surface with BaO termination is more stable than with TiO2 termination. Consequently, a surface with BaO termination was chosen to adsorb either O atom or O2 molecule and the corresponding calculations were performed with a coverage 1 on a (1×1) cell. A series of cases with O2 molecule adsorbed in various geometrical configurations are also analyzed. For O2, the most favorable adsorption is obtained when the molecule is placed horizontally, with its axis, directed along the Ba-Ba axis and with its centre of gravity located above a Ba atom. The corresponding value of the adsorption energy is -9.70 eV per molecule (-4.85 eV per O atom). The molecule is then rather extended since the O O distance measures 1.829 Å. By comparison, the adsorption energy of an O atom directly located above a Ba atom is only -3.50 eV. Therefore we are allowed to conclude that the O O interaction stabilizes atomic adsorption. Also the local densities of states (LDOS) corresponding to

  14. Kinetics and equilibrium adsorption studies of dimethylamine (DMA) onto ion-exchange resin.

    PubMed

    Hu, Qinhai; Meng, Yuanyuan; Sun, Tongxi; Mahmood, Qaisar; Wu, Donglei; Zhu, Jianhang; Lu, George

    2011-01-30

    The fine grained resin ZGSPC106 was used to adsorb dimethylamine (DMA) from aqueous solution in the present research. Batch experiments were performed to examine the effects of initial pH of solution and agitation time on the adsorption process. The thermodynamics and kinetics of adsorption were also analyzed. The maximum adsorption was found at natural pH of DMA solution and equilibrium could be attained within 12 min. The equilibrium adsorption data were conformed satisfactorily to the Langmuir equation. The evaluation based on Langmuir isotherm gave the maximal static saturated adsorption capacity of 138.89 mg/g at 293K. Various thermodynamic parameters such as free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) showed that the adsorption was spontaneous, endothermic and feasible. DMA adsorption on ZGSPC106 fitted well to the pseudo-second-order kinetic model. Furthermore, the adsorption mechanism was discussed by Fourier transform infrared spectroscopy (FT-IR) analysis.

  15. Some studies on successive ionic layer adsorption and reaction (SILAR) grown indium sulphide thin films

    SciTech Connect

    Pathan, H.M.; Lokhande, C.D. . E-mail: l_chandrakant@yahoo.com; Kulkarni, S.S.; Amalnerkar, D.P.; Seth, T.; Han, Sung-Hwan . E-mail: shhan@hanyang.ac.kr

    2005-06-15

    Indium sulphide (In{sub 2}S{sub 3}) thin films were grown on amorphous glass substrate by the successive ionic layer adsorption and reaction (SILAR) method. X-ray diffraction, optical absorption, scanning electron microscopy (SEM) and Rutherford back scattering (RBS) were applied to study the structural, optical, surface morphological and compositional properties of the indium sulphide thin films. Utilization of triethanolamine and hydrazine hydrate complexed indium sulphate and sodium sulphide as precursors resulted in nanocrystalline In{sub 2}S{sub 3} thin film. The optical band gap was found to be 2.7 eV. The film appeared to be smooth and homogeneous from SEM study.

  16. 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.

  17. Revealing fibrinogen monolayer conformations at different pHs: electrokinetic and colloid deposition studies.

    PubMed

    Nattich-Rak, Małgorzata; Adamczyk, Zbigniew; Wasilewska, Monika; Sadowska, Marta

    2015-07-01

    Adsorption mechanism of human fibrinogen on mica at different pHs is studied using the streaming potential and colloid deposition measurements. The fibrinogen monolayers are produced by a controlled adsorption under diffusion transport at pH of 3.5 and 7.4. Initially, the electrokinetic properties of these monolayers and their stability for various ionic strength are determined. It is shown that at pH 3.5 fibrinogen adsorbs irreversibly on mica for ionic strength range of 4×10(-4) to 0.15 M. At pH 7.4, a partial desorption is observed for ionic strength below 10(-2) M. This is attributed to the desorption of the end-on oriented molecules whereas the side-on adsorbed molecules remain irreversibly bound at all ionic strengths. The orientation of molecules and monolayer structure is evaluated by the colloid deposition measurements involving negatively charged polystyrene latex microspheres, 820 nm in diameter. An anomalous deposition of negative latex particles on substrates exhibiting a negative zeta potential is observed. At pH 3.5 measurable deposition of latex is observed even at low ionic strength where the approach distance of latex particles exceeded 70 nm. At pH 7.4 this critical distance is 23 nm. This confirms that fibrinogen monolayers formed at both pHs are characterized by the presence of the side-on and end-on oriented molecules that prevail at higher coverage range. It is also shown that positive charge is located at the end parts of the αA chains of the adsorbed fibrinogen molecules. Therefore, it is concluded that the colloid deposition method is an efficient tool for revealing protein adsorption mechanisms at solid/electrolyte interfaces.

  18. A study of Reactive Red 198 adsorption on iron filings from aqueous solutions.

    PubMed

    Azhdarpoor, Abooalfazl; Nikmanesh, Roya; Khademi, Fahime

    2014-01-01

    In recent years, reactive dyes have been widely used in textile industries with particular efficiency. They dyes are often toxic, carcinogenic and mutagenic. Improper treatment and non-scientific disposal of dyed wastewater from these industries into water sources has created many environmental problems and concerns around the world. The purpose of the present study is to investigate the efficiency of iron filings in adsorption of Reactive Red 198 from aqueous solutions. This study was conducted using an experimental method at the laboratory scale. In this study, the effects of operating parameters such as pH (1-11), initial dye concentration (40-400 mg/L), contact time (5-120 min) and iron dose (0.1-1 g) with a mesh of<100 were studied. Dye concentration was determined using a spectrophotometer at a wavelength of 520 nm. The results indicated that maximum adsorption capacity of the dye in question was obtained at pH 3, contact time of 60 min and adsorbent dose of 1 g. At initial dye concentration of 100 and 200 mg/L, by increasing the dose of waste iron from 0.1 to 1 g, the removal percentage increased from approximately 76.89% to 97.28% and from 22.64% to 68.03%, respectively. At pH 3, contact time of 5 min and constant waste iron dose of 0.8 g, the dye removal efficiency was 85.34%. By increasing the contact time to 120 min, the removal efficiency increased to 99.2%. Welding iron waste as an inexpensive and available adsorbent has an optimum ability for adsorption of Reactive Red 198 from aqueous solutions.

  19. Removal of mercury(II) ions in aqueous solution using the peel biomass of Pachira aquatica Aubl: kinetics and adsorption equilibrium studies.

    PubMed

    Santana, Andrea J; dos Santos, Walter N L; Silva, Laiana O B; das Virgens, Cesário F

    2016-05-01

    Mercury is a highly toxic substance that is a health hazard to humans. This study aims to investigate powders obtained from the peel of the fruit of Pachira aquatica Aubl, in its in natura and/or acidified form, as an adsorbent for the removal of mercury ions in aqueous solution. The materials were characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. The infrared spectra showed bands corresponding to the axial deformation of carbonyls from carboxylic acids, the most important functional group responsible for fixing the metal species to the adsorbent material. The thermograms displayed mass losses related to the decomposition of three major components, i.e., hemicellulose, cellulose, and lignin. The adsorption process was evaluated using cold-vapor atomic fluorescence spectrometry (CV AFS) and cold-vapor atomic absorption spectrometry (CV AAS). Three isotherm models were employed. The adsorption isotherm model, Langmuir-Freundlich, best represented the adsorption process, and the maximum adsorption capacity was predicted to be 0.71 and 0.58 mg g(-1) at 25 °C in nature and acidified, respectively. Adsorption efficiencies were further tested on real aqueous wastewater samples, and removal of Hg(II) was recorded as 69.6 % for biomass acidified and 76.3 % for biomass in nature. Results obtained from sorption experiments on real aqueous wastewater samples revealed that recovery of the target metal ions was very satisfactory. The pseudo-second-order model showed the best correlation to the experimental data. The current findings showed that the investigated materials are potential adsorbents for mercury(II) ion removal in aqueous solution, with acidified P. aquatica Aubl being the most efficient adsorbent.

  20. Equilibrium isotherms, kinetics, and thermodynamics studies for congo red adsorption using calcium alginate beads impregnated with nano-goethite.

    PubMed

    Munagapati, Venkata Subbaiah; Kim, Dong-Su

    2017-03-24

    The present study is concerned with the batch adsorption of congo red (CR) from an aqueous solution using calcium alginate beads impregnated with nano-goethite (CABI nano-goethite) as an adsorbent. The optimum conditions for CR removal were determined by studying operational variables viz. pH, adsorbent dose, contact time, initial dye ion concentration and temperature. The CABI nano-goethite was characterized by Fourier transform infrared spectroscopy (FTIR), X- ray diffraction (XRD) and Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) analysis. The CR sorption data onto CABI nano-goethite were described using Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherm models. The results show that the best fit was achieved with the Langmuir isotherm model. The maximum adsorption capacity (181.1mg/g) of CR was occurred at pH 3.0. Kinetic studies showed that the adsorption followed a pseudo-second-order model. Desorption experiments were carried out to explore the feasibility of regenerating the adsorbent and the adsorbed CR from CABI nano-goethite. The best desorbing agent was 0.1M NaOH with an efficiency of 94% recovery. The thermodynamic parameters ΔG°, ΔH°, and ΔS° for the CR adsorption were determined by using adsorption capacities at five different temperatures (293, 303, 313, 323 and 303K). Results show that the adsorption process was endothermic and favoured at high temperature.

  1. Application of zeolite-activated carbon macrocomposite for the adsorption of Acid Orange 7: isotherm, kinetic and thermodynamic studies.

    PubMed

    Lim, Chi Kim; Bay, Hui Han; Neoh, Chin Hong; Aris, Azmi; Abdul Majid, Zaiton; Ibrahim, Zaharah

    2013-10-01

    In this study, the adsorption behavior of azo dye Acid Orange 7 (AO7) from aqueous solution onto macrocomposite (MC) was investigated under various experimental conditions. The adsorbent, MC, which consists of a mixture of zeolite and activated carbon, was found to be effective in removing AO7. The MC were characterized by scanning electron microscopy (SEM), energy dispersive X-ray, point of zero charge, and Brunauer-Emmett-Teller surface area analysis. A series of experiments were performed via batch adsorption technique to examine the effect of the process variables, namely, contact time, initial dye concentration, and solution pH. The dye equilibrium adsorption was investigated, and the equilibrium data were fitted to Langmuir, Freundlich, and Tempkin isotherm models. The Langmuir isotherm model fits the equilibrium data better than the Freundlich isotherm model. For the kinetic study, pseudo-first-order, pseudo-second-order, and intraparticle diffusion model were used to fit the experimental data. The adsorption kinetic was found to be well described by the pseudo-second-order model. Thermodynamic analysis indicated that the adsorption process is a spontaneous and endothermic process. The SEM, Fourier transform infrared spectroscopy, ultraviolet-visible spectral and high performance liquid chromatography analysis were carried out before and after the adsorption process. For the phytotoxicity test, treated AO7 was found to be less toxic. Thus, the study indicated that MC has good potential use as an adsorbent for the removal of azo dye from aqueous solution.

  2. Adsorption Behavior of Pb(II) Onto Potassium Polytitanate Nanofibres.

    PubMed

    Shahid, Mohammad; Tiling, Leonard D; El Saliby, Ibrahim; McDonagh, Andrew; Kim, Jong-Beom; Kim, Jong-Ho; Shon, Ho Kyong

    2016-02-01

    Potassium polytitanate nanofibres prepared by a hydrothermal method were investigated for their possible application in removing toxic metals from aqueous solution. Particular attention was paid to employing the titanate as a novel effective adsorbent for the removal of Pb(II). Batch adsorption experiments demonstrated that the adsorption was influenced by various conditions such as solution pH, adsorbent dosage and initial Pb(II) concentration. The results showed that the adsorption rate was faster in the first 5 min and equilibrium was achieved after 180 min. The maximum amount of adsorption was detected at pH 5. Potassium titanate showed much higher adsorption capacity compared to P25. The kinetic studies indicated that the adsorption of Pb(II) onto titanate best fit the pseudo-second-order kinetic model. FTIR spectra revealed that the hydroxyl groups in titanate were responsible for Pb(II) adsorption. The principal mechanism of the adsorption of Pb(II) in the present study is attributed to both ion exchange and oxygen bonding. The adsorption-desorption results demonstrated that the titanate could be readily regenerated after adsorption. Therefore, the present titanate exhibits great potential for the removal of Pb(II) from wastewater.

  3. Adsorption of alexa-labeled Bt toxin on mica, glass, and hydrophobized glass: study by normal scanning confocal fluorescence.

    PubMed

    Janot, Jean-Marc; Boissière, Michel; Thami, Thierry; Tronel-Peyroz, Emmanuel; Helassa, Nordine; Noinville, Sylvie; Quiquampoix, Hervé; Staunton, Siobhán; Déjardin, Philippe

    2010-06-14

    We studied the kinetics of adsorption of alexa-labeled Bt toxin Cry1Aa, in monomer and oligomer states, on muscovite mica, acid-treated hydrophilic glass, and hydrophobized glass, in the configuration of laminar flow of solution in a slit. Normal confocal fluorescence through the liquid volume allows the visualization of the concentration in solution over the time of adsorption, in addition to the signal due to the adsorbed molecules at the interface. The solution signal is used as calibration for estimation of interfacial concentration. We found low adsorption of the monomer compared to oligomers on the three types of surface. The kinetic adsorption barrier for oligomers increases in the order hydrophobized glass, muscovite mica, acid-treated hydrophilic glass. This suggests enhanced immobilization in soil if toxin is under oligomer state.

  4. A comparative study of the adsorption equilibrium of progesterone by a carbon black and a commercial activated carbon

    NASA Astrophysics Data System (ADS)

    Valenzuela-Calahorro, Cristóbal; Navarrete-Guijosa, Antonio; Stitou, Mostafa; Cuerda-Correa, Eduardo M.

    2007-04-01

    In this paper the adsorption process of a natural steroid hormone (progesterone) by a carbon black and a commercial activated carbon has been studied. The corresponding equilibrium isotherms have been analyzed according to a previously proposed model which establishes a kinetic law satisfactorily fitting the C versus t isotherms. The analysis of the experimental data points out the existence of two well-defined sections in the equilibrium isotherms. A general equation including these two processes has been proposed, the global adsorption process being fitted to such equation. From the values of the kinetic equilibrium constant so obtained, values of standard average adsorption enthalpy ( ΔH°) and entropy ( ΔS°) have been calculated. Finally, information related to variations of differential adsorption enthalpy ( ΔH) and entropy ( ΔS) with the surface coverage fraction ( θ) was obtained by using the corresponding Clausius-Clapeyron equations.

  5. Multiscale Study of Hydrogen Adsorption on Six Designed Covalent Organic Frameworks Based on Porphyrazine, Cyclobutane and Scandium

    NASA Astrophysics Data System (ADS)

    Li, Le-Le; Gao, Teng-Fei; Zhang, Ruan-Yu; Zhang, Hong

    2014-09-01

    The first-principles method of hydrogen adsorption is used to investigate the interaction of H2 with the scandium-porphyrazine (Sc-Pz) and porphyrazine (Pz) clusters. The result shows that the interaction of H2 with Sc-Pz is stronger than with Pz. Then grand canonical Monte Carlo simulations are used to investigate hydrogen adsorption in six designed covalent organic frameworks (COFs), which are designed based on porphyrazine, cyclobutane and scandium. When the pressure is from 0.1 to 100 bar and the temperature is 298 K and 77 K, the hydrogen adsorption capacities of the six COFs are calculated. We further study the importance of Sc and fillers to improve the H2 uptake in the modified COFs by analyzing the isosteric heat of hydrogen adsorption.

  6. Porosity of microporous zeolites A, X and ZSM-5 studied by small angle X-ray scattering and nitrogen adsorption

    NASA Astrophysics Data System (ADS)

    Du, Xiaoming; Wu, Erdong

    2007-09-01

    Small-angle X-ray scattering (SAXS) using synchrotron radiation and nitrogen adsorption have been applied to characterizations of porosities and microporous structures for the zeolites of NaA, KA, CaA, NaX and ZSM-5. Besides the information on the external morphology of the particles of the zeolites, the complementation of the two techniques has revealed rich and consistent structural and surface information on the molecular scale crystalline pores of these zeolites. Analyses of the data suggest that the determined sizes of the micropores imply the pore spaces occupied by the probe molecules of water in the SAXS and nitrogen in adsorption techniques, respectively. The microporous information of NaA and KA are difficult to obtain from nitrogen adsorption, due to the blocking of nitrogen by their narrow channels, but have been satisfactorily measured by SAXS. The factors causing variations of the measured values of the parameters in different analysis methods have been discussed.

  7. Adsorption of chromium (VI) by ethylenediamine-modified cross-linked magnetic chitosan resin: isotherms, kinetics and thermodynamics.

    PubMed

    Hu, Xin-jiang; Wang, Jing-song; Liu, Yun-guo; Li, Xin; Zeng, Guang-ming; Bao, Zheng-lei; Zeng, Xiao-xia; Chen, An-wei; Long, Fei

    2011-01-15

    The adsorption of chromium (VI) ions from aqueous solution by ethylenediamine-modified cross-linked magnetic chitosan resin (EMCMCR) was studied in a batch adsorption system. Chromium (VI) removal is pH dependent and the optimum adsorption was observed at pH 2.0. The adsorption rate was extremely fast and the equilibrium was established within 6-10min. The adsorption data could be well interpreted by the Langmuir and Temkin model. The maximum adsorption capacities obtained from the Langmuir model are 51.813mgg(-1), 48.780mgg(-1) and 45.872mgg(-1) at 293, 303 and 313K, respectively. The adsorption process could be described by pseudo-second-order kinetic model. The intraparticle diffusion study revealed that film diffusion might be involved in the present case. Thermodynamic parameters revealed the feasibility, spontaneity and exothermic nature of adsorption. The sorbents were successfully regenerated using 0.1N NaOH solutions.

  8. Atomic and molecular adsorption on transition-metal carbide (111) surfaces from density-functional theory: a trend study of surface electronic factors.

    PubMed

    Vojvodic, A; Ruberto, C; Lundqvist, B I

    2010-09-22

    This study explores atomic and molecular adsorption on a number of early transition-metal carbides (TMCs) in NaCl structure by means of density-functional theory calculations. The investigated substrates are the TM-terminated TMC(111) surfaces, of interest because of the presence of different types of surface resonances (SRs) on them and because of their technological importance in growth processes. Also, TM compounds have shown potential in catalysis applications. Trend studies are conducted with respect to both period and group in the periodic table, choosing the substrates ScC, TiC, VC, ZrC, NbC, δ-MoC, TaC, and WC (in NaCl structure) and the adsorbates H, B, C, N, O, F, NH, NH(2), and NH(3). Trends in adsorption strength are explained in terms of surface electronic factors, by correlating the calculated adsorption-energy values with the calculated surface electronic structures. The results are rationalized by use of a concerted-coupling model (CCM), which has previously been applied successfully to the description of adsorption on TiC(111) and TiN(111) surfaces (Ruberto et al 2007 Solid State Commun. 141 48). First, the clean TMC(111) surfaces are characterized by calculating surface energies, surface relaxations, Bader charges, and surface-localized densities of states (DOSs). Detailed comparisons between surface and bulk DOSs reveal the existence of transition-metal localized SRs (TMSRs) in the pseudogap and of several C-localized SRs (CSRs) in the upper valence band on all considered TMC(111) surfaces. The spatial extent and the dangling bond nature of these SRs are supported by real-space analyses of the calculated Kohn-Sham wavefunctions. Then, atomic and molecular adsorption energies, geometries, and charge transfers are presented. An analysis of the adsorbate-induced changes in surface DOSs reveals a presence of both adsorbate-TMSR and adsorbate-CSRs interactions, of varying strengths depending on the surface and the adsorbate. These variations are

  9. A density-functional theory study of electrochemical adsorption of sulfuric acid anions on Pt(111).

    PubMed

    Santana, Juan A; Cabrera, Carlos R; Ishikawa, Yasuyuki

    2010-08-28

    A density-functional theory study of the electrochemical adsorption of sulfuric acid anions was conducted at the Pt(111)/electrolyte interface over a wide range of electrode potential, including the anomalous region of the hydrogen voltammogram of this electrode. We focus on the precise nature of the binding species and their bonding to the surface, identifying the adsorbed species as a function of electrode potential. In particular, the origin of anomalous or so-called "butterfly" feature in this voltammogram between +0.30 and +0.50 V vs. the reference hydrogen electrode and the nature of the adsorbed species on the Pt(111) surface in this potential range were explicated.

  10. Adsorption of CGA on colloidal silver particles: DFT and SERS study

    NASA Astrophysics Data System (ADS)

    Biswas, Nandita; Kapoor, Sudhir; Mahal, Harbir S.; Mukherjee, Tulsi

    2007-08-01

    Raman and surface-enhanced Raman scattering (SERS) of chlorogenic acid (CGA) have been investigated. CGA is an important plant metabolite with anti-viral and anti-bacterial properties and thus, it is useful to study its surface adsorption characteristics. The experimental Raman data is supported with DFT calculations using B3LYP functional with 6-31G ∗ and LANL2DZ basis set. This is the first report on the vibrational analysis of CGA and its silver complex. From the SERS spectra as well as theoretical calculations, it has been inferred that the molecule is chemisorbed to the silver surface through the oxygen atoms of the carboxylate group.

  11. Study of structural irregularities of smectite clay systems by small-angle neutron scattering and adsorption

    NASA Astrophysics Data System (ADS)

    De Stefanis, A.; Tomlinson, A. A. G.; Steriotis, Th. A.; Charalambopoulou, G. Ch.; Keiderling, U.

    2007-04-01

    Small angle neutron scattering (SANS) and its contrast-matching variant are employed in order to determine structural properties (inter-pillar distances and mass/surface fractal dimensions of the clay layers and pillars) of a series of smectite natural clays (montmorillonite, beidellite, and bentonite) and their pillared and pillared/ion-exchanged analogues. Moreover, a comparative analysis with the adsorption data is carried out on the basis of a systematic study of the structural changes induced by a particular treatment or modification (e.g. pillaring) of the clay systems.

  12. Two-step kinetic study on the adsorption and desorption of reactive dyes at cationic polymer/bentonite.

    PubMed

    Li, Qian; Yue, Qin-Yan; Su, Yuan; Gao, Bao-Yu; Li, Jing

    2009-06-15

    The adsorption kinetics of two reactive dyes, namely, Reactive Blue K-GL and Reactive Yellow K-4G onto the new cationic polymer/bentonite, i.e., polyepicholorohydrin-dimethylamine/bentonite (EPI-DMA/bentonite), were studied under different conditions. The result indicated that the adsorption processes were found to follow the two-step kinetic rate equation with two different adsorption rate constants (k(1) and k(2)) and also to follow the intraparticle diffusion model with two different diffusion rate constants (k(int,1) and k(int,2)). The corresponding values of energies of activation of adsorption, enthalpies of activation and entropies of activation for both the two adsorption kinetic steps have been calculated, suggesting that the adsorption processes were endothermic and physical. The desorption kinetics of two dyes from EPI-DMA/bentonite were studied in NaOH solution with different concentrations, which were also found to obey the two-step kinetic rate equation with two different desorption rate constants (k(d,1) and k(d,2)).

  13. Removal of phenol from aqueous solutions by adsorption onto organomodified Tirebolu bentonite: equilibrium, kinetic and thermodynamic study.

    PubMed

    Senturk, Hasan Basri; Ozdes, Duygu; Gundogdu, Ali; Duran, Celal; Soylak, Mustafa

    2009-12-15

    A natural bentonite modified with a cationic surfactant, cetyl trimethylammonium bromide (CTAB), was used as an adsorbent for removal of phenol from aqueous solutions. The natural and modified bentonites (organobentonite) were characterized with some instrumental techniques (FTIR, XRD and SEM). Adsorption studies were performed in a batch system, and the effects of various experimental parameters such as solution pH, contact time, initial phenol concentration, organobentonite concentration, and temperature, etc. were evaluated upon the phenol adsorption onto organobentonite. Maximum phenol removal was observed at pH 9.0. Equilibrium was attained after contact of 1h only. The adsorption isotherms were described by Langmuir and Freundlich isotherm models, and both model fitted well. The monolayer adsorption capacity of organobentonite was found to be 333 mg g(-1). Desorption of phenol from the loaded adsorbent was achieved by using 20% acetone solution. The kinetic studies indicated that the adsorption process was best described by the pseudo-second-order kinetics (R(2) > 0.99). Thermodynamic parameters including the Gibbs free energy (DeltaG degrees), enthalpy (DeltaH degrees), and entropy (DeltaS degrees) were also calculated. These parameters indicated that adsorption of phenol onto organobentonite was feasible, spontaneous and exothermic in the temperature range of 0-40 degrees C.

  14. Methane adsorption on porous nano-silica in the presence of water: An experimental and ab initio study.

    PubMed

    Wang, Lu; Yu, Qingchun

    2016-04-01

    This study investigated the effects of silanol groups and water content on methane adsorption on hydrophilic nano-silica H-380 through experiments and ab initio calculations. Fourier transform infrared (FTIR) spectroscopy was used to confirm the presence of silanol groups on the solid surface, and the pore size distribution between 0 and 40nm was determined using CO2 and N2 sorption experiments. Ab initio MP2 and complete basis set model (CBS-4) calculations were performed to optimize four different silica surfaces with and without silanol groups using different basis sets. The theoretical calculations and experiments indicated that the adsorption of methane slightly decreased when the water content was low. As the water content increased from 29.03wt% to 40.54wt%, the confined water molecules (water within the pores) promoted the adsorption of CH4 by forming deeper adsorption potential energy wells, thus rendering the system more stable. The experimental isotherms at 308.15-318.15K were obtained over a wide range of water contents up to 75.05wt%. The experimental data are consistent with the theoretical analysis, indicating an increase in the adsorption of CH4 as the water content increased from 39.75wt% to 50.35wt%. Additionally, the adsorption of CH4 sharply decreased when the water content was greater than 63.12wt%. This study contributes essential data on methane-confined H2O interactions on nano-silica surfaces to the scientific literature.

  15. Enhancing adsorption capacity of toxic malachite green dye through chemically modified breadnut peel: equilibrium, thermodynamics, kinetics and regeneration studies.

    PubMed

    Chieng, Hei Ing; Lim, Linda B L; Priyantha, Namal

    2015-01-01

    Breadnut skin, in both its unmodified (KS) and base-modified (BM-KS) forms, was investigated for its potential use as a low-cost adsorbent for the removal of toxic dye, malachite green (MG). Characterization of the adsorbents was carried out using scanning electron microscope, X-ray fluorescence and Fourier transform infra-red spectroscopy. Batch adsorption experiments, carried out under optimized conditions, for the adsorption of MG were fitted using five isotherm models (Langmuir, Freundlich, Dubinin-Radushkevich, Temkin and Sips) and six error functions to determine the best-fit model. The adsorption capacity was greatly enhanced when breadnut skin was chemically modified with NaOH, leading to an adsorption capacity of 353.0 mg g(-1), that was far superior to most reported adsorbents for the removal of MG. Thermodynamics studies indicated that the adsorption of MG was spontaneous on KS and BM-KS, and the reactions were endothermic and exothermic, respectively. Kinetics studies showed that both followed the pseudo-second order. Regeneration experiments on BM-KS indicated that its adsorption capacity was still maintained at>90% even after five cycles. It can be concluded that NaOH-modified breadfruit skin has great potential to be utilized in real-life application as a low-cost adsorbent for the removal of MG in wastewater treatment.

  16. Study of Cs adsorption on (100) surface of [001]-oriented GaN nanowires: A first principle research

    NASA Astrophysics Data System (ADS)

    Xia, Sihao; Liu, Lei; Kong, Yike; Wang, Honggang; Wang, Meishan

    2016-11-01

    Based on first-principle study, the adsorption mechanism of Cs on (100) crystal plane of GaN nanowire surface with coverage of 1/12 monolayer is explored. It is discovered that the most stable adsorption site is BN because of its lowest adsorption energy. The work function of GaN nanowire surface is reduced by 1.69 eV and will be further reduced with increasing Cs adsorption, which promotes the development of negative electron affinity (NEA) state of the materials. Furthermore, Cs adatom will make a great influence on the surface atomic structure, oppositely, little influence on the center atomic structure. There appears a dipole moment valued -6.93 Debye on the nanowire surface contributed to the formation the heterojunction on the surface, which is beneficial to the photoelectrons liberation. After Cs adsorption, the valence band and conduction band both move to lower energy side. The surface states mainly result from the hybridization of Cs 5s state with Ga 4p state and N 2p state. This study can help us to further experiment on the Cs adsorption processing on GaN nanowire and improve the photoemission performance of GaN nanowire devices.

  17. Relationship between the adsorption species of cesium and radiocesium interception potential in soils and minerals: an EXAFS study.

    PubMed

    Fan, Qiaohui; Yamaguchi, Noriko; Tanaka, Masato; Tsukada, Hirofumi; Takahashi, Yoshio

    2014-12-01

    This study examined the radiocesium (RCs) interception potential (RIP), cation exchange capacity (CEC), total organic carbon (TOC) content, and adsorption species in soils and minerals by using extended X-ray absorption fine structure (EXAFS) spectroscopy. The RIP related to Cs(+) adsorption by frayed-edge site (FES) has often been used to measure the mobility and bioavailability of RCs in the environment. This study found that the presence of organic matter (OM) can reduce RIP to a certain extent. The adsorption amount (=Q(T)) in soil was obviously correlated to RIP at a small [Cs(+)] region, whereas a linear relationship between Q(T) and CEC was observed at a large [Cs(+)] region. Both the inner-sphere (IS) and outer-sphere (OS) complexes of Cs(+) were observed through EXAFS at a molecular scale. The linear correlation between log (RIP/CEC) and the ratio of the coordination number (CN) of IS (=CNIS) and OS (=CNOS) complexes noted as CNIS/(CNIS + CNOS) suggested that the ratio of CN is very sensitive to Cs(+) adsorption species with variable RIP and CEC. The adsorption species of Cs(+) in soil was mainly dependent on the clay mineral content of soil. RIP was affected not only by FES but also by other strong adsorption sites, such as the interlayers and cavities identified as the IS complex in EXAFS analysis. Findings indicated that the EXAFS approach is a powerful and efficient tool to explore the behavior of Cs(+) in a given environment.

  18. Adsorption of reactive dyes from aqueous solutions by fly ash: kinetic and equilibrium studies.

    PubMed

    Dizge, N; Aydiner, C; Demirbas, E; Kobya, M; Kara, S

    2008-02-11

    Adsorption kinetic and equilibrium studies of three reactive dyes namely, Remazol Brillant Blue (RB), Remazol Red 133 (RR) and Rifacion Yellow HED (RY) from aqueous solutions at various initial dye concentration (100-500 mg/l), pH (2-8), particle size (45-112.5 microm) and temperature (293-323 K) on fly ash (FA) were studied in a batch mode operation. The adsorbent was characterized with using several methods such as SEM, XRD and FTIR. Adsorption of RB reactive dye was found to be pH dependent but both RR and RY reactive dyes were not. The result showed that the amount adsorbed of the reactive dyes increased with increasing initial dye concentration and contact time. Batch kinetic data from experimental investigations on the removal of reactive dyes from aqueous solutions using FA have been well described by external mass transfer and intraparticle diffusion models. It was found that external mass transfer and intraparticle diffusion had rate limiting affects on the removal process. This was attributed to the relatively simple macropore structure of FA particles. The adsorption data fitted well with Langmuir and Freundlich isotherm models. The optimum conditions for removal of the reactive dyes were 100mg/l initial dye concentration, 0.6g/100ml adsorbent dose, temperature of 293 K, 45 microm particle size, pH 6 and agitation speed of 250 rpm, respectively. The values of Langmuir and Freundlich constants were found to increase with increasing temperature in the range 135-180 and 15-34 mg/g for RB, 47-86 and 1.9-3.7 mg/g for RR and 37-61 and 3.0-3.6 mg/g for RY reactive dyes, respectively. Different thermodynamic parameters viz., changes in standard free energy, enthalpy and entropy were evaluated and it was found that the reaction was spontaneous and endothermic in nature.

  19. Batch studies of adsorption of copper and lead on activated carbon from Eucalyptus camaldulensis dehn. bark.

    PubMed

    Patnukao, Phussadee; Kongsuwan, Apipreeya; Pavasant, Prasert

    2008-01-01

    Powdered activated carbon (PAC) prepared from Eucalyptus camaldulensis Dehn. bark was tested for its adsorption capacity for Cu(II) and Pb(II). The experiment was conducted to investigate the effects of pH, contact time, initial metal concentration, and temperature. The best adsorption of both Cu(II) and Pb(II) occurred at pH 5, where the adsorption reached equilibrium within 45 min for the whole range of initial heavy metal concentrations (0.1-10 mmol/L). The adsorption kinetics was found to follow the pseudo-second order model where equilibrium adsorption capacities and adsorption rate constants increased with initial heavy metal concentrations. The adsorption isotherm followed Langmuir better than Freundlich models within the temperature range (25-60 degrees C). The maximum adsorption capacities (qm) occurred at 60 degrees C, where qm for Cu(II) and Pb(II) were 0.85 and 0.89 mmol/g, respectively. The enthalpies of Cu(II) and Pb(II) adsorption were 43.26 and 58.77 kJ/mol, respectively. The positive enthalpy of adsorption indicated an endothermic nature of the adsorption.

  20. Mechanisms for strong adsorption of tetracycline to carbon nanotubes: a comparative study using activated carbon and graphite as adsorbents.

    PubMed

    Ji, Liangliang; Chen, Wei; Duan, Lin; Zhu, Dongqiang

    2009-04-01

    Significant concerns have been raised over the presence of antibiotics including tetracyclines in aquatic environments. We herein studied single-walled carbon nanotubes (SWNT) and multi-walled carbon nanotubes (MWNT) as potential effective adsorbents for removal of tetracycline from aqueous solution. In comparison, a nonpolar adsorbate, naphthalene, and two other carbonaceous adsorbents, pulverized activated carbon (AC) and nonporous graphite, were used. The observed adsorbent-to-solution distribution coefficient (Kd, L/kg) of tetracycline was in the order of 10(4)-10(6) L/kg for SWNT, 10(3)-10(4) L/kg for MWNT, 10(3)-10(4) L/kg for AC, and 10(3)-10(5) L/kg for graphite. Upon normalization for adsorbent surface area, the adsorption affinity of tetracycline decreased in the order of graphite/ SWNT > MWNT > AC. The weaker adsorption of tetracycline to AC indicates that for bulky adsorbates adsorption affinity is greatly affected by the accessibility of available adsorption sites. The remarkably strong adsorption of tetracycline to the carbon nanotubes and to graphite can be attributed to the strong adsorptive interactions (van der Waals forces, pi-pi electron-donor-acceptor interactions, cation-pi bonding) with the graphene surface. Complexation between tetracycline and model graphene compounds (naphthalene, phenanthrene, pyrene) in solution phase was verified by ring current-induced 1H NMR upfield chemical shifts of tetracycline moieties.

  1. The role of nanostructures and hydrophilicity in osseointegration: In-vitro protein-adsorption and blood-interaction studies.

    PubMed

    Kopf, Brigitte S; Ruch, Sylvie; Berner, Simon; Spencer, Nicholas D; Maniura-Weber, Katharina

    2015-08-01

    Protein adsorption and blood coagulation play important roles in the early stages of osseointegration and are strongly influenced by surface properties. We present a systematic investigation of the influence of different surface properties on the adsorption of the blood proteins fibrinogen and fibronectin and the degree of early blood coagulation. Experiments on custom-made and commercially available, microroughened hydrophobic titanium (Ti) surfaces (Ti SLA-Hphob ), hydrophilic (Hphil ) microroughened Ti surfaces with nanostructures (Ti SLActive-Hphil NS), and on bimetallic Ti zirconium alloy (TiZr, Roxolid®) samples were performed, to study the biological response in relation to the surface wettability and the presence of nanostructures (NS). Protein adsorption on the different substrates showed a highly significant effect of surface NS. Hydrophilicity alone did not significantly enhance protein adsorption. Overall, the combination of NS and hydrophilicity led to the highest adsorption levels; independent of whether Ti or TiZr were used. Hydrophilicity induced a strong effect on blood coagulation, whereas the effect of NS alone was weak. The combination of both surface characteristics led to early and most pronounced blood-coagulation. Therefore, nanostructured, hydrophilic Ti and TiZr surfaces may perform better in terms of osseointegration due to continuous protein adsorption and the formation of a layer of blood components on the implant surface.

  2. Isotherm and thermodynamic studies of Zn (II) adsorption on lignite and coconut shell-based activated carbon fiber.

    PubMed

    Shrestha, Sohan; Son, Guntae; Lee, Seung Hwan; Lee, Tae Gwan

    2013-08-01

    The Zn (II) adsorption capacity of lignite and coconut shell-based activated carbon fiber (ACF) was evaluated as a function of initial Zn (II) concentration, temperature and contact time in batch adsorption process in this study. Adsorption uptake increased with initial Zn (II) concentration and temperature. Optimal contact time for the adsorption of Zn (II) ions onto lignite and coconut shell-based ACF was found to be 50 min. Removal percentage decreased from 88.0% to 78.54% with the increment in initial Zn (II) concentration from 5 to 50 mg L(-1). Equilibrium data fit well with Langmuir-I isotherm indicating homogeneous monolayer coverage of Zn (II) ions on the adsorbent surface. Maximum monolayer adsorption capacity of Zn (II) ions on ACF was found to be 9.43 mg g(-1). Surface morphology and functionality of ACF prior to and after adsorption were characterized by electron microscopy and infrared spectroscopy. Various thermodynamic parameters such as standard Gibbs free energy (ΔG°), standard enthalpy (ΔH°), and standard entropy (ΔS°) were evaluated.

  3. Adsorption study of anionic reactive dye from aqueous solution to Mg-Fe-CO3 layered double hydroxide (LDH)

    NASA Astrophysics Data System (ADS)

    Ahmed, I. M.; Gasser, M. S.

    2012-10-01

    Mg-Fe-Cl Layered double hydroxides (LDHs) have been prepared using a method involving separate nucleation and aging steps with Mg/Fe = 3. The interlayer anions readily replaced by carbonate are characterized by X-ray diffraction (XRD) and FTIR. The effects of different parameters, such as pH, contact time, concentration of dye and temperature on the capacity and adsorption mechanism of Mg-Fe-CO3-LDH in removing an anionic dye (congo red, CR) from aqueous solution were separately investigated. The results show that Mg-Fe-CO3-LDH is particularly efficient in removing CR and the dye removal increases with decreasing pH. The adsorption of CR on Mg-Fe-CO3-LDH reached equilibrium after 15 min where 100 mg/L CR was removed. The equilibrium isotherm indicates that the adsorption of CR onto Mg-Fe-CO3-LDH fits to Langmuir and Freundlich equation as well. The adsorption data obtained from the Langmuir model gave good values of the determination coefficient and the saturated adsorption capacity of Mg-Fe-CO3-LDH for CR was found to be 104.6 mg/g. The regeneration study indicates that the prepared LDH could be used for several cycles. The thermodynamic parameters have been calculated, and the adsorption process was found to be spontaneous, endothermic in nature and follows a pseudo-second-order kinetic model.

  4. Adsorption of cesium from aqueous solution using agricultural residue--walnut shell: equilibrium, kinetic and thermodynamic modeling studies.

    PubMed

    Ding, Dahu; Zhao, Yingxin; Yang, Shengjiong; Shi, Wansheng; Zhang, Zhenya; Lei, Zhongfang; Yang, Yingnan

    2013-05-01

    A novel biosorbent derived from agricultural residue - walnut shell (WS) is reported to remove cesium from aqueous solution. Nickel hexacyanoferrate (NiHCF) was incorporated into this biosorbent, serving as a high selectivity trap agent for cesium. Field emission scanning electron microscope (FE-SEM) and thermogravimetric and differential thermal analysis (TG-DTA) were utilized for the evaluation of the developed biosorbent. Determination of kinetic parameters for adsorption was carried out using pseudo first-order, pseudo second-order kinetic models and intra-particle diffusion models. Adsorption equilibrium was examined using Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherms. A satisfactory correlation coefficient and relatively low chi-square analysis parameter χ(2) between the experimental and predicted values of the Freundlich isotherm demonstrate that cesium adsorption by NiHCF-WS is a multilayer chemical adsorption. Thermodynamic studies were conducted under different reaction temperatures and results indicate that cesium adsorption by NiHCF-WS is an endothermic (ΔH° > 0) and spontaneous (ΔG° < 0) process.

  5. An explanation for differences in the process of colloid adsorption in batch and column studies

    NASA Astrophysics Data System (ADS)

    Treumann, Svantje; Torkzaban, Saeed; Bradford, Scott A.; Visalakshan, Rahul M.; Page, Declan

    2014-08-01

    It is essential to understand the mechanisms that control virus and bacteria removal in the subsurface environment to assess the risk of groundwater contamination with fecal microorganisms. This study was conducted to explicitly provide a critical and systematic comparison between batch and column experiments. The aim was to investigate the underlying factors causing the commonly observed discrepancies in colloid adsorption process in column and batch systems. We examined the colloid adsorption behavior of four different sizes of carboxylate-modified latex (CML) microspheres, as surrogates for viruses and bacteria, on quartz sand in batch and column experiments over a wide range of solution ionic strengths (IS). Our results show that adsorption of colloids in batch systems should be considered as an irreversible attachment because the attachment/detachment model was found to be inadequate in describing the batch results. An irreversible attachment-blocking model was found to accurately describe the results of both batch and column experiments. The rate of attachment was found to depend highly on colloid size, solution IS and the fraction of the sand surface area favorable for attachment (Sf). The rate of attachment and Sf values were different in batch and column experiments due to differences in the hydrodynamic of the system, and the role of surface roughness and pore structure on colloid attachment. Results from column and batch experiments were generally not comparable, especially for larger colloids (≥ 0.5 μm). Predictions based on classical DLVO theory were found to inadequately describe interaction energies between colloids and sand surfaces.

  6. An explanation for differences in the process of colloid adsorption in batch and column studies.

    PubMed

    Treumann, Svantje; Torkzaban, Saeed; Bradford, Scott A; Visalakshan, Rahul M; Page, Declan

    2014-08-01

    It is essential to understand the mechanisms that control virus and bacteria removal in the subsurface environment to assess the risk of groundwater contamination with fecal microorganisms. This study was conducted to explicitly provide a critical and systematic comparison between batch and column experiments. The aim was to investigate the underlying factors causing the commonly observed discrepancies in colloid adsorption process in column and batch systems. We examined the colloid adsorption behavior of four different sizes of carboxylate-modified latex (CML) microspheres, as surrogates for viruses and bacteria, on quartz sand in batch and column experiments over a wide range of solution ionic strengths (IS). Our results show that adsorption of colloids in batch systems should be considered as an irreversible attachment because the attachment/detachment model was found to be inadequate in describing the batch results. An irreversible attachment-blocking model was found to accurately describe the results of both batch and column experiments. The rate of attachment was found to depend highly on colloid size, solution IS and the fraction of the sand surface area favorable for attachment (Sf). The rate of attachment and Sf values were different in batch and column experiments due to differences in the hydrodynamic of the system, and the role of surface roughness and pore structure on colloid attachment. Results from column and batch experiments were generally not comparable, especially for larger colloids (≥0.5μm). Predictions based on classical DLVO theory were found to inadequately describe interaction energies between colloids and sand surfaces.

  7. Quantum Mechanical Study of N-Heterocyclic Carbene Adsorption on Au Surfaces.

    PubMed

    Chang, Kuan; Chen, Jingguang G; Lu, Qi; Cheng, Mu-Jeng

    2017-03-27

    There is increasing interest in using N-heterocyclic carbenes (NHCs) as surface ligands to stabilize transition-metal nanoparticles (NPs) and to replace thiols for the preparation of self-assembled monolayers (SAMs) on gold surfaces. This type of surface decoration is advantageous because it leads to improved catalytic activity of NPs and increased stability of SAM, as shown by recent experiments. In this work, we used quantum mechanics combined with periodic surface models to study the adsorption of NHCs on the Au(111) surface. We found that NHCs prefer to bind to the top site with adsorption energies (ΔEs) varying from 1.69 to 2.34 eV, depending on the type of NHC, and the inclusion of solvents in the calculations leads to insignificant variation in the calculated ΔEs. Three types of NHCs were found to bind to Au(111) more tightly and therefore should be better stabilizers than those commonly used. Importantly, by analyzing electronic structures using the Bader charge and energy decomposition analysis, we find that during adsorption NHC acts as an electron donor, transferring its electron density from the lone pair orbital at the carbene center to the empty d orbital of Au with negligible π-back-donation. This binding pattern is very different from that of CO, a ligand commonly used in organometallics, where both interactions are equally important. This leads to the identification of the protonation energies of NHCs as a descriptor for predicting ΔEs, providing a convenient method for computational high-throughput screening for better NHC-type surface ligands.

  8. Equilibrium and kinetics of water adsorption in carbon molecular sieve: theory and experiment.

    PubMed

    Rutherford, S W; Coons, J E

    2004-09-28

    Measurements of water adsorption equilibrium and kinetics in Takeda carbon molecular sieve (CMS) were undertaken in an effort to characterize fundamental mechanisms of adsorption and transport. Adsorption equilibrium revealed a type III isotherm that was characterized by cooperative multimolecular sorption theory. Water adsorption was found to be reversible and did not display hysteresis upon desorption over the conditions studied. Adsorption kinetics measurements revealed that a Fickian diffusion mechanism governed the uptake of water and that the rate of adsorption decreased with increasing relative pressure. Previous investigations have attributed the observed decreasing trend in the rate of adsorption to blocking of micropores. Here, it is proposed that the decrease is attributed to the thermodynamic correction to Fick's law which is formulated on the basis of the chemical potential as the driving force for transport. The thermodynamically corrected formulation accounted for observations of transport of water and other molecules in CMS.

  9. Surfactant loss control in chemical flooding: Spectroscopic and calorimetric study of adsorption and precipitation on reservoir minerals. Annual report, September 30, 1992--September 30, 1993

    SciTech Connect

    Somasundaran, P.

    1994-07-01

    The aim of this research project is to investigate mechanisms underlying adsorption and surface precipitation of flooding surfactants on reservoir minerals. Effects of surfactant structure, surfactant combinations, various inorganic and polymeric species, and solids mineralogy will be determined. A multi-pronged approach consisting of micro & nano spectroscopy, microcalorimetry, electrokinetics, surface tension and wettability; is used in this study. The results obtained should help in controlling surfactant loss in chemical flooding and in developing optimum structures and conditions for efficient chemical flooding processes. During the first year of this three year contract, adsorption of single surfactants and select surfactant mixtures was studied at the solid-liquid and gas-liquid interfaces. Surfactants studied include alkyl xylene sulfonates, polyethoxylated alkyl phenols, octaethylene glycol mono n-decyl ether, and tetradecyl trimethyl ammonium chloride. Adsorption of surfactant mixtures of varying composition was also investigated. The microstructure of the adsorbed layer was characterized using fluorescence spectroscopy. Changes interfacial properties such as wettability, electrokinetics and stability of reservoir minerals were correlated with the amount of reagent adsorbed. Strong effects of the structure of the surfactant and position of functional groups were revealed.

  10. Adsorption of small molecules on helical gold nanorods: a relativistic density functional study.

    PubMed

    Liu, Xiao-Jing; Hamilton, Ian

    2014-10-15

    We study the adsorption of a variety of small molecules on helical gold nanorods using relativistic density functional theory. We focus on Au40 which consists of a central linear strand of five gold atoms with seven helical strands of five gold atoms on a coaxial tube. All molecules preferentially adsorb at a single low-coordinated gold atom on the coaxial tube at an end of Au40. In most cases, there is significant charge transfer (CT) between Au40 and the adsorbate, for CO and NO2, there is CT from the Au40 to adsorbate while for all other molecules there is CT from the adsorbate to Au40. Thus, Au40-adsorbate can be described as a donor-accepter complex and we use charge decomposition analysis to better understand the adsorption process. We determine the adsorption energy order to be C5H5N >NO2  > CO > NH3  > CH2=CH2  > CH2=CH-CHO > NO > HC≡CH > H2S > SO2  > HCN > CH3OH > H2C=O > O2  > H2O > CH4  > N2. We find that the Au-C, Au-N, Au-S, and Au-O bonds are surprisingly strong, with clear implications for reactivity enhancement of the adsorbate. The Au-H bond is relatively weak but, for interactions via an H atom that is bonded to a carbon atom (e.g., CH4), we find that there is large charge polarization of the Au-H-C moiety and partial activation of the inert C-H bond. Although the Au-S and Au-O bonds are generally weaker than the Au-C and Au-N bonds, we find that adsorption of H2S or H2O causes greater distortion of Au40 in the binding region. However, the degree of distortion is small and the helical structure is retained, demonstrating the stability of the helical Au40 nanorod under perturbations.

  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. Analytical study of a gas-fired adsorptive air-conditioning system

    SciTech Connect

    Poyelle, F.; Guilleminot, J.J.; Meunier, F.

    1996-11-01

    Adsorptive air conditioning represents a potential alternative to chlorofluorocarbon (CFC) systems. But to compete with other systems, adsorption systems must exhibit sufficient figures of merit and energetic densities. An analytical study to predict the overall heat transfer coefficient in an adsorber has been conducted and is presented here. This study, based on a method-of-moment analysis, shows the influence of three parameters limiting the heat transfer in adsorbent beds. Heat transfer in adsorbent beds has been intensified. Using new consolidated materials, the machine utilizes two uniform temperature adsorbent beds in a cycle that incorporates both heat and mass recovery. It uses a zeolite-water pair. It is designed to produce 3 kW of cooling. Expected cooling performances are 300 W/kg of adsorbent with a coefficient of performance (COP) close to 0.8 and a cycle time of 20 minutes. The thermal conditions used to test the cycle are: the heater, 220 C; the cooler, 40 C; and the evaporation temperature, 3 C.

  13. Platinum adsorption on ceria: A comparative theoretical study of different surfaces

    NASA Astrophysics Data System (ADS)

    Ma, Dongwei; Li, Tingxian; Wang, Qinggao; Yang, Gui; He, Chaozheng; He, Bingling; Lu, Zhansheng; Yang, Zongxian

    2017-02-01

    A comparative study, based on the density functional theory, on the adsorption of single Pt atoms on the CeO2(111), (110), and (100) surfaces has been performed. According to the calculated adsorption energies, it is suggested that the deposited Pt atoms on the CeO2(111) surface are easy to aggregate and form nanoparticles compared with those on the CeO2(110) and (100) surfaces. Further, the interaction strength between Pt and the three CeO2 surfaces follows the order of (100) > (110) > (111). It is also found that there is a correlation between the formal oxidation state of the adsorbed Pt and its coordination number with respect to O. The Pt atom coordinated by one O atom on the CeO2 surfaces is only slightly charged and almost neutral, and that coordinately by four O atoms exclusively has the formal oxidation state of Pt2+. The possible reasons for these findings have been discussed. And the present theoretical results have been compared with the available experimental reports. It is expected that our studies will give useful insights into the shape-dependent interaction between Pt with CeO2 nanocrystals and the shape-dependent oxidation state of the deposited Pt.

  14. Statistical physics studies of multilayer adsorption isotherm in food materials and pore size distribution

    NASA Astrophysics Data System (ADS)

    Aouaini, F.; Knani, S.; Ben Yahia, M.; Ben Lamine, A.

    2015-08-01

    Water sorption isotherms of foodstuffs are very important in different areas of food science engineering such as for design, modeling and optimization of many processes. The equilibrium moisture content is an important parameter in models used to predict changes in the moisture content of a product during storage. A formulation of multilayer model with two energy levels was based on statistical physics and theoretical considerations. Thanks to the grand canonical ensemble in statistical physics. Some physicochemical parameters related to the adsorption process were introduced in the analytical model expression. The data tabulated in literature of water adsorption at different temperatures on: chickpea seeds, lentil seeds, potato and on green peppers were described applying the most popular models applied in food science. We also extend the study to the newest proposed model. It is concluded that among studied models the proposed model seems to be the best for description of data in the whole range of relative humidity. By using our model, we were able to determine the thermodynamic functions. The measurement of desorption isotherms, in particular a gas over a solid porous, allows access to the distribution of pore size PSD.

  15. Speciation study of aluminium in beverages by Competitive Ligand Exchange-Adsorptive Stripping Voltammetry.

    PubMed

    Magnier, A; Fekete, V; Van Loco, J; Bolle, F; Elskens, M

    2014-05-01

    Competitive Ligand Exchange-Adsorptive Stripping Voltammetry (CLE-AdSV) was used for determining the speciation of aluminium in commonly consumed beverages (water, tea, infusion, coffee, orange juice, tomato juice, beer and red wine). Aluminium determination involves the adsorption of Al-complexes with the ligand cupferron onto a hanging mercury drop electrode. All samples were studied at pH 6.5 with an accumulation step at -0.60 V (all potential values in the paper are given versus the Ag/AgCl, [KCl]=3 M reference electrode) during 60 s, and a final cupferron concentration of 4 × 10(-4)M. These conditions were used to establish (i) the concentration of electro-labile aluminium, (ii) the range of ligand concentrations and (iii) the conditional stability constants of beverage samples using titration procedures. The results based on Ruzic plots were compared to computer simulation with Visual MINTEQ. This comparison suggests that labile monomeric Al-forms and soluble organic complexes of low molecular weight can be quantified by the CLE-AdSV procedure. Overall the relative uncertainties on the determination of the electro-active Al fraction and the complexing parameters, i.e., concentration and conditional stability constant of natural ligands in the samples, are less than 15%. Thanks to these results, information on Al bioavailability in beverages was collected and discussed. This study also illustrates the value of computer simulations when complex, time-consuming voltammetric techniques are applied.

  16. CO/Pt(111) : GGA density functional study of site preference for adsorption

    NASA Astrophysics Data System (ADS)

    Alaei, M.; Akbarzadeh, H.; Gholizadeh, H.; de Gironcoli, S.

    2008-02-01

    Based on density functional formalism, we investigate the site preference for the adsorption of CO on Cu, Rh, Ag, Pt, and Au(111) surfaces. The exchange-correlation term was approximated by BLYP, a functional within the generalized gradient approximation (GGA) family that combines Becke’s exchange functional with the Lee-Yang-Parr correlation functional. Our study shows that BLYP, although not a hybrid functional, can correctly predict the adsorption site for CO. This invalidate the general belief that only hybrid functionals are able to predict the correct site preference. We analyze our results by repeating all calculations using another well-known GGA functional, Perdew-Burke-Ernzerhof, which could trace back the origin of the success of BLYP to the different behavior of the two GGA functionals at large values of the reduced density gradients, s∝(∣∇n∣)/(n3/4) . This is a region where different functionals in the GGA family may legitimately behave very differently as it is poorly constrained on physical ground. Our present observation points to the possibility of further improving the accuracy of exchange-correlation functionals in the GGA family by properly constraining the remaining flexibility in the exchange-correlation kernel in this underdetermined region so as to reproduce known results in simple but critically important systems like the one studied here.

  17. Lithium ion adsorption and diffusion on black phosphorene nanotube: A first-principles study

    NASA Astrophysics Data System (ADS)

    Cao, Jin; Shi, Jing; Hu, Yinquan; Wu, Musheng; Ouyang, Chuying; Xu, Bo

    2017-01-01

    Li ion storage performance of the single-walled black phosphorene nanotube (PNT), which is considered as potential anode materials for high-performance Li-ion batteries (LIBs), is studied from first-principles calculations. The Li ion adsorption, diffusion and structural evolution of the one-dimensional armchair type PNT (aPNT) upon Li intercalation on the inside (in-PNT) and outside (out-PNT) surfaces were explored, comparing with that of the two-dimensional phosphorene (Psheet). A maximum Li storage capacity (at the intercalated state of Li22P44) is evaluated to be 432 mAh/g. It is also shown that the in-PNT system has higher adsorption energy and lower Li diffusion energy barrier compared with that of the Psheet and the out-PNT systems. The reason on why the better Li storage performance of the in-PNT is also studied from charge distribution and transfer analysis. These results suggest that PNT can be served as potential anode material for LIBs.

  18. Computational studies of adsorption in metal organic frameworks and interaction of nanoparticles in condensed phases

    SciTech Connect

    Annapureddy, Harsha V.; Motkuri, Radha K.; Nguyen, Phuong T.; Truong, T. B.; Thallapally, Praveen K.; McGrail, B. Peter; Dang, Liem X.

    2014-01-08

    In this review, we describe recent efforts in which computer simulations were used to systematically study nano-structured metal organic frameworks, with particular emphasis on their application in heating and cooling processes. These materials also are known as metal organic heat carriers. We used both molecular dynamics and Grand Canonical Monte Carlo simulation techniques to gain a molecular-level understanding of the adsorption mechanism of gases in these porous materials. We investigated the uptake of various gases such as refrigerants R12 and R143a and also the elemental gases Xe and Rn by the metal organic framework (i.e., Ni2(dhtp)). We also evaluated the effects of temperature and pressure on the uptake mechanism. Our computed results compared reasonably well with available experimental measurements, thus validating our potential models and approaches. In addition, we also investigated the structural, diffusive, and adsorption properties of different hydrocarbons in Ni2(dhtp). To elucidate the mechanism of nanoparticle dispersion in condensed phases, we also studied the interactions among nanoparticles in various liquids, such as n-hexane, water and methanol. This work was performed at Pacific Northwest National Laboratory (PNNL) and was supported by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy (DOE). PNNL is operated by Battelle for the DOE. The authors also gratefully acknowledge support received from the National Energy Technology Laboratory of DOE's Office of Fossil Energy.

  19. A comparative study of CO adsorption on tetrahexahedral Pt nanocrystals and interrelated Pt single crystal electrodes by using cyclic voltammetry and in situ FTIR spectroscopy.

    PubMed

    Liu, Hai-Xia; Tian, Na; Ye, Jin-Yu; Lu, Bang-An; Ren, Jie; Huangfu, Zhi-Chao; Zhou, Zhi-You; Sun, Shi-Gang

    2014-01-01

    This study focuses on CO adsorption at tetrahexahedral Pt nanocrystals (THH Pt NCs) by using cyclic voltammetry and in situ FTIR spectroscopy. Since the electrochemically prepared THH Pt NCs in this study are enclosed by {730} facets which could be considered by a subfacet configuration of 2{210} + {310}, we have also studied CO adsorption on the interrelated Pt(310) and Pt(210) single crystal electrodes as a comparison. Cyclic voltammetry results demonstrated that CO adsorbs dominantly on the (100) sites of THH Pt NCs at low CO coverage (θ(CO)≤ 0.135), while on both (100) and (110) sites at higher CO coverage. On ordered Pt(310) and Pt(210), i.e. they were flame annealed and then cooled in H(2) + Ar, CO adsorption also illustrates relative priority on (100) sites at low CO coverage; while at high CO coverage or on oxygen-disordered Pt(310) and Pt(210) when they were cooled in air after flame annealing, the adsorption of CO presents a weak preference on (100) sites of Pt(310) and even no preference at all on (100) sites of Pt(210). In situ FTIR spectroscopic studies illustrated that CO adsorption on THH Pt NCs yields anomalous infrared effects (AIREs), which are depicted by the Fano-like IR feature on a dense distribution (60 μm(-2)) and the enhancement of abnormal IR absorption on a sparse distribution (22 μm(-2)) of THH Pt NCs on glassy carbon substrate. Systematic investigation of CO coverage dependence of IR features revealed that, on THH Pt NCs, the IR band center (ν(COL)) of linearly bonded CO (COL) is rapidly shifted to higher wavenumbers along with the increase of CO coverage to 0.184, yielding a fast linear increase rate with a high slope (dν(COL)/dθ(IR)(CO) = 219 cm(-1)); when θ > 0.184, the increase of ν(COL) with θCO slows down and deviates drastically from linearity. In contrast, the ν(COL) on the ordered Pt(310) electrode maintains a linear increase with θ(IR)(CO) for the whole range of θ(IR)(CO) variation, and gives a much smaller

  20. Study on the electronic properties and molecule adsorption of W18O49 nanowires as a catalyst support in the cathodes of direct methanol fuel cells

    NASA Astrophysics Data System (ADS)

    Karim, N. A.; Kamarudin, S. K.; Shyuan, L. K.; Yaakob, Z.; Daud, W. R. W.; Kadhum, A. A. H.

    2015-08-01

    Catalyst supports have been used to increase the catalytic activity of reactions in the cathode of Direct Methanol Fuel Cells (DMFCs). The properties of tungsten oxide (W18O49) nanowires were studied, and their adsorption capability was evaluated using density functional theory. The electronic properties of the bulk material and two different diameter nanowires were calculated. Moreover, the molecules involved in adsorption were carbon monoxide, methanol, oxygen and hydrogen peroxide. The results showed that the high adsorption energy produced is primarily the result of the adsorption of methanol, followed by that of hydrogen peroxide, carbon monoxide and oxygen. The negative adsorption energies obtained showed that the adsorption reactions were exothermic, and only oxygen was stable. Therefore, a new surface model was described where cobalt atoms were adsorbed on tungsten atoms on the surface of a 12 Å nanowire. In this new nanowire doped with cobalt atoms, the adsorption energy was reduced.

  1. Response surface optimization of a dynamic dye adsorption process: a case study of crystal violet adsorption onto NaOH-modified rice husk.

    PubMed

    Chowdhury, Shamik; Chakraborty, Sagnik; Saha, Papita Das

    2013-03-01

    The adsorption of crystal violet from aqueous solution by NaOH-modified rice husk was investigated in a laboratory-scale fixed-bed column. A two-level three factor (2(3)) full factorial central composite design with the help of Design Expert Version 7.1.6 (Stat Ease, USA) was used for optimisation of the dynamic dye adsorption process and evaluation of interaction effects of different operating parameters: initial dye concentration (100-200 mg L(-1)), flow rate (10-30 mL min(-1)) and bed height (5-25 cm). A correlation coefficient (R (2)) value of 0.999, model F value of 1,936.59 and its low p value (<0.0001) along with lower value of coefficient of variation (1.38 %) indicated the fitness of the response surface quadratic model developed during the present study. Numerical optimisation applying desirability function was used to identify the optimum conditions for a targeted breakthrough time of 12 h. The optimum conditions were found to be initial solution pH=8.00, initial dye concentration=100 mg L(-1), flow rate=22.88 mL min(-1) and bed height=18.75 cm. A confirmatory experiment was performed to evaluate the accuracy of the optimised procedure. Under the optimised conditions, breakthrough appeared after 12.2 h and the column efficiency was determined as 99 %. The Thomas model showed excellent fit to the dynamic dye adsorption data obtained from the confirmatory experiment. Thereby, it was concluded that the current investigation gives valuable insights for designing and establishing a continuous wastewater treatment plant.

  2. Adsorption of Pb(II) on mesoporous activated carbons fabricated from water hyacinth using H3PO4 activation: Adsorption capacity, kinetic and isotherm studies

    NASA Astrophysics Data System (ADS)

    Huang, Yang; Li, Shunxing; Chen, Jianhua; Zhang, Xueliang; Chen, Yiping

    2014-02-01

    Activated carbons with high mesoporosity and abundant oxygen-containing functional groups were prepared from water hyacinth using H3PO4 activation (WHAC) to eliminate Pb(II) in water. Characterizations of the WHAC were performed using Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The BET analysis showed that WHAC possesses a high mesoporosity (93.9%) with a BET surface area of 423.6 m2/g. The presence of oxygen-containing functional groups including hydroxyl, carbonyl, carboxyl and phosphate groups renders the WHAC a favorable adsorbent for Pb(II) with the maximum monolayer capacity (qm) 118.8 mg/g. The adsorption behavior follows pseudo-first order kinetic and Langmuir isotherm. The desorption study demonstrated that the WHAC could be readily regenerated using 0.1 M HCl (pH = 1.0). The desorbed WHAC could be reused at least six times without significant adsorption capacity reduction. The adsorption process was spontaneous and endothermic with ΔG (-0.27, -1.13, -3.02, -3.62, -5.54, and -9.31 kJ/mol) and ΔH (38.72 kJ/mol). Under the optimized conditions, a small amount of the adsorbent (1.0 g/L) could remove as much as 90.1% of Pb(II) (50 mg/L) in 20 min at pH 6.0 and temperature of 298 K. Therefore, the WHAC has a great potential to be an economical and efficient adsorbent in the treatment of lead-contaminated water.

  3. Adsorption and Quantum Chemical Studies on the Inhibition Potentials of Some Thiosemicarbazides for the Corrosion of Mild Steel in Acidic Medium

    PubMed Central

    Ebenso, Eno E.; Isabirye, David A.; Eddy, Nnabuk O.

    2010-01-01

    Three thiosemicarbazides, namely 2-(2-aminophenyl)-N phenylhydrazinecarbothioamide (AP4PT), N,2-diphenylhydrazinecarbothioamide (D4PT) and 2-(2-hydroxyphenyl)-N-phenyl hydrazinecarbothioamide (HP4PT), were investigated as corrosion inhibitors for mild steel in H2SO4 solution using gravimetric and gasometric methods. The results revealed that they all inhibit corrosion and their % inhibition efficiencies (%IE) follow the order: AP4PT > HP4PT > D4PT. The %IE obtained from the gravimetric and gasometric experiments were in good agreement. The thermodynamic parameters obtained support a physical adsorption mechanism and the adsorption followed the Langmuir adsorption isotherm. Some quantum chemical parameters were calculated using different methods and correlated with the experimental %IE. Quantitative structure activity relationship (QSAR) approach was used on a composite index of some quantum chemical parameters to characterize the inhibition performance of the studied molecules. The results showed that the %IE were closely related to some of the quantum chemical parameters, but with varying degrees. The calculated/theoretical %IE of the molecules were found to be close to their experimental %IE. The local reactivity has been studied through the Fukui and condensed softness indices in order to predict both the reactive centers and to know the possible sites of nucleophilic and electrophilic attacks. PMID:20640164

  4. Adsorption and quantum chemical studies on the inhibition potentials of some thiosemicarbazides for the corrosion of mild steel in acidic medium.

    PubMed

    Ebenso, Eno E; Isabirye, David A; Eddy, Nnabuk O

    2010-06-15

    Three thiosemicarbazides, namely 2-(2-aminophenyl)-N phenylhydrazinecarbothioamide (AP4PT), N,2-diphenylhydrazinecarbothioamide (D4PT) and 2-(2-hydroxyphenyl)-N-phenyl hydrazinecarbothioamide (HP4PT), were investigated as corrosion inhibitors for mild steel in H(2)SO(4) solution using gravimetric and gasometric methods. The results revealed that they all inhibit corrosion and their % inhibition efficiencies (%IE) follow the order: AP4PT > HP4PT > D4PT. The %IE obtained from the gravimetric and gasometric experiments were in good agreement. The thermodynamic parameters obtained support a physical adsorption mechanism and the adsorption followed the Langmuir adsorption isotherm. Some quantum chemical parameters were calculated using different methods and correlated with the experimental %IE. Quantitative structure activity relationship (QSAR) approach was used on a composite index of some quantum chemical parameters to characterize the inhibition performance of the studied molecules. The results showed that the %IE were closely related to some of the quantum chemical parameters, but with varying degrees. The calculated/theoretical %IE of the molecules were found to be close to their experimental %IE. The local reactivity has been studied through the Fukui and condensed softness indices in order to predict both the reactive centers and to know the possible sites of nucleophilic and electrophilic attacks.

  5. Minimizing adsorption of histidine-tagged proteins for the study of protein-deoxyribonucleic acid interactions by kinetic capillary electrophoresis.

    PubMed

    Liyanage, Ruchi; Krylova, Svetlana M; Krylov, Sergey N

    2013-12-27

    Affinity interactions between DNA and proteins play a crucial role in many cellular processes. Kinetic Capillary Electrophoresis is a highly efficient tool for kinetic and equilibrium studies of protein-DNA interactions. Recombinant proteins, which are typically used for in vitro studies of protein-DNA interactions, are often expressed with a His tag to aid in their purification. In this work, we study how His tags affect Kinetic Capillary Electrophoresis analysis of protein-DNA interactions. We found that the addition of a His tag can increase or decrease protein adsorption to a bare-silica capillary wall, dependent on the protein. For Kinetic Capillary Electrophoresis measurements, it is essential to have as little protein adsorption as possible. We screened a number of capillary coatings to reduce adsorption of the His-tagged DNA mismatch repair protein MutS to the capillary wall and found that UltraTrol LN was the most effective coating. The effectiveness of the coating was confirmed with the prevention of adsorption of His-tagged fat mass and obesity-associated protein. Under typical conditions, the coating reduced protein adsorption to a level at which accurate Kinetic Capillary Electrophoresis analysis of protein-DNA interactions was possible. We further used Kinetic Capillary Electrophoresis to study how the His tag affected Kd of protein-DNA interactions for the MutS protein. Using UltraTrol LN, we found that the effect of the His tag was insignificant.

  6. The study of dehumidifying of carbon monoxide and ammonia adsorption by Iranian natural clinoptilolite zeolite

    NASA Astrophysics Data System (ADS)

    Tehrani, R. M. A.; Salari, A. A.

    2005-10-01

    The natural zeolite (clinoptilolite type) was obtained from the Neibagh region of Mianeh, the city in the west of Iran. The raw zeolite was tested for quality and quantity measurements including surface area and volumetric characteristics as well as thermogravimetry analysis. The acid activation process was used to increase the adsorption rate of zeolite and in order to obtain the optimum conditions: the effect of acid concentration, reaction time and the temperature were studied. A surface area measurement test was performed in each stage to get the best results. Thus, efficient condition was selected according to the produced highest surface area. The reaction was first obtained with hydrochloric acid, and then a comparison was made using the sulfuric acid. The hydrochloric reaction proved to be better. The result of activation was 2.5 times the increase in the surface area in relation to the raw sample. The result of elemental analysis conducted once again on the activated sample showed an increase in the ratio of Si/Al (approximately 0.6). Then, using CO, NH 3 and steam, the gas adsorption capacity of both the raw and activated samples was measured and compared. Since CO was not adsorbed at ambient temperature, but steam was adsorbed relatively well, the natural clinoptilolite zeolite of Iran was suggested as a suitable material for adsorbing humidity form carbon monoxide as well as synthesis gas (H 2 and CO mixture).

  7. An XPS study for mechanisms of arsenate adsorption onto a magnetite-doped activated carbon fiber.

    PubMed

    Zhang, Shujuan; Li, Xiao-yan; Chen, J Paul

    2010-03-01

    The surface and bulk structures of a newly developed carbon-based iron-containing adsorbent for As(V) adsorption were investigated by using X-ray diffraction (XRD), field emission scanning electronic microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). XRD patterns of the adsorbents indicated that the modified activated carbon fiber (MACF) was a simple mixture of the raw activated carbon fiber (RACF) and magnetite. After modification, a porous film was formed on the surface of the MACF with nano-sized magnetite on it. The As(V) uptake on the MACF was highly pH dependent and was facilitated in acidic solutions. XPS studies demonstrated that the surface oxygen-containing functional groups were involved in the adsorption and that magnetite played a key role in As(V) uptake. The dominance of HAsO(4)(2-) in surface complexes and the pH effect on As(V) uptake demonstrated that the monoprotonated bidentate complexes were dominant on the surface of the MACF. No reduction of As(V) was observed on the surface of the ACFs.

  8. A Case Study of a Low Power Vapour Adsorption Refrigeration System

    NASA Astrophysics Data System (ADS)

    Dinesh, Banala; Sai Manikanta, M.; Dishal Kumar, T.; Sahu, Debjyoti

    2016-09-01

    Industrial refrigeration is one of the most energy consuming sector. In conventional Vapor Compression refrigeration system, compressor is the major power consuming element. Vapor Adsorption refrigeration system is one of the best replacement for the Vapor Compression refrigeration system. Our main objective is to analyze, design and develop a Vapor Adsorption refrigeration system which is cost effective and environmental friendly. A prototype model that is capable of producing a temperature drop in closed evaporator chamber was designed, fabricated and tested. Activated carbon/Methanol pair is chosen as Adsorbent/Refrigerant pair. The system is analyzed in ANSYS 14.5 using the inlet conditions obtained from the experimental setup. The performances and effectiveness of the unit was studied by determining Refrigeration Effect (RE), Coefficient of Performance (COP) and explaining operational issues of the unit. The results obtained from the analysis and experiments have marginal difference in COP i.e. with an error percentage of 5.94%. The overall COP obtained is 0.34 through experiments and from analysis the COP obtained is approximately 0.32.

  9. Adsorption of methylene blue onto bamboo-based activated carbon: kinetics and equilibrium studies.

    PubMed

    Hameed, B H; Din, A T M; Ahmad, A L

    2007-03-22

    Bamboo, an abundant and inexpensive natural resource in Malaysia was used to prepare activated carbon by physiochemical activation with potassium hydroxide (KOH) and carbon dioxide (CO(2)) as the activating agents at 850 degrees C for 2h. The adsorption equilibrium and kinetics of methylene blue dye on such carbon were then examined at 30 degrees C. Adsorption isotherm of the methylene blue (MB) on the activated carbon was determined and correlated with common isotherm equations. The equilibrium data for methylene blue adsorption well fitted to the Langmuir equation, with maximum monolayer adsorption capacity of 454.2mg/g. Two simplified kinetic models including pseudo-first-order and pseudo-second-order equation were selected to follow the adsorption processes. The adsorption of methylene blue could be best described by the pseudo-second-order equation. The kinetic parameters of this best-fit model were calculated and discussed.

  10. [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.

  11. Study and numerical solution of a generalized mathematical model of isothermal adsorption

    SciTech Connect

    Komissarov, Yu.A.; Vetokhin, V.N.; Tsenev, V.A.; Gordeeva, E.L.

    1995-06-01

    A generalized mathematical model of isothermal adsorption that takes into account mass transfer on the surface of a particle, diffusion in micro- and macropores, and dispersion along the length of the apparatus is considered The parameters {lambda} and {var_phi}{sup 2} determine the dominating effect of any of the mass transfer mechanisms of the adsorption process. A numerical algorithm for solving the generalized adsorption model is suggested.

  12. [Adsorption kinetic and thermodynamic studies of lead onto activated carbons from cotton stalk].

    PubMed

    Li, Kun-quan; Zheng, Zheng; Jiang, Jian-chun; Zhang, Ji-biao

    2010-05-01

    Low-cost high surface area microporous carbons were prepared from cotton stalk and cotton stalk fiber by H3PO4 activation. The adsorption of lead ions on the carbons was investigated by conducting a series of batch adsorption experiments. The influence of solution pH value, contact time and temperature was investigated. The adsorption kinetics, thermodynamic behavior and mechanism were also discussed. The surface area and pore structure of the activated carbons were analyzed by BET equation, BJH method and H-K method according to the data from nitrogen adsorption at 77K. Boehm titration, Fourier transform infrared spectroscopy (FTIR), the point of zero charge (pH(PZC)) measurement and elemental analysis were used to characterize the surface properties. The results show that the carbons from cotton stalk and cotton stalk fiber have high surface area of 1570 and 1731 m2 x g(-1), and high content of oxygen-containing functional groups of 1.43 and 0.83 mmol x g(-1). The adsorption experiments show that the carbons have high adsorption capacity for lead, and the maximum adsorption equilibrium amount was found to be 120 mg x g(-1). The adsorption amount increased with contact time, and almost 80% of the adsorption occurred in the first 5 min. The pseudo-second-order model describes the adsorption kinetics most effectively. The Freundlich isotherm was found to the best explanation for experimental data. The negative change in free energy (delta G0) and positive change in enthalpy (delta H0) indicate that the adsorption is a spontaneous and endothermic process, and the adsorption of lead ions onto the carbons might be involved in an ion-exchange mechanism.

  13. The influence of the potassium promoter on the kinetics and thermodynamics of CO adsorption on a bulk iron catalyst applied in Fischer-Tropsch synthesis: a quantitative adsorption calorimetry, temperature-programmed desorption, and surface hydrogenation study.

    PubMed

    Graf, Barbara; Muhler, Martin

    2011-03-07

    The adsorption of carbon monoxide on an either unpromoted or potassium-promoted bulk iron catalyst was investigated at 303 K and 613 K by means of pulse chemisorption, adsorption calorimetry, temperature-programmed desorption and temperature-programmed surface reaction in hydrogen. CO was found to adsorb mainly molecularly in the absence of H(2) at 303 K, whereas the presence of H(2) induced CO dissociation at higher temperatures leading to the formation of CH(4) and H(2)O. The hydrogenation of atomic oxygen chemisorbed on metallic iron was found to occur faster than the hydrogenation of atomically adsorbed carbon. At 613 K CO adsorption occurred only dissociatively followed by recombinative CO(2) formation according to C(ads) + 2O(ads)→ CO(2(g)). The presence of the potassium promoter on the catalyst surface led to an increasing strength of the Fe-C bond both at 303 K and 613 K: the initial differential heat of molecular CO adsorption on the pure iron catalyst at 303 K amounted to 102 kJ mol(-1), whereas it increased to 110 kJ mol(-1) on the potassium-promoted sample, and the initial differential heat of dissociative CO adsorption on the unpromoted iron catalyst at 613 K amounted to 165 kJ mol(-1), which increased to 225 kJ mol(-1) in the presence of potassium. The calorimetric CO adsorption experiments also reveal a change of the energetic distribution of the CO adsorption sites present on the catalyst surface induced by the potassium promoter, which was found to block a fraction of the CO adsorption sites.

  14. Adsorptive removal of α-endosulfan from water by hydrophobic zeolites. An isothermal study.

    PubMed

    Yonli, Arsène H; Batonneau-Gener, Isabelle; Koulidiati, Jean

    2012-02-15

    This paper deals with the removal of α-endosulfan from water over HY and steamed HBEA zeolites. Experiments were performed to understand the adsorption mechanisms of α-endosulfan on zeolites and to determine the most efficient adsorbent for the purification of water contaminated by this pesticide. The experiments exhibit that α-endosulfan was adsorbed in the micropores. In the case of HY zeolites an adsorption of α-endosulfan molecules on BrØnsted sites was pointed out, due to a preferential water adsorption in mesopores. Moreover a physisorption of α-endosulfan occurred in micropores. For steamed HBEA zeolites physisorption in micropores was pointed out as the adsorption mode. For both types of zeolites a decrease of the adsorption capacities was noticed when the acidity of zeolites increased. There was also a linear relation between the adsorption capacities of α-endosulfan and the hydrophobicity (HI) of the samples and by determining the values of HI for a type of zeolite it was possible to deduce the uptake of α-endosulfan. The HY(40) sample was the most efficient for the removal of α-endosulfan from water because of preferential adsorption of water molecules in mesopores and lower acidity. For this sample the adsorption capacity for α-endosulfan was about 833.33 mg/g where for the most effective HBEA sample (St700(3)) the adsorption capacity was about 793.65 mg/g.

  15. Protein nanoparticle interaction: A spectrophotometric approach for adsorption kinetics and binding studies

    NASA Astrophysics Data System (ADS)

    Vaishanav, Sandeep K.; Chandraker, Kumudini; Korram, Jyoti; Nagwanshi, Rekha; Ghosh, Kallol K.; Satnami, Manmohan L.

    2016-08-01

    Investigating the protein nanoparticle interaction is crucial to understand how to control the biological interactions of nanoparticles. In this work, Model protein Bovine serum albumin (BSA) was used to evaluate the process of protein adsorption to the gold nanoparticles (GNPs) surface. The binding of a model protein (BSA) to GNPs was investigated through fluorescence quenching measurements. The strong affinities of BSA for GNPs were confirmed by the high value of binding constant (Ks) which was calculated to be 2.2 × 1011 L/mol. In this consequence, we also investigated the adsorption behavior of BSA on GNPs surface via UV-Vis spectroscopy. The effect of various operational parameters such as pH, contact time, initial BSA concentration, and temperature on adsorption of BSA was investigated using batch adsorption experiments. Kinetics of adsorption was found to follow the pseudo-second order rate equation. The suitability of Freundlich and Langmuir adsorption models to the equilibrium data was investigated. The equilibrium adsorption was well described by the Freundlich isotherm model. The maximum adsorption capacity for BSA adsorbed on GNPs was 58.71 mg/g and equilibrium constant was 0.0058 calculated by the Langmuir model at 298 K and pH = 11.0. Thermodynamic parameters showed that the adsorption of BSA onto GNPs was feasible, spontaneous, and exothermic.

  16. Study on Adsorption of Cu(II) on Chitosan Nanofiber Membranes

    NASA Astrophysics Data System (ADS)

    Cao, Jianhua; Li, Dongzhou; Liang, Weihua; Wu, Dayong

    2014-12-01

    Chitosan nanofiber membranes by electrospinning technique were used to remove Cu(II) from aqueous solution. The adsorption kinetics, equilibrium isotherms, and pH effect were investigated in batch experiments. The Langmuir isotherm and pseudo second-order kinetic models agree well with the experimental data. The chitosan nanofiber membranes are effective for Cu(II) adsorption at pH6. Results showed that the maximum adsorption capacity of the chitosan nanofiber membranes with Cu(II) is 118.62 mg g-1. The chitosan nanofiber membranes can be used as an effective adsorbent for the removal of Cu(II) in aqueous solution due to high adsorption capacity.

  17. Adsorption of mercury from water by modified multi-walled carbon nanotubes: adsorption behaviour and interference resistance by coexisting anions.

    PubMed

    Chen, Paris Honglay; Hsu, Cheng-Feng; Tsai, David Dah-wei; Lu, Yen-Ming; Huang, Winn-Jung

    2014-08-01

    This investigation reports the use of modified multi-walled carbon nanotubes (MWCNTs) with various functional groups for adsorbing inorganic divalent mercury (Hg(II)) from water samples. To elucidate the behaviours and mechanisms of Hg(II) adsorption by modified MWCNTs, their adsorption capacity was studied by considering adsorption isotherms and kinetics. Particular attention was paid to interference of coexisting inorganic ions with Hg(II) adsorption. The results reveal that functionalization with oxygen-containing groups improved the Hg(II) adsorption capacity of the MWCNTs. Kinetic analysis demonstrated that the adsorption of Hg(II) by MWCNTs was closely described by the pseudo-second-order and Elovich models, suggesting that the adsorption of Hg(II) by MWCNTs was significantly affected by chemical adsorption. The kinetic results were also analysed using the intraparticle diffusion model, which revealed that intraparticle diffusion was not the only rate-controlling mechanism. The adsorption of Hg(II) on MWCNTs fell drastically as the ionic strength increased from 0 to 1.0mol/L chloride ions, and declined significantly as the pH increased from 2.2 to 10.5. The elemental maps obtained by energy-dispersive spectrometer (EDS) revealed the formation of surface complexes of chloride ions with functional groups on MWCNTs, which reduced the number of available sites for the adsorption of Hg(II) and strengthened the repulsive forces between Hg(II) and MWCNTs. The EDS results suggest that chloride ions are important in controlling Hg(II) speciation and adsorption on the surfaces of MWCNTs.

  18. 2, 4 dichlorophenol (2, 4-DCP) sorption from aqueous solution using granular activated carbon and polymeric adsorbents and studies on effect of temperature on activated carbon adsorption.

    PubMed

    Ghatbandhe, A S; Yenkie, M K N

    2008-04-01

    Adsorption equilibrium, kinetics and thermodynamics of 2,4-dichlorophenol (2,4-DCP), one of the most commonly used chlorophenol, onto bituminous coal based Filtrasorb-400 grade granular activated carbon, were studied in aqueous solution in a batch system with respect to temperature. Uptake capacity of activated carbon found to increase with temperature. Langmuir isotherm models were applied to experimental equilibrium data of 2, 4-DCP adsorption and competitive studies with respect to XAD resin were carried out. Equilibrium data fitted very well to the Langmuir equilibrium model. Adsorbent monolayer capacity 'Q0, Langmuir constant 'b' and adsorption rate constant 'k(a)' were evaluated at different temperatures for activated carbon adsorption. This data was then used to calculate the energy of activation of adsorption and also the thermodynamic parameters, namely the free energy of adsorption, deltaG0, enthalpy of adsorption, deltaH0 and the entropy of adsorption deltaS0. The obtained results showed that the monolayer capacity increases with the increase in temperatures. The obtained values of thermodynamic parameters showed that adsorption of 2,4 DCP is an endothermic process. Synthetic resin was not found efficient to adsorb 2,4 DCP compared to activated carbon. The order of adsorption efficiencies of three resins used in the study found as XAD7HP > XAD4 > XAD1180.

  19. Studies on adsorption-desorption of xenon on surface of BC-404 plastic scintillator based on soaking method

    NASA Astrophysics Data System (ADS)

    Yongchun, Xiang; Tieshuan, Fan; Chuanfei, Zhang; Fei, Luo; Qian, Wang; Rende, Ze; Qingpei, Xiang

    2017-03-01

    The phoswich coincidence detector is used to verify the CTBT treaty by measuring radioxenon and as such needs to possess high detection sensitivity. However, residual xenon adsorbed onto the surface of β detectors greatly influences subsequent measurements of weak samples. In this study, we investigate the adsorption-desorption behavior of xenon on BC-404 scintillator surfaces with different coating thicknesses using the soaking method. The results present the desorption behavior of xenon on a BC-404 surface for the first time. The calculated adsorption capacity for an uncoated surface is consistent with that from previous studies. However, due to factors such as limitations in coating technology, the effectiveness of coating on reducing the "memory effect" of the detector was poor. The proposed method is suitable for studying the adsorption-desorption behavior of gases on solid surfaces due to its simplicity and flexibility.

  20. Column adsorption studies for the removal of U by phosphonated cross-linked polyethylenimine: modelling and optimization

    NASA Astrophysics Data System (ADS)

    Saad, Dalia M.; Cukrowska, Ewa; Tutu, Hlanganani

    2015-03-01

    A continuous fixed-bed adsorption study was carried out by using phosphonated cross-linked polyethylenimine as an adsorbent for the removal of uranium (U) from aqueous solutions. The effect of inlet metal ion concentration (40, 70, and 100 mg L-1), feed flow rate (1, 2, and 3 mL min-1), and polymer bed height (2.5, 3.2 and 4.5 cm) on the breakthrough characteristics of the fixed-bed adsorption system at pH 2 were studied. The results showed that the breakthrough time appeared to increase with increase of bed height but decreased with increase of both influent U concentration and flow rate. Modelling of the dynamics of the fixed-bed adsorption process was studied and the application of different models to describe the breakthrough curves showed that the Thomas and Yoon-Nelson model gave better results for the operating conditions.

  1. Influence of heat treatment of rayon-based activated carbon fibers on the adsorption of formaldehyde.

    PubMed

    Rong, Haiqin; Ryu, Zhenyu; Zheng, Jingtang; Zhang, Yuanli

    2003-05-15

    The influence of heat treatment of rayon-based activated carbon fibers on the adsorption behavior of formaldehyde was studied. Heat treatment in an inert atmosphere of nitrogen for rayon-based activated carbon fibers (ACFs) resulted in a significant increase in the adsorption capacities and prolongation of breakthrough time on removing of formaldehyde. The effect of different heat-treatment conditions on the adsorption characteristics was investigated. The porous structure parameters of the samples under study were investigated using nitrogen adsorption at the low temperature 77.4 K. The pore size distributions of the samples under study were calculated by density functional theory. With the aid of these analyses, the relationship between structure and adsorption properties of rayon-based ACFs for removing formaldehyde was revealed. Improvement of their performance in terms of adsorption selectivity and adsorption rate for formaldehyde were achieved by heat post-treatment in an inert atmosphere of nitrogen.

  2. A computational study on the adsorption configurations and reactions of SiHx(x = 1-4) on clean and H-covered Si(100) surfaces

    NASA Astrophysics Data System (ADS)

    Le, Thong N.-M.; Raghunath, P.; Huynh, Lam K.; Lin, M. C.

    2016-11-01

    Possible adsorption configurations of H and SiHx (x = 1 - 4) on clean and H-covered Si(100) surfaces are determined by using spin-polarized DFT calculations. The results show that, on the clean surface, the gas-phase hydrogen atom and SiH3 radicals effectively adsorb on the top sites, while SiH and SiH2 prefer the bridge sites of the first layer. Another possibility for SiH is to reside on the hollow sites with a triple-bond configuration. For a partially H-coverd Si(100) surface, the mechanism is similar but with higher adsorption energies in most cases. This suggests that the surface species become more stable in the presence of surface hydrogens. The minimum energy paths for the adsorption/migration and reactions of H/SiHx species on the surfaces are explored using the climbing image-nudged elastic band method. The competitive surface processes for Si thin-film formation from SiHx precursors are also predicted. The study reveals that the migration of hydrogen adatom is unimportant with respect to leaving open surface sites because of its high barriers (>29.0 kcal/mol). Alternatively, the abstraction of hydrogen adatoms by H/SiHx radicals is more favorable. Moreover, the removal of hydrogen atoms from adsorbed SiHx, an essential step for forming Si layers, is dominated by abstraction rather than the decomposition processes.

  3. A ToF-SIMS and XPS study of protein adsorption and cell attachment across PEG-like plasma polymer films with lateral compositional gradients

    NASA Astrophysics Data System (ADS)

    Menzies, Donna J.; Jasieniak, Marek; Griesser, Hans J.; Forsythe, John S.; Johnson, Graham; McFarland, Gail A.; Muir, Benjamin W.

    2012-12-01

    In this work we report a detailed X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) study of poly(ethylene glycol) PEG-like chemical gradients deposited via plasma enhanced chemical vapour deposition (PECVD) at two different load powers using diethylene glycol dimethyl ether (DG) as a monomer. Principal component analysis (PCA) was applied to the ToF-SIMS data both before and after protein adsorption on the plasma polymer thin films. Results of the PCA loadings indicated a higher content of hydrocarbon fragments across the higher load power gradient, which adsorbed higher amounts of proteins. Gradients deposited at a lower load power retained a higher degree of monomer like functionality as did the central region directly underneath the knife edge electrode. Analysis of the adsorption of serum proteins (human serum albumin and fetal bovine serum) was monitored across the gradient films and increased with decreasing ether (PEG-like) film chemistries. The effect of protein incubation time on the levels adsorbed fetal bovine serum on the plasma polymer films was critical, with significantly more protein adsorbing after 24 hour incubation times on both gradient films. The attachment of HeLa cells on the gradients appeared to be dictated not only by the surface chemistry, but also by the adsorption of serum proteins. XPS analysis revealed that at surface ether concentrations of less than 70% in the gradient films, significant increases in protein and cell attachment were observed.

  4. Study on the Adsorption Capacities for Airborne Particulates of Landscape Plants in Different Polluted Regions in Beijing (China).

    PubMed

    Zhang, Wei-Kang; Wang, Bing; Niu, Xiang

    2015-08-14

    Urban landscape plants are an important component of the urban ecosystem, playing a significant role in the adsorption of airborne particulates and air purification. In this study, six common landscape plants in Beijing were chosen as research subjects, and the adsorption capacities for each different plant leaf and the effects of the leaf structures for the adsorption capacities for particulates were determined. Preliminary results show that needle-leaved tree species adsorbed more airborne particulates than broad-leaved tree species for the same leaf area. Pinus tabuliformis exhibits the highest adsorption capacity, at 3.89 ± 0.026 μg·cm(-2), almost two times as much as that of Populus tomentosa (2.00 ± 0.118 μg·cm(-2)). The adsorption capacities for PM10 of the same tree species leaves, in different polluted regions had significant differences, and the adsorption capacities for PM10 of the tree species leaf beside the Fifth Ring Road were higher than those of the tree species leaves in the Botanical Garden, although the adsorption capacities for PM2.5 of the same tree species in different polluted regions had no significant differences. By determining the soluble ion concentrations of the airborne particulates in two regions, it is suggested that the soluble ion concentrations of PM10 in the atmosphere in the Botanical Garden and beside the Fifth Ring Road have significant differences, while those of PM2.5 in the atmosphere had no significant differences. In different polluted regions there are significant adaptive changes to the leaf structures, and when compared with slightly polluted region, in the seriously polluted region the epidermis cells of the plant leaves shrinked, the surface textures of the leaves became rougher, and the stomas' frequency and the pubescence length increased. Even though the plant leaves exposed to the seriously polluted region changed significantly, these plants can still grow normally and healthily.

  5. Study on the Adsorption Capacities for Airborne Particulates of Landscape Plants in Different Polluted Regions in Beijing (China)

    PubMed Central

    Zhang, Wei-Kang; Wang, Bing; Niu, Xiang

    2015-01-01

    Urban landscape plants are an important component of the urban ecosystem, playing a significant role in the adsorption of airborne particulates and air purification. In this study, six common landscape plants in Beijing were chosen as research subjects, and the adsorption capacities for each different plant leaf and the effects of the leaf structures for the adsorption capacities for particulates were determined. Preliminary results show that needle-leaved tree species adsorbed more airborne particulates than broad-leaved tree species for the same leaf area. Pinus tabuliformis exhibits the highest adsorption capacity, at 3.89 ± 0.026 μg·cm−2, almost two times as much as that of Populus tomentosa (2.00 ± 0.118 μg·cm−2). The adsorption capacities for PM10 of the same tree species leaves, in different polluted regions had significant differences, and the adsorption capacities for PM10 of the tree species leaf beside the Fifth Ring Road were higher than those of the tree species leaves in the Botanical Garden, although the adsorption capacities for PM2.5 of the same tree species in different polluted regions had no significant differences. By determining the soluble ion concentrations of the airborne particulates in two regions, it is suggested that the soluble ion concentrations of PM10 in the atmosphere in the Botanical Garden and beside the Fifth Ring Road have significant differences, while those of PM2.5 in the atmosphere had no significant differences. In different polluted regions there are significant adaptive changes to the leaf structures, and when compared with slightly polluted region, in the seriously polluted region the epidermis cells of the plant leaves shrinked, the surface textures of the leaves became rougher, and the stomas’ frequency and the pubescence length increased. Even though the plant leaves exposed to the seriously polluted region changed significantly, these plants can still grow normally and healthily. PMID:26287227

  6. Adsorption coefficients for TNT on soil and clay minerals

    NASA Astrophysics Data System (ADS)

    Rivera, Rosángela; Pabón, Julissa; Pérez, Omarie; Muñoz, Miguel A.; Mina, Nairmen

    2007-04-01

    To understand the fate and transport mechanisms of TNT from buried landmines is it essential to determine the adsorption process of TNT on soil and clay minerals. In this research, soil samples from horizons Ap and A from Jobos Series at Isabela, Puerto Rico were studied. The clay fractions were separated from the other soil components by centrifugation. Using the hydrometer method the particle size distribution for the soil horizons was obtained. Physical and chemical characterization studies such as cation exchange capacity (CEC), surface area, percent of organic matter and pH were performed for the soil and clay samples. A complete mineralogical characterization of clay fractions using X-ray diffraction analysis reveals the presence of kaolinite, goethite, hematite, gibbsite and quartz. In order to obtain adsorption coefficients (K d values) for the TNT-soil and TNT-clay interactions high performance liquid chromatography (HPLC) was used. The adsorption process for TNT-soil was described by the Langmuir model. A higher adsorption was observed in the Ap horizon. The Freundlich model described the adsorption process for TNT-clay interactions. The affinity and relative adsorption capacity of the clay for TNT were higher in the A horizon. These results suggest that adsorption by soil organic matter predominates over adsorption on clay minerals when significant soil organic matter content is present. It was found that, properties like cation exchange capacity and surface area are important factors in the adsorption of clayey soils.

  7. Adsorption and decomposition mechanism of formic acid on the Ga2O3 surface by first principle studies

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Li, Zhen Hua

    2017-02-01

    The adsorption and decomposition of formic acid (FA) on the Ga2O3(100) surface was studied with density functional theory. On the perfect Ga2O3(100) surface, the preferred adsorption state of FA is a monodentate configuration while the most stable adsorption state is a bridging configuration. Heating the surface would convert FA from monodentate to bridging configuration and further heating would decompose FA into CO2 and two surface hydroxyl groups. On the other hand, on the O(2)-defect Ga2O3(100) surface the preferred adsorption state of FA is a bridging formate with one O atom of formate filling the O(2) vacancy. Heating the surface would generate CO and two surface hydroxyl groups. If the Ga2O3(100) surface is used as decomposition catalyst, then at low temperature the formation of a small amount of CO2 can be observed. On the other hand, at high temperature continuous formation of CO and H2O can be observed. The active sites for FA decomposition are the O(2) defects on the surface formed in situ from the removal of water from surface hydroxyl groups. The strong dependence of mechanism on experimental conditions explains why no consensus has been reached in the previous experimental studies regarding the adsorption and decomposition mechanism of FA.

  8. Multiprotein Interactions during Surface Adsorption: a Molecular Dynamics Study of Lysozyme Aggregation at a Charged Solid Surface

    PubMed Central

    2011-01-01

    Multiprotein adsorption of hen egg white lysozyme at a model charged ionic surface is studied using fully atomistic molecular dynamics simulations. Simulations with two, three, and five proteins, in various orientations with respect the surface, are performed over a 100 ns time scale. Mutated proteins with point mutations at the major (Arg128 and Arg125) and minor (Arg68) surface adsorption sites are also studied. The 100 ns time scale used is sufficient to observe protein translations, rotations, adsorption, and aggregation. Two competing processes of particular interest are observed, namely surface adsorption and protein–protein aggregation. At low protein concentration, the proteins first adsorb in isolation and can then reorientate on the surface to aggregate. At high concentration, the proteins aggregate in the solution and then adsorb in nonspecific ways. This work demonstrates the role of protein concentration in adsorption, indicates the residues involved in both types of interaction (protein–protein and protein–surface), and gives an insight into processes to be considered in the development of new functionalized material systems. PMID:21671567

  9. Investigation of graphene-based nanomaterial as nanocarrier for adsorption of paclitaxel anticancer drug: a molecular dynamics simulation study.

    PubMed

    Hasanzade, Zohre; Raissi, Heidar

    2017-02-01

    In this work, molecular dynamics simulations are used to study the adsorption of paclitaxel (PTX) drug on the graphene-based nanomaterials including graphene (G), graphene oxide (GO), and functionalized GO with chitosan (GO-CS). The drug is adsorbed through different patterns on the surface of graphene-based nanomaterials. Our results show that PTX on graphene is adsorbed more quickly than other systems. Comparing center of mass (COM) in GO and GO-CS systems indicated that PTX approaches GO-CS surface faster than GO surface. The binding of PTX molecule to graphene surface is stronger than the other investigated systems. Our study indicated that π-π stacking and hydrophobic interactions are the main driving forces for the adsorption of the drug on graphene, while the adsorption of PTX on GO-CS is dominated by the formation of hydrogen bonds. It is found that the number of hydrogen bonds in PTX-GO-CS system is more than that of PTX-GO emphasizing the advantages of the functional group of chitosan in improving the adsorption of the drug onto nanomaterial. These results suggest that hydrogen bond, π-π stacking, and hydrophobic interactions play a key role in the adsorption of PTX in graphene-based nanomaterials. In spite of similar dimensions of investigated nanomaterials, the difference in surface chemistries and also the type of functional group can be effective factors in determining their interactions with PTX.

  10. IR and quantum-chemical studies of carboxylic acid and glycine adsorption on rutile TiO2 nanoparticles.

    PubMed

    Ojamäe, Lars; Aulin, Christian; Pedersen, Henrik; Käll, Per-Olov

    2006-04-01

    Nanocrystalline TiO2 powders of the rutile polymorph, synthesized by a sol-gel method, were treated with water solutions containing, respectively, formic, acetic, and citric acid and glycine in order to study the adsorption properties of these organic species. The samples were characterized by FTIR, Raman, powder XRD, and TEM. It was found that HCOOH, CH3COOH and HOC(COOH)(CH2COOH)2--but not NH2CH2COOH--adsorbed onto TiO2. The adsorption of HCOOH, CH3COOH and NH2CH2COOH onto the (110) surface of rutile was also studied by quantum-chemical periodic density functional theory (DFT) calculations. The organic molecules were from the computations found to adsorb strongly to the surfaces in a bridge-coordinating mode, where the two oxygens of the deprotonated carboxylic acid bind to two surface titanium ions. Surface relaxation is found to influence adsorption geometries and energies significantly. The results from DFT calculations and ab initio molecular-dynamics simulations of formic acid adsorption onto TiO2 are compared and match well with the experimental IR measurements, supporting the bridge-binding geometry of carboxylic-acid adsorption on the TiO2 nanoparticles.

  11. Comparative theoretical study of adsorption of lithium polysulfides (Li2Sx) on pristine and defective graphene

    NASA Astrophysics Data System (ADS)

    Jand, Sara Panahian; Chen, Yanxin; Kaghazchi, Payam

    2016-03-01

    Adsorption of Li2Sx on pristine and defective (Stone-Wales (SW) and vacancy) graphene is studied using density functional theory. Results show that the interaction between Li2Sx and graphene is dominated by dispersion interaction (physisorption), which depends on the size of molecule as well as the existence and type of defect sites on graphene. We find that single Li2Sx molecules interact only slightly stronger to the SW sites than to the defect-free sites, but they interact very strongly with single-vacant defects. In the later cases, the vacant site catches one S atom from the Li2Sx molecule, leading to the formation of a Li2Sx-1 molecule, which adsorbs weakly on the created S-doped graphene. This study suggests that defect sites can not improve the ability of graphene to catch lithium polysulfides in Li-S batteries.

  12. In vitro studies of dental plaque formation: adsorption of oral streptococci to hydroxyaptite.

    PubMed Central

    Appelbaum, B; Golub, E; Holt, S C; Rosan, B

    1979-01-01

    A mixture of saliva-coated hydroxyapatite beads and radioactively labeled bacteria has been employed as an in vitro model for the initial phase of dental plaque formation. Adsorption in this model can be expressed by the Langmuir adsorption isotherm, and the adherence of oral streptococci can be expressed as the product of the affinity constant (Ka) and the number of binding sites (N), KaN. With this approach, Streptococcus sanguis serotype 1 strains adhered better (KaN = [187 +/- 72] X 10(-2)) than serotype 2 strains (KaN = [97 +/- 84] X 10(-2)); a t test showed this difference to be statistically significant to the 99.99% confidence level. Strains of S. mitis, S. mutans, and S. salivarius did not appear to adhere as well. To analyze the bacterial receptors involved in adherence, competition studies in which increasing quantities of unlabeled bacteria were added to a fixed quantity (4 X 10(9) cells per ml) of 3H-labeled serotype 1, reference strain S. sanguis G9B, were performed. These studies indicated that the type 1 strains competed for the same, or closely related, binding sites. Competition studies using serotype 2 S. sanguis strains resulted in an increased binding of reference strain G9B to hydroxyapatite. Scanning electron microscopy indicated this effect was due to the formation of localized aggregations of bacteria, presumably representing the two bacterial types. The results of competition studies with S. mitis were variable, and several strains of other oral bacteria showed little or no competition. Images PMID:489128

  13. Study of adsorption of detergent-dispersion additives on solid particles dispersed in oil using the method of electrical conductivity measurement

    SciTech Connect

    Waligora, B.; Buczak, H.; Olszewska, A.; Szeglowski, Z.

    1984-01-01

    By measuring electrical conductivity of paraffin oil solutions in isooctane (1:1 by volume) the variation in concentration of detergent-dispersant additives is studied; this variation is caused by their adsorption on solid particles (carbon black, aluminum powder). It is shown that dispersants have an improved ability to undergo adsorption, compared with detergents. Studies of adsorption of additives on model sorbents may be used to develop tests for evaluating additive properties. 7 references, 4 figures.

  14. Combined HPLC/HPSEC study of Suwannee River Fulvic Acid adsorptive fractionation on α-aluminum oxide.

    PubMed

    Kreller, David I; Schlautman, Mark A; McGunigale, Samantha L

    2013-01-15

    A novel liquid chromatographic (LC) method with repeated injections of Suwannee River Fulvic Acid (SRFA) was used to investigate its adsorptive fractionation by synthetic α-Al(2)O(3). Eluent (i.e., non-retained) SRFA for each injection was monitored by two ultraviolet (UV) absorbance detection channels (300 and 365 nm) and one fluorescence detection channel (λ(ex)=350 nm, λ(em)=450 nm). Preferential adsorption of SRFA constituents was revealed by the different responses of the three LC detection channels. Samples of non-retained SRFA from injections of three independent replicate experiments were collected and aggregated for subsequent analysis by steady state ultraviolet-visible (UV/vis) absorption spectrometry and size exclusion chromatography (SEC). The ratio of absorbance at 254 and 204 nm, a surrogate for specific UV absorbance at 254 nm, increased with increasing injection number for the non-retained SRFA, indicating the preferential adsorption of SRFA constituents containing aromatic moieties. SEC analysis confirmed the preferential adsorption of higher molecular weight (MW) SRFA constituents as the non-adsorbed SRFA fractions increased in MW across the series of injections. The SEC results also suggested that certain SRFA constituents in the ca. 2-5 kDa MW range adsorbed in early injections were displaced by higher MW species (ca. 5-10 kDa) in later injections.

  15. High adsorption capacity of heavy metals on two-dimensional MXenes: an ab initio study with molecular dynamics simulation.

    PubMed

    Guo, Xun; Zhang, Xitong; Zhao, Shijun; Huang, Qing; Xue, Jianming

    2016-01-07

    Density functional theory (DFT) calculation is employed to study the adsorption properties of Pb and Cu on recently synthesized two-dimensional materials MXenes, including Ti3C2, V2C1 and Ti2C1. The influence of surface decoration with functional groups such as H, OH and F have also been investigated. Most of these studied MXenes exhibit excellent capability to adsorb Pb and Cu, especially the adsorption capacity of Pb on Ti2C1 is as high as 2560 mg g(-1). Both the binding energies and the adsorption capacities are sensitive to the functional groups attached to the MXenes' surface. Ab initio molecular dynamics (ab-init MD) simulation confirms that Ti2C1 remains stable at room temperature after adsorbing Pb atoms. Our calculations imply that these newly emerging two-dimensional MXenes are promising candidates for wastewater treatment and ion separation.

  16. Modeling and Experimental Studies of Mercury Oxidation and Adsorption in a Fixed-Bed and Entrained-Flow Reactor

    SciTech Connect

    Buitrago, Paula A.; Morrill, Mike; Lighty, JoAnn S.; Silcox, Geoffrey D.

    2009-06-01

    This report presents experimental and modeling mercury oxidation and adsorption data. Fixed-bed and single-particle models of mercury adsorption were developed. The experimental data were obtained with two reactors: a 300-W, methane-fired, tubular, quartz-lined reactor for studying homogeneous oxidation reactions and a fixed-bed reactor, also of quartz, for studying heterogeneous reactions. The latter was attached to the exit of the former to provide realistic combustion gases. The fixed-bed reactor contained one gram of coconut-shell carbon and remained at a temperature of 150°C. All methane, air, SO2, and halogen species were introduced through the burner to produce a radical pool representative of real combustion systems. A Tekran 2537A Analyzer coupled with a wet conditioning system provided speciated mercury concentrations. At 150°C and in the absence of HCl or HBr, the mercury uptake was about 20%. The addition of 50 ppm HCl caused complete capture of all elemental and oxidized mercury species. In the absence of halogens, SO2 increased the mercury adsorption efficiency to up to 30 percent. The extent of adsorption decreased with increasing SO2 concentration when halogens were present. Increasing the HCl concentration to 100 ppm lessened the effect of SO2. The fixed-bed model incorporates Langmuir adsorption kinetics and was developed to predict adsorption of elemental mercury and the effect of multiple flue gas components. This model neglects intraparticle diffusional resistances and is only applicable to pulverized carbon sorbents. It roughly describes experimental data from the literature. The current version includes the ability to account for competitive adsorption between mercury, SO2, and NO2. The single particle model simulates in-flight sorbent capture of elemental mercury. This model was developed to include Langmuir and Freundlich isotherms, rate equations, sorbent feed rate, and

  17. Column study of chromium(VI) adsorption from electroplating industry by coconut coir pith.

    PubMed

    Suksabye, Parinda; Thiravetyan, Paitip; Nakbanpote, Woranan

    2008-12-15

    The removal of Cr(VI) from electroplating wastewater by coir pith was investigated in a fixed-bed column. The experiments were conducted to study the effect of important parameters such as bed depth (40-60cm) and flow rate (10-30ml min(-1)). At 0.05 C(t)/C(0), the breakthrough volume increased as flow rate decreased or a bed depth increased due to an increase in empty bed contact time (EBCT). The bed depth service time model (BDST) fit well with the experimental data in the initial region of the breakthrough curve, while the simulation of the whole curve using non-linear regression analysis was effective using the Thomas model. The adsorption capacity estimated from the BDST model was reduced with increasing flow rate, which was 16.40mg cm(-3) or 137.91mg Cr(VI)g(-1) coir pith for the flow rates of 10ml min(-1) and 14.05mg cm(-3) or 118.20mg Cr(VI)g(-1) coir pith for the flow rates of 30ml min(-1). At the highest bed depth (60cm) and the lowest flow rate (10mlmin(-1)), the maximum adsorption reached 201.47mg Cr(VI)g(-1) adsorbent according to the Thomas model. The column was regenerated by eluting chromium using 2M HNO(3) after adsorption studies. The desorption of Cr(III) in each of three cycles was about 67-70%. The desorption of Cr(III) in each cycle did not reach 100% due to the fact that Cr(V) was present through the reduction of Cr(VI), and was still in coir pith, possibly bound to glucose in the cellulose part of coir pith. Therefore, the Cr(V) complex cannot be desorbed in solution. The evidence of Cr(V) signal was observed in coir pith, alpha-cellulose and holocellulose extracted from coir pith using electron spin resonance (ESR).

  18. Drug adsorption on bovine and porcine sclera studied with streaming potential.

    PubMed

    Murtomäki, Lasse; Vainikka, Tuomas; Pescina, Silvia; Nicoli, Sara

    2013-07-01

    The affinity of a drug to a biological membrane can affect the distribution and the availability of the active compound to its target. Adsorption is usually determined with in vitro distribution studies based on partitioning of the drug between buffer and tissue, which have limitations such as the high variability of the uptake data and the need for high accuracy in the measurement of drug concentration. Furthermore, distribution studies yield solute concentrations in the bulk of the tissue, whereas electrokinetic phenomena such as streaming potential and electroosmosis reflect the electric charge density on a membrane surface. Streaming potential thus can be used in studying the conditions, by which the charge sign and density can be regulated. That, in turn, has significance to electroosmotic transport mechanism during iontophoresis. In this communication, the adsorption of model compounds methylprednisolone sodium succinate, propranolol, and cytochrome C on bovine and porcine sclera is determined as a function of their concentration by measuring streaming potential. Both membranes had negative streaming potential, proving that they carry negative charge, but had different values at negative and positive pressure differences, which is addressed to the structural asymmetry of these membranes. Bovine sclera had a clearly higher value of streaming potential, ca. -26 nV/Pa, than porcine sclera, ca. -7 nV/Pa (10 mM NaCl solution). All the model compounds were adsorbed on bovine and porcine sclera already in the millimolar concentration range and can have an impact to electroosmosis during transscleral iontophoresis. The results obtained help to better elucidate the phenomena involved in transscleral transport, both in passive diffusion and in iontophoresis, supporting the future application of iontophoresis to the noninvasive delivery of drugs to the posterior segment of the human eye.

  19. First-principles study of the adsorption of MgO molecules on a clean Fe(001) surface

    NASA Astrophysics Data System (ADS)

    Wiśnios, Damian; Kiejna, Adam; Korecki, Józef

    2015-10-01

    The adsorption of MgO molecules on a Fe(001) surface was studied using density functional theory and projector augmented-wave methods. The energetically most favored configurations for different adsorption sites considered were identified. The most preferable adsorption geometry is when the MgO molecules are parallel to the surface, with Mg in the interstitial site and O in the on-top site of the Fe atom. During the adsorption of subsequent MgO molecules in this geometry, a sharp, nonoxidized interface is formed between the MgO adlayer and the Fe(001) surface. The adsorption of MgO perpendicular to the surface, with oxygen incorporated in the topmost Fe layer, is less probable, but it may lead to the formation of the FeO layer when stabilized with an excess of oxygen atoms. Structural, electronic, and magnetic properties of both interface types were examined for the MgO coverage from 1/9 to 1 monolayer (ML). Electronic and magnetic properties are sensitive to the MgO coverage. For lower coverage of MgO, clear hybridization between the Fe 3 d and O 2 p states is shown. The average magnetic moment of the surface Fe atoms is reduced with coverage, achieving 2.78 μB for 1 ML of MgO.

  20. Kinetics and isotherm studies of Cd(II) adsorption from aqueous solution utilizing seeds of bottlebrush plant ( Callistemon chisholmii)

    NASA Astrophysics Data System (ADS)

    Rao, Rifaqat Ali Khan; Kashifuddin, Mohammad

    2014-12-01

    Seeds of bottlebrush, a novel plant material, were found to exhibit excellent adsorption capacity over a wide range of Cd(II) concentration. It was characterized by Fourier transform infrared spectroscopy and Scanning Electron Microscopy to support the adsorption of Cd(II) ions. Effect of various parameters like pH, contact time, initial concentration and different electrolytes was investigated using batch process to optimize conditions for maximum adsorption. The adsorbent data were analyzed using Langmuir, Freundlich, Temkin and Dubinin-Redushkeuich isotherm equations at 30°, 40° and 50 °C. Thermodynamic parameters such as standard enthalpy change (Δ H°), free energy change (Δ G°) and entropy change (Δ S°) were also evaluated and the results indicated that adsorption of Cd(II) are spontaneous and endothermic. Various kinetics models including the Pseudo-first-order kinetics, Pseudo-second-order kinetics and Intraparticle diffusion models have been applied to the experimental data to predict the adsorption kinetics. Kinetic study was carried out by varying initial concentration of Cd(II) at constant temperature and it was found that pseudo-second-order rate equation was better obeyed than pseudo-first-order equation supporting that chemisorption process was involved.

  1. Study of adsorption Ag and Pb in liquid sample using Berea sandstone by commercial laser-induced breakdown spectroscopy (LIBS)

    NASA Astrophysics Data System (ADS)

    Suyanto, H.; Wendri, N.; Agustiningrum, U.; Manurung, M.

    2016-11-01

    Qualitative and quantitative analysis of Pb and Ag elements in liquid samples had been done by commercial laser-induced breakdown spectroscopy (LIBS) using adsorption method on a Berea Sandstone. The aim of this study is to identify the thickness of the Berea Sandstone for adsorbing Pb and Ag elements in liquid. The experiment was started with characterizing the Berea Sandstone that contains Si, Na, H, Li, K, Ca, O, N, Be, Ti, Al, Mg and Ba. Some of these elements have ability to adsorb Pb and Ag elements in the liquid. To prove this phenomenon, it is required to look for the experiment parameter optimum conditions such as laser energy, adsorption time and sample temperature. The experiment was conducted by dropping 2 ml standard liquid containing 1000 ppm of Pb and Ag to the Berea Sandstone surface. The result showed that the parameter optimum conditions for analyzing Pb and Ag elements in liquid sample with adsorption method were adsorption delay-time of 15 minutes, laser energy of 120 mJ and sample heating of 80 °C. The next experiment was focused on the number of adsorption as a function of depth. The data showed that Pb and Ag elements in liquid sample of 2 ml, 1000 ppm were fully adsorbed by the Berea Sandstone until the depth of 0.372 mm and 10.40 mm from the surface, respectively. The data also showed that the limit of detection predicted to about 22.76 ppm.

  2. Soil adsorption studies of a rice herbicide, cyhalofop-butyl, in two texturally different soils of India.

    PubMed

    Sondhia, Shobha; Khare, Rishi Raj

    2014-10-01

    The ability of herbicides to be adsorbed by the soil and sediment and their tendency to be desorbed are some of the most important factors affecting soil and water contamination. Therefore, a sorption study was conducted to evaluate the adsorption of cyhalofop-butyl, butyl (2R)-2-[4-(4-cyano-2-fluorophenoxy) phenoxy] propanoate, in the sandy clay loam and clayey soils using a batch equilibrium method. The adsorption of cyhalofop-butyl was found positively related with the clay and organic carbon content. Freundlich constants (Kf) of cyhalofop-butyl in the clayey and sandy clay loam were found to be 13.39 and 2.21, respectively. Sorption coefficients (Koc) and distribution coefficients (Kd) were found to be 265.38 and 2,092.79, and 1.38 and 11.48, for sandy clay loam and clayey soils, respectively. The adsorption isotherm suggested a relatively higher affinity of cyhalofop-butyl to the adsorption sites at low equilibrium concentrations. The low value of the soil organic carbon partition coefficient (Koc) of cyhalofop-butyl in the sandy loam soil suggested its weaker adsorption in soil and thus increased its risk of mobility into water sources; hence, it should be used judiciously to prevent groundwater contamination.

  3. Adsorption of bovine serum albumin (BSA) onto lecithin studied by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy.

    PubMed

    Tantipolphan, R; Rades, T; McQuillan, A J; Medlicott, N J

    2007-06-07

    The adsorption of bovine serum albumin (BSA) to lecithin was investigated by ATR-FTIR spectroscopy. Lecithin films were prepared by casting aliquots of 3.2 microg lecithin in methanol onto ZnSe ATR prisms. Surface morphology and the thickness of the films were investigated by laser scanning confocal electron microscopy and scanning electron microscopy and the thickness of the films used for adsorption studies was estimated to be 40 A. The dependency of the CO peak area on the lecithin mass in the calibration curve confirms that the thickness of the film is below the penetration depth of the infrared evanescent wave. Size exclusion HPLC and fluorescence spectroscopy show that BSA conformation in up to 1M NaCl and CaCl(2) solutions is similar to that in water with no aggregation or changes in protein conformation seen over 4h. The kinetics of BSA adsorption on the lecithin film from water, NaCl and CaCl(2) solutions demonstrates that ions promote the protein adsorption. BSA bound more in the presence of NaCl compared to CaCl(2) at equivalent concentrations. The adsorption appeared greatest at a 0.1M concentration for both NaCl and CaCl(2). The results are explained in terms of absorptive reactivity of BSA and lecithin surfaces upon salt addition.

  4. Ab Initio Study of Water Adsorption and Reactivity on the (211) Surface of Anatase TiO2

    NASA Astrophysics Data System (ADS)

    Xu, Jing; Xu, Li-Fang; Li, Zhen-Zhen; Wang, Jian-Tao; Lin, Zhe-Shuai; Liu, Kai; Cao, Yong-Ge; Selloni, Annabella

    2016-06-01

    The reactivity of the anatase TiO2 (211) surface is systematically studied by ab initio calculations of the surface energy and water-adsorption energy. We find that anatase (211) has a high surface energy of 0.97 J /m2 , close to that of the (001) surface, and the unsaturated fourfold-coordinated Ti4 atom is more reactive than the unsaturated fivefold-coordinated Ti5 atom. Accordingly, for water adsorption on the (211) surface, a dissociative form is favored on Ti4 sites, with a large adsorption energy Δ HH ,OH˜1.28 eV , while a nondissociative molecular form is favored on Ti5 sites, with a smaller adsorption energy Δ HH2O˜0.78 eV . Such distinct surface properties lead to a mixed dissociative and molecular adsorption configuration when the coverage is increased from 1 /3 to 1 monolayer. These results suggest that, similar to the (001) surface, the anatase (211) surface exhibits high reactivity and may be useful in catalytic and photocatalytic applications as well.

  5. Adsorption of Toluene and Paraxylene from Aqueous Solution Using Pure and Iron Oxide Impregnated Carbon Nanotubes: Kinetics and Isotherms Study

    PubMed Central

    Abbas, Aamir; Ihsanullah; Al-Baghli, Nadhir A. H.

    2017-01-01

    Multiwall carbon nanotubes (CNTs) and iron oxide impregnated carbon nanotubes (CNTs-iron oxide) were investigated for the adsorption of hazardous toluene and paraxylene (p-xylene) from aqueous solution. Pure CNTs were impregnated with iron oxides nanoparticles using wet impregnation technique. Various characterization techniques including thermogravimetric analysis, scanning electron microscopy, elemental dispersion spectroscopy, X-ray diffraction, and nitrogen adsorption analysis were used to study the thermal degradation, surface morphology, purity, and surface area of the materials. Batch adsorption experiments show that iron oxide impregnated CNTs have higher degree of removal of p-xylene (i.e., 90%) compared with toluene (i.e., 70%), for soaking time 2 h, with pollutant initial concentration 100 ppm, at pH 6 and shaking speed of 200 rpm at 25°C. Pseudo-second-order model provides better fitting for the toluene and p-xylene adsorption. Langmuir and Freundlich isotherm models demonstrate good fitting for the adsorption data of toluene and p-xylene. PMID:28386208

  6. Equilibrium, Kinetic, and Thermodynamic Studies on the Adsorption of Cadmium from Aqueous Solution by Modified Biomass Ash

    PubMed Central

    Zheng, Xuebo; Cui, Hongbiao; Zhu, Zhenqiu; Liang, Jiani

    2017-01-01

    Natural biomass ash of agricultural residuals was collected from a power plant and modified with hexagonal mesoporous silica and functionalized with 3-aminopropyltriethoxysilane. The physicochemical and morphological properties of the biomass ash were analyzed by ICP-OES, SEM, TEM-EDS, FTIR, and BET analysis. The adsorption behavior of the modified product for Cd2+ in aqueous solution was studied as a function of pH, initial metal concentration, equilibrium time, and temperature. Results showed that the specific surface area of the modified product was 9 times that of the natural biomass ash. The modified biomass ash exhibited high affinity for Cd2+ and its adsorption capacity increased sharply with increasing pH from 4.0 to 6.0. The maximum adsorption capacity was 23.95 mg/g in a pH 5 solution with an initial metal concentration of 50 mg/L and a contact time of 90 min. The adsorption of Cd2+ onto the modified biomass ash was well fitted to the Langmuir model and it followed pseudo-second-order kinetics. Thermodynamic analysis results showed that the adsorption of Cd2+ was spontaneous and endothermic in nature. The results suggest that the modified biomass ash is promising for use as an inexpensive and effective adsorbent for Cd2+ removal from aqueous solution. PMID:28348509

  7. DFT study on the adsorption of diethyl, ethyl methyl, and dimethyl ethers on the surface of gallium doped graphene

    NASA Astrophysics Data System (ADS)

    Shokuhi Rad, Ali; Sani, Emad; Binaeian, Ehsan; Peyravi, Majid; Jahanshahi, Mohsen

    2017-04-01

    In this study, we used density functional theory (DFT) to search on the adsorption properties of three important compounds of ether family; diethyl ether (DEE), ethyl methyl ether (EME), and dimethyl ether (DME) on the surface of Gallium doped graphene (GaG). We used three functionals (B3LYP, wb97xd, and MPW1PW91) for optimization and calculation of adsorption energy. After fully optimization, we scrutinized on the charge allocations on the adsorbed ethers as well as GaG (at the area of interaction) based on natural bond orbitals (NBO). Besides, we have calculated the amount of charge transfer upon adsorption of each analyte. We revel that GaG is an ideal adsorbent for chemisorption of all above-mentioned ethers. There is a little difference between the values of adsorption; -123.5, -120, and -118.3 kJ/mol (based on wb97xd) for DEE, EME, and DME, respectively. We found significant changes in the electronic structure of both adsorbent and adsorbate upon adsorption. Moreover, results of charge analyses confirm GaG is a p-type semiconductor.

  8. Development of equations for differential and integral enthalpy change of adsorption for simulation studies.

    PubMed

    Do, D D; Nicholson, D; Fan, Chunyan

    2011-12-06

    We present equations to calculate the differential and integral enthalpy changes of adsorption for their use in Monte Carlo simulation. Adsorption of a system of N molecules, subject to an external potential energy, is viewed as one of transferring these molecules from a reference gas phase (state 1) to the adsorption system (state 2) at the same temperature and equilibrium pressure (same chemical potential). The excess amount adsorbed is the difference between N and the hypothetical amount of gas occupying the accessible volume of the system at the same density as the reference gas. The enthalpy change is a state function, which is defined as the difference between the enthalpies of state 2 and state 1, and the isosteric heat is defined as the negative of the derivative of this enthalpy change with respect to the excess amount of adsorption. It is suitable to determine how the system behaves for a differential increment in the excess phase adsorbed under subcritical conditions. For supercritical conditions, use of the integral enthalpy of adsorption per particle is recommended since the isosteric heat becomes infinite at the maximum excess concentration. With these unambiguous definitions we derive equations which are applicable for a general case of adsorption and demonstrate how they can be used in a Monte Carlo simulation. We apply the new equations to argon adsorption at various temperatures on a graphite surface to illustrate the need to use the correct equation to describe isosteric heat of adsorption.

  9. UPS STUDY OF THE ADSORPTION OF OXYGEN ON REDUCED SrTiO{sub 3} SURFACES

    SciTech Connect

    Ferrer, S.; Somorjai, G. A.

    1980-10-01

    The adsorption of oxygen on a reduced SrTiO{sub 3} (111) surface occurs in two distinct phases. At low exposures (less than 1 L), the adsorption leads to the incorporation of O{sup =} ions into the vacant lattice oxygen sites. At higher exposures a second different oxygen species adsorbs.

  10. Adsorption of leather dye onto activated carbon prepared from bottle gourd: equilibrium, kinetic and mechanism studies.

    PubMed

    Foletto, Edson Luiz; Weber, Caroline Trevisan; Paz, Diego Silva; Mazutti, Marcio Antonio; Meili, Lucas; Bassaco, Mariana Moro; Collazzo, Gabriela Carvalho

    2013-01-01

    Activated carbon prepared from bottle gourd has been used as adsorbent for removal of leather dye (Direct Black 38) from aqueous solution. The activated carbon obtained showed a mesoporous texture, with surface area of 556.16 m(2) g(-1), and a surface free of organic functional groups. The initial dye concentration, contact time and pH significantly influenced the adsorption capacity. In the acid region (pH 2.5) the adsorption of dye was more favorable. The adsorption equilibrium was attained after 60 min. Equilibrium data were analyzed by the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherm models. The equilibrium data were best described by the Langmuir isotherm, with maximum adsorption capacity of 94.9 mg g(-1). Adsorption kinetic data were fitted using the pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion models. The adsorption kinetic was best described by the second-order kinetic equation. The adsorption process was controlled by both external mass transfer and intraparticle diffusion. Activated carbon prepared from bottle gourd was shown to be a promising material for adsorption of Direct Black 38 from aqueous solution.

  11. Kinetic Study of Adsorption Processes in Solution: An Undergraduate Physical Chemistry Experiment.

    ERIC Educational Resources Information Center

    Casado, Julio; And Others

    1985-01-01

    Background information, apparatus needed, procedures used, and results obtained are provided for a simple kinetic method for the monitoring of adsorption processes. The method, which involved adsorption of crystal violet onto activated carbon, is suitable for classroom and/or research purposes. (JN)

  12. Promoting the Adsorption of Metal Ions on Kaolinite by Defect Sites: A Molecular Dynamics Study

    PubMed Central

    Li, Xiong; Li, Hang; Yang, Gang

    2015-01-01

    Defect sites exist abundantly in minerals and play a crucial role for a variety of important processes. Here molecular dynamics simulations are used to comprehensively investigate the adsorption behaviors, stabilities and mechanisms of metal ions on defective minerals, considering different ionic concentrations, defect sizes and contents. Outer-sphere adsorbed Pb2+ ions predominate for all models (regular and defective), while inner-sphere Na+ ions, which exist sporadically only at concentrated solutions for regular models, govern the adsorption for all defective models. Adsorption quantities and stabilities of metal ions on kaolinite are fundamentally promoted by defect sites, thus explaining the experimental observations. Defect sites improve the stabilities of both inner- and outer-sphere adsorption, and (quasi) inner-sphere Pb2+ ions emerge only at defect sites that reinforce the interactions. Adsorption configurations are greatly altered by defect sites but respond weakly by changing defect sizes or contents. Both adsorption quantities and stabilities are enhanced by increasing defect sizes or contents, while ionic concentrations mainly affect adsorption quantities. We also find that adsorption of metal ions and anions can be promoted by each other and proceeds in a collaborative mechanism. Results thus obtained are beneficial to comprehend related processes for all types of minerals. PMID:26403873

  13. Development, Construction, and Operation of a Multisample Volumetric Apparatus for the Study of Gas Adsorption Equilibrium

    ERIC Educational Resources Information Center

    Ribeiro, Rui P. P. L.; Silva, Ricardo J. S.; Esteves, Isabel A. A. C.; Mota, Jose´ P. B.

    2015-01-01

    The construction of a simple volumetric adsorption apparatus is highlighted. The setup is inexpensive and provides a clear demonstration of gas phase adsorption concepts. The topic is suitable for undergraduate chemistry and chemical engineering students. Moreover, this unit can also provide quantitative data that can be used by young researchers…

  14. Theoretical study on (Al2O3)n (n = 1-10 and 30) fullerenes and H2 adsorption properties.

    PubMed

    Sun, Jiao; Lu, Wen-Cai; Zhang, Wei; Zhao, Li-Zhen; Li, Ze-Sheng; Sun, Chia-Chung

    2008-04-07

    The structures and stabilities of (Al2O3)n (n = 1-10 and 30) clusters were studied by means of first principles calculations. The calculated results reveal that the global minima of small (Al2O3)n (n = 1-5) clusters are cage structures with high symmetries, in which Al and O atoms are three- and two-coordinated, respectively, and are linked to neighbors via single bonds. Beyond (Al2O3)5, we calculated both cage and cage-dimer structures for (Al2O3)n (n = 6-10), and the results show that, at this size range, cage-dimer structures are more stable than cage structures. Furthermore, an onion-like motif for (Al2O3)10 was studied, and it is interesting to find that, at this size, the onion structure is more favorable than cage and cage-dimer structures. For large clusters, a shell structure of Al60O90 is suggested. Electronic properties and calculations on hydrogen adsorption of these aluminum oxide structures are reported, and we discuss their possible use as hydrogen storage materials.

  15. Mechanism of Pb Adsorption to Fatty Acid Langmuir Monolayers Studied by X-ray Absorption Fine Structure Spectroscopy

    SciTech Connect

    Boyanov, M.I.; Kmetko, J.; Shibata, T.; Datta, A.; Dutta, P.; Bunker, B.A.

    2010-09-30

    The local atomic environment of lead (Pb) adsorbed to a CH{sub 3}(CH{sub 2}){sub 19}COOH Langmuir monolayer was investigated in situ using grazing-incidence X-ray absorption fine structure (GI-XAFS) spectroscopy at the Pb L{sub III} edge. Measurements were performed at pH 6.5 of the 10{sup -5} M PbCl{sub 2} solution subphase, a condition under which grazing incidence diffraction (GID) revealed a large-area commensurate superstructure underneath the close-packed organic monolayer. The XAFS results indicate covalent binding of the Pb cations to the carboxyl headgroups, and the observed Pb-Pb coordination suggests that the metal is adsorbed as a hydrolysis polymer, rather than as individual Pb{sup 2+} ions. The data are consistent with a bidentate chelating mechanism and a one Pb atom to one carboxyl headgroup binding stoichiometry. We discuss how this adsorption model can explain the peculiarities observed with Pb in previous metal-Langmuir monolayer studies. A systematic study of lead perchlorate and lead acetate aqueous solutions is presented and used in the analysis. XAFS multiple scattering effects from alignment of the Pb-C-C atoms in the lead acetate solutions are reported.

  16. A Simple Adsorption Experiment

    ERIC Educational Resources Information Center

    Guirado, Gonzalo; Ayllon, Jose A.

    2011-01-01

    The study of adsorption phenomenon is one of the most relevant and traditional physical chemistry experiments performed by chemistry undergraduate students in laboratory courses. In this article, we describe an easy, inexpensive, and straightforward way to experimentally determine adsorption isotherms using pieces of filter paper as the adsorbent…

  17. Theoretical and experimental studies on low-temperature adsorption drying of fresh ginger

    NASA Astrophysics Data System (ADS)

    Yang, Xiaoxi; Xu, Wei; Ding, Jing; Zhao, Yi

    2006-03-01

    The working principle of low-temperature adsorption drying and the advantages of its application for biological materials drying were introduced in this paper. By using fresh ginger as the drying material, the effects of temperature and relative humidity on its drying characteristics were examined. The results show that the drying rate increases with the temperature increasing or the humidity decreasing. The drying time to the equilibrium is almost the same under different humidity conditions, but low equilibrium moisture content can be acquired under low humidity. The shrinkage characteristics of fresh ginger were also studied. The change of its surface appearance during the drying process was characterized by the new Charged Coupled Device (CCD) and the Environmental Scanning Electron Microscopy (ESEM) technique. A mathematical model of drying dynamics was set up according to the experiments.

  18. DFT STUDY OF CO AND NO ADSORPTION ON BORON NITRIDE (BN)n = 3 - 5 NANOCLUSTERS

    NASA Astrophysics Data System (ADS)

    Zahedi, Ehsan; Pangh, Abdolhakim; Ghorbanpour, Hamed

    2015-11-01

    Interaction of CO and NO molecules by different orientations on (BN)n=3-5 clusters have been studied at the B3LYP/6-311+G* level of theory. Total electronic energies have been corrected for geometrical counterpoise (gCP) and dispersion (D3) energies at the B3LYP/6-31G* level. Formation of a new sigma bond between the gas and (BN)3 cluster, atom in molecules (AIM) results, density of states spectrums (DOS), molecular electrostatic potential (MEP) surfaces, and visualization of wave function of molecular orbitals in the nearest bonding regions to the Fermi level have confirmed that adsorption of CO by carbon end atom, and NO by nitrogen end atom is covalent in nature, so that the charge transfer is occurred from gas molecule to the cluster.

  19. Solvation Dynamics and Adsorption on Ag Hydrosols of Oxazole: A Raman and Computational Study

    NASA Astrophysics Data System (ADS)

    Pagliai, Marco; Muniz-Miranda, Maurizio; Cardini, Gianni; Schettino, Vincenzo

    2009-09-01

    The interactions between oxazole and water or silver nanoparticles in aqueous dispersions have been studied with a computational approach based on ab initio molecular dynamics simulations, with the Car-Parrinello method, and density functional calculations in combination with Raman and surface enhanced Raman scattering (SERS) experiments. The solvation dynamics of oxazole in water allowed for the characterization of the hydrogen bond between water and solute, which has been shown to occur essentially through the nitrogen atom of the heterocyclic molecule. To mimic the solvation process or the adsorption on silver and interpreting the corresponding Raman and SERS spectra in aqueous solution or in Ag hydrosols, density functional calculations have been carried out on model systems made up by oxazole bound to water molecules or to positively charged silver clusters. Also, the chemisorption on Ag nanoparticles is found to occur by means of the nitrogen atom of oxazole interacting with the metal substrate.

  20. Neutron scattering study of H2 adsorption in single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Ren, Y.; Price, D. L.

    2001-11-01

    H2 adsorption in single-walled carbon nanotubes (SWCNTs) has been studied with quasielastic and inelastic neutron scattering. At 80 K, under a H2 pressure of 110 atm, H2 molecules gradually condense in the SWCNT sample. After pumping out at 25 K and 20 mTorr, the remaining H2 molecules show a quantum rotational transition at 14.5±0.1 meV, with a peak width that increases linearly with increasing temperature from 4.2 to 35 K. The H2 molecules remain in the sample up to 65 K and then start to desorb with increasing temperature. A broad inelastic scattering spectrum from the adsorbed hydrogen is also observed. The time scale of the dynamics is longer than 15 ps even at 200 K. Our results imply that hydrogen molecules are physisorbed in the interstitial tunnels of the SWCNT bundles.

  1. Adsorption and Corrosion Inhibition Studies of Some Selected Dyes as Corrosion Inhibitors for Mild Steel in Acidic Medium: Gravimetric, Electrochemical, Quantum Chemical Studies and Synergistic Effect with Iodide Ions.

    PubMed

    Peme, Thabo; Olasunkanmi, Lukman O; Bahadur, Indra; Adekunle, Abolanle S; Kabanda, Mwadham M; Ebenso, Eno E

    2015-09-02

    The corrosion inhibition properties of some organic dyes, namely Sunset Yellow (SS), Amaranth (AM), Allura Red (AR), Tartrazine (TZ) and Fast Green (FG), for mild steel corrosion in 0.5 M HCl solution, were investigated using gravimetric, potentiodynamic polarization techniques and quantum chemical calculations. The results showed that the studied dyes are good corrosion inhibitors with enhanced inhibition efficiencies. The inhibition efficiency of all the studied dyes increases with increase in concentration, and decreases with increase in temperature. The results showed that the inhibition efficiency of the dyes increases in the presence of KI due to synergistic interactions of the dye molecules with iodide (I(-)) ions. Potentiodynamic polarization results revealed that the studied dyes are mixed-type inhibitors both in the absence and presence of KI. The adsorption of the studied dyes on mild steel surface, with and without KI, obeys the Langmuir adsorption isotherm and involves physical adsorption mechanism. Quantum chemical calculations revealed that the most likely sites in the dye molecules for interactions with mild steel are the S, O, and N heteroatoms.

  2. First Principles and STM Studies of Cl Adsorption on TiO2 (110) Surfaces

    NASA Astrophysics Data System (ADS)

    Vogtenhuber, D.; Podloucky, R.; Redinger, J.; Hebenstreit, E. L. D.; Hebenstreit, W.; Diebold, U.

    2000-03-01

    Atomic Cl adsorption on reduced and stoichiometric TiO2 (110) surfaces was calculated by applying a Full Potential Linearized Augmented Plane Wave method (FLEUR), and the Tersoff-Hamann model for simulating STM images. The electronic structure results are compared to experimental ISS, STM and XPS data for dissociative adsorption of Cl_2. Adsorption on O-defect sites, which is favored from our results of the adsorption energies, is found experimentally at elevated T (> 200^circ C) only. According to measurements at low T, adsorption in registry with the bridging O seems to be kinetically hindered. Distinct differences between high- and low T adsoption types are found for ISS, STM, \\varphi and Cl-2p bonding energies, in excellent agreement between calculations and experiment.

  3. Petroleum resins adsorption onto quartz sand: near infrared (NIR) spectroscopy study.

    PubMed

    Balabin, Roman M; Syunyaev, Rustem Z

    2008-02-15

    In this paper we have tried to evaluate adsorption parameters of petroleum resins. Near infrared (NIR) spectroscopy is applied for resins bulk concentration evaluation during adsorption process. NIR experimental scheme and parameters are provided. NIR spectra range of 9000-13,000 cm(-1) is chosen. Quartz sand (0.2-0.8 mm fraction) is used as adsorbent; benzene is used as solvent. Different approaches of "NIR spectra-resins concentration" calibration model building are discussed. Partial least squares (PLS) regression method is used. Langmuir model is chosen for experimental data fitting. Combined usage of kinetic and isothermic data gives us ability to evaluate the maximal adsorbed mass density, the equilibrium constant of adsorption, and the rate constants of adsorption (and desorption). The rate constants of resins adsorption and desorption are found to be concentration independent.

  4. ADSORPTION AND DISSOCIATION OF O2 ON Ti3Al (0001) STUDIED BY FIRST-PRINCIPLES

    NASA Astrophysics Data System (ADS)

    Wei, Li-Jing; Guo, Jian-Xin; Dai, Xiu-Hong; Wang, Ying-Long; Liu, Bao-Ting

    2015-05-01

    The adsorption and dissociation of oxygen molecule on Ti3Al (0001) surface have been investigated by density functional theory (DFT) with the generalized gradient approximation (GGA). All possible adsorption sites including nine vertical and fifteen parallel sites of O2 are considered on Ti3Al (0001) surface. It is found that all oxygen molecules dissociate except for three vertical adsorption sites after structure optimization. This indicates that oxygen molecules prefer to dissociate on the junction site between Ti and Al atoms. Oxygen atoms coming from dissociation of oxygen molecule tend to occupy the most stable adsorption sites of the Ti3Al (0001) surface. The distance of O-O is related to the surface dissociation distance of Ti3Al (0001) surface. The valence electron localization function (ELF) and projected density of states (DOS) show that the bonds of O-O are breakaway at parallel adsorption end structures.

  5. An experimental study of adsorption interference in binary mixtures flowing through activated carbon

    NASA Technical Reports Server (NTRS)

    Madey, R.; Photinos, P. J.

    1983-01-01

    The isothermal transmission through activated carbon adsorber beds at 25 C of acetaldehyde-propane and acetylene-ethane mixtures in a helium carrier gas was measured. The inlet concentration of each component was in the range between 10 ppm and 500 ppm. The constant inlet volumetric flow rate was controlled at 200 cc (STP)/min in the acetaldehyde-propane experiments and at 50 cc (STP)/min in the acetaldehyde-ethane experiments. Comparison of experimental results with the corresponding single-component experiments under similar conditions reveals interference phenomena between the components of the mixtures as evidenced by changes in both the adsorption capacity and the dispersion number. Propane was found to displace acetaldehyde from the adsorbed state. The outlet concentration profiles of propane in the binary mixtures tend to become more diffuse than the corresponding concentration profiles of the one-component experiments. Similar features were observed with mixtures of acetylene and ethane; however, the displacement of acetylene by ethane is less pronounced.

  6. Adsorption of desflurane by the silica gel filters in breathing circuits: an in vitro study

    PubMed Central

    Song, Seok Young; Lim, Bo Reum

    2015-01-01

    Background During general anesthesia, a heated breathing circuit (HBC) is used to replace the heat and moisture exchange function of the upper airway. One HBC uses an air dryer filter that employs silica gel (SG) as a desiccant. SG is capable of adsorbing many organic compounds. Therefore, we undertook an in vitro study of the adsorption of desflurane by SG filters. Methods An HBC was connected to an anesthesia machine, and a test lung was connected to the circuit. The test lung was mechanically ventilated with 2 or 4 L/min of fresh gas flow, with and without the air dryer filter. Desflurane was administered at a 6 vol% on the vaporizer dial setting. The experiment was repeated 15 times in each group. The end-tidal concentrations were measured during the experiments. The air dryer filter weights were measured before and after the experiments, and the times required to achieve the specific end-tidal desflurane concentrations were determined. Results Significant differences in the end-tidal concentrations of desflurane were observed between the control and filter groups (P < 0.001). The filter weights increased significantly after the experiments (P < 0.001). The times required to achieve the same end-tidal desflurane concentrations were different with the application of the air dryer filter (P < 0.001). Conclusions The adsorption of desflurane with the use of an air dryer filter was verified in this in vitro study. Careful attention is needed when using air dryer gel filters during general anesthesia. PMID:26045931

  7. A comparative study and evaluation of sulfamethoxazole adsorption onto organo-montmorillonites.

    PubMed

    Lu, Laifu; Gao, Manglai; Gu, Zheng; Yang, Senfeng; Liu, Yuening

    2014-12-01

    Three organo-montmorillonites were prepared using surfactants, and their adsorption behaviors toward sulfamethoxazole (SMX) were investigated. The surfactants used were cetyltrimethyl ammonium bromide (CTMAB), 3-(N,N-dimethylhexadecylammonio) propane sulfonate (HDAPS) and 1,3-bis(hexadecyldimethylammonio)-propane dibromide (BHDAP). The properties of the organo-montmorillonites were characterized by X-ray diffraction, scanning electron microscopy and N2 adsorption-desorption isotherm measurements. Results showed that the interlayer spacing of montmorillonite was increased and the surface area as well as the morphology were changed. Batch adsorption experiments showed that the surfactant loading amount had a great effect on the adsorption of SMX. The adsorption process was pH dependent and the maximum adsorption capacity was obtained at pH3 for HDAPS-Mt, while CTMAB-Mt and BHDAP-Mt showed a high removal efficiency at 3-11. The adsorption capacity increased with the initial SMX concentration and contact time but decreased with increasing solution ionic strength. Kinetic data were best described by the pseudo second-order model. Equilibrium data were best represented by the Langmuir model, and the Freundlich constant (n) indicated a favorable adsorption process. The maximum adsorption capacity of SMX was 235.29 mg/g for CTMAB-Mt, 155.28 mg/g for HDAPS-Mt and 242.72 mg/g for BHDAP-Mt. Thermodynamic parameters were calculated to evaluate the spontaneity and endothermic or exothermic nature. The adsorption mechanism was found to be dominated by electrostatic interaction, while hydrophobic interaction played a secondary role.

  8. Study of protein adsorption on indigo particles confirms the existence of enzyme--indigo interaction sites in cellulase molecules.

    PubMed

    Gusakov, A V; Sinitsyn, A P; Markov, A V; Sinitsyna, O A; Ankudimova, N V; Berlin, A G

    2001-04-27

    Adsorption of several crude and purified cellulases (from Trichoderma reesei, Penicillium verruculosum and Chrysosporium lucknowense) on indigo particles and Avicel cellulose was studied. Much higher amounts of protein were bound to indigo than to cellulose under similar conditions. For different purified enzymes, the quantity of bound protein per mg of adsorbent (indigo or cellulose) varied in the range of 57-111 and 0-62 microg x mg(-1), respectively. However, in general, the enzyme adsorption on indigo was less specific than the adsorption on cellulose. Three endoglucanases, having the highest indigo-binding ability, demonstrated the best washing performance in the process of enzymatic denim treatment. These data confirmed our previous findings that certain cellulases, which have indigo-binding sites (clusters of closely located aromatic and other non-polar residues) on the surface of their molecules, may remove indigo from the denim fabric better than cellulases with lower content of hydrophobic residues exposed to solvent.

  9. Preparation of a porous clay heterostructure and study of its adsorption capacity of phenol and chlorinated phenols from aqueous solutions.

    PubMed

    Arellano-Cárdenas, Sofía; Gallardo-Velázquez, Tzayhrí; Osorio-Revilla, Guillermo; López-Cortez, Ma del Socorro

    2008-01-01

    A porous clay heterostructure (PCH) from a Mexican clay was prepared and characterized, and its aqueous phenol and dichlorophenols (DCPs) adsorption capacities were studied using a batch equilibrium technique. The PCH displayed a surface area of 305.5 m2/g, 37.2 A average porous diameter, and a basal space of 23.2 A. The adsorption capacity shown by the PCH for both phenol and DCPs from water (14.5 mg/g for phenol; 48.7 mg/g for 3,4-DCP; and 45.5 mg/g for 2,5-DCP) suggests that the PCH has both hydrophobic and hydrophilic characteristics, as a result of the presence of silanol and siloxane groups formed during the pillaring and calcination of the PCH. The values of maximal adsorption capacity for dichlorophenols were higher than those reported for aluminum pillared clays and some inorgano-organo clays and comparable with some ionic exchange resins.

  10. Neutron and X-ray reflectivity studies on DNA adsorption on mixed DPPC/DC-Cholesterol monolayers

    NASA Astrophysics Data System (ADS)

    Wu, Jui-Ching; Lin, Tsang-Lang; Jeng, U.-Ser; Lee, Hsin-Yi; Gutberlet, Thomas

    2006-11-01

    We have studied DNA adsorption on mixed DPPC/DC-Chol monolayers. Solid supported mixed monolayers on silicon wafers were prepared using Langmuir-Blodgett (LB) dipping technique. Neutron and X-ray reflectivity measurements were used to characterize these LB monofilms. For LB monofilms with DNA adsorption, the reflectivity data of the DPPC/DNA film are very close to that from the DPPC film, which indicates only minor DNA adsorption on the pure DPPC monolayer. Increasing the percentage of DC-Chol, film thickness increases. The DC-Chol/DNA film is thicker than the pure DC-Chol film (film thickness 18 Å) by about 9 Å due to the presence of adsorbed DNA. A model is presented to explain the structure of the lipid/DNA film.

  11. ISS and TPD study of the adsorption and interaction of CO and H2 on polycrystalline Pt

    NASA Technical Reports Server (NTRS)

    Melendez, Orlando; Hoflund, Gar B.; Schryer, David R.

    1990-01-01

    The adsorption and interaction of CO and H2 on polycrystalline Pt has been studied using ion scattering spectroscopy (ISS) and temperature programmed desorption (TPD). The ISS results indicate that the initial CO adsorption on Pt takes place very rapidly and saturates the Pt surface with coverage close to a monolayer. ISS also shows that the CO molecules adsorb at an angular orientation from the surface normal and perhaps parallel to the surface. A TPD spectrum obtained after coadsorbing C-12 O-16 and C-13 O-18 on Pt shows no isotopic mixing, which is indicative of molecular CO adsorption. TPD spectra obtained after coadsorbing H2 and CO on polycrystalline Pt provides evidence for the formation of a CO-H surface species.

  12. Adsorption and hydrogenation of simple alkenes at Pt-group metal electrodes studied by DEMS: influence of the crystal orientation

    NASA Astrophysics Data System (ADS)

    Müller, Ulrich; Schmiemann, Udo; Dülberg, Andreas; Baltruschat, Helmut

    1995-07-01

    The adsorption of ethene and cyclohexene on mono-and polycrystalline Pt and on polycrystalline Pd electrodes was studied using differential electrochemical mass spectrometry (DEMS). Both molecules are partially hydrated to an oxygen containing species upon adsorption on Pt. In the case of ethene, this species dissociated to methane and adsorbed CO at negative potentials. Another part of the adsorbed ethene can be cathodically desorbed as ethane and butane. The ratio of the various species formed strongly depends on crystal orientation and adsorption potential. Contrary to heterogenous gas phase hydrogenation (and also contrary to some earlier reports on electrochemical hydrogenation), the rate of the Faradaic hydrogenation reaction is also strongly dependent on the crystallographic orientation, being faster on Pt(110) or roughened surfaces. During hydrogenation, H/D exchange occurs to an appreciable degree, suggesting the participation of adsorbed intermediates.

  13. Lysozyme immobilization via adsorption process using sulphonic acid functionalized silane grafted copolymer.

    PubMed

    Anirudhan, T S; Rauf, Tharun A

    2013-07-01

    A unique silane based adsorbent material, [stearyl alcohol (SA)-grafted-epichlorohydrin (E)]-grafted-aminoproypyl silanetriol (APST) was synthesized and functionalized with sulphonyl groups via sulphonation process [(SA-g-E)-g-APST/SO3H]. The adsorbent material characterization was done by FTIR, XRD, and TGA analysis. Immobilization of protein Lysozyme (LYZ) using batch adsorption process was carried out for studying the protein-particle interaction. The most suitable pH for maximum adsorption was found to be 7.0. Pseudo-second-order kinetic model was found to be the best fit and the adsorption equilibrium was attained within 3h. Studies on diffusion parameters explained that the adsorption mechanism was controlled by film diffusion mode. The adsorption process was then evaluated using the various isotherm models and the Sips isotherm model proved to be the best fit with a maximum adsorption capacity of 37.68 mg/g. The isotherm favorability of the adsorption process was calculated by calculating the separation factor (R(L)) and the values confirmed the favorability of the adsorption process. Studies on adsorption percentage with respect to temperature and thermodynamic studies revealed that adsorption process is exothermic, spontaneous with maximum entropy. Batch adsorption/desorption studies in acidic medium, for over six cycles showed the repeatability and regeneration capability of the adsorbent material (SA-g-E)-g-APST/SO3H.

  14. Fibronectin and bovine serum albumin adsorption and conformational dynamics on inherently conducting polymers: a QCM-D study.

    PubMed

    Molino, Paul J; Higgins, Michael J; Innis, Peter C; Kapsa, Robert M I; Wallace, Gordon G

    2012-06-05

    Quartz crystal microbalance with dissipation monitoring (QCM-D) was employed to characterize the adsorption of the model proteins, bovine serum albumin (BSA) and fibronectin (FN), to polypyrrole doped with dextran sulfate (PPy-DS) as a function of DS loading and surface roughness. BSA adsorption was greater on surfaces of increased roughness and was above what could be explained by the increase in surface area alone. Furthermore, the additional mass adsorbed on the rough films was concomitant with an increase in the rigidity of the protein layer. Analysis of the dynamic viscoelastic properties of the protein adlayer reveal BSA adsorption on the rough films occurs in two phases: (1) arrival and initial adsorption of protein to the polymer surface and (2) postadsorption molecular rearrangement to a more dehydrated and compact conformation that facilitates further recruitment of protein to the polymer interface, likely forming a multilayer. In contrast, FN adsorption was independent of surface roughness. However, films prepared from solutions containing the highest concentration of DS (20 mg/mL) demonstrated both an increase in adsorbed mass and adlayer viscoelasticity. This is attributed to the higher DS loading in the conducting polymer film resulting in presentation of a more hydrated molecular structure indicative of a more unfolded and bioactive conformation. Modulating the redox state of the PPy-DS polymers was shown to modify both the adsorbed mass and viscoelastic nature of FN adlayers. An oxidizing potential increased both the total adsorbed mass and the adlayer viscoelasticity. Our findings demonstrate that modification of polymer physicochemical and redox condition alters the nature of protein-polymer interaction, a process that may be exploited to tailor the bioactivity of protein through which interactions with cells and tissues may be controlled.

  15. Quartz crystal microbalance with dissipation monitoring and surface plasmon resonance studies of carboxymethyl cellulose adsorption onto regenerated cellulose surfaces.

    PubMed

    Liu, Zelin; Choi, Heejun; Gatenholm, Paul; Esker, Alan R

    2011-07-19

    Adsorption of anionic polyelectrolytes, sodium salts of carboxymethyl celluloses (CMCs) with different degrees of substitution (DS = 0.9 and 1.2), from aqueous electrolyte solutions onto regenerated cellulose surfaces was studied using quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) experiments. The influence of both calcium chloride (CaCl(2)) and sodium chloride (NaCl) on CMC adsorption was examined. The QCM-D results demonstrated that CaCl(2) (divalent cation) caused significantly greater CMC adsorption onto regenerated cellulose surfaces than NaCl (monovalent cation) at the same ionic strength. The CMC layers adsorbed onto regenerated cellulose surfaces from CaCl(2) solutions exhibited greater stability upon exposure to flowing water than layers adsorbed from NaCl solutions. Both QCM-D and SPR results showed that CMC adsorption onto regenerated cellulose surfaces from CaCl(2) solutions increased with increasing CaCl(2) concentration up to the solubility limit (10 mM). Voigt-based viscoelastic modeling of the QCM-D data indicated that the CMC layers adsorbed onto regenerated cellulose surfaces had shear viscosities of η(f) ≈ 10(-3) N·s·m(-2) and elastic shear moduli of μ(f) ≈ 10(5) N·m(-2). Furthermore, the combination of SPR spectroscopy and QCM-D showed that the CMC layers contained 90-95% water. Adsorption isotherms for CMCs in CaCl(2) solutions were also obtained from QCM-D and were fit by Freundlich isotherms. This study demonstrated that CMC adsorption from CaCl(2) solutions is useful for the modification of cellulose surfaces.

  16. Effect of grafted PEG chain conformation on albumin and lysozyme adsorption: A combined study using QCM-D and DPI.

    PubMed

    Jin, Jing; Han, Yuanyuan; Zhang, Chang; Liu, Jingchuan; Jiang, Wei; Yin, Jinghua; Liang, Haojun

    2015-12-01

    In this study, elucidation of protein adsorption mechanism is performed using dual polarization interferometry (DPI) and quartz crystal microbalance with dissipation (QCM-D) to study adsorption behaviors of bovine serum albumin (BSA) and lysozyme (LYZ) on poly (ethylene glycol) (PEG) layers. From the analysis of DPI, PEG2000 and PEG5000 show tight and loose mushroom conformations, respectively. Small amount of LYZ could displace the interfacial water surrounding the tight mushroomed PEG2000 chains by hydrogen bond attraction, leading to protein adsorption. The loose mushroomed PEG5000 chains exhibit a more flexible conformation and high elastic repulsion energy that could prevent protein adsorption of all BSA and most of LYZ. From the analysis of QCM, PEG2000 and PEG5000 show tight and extended brush conformations. The LYZ adsorbed mass has critical regions of PEG2000 (0.19 chain/nm(2)) and PEG5000 (0.16 chain/nm(2)) graft density. When graft density of PEG is higher than the critical region (brush conformations), the attraction of hydrogen bonds between PEG and LYZ is the dominant factor. When graft density of PEG is lower than the critical region (mushroom conformations), elastic repulsion between PEG and proteins is driven by the high conformation entropy of PEG chains, which is the dominant force of steric repulsion in PEG-protein systems. Therefore, the adsorption of BSA is suppressed by the high elastic repulsion energy of PEG chains, whereas the adsorption of LYZ is balanced by the interactions between the repulsion of entropy elasticity and the attraction of hydrogen bonds.

  17. Study of polyethyleneimine- and amidoxime-functionalized hybrid biomass of Spirulina (Arthrospira) platensis for adsorption of uranium (VI) ion.</