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Sample records for adsorption studies showed

  1. 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.

  2. 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.

  3. Kinetic Interpretation of Water Vapor Adsorption-Desorption Behavior of a Desiccant Rotor Showing S-shaped Adsorption Isotherm

    NASA Astrophysics Data System (ADS)

    Okamoto, Kumiko; Oshima, Kazunori; Takewaki, Takahiko; Kodama, Akio

    Adsorption / desorption behavior of water vapor in a desiccant rotor containing an iron aluminophosphate type zeolite FAM-Z01 (Functional Adsorbent Material Zeolite 01) was experimentally investigated for humidity swing. This rotor exhibited an S-shaped adsorption isotherm with its temperature dependence. Humidity swing, using a small piece of the rotor, could be usefully applied to interpret adsorption / desorption mechanisms by observing their rates. The most significant finding was that the adsorption / desorption rates in humidity swing could be described by the amount of adsorption, temperature and amplitude of the humidity swing, not by cycle time. Also, using the liner driving force (LDF) model, the overall mass transfer coefficient changed with the elapse of time or with the amount of adsorbed water. This implied that the LDF model, considering constant value of the overall mass transfer coefficient, was probably unable to explain the water adsorption / desorption behavior of FAM-Z01 desiccant rotor.

  4. 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.

  5. 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.

  6. Studies of gas adsorption in flexible Metal-Organic frameworks

    NASA Astrophysics Data System (ADS)

    Sircar, Sarmishtha

    Flexible Metal-Organic frameworks that exhibit a gate-opening (GO) adsorption mechanism have potential for gas separations and gas storage. The GO phenomenon occurs when molecular gates in the structure expand/contract in response to the activation/de-activation of a system variable e.g. temperature, pressure or gas. Sharp discontinuities in the isotherm leading to S-shapes and large adsorption-desorption hysteresis are typical of this phenomenon. This study investigates the kinetics and thermodynamics of the GO behavior by combining adsorption measurements and analytical modeling of adsorption kinetics and capacity as a function of adsorbate, GO pressure, and temperature. Basic understanding of GO mechanism will help harness GO-MOF's as adsorbents for gas separations and storage. Experiments were performed on two precharacterized MOFs with verified GO behavior. These are (1) Zn2(bpdc)2(bpee), which expands from a relative amorphous to crystalline structure and (2) Cu[(dhbc) 2(4,4f-bpy)]H2O, a mutually interdigitated 2-D structure (bpdc = biphenyldicarboxylate, bpee = 1,2]bipyridylethene; DMF = N,N-dimethyl formamide, dhbc= 2,5-dihydroxybenzoic acid, bpy=bipyridine). Both sub- and super-critical adsorption data were collected using three adsorption units: a standard low-pressure volumetric adsorption unit, a commercial high-pressure gravimetric analyzer and a custom-built high-pressure differential volumetric unit. Collected laboratory data were combined with published adsorption rate and isotherm data for analysis to broaden the range of data collection. The accuracy of the high-pressure differential unit was improved by over 300-fold by changing analytical methods of processing data to establish a reliable null correction. A pronounced effect of the allowed experimental time was found at cryogenic temperatures on (1). Tightening the stability criteria used by the adsorption equipment to determine equilibration increased the experimental time from the order of

  7. 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.

  8. A Density Functional Theory Study of Formaldehyde Adsorption on Ceria

    SciTech Connect

    Mei, Donghai; Deskins, N. Aaron; Dupuis, Michel

    2007-11-01

    Molecular adsorption of formaldehyde on the stoichiometric CeO2(111) and CeO2(110) surfaces was studied using periodic density functional theory. Two adsorption modes (strong chemisorbed and weak physisorbed) were identified on both surfaces. This is consistent with recent experimental observations. On the (111) surface, formaldehyde strongly chemisorbs with an adsorption energy of 0.86 eV to form a dioxymethylene-like structure, in which a surface O lifts from the surface to bind with the C of formaldehyde. A weak physisorbed state with adsorption energy of 0.28 eV was found with the O of formaldehyde interacting with a surface Ce. On the (110) surface, dioxymethyelene formation was also observed, with an adsorption energy of 1.31 eV. The weakly adsorbed state of formaldehyde on the (110) surface was energetically comparable to the weak adsorption state on the (111) surface, but adsorption occurred through a formaldehyde C and surface O interaction. Analysis of the local density of states and charge density differences after adsorption shows that strong covalent bonding occurs between the C of formaldehyde and surface O when dioxymethylene forms. Calculated vibrational frequencies also confirm dioxymethylene formation. Our results also show that as the coverage increases, the adsorption of formaldehyde on the (111) surface becomes weak, but is nearly unaffected on the (110) surface. This work was supported by a Laboratory Directed Research and Development (LDRD) project of the Pacific Northwest National Laboratory (PNNL). The computations were performed using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory, which is a U.S. Department of Energy national scientific user facility located at PNNL in Richland, Washington. Computing time was made under a Computational Grand Challenge “Computational Catalysis”. Part of the computing time was also granted by the National Energy Research Scientific Computing

  9. Adsorption of atrazine on soils: model study.

    PubMed

    Kovaios, Ilias D; Paraskeva, Christakis A; Koutsoukos, Petros G; Payatakes, Alkiviades Ch

    2006-07-01

    The adsorption of the widely used herbicide atrazine onto three model inorganic soil components (silica gel, gamma-alumina, and calcite (CaCO(3)) was investigated in a series of batch experiments in which the aqueous phase equilibrated with the solid, under different solution conditions. Atrazine did not show discernible adsorption on gamma-alumina (theta=25 degrees C, 3.8adsorption from solutions was found for silica gel suspensions. The adsorption isotherms obtained for atrazine uptake on silica gel particles were best fitted with the Freundlich model. An increase of the ionic strength of the electrolytic solution induced an increase of the surface concentration of atrazine on silica gel, indicating significant electrostatic interactions between atrazine and silica gel particles, possibly through interaction with the surface silanol groups of the solid substrate. Increase of the pH value of the electrolyte solution from 6 to 9 considerably decreased the amount of atrazine adsorbed on the silica gel substrate. Decrease of the solution pH from 6 to 3 had only a slight effect on the surface concentration of the adsorbed atrazine. The adsorption of atrazine on silica gel increased when the temperature was decreased from 40 to 25 degrees C, an indication that the adsorption is exothermic. The calculated enthalpy of adsorption ( approximately 10 kJ/mol) indicates that the uptake at the solid-liquid equilibrium pH (6.1) was largely due to physisorption. PMID:16556447

  10. 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

  11. 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.

  12. 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.

  13. Molecular structure-adsorption study on current textile dyes.

    PubMed

    Örücü, E; Tugcu, G; Saçan, M T

    2014-01-01

    This study was performed to investigate the adsorption of a diverse set of textile dyes onto granulated activated carbon (GAC). The adsorption experiments were carried out in a batch system. The Langmuir and Freundlich isotherm models were applied to experimental data and the isotherm constants were calculated for 33 anthraquinone and azo dyes. The adsorption equilibrium data fitted more adequately to the Langmuir isotherm model than the Freundlich isotherm model. Added to a qualitative analysis of experimental results, multiple linear regression (MLR), support vector regression (SVR) and back propagation neural network (BPNN) methods were used to develop quantitative structure-property relationship (QSPR) models with the novel adsorption data. The data were divided randomly into training and test sets. The predictive ability of all models was evaluated using the test set. Descriptors were selected with a genetic algorithm (GA) using QSARINS software. Results related to QSPR models on the adsorption capacity of GAC showed that molecular structure of dyes was represented by ionization potential based on two-dimensional topological distances, chromophoric features and a property filter index. Comparison of the performance of the models demonstrated the superiority of the BPNN over GA-MLR and SVR models. PMID:25529487

  14. 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. PMID:27391585

  15. Studies of gas adsorption in flexible Metal-Organic frameworks

    NASA Astrophysics Data System (ADS)

    Sircar, Sarmishtha

    Flexible Metal-Organic frameworks that exhibit a gate-opening (GO) adsorption mechanism have potential for gas separations and gas storage. The GO phenomenon occurs when molecular gates in the structure expand/contract in response to the activation/de-activation of a system variable e.g. temperature, pressure or gas. Sharp discontinuities in the isotherm leading to S-shapes and large adsorption-desorption hysteresis are typical of this phenomenon. This study investigates the kinetics and thermodynamics of the GO behavior by combining adsorption measurements and analytical modeling of adsorption kinetics and capacity as a function of adsorbate, GO pressure, and temperature. Basic understanding of GO mechanism will help harness GO-MOF's as adsorbents for gas separations and storage. Experiments were performed on two precharacterized MOFs with verified GO behavior. These are (1) Zn2(bpdc)2(bpee), which expands from a relative amorphous to crystalline structure and (2) Cu[(dhbc) 2(4,4f-bpy)]H2O, a mutually interdigitated 2-D structure (bpdc = biphenyldicarboxylate, bpee = 1,2]bipyridylethene; DMF = N,N-dimethyl formamide, dhbc= 2,5-dihydroxybenzoic acid, bpy=bipyridine). Both sub- and super-critical adsorption data were collected using three adsorption units: a standard low-pressure volumetric adsorption unit, a commercial high-pressure gravimetric analyzer and a custom-built high-pressure differential volumetric unit. Collected laboratory data were combined with published adsorption rate and isotherm data for analysis to broaden the range of data collection. The accuracy of the high-pressure differential unit was improved by over 300-fold by changing analytical methods of processing data to establish a reliable null correction. A pronounced effect of the allowed experimental time was found at cryogenic temperatures on (1). Tightening the stability criteria used by the adsorption equipment to determine equilibration increased the experimental time from the order of

  16. Study the adsorption of phenol from aqueous solution on hydroxyapatite nanopowders.

    PubMed

    Lin, Kaili; Pan, Jiayong; Chen, Yiwei; Cheng, Rongming; Xu, Xuecheng

    2009-01-15

    In this study, the hydroxyapatite (HAp) nanopowders prepared by chemical precipitation method were used as the adsorbent, and the potential of HAp nanopowders for phenol adsorption from aqueous solution was studied. The effect of contact time, initial phenol concentration, pH, adsorbent dosage, solution temperature and adsorbent calcining temperature on the phenol adsorption, and the adsorption kinetic, equilibrium and thermodynamic parameters were investigated. The results showed that the HAp nanopowders possessed good adsorption ability to phenol. The adsorption process was fast, and it reached equilibrium in 2h of contact. The initial phenol concentration, pH and the adsorbent calcining temperature played obvious effects on the phenol adsorption capacity onto HAp nanopowders. Increase in the initial phenol concentration could effectively increase the phenol adsorption capacity. At the same time, increase in the pH to high-acidity or to high-alkalinity also resulted in the increase in the phenol adsorption capacity. Increase in the HAp dosage could effectively increase the phenol adsorption percent. However, the higher calcining temperature of HAp nanopowders could obviously decrease the adsorption capacity. The maximum phenol adsorption capacity was obtained as 10.33mg/g for 400mg/L initial phenol concentrations at pH 6.4 and 60 degrees C. The adsorption kinetic and the isotherm studies showed that the pseudo-second-order model and the Freundlich isotherm were the best choices to describe the adsorption behaviors. The thermodynamic parameters suggested that the adsorption of phenol onto HAp was physisorption, spontaneous and endothermic in nature. PMID:18573599

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

    SciTech Connect

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

    2015-03-15

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

  18. Malaria Vaccine Shows Promise in Small Study

    MedlinePlus

    ... nih.gov/medlineplus/news/fullstory_158765.html Malaria Vaccine Shows Promise in Small Study It protected more ... May 10, 2016 (HealthDay News) -- An experimental malaria vaccine protects a majority of adults against the mosquito- ...

  19. Malaria Vaccine Shows Promise in Small Study

    MedlinePlus

    ... https://medlineplus.gov/news/fullstory_158765.html Malaria Vaccine Shows Promise in Small Study It protected more ... May 10, 2016 (HealthDay News) -- An experimental malaria vaccine protects a majority of adults against the mosquito- ...

  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. Interfacial adsorption of antifreeze proteins: a neutron reflection study.

    PubMed

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

    2008-06-01

    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 SiO(2) substrate. The layer thickness of 32 A 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 A. 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

  2. Study on adsorption and desorption of ammonia on graphene.

    PubMed

    Zhang, Zhengwei; Zhang, Xinfang; Luo, Wei; Yang, Hang; He, Yanlan; Liu, Yixing; Zhang, Xueao; Peng, Gang

    2015-12-01

    The gas sensor based on pristine graphene with conductance type was studied theoretically and experimentally. The time response of conductance measurements showed a quickly and largely increased conductivity when the sensor was exposed to ammonia gas produced by a bubble system of ammonia water. However, the desorption process in vacuum took more than 1 h which indicated that there was a larger number of transferred carriers and a strong adsorption force between ammonia and graphene. The desorption time could be greatly shortened down to about 2 min by adding the flow of water-vapor-enriched air at the beginning of the recovery stage which had been confirmed as a rapid and high-efficiency desorption process. Moreover, the optimum geometries, adsorption energies, and the charge transfer number of the composite systems were studied with first-principle calculations. However, the theoretical results showed that the adsorption energy between NH3 and graphene was too small to fit for the experimental phenomenon, and there were few charges transferred between graphene and NH3 molecules, which was completely different from the experiment measurement. The adsorption energy between NH4 and graphene increased stage by stage which showed NH4 was a strong donor. The calculation suggested that H2O molecule could help a quick desorption of NH4 from graphene by converting NH4 to NH3 or (NH3)n(H2O)m groups, which was consistent with the experimental results. This study demonstrates that the ammonia gas produced by a bubble system of ammonia water is mainly ammonium groups of NH3 and NH4, and the NH4 moleculars are ideal candidates for the molecular doping of graphene while the interaction between graphene and the NH3 moleculars is weak. PMID:26377212

  3. Study on adsorption and desorption of ammonia on graphene

    NASA Astrophysics Data System (ADS)

    Zhang, Zhengwei; Zhang, Xinfang; Luo, Wei; Yang, Hang; He, Yanlan; Liu, Yixing; Zhang, Xueao; Peng, Gang

    2015-09-01

    The gas sensor based on pristine graphene with conductance type was studied theoretically and experimentally. The time response of conductance measurements showed a quickly and largely increased conductivity when the sensor was exposed to ammonia gas produced by a bubble system of ammonia water. However, the desorption process in vacuum took more than 1 h which indicated that there was a larger number of transferred carriers and a strong adsorption force between ammonia and graphene. The desorption time could be greatly shortened down to about 2 min by adding the flow of water-vapor-enriched air at the beginning of the recovery stage which had been confirmed as a rapid and high-efficiency desorption process. Moreover, the optimum geometries, adsorption energies, and the charge transfer number of the composite systems were studied with first-principle calculations. However, the theoretical results showed that the adsorption energy between NH3 and graphene was too small to fit for the experimental phenomenon, and there were few charges transferred between graphene and NH3 molecules, which was completely different from the experiment measurement. The adsorption energy between NH4 and graphene increased stage by stage which showed NH4 was a strong donor. The calculation suggested that H2O molecule could help a quick desorption of NH4 from graphene by converting NH4 to NH3 or (NH3)n(H2O)m groups, which was consistent with the experimental results. This study demonstrates that the ammonia gas produced by a bubble system of ammonia water is mainly ammonium groups of NH3 and NH4, and the NH4 moleculars are ideal candidates for the molecular doping of graphene while the interaction between graphene and the NH3 moleculars is weak.

  4. 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

    above parameters were varied one at a time to study their effects on roxarsone adsorption. Desorption studies were carried out using 125 mg/L phosphorous at predetermined interval of time. In addition to analyzing for total As by an ICP-MS, aqueous speciation of As was performed using a coupled HPLC-ICP-MS system. Preliminary studies show significant roxarsone adsorption capacity of the WTRs.

  5. 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.

  6. 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.

  7. Kinetic studies of the sucrose adsorption onto an alumina interface

    NASA Astrophysics Data System (ADS)

    Singh, Kaman; Mohan, Sudhanshu

    2004-01-01

    An account is given of an experimental kinetic study of adsorption of analar reagent sucrose (ARS) onto an alumina interface spectrometrically ( λmax=570 nm) at pH 8.0 and at room temperature. The adsorption isotherm is a typical Langmuirian isotherm (S-type) and adsorption parameters have been deduced according to the Langmuir's model. The adsorption coefficient evaluated from the Langmuir's equation was found to be 2.52×10 2 l mol -1. Adsorption mechanism has been interpreted on the basis of metal-saccharide interaction as found in organometallic compounds and interaction due to negatively charged ends on the disaccharide molecules and positively charge groups on the surface on alumina which depends on the pH value. The effects of variation in experimental conditions of the adsorption system have also been investigated. The adsorption exhibited a typical response to the pH effect and on going towards the PZC the net charge decreases and any reaction making dependence on charge and maximum adsorption (amount) was found near the isoelectric point of alumina (pH 9.0). The presence of ions like Cl -, SO 42- and PO 43- affect the adsorbed amount quantitatively and it seems that these anions compete with sucrose for the positively charged surface sites. The addition of similar concentration of cations was found to reduce the adsorbed amount. The temperature was found to have an inverse effect on adsorption. The additions of catonic and anionic detergents influence both the adsorbed amount and the adsorption rate. The thermodynamics of the titled adsorption model indicates the spontaneous and exothermic nature. The negative value of entropy is an indication of probability of favorable and complex nature of the adsorption.

  8. 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. PMID:27039361

  9. [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. PMID:23002621

  10. Experimental study of water adsorption on activated carbons

    SciTech Connect

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

    1999-01-19

    Two carbons of different origins (wood and coal) were oxidized with nitric acid. The materials were characterized using sorption of nitrogen. Boehm titration, and potentiometric titration. The water adsorption isotherms were measured at various temperatures close to ambient (relative pressure from 0.001 to 0.3). From these isotherms heats of adsorption were calculated using virial equation. The results showed that the isosteric heats of water adsorption are affected by surface chemical heterogeneity only at low surface coverage. The shapes of heats obtained indicate strong water-water interactions as a result of adsorption on secondary sites and cluster formation. In all cases the limiting heat of adsorption equal to the heat of water condensation (45 kJ/mol) was obtained.

  11. 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.

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

    SciTech Connect

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

    2014-12-01

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

  13. Study of Gas Adsorption on Biphasic Nanostructured Surfaces

    NASA Astrophysics Data System (ADS)

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

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

  14. Kinetic study of lead adsorption to composite biopolymer adsorbent

    SciTech Connect

    Seki, H.; Suzuki, A.

    1999-03-15

    A kinetic study of lead adsorption to composite biopolymer adsorbents was carried out. Spherical and membranous adsorbents containing two biopolymers, humic acid and alginic acid, were used for lead adsorption in dilute acidic solutions. The shrinking core model derived by M.G. Rao and A.K. Gupta was applied to describe the rate process of lead adsorption to spherical adsorbents (average radii of 0.12, 0.15, and 0.16 cm). Furthermore, the shrinking core model was modified and adapted for description of the rate process of lead adsorption to membranous adsorbent (average thickness of 0.0216 cm). The adsorption rate process for both the cases was well described and average apparent lead diffusion coefficients of about 6 {times} 10{sup {minus}6} and 7 {times} 10{sup {minus}6} cm{sup 2}/s were found for the spherical and membranous adsorbents, respectively.

  15. Kinetic Study of Lead Adsorption to Composite Biopolymer Adsorbent.

    PubMed

    Seki; Suzuki

    1999-03-15

    A kinetic study of lead adsorption to composite biopolymer adsorbents was carried out. Spherical and membranous adsorbents containing two biopolymers, humic acid and alginic acid, were used for lead adsorption in dilute acidic solutions. The shrinking core model derived by M. G. Rao and A. K. Gupta (Chem. Eng. J. 24, 181, 1982) was applied to describe the rate process of lead adsorption to spherical adsorbents (average radii of 0.12, 0.15, and 0.16 cm). Furthermore, the shrinking core model was modified and adapted for description of the rate process of lead adsorption to membranous adsorbent (average thickness of 0.0216 cm). The adsorption rate process for the both cases was well described and average apparent lead diffusion coefficients of about 6 x 10(-6) and 7 x 10(-6) cm2 s-1 were found for the spherical and membranous adsorbents, respectively. Copyright 1999 Academic Press. PMID:10049553

  16. Density functional study of the cysteine adsorption on Au nanoclusters

    NASA Astrophysics Data System (ADS)

    Pérez, L. A.; López-Lozano, X.; Garzón, I. L.

    2009-04-01

    The adsorption of the cysteine amino acid (H-SCβH2-CαH-NH2-COOH) on the Au55 cluster is investigated through density functional theory calculations. Two isomers, with icosahedral (Ih) and chiral (C1) geometries, of the Au55 cluster are used to calculate the adsorption energy of the cysteine on different facets of these isomers. Results, only involving the S(thiolate)-Au bonding show that the higher adsorption energies are obtained when the sulfur atom is bonded to an asymmetrical bridge site at the facet containing Au atoms with the lowest coordination of the C1 cluster isomer.

  17. 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.

  18. Adsorption of 2-propanol on MgO surface: A combined experimental and theoretical study

    NASA Astrophysics Data System (ADS)

    Fuente, Silvia A.; Ferretti, Cristián A.; Domancich, Nicolás F.; Díez, Verónica K.; Apesteguía, Carlos R.; Di Cosimo, J. Isabel; Ferullo, Ricardo M.; Castellani, Norberto J.

    2015-02-01

    The adsorption of 2-propanol (or isopropanol) on MgO was studied using infrared (IR) spectroscopy and density functional theory (DFT) simulations. The analysis of IR spectra indicates that the molecule can adsorb either molecularly or dissociatively. DFT calculations show that the adsorption mode depends on the active site of the catalyst. While on perfect terrace it adsorbs non-dissociatively, on edge and on threefold coordinated O anion (O-corner sites) the adsorption occurs dissociatively by breaking the Osbnd H bond without activation barrier giving 2-propoxide and a surface hydroxyl group. Calculations also suggest that vacant oxygen centers on terrace, edge and corner are also possible sites for non-dissociative adsorption. On Mg ions located at corners the adsorption is strong but non-dissociative, while on a Mg vacancy at the same position the molecule easily dissociates. Frequency modes are also calculated and compared in detail with experimental IR spectra.

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

    PubMed

    Harmayani, Kadek D; Faisal Anwar, A H M

    2016-01-01

    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. PMID:27438245

  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

    2013-09-01

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

  1. GRANULAR ACTIVATED CARBON ADSORPTION AND INFRARED REACTIVATION: A CASE STUDY

    EPA Science Inventory

    A study evaluated the effectiveness and cost of removing trace organic contaminants and surrogates from drinking water by granular activated carbon (GAC) adsorption. The effect of multiple reactivations of spent GAC was also evaluated. Results indicated that reactivated GAC eff...

  2. 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.

  3. Adsorption of metal ions onto Moroccan stevensite: kinetic and isotherm studies.

    PubMed

    Benhammou, A; Yaacoubi, A; Nibou, L; Tanouti, B

    2005-02-15

    The aim of this paper is to study the adsorption of the heavy metals (Cd(II), Cu(II), Mn(II), Pb(II), and Zn(II)) from aqueous solutions by a natural Moroccan stevensite called locally rhassoul. We carried out, first, a mineralogical and physicochemical characterization of stevensite. The surface area is 134 m2/g and the cation exchange capacity (CEC) is 76.5 meq/100 g. The chemical formula of stevensite is Si3.78Al0.22Mg2.92Fe0.09Na0.08K0.08O10(OH)2.4H2O. Adsorption tests of Cd(II), Cu(II), Mn(II), Pb(II), and Zn(II) in batch reactors were carried out at ambient temperature and at constant pH. Two simplified models including pseudo-first-order and pseudo-second- order were used to test the adsorption kinetics. The equilibrium time and adsorption rate of adsorption were determined. The increasing order of the adsorption rates follows the sequence Mn(II) > Pb(II) > Zn(II) > Cu(II) > Cd(II). The Dubinin-Radushkevich (D-R), Langmuir, and Redlich-Peterson (R-P) models were adopted to describe the adsorption isotherms. The maximal adsorption capacities at pH 4.0 determined from the D-R and Langmuir models vary in the following order: Cu(II) > Mn(II) > Cd(II) > Zn(II) > Pb(II). The equilibrium data fitted well with the three-parameter Redlich-Peterson model. The values of mean energy of adsorption show mainly an ion-exchange mechanism. Also, the influence of solution pH on the adsorption onto stevensite was studied in the pH range 1.5-7.0. PMID:15589536

  4. 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. PMID:18513862

  5. Mercury's Core Molten, Radar Study Shows

    NASA Astrophysics Data System (ADS)

    2007-05-01

    100 times, and showed that Mercury's spin axis is almost, but not exactly, perpendicular to the plane of its rotation around the Sun," Margot said. Margot worked with Stanton Peale of the University of California, Santa Barbara, Raymond Jurgens and Martin Slade of NASA's Jet Propulsion Laboratory, and Igor Holin of the Space Research Institute in Moscow. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. The Arecibo Observatory is part of the National Astronomy and Ionosphere Center, which is operated by Cornell University under a cooperative agreement with the NSF. Part of this work was supported by the Jet Propulsion Laboratory, operated by Caltech under contract with NASA.

  6. Theoretical study of adsorption and dissociation of NH3 on pentanuclear Fe(111) surface

    NASA Astrophysics Data System (ADS)

    Purwiandono, G.; Triyono; Wijaya, K.

    2016-02-01

    Theoretical study regarding the adsorption and dissociation of NH3 molecule on Fe(111) surface has been carried out. The method used was DFT-B3LYP, and the basis sets used were ECP and 6-311G**. This research aimed at giving the theoretical understanding of adsorption and dissociation of NH3 molecule on Fe(111) surface. The adsorption and dissociation were studied based on the energetic parameter, bond length, electron population, vibration and orbital interaction. The result of theoretical calculation revealed that the on top position is the interaction position with the minimum energy for the adsorption of NH3 molecule on Fe(111) surface. The analysis of electron population of the two composing molecular orbitals indicated that the transfer of electron has an important role in the mechanism of adsorption. The visualization of molecular orbital showed that the transfer of electron occurred in the electron pairs of the interacting orbital. Relating to the adsorption mechanism and the overlapping of interaction orbitals, NH3 molecule provides the Highest Occupied Molecular Orbital (HOMO) as the interaction pair for the Lowest Unoccupied Molecular Orbital (LUMO) on Fe surface. The insignificant difference between the oxidation state of N and H atoms as well as the higher hemolytic N-H bond dissociation energy (compared to heterolytic dissociation) cause the adsorption mechanism of NH3 on Fe(111) model to occur through homolytic-dissociative chemisorption.

  7. Physical Adsorption of Gases on Heterogeneous Solids and Equilibrium Studies of the Pressure Swing Adsorption Process.

    NASA Astrophysics Data System (ADS)

    Lu, Xiaochun

    1990-01-01

    -parameter isotherm equation based on benzene adsorption isotherms. We extended further the TVFM to derive thermodynamic functions, such as the adsorption entropy, the adsorption enthalpy, and the adsorption energy distribution, and constructed these functions for various adsorption systems based on their adsorption isotherms. To explore the energetic heterogeneity of the adsorbent, we used two approaches. First, we used the overall integral isotherm equation to obtain the Langmuir -Freundlich isotherm; and second, we used the Gibb's relation to obtain an exponential isotherm equation. The adsorption energy-distribution function can be obtained from these isotherm equations. The pressure swing adsorption (PSA) process was studied based on Shandalman and Mitchell's equilibrium theory for a PSA system with a linear isotherm. This theory was extended to a PSA system with a non-linear isotherm. Relationships were established between the isotherms and process parameters, such as the enrichment factor, the critical recycle ratio, and the extent of the recovery.

  8. 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.

  9. 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. PMID:15533408

  10. Adsorption removal of tetracycline from aqueous solution by anaerobic granular sludge: equilibrium and kinetic studies.

    PubMed

    Li, Ke; Ji, Feng; Liu, Yuanlu; Tong, Zilin; Zhan, Xinmin; Hu, Zhenhu

    2013-01-01

    High concentration animal wastewater is often contaminated by tetracycline and an upflow anaerobic sludge bioreactor (UASB) with granular sludge is often used to treat the wastewater. The investigation of the adsorption process of tetracycline on anaerobic granular sludge during anaerobic digestion of animal wastewater will increase the understanding of antibiotics behavior in the UASB reactor. In this study, the effects of initial pH, humic acid concentration, and temperature on the removal of tetracycline by anaerobic granular sludge from aqueous solution were investigated using the batch adsorption technique in 100 mL flasks with 75 mL of work volume. The results show that the highest removal efficiency of 93.0% was achieved around pH 3.0 and the removal efficiency at the neutral pH range (pH 6.0-8.0) is about 91.5%. The thermodynamic analysis indicates that the adsorption is a spontaneous and endothermic process. The adsorption kinetics followed the pseudo-second-order equation. The adsorption isotherms analysis indicates that the Langmuir model is better than the Freundlich model for the description of the adsorption process and confirms the result of thermodynamics analysis. The maximum adsorption capacities were 2.984, 4.108 and 4.618 mg/g at 25, 35 and 45 °C, respectively. These results provide useful information for understanding the fate and transformation of tetracycline in a UASB digestion system and improving the management of tetracycline contaminated animal wastewater. PMID:23552236

  11. Adsorption of uranyl on hydroxylated α-SiO₂(001): a first-principle study.

    PubMed

    Wang, Hui; Chai, Zhifang; Wang, Dongqi

    2015-01-28

    The adsorption of [UO2(H2O)5](2+) on a hydroxylated α-SiO2(001) surface was studied by periodic density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulation. The effects of pH, CO2, aqua solution and anionic ligands (OH(-), NO3(-) and Cl(-)) on the adsorption geometry and stability were investigated. The results show that the adsorption of uranyl on a hydroxylated α-SiO2(001) surface leads to the formation of inner-sphere complexes, in which the bidentate complex at the double deprotonated site is most favored. The binding strengths of bidentate and monodentate complexes at the same site are similar, and they become weaker as the number of protons increases at the adsorption site, indicating an enhancement of the adsorption strength at higher pH values within a certain range. Strong chemical interaction plays an important role in all inner-sphere complexes. The hydrogen bonds are formed between uranyl and the hydroxylated surface in all inner- and outer-sphere complexes. The presence of CO2 weakens the adsorption of uranyl on the surface by forming uranyl carbonate (CO3(2-), HCO3(-)) complexes. The effect of the anion ligands depends on their charged state and their concentration in solutions. The explicit treatment of water environment in the models has a slight effect on the adsorption configuration. These results are consistent with the experimental observations. PMID:25437449

  12. Microcolumn studies of dye adsorption onto manganese oxides modified diatomite.

    PubMed

    Al-Ghouti, M A; Khraisheh, M A M; Ahmad, M N; Allen, S J

    2007-07-19

    The method described here cannot fully replace the analysis of large columns by small test columns (microcolumns). The procedure, however, is suitable for speeding up the determination of adsorption parameters of dye onto the adsorbent and for speeding up the initial screening of a large adsorbent collection that can be tedious if a several adsorbents and adsorption conditions must be tested. The performance of methylene blue (MB), a basic dye, Cibacron reactive black (RB) and Cibacron reactive yellow (RY) was predicted in this way and the influence of initial dye concentration and other adsorption conditions on the adsorption behaviour were demonstrated. On the basis of the experimental results, it can be concluded that the adsorption of RY onto manganese oxides modified diatomite (MOMD) exhibited a characteristic "S" shape and can be simulated effectively by the Thomas model. It is shown that the adsorption capacity increased as the initial dye concentration increased. The increase in the dye uptake capacity with the increase of the adsorbent mass in the column was due to the increase in the surface area of adsorbent, which provided more binding sites for the adsorption. It is shown that the use of high flow rates reduced the time that RY in the solution is in contact with the MOMD, thus allowing less time for adsorption to occur, leading to an early breakthrough of RY. A rapid decrease in the column adsorption capacity with an increase in particle size with an average 56% reduction in capacity resulting from an increase in the particle size from 106-250 microm to 250-500 microm. The experimental data correlated well with calculated data using the Thomas equation and the bed depth-service time (BDST) equation. Therefore, it might be concluded that the Thomas equation and the BDST equations can produce accurate predication for variation of dye concentration, mass of the adsorbent, flow rate and particle size. In general, the values of adsorption isotherm capacity

  13. 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.

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

    PubMed

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

    2016-08-21

    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. PMID:27544117

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

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

  16. 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...

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

    PubMed

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

    2015-07-13

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

  18. 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. PMID:26997239

  19. Density functional study of CO adsorption on d-metal surface using TPSS functional

    NASA Astrophysics Data System (ADS)

    Sun, Jianwei; Perdew, John

    2009-03-01

    Feibelman et al^[1] presented the puzzle of CO at the Pt(111) surface, showing that the LDA and Perdew-type GGA put the molecule at the wrong, high-coordination site. However, a recent study ^[2] showed that the BLYP yielded very satisfactory adsorption energies and the correct adsorption sites for CO adsorption on late 4d and 5d transition metal (111) surfaces, although at the price of large errors in the volume of the d metals. Since PBE and BLYP have similar accuracy, it seems the probable reason for the wrong adsorption site is due to the fact that the LDA and Perdew-type GGA's are ``jellium derived'' and hence prefer a more delocalized bonding, rather than that the LDA and GGA inaccurately describe the CO molecule's chemical bond. TPSS meta-GGA is also ``jellium derived'', but improves accuracy for molecules^[3]. Therefore, as a possible candidate to identify the major reason for the wrong adsorption site, TPSS is used to calculate the adsorption energies and sites of CO on the d-metal surface in the more accurate geometric structure obtained by PBEsol^[4]. [1] P.J. Feibelman et al, J. Phys. Chem. 105, 4018(2001). [2] A. Stroppa and G. Kresse, New Journal of Physics 10, 063020(2008). [3] V.N. Staroverov et al, J. Chem. Phys., 119, 12129(2003). [4] J.P. Perdew et al, Phys. Rev. Lett., 100, 136406(2008).

  20. 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. PMID:27148722

  1. 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.

  2. 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

  3. 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

  4. Study of adsorption and degradation of dimethylphthalate on TiO2-based photocatalysts

    NASA Astrophysics Data System (ADS)

    Pulido Melián, E.; Henríquez-Cárdenes, E.; González Díaz, O.; Doña Rodríguez, J. M.

    2016-08-01

    This work studied the degradation and adsorption of dimethylphthalate (DMP) using various TiO2-based photocatalysts: TiO2 Aeroxide P25, Kronos vlp7000, Hombikat UV-100, Kemira 650 and a synthesized photocatalyst named SG750. As the photocatalysts with mixed anatase and rutile phases, P25 and SG750, showed greater activity than those of pure phase, an in-depth study was undertaken of these two catalysts in the adsorption and degradation of DMP. The degradation results were fitted with a high degree of correlation to the Langmuir-Hinshelwood model and those for adsorption to the Freundlich model. The Freundlich constants showed good correlation with FTIR observations of the DMP-P25 and DMP-SG750 interactions. These two photocatalysts were additionally modified by photodeposition with Pt and Au (0.5-1.5 wt%) to study the effect of these metals on degradation and mineralization kinetics.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Isotherm study of reactive Blue 19 adsorption by an alum sludge

    NASA Astrophysics Data System (ADS)

    Khim, Ong Keat; Nor, Mohd Asri Md; Mohamad, Syuriya; Nasaruddin, Nas Aulia Ahmad; Jamari, Nor Laili-Azua; Yunus, Wan Md Zin Wan

    2015-05-01

    This study investigates the adsorption of Reactive Blue 19 using dewatered alum sludge. The dewatered alum sludge was a sludge produced from drinking water treatment plant. Batch adsorption experiments were performed to investigate the mechanism of the dye adsorption. The adsorption was rapid at its initial stage but the rate decreased as it approached equilibrium. The adsorption data were evaluated by Langmuir and Freundlich isotherm models but was best described by the Langmuir isotherm model as it gave the highest correlation.

  10. Experimental study of neptunyl adsorption onto Bacillus subtilis

    NASA Astrophysics Data System (ADS)

    Gorman-Lewis, D.; Fein, J. B.; Soderholm, L.; Jensen, M. P.; Chiang, M.-H.

    2005-10-01

    The subsurface mobility of Np is difficult to predict in part due to uncertainties associated with its sorption behavior in geologic systems. In this study, we measured Np adsorption onto a common gram-positive soil bacterium, Bacillus subtilis. We performed batch adsorption experiments with Np(V) solutions as a function of pH, from 2.5 to 8, as a function of total Np concentration from 1.29 × 10 -5 M to 2.57 × 10 -4 M, and as a function of ionic strength from 0.001 to 0.5 M NaClO 4. Under most pH conditions, Np adsorption is reversible and exhibits an inverse relationship with ionic strength, with adsorption increasing with increasing pH. At low pH in the 0.1 M ionic strength systems, we observed irreversible adsorption, which is consistent with reduction of Np(V) to Np(IV). We model the adsorption reaction using a nonelectrostatic surface complexation approach to yield ionic strength dependent NpO 2+-bacterial surface stability constants. The data require two bacterial surface complexation reactions to account for the observed adsorption behavior: R-L 1- + NpO 2+ ↔ R-L 1-NpO 2° and R-L 2- + NpO 2+ ↔ R-L 2-NpO 2°, where R represents the bacterium to which each functional group is attached, and L 1 and L 2 represent the first and second of four discrete site types on the bacterial surface. Stability constants (log K values) for the L 1 and L 2 reactions in the 0.001 M system are 2.3 ± 0.3 and 2.3 ± 0.2, and in the 0.1 M system the values are 1.7 ± 0.2 and 1.6 ± 0.2, respectively. The calculated neptunyl-bacterial surface stability constants are not consistent with values predicted using the linear free energy correlation approach from Fein et al. (2001), suggesting that possible unfavorable steric interactions and the low charge of NpO 2+ affects Np-bacterial adsorption.

  11. 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. PMID:17910372

  12. An in vitro Study of Protein Adsorption to Biocompatible Coatings.

    PubMed

    Seeberg, Trine M; Austad, Hanne O; Clausen, Ingelin; Cederkvist, Henning; Bjørås, Magnar; Johansen, Rune Forstrøm

    2015-01-01

    The motivation for these experiments was to investigate the amount and type of protein adsorption on surfaces that can be used as protective coatings on membrane based in vivo devices. Adsorption of proteins to a selection of biocompatible coatings (titanium oxide, diamond-like carbon, parylene C) and typical construction materials for Micro Electro Mechanical Systems (silicon, silicon nitride), were investigated during in vitro tests. The samples were incubated in human liver extract and bovine serum albumin (BSA) for up to 12 hours. The amount of protein adsorption was found to be low for all surfaces. Measurements of bound Iodine-125 labeled BSA, showed a protein adsorption of up to 0.2 μg BSA/cm2. The specific proteins adsorbed to the surfaces after incubation in human liver extract were identified using mass spectrometry. Most of the identified adsorbed proteins were intracellular, but plasma proteins like Immunoglobulin (Ig) and serum albumin as well as hemoglobin were also identified. PMID:25980864

  13. 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. PMID:16083768

  14. Equilibrium and kinetic adsorption study of Basic Yellow 28 and Basic Red 46 by a boron industry waste.

    PubMed

    Olgun, Asim; Atar, Necip

    2009-01-15

    In this study, the adsorption characteristics of Basic Yellow 28 (BY 28) and Basic Red 46 (BR 46) onto boron waste (BW), a waste produced from boron processing plant were investigated. The 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 two dyes could be described reasonably well by a generalized isotherm. Kinetic studies indicated that the kinetics of the adsorption of BY 28 and BR 46 onto BW follows a pseudo-second-order model. The result showed that the BW exhibited high-adsorption capacity for basic dyes and the capacity slightly decreased with increasing temperature. The maximum adsorption capacities of BY 28 and BR 46 are reported at 75.00 and 74.73mgg(-1), respectively. The dye adsorption depended on the initial pH of the solution with maximum uptake occurring at about pH 9 and electrokinetic behavior of BW. Activation energy of 15.23kJ/mol for BY 28 and 18.15kJ/mol for BR 46 were determined confirming the nature of the physisorption onto BW. These results indicate that BW could be employed as low-cost material for the removal of the textile dyes from effluents. PMID:18434000

  15. 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. PMID:24645464

  16. 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 .

  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. 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.

  19. 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.

  20. 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

  1. Removal Rate of Organic Matter Using Natural Cellulose via Adsorption Isotherm and Kinetic Studies.

    PubMed

    Din, Mohd Fadhil Md; Ponraj, Mohanadoss; Low, Wen-Pei; Fulazzaky, Mohamad Ali; Iwao, Kenzo; Songip, Ahmad Rahman; Chelliapan, Shreeshivadasan; Ismail, Zulhilmi; Jamal, Mohamad Hidayat

    2016-02-01

    In this study, the removal of natural organic matter (NOM) using coconut fiber (CF) and palm oil fiber (POF) was investigated. Preliminary analysis was performed using a jar test for the selection of optimal medium before the fabricated column model experiment. The equilibrium studies on isotherms and kinetic models for NOM adsorption were analyzed using linearized correlation coefficient. Results showed that the equilibrium data were fitted to Langmuir isotherm model for both CF and POF. The most suitable adsorption model was the pseudo-first-order kinetic model for POF and pseudo-second-order kinetic model for CF. The adsorption capacities achieved by the CF and POF were 15.67 and 30.8 mg/g respectively. Based on this investigation, it can be concluded that the POF is the most suitable material for the removal of NOM in semi polluted river water. PMID:26803100

  2. Comparative study on adsorption of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) by different adsorbents in water.

    PubMed

    Yao, Yuan; Volchek, Konstantin; Brown, Carl E; Robinson, Adam; Obal, Terry

    2014-01-01

    Perfluorinated compounds (PFCs) are emerging environmental pollutants. Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are the two primary PFC contaminants that are widely found in water, particularly in groundwater. This study compared the adsorption behaviors of PFOS and PFOA on several commercially available adsorbents in water. The tested adsorbents include granular activated carbon (GAC: Filtrasorb 400), powdered activated carbon, multi-walled carbon nanotube (MCN), double-walled carbon nanotube, anion-exchange resin (AER: IRA67), non-ion-exchange polymer, alumina, and silica. The study demonstrated that adsorption is an effective technique for the removal of PFOS/PFOA from aqueous solutions. The kinetic tests showed that the adsorption onto AER reaches equilibrium rapidly (2 h), while it takes approximately 4 and 24 h to reach equilibrium for MCN and GAC, respectively. In terms of adsorption capacity, AER and GAC were identified as the most effective adsorbents to remove PFOS/PFOA from water. Furthermore, MCN, AER, and GAC proved to have high PFOS/PFOA removal efficiencies (≥98%). AER (IRA67) and GAC (Filtrasorb 400) were thus identified as the most promising adsorbents for treating PFOS/PFOA-contaminated groundwater at mg L(-1) level based on their equilibrium times, adsorption capacities, removal efficiencies, and associated costs. PMID:25521134

  3. 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.

  4. 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.

  5. 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.

  6. FTIR spectroscopic and computational studies on hydrogen adsorption on the zeolite Li-FER.

    PubMed

    Nachtigall, P; Garrone, E; Palomino, G Turnes; Delgado, M Rodríguez; Nachtigallová, D; Areán, C Otero

    2006-05-21

    The interaction, at a low temperature, between molecular hydrogen and the zeolite Li-FER was studied by means of variable temperature infrared spectroscopy and theoretical calculations using a periodic DFT model. The adsorbed dihydrogen molecule becomes infrared active, giving a characteristic IR absorption band (H-H stretching) at 4090 cm(-1). Three different Li(+) site types with respect to H(2) adsorption were found in the zeolite, two of which adsorb H(2). Calculations showed a similar interaction energy for these two sites, which was found to agree with the experimentally determined value of standard adsorption enthalpy of DeltaH(0) = -4.1 (+/-0.8) kJ mol(-1). The results are discussed in the broader context of previously reported data for H(2) adsorption on Na-FER and K-FER. PMID:16688311

  7. 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. PMID:26414422

  8. Microcalorimetric study of protein adsorption onto calcium hydroxyapatites.

    PubMed

    Kandori, Kazuhiko; Murata, Kanae; Ishikawa, Tatsuo

    2007-02-13

    To clarify the adsorption mechanism of proteins onto calcium hydroxyapatite (Hap), the present study measured adsorption (DeltaHads) and desorption (DeltaHdes) enthalpies of bovine serum albumin (BSA; isoelectric point (iep) 4.7, molecular mass (Ms) 67,200 Da, acidic protein), myoglobin (MGB; iep=7.0, Ms=17,800 Da, neutral protein), and lysozyme (LSZ; iep=11.1, Ms=14,600 Da, basic protein) onto Hap by a flow microcalorimeter (FMC). Five kinds of large platelike particles of CaHPO4.2H2O (DCPD) after hydrolyzing at room temperature with different concentrations of NaOH aqueous solution ([NaOH]) for 1 h were used. DCPD converted completely to Hap after treatment at [NaOH]>or=2%, and the crystallinity of Hap was increased with an increase in [NaOH] up to 10%. The amounts of protein adsorbed (Deltanads) and desorbed (Deltandes) were measured simultaneously by monitoring the protein concentration downstream from the FMC with a UV detector. The Deltanads values were also measured statically by a batch method in each system. The Deltanads values measured by the FMC and static measurements fairly agreed with each other. Results revealed that DeltaHBSAads was decreased with an increase in [NaOH]; in other words, DeltaHBSAads was decreased with the improvement of Hap's crystallinity, suggesting that the BSA adsorption readily proceeded onto Hap. This fact indicated a high affinity of Hap to protein. This affinity was further recognized by DeltaHBSAdes because its positive value was increased by increasing [NaOH]. These opposite tendencies in DeltaHBSAads and DeltaHBSAdes revealed that Hap possessed a high adsorption affinity to BSA (i.e., enthalpy facilitated protein adsorption but hindered its desorption). The fraction of BSA desorption was also decreased with an increase in [NaOH], confirming the high affinity of Hap to protein. Similar results were observed on the LSZ system, though the enthalpy values were smaller than those of BSA. In the case of neutral MGB, Delta

  9. Hydrogen Adsorption in Carbon-Based Materials Studied by NMR

    NASA Astrophysics Data System (ADS)

    Wu, Yue; Kleinhammes, Alfred; Anderson, Robert; Mao, Shenghua

    2007-03-01

    Hydrogen adsorption in carbon-based materials such as boron-doped graphite and boron-doped single-walled carbon nanotubes (SWNTs) were investigated by nuclear magnetic resonance (NMR). ^1H NMR is shown to be a sensitive and quantitative probe for detecting adsorbed gas molecules such as H2, methane, and ethane. NMR measurements were carried out in-situ under given H2 pressure up to a pressure of over 100 atm. From such ^1H NMR measurement, the amount of adsorbed H2 molecules was determined versus pressure. This gives an alternative method for measuring the adsorption isotherms where the H2 signature is identified based on spin properties rather than weight or volume as in gravimetric and volumetric measurements. The measurement shows that boron doping has a favorable effect on increasing the adsorption enthalpy of H2 in carbon-based systems. This work was done in collaboration with NREL and Department of Chemistry, University of Pennsylvania, within the DOE Center of Excellence on Carbon-based Hydrogen Storage Materials and is supported by DOE.

  10. 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.

  11. 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.

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

    PubMed

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

    2016-05-14

    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. PMID:27179497

  13. 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

  14. First principles total energy studies of the adsorption of disilane on Ge(001)-c(2x4)

    NASA Astrophysics Data System (ADS)

    Cocoletzi, Gregorio H.; Sanchez-Castillo, A.; Takeuchi, N.

    2004-03-01

    We perform first principles total energy calculations to investigate the energetics and the atomic structure of the adsorption of silane (SiH_4) and disilane (Si_2H_6) on the Ge(001)-c(2× 4) surface. The adsorption of Si_2H6 is a dissociative process which first yields SiH3 and then SiH2 fragments. We first study the adsorption of SiH2 considering two different models; the intra-row and the on-dimer geometries. Our results show that the on-dimer site is more stable than the intra-row geometry. This is not a surprise since in the absence of H atoms adsorption in the on-dimer site leaves no dangling bonds. In contrast, when the SiH2 fragment is considered together with two H atoms, the intra-row geometry is favored energetically as compared with the on-dimer site. Similar results have been previously obtained for the adsorption of SiH2 on Si(001). Disilane adsorption is explored according to two different geometries. In the first one, we have considered the adsorption as two SiH3 fragments, while in the second, we have considered the adsorption as two SiH2 fragments plus 2 H fragments. It is found that the later geometry is energetically more favorable.

  15. Theoretical study of the adsorption of benzene on coinage metals

    PubMed Central

    Reckien, Werner; Eggers, Melanie

    2014-01-01

    Summary The adsorption of benzene on the M(111), M(100) and M(110) surfaces of the coinage metals copper (M = Cu), silver (M = Ag) and gold (M = Au) is studied on the basis of density functional theory (DFT) calculations with an empirical dispersion correction (D3). Variants of the Perdew–Burke–Ernzerhof functionals (PBE, RPBE and RevPBE) in combination with different versions of the dispersion correction (D3 and D3(BJ)) are compared. PBE-D3, PBE-D3(BJ) and RPBE-D3 give similar results which exhibit a good agreement with experimental data. RevPBE-D3 and RevPBE-D3(BJ) tend to overestimate adsorption energies. The inclusion of three-center terms (PBE-D3(ABC)) leads to a slightly better agreement with the experiment in most cases. Vertical adsorbate–substrate distances are calculated and compared to previous theoretical results. The observed trends for the surfaces and metals are consistent with the calculated adsorption energies. PMID:25161736

  16. 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

    Though it is well-known that adsorption reactions frequently assist deformation of porous rocks, very little understanding exists on the direct coupling with stress state and strain. One of the materials in which adsorption plays a large role is coal, as is observed in the particular case of Enhanced Coalbed Methane Production (ECBM), which involves the geological storage of CO2 and the recovery of CH4. In this case, adsorption and the associated swelling cause significant injectivity problems, which is experienced in almost all pilot field projects to date. This suggests that indeed a strong fundamental coupling exists between CO2 sorption, changes in the mechanical state of the coal matrix and changes in the transport properties of the system, and illustrates the need to understand coupled stress-strain-sorption behaviour. In this contribution, we describe several important observations made on coal-CO2 systems that can learn us about many other natural, stressed adsorbate-adsorbent systems. In our experiments, first of all, the adsorption of CO2 in the coal matrix gave rise to swelling. Although this is well-known, we found that the total volumetric strain occurring under unconfined conditions can be realistically modelled (up to at least 100 MPa) as the sum of an adsorption-related expansion term and an elastic compression term. Second, effective in situ stresses will directly reduce the sorption capacity, and associated swelling of the coal matrix significantly. Our general thermodynamic model for the effect of a 3D stress state on adsorbed CO2 concentration supports this observation, and also shows that "self-stressing", as a result of CO2 adsorption occurring under conditions of restricted or zero strain (i.e. fully constrained conditions), will more than double the expected in situ stresses. A constitutive equation was developed to describe the full coupling between stress state, total strain (i.e. combined strain of adsorption processes and poroelasticity

  17. 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.

  18. A DFT study of arsine adsorption on palladium doped graphene: Effects of palladium cluster size

    NASA Astrophysics Data System (ADS)

    Kunaseth, Manaschai; Mudchimo, Tanabat; Namuangruk, Supawadee; Kungwan, Nawee; Promarak, Vinich; Jungsuttiwong, Siriporn

    2016-03-01

    In this study, we have investigated the size effects of palladium (Pd) doped single-vacancy defective graphene (SDG) surface to the adsorption of AsH3 and its dehydrogenated products on Pd using density functional theory calculations. Here, Pd cluster binding study revealed that Pd6 nanocluster bound strongest to the SDG surface, while adsorption of AsHx (x = 0-3) on the most stable Pdn doped SDG showed that dehydrogenated arsine compounds adsorbed onto the surface stronger than the pristine AsH3 molecule. Charge analysis revealed that considerable amount of charge migration from Pd to dehydrogenated arsine molecules after adsorption may constitute strong adsorption for dehydrogenated arsine. In addition, study of thermodynamic pathways of AsH3 dehydrogenation on Pdn doped SDG adsorbents indicated that Pd cluster doping on SDG adsorbent tends to be thermodynamically favorable for AsH3 decomposition than the single-Pd atom doped SDG. Hence, our study has indicated that Pd6 clusters doped SDG is more advantageous as adsorbent material for AsH3 removal.

  19. 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.

  20. Studies on chelating adsorption properties of novel composite material polyethyleneimine/silica gel for heavy-metal ions

    NASA Astrophysics Data System (ADS)

    Gao, Baojiao; An, Fuqiang; Liu, Kangkai

    2006-12-01

    Firstly, the coordination processes of line-type polyethyleneimine with Cu 2+, Cd 2+ and Zn 2+ were studied by using visible light absorption spectroscopy and chelation conductivity titration method, and the structures of the chelates were determined. Afterwards, polyethyleneimine (PEI) was grafted onto the surface of silica gel particles via the coupling effect of γ-chloropropyl trimethoxysilane (CP), and the novel composite adsorption material PEI/SiO 2 with strong adsorption ability towards heavy-metal ions was prepared. The chelating adsorption properties of PEI/SiO 2 for Cu 2+, Cd 2+ and Zn 2+ were researched by both static (batch) and dynamic (flow) methods. The experiment results show that water-soluble polyamine PEI with line-type structure reacts with Cu 2+, Cd 2+ and Zn 2+ easily and quantitatively, and water-soluble chelates with four ligands are formed. The composite material PEI/SiO 2 possesses very strong chelating adsorption ability for heavy-metal ions, and the saturated adsorption amount can reach 25.94 mg g -1 and 50.01 mg g -1 for Cu 2+ under static and dynamic conditions, respectively. The isothermal adsorption data fit to Langmuir equation, and the adsorption is typical chemical adsorption with monomolecular layer. The adsorbing ability of PEI/SiO 2 towards the three kinds of the ions follows the order of Cu 2+ > Cd 2+ > Zn 2+. The pH value has great influence on the sorption, and at pH 6-7, the adsorption capacity is the greatest. The fact that adsorption capacity increases with temperature rising indicates the adsorbing process of PEI/SiO 2 for metal ions is endothermic. As diluted hydrochloric acid is used as eluent, the adsorbed heavy-metal ions are eluted easily from PEI/SiO 2, and the regeneration and reuse without decreasing sorption for PEI/SiO 2 are demonstrated.

  1. Methanol adsorption on the clean CeO₂(111) surface: A density functional theory study

    SciTech Connect

    Mei, Donghai; Deskins, N. Aaron; Dupuis, Michel; Ge, Qingfeng

    2007-07-19

    Molecular and dissociative adsorption of methanol at various sites on the stoichiometric CeO₂(111) surface have been studied using density functional theory periodic calculations. At 0.25 monolayer (ML) coverage, the dissociative adsorption with an adsorption energy of 0.55 eV is slightly favored. The most stable state is the dissociative adsorption of methanol via C-H bond breaking, forming a coadsorbed hydroxymethyl group and hydrogen adatom on two separate O₃C surface sites. The strongest molecular adsorption occurs through an O-Ce₇subC connection with an adsorption energy of 0.48 eV. At methanol coverage of 0.5 ML, the dissociative adsorption and the molecular adsorption became competitive. The adsorption energy per methanol molecule for both adsorption modes falls into a narrow range of 0.46-0.55 eV. As methanol coverage increases beyond 0.5 ML, the molecular adsorption becomes more energetically favorable than the dissociative adsorption because of the attractive hydrogen bonding between coadsorbed methanol molecules. At full monolayer, the adsorption energy of molecular adsorption is 0.40 eV per molecule while the adsorption energy for total dissociative adsorption of methanol is only 0.17 eV. The results at different methanol coverages indicate that methanol can adsorb on a defect-free CeO₂(111) surface, which are also consistent with experimental observations. This research was performed using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory, which is a U.S. Department of Energy national scientific user facility located at Pacific Northwest National Laboratory (PNNL) in Richland, Washington. Computing time was made available under a Computational Grand Challenge “Computational Catalysis”. This work also financially supported by the Laboratory Directed Research and Development project of PNNL.

  2. Ab initio study of hydrogen adsorption in MOF-5.

    PubMed

    Sillar, Kaido; Hofmann, Alexander; Sauer, Joachim

    2009-03-25

    Metal-organic frameworks (MOFs) are promising adsorbents for hydrogen storage. Density functional theory and second-order Møller-Plesset perturbation theory (MP2) are used to calculate the interaction energies between H(2) and individual structural elements of the MOF-5 framework. The strongest interaction, DeltaH(77) = -7.1 kJ/mol, is found for the alpha-site of the OZn(4)(O(2)Ph)(6) nodes. We show that dispersion interactions and zero-point vibrational energies must be taken into account. Comparison of calculations done under periodic boundary conditions for the complete structure with those done for finite models cut from the MOF-5 framework shows that the interactions with H(2) originate mainly from the local environment around the adsorption site. When used within a Multi-Langmuir model, the MP2 results reproduce measured adsorption isotherms (the predicted amount is 6 wt % at 77 K and 40 bar) if we assume that the H(2) molecules preserve their rotational degrees of freedom in the adsorbed state. This allows to discriminate between different isotherms measured for different MOF-5 samples and to reliably predict isotherms for new MOF structures. PMID:19253977

  3. Arsenic Adsorption and Desorption by Drinking Water Treatment Residuals: Incubation Studies

    NASA Astrophysics Data System (ADS)

    Vandanapu, V.; Sarkar, D.; Datta, R.; Makris, K.

    2005-05-01

    Arsenic (As) has been used for a long time in agricultural practices, primarily to control pests and noxious weeds. In many cases, the indiscriminate usage of toxic arsenical compounds has left a legacy of contaminated soils. Recent awareness of the toxicity of As at much lower concentrations than previously deemed to be dangerous has led to increased interest in the environmental chemistry of As. The immediate challenge, as perceived by various regulatory bodies is to develop a cost-effective, reliable and environmentally sound approach to cleaning up such contaminated soils. In-situ immobilization technologies are an attractive alternative to conventional remediation methods. One of the most interesting of these in-situ techniques is the use of Water Treatment Residuals (WTRs). The WTRs are by-products of drinking water purification processes and generally contain sediments, organic carbon, and Al/Fe oxides. The oxides are typically amorphous (with very high specific surface area) and have tremendous affinity for oxyanions (e.g., arsenate), due to their high positive surface charge. Recent studies conducted by our group have suggested that WTRs retain As and decrease arsenic mobility. However, a better understanding of As adsorption/desorption by WTRs is necessary for effective implementation of appropriate in-situ remedial strategies. Hence, the present study examines the potential use of WTRs (Al-WTR and Fe-WTR) as adsorbents for the removal of arsenate in solutions. Furthermore, it investigates the extent of desorption of the pre-adsorbed arsenate onto the WTR surfaces. Effects of various key parameters, such as solid solution ratio, equilibration time and arsenic concentration were examined to achieve the optimized conditions for arsenate adsorption. Preliminary batch adsorption experiments showed the optimum equilibration time to be 24 h and the solid/solution ratio to be 1:5 for arsenate adsorption. Sorption data has been evaluated using both Langmuir and

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  5. Simple fabrication of carbon/TiO2 composite nanotubes showing dual functions with adsorption and photocatalytic decomposition of Rhodamine B.

    PubMed

    Im, Ji Hyuk; Yang, Seung Jae; Yun, Chang Hun; Park, Chong Rae

    2012-01-27

    Carbon/TiO2 composite nanotubes were fabricated via a very simple electrospinning process and their dual functionalities of adsorptivity and photocatalytic activity were evaluated using Rhodamine B (RhB) as a model organic pollutant. A poly(vinyl alcohol) (PVA) aqueous solution was directly electrospun into a coagulation bath containing titanium (IV) tetraisopropoxide (TTIP) solution so that PVA-core/TiO2-shell composite nanofibers were formed through the in situ sol-gel reaction of TTIP. The carbon/TiO2 composite nanotubes were then fabricated by heat treatment of composite nanofibers under nitrogen atmosphere. By using several characterization methods, we confirmed that the resultant nanotubes consisted of anatase TiO2 nanocrystallites embedded in a carbonaceous matrix. The prepared nanotubes exhibited fast adsorption of RhB with high capacity compared with a commercial porous carbon, and they also showed the photocatalytic decomposition activity for the dye molecules under UV irradiation comparable to the degradation by P-25 and ST-01 (commercial TiO2). Finally, the carbon/TiO2 composite nanotubes exhibited several cycle performances of adsorption-photodegradation for RhB. This indicates that the composite nanotubes can adsorb and photodecompose organic pollutants repeatedly without additional activating processes. PMID:22172680

  6. Simple fabrication of carbon/TiO2 composite nanotubes showing dual functions with adsorption and photocatalytic decomposition of Rhodamine B

    NASA Astrophysics Data System (ADS)

    Im, Ji Hyuk; Yang, Seung Jae; Yun, Chang Hun; Park, Chong Rae

    2012-01-01

    Carbon/TiO2 composite nanotubes were fabricated via a very simple electrospinning process and their dual functionalities of adsorptivity and photocatalytic activity were evaluated using Rhodamine B (RhB) as a model organic pollutant. A poly(vinyl alcohol) (PVA) aqueous solution was directly electrospun into a coagulation bath containing titanium (IV) tetraisopropoxide (TTIP) solution so that PVA-core/TiO2-shell composite nanofibers were formed through the in situ sol-gel reaction of TTIP. The carbon/TiO2 composite nanotubes were then fabricated by heat treatment of composite nanofibers under nitrogen atmosphere. By using several characterization methods, we confirmed that the resultant nanotubes consisted of anatase TiO2 nanocrystallites embedded in a carbonaceous matrix. The prepared nanotubes exhibited fast adsorption of RhB with high capacity compared with a commercial porous carbon, and they also showed the photocatalytic decomposition activity for the dye molecules under UV irradiation comparable to the degradation by P-25 and ST-01 (commercial TiO2). Finally, the carbon/TiO2 composite nanotubes exhibited several cycle performances of adsorption-photodegradation for RhB. This indicates that the composite nanotubes can adsorb and photodecompose organic pollutants repeatedly without additional activating processes.

  7. 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.

  8. 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. PMID:19295102

  9. Melanoidin Removal Mechanism in An Aqueous Adsorption System: An Equilibrium, Kinetic and Thermodynamic Study.

    PubMed

    Nunes, Diego L; Oliveira, Leandro S; Franca, Adriana S

    2015-01-01

    Melanoidins are colored products that can be found in food and drinks, formed by Maillard reactions. Sometimes these compounds are considered undesirable in certain food products, because they impart a brownish color and must be removed. An overview of recent patents related to melanoidin removal indicates that it can be performed by chemical/biological degradation or by adsorption processes. Therefore, in the present study, the adsorption mechanism for synthetic melanoidin removal from aqueous solutions was studied using different Raphanus sativus press-cake sorbents, with the precursor material being carbonized in a microwave oven, either with direct heating or after a chemical activation process with phosphoric acid, nitric acid or potassium hydroxide. Physical and chemical modifications were evaluated by FTIR, pHPZC, thermogravimetry and BET. The adsorption kinetics was better described by a pseudo-second order model for all activated carbons (ACs). Evaluation of the diffusion process showed dependence on the initial melanoidin concentration due to the wide range of sizes of the adsorbed molecules. The equilibrium data were best fitted by the Langmuir model for the acid-treated AC and by the Freundlich model for the base-treated and non-chemically treated ACs. Melanoidin adsorption was characterized as a spontaneous, favorable and endothermic process involving hydrogen bonds and π-π interactions between the adsorbents surfaces and the adsorbed molecules. PMID:26013772

  10. First-principles study of SO2 molecule adsorption on the pristine and Mn-doped boron nitride nanotubes

    NASA Astrophysics Data System (ADS)

    Deng, Zun-Yi; Zhang, Jian-Min; Xu, Ke-Wei

    2015-08-01

    To exploit the potential application of nitride nanotube (BNNT), the adsorption of sulfur dioxide (SO2) on pristine and Mn-doped BNNT was theoretically studied using first-principles approach based on density functional theory (DFT). The most stable adsorption geometry, adsorption energy, magnetic moment, charge transfer and density of states of these systems are discussed. SO2 molecule is weakly adsorbed on the pristine BNNT. The Mn-doped BNNT show high reactivity toward SO2 regardless of the MnB site or MnN site adsorption. The larger formation energies and analysis of density of states show the SO2 molecules are chemically bonded to Mn-doped BNNT and the covalent interaction between the SO2 molecule and Mn atom can be formed. Therefore, the Mn-doped BNNT can be used as SO2 gas sensor manufacturing raw materials, and it may be a potential material for nanodevice applications.

  11. Column studies for the adsorption of cationic surfactant onto an organic polymer resin and a granular activated carbon.

    PubMed

    Vergili, Ilda; Kaya, Yasemin; Gönder, Zeren Beril; Barlas, Hulusi

    2010-03-01

    Adsorption beds containing granular activated carbon and organic polymer resin are used widely to remove organic pollutants from wastewaters and water streams. Adsorption polymers are becoming alternatives to activated carbon for removal of surfactants by adsorption techniques. This study investigated the adsorption characteristics of cetyl trimethylammonium bromide (CTAB) as a cationic surfactant for selected concentrations below and above critical micelle concentration (CMC). A series of column tests were performed to determine the breakthrough curves by using two different adsorbents: (1) Hydraffin CC 8 x 30 as a commercial granular activated carbon (GAC) and (2) Lewatit VPOC 1064 MD PH as a commercial organic polymer resin. In the experiments, the volumetric flow rate was maintained at 10.5 mL/min (approximately 2 m3/ m2 x h). Loading of adsorbents was continued until breakthrough was 10% of the feed concentration. The breakthrough took place at 488 bed volume (BV) below CMC (C0 = 40 mg/L) and 39 BV above CMC (C0 = 400 mg/ L) onto GAC. The organic polymer resin, however, showed a higher adsorption capacity than GAC (1412 BV below CMC and 287 BV above CMC). From the Logit method, the value of adsorption rate coefficient (K) and adsorption capacity coefficient (N) were obtained. PMID:20369564

  12. Salinity and pH affect Na+-montmorillonite dissolution and amino acid adsorption: a prebiotic chemistry study

    NASA Astrophysics Data System (ADS)

    Farias, Ana Paula S. F.; Tadayozzi, Yasmin S.; Carneiro, Cristine E. A.; Zaia, Dimas A. M.

    2014-06-01

    The adsorption of amino acids onto minerals in prebiotic seas may have played an important role for their protection against hydrolysis and formation of polymers. In this study, we show that the adsorption of the prebiotic amino acids, glycine (Gly), α-alanine (α-Ala) and β-alanine (β-Ala), onto Na+-montmorillonite was dependent on salinity and pH. Specifically, adsorption decreased from 58.3-88.8 to 0-48.9% when salinity was increased from 10 to 100-150% of modern seawater. This result suggests reduced amino acid adsorption onto minerals in prebiotic seas, which may have been even more saline than the tested conditions. Amino acids also formed complexes with metals in seawater, affecting metal adsorption onto Na+-montmorillonite, and amino acid adsorption was enhanced when added before Na+-montmorillonite was exposed to high saline solutions. Also, the dissolution of Na+-montmorillonite was reduced in the presence of amino acids, with β-Ala being the most effective. Thus, prebiotic chemistry experiments should also consider the integrity of minerals in addition to their adsorption capacity.

  13. Simultaneous removal of potent cyanotoxins from water using magnetophoretic nanoparticle of polypyrrole: adsorption kinetic and isotherm study.

    PubMed

    Hena, S; Rozi, R; Tabassum, S; Huda, A

    2016-08-01

    Cyanotoxins, microcystins and cylindrospermopsin, are potent toxins produced by cyanobacteria in potable water supplies. This study investigated the removal of cyanotoxins from aqueous media by magnetophoretic nanoparticle of polypyrrole adsorbent. The adsorption process was pH dependent with maximum adsorption occurring at pH 7 for microcystin-LA, LR, and YR and at pH 9 for microcystin-RR and cylindrospermopsin (CYN). Kinetic studies and adsorption isotherms reflected better fit for pseudo-second-order rate and Langmuir isotherm model, respectively. Thermodynamic calculations showed that the cyanotoxin adsorption process is endothermic and spontaneous in nature. The regenerated adsorbent can be successfully reused without appreciable loss of its original capacity. PMID:27072032

  14. 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. PMID:27375818

  15. Adsorption of quantum dots onto polymer and Gemini surfactant films: a quartz crystal microbalance study.

    PubMed

    Alejo, T; Merchán, M D; Velázquez, M M

    2014-08-26

    We used quartz crystal microbalance with dissipation to study the mechanical properties, the kinetics of adsorption, and the amount of CdSe quantum dots (QDs) adsorbed onto a SiO2 sensor, referred as bare sensor, onto the sensor modified with a film of the polymer poly(maleic anhydride-alt-1-octadecene), PMAO, or with a film of the Gemini surfactant ethyl-bis(dimethyl octadecyl ammonium bromide), abbreviated as 18-2-18. Results showed that when the sensor is coated with polymer or surfactant molecules, the coverage increases compared with that obtained for the bare sensor. On the other hand, rheological properties and kinetics of adsorption of QDs are driven by QD nanoparticles. Thus, the QD films present elastic behavior, and the elasticity values are independent of the molecule used as coating and similar to the elasticity value obtained for QDs films on the bare sensor. The QD adsorption is a two-step mechanism in which the fastest process is attributed to the QD adsorption onto the solid substrate and the slowest one is ascribed to rearrangement movements of the nanoparticles adsorbed at the surface. PMID:25093530

  16. Equilibrium study of selected divalent d-electron metals adsorption on A-type zeolite.

    PubMed

    Majdan, Marek; Pikus, Stanisław; Kowalska-Ternes, Monika; Głdysz-Płaska, Agnieszka; Staszczuk, Piotr; Fuks, Leon; Skrzypek, Henryk

    2003-06-15

    The objective of the presented study was to investigate the adsorption of Cu, Co, Mn, Zn, Cd and Mn on A-type zeolite. The isotherms for adsorption of metals from their nitrates were registered. The following adsorption constants K of metals were found: 162,890, 124,260, 69,025, 16,035, 10,254, and 151 [M(-1)] for Cu, Co, Mn, Zn, Cd, and Ni, respectively, for the concentration range 10(-4)-10(-3) M. On the other hand, the investigation of pH influence on the distribution constants of metals showed that the adsorption of metals proceeds essentially through an ion-exchange process, surface hydrolysis, and surface complexation. The supplementary results from DRIFT, scanning electron microscopy, and X-ray diffraction methods confirmed the presumption about the possible connection between the electronic structure of divalent ions and their adsorption behavior, showing that ions with d5 and d10 configurations such as Mn2+, Zn2+, Cd2+, with much weaker hydrolytic properties than Cu2+ and Ni2+, strongly interact with the zeolite framework and therefore their affinity to the zeolite phase is much stronger when compared with that of the Ni2+ ion, but at the same time not as strong as the affinity of the Cu2+ ion, the latter forming a new phase during the interaction with zeolite framework. For Zn2+, during inspection of the correlation between the proton concentration H/Al and zinc concentration Zn/Al on the zeolite surface, the formation of the surface complex [triple bond]S-OZn(OH) was proposed. A correlation between the heterogeneity of proton concentrations H/Al on Me-zeolite surfaces and the hydrolysis constants pKh of Me2+ ions was found. PMID:16256612

  17. Adsorption and desorption studies of cesium on sapphire surfaces

    SciTech Connect

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

    1993-12-01

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

  18. Iodine adsorption on Ni(111): STM and DFT study

    NASA Astrophysics Data System (ADS)

    Komarov, N. S.; Pavlova, T. V.; Andryushechkin, B. V.

    2016-09-01

    Iodine adsorption on the Ni(111) surface has been studied in ultra-high vacuum conditions with scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and density functional theory (DFT) calculations. At the first stage of adsorption, iodine was found to form a simple commensurate (√{ 3 } ×√{ 3 }) R 30∘ structure at the coverage of 0.33 ML. According to DFT calculations, all iodine atoms in the (√{ 3 } ×√{ 3 }) R 30∘ structure occupy fcc hollow sites. Increase of the coverage in the range of (0.333 ML <θ < 0.364 ML) results in the uniaxial compression of the iodine lattice and the formation of the high-order commensurate structure (11 ×√{ 3 } R 30∘). The mechanism of compression involves the formation and the development of the striped super-heavy domain wall network. Further iodine dosing gives rise to nucleation and growth of flat 2D islands of surface nickel iodide. Atomic resolution STM images of iodide islands, in addition to atomic modulation, exhibit clear visible moiré-like superstructures with a period about 26 Å. The origin of the moiré-patterns was explained by the incommensurability of lattices of the surface nickel iodide and underlying Ni(111).

  19. Theoretical and practical aspects of chemical functionalization of carbon nanofibers (CNFs): DFT calculations and adsorption study.

    PubMed

    Rokhina, Ekaterina V; Lahtinen, Manu; Makarova, Katerina; Jegatheesan, Veeriah; Virkutyte, Jurate

    2012-06-01

    The nitric acid-functionalized commercial carbon nanofibers (CNFs) were comprehensively studied by instrumental (XRD, BET, SEM, TGA) and theoretical (DFT calculations) methods. The detailed surface study revealed the variation in the characteristics of functionalized CNFs, such as a decreased (up to 34%) surface area and impacted structural, electronic and chemical properties. The effects of functional groups were studied by comparison with pristine nanofibers. The results showed that the C-C bond lengths of the modified CNFs varied significantly. Chemical functionalization altered the frontier orbitals of the pristine material, and therefore altered the nature of their interactions with other substances. Moreover, the pristine and modified CNFs were tested for the removal of phenol from aqueous solutions. It was observed that surface modification tuned the adsorption capacity of carbon nanofibers (up to 0.35 mmol g(-1)), whereas original fibers did not demonstrate any adsorption capacity of phenol. PMID:22209137

  20. 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. PMID:16427273

  1. Penis Reconstructions 'Life-Altering' for Men, Studies Show

    MedlinePlus

    ... gov/medlineplus/news/fullstory_158725.html Penis Reconstructions 'Life-Altering' for Men, Studies Show Both transgender patients ... in the studies. But the procedure can be "life-altering," both for transgender men and for those ...

  2. A first-principles study of CO dissociative adsorption on iron nanoparticles supported on doped graphene

    NASA Astrophysics Data System (ADS)

    Kim, Sol; Jhi, Seung-Hoon

    2015-12-01

    We study Fe13 nanoparticles supported on doped graphene and investigate the dissociative adsorption of CO on the nanoparticles using first-principle calculations. It is found that boron doping enhances the binding energy of Fe13 on the graphene but nitrogen doping reduces it. We show that difference in the work-function and subsequently in the charge transfer causes such behavior in the binding energies. Calculated d-band width and d-band center are well correlated with the Fe binding energy, mostly because of the orbital hybridization effect. We also show that the dissociative adsorption of CO on the Fe-graphene substrate is strongly correlated with the d-band center, which is in turn modulated by the doping concentration.

  3. 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. PMID:27348137

  4. [Study of adsorption and desorption of behaviors of Pb2+ on thiol-modified bentonite by flame atomic absorption spectrometry].

    PubMed

    Chen, Wen; Xiong, Qiong-Xian; Pang, Xiao-Feng; Zhu, Xia-Ping; Han, Mei; Zhao, Qiu-Xiang; Liu, Wen-Hua

    2013-03-01

    A comparative analysis of the functional groups and surface structure of the Ca-bentonite (RB) and thiol-modified bentonite (TMB) were characterized by means of FTIR and SEM. The absorptive property of Pb2+ on TMB and RB and its influential factors was studied and the conditions for the adsorption were optimized by using FAAS method. Then the conditions for desorption of Pb2+ from the TMB by using simulated acid rain were studied and the contrast analysis of absorptive stability of Pb2+ on TMB and RB was given. The results showed that the adsorption rate of Pb2+ by TMB could reach more than 98%, when the initial Pb2+ concentration was 100 mg.L-1, the liquid-solid ratio was 5 g.L-1, pH was 6. 0, KNO3 ionic strength was 0. 1 mol.L-1 and adsorption period was 60min at 25 C. The saturated adsorption capacity of TMB was 67.27 mg.g-1; it's much more than that of RB (9.667 mg.g-1). The adsorption of Pb2+ on TMB follows Langmuir and Freundlich isotherm models well. Desorption experiments of Pb2+ from TMB with simulated acid rain (pH 3. 50) were done, and the desorption rate was 0. The results showed that TMB has a strong adsorption and fixation capacity for PbZ+; it is adapted to lead contaminated soil for chemical remediation. PMID:23705461

  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. 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. PMID:25875917

  7. 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.

  8. Process development for removal and recovery of cadmium from wastewater by a low-cost adsorbent: Adsorption rates and equilibrium studies

    SciTech Connect

    Periasamy, K.; Namasivayam, C. . Dept. of Environmental Sciences)

    1994-02-01

    Activated carbon prepared from peanut hulls (PHC), an agricultural waste by-product, has been used for the adsorption of Cd(II) from synthetic wastewater. The adsorption data fit better with the Freundlich adsorption isotherm. The applicability of the Lagergren kinetic model has also been investigated. An almost quantitative removal of 20 mg/L Cd(II) by 0.7 g of PHC/L of aqueous solution was observed in the pH range 3.5--9.5. A comparative study with a commercial granular activated carbon (CAC) showed that the adsorption capacity (K[sub f]) of PHC was 31 times larger than that of CAC.

  9. Oxygen adsorption on single layer graphyne: a DFT study.

    PubMed

    Kang, Baotao; Liu, Hongguang; Lee, Jin Yong

    2014-01-21

    Graphyne is a rising two-dimensional (2D) carbon allotrope with excellent electronic properties. In this paper, theoretical calculations were performed to study the corresponding electronic properties of the oxygenated graphyne. Atomic oxygen when bound to the carbon atom of graphyne forms a stable oxide, with a much larger binding energy compared to that on graphene. Owing to the oxygen adsorption, the α- and β-graphyne change from a zero-band-gap material to a semiconductor as indicated in the band structure calculations. Moreover, spin splitting was observed from the band structure of the oxygenated γ-graphyne. These electronic properties are tunable by altering the oxygen coverage through changing the supercell size. Our results based on the first-principles calculations imply that oxygenation is a promising method to functionalize graphyne to achieve designated properties. PMID:24281199

  10. Adsorption of water on porous Vycor glass studied by ellipsometry.

    PubMed

    Alvarez-Herrero, A; Heredero, R L; Bernabeu, E; Levy, D

    2001-02-01

    The variation of the optical properties of porous Vycor glass (Corning, Model 7930) under different relative-humidity conditions was studied. The adsorption of water into the glass pores was investigated with spectroscopic ellipsometry. The change of the refractive index was Deltan approximately 0.04 between 5% and 90% relative humidity. A linear relation between the ellipsometer parameter tan Psi, the amount of water adsorbed in the glass pores, and information about the pore-size distributions was established. The results are in accord with the values obtained from N2 isotherms, transmission electron microscope micrographs, and the manufacturer's specifications (radius of approximately 20 A). The possibility of using this material as a transducer for implementation in a fiber-optic sensor to measure humidity was evaluated. PMID:18357027

  11. Theoretical study of xenon adsorption in UO2 nanoporous matrices.

    PubMed

    Colbert, Mehdi; Tréglia, Guy; Ribeiro, Fabienne

    2014-12-01

    We present a theoretical study of xenon incorporation in UO2 nanocavities, by means of Grand Canonical Monte Carlo calculations based on semi-empirical potentials. We first characterize the reconstruction of the matrix around an empty cavity which leads to a stoechiometry change from UO2 to UO in this region. Then, we determine xenon adsorption isotherms which exhibit an abrupt transition from a dilute phase to a dense one and an increase in the density of the latter phase as a function of temperature. This last result is attributed to a vibrational entropy effect by means of a mean field analysis. Finally, the pressure calculation inside the bubble proves the limitations of the usual mesoscopic models based on gas state behaviour. PMID:25388362

  12. Adsorption of caffeic acid on titanium dioxide: A spectroscopic study

    NASA Astrophysics Data System (ADS)

    Barreto, Wagner José; Ando, Rômulo A.; Estevão, Bianca Martins; Zanoni, Kassio Papi da Silva

    2012-06-01

    Caffeic acid is an ortho-phenol found in vegetable tissues presenting important properties such as carcinogenesis inhibitor, anti-oxidant, anti-viral, anti-inflammatory and anti-rheumatic actions. It was observed that caffeic acid was not degraded in daylight during the adsorption on TiO2 at pH 4.8. The adsorption fit very well to a Brunauer-Emmett-Teller isotherm equation with a monolayer coverage of 68.15 mg gTiO-1 and saturation coverage of 195.4 mg gTiO-1. A strong adsorption of caffeic acid was verified on TiO2 for the dry solid obtained from the mixture. The Raman and IR spectroscopies revealed that the adsorption should occur through the interaction of the diphenol oxygens with contribution of CC double bond of the acrylic group, however, the carboxylic acid group did not have participation in the adsorption.

  13. Ab initio theoretical study of non-covalent adsorption of aromatic molecules on boron nitride nanotubes.

    PubMed

    Zhao, Yu; Wu, Xiaojun; Yang, Jinlong; Zeng, Xiao Cheng

    2011-06-28

    We have studied non-covalent functionalization of boron nitride nanotubes (BNNTs) with benzene molecule and with seven other different heterocyclic aromatic rings (furan, thiophene, pyrrole, pyridine, pyrazine, pyrimidine, and pyridazine, respectively). A hybrid density functional theory (DFT) method with the inclusion of dispersion correction is employed. The structural and electronic properties of the functionalized BNNTs are obtained. The DFT calculation shows that upon adsorption to the BNNT, the center of aromatic rings tend to locate on top of the nitrogen site. The trend of adsorption energy for the aromatic rings on the BNNTs shows marked dependence on different intermolecular interactions, including the dispersion interaction (area of the delocalized π bond), the dipole-dipole interaction (polarization), and the electrostatic repulsion (lone pair electrons). The DFT calculation also shows that non-covalent functionalization of BNNTs with aromatic rings can give rise to new impurity states within the band gap of pristine BNNTs, suggesting possible carrier doping of BNNTs via selective adsorption of aromatic rings. PMID:21603684

  14. Concussion Study Shows Player-To-Player Hits Most Damaging

    MedlinePlus

    ... Study Shows Player-to-Player Hits Most Damaging Running longer before the contact happens also spells more ... the University of Georgia. "We also found that running a long distance before colliding with an opponent ...

  15. Abortion Rates Rising in Zika-Affected Countries, Study Shows

    MedlinePlus

    ... news/fullstory_159500.html Abortion Rates Rising in Zika-Affected Countries, Study Shows Brazil, Ecuador have seen ... News) -- Fears over birth defects from mosquito-borne Zika may be driving up abortion rates in Latin ...

  16. Abortion Rates Rising in Zika-Affected Countries, Study Shows

    MedlinePlus

    ... nlm.nih.gov/medlineplus/news/fullstory_159500.html Abortion Rates Rising in Zika-Affected Countries, Study Shows ... from mosquito-borne Zika may be driving up abortion rates in Latin American countries affected by the ...

  17. For 'Ironman' Athletes, Study Shows Danger of Too Much Water

    MedlinePlus

    ... Ironman' Athletes, Study Shows Danger of Too Much Water Frequent fluid stops entice racers to drink more ... News) -- Long-distance triathletes who drink too much water during competition may end up with dangerously low ...

  18. Laser Unlocks Blood-Brain Barrier for Chemotherapy, Study Shows

    MedlinePlus

    ... nlm.nih.gov/medlineplus/news/fullstory_157444.html Laser Unlocks Blood-Brain Barrier for Chemotherapy, Study Shows ... 24, 2016 WEDNESDAY, Feb. 24, 2016 (HealthDay News) -- Laser surgery can open the protective blood-brain barrier, ...

  19. Adsorption and growth morphology of rare-earth metals on graphene studied by ab initio calculations and scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Liu, Xiaojie; Wang, C. Z.; Hupalo, M.; Yao, Y. X.; Tringides, M. C.; Lu, W. C.; Ho, K. M.

    2010-12-01

    Adsorption of rare-earth (RE) adatoms (Nd, Gd, Eu, and Yb) on graphene was studied by first-principles calculations based on the density-functional theory. The calculations show that the hollow site of graphene is the energetically favorable adsorption site for all the RE adatoms studied. The adsorption energies and diffusion barriers of Nd and Gd on graphene are found to be larger than those of Eu and Yb. Comparison with scanning tunneling microscopy experiments for Gd and Eu epitaxially grown on graphene confirms these calculated adsorption and barrier differences, since fractal-like islands are observed for Gd and flat-topped crystalline islands for Eu. The formation of flat Eu islands on graphene can be attributed to its low diffusion barrier and relatively larger ratio of adsorption energy to its bulk cohesive energy. The interactions between the Nd and Gd adatoms and graphene cause noticeable in-plane lattice distortions in the graphene layer. Adsorption of the RE adatoms on graphene also induces significant electric dipole and magnetic moments.

  20. 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. PMID:25409587

  1. Hydrous ferric oxide doped alginate beads for fluoride removal: Adsorption kinetics and equilibrium studies

    NASA Astrophysics Data System (ADS)

    Sujana, M. G.; Mishra, A.; Acharya, B. C.

    2013-04-01

    A new biopolymer beads, composite of hydrous ferric oxide (HFO) and alginate were synthesised, characterised and studied for its fluoride efficiency from water. The beads were characterised by chemical analysis, BET surface area, pHPZC and X-ray diffraction (XRD) analysis. The optimum conditions for fluoride removal were determined by studying operational variables viz. pH, contact time, initial F- concentration, bead dose and temperature. Presence of other anions like SO42-, PO43-, NO3-, Cl- and HCO3- effect on fluoride removal efficiency of prepared beads was also tested. The beads were 0.8-0.9 mm in size and contain 32-33% Fe (III) and showed specific surface area of 25.80 m2 g-1 and pHPZC of 5.15. Modified beads demonstrated Langmuir F- adsorption capacity of 8.90 mg g-1 at pH 7.0. The adsorption kinetics were best described by the pseudo-second order kinetic model followed by intra-particle diffusion as the rate determining step. It was found that about 80% of the adsorbed fluoride could be desorbed by using 0.05 M HCl. The FTIR, Raman and SEM-EDAX analysis were used to study the fluoride adsorption mechanisms on beads. Studies were also conducted to test the potential application of beads for F- removal from drinking water and the treated water quality.

  2. 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%.

  3. Interfacial adsorption of fibrinogen and its inhibition by RGD peptide: a combined physical study

    NASA Astrophysics Data System (ADS)

    Armstrong, Johanna; Salacinski, Henryk J.; Mu, Qingshan; Seifalian, Alex M.; Peel, Louise; Freeman, Neville; Holt, Cathy M.; Lu, Jian R.

    2004-07-01

    The Arg-Gly-Asp (RGD) peptide sequence is known as a cell recognition site for numerous adhesive proteins present in the extracellular matrix (ECM) and in blood. Whilst surface immobilized RGD groups enhance cell attachment, RGD components present in solution can effectively inhibit cell attachment by competing with endogenous ligands for the same recognition site. In contrast to the widely reported binding to cell integrin, this study demonstrates a new RGD feature: its inhibitive effect on fibrinogen adsorption. Through a combined analysis of spectroscopic ellipsometry, neutron reflection and dual polarization interferometry, we show that the kinetic process of fibrinogen adsorption as a model pro-coagulant at the silica/solution interface and in the absence of any cells can be substantially reduced by the addition of RGD in solution and that the extent of the reduction is dependent on the relative concentration of RGD.

  4. Kinetic, equilibrium and thermodynamic studies of cadmium (II) adsorption by modified agricultural wastes.

    PubMed

    Othman, Zeid A Al; Hashem, Ali; Habila, Mohamed A

    2011-01-01

    Agricultural wastes have great potential for the removal of heavy metal ions from aqueous solution. The contamination of water by toxic heavy metals is a worldwide environmental problem. Unlike organic pollutants, the majority of which are susceptible to biological degradation, heavy metals do not degrade into harmless end products. Discharges containing cadmium, in particular, are strictly controlled because of the highly toxic nature of this element and its tendency to accumulate in the tissues of living organisms. This work aims to develop inexpensive, highly available, effective metal ion adsorbents from natural wastes as alternatives to existing commercial adsorbents. In particular, Tamrix articulata wastes were modified chemically by esterification with maleic acid to yield a carboxyl-rich adsorbent. The adsorption behavior of treated Tamrix articulata wastes toward cadmium ions in aqueous solutions in a batch system has been studied as a function of equilibration time, adsorbent dose, temperature and pH. Results showed that the maximum adsorption capacity was 195.5 mg/g in a pH 4 solution at 30 °C with a contact time of 120 min, an initial concentration of 400 mg/L and an adsorbent dose of 0.3 g/L. The kinetic data were analyzed using pseudo-first-order and pseudo-second-order kinetic models. It was shown that the adsorption of cadmium could be described by a pseudo-second-order equation. The experimental data were also analyzed using the Langmuir and Freundlich models of adsorption. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° have been evaluated and it has been found that the sorption process was spontaneous and exothermic in nature. From all of our data, we conclude that the treated Tamrix articulata wastes investigated in this study showed good potential for cadmium removal from aqueous solutions. PMID:22173337

  5. Adsorption and dissociation of O2 on MoSe2 and MoTe2 monolayers: ab initio study

    NASA Astrophysics Data System (ADS)

    Zhu, X. F.; Wang, L.; Chen, L. F.

    2014-07-01

    Adsorption and dissociation of O2 molecule on the MoSe2 and MoTe2 monolayers are studied by using density functional theory (DFT) within the generalized gradient approximation (GGA) and a supercell approach. The physisorbed O2 molecule on MoSe2 and MoTe2 with a magnetic moment (MM) close to that for an isolated O2 molecule has small adsorption energy and long distance from the surface. The dissociative adsorption of configuration R5(R6) is the most stable adsorption site, whereas the chemisorption of O2 is unfavorable at all adsorption sites. The dissociative adsorption of configuration R4 induces dramatic changes of electronic structures and localized spin polarization both for monolayer MoSe2 and MoTe2. The analysis of electronic density of states (DOSs) shows that the contribution of spin polarization is mainly from the hybridization between O-p, Se(Te)-p and Mo-d orbitals.

  6. Experimental study on removal of NO using adsorption of activated carbon/reduction decomposition of microwave heating.

    PubMed

    Shuang-Chen, Ma; Yao, Juan-Juan; Gao, Li

    2012-01-01

    Experimental studies were carried out on flue gas denitrification using activated carbon irradiated by microwave. The effects of microwave irradiation power (reaction temperature), the flow rate of flue gas, the concentration of NO and the flue gas coexisting compositions on the adsorption property of activated carbon and denitrification efficiency were investigated. The results show that: the higher of microwave power, the higher of denitrification efficiency; denitrification efficiency would be greater than 99% and adsorption capacity of NO is relatively stable after seven times regeneration if the microwave power is more than 420 W; adsorption capacity of NO in activated carbon bed is 33.24 mg/g when the space velocity reaches 980 per hour; adsorption capacity declines with increasing of the flow rate of flue gas; the change in denitrification efficiency is not obvious with increasing oxygen content in the flue gas; and the maximum adsorption capacity of NO was observed when moisture in flue gas was about 5.88%. However, the removal efficiency of NO reduces with increasing moisture, and adsorption capacity and removal efficiency of NO reduce with increasing of SO2 concentration in the flue gas. PMID:22988643

  7. 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.

  8. 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.

  9. 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...

  10. [Comparison study on adsorption of middle molecular substances with multiwalled carbon nanotubes and activated carbon].

    PubMed

    Li, Guifeng; Wan, Jianxin; Huang, Xiangqian; Zeng, Qiao; Tang, Jing

    2011-08-01

    In recent years, multi-walled carbon nanotubes (MWCTs) are very favorable to the adsorption of middle molecular substances in the hemoperfusion because of their multiporous structure, large surface area and high reactivity, which are beneficial to the excellent absorption properties. The purpose of this study was to study the MWCTs on the adsorption capacity of the middle molecular substances. Vitamin B12 (VB12) was selected as a model of the middle molecular substances. The morphologies of MWCTs and activated carbon from commercial "carbon kidney" were observed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The adsorption behavior of VB12 was compared to each other with UV-visible absorption spectra. The MWCTs formed a sophistaicate gap structure, and compared to the activated carbon, MWCTs had a larger surface area. By Langmuir equation and Freundlich equation fitting analysis, VB12 adsorption on MWCTs is fit for multi-molecular layer adsorption, and the adsorption type of activated carbon is more inclined to the model corresponding to Langmuir monolayer adsorption. The adsorption rate of MWCTs is faster than that of the activated carbon and the adsorption capacity is greater, which could be expected to become the new adsorbent in the hemoperfusion. PMID:21936376

  11. Coulometric study of ethanol adsorption at a polycrystalline platinum electrode

    NASA Astrophysics Data System (ADS)

    Gilman, Sol

    2012-01-01

    For the first time, use of a novel pre-conditioning sequence and measurements of hydrogen blockage during fast cathodic scans has enabled the determination of rates of accumulation of ethanolic species on the surface of a platinum electrode under well-controlled conditions of surface cleanliness/activity and mass transport. For dilute solutions of ethanol in 1 N perchloric acid (HClO4), oxidative adsorption rates maximize at 0.3 V, drop off at more cathodic potentials due to competition with adsorbed hydrogen and drop off at more anodic potentials due to oxidative processes that produce products released to the electrolyte. The time and concentration dependence of adsorption follows relationships that are common for adsorption on a heterogeneous surface. Some evidence are presented supporting a mechanism for production of soluble products that does not involve the adsorbed species that are detected through the measurement of blockage of hydrogen adsorption sites.

  12. 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.

  13. 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. PMID:27343464

  14. Adsorption of organic molecules on the TiO2(011) surface: STM study.

    PubMed

    Godlewski, Szymon; Tekiel, Antoni; Prauzner-Bechcicki, Jakub S; Budzioch, Janusz; Gourdon, Andre; Szymonski, Marek

    2011-06-14

    High resolution scanning tunneling microscopy has been applied to investigate adsorption and self-assembly of large organic molecules on the TiO(2)(011) surface. The (011) face of the rutile titania has been rarely examined in this context. With respect to possible industrial applications of rutile, quite often in a powder form, knowledge on behavior of organic molecules on that face is required. In the presented study we fill in the gap and report on experiments focused on the self-assembly of organic nanostructures on the TiO(2)(011) surface. We use three different kinds of organic molecules of potential interest in various applications, namely, PTCDA and CuPc representing flat, planar stacking species, and Violet Landers specially designed for new applications in molecular electronics. In order to reach a complete picture of molecular behavior, extended studies with different surface coverage ranging from single molecule up to 2 monolayer (ML) thick films are performed. Our results show that the adsorption behavior is significantly different from previously observed for widely used metallic templates. Creation of highly ordered molecular lines, quasi-ordered wetting layers, controlled geometrical reorientation upon thermal treatment, existence of specific adsorption geometries, and prospects for tip-induced molecule ordering and manipulation provide better understanding and add new phenomena to the knowledge on the (011) face of rutile titania. PMID:21682527

  15. 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

  16. 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.

  17. CO2 study shows effects on scrub oak environment

    NASA Technical Reports Server (NTRS)

    2000-01-01

    CO2 study site manager and plant physiologist Graham Hymus (left) examines scrub oak foliage while project engineer David Johnson (right) looks on. The life sciences study is showing that rising levels of carbon dioxide in our atmosphere, caused by the burning of fossil fuels, could spur plant growth globally. The site of KSC's study is a natural scrub oak area near the Vehicle Assembly Building. Twelve-foot areas of scrub oak have been enclosed in 16 open-top test chambers into which CO2 has been blown. Five scientists from NASA and the Smithsonian Environmental Research Center in Edgewater, Md., work at the site to monitor experiments and keep the site running. Scientists hope to continue the study another five to 10 years. More information on this study can be found in Release No. 57- 00.

  18. 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. PMID:25499502

  19. Systematic DFT-GGA study of hydrogen adsorption on transition metals

    NASA Astrophysics Data System (ADS)

    Vasić, D.; Ristanović, Z.; Pašti, I.; Mentus, S.

    2011-12-01

    Computational study of hydrogen adsorption on (111) surface of transition metals with face centered cubic (fcc) lattice is reported and the results are compared with available experimental and theoretical data. In addition, dissociative adsorption of hydrogen on Pt(111), Pt(100) and Pt(110) is studied in the range of coverage from 0.25 to 1 monolayer. In the case of Pt(111) preferential adsorption site was found to be three-coordinated fcc-hollow site, while on Pt(100) and Pt(110) surface hydrogen settles on two-coordinated bridge and short bridge site, respectively. Hydrogen adsorption energy was found to decrease with the increasing coverage. Structural changes of studied Pt surfaces upon hydrogen adsorption have been compared with the experimental data existing in the literature and good qualitative agreement has been obtained.

  20. How polyelectrolyte adsorption depends on history: A combined Fourier transform infrared spectroscopy in attenuated total reflection and surface forces study

    SciTech Connect

    Sukhishvili, S.A.; Dhinojwala, A.; Granick, S.

    1999-11-23

    The authors present a systematic study of how adsorption history affects the thickness, surface forces, and interfacial rheology of a model cationic polymer. The polymer was quaternized poly-4-vinylpyridine, QPVP (weight average degree of polymerization n{sub w} = 325 and 98% quaternized with ethyl bromide). The main comparisons concerned one-step adsorption from solution at a variable salt concentration up to 0.5 NaCl, versus two-step adsorption (initial adsorption from buffer solution without added salt, then NaCl added later). The aqueous solutions were buffered at pH = 9.2 such that the surfaces (mica in the case of surfaces forces (SFA) experiments, oxidized silicon in the case of in situ infrared (FTIR-ATR) experiments) in each case carried a large negative charge. The SFA and FTIR-ATR experiments gave consistent estimates of the amount of polymer adsorbed, confirming the expectation that adsorption should be driven by electrostatic attraction to the surface of large opposite charge. The adsorbed amount showed little dependence on path, validating the common assumption of equilibration in this respect. However the layer thickness measured by surface forces, the shear nanorheology response at a given surface force, and the dichroism of pendant side groups of the polymer all showed a pronounced dependence on the path to reach the adsorbed state. The authors interpret the measurements to suggest that two-step adsorption produces an inhomogeneous layer comprised of a dense layer of segments closest to the solid surface and a sparse outer layer. In particular, two-step adsorption produced thicker layers and a greater tendency to decouple shear forces from those that resist compression in the normal direction, thereby lessening the shear forces at a given level of normal force.

  1. Magnetic vinylphenyl boronic acid microparticles for Cr(VI) adsorption: kinetic, isotherm and thermodynamic studies.

    PubMed

    Kara, Ali; Demirbel, Emel; Tekin, Nalan; Osman, Bilgen; Beşirli, Necati

    2015-04-01

    Magnetic vinylphenyl boronic acid microparticles, poly(ethylene glycol dimethacrylate(EG)-vinylphenyl boronic acid(VPBA)) [m-poly(EG-VPBA)], produced by suspension polymerization and characterized, was found to be an efficient solid polymer for Cr(VI) adsorption. The m-poly(EG-VPBA) microparticles were prepared by copolymerizing of ethylene glycol dimethylacrylate (EG) with 4-vinyl phenyl boronic acid (VPBA). The m-poly(EG-VPBA) microparticles were characterized by N2 adsorption/desorption isotherms, electron spin resonance (ESR), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), elemental analysis, scanning electron microscope (SEM) and swelling studies. The m-poly(EG-VPBA) microparticles were used at adsorbent/Cr(VI) ion ratios. The influence of pH, Cr(VI) initial concentration, temperature of the removal process was investigated. The maximum removal of Cr(VI) was observed at pH 2. Langmuir isotherm and Dubinin-Radushkvich isotherm were found to better fit the experiment data rather than Fruendlich isotherm. The kinetics of the adsorption process of Cr(VI) on the m-poly(EG-VPBA) microparticles were investigated using the pseudo first-order, pseudo-second-order, Ritch-second-order and intraparticle diffusion models, results showed that the pseudo-second order equation model provided the best correlation with the experimental results. The thermodynamic parameters (free energy change, ΔG(0) enthalpy change, ΔH(0); and entropy change, ΔS(0)) for the adsorption have been evaluated. PMID:25666882

  2. 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.

  3. Phenothiazine-modified electrodes: a useful platform for protein adsorption study.

    PubMed

    Chiou, Bo-Hao; Tsai, Yi-Ting; Wang, Chong Mou

    2014-02-18

    Using glucose oxidase (GOx) as a target protein, we studied the adsorption of protein on the phenothiazine-modified electrodes and assessed the potential of using the electrodes in biochemical applications. Experiment results showed that thionine chloride (TC) and its structural analogues, such as toluidine blue and methylene blue, fluoresced under photochemical excitation after being immobilized on indium-doped tin oxide (ITO) electrodes fabricated using either diazotization-reduction or oxidative polymerization. The surface-bound phenothiazines exhibited substantial binding affinities to the protein. At a pH > 5, the adsorbate showed no sign of desorption even the electrodes were electrically biased with voltages between ±0.3 V vs SCE. Thus, emission decay occurred while GOx was injected over the electrodes, which was consistent with the observations made using conductive-mode atomic force microscopy (CM-AFM). Under a quiescent condition, the protein interacted with the immobilized TC via a pseudo-first-order kinetic mechanism. The reaction reached a maximum rate at a pH > 5, at which the rate constant was approximately 7 × 10(-8) L/(U s). Under this condition, the adsorption rate increased as the level of the protein increased, regardless of pH, revealing application potential for GOx quantitation. The adsorption rate, however, decreased with a decrease in pH if the pH < 5. We concluded that static interactions played a crucial role. By monitoring Fe(CN)6(3-/4-) taking place at the TC-modified electrodes in pH 7 solutions, we observed that the adsorption of GOx imposed impedance on Fe(CN)6(3-/4-). The resulting charge-transfer resistance (RCT) increased as the amount of the protein increased, leading to a conclusion that the protein could reach the maximum surface coverage when its concentrations were greater than 100 U/mL. The protein molecules were likely repel each other as approaching the TC sites. Despite this, they maintained the native bioactivity after

  4. DFT studies of the phenol adsorption on boron nitride sheets.

    PubMed

    Hernández, Jose Mario Galicia; Cocoletzi, Gregorio Hernández; Anota, Ernesto Chigo

    2012-01-01

    We perform first principles total energy calculations to investigate the atomic structures of the adsorption of phenol (C(6)H(5)OH) on hexagonal boron nitride (BN) sheets. Calculations are done within the density functional theory as implemented in the DMOL code. Electron-ion interactions are modeled according to the local-spin-density-approximation (LSDA) method with the Perdew-Wang parametrization. Our studies take into account the hexagonal h-BN sheets and the modified by defects d-BN sheets. The d-BN sheets are composed of one hexagon, three pentagons and three heptagons. Five different atomic structures are investigated: parallel to the sheet, perpendicular to the sheet at the B site, perpendicular to the sheet at the N site, perpendicular to the central hexagon and perpendicular to the B-N bond (bridge site). To determine the structural stability we apply the criteria of minimum energy and vibration frequency. After the structural relaxation phenol molecules adsorb on both h-BN and d-BN sheets. Results of the binding energies indicate that phenol is chemisorbed. The polarity of the system increases as a consequence of the defects presence which induces transformation from an ionic to covalent bonding. The elastic properties on the BN structure present similar behavior to those reported in the literature for graphene. PMID:21523546

  5. 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. PMID:23128640

  6. Experimental studies on irreversibility of electrostatic adsorption of silica nanoparticles at solid-liquid interface.

    PubMed

    Li, Xue; Niitsoo, Olivia; Couzis, Alexander

    2014-04-15

    Adsorption of colloidal nanoparticles (NPs) at solid-liquid interface is a scientifically interesting and technologically important phenomenon due to its fundamental importance in many industrial, environmental, and biological processes, such as wastewater treatment, printing, coating of surfaces, chromatography, papermaking, or biocompatibility. The process is well understood theoretically by the random sequential adsorption (RSA) model, based on the assumption of irreversible adsorption. Irreversible adsorption is defined as a process in which, once adsorbed, a particle can neither desorb, nor to move laterally on the surface. However, published experimental data that verifies the irreversibility of particle adsorption are very limited. In this study, we demonstrate the irreversibility of electrostatically driven nanoparticle adsorption utilizing a carefully selected set of experiments. A simple method was employed by uniquely introducing Ag@SiO2 core/shell NPs to perform exchange adsorptions experiments. Stöber SiO2 NPs with a diameter of 50-80 nm were initially electrostatically adsorbed onto amino-functionalized silicon wafer substrates followed by the subsequent adsorption of Ag@SiO2 NPs. The Ag@SiO2 NPs have the same surface chemistry as the neat SiO2 NPs. For the second step the adsorption time was varied from 1 min to 1 week so as to get a thorough understanding of the process irreversibility. Surface coverage quantification has shown that the surface coverage of the initially adsorbed SiO2 NPs stays the same independent of the duration of the second step adsorption using the Ag@SiO2 core/shell NPs. This observation directly confirms the irreversibility of electrostatic adsorption of NPs. PMID:24559699

  7. Adsorption of carbon monoxide on boroxol-ring-doped zigzag boron nitride nanotube: Electronic study via DFT

    NASA Astrophysics Data System (ADS)

    Zahedi, Ehsan; Yari, Maryam; Bahmanpour, Hooman

    2016-04-01

    Previous works have already demonstrated that reactivity and sensitivity of boron nitride nanotubes (BNNTs) toward gas molecules can be modified by impurity. In this work, three nitrogen atoms of BNNT (7,0) are replaced with oxygen to study the adsorption of CO molecule through the surface of boroxol ring with different adsorption patterns, including side-on and end-on. All calculations have been done using the DFT-B3LYP/6-31G * level of theory, and their electronic energies are corrected by gCP and D3 correction terms. The calculated binding energies are large, which indicates that CO molecule undergoes chemical adsorption. NBO results showed that the charge transfer occurs from the tube to the gas molecule, which can slightly change the electronic properties of the tube. Density of state (DOS) and partial DOS (PDOS) analysis revealed that adsorption of CO molecule on the boroxol ring position is covalent in nature. The Laplacian of electron density, Lagrangian kinetic energy density, Hamiltonian kinetic energy density, and potential energy density at bond critical points between the tube and CO indicate that the interaction between the tube and CO molecule is covalent in nature. Topological analysis of the electron localization function shows that electrons in the new formed bonds are approximately localized, meaning that the nature of the adsorption process is chemical covalent.

  8. Adsorption and dissociation of O 2 on CuCl(1 1 1) surface: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Zhang, Riguang; Liu, Hongyan; Wang, Baojun; Ren, Jun; Li, Zhong

    2011-10-01

    The adsorption and dissociation of O 2 on CuCl(1 1 1) surface have been systematically studied by the density functional theory (DFT) slab calculations. Different kinds of possible modes of atomic O and molecular O 2 adsorbed on CuCl(1 1 1) surface and possible dissociation pathways are identified, and the optimized geometry, adsorption energy, vibrational frequency and Mulliken charge are obtained. The calculated results show that the favorable adsorption occurs at hollow site for O atom, and molecular O 2 lying flatly on the surface with one O atom binding with top Cu atom is the most stable adsorption configuration. The O-O stretching vibrational frequencies are significantly red-shifted, and the charges transferred from CuCl to oxygen. Upon O 2 adsorption, the oxygen species adsorbed on CuCl(1 1 1) surface mainly shows the characteristic of the superoxo (O 2-), which primarily contributes to improving the catalytic activity of CuCl, meanwhile, a small quantity of O 2 dissociation into atomic O also occur, which need to overcome very large activation barrier. Our results can provide some microscopic information for the catalytic mechanism of DMC synthesis over CuCl catalyst from oxidative carbonylation of methanol.

  9. Kinetic and thermodynamic studies of Hg(II) adsorption onto MCM-41 modified by ZnCl2

    NASA Astrophysics Data System (ADS)

    Raji, Foad; Pakizeh, Majid

    2014-05-01

    Kinetics and thermodynamics of mercury ions sorption onto ZnCl2-MCM-41 sorbent were studied. Several rate models in the form of two main classes of mathematic kinetic models (adsorption reaction models and adsorption diffusion models) were investigated. Pseudo-first-order, pseudo-second-order, Elovich, film and intraparticle diffusion models were used to analyze the kinetic data. Results showed that the pseudo-second order model can well describe the adsorption kinetic data. The thermodynamic parameters, such as Gibb's free energy change (ΔG°), standard enthalpy change (ΔH°) and standard entropy change (ΔS°) were also evaluated. Negative value of free energy at temperature range of 20-55 °C, indicates the spontaneous nature of Hg(II) sorption by ZnCl2-MCM-41 sorbent. The adsorption capacity which was found to decrease with temperature showed the exothermic nature of the mercury sorption process (ΔH° = -49.4 kJ mol-1). The negative ΔS° value (-148.9 J mol-1 K-1) revealed a decrease in the randomness at the solid/solution interface and also indicated the fast adsorption of the Hg(II) onto active sites.

  10. 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. PMID:26683820

  11. A one-dimensional stochastic approach to the study of cyclic voltammetry with adsorption effects

    NASA Astrophysics Data System (ADS)

    Samin, Adib J.

    2016-05-01

    In this study, a one-dimensional stochastic model based on the random walk approach is used to simulate cyclic voltammetry. The model takes into account mass transport, kinetics of the redox reactions, adsorption effects and changes in the morphology of the electrode. The model is shown to display the expected behavior. Furthermore, the model shows consistent qualitative agreement with a finite difference solution. This approach allows for an understanding of phenomena on a microscopic level and may be useful for analyzing qualitative features observed in experimentally recorded signals.

  12. Amphiphilic agarose-based adsorbents for chromatography. Comparative study of adsorption capacities and desorption efficiencies.

    PubMed

    Oscarsson, S; Angulo-Tatis, D; Chaga, G; Porath, J

    1995-01-01

    A number of hydrophobic derivatives attached to cross-linked agarose were studied as protein adsorbents. Differences in the adsorption and desorption behaviour were determined as functions of type and concentration of selected salts. Whereas octyl- and phenyl-Sepharose adsorb serum albumin preferentially, pyridyl-S-agarose shows a much stronger preferential affinity for IgG in the presence of high concentrations of lyotropic salts, such as sulphates. In contrast to pyridyl-S-agarose, a large portion of proteins remained fixed to octyl- and phenyl-Sepharose after extensive washing with 1 M NaOH. PMID:7881534

  13. 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

  14. Fundamental studies of methyl iodide adsorption in DABCO impregnated activated carbons.

    PubMed

    Herdes, Carmelo; Prosenjak, Claudia; Román, Silvia; Müller, Erich A

    2013-06-11

    Methyl iodide capture from a water vapor stream using 1,4-diazabicyclo[2.2.2]octane (DABCO)-impregnated activated carbons is, for the first time, fundamentally described here on the atomic level by means of both molecular dynamics and grand canonical Monte Carlo simulations. A molecular dynamics annealing strategy was adopted to mimic the DABCO experimental impregnation procedure in a selected slitlike carbon pore. Predictions, restricted to the micropore region, are made about the adsorption isotherms of methyl iodide, water, and nitrogen on both impregnated and bare activated carbon models. Experimental and simulated nitrogen adsorption isotherms are compared for the validation of the impregnation strategy. Selectivity analyses of the preferential adsorption toward methyl iodide over water are also reported. These simulated adsorption isotherms sum up to previous experimental studies to provide an enhanced picture for this adsorption system of widespread use at nuclear plant HVAC facilities for the capture of radioactive iodine compounds. PMID:23679202

  15. 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

  16. Manual restraint and shows of force: the City-128 study.

    PubMed

    Bowers, Len; Van Der Merwe, Marie; Paterson, Brodie; Stewart, Duncan

    2012-02-01

    Manual restraint is used to manage disturbed behaviour by patients. This study aimed to assess the relationship of manual restraint and show of force to conflict behaviours, the use of containment methods, service environment, physical environment, patient routines, staff characteristics, and staff group variables. Data from a multivariate, cross-sectional study of 136 acute psychiatric wards in England were used to conduct this analysis. Manual restraint was used less frequently on English acute psychiatric wards (0.20 incidents per day) than show of force (0.28 incidents per day). Both were strongly associated with the proportion of patients subject to legal detention, aggressive behaviours, and the enforcement of treatment and detention. Medical, nursing, and security guard staff provision were associated in different ways with variations in the use of these coercive interventions. An effective ward structure of rules and routines was associated with less dependence on these control methods. Training for manual restraint should incorporate the scenarios of attempted absconding and enforcement of treatment, as well as violent behaviour. Attempts to lessen usage of these interventions could usefully focus on increasing the availability of medical staff to patients, reducing reliance on security guards and establishing a good ward structure. PMID:21733054

  17. Polymeric micelles with α-glutamyl-terminated PEG shells show low non-specific protein adsorption and a prolonged in vivo circulation time.

    PubMed

    Wang, Xiaoju; Yang, Cuiping; Wang, Chenhong; Guo, Leijia; Zhang, Tianhong; Zhang, Zhenqing; Yan, Husheng; Liu, Keliang

    2016-02-01

    Although PEG remains the gold standard for stealth functionalization in drug delivery field up to date, complete inhibition of protein corona formation on PEG-coated nanoparticles remains a challenge. To improve the stealth property of PEG, herein an α-glutamyl group was conjugated to the end of PEG and polymeric micelles with α-glutamyl-terminated PEG shells were prepared. After incubation with bovine serum albumin or in fetal calf serum, the size of the micelles changed slightly, while the size of the micelles of similar diblock copolymer but without α-glutamyl group increased markedly. These results indicated that the micelles with α-glutamyl-terminated PEG shells showed low non-specific protein adsorption. In vivo blood clearance kinetics assay showed that the micelles with α-glutamyl-terminated PEG shells exhibited a longer in vivo blood circulation time compared with similar micelles but without α-glutamyl groups. The better stealth property of the micelles with α-glutamyl-terminated PEG shells was presumably attributed to the zwitterionic property of the α-glutamyl groups. PMID:26652431

  18. Theoretical study on the adsorption of carbon dioxide on individual and alkali-metal doped MOF-5s

    NASA Astrophysics Data System (ADS)

    Ha, Nguyen Thi Thu; Lefedova, O. V.; Ha, Nguyen Ngoc

    2016-01-01

    Density functional theory (DFT) calculations were performed to investigate the adsorption of carbon dioxide (CO2) on metal-organic framework (MOF-5) and alkali-metal (Li, K, Na) doped MOF-5s. The adsorption energy calculation showed that metal atom adsorption is exothermic in MOF-5 system. Moreover, alkali-metal doping can significantly improve the adsorption ability of carbon dioxide on MOF-5. The best influence is observed for Li-doping.

  19. 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

    2007-06-01

    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. PMID:17240095

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

    PubMed

    Gor, Gennady Y; Bernstein, Noam

    2016-05-31

    Adsorption-induced deformation is expansion or contraction of a solid due to adsorption on its surface. This phenomenon is important for a wide range of applications, from chemomechanical sensors to methane recovery from geological formations. The strain of the solid is driven by the change of the surface stress due to adsorption. Using ab initio molecular dynamics, we calculate the surface stresses for the dry α-quartz surfaces, and investigate how these stresses change when the surfaces are exposed to water. We find that the nonhydroxylated surface shows small and approximately isotropic changes in stress, while the hydroxylated surface, which interacts more strongly with the polar water molecules, shows larger and qualitatively anisotropic (opposite sign in xx and yy) surface stress changes. All of these changes are several times larger than the surface tension of water itself. The anisotropy and possibility of positive surface stress change can explain experimentally observed surface area contraction due to adsorption. PMID:27159032

  1. Adsorption of cellulase Aspergillus niger on a commercial activated carbon: kinetics and equilibrium studies.

    PubMed

    Daoud, Fatima Boukraa-Oulad; Kaddour, Samia; Sadoun, Tahar

    2010-01-01

    The adsorption kinetics of cellulase Aspergillus niger on a commercial activated carbon has been performed using a batch-adsorption technique. The effect of various experimental parameters such as initial enzyme concentration, contact time and temperature were investigated. The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetic data which shows that the adsorption of the enzyme followed the pseudo-second-order rate expression and the rate constants were evaluated. The Langmuir and Freundlich adsorption isotherm models were applied to describe the equilibrium isotherms, and the isotherm constants were determined. It was found that Langmuir model was more suitable for our data. The activation energy of adsorption was also evaluated for the adsorption of enzyme onto activated carbon. It was found 11.37 kJ mol(-1). Thermodynamic parameters Delta G(0), Delta H(0) and DeltaS(0) were calculated, indicating that this process can be spontaneous and endothermic. The adsorption enthalpy and entropy were found 11.12 kJ mol(-1) and 0.084 kJ mol(-1)K(-1), respectively. At 30 degrees C and at pH 4.8, 1g activated carbon adsorbed about 1565 mg of cellulase, with a retention of 70% of the native enzyme activity up to five cycles of repeated batch enzyme reactions. PMID:19744839

  2. 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.

  3. Kinetic and equilibrium studies of adsorptive removal of phenol onto eggshell waste.

    PubMed

    Daraei, H; Mittal, A; Noorisepehr, M; Daraei, F

    2013-07-01

    The aim of the present research is to develop economic, fast, and versatile method for the removal of toxic organic pollutant phenol from wastewater using eggshell. The batch experiments are conducted to evaluate the effect of pH, phenol concentration, dosage of adsorbent, and contact time on the removal of phenol. The paper includes in-depth kinetic studies of the ongoing adsorption process. Attempts have also been made to verify Langmuir and Freundlich adsorption isotherms. The morphology and characteristics of eggshell have also been studied using scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray fluorescence analysis. At ambient temperature, the maximum adsorption of phenol onto eggshells has been achieved at pH 9 and the contact time, 90 min. The experimental data give best-fitted straight lines for pseudo-first-order as well as pseudo-second-order kinetic models. Furthermore, the adsorption process verifies Freundlich and Langmuir adsorption isotherms, and on the basis of mathematical expressions of these models, various necessary adsorption constants have been calculated. Using adsorption data, various thermodynamic parameters like change in enthalpy (∆H(0)), change in entropy (∆S(0)), and change in free energy ∆G(0) have also been evaluated. Results clearly reveal that the solid waste material eggshell acts as an effective adsorbent for the removal of phenol from aqueous solutions. PMID:23274804

  4. 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.

  5. 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.

  6. NMR characterization of hydrocarbon adsorption on calcite surfaces: a first principles study.

    PubMed

    Bevilaqua, Rochele C A; Rigo, Vagner A; Veríssimo-Alves, Marcos; Miranda, Caetano R

    2014-11-28

    The electronic and coordination environment of minerals surfaces, as calcite, are very difficult to characterize experimentally. This is mainly due to the fact that there are relatively few spectroscopic techniques able to detect Ca(2+). Since calcite is a major constituent of sedimentary rocks in oil reservoir, a more detailed characterization of the interaction between hydrocarbon molecules and mineral surfaces is highly desirable. Here we perform a first principles study on the adsorption of hydrocarbon molecules on calcite surface (CaCO3 (101¯4)). The simulations were based on Density Functional Theory with Solid State Nuclear Magnetic Resonance (SS-NMR) calculations. The Gauge-Including Projector Augmented Wave method was used to compute mainly SS-NMR parameters for (43)Ca, (13)C, and (17)O in calcite surface. It was possible to assign the peaks in the theoretical NMR spectra for all structures studied. Besides showing different chemical shifts for atoms located on different environments (bulk and surface) for calcite, the results also display changes on the chemical shift, mainly for Ca sites, when the hydrocarbon molecules are present. Even though the interaction of the benzene molecule with the calcite surface is weak, there is a clearly distinguishable displacement of the signal of the Ca sites over which the hydrocarbon molecule is located. A similar effect is also observed for hexane adsorption. Through NMR spectroscopy, we show that aromatic and alkane hydrocarbon molecules adsorbed on carbonate surfaces can be differentiated. PMID:25429955

  7. NMR characterization of hydrocarbon adsorption on calcite surfaces: A first principles study

    NASA Astrophysics Data System (ADS)

    Bevilaqua, Rochele C. A.; Rigo, Vagner A.; Veríssimo-Alves, Marcos; Miranda, Caetano R.

    2014-11-01

    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 Ca2+. Since calcite is a major constituent of sedimentary rocks in oil reservoir, a more detailed characterization of the interaction between hydrocarbon molecules and mineral surfaces is highly desirable. Here we perform a first principles study on the adsorption of hydrocarbon molecules on calcite surface (CaCO3 ( {10bar 14} )). 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 43Ca, 13C, and 17O 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.

  8. Pore Size Effect on Methane Adsorption in Mesoporous Silica Materials Studied by Small-Angle Neutron Scattering.

    PubMed

    Chiang, Wei-Shan; Fratini, Emiliano; Baglioni, Piero; Chen, Jin-Hong; Liu, Yun

    2016-09-01

    Methane adsorption in model mesoporous silica materials with the size range characteristic of shale is studied by small-angle neutron scattering (SANS). Size effect on the temperature-dependent gas adsorption at methane pressure about 100 kPa is investigated by SANS using MCM-41 and SBA-15 as adsorbents. Above the gas-liquid condensation temperature, the thickness of the adsorption layer is found to be roughly constant as a function of the temperature. Moreover, the gas adsorption properties, such as the adsorbed layer thickness and the specific amount of adsorbed gas, have little dependence on the pore size being studied, i.e., pore radius of 16.5 and 34.1 Å, but are mainly affected by the roughness of the pore surfaces. Hence, the surface properties of the pore wall are more dominant than the pore size in determining the methane gas adsorption of pores at the nanometer size range. Not surprisingly, the gas-liquid condensation temperature is observed to be sensitive to pore size and shifts to higher temperature when the pore size is smaller. Below the gas-liquid condensation temperature, even though the majority of gas adsorption experiments/simulations have assumed the density of confined liquid to be the same as the bulk density, the measured methane mass density in our samples is found to be appreciably smaller than the bulk methane density regardless of the pore sizes studied here. The mass density of liquid/solid methane in pores with different sizes shows different temperature dependence below the condensation temperature. With decreasing temperature, the methane density in larger pores (SBA-15) abruptly increases at approximately 65 K and then plateaus. In contrast, the density in smaller pores (MCM-41) monotonically increases with decreasing temperature before reaching a plateau at approximately 30 K. PMID:27512895

  9. 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

    , which act as adsorption sites either as a proton-donor or as a donor of the lone pair of electrons. Such adsorption-induced relaxation explains the dependence of physico-chemical properties of icy particles on the presence of atmospheric gases. Spectra HCN/D2O and ND3/D2O mixed icy films with low (1:10) dopant/water ratios do not manifest any changes in the acidic or basic properties of dangling hydroxyl groups or surface oxygen atoms, but reveal a difference in the proportion between the concentrations of these sites as compared with that for pure water ice. For high dopant concentrations (1:1), the dangling hydroxyls were not observed; the dominant adsorption sites for CO are likely to be the unsaturated oxygen atoms, while serious structural changes occur in the bulk of ices. Ecologically important reactions of atmospheric pollutants such as ozonolysis of ethene, chlorinated ethenes, hydrogen cyanide, and methyl bromide adsorbed on water ice film as well as the influence of UV radiation on this process have been studied in 77 - 200 K temperature range by FTIR spectroscopy. Ozone co-adsorption with ethene or C2H3Cl readily leads to ozonolysis reaction, which also starts for C2H2Cl2 isomers but only at temperatures elevated up to 120 - 150 K. Co-adsorption of O3 with HCN or CH3Br molecules in the dark does not lead to any noticeable spectral changes. Irradiation of HCN or CH3Br deposited on ice films in the presence of ozone leads to appearance of new bands revealing the formation of ozonolysis products. The same "synergetic effect" of simultaneous action of ozone and UV radiation at 77 K, was found for C2H2Cl2 isomers and C2Cl4, which are resistant against O3 even at higher temperatures. The obtained spectral dependence of photo-ozonolysis of C2Cl4 and HCN at 77 K shows that photoexcitation or photodissociation of ozone, evidently, accounts for the observed processes. The surface of ice particles, thus, plays the role of a condenser of atmospheric pollutants and acts

  10. Adsorption of NO2 on WSe2: DFT and photoelectron spectroscopy studies.

    PubMed

    Ovcharenko, R; Dedkov, Yu; Voloshina, E

    2016-09-14

    The electronic structure modifications of WSe2 upon NO2-adsorption at room and low temperatures were studied by means of photoelectron spectroscopy. We found only moderate changes in the electronic structure, which are manifested as an upward shift of the WSe2-related bands to the smaller binding energies. The observed effects are modelled within the density functional theory approach, where a small adsorption energy of gas molecules on the surface of WSe2 was deduced. The obtained experimental data are explained as a valence bands polarisation effect, which causes their energy shift depending on the adsorption geometry and the formed dipole moment. PMID:27392163

  11. Adsorption of NO2 on WSe2: DFT and photoelectron spectroscopy studies

    NASA Astrophysics Data System (ADS)

    Ovcharenko, R.; Dedkov, Yu; Voloshina, E.

    2016-09-01

    The electronic structure modifications of WSe2 upon NO2-adsorption at room and low temperatures were studied by means of photoelectron spectroscopy. We found only moderate changes in the electronic structure, which are manifested as an upward shift of the WSe2-related bands to the smaller binding energies. The observed effects are modelled within the density functional theory approach, where a small adsorption energy of gas molecules on the surface of WSe2 was deduced. The obtained experimental data are explained as a valence bands polarisation effect, which causes their energy shift depending on the adsorption geometry and the formed dipole moment.

  12. Study of polyethyleneimine- and amidoxime-functionalized hybrid biomass of Spirulina (Arthrospira) platensis for adsorption of uranium (VI) ion.

    PubMed

    Bayramoglu, Gulay; Akbulut, Aydin; Arica, M Yakup

    2015-11-01

    This study investigates the potential application of the polyethyleneimine- (PEI) and amidoxime-modified Spirulina (Arthrospira) platensis biomasses for the removal of uranium ion in batch mode using the native biomass as a control system. The uranium ion adsorption was also characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra, zeta potential analysis, and surface area measurement studies. The effects of pH, biomass amount, contact time, initial uranium ion concentration, and ionic strength were evaluated by using native and modified algal biomass preparations. The uranium ion removal was rapid, with more than 70% of total adsorption taking place in 40 min, and equilibrium was established within 60 min. From the experimental data, it was found that the amount of adsorption uranium ion on the algal preparations decreased in the following series: amidoxime-modified algal biomass > PEI-modified algal biomass > native algal biomass. Maximum adsorption capacities of amidoxime- and PEI-modified, and native algal biomasses were found to be 366.8, 279.5, and 194.6 mg/g, respectively, in batchwise studies. The adsorption rate of U(VI) ion by amidoxime-modified algal biomass was higher than those of the native and PEI-modified counterparts. The adsorption processes on all the algal biomass preparations followed by the Dubinin-Radushkevitch (D-R) and Temkin isotherms and pseudo-second-order kinetic models. The thermodynamic parameters were determined at four different temperatures (i.e., 15, 25, 35, and 45 °C) using the thermodynamics constant of the Temkin isotherm model. The ΔH° and ΔG° values of U(VI) ion adsorption on algal preparations show endothermic heat of adsorption; higher temperatures favor the process. The native and modified algal biomass preparations were regenerated using 10 mM HNO3. These results show that amidoxime-modified algal biomass can be a potential candidate for effective removal of U(VI) ion from

  13. Surface Enhanced Infrared Studies of 4-Methoxypyridine Adsorption on Gold Film Electrodes.

    PubMed

    Quirk, Amanda; Unni, Bipinlal; Burgess, Ian J

    2016-03-01

    This work uses electrochemical surface sensitive vibrational spectroscopy to characterize the adsorption of a known metal nanoparticle stabilizer and growth director, 4-methoxypyridine (MOP). Surface enhanced infrared absorption spectroscopy (SEIRAS) is employed to study the adsorption of 4-methoxypyridine on gold films. Experiments are performed under electrochemical control and in different electrolyte acidities to identify both the extent of protonation of the adsorbed species as well as its orientation with respect to the electrode surface. No evidence of adsorbed conjugated acid is found even when the electrolyte pH is considerably lower than the pKa. Through an analysis of the transition dipole moments, determined from DFT calculations, the SEIRA spectra support an adsorption configuration through the ring nitrogen which is particularly dominant in neutral pH conditions. Adsorption is dependent on both the electrical state of the Au film electrode as well as the presence of ions in the electrolyte that compete for adsorption sites at positive potentials. Combined differential capacitance measurements and spectroscopic data demonstrate that both a horizontal adsorption geometry and a vertical adsorption phase can be induced, with the former being found on negatively charged surfaces in acidic media and the latter over a wide range of polarizations in neutral solutions. PMID:26862774

  14. 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. PMID:17574338

  15. Enhanced and adjustable adsorption of organo-functional groups on Li decorated carbon nanotubes: A first principle study

    NASA Astrophysics Data System (ADS)

    Li, Yutao; Wang, Xiaojie; Shi, Wenhao; Yan, Zeyu; Zhao, Chengbo; Chen, Chi; Miao, Ling; Jiang, Jianjun

    2014-08-01

    The adsorption of several organo-functional groups (-NH2, -CH3, -COOH, -CHO, and -OH) and alanine on Li decorated carbon nanotubes (CNTs) are studied, based on the first-principle calculations. The calculated binding energies on Li-CNTs show obvious enhancement relative to the cases on pure CNTs, from about 0.3 eV to about 1.4 eV except -CH3, which is attributed to strong electrostatic dipole attraction between positive Li ion and polarized organo-functional groups by charge population analysis. It is interesting that the adsorption could be effectively adjusted under external electric field for the interaction with Li-group dipole. For the combinational contribution of charge redistribution and interaction of inherent electric dipole with external electric field, the adsorption of these organo-functional groups shows two discriminative variety trends. Finally, the adsorption of alanine including -NH2, -CH3, and -COOH groups is studied as an illustration to generalize above conclusions to organic macromolecule on Li decorated CNTs.

  16. Indigo adsorption on a silicate surface: a theoretical density functional study.

    PubMed

    Iuga, Cristina; Sainz-Díaz, C Ignacio; Ortíz, Elba; Vivier-Bunge, Annik

    2014-07-01

    The applicability of naturally available low-cost and eco-friendly adsorbent materials for the removal of hazardous dyes from aqueous waste is of increasing environmental interest. Among the adsorption treatments available, clays seem to be economically attractive due to their abundance and adsorption capabilities. Indeed, many ancient coloring materials utilized clays mixed with natural dyes (e.g., indigo in Maya Blue). In this work, we performed a quantum-mechanical theoretical study of the adsorption of the indigo molecule onto the (001) surface of a phyllosilicate. Different methods and approaches were applied and compared. We found that the presence of a tetrahedral charge and a sodium counterion significantly increased the adsorption energy of the indigo molecule. The vibrational spectrum of the dye-surface system was also studied, and some interesting shifts in the frequencies of the main vibrational modes of indigo due to its interaction with the surface of the clay mineral were identified. PMID:24958302

  17. A comparative adsorption study: 17β-estradiol onto aerobic granular sludge and activated sludge.

    PubMed

    Zheng, Xiao-ying; He, Yu-jie; Chen, Wei; Wang, Ming-yang; Cao, Su-lan; Ni, Ming; Chen, Yu

    2016-01-01

    Adsorption plays a significant role in removing hydrophobic 17β-estradiol (E2) from wastewater. Batch experiments were conducted to compare the adsorption of E2 onto activated aerobic granular sludge (AGS) and activated sludge (AS), and features evaluated included the adsorption kinetics, thermodynamics, and influence of other environmental factors. By using a non-chemical wet-heat technique, both AGS and AS were treated to inactivated status. Then, after loading E2, the adsorption equilibrium capacity of the AGS was found to be greater than that of the AS at the same initial concentration of E2. Moreover, both the adsorption processes corresponded to a pseudo-second-order kinetic model; the adsorption rate constant of AGS was found to be higher and the half-adsorption time was shorter than that of AS. Next, evaluations of adsorption isotherms and thermodynamics indicated that the adsorption process was mainly a physical process. Lower temperatures facilitated a higher equilibrium adsorption capacity. However, the adsorption binding sites of AGS were distributed more uniformly at higher temperature, in contrast to the distribution found for AS. Finally, acidic conditions and an appropriate ionic strength (0.4 mol/L) were found to be particularly conducive to the adsorption process. Overall, the results showed that AGS has the potential to adsorb E2 with significant efficiency, thereby offering a new and more efficient means of treating E2 and trace oestrogens in wastewater. PMID:26209151

  18. 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.

  19. 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

  20. 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.

  1. CO Adsorption on Pd(111) at 0.5ML: a First Principles Study

    NASA Astrophysics Data System (ADS)

    Hooshmand Gharehbagh, Zahra; Le, Duy; Rahman, Talat S.

    2015-03-01

    While the adlayer structures formed by CO molecules on Pd(111) are well-understood both experimentally and theoretically, for low and high coverages, it is still a matter of discussion for medium coverage (0.5ML). At this medium coverage, it is well-known that the c(4 × 2) phase is formed but the adsorption sites of CO molecules have been reported differently by various studies: at the bridge sites, at the hollow sites, or at both bridge and hollow sites. Using density functional theory calculations we studied the overlayer structure of CO at 0.5ML on Pd(111) with all possible highly symmetric adsorption sites leading to c(4 × 2) structures. We will show that, on the same surface, CO molecules adsorb either only on bridge or hollow sites and that there is no overlayer structure in which CO binds at both bridge and hollow sites. By means of ab initio thermodynamics simulation, we will also report the conditions (temperature, pressure) in which each overlayer structure exists. Work support in part by NSF Grant CHE-1310327.

  2. In Situ X-ray Reflectivity Studies of Protein Adsorption onto Functionalized Surfaces

    NASA Astrophysics Data System (ADS)

    Richter, Andrew

    2007-03-01

    The adsorption of protein films onto solid surfaces, both artificial and naturally occurring, have been widely studied using a variety of techniques due to their importance in medicine, biomedical applications, and the general understanding of protein structure and function. What have yet to be performed are in situ, time-resolved, high-resolution structural studies of these systems. We have begun a project that uses the technique of in situ x-ray reflectivity to obtain highly resolved structural information with time resolution on the order of minutes. This talk will present our first findings of serum albumin and immunoglobulin G films on hydrophobic self-assembled monolayers. The protein films are readily observable, showing extensive denaturing after adsorption with a slow decay of density into the aqueous solution. Additionally, a thin low-density region that occurs between the hydrophobic film and the solution persists after protein deposition. Comparisons to films that are removed from solution, the influence of solution concentration, the effects of x-ray damage, and the time scales for protein film formation and evolution will also be discussed.

  3. Enthalpy of adsorption and isotherms for adsorption of naphthenic acid onto clays

    SciTech Connect

    Zou, L.; Han, B.; Yan, H.; Kasperski, K.L.; Xu, Y.; Hepler, L.G.

    1997-06-15

    The enthalpies of adsorption and the isotherms for adsorption of naphthenic acid onto Na-montmorillonite, Na-kaolinite, and Na-illite were studied by means of calorimetry and the static method at 298.15 K. The results show that the enthalpies of adsorption and saturated adsorption amounts of naphthenic acid on different clays change in the order Na-montmorillonite > Na-illite > Na-kaolinite. The interaction between naphthenic acid and clays is discussed.

  4. Studies on adsorption, reaction mechanisms and kinetics for photocatalytic degradation of CHD, a pharmaceutical waste.

    PubMed

    Sarkar, Santanu; Bhattacharjee, Chiranjib; Curcio, Stefano

    2015-11-01

    The photocatalytic degradation of chlorhexidine digluconate (CHD), a disinfectant and topical antiseptic and adsorption of CHD catalyst surface in dark condition has been studied. Moreover, the value of kinetic parameters has been measured and the effect of adsorption on photocatalysis has been investigated here. Substantial removal was observed during the photocatalysis process, whereas 40% removal was possible through the adsorption route on TiO2 surface. The parametric variation has shown that alkaline pH, ambient temperature, low initial substrate concentration, high TiO2 loading were favourable, though at a certain concentration of TiO2 loading, photocatalytic degradation efficiency was found to be maximum. The adsorption study has shown good confirmation with Langmuir isotherm and during the reaction at initial stage, it followed pseudo-first-order reaction, after that Langmuir Hinshelwood model was found to be appropriate in describing the system. The present study also confirmed that there is a significant effect of adsorption on photocatalytic degradation. The possible mechanism for adsorption and photocatalysis has been shown here and process controlling step has been identified. The influences of pH and temperature have been explained with the help of surface charge distribution of reacting particles and thermodynamic point of view respectively. PMID:25956186

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

    PubMed

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

    2015-10-14

    Sum-frequency vibrational spectroscopy was employed to probe polymer contaminants on chemical vapor deposition (CVD) graphene and to study alkane and polyethylene (PE) adsorption on graphite. In comparing the spectra from the two surfaces, it was found that the contaminants on CVD graphene must be long-chain alkane or PE-like molecules. PE adsorption from solution on the honeycomb surface results in a self-assembled ordered monolayer with the C-C skeleton plane perpendicular to the surface and an adsorption free energy of ∼42 kJ/mol for PE(H(CH2CH2)nH) with n ≈ 60. Such large adsorption energy is responsible for the easy contamination of CVD graphene by impurity in the polymer during standard transfer processes. Contamination can be minimized with the use of purified polymers free of PE-like impurities. PMID:26367247

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

    SciTech Connect

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

    1999-02-15

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

  7. 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.

  8. Adsorption of fluoride to UiO-66-NH2 in water: Stability, kinetic, isotherm and thermodynamic studies.

    PubMed

    Lin, Kun-Yi Andrew; Liu, Yu-Ting; Chen, Shen-Yi

    2016-01-01

    To provide safe drinking water, fluoride in water must be removed and adsorption processes appear to be the most widely used method. Metal organic frameworks (MOFs) represent a new class of adsorbents that have been used in various adsorption applications. To study the adsorption mechanism of fluoride to MOFs in water and obtain related adsorption parameters, we synthesized a zirconium-based MOF with a primary amine group on its ligand, named UiO-66-NH2. The kinetics, adsorption isotherm and thermodynamics of fluoride adsorption to UiO-66-NH2 were investigated. The crystalline structure of UiO-66-NH2 remained intact and the local structure of zirconium in UiO-66-NH2 did not change significantly after being exposed to fluoride. The kinetics of the fluoride adsorption in UiO-66-NH2 could be well represented by the pseudo second order rate law. The enthalpy of the adsorption indicates that the F(-) adsorption to UiO-66-NH2 was classified as a physical adsorption. However, the comparison between the adsorption capacities of UiO-66-NH2 and UiO-66 suggests that the fluoride adsorption to UiO-66-NH2 might primarily involve a strong interaction between F(-) and the metal site. The fluoride adsorption capacity of UiO-66-NH2 was found to decrease when pH>7. While the presence of chloride/bromide ions did not noticeably change the adsorption capacity of UiO-66-NH2, the ionic surfactants slightly affected the adsorption capacity of UiO-66-NH2. These findings provide insights to further optimize the adsorption process for removal of fluoride using zirconium-based MOFs. PMID:26397913

  9. 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

    of the Ni-Re/CeO2 catalyst was reduced by only 20% in the presence of sulfur compared to a 50% reduction with the Ni/CeO 2 catalyst. These results show that Re not only promotes the water-gas shift reaction but also enhances the sulfur tolerance of the Ni/CeO2 catalyst. Novel amine based solid sorbents have been developed to capture CO 2 reversibly using temperature-swing adsorption process. The IR study shows that CO2 adsorbs on amine grafted SBA-15 to form carbonates and bicarbonates. Comparison of monoamine and diamine-grafted SBA-15 showed that diamine grafted SBA-15 provides almost twice the active sites for CO 2 adsorption. The adsorption of SO2 on the amine-grafted SBA-15 revealed that SO2 adsorbs irreversibly and the sorbent cannot be regenerated under normal operating conditions. Results of these studies can be used to enhance the overall conversion of CH4 to H2 thus lowering the cost of H2 product.

  10. Facile preparation of hierarchical hollow structure gamma alumina and a study of its adsorption capacity

    NASA Astrophysics Data System (ADS)

    Lan, Shi; Guo, Na; Liu, Lu; Wu, Xiaomin; Li, Linlin; Gan, Shucai

    2013-10-01

    The hierarchical shell and hollow core structure gamma alumina (γ-Al2O3) with high adsorption affinity toward organic pollutants was fabricated via a facile homogeneous precipitation method. The microstructure, morphology, and functional groups of the as-synthesized γ-Al2O3 were characterized in detail. The N2 adsorption-desorption measurement (BET) experimental result showed the surface area of γ-Al2O3 (Al90-600) is 320.6 m2/g and the average pore size is 17.8 nm. The effects of reaction parameters on the synthesis of hierarchical hollow structure were systematically investigated. The dye removal ability of this adsorbent was determined by batch adsorption procedure. The isotherms and kinetics of adsorption process were determined and analyzed in detail, which were found to obey the Langmuir isotherm model and the pseudo-second-order for both the Congo red (CR) and Methyl orange (MO). The maximum adsorption capacity of γ-Al2O3 for CR is 835.0 mg/g, which is higher than that of many other previously reported hierarchical structured adsorbents. This facile synthetic approach is a very promising way for the design and synthesis of the typical hierarchical hollow structure materials with powerful adsorption capacity for the removal of organic contaminants from wastewater.

  11. Dibenzothiophene adsorption at boron doped carbon nanoribbons studied within density functional theory

    SciTech Connect

    López-Albarrán, P.; Navarro-Santos, P.; Garcia-Ramirez, M. A.; Ricardo-Chávez, J. L.

    2015-06-21

    The adsorption of dibenzothiophene (DBT) on bare and boron-doped armchair carbon nanoribbons (ACNRs) is being investigated in the framework of the density functional theory by implementing periodic boundary conditions that include corrections from dispersion interactions. The reactivity of the ACNRs is characterized by using the Fukui functions as well as the electrostatic potential as local descriptors. Non-covalent adsorption mechanism is found when using the local Perdew-Becke-Ernzerhof functional, regardless of the DBT orientation and adsorption location. The dispersion interactions addition is a milestone to describe the adsorption process. The charge defects introduced in small number (i.e., by doping with B atoms), within the ACNRs increases the selectivity towards sulfur mainly due to the charge depletion at B sites. The DBT magnitude in the adsorption energy shows non-covalent interactions. As a consequence, the configurations where the DBT is adsorbed on a BC{sub 3} island increase the adsorption energy compared to random B arrangements. The stability of these configurations can be explained satisfactorily in terms of dipole interactions. Nevertheless, from the charge-density difference analysis and the weak Bader charge-distribution interactions cannot be ruled out completely. This is why the electronic properties of the ribbons are analyzed in order to elucidate the key role played by the B and DBT states in the adsorbed configurations.

  12. 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. PMID:22648351

  13. Mentally Ill Still Gain Illegal Possession of Guns, Study Shows

    MedlinePlus

    ... 1 in 3 suicides shouldn't have included firearms To use the sharing features on this page, ... who were already legally prohibited from having a firearm, a new study from Florida reveals. "That's a ...

  14. 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. PMID:25022481

  15. Adsorption of guanidinium collectors on aluminosilicate minerals - a density functional study.

    PubMed

    Nulakani, Naga Venkateswara Rao; Baskar, Prathab; Patra, Abhay Shankar; Subramanian, Venkatesan

    2015-10-01

    In this density functional theory based investigation, we have modelled and studied the adsorption behaviour of guanidinium cations and substituted (phenyl, methoxy phenyl, nitro phenyl and di-nitro phenyl) guanidinium cationic collectors on the basal surfaces of kaolinite and goethite. The adsorption behaviour is assessed in three different media, such as gas, explicit water and pH medium, to understand the affinity of GC collectors to the SiO4 tetrahedral and AlO6 octahedral surfaces of kaolinite. The tetrahedral siloxane surface possesses a larger binding affinity to GC collectors than the octahedral sites due to the presence of surface exposed oxygen atoms that are active in the intermolecular interactions. Furthermore, the inductive electronic effects of substituted guanidinium cations also play a key role in the adsorption mechanism. Highly positive cations result in a stronger electrostatic interaction and preferential adsorption with the kaolinite surfaces than low positive cations. Computed interaction energies and electron densities at the bond critical points suggest that the adsorption of guanidinium cations on the surfaces of kaolinite and goethite is due to the formation of intra/inter hydrogen bonding networks. Also, the electrostatic interaction favours the high adsorption ability of GC collectors in the pH medium than gas phase and water medium. The structures and energies of GC collectors pave an intuitive view for future experimental studies on mineral flotation. PMID:26303845

  16. On the adsorption/photodegradation of amoxicillin in aqueous solutions by an integrated photocatalytic adsorbent (IPCA): experimental studies and kinetics analysis.

    PubMed

    Basha, Shaik; Barr, Colin; Keane, David; Nolan, Kieran; Morrissey, Anne; Oelgemöller, Michael; Tobin, John M

    2011-06-01

    Activated carbon-supported TiO(2) nanoparticles, termed integrated photocatalytic adsorbents (IPCAs), were prepared using an ultrasonic impregnation technique and investigated for the photocatalytic degradation of amoxicillin (AMO), a β-lactam antibiotic. The IPCAs had high adsorption affinity for AMO with the amount adsorbed proportional to the TiO(2) loading and the highest adsorption was at 10 wt% TiO(2) loading. A pseudo-second-order model was found to fit the experimental data and consistently predicted the amount of AMO adsorbed over the adsorption period. Equilibrium isotherm studies showed that the adsorption followed the Redlich-Peterson model with maximum adsorption capacity of 441.3 mg g(-1) for 10% IPCA, 23% higher than the pure activated carbon (AC). Kinetic studies on the photocatalytic degradation of AMO using non-linear regression analysis suggest that the degradation followed Langmuir-Hinshelwood (L-H) kinetics. The adsorption rate constant (K(ad)) was considerably higher than the photocatalytic rate constant (k(L-H)), indicating that the photocatalysis of AMO is the rate-determining step during the adsorption/photocatalysis process. The 10% IPCA exhibited excellent stability and reusability over four photodegradation cycles. PMID:21380442

  17. Debate over Social Studies Shows Little Sign of Abating

    ERIC Educational Resources Information Center

    Robelen, Erik W.

    2010-01-01

    The Texas board of education which consists of 15-member elected body drew national attention as a bloc of staunch conservatives largely succeeded in putting its stamp on a revised set of social studies standards. The debate was marked by tussles over such matters as the separation of church and state, the representation of minority figures and…

  18. Ghana Fiasco Shows Risks of Faculty-Led Study Trips

    ERIC Educational Resources Information Center

    Fischer, Karin

    2007-01-01

    This article illustrates the importance of preparation for professors who take students overseas. A University of Washington study-abroad program in Ghana that was cut short last summer after the medical evacuation of half of its participants highlights the potential hazards associated with programs led by individual faculty members who may lack…

  19. From porphyrins to pyrphyrins: adsorption study and metalation of a molecular catalyst on Au(111).

    PubMed

    Mette, Gerson; Sutter, Denys; Gurdal, Yeliz; Schnidrig, Stephan; Probst, Benjamin; Iannuzzi, Marcella; Hutter, Jürg; Alberto, Roger; Osterwalder, Jürg

    2016-04-14

    The molecular ligand pyrphyrin, a tetradentate bipyridine based macrocycle, represents an interesting but widely unexplored class of molecules. It resembles the well-known porphyrin, but consists of pyridyl subunits instead of pyrroles. Metal complexes based on pyrphyrin ligands have recently shown promise as water reduction catalysts in homogeneous photochemical water splitting reactions. In this study, the adsorption and metalation of pyrphyrin on a single crystalline Au(111) surface is investigated in an ultrahigh vacuum by means of scanning tunneling microscopy, low-energy electron diffraction, X-ray photoelectron spectroscopy and density functional theory. Pyrphyrin coverages of approximately one monolayer and less are obtained by sublimation of the molecules on the substrate kept at room temperature. The molecules self-assemble in two distinct phases of long-range molecular ordering depending on the surface coverage. The deposition of cobalt metal and subsequent annealing lead to the formation of Co-ligated pyrphyrin molecules accompanied by a pronounced change of the molecular self-assembly. Electronic structure calculations taking the herringbone reconstruction of Au(111) into account show that the molecules are physisorbed, but preferred adsorption sites are identified where Co and the N atoms of the two terminal cyano groups are optimally coordinated to the surface Au atoms. An intermediate state of the metalation reaction is observed and the reaction steps for the Co metalation of pyrphyrin molecules on Au(111) are established in a joint experimental and computational effort. PMID:27006307

  20. Adsorption studies of divalent, dinuclear coordination complexes as molecular spacers on SWCNTs.

    PubMed

    Alston, Jeffrey R; Banks, David J; McNeill, Chauncey X; Mitchell, James B; Popov, Leonid D; Shcherbakov, Igor N; Poler, J C

    2015-11-28

    In order to enhance the electrical energy storage capabilities of nanostructured carbon materials, inter-particle spacer strategies are needed to maintain ion-accessible surface area between the nanoparticles. This paper presents a comparison between different classes of divalent, dinuclear coordination complexes which both show strong adsorption to SWCNTs and have molecular spacer properties that maintain electrochemical activity. We find that a novel, dinuclear zinc hydrazone complex binds as an ion-pair at very high loading while not inducing significant aggregation as compared to our previously studies of dinuclear ruthenium complexes. These conclusions are supported by conductivity and dispersion stability data. Moreover, since zinc is an earth abundant metal, these complexes can be used as components in sustainable energy storage materials. Binding kinetics and binding equilibrium data are presented. Modeling of the adsorption isotherm is best fit with the BET model. Kinetics data support an independent binding model. Preliminary capacitance and membrane resistance data are consistent with the complexes acting as molecular spacers between the SWCNTs in a condensed thin film. PMID:26457656

  1. First-principles study for the adsorption of segments of BPA-PC on α-Al2O3(0001)

    NASA Astrophysics Data System (ADS)

    Blomqvist, Janne; Salo, Petri

    2011-10-01

    We have studied the adsorption of bisphenol-A-polycarbonate (BPA-PC) on the α-Al2O3(0001) surface using density functional theory (DFT) with van der Waals (vdW) corrections. The BPA-PC polymer can be divided into its chemical fragments, which are phenylene, carbonate, and isopropylidene groups. We have calculated the adsorption energy and geometry of the BPA-PC segments that consist of two to three adjacent groups of the polymer. Our DFT results show that the adsorption is dominated by the vdW interaction. It is also important to include the interaction of nearest-neighbor groups in order to provide a realistic environment for the adsorption of the polymer onto the surface. Our results also show that the BPA-PC molecule attaches to the alumina surface via the carbonate group located in the middle of the molecule chain.

  2. 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.

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

    PubMed

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

    2014-05-01

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

  4. Density functional study of CO adsorption on Sc(n) (n=2-13) clusters.

    PubMed

    Wu, Guangfen; Wang, Jinlan; Lu, Yiming; Yang, Mingli

    2008-06-14

    The adsorption properties of a single CO molecule on Sc(n) (n=2-13) clusters are studied by means of a density functional theory with the generalized gradient approximation. Two adsorption patterns are identified. Pattern a (n=3, 4, 6, 8, 11, and 12), CO binds to hollow site while Pattern b (n=5, 7, 9, 10, and 13), CO binds to bridge site accompanied by significantly lengthening of the Sc-Sc bond. The adsorption energy exhibits clear size-dependent variation and odd-even oscillation for n<10 and reach the peak at n=5, 7, and 9, implying their high chemical reactivity. Similar variations are noted in C-O bond length, vibrational frequency, and charge transferred between CO and the clusters. This can be understood in light of the adsorption pattern, the atomic motif, and the relative stability of the bare Sc clusters. Compared with the free Sc clusters, the magnetic nature remains upon adsorption except n=2, 4, 12, and 13. Particularly, the moments of n=13 reduce significantly from 19 to 5 micro(B), implying the adsorption plays an attenuation influence on the magnetism of the cluster. PMID:18554021

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  7. What gastric cancer proteomic studies show about gastric carcinogenesis?

    PubMed

    Leal, Mariana Ferreira; Wisnieski, Fernanda; de Oliveira Gigek, Carolina; do Santos, Leonardo Caires; Calcagno, Danielle Queiroz; Burbano, Rommel Rodriguez; Smith, Marilia Cardoso

    2016-08-01

    Gastric cancer is a complex, heterogeneous, and multistep disease. Over the past decades, several studies have aimed to determine the molecular factors that lead to gastric cancer development and progression. After completing the human genome sequencing, proteomic technologies have presented rapid progress. Differently from the relative static state of genome, the cell proteome is dynamic and changes in pathologic conditions. Proteomic approaches have been used to determine proteome profiles and identify differentially expressed proteins between groups of samples, such as neoplastic and nonneoplastic samples or between samples of different cancer subtypes or stages. Therefore, proteomic technologies are a useful tool toward improving the knowledge of gastric cancer molecular pathogenesis and the understanding of tumor heterogeneity. This review aimed to summarize the proteins or protein families that are frequently identified by using high-throughput screening methods and which thus may have a key role in gastric carcinogenesis. The increased knowledge of gastric carcinogenesis will clearly help in the development of new anticancer treatments. Although the studies are still in their infancy, the reviewed proteins may be useful for gastric cancer diagnosis, prognosis, and patient management. PMID:27126070

  8. 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).

  9. 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. PMID:17092643

  10. First-principles study of sulfur atom doping and adsorption on α-Fe2O3 (0001) film

    NASA Astrophysics Data System (ADS)

    An, Jiao; Wanaguru, Prabath; Xia, Congxin; Tao, Meng; Zhang, Qiming

    2016-09-01

    Using the spin-polarized density functional theory (DFT) and the DFT + U method, the geometric and electronic properties of the hematite α-Fe2O3 (0001) film with the sulfur (S) atom doping and adsorption have been investigated systematically. The most stable hematite α-Fe2O3 (0001) film with an anti-ferromagnetic arrangement is identified. For the study of sulfur adsorption on the film, the S adatom prefers to bond with three O atoms, in the center of a triangle formed by the three O atoms. The S acts as a cation at this site. The sulfur adsorption has introduced two gap states, in addition to the unoccupied surface states. Furthermore, with the most stable S-adsorption configuration, the diffusion of the S adatom from the surface to the inside is searched and the transition state along the minimum-energy pathway is also evaluated. For S-doping in the film, it is found that S substitution of O in the top layer is energetically favored than that in the deeper layer. It shows that the value of the band gap is reduced to ∼1.26 eV from ∼1.43 eV of the clean film. The formation energy of S substitution of O in the film is also obtained.

  11. 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

  12. 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.

  13. Insights on finite size effects in ab initio study of CO adsorption and dissociation on Fe 110 surface

    NASA Astrophysics Data System (ADS)

    Chakrabarty, Aurab; Bouhali, Othmane; Mousseau, Normand; Becquart, Charlotte S.; El-Mellouhi, Fedwa

    2016-08-01

    Adsorption and dissociation of hydrocarbons on metallic surfaces represent crucial steps on the path to carburization, eventually leading to dusting corrosion. While adsorption of CO molecules on Fe surface is a barrier-less exothermic process, this is not the case for the dissociation of CO into C and O adatoms and the diffusion of C beneath the surface that are found to be associated with large energy barriers. In practice, these barriers can be affected by numerous factors that combine to favour the CO-Fe reaction such as the abundance of CO and other hydrocarbons as well as the presence of structural defects. From a numerical point of view, studying these factors is challenging and a step-by-step approach is necessary to assess, in particular, the influence of the finite box size on the reaction parameters for adsorption and dissociation of CO on metal surfaces. Here, we use density functional theory (DFT) total energy calculations with the climbing-image nudged elastic band method to estimate the adsorption energies and dissociation barriers for different CO coverages with surface supercells of different sizes. We further compute the effect of periodic boundary condition for DFT calculations and find that the contribution from van der Waals interaction in the computation of adsorption parameters is important as they contribute to correcting the finite-size error in small systems. The dissociation process involves carbon insertion into the Fe surface causing a lattice deformation that requires a larger surface system for unrestricted relaxation. We show that, in the larger surface systems associated with dilute CO-coverages, C-insertion is energetically more favourable, leading to a significant decrease in the dissociation barrier. This observation suggests that a large surface system with dilute coverage is necessary for all similar metal-hydrocarbon reactions in order to study their fundamental electronic mechanisms, as an isolated phenomenon, free from

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  15. Adsorption of azo dyes using peanut hull and orange peel: a comparative study.

    PubMed

    do Nascimento, Graziele Elisandra; Duarte, Marta Maria Menezes Bezerra; Campos, Natália Ferreira; da Rocha, Otidene Rossiter Sá; da Silva, Valdinete Lins

    2014-01-01

    This work proposes the use of agro-industrial wastes, specifically peanut hull (HP) and orange peel (OP), as adsorbents for dyes, such as Remazol Golden Yellow RNL-150% (RYG), Gray Reactive BF-2R (RG) and Reactive Turquoise Q-G125 (RT). Characterization by Brunauer-Emmett-Teller indicates that the adsorbents are mesoporous, with pHzpc values of 5.0 for HP and 4.0 for OP. Fourier transform-infrared spectroscopy identified carbonyl and sulphonic groups. The initial pH of the best-adsorbing solution of the three colours was 2.0. Increasing the concentration of the adsorbent promoted an increase in the percentage of removal until saturation of the adsorbent. In a factorial design, the largest value of q was obtained with 0.25 g of the adsorbent, with a particle size of < 0.4 mm and a stirring speed of 300 rpm. Such conditions were used in kinetic studies and studies of adsorption equilibrium. The evolution kinetics were rapid in the first few minutes, and after 180 min the system reached equilibrium. The kinetic model that best fit the experimental data to a 95% confidence level for the F test was the pseudo-second-order model for RYG/HP, RG/OP and RT/OP. There was no significant difference between the kinetic models as evaluated by the F test for RYG/OP, RG/HP and RT/HP. The experimental results indicated favourable dye adsorption characteristics for the adsorbents studied. The results of the F test showed that for RYG and RG, there was no significant difference between the two evaluated models. This study suggests that HP and OP are viable alternatives for the treatment of effluents containing RYG, RG and RT dyes. PMID:24701942

  16. Fibronectin Terminated Multilayer Films: Protein Adsorption and Cell Attachment Studies

    PubMed Central

    Wittmer, Corinne R.; Phelps, Jennifer A.; Saltzman, W. Mark; Van Tassel, Paul R.

    2006-01-01

    Electrostatically driven layer-by-layer (LbL) assembly is a simple and robust method for producing structurally tailored thin film biomaterials, of thickness ca. 10 nanometers, containing biofunctional ligands. We investigate the LbL formation of multilayer films composed of polymers of biological origin (poly(L-lysine) (PLL) and dextran sulfate (DS)), the adsorption of fibronectin (Fn) - a matrix protein known to promote cell adhesion - onto these films, and the subsequent spreading behavior of human umbilical vein endothelial cells (HUVEC). We employ optical waveguide lightmode spectroscopy (OWLS) and quartz crystal microgravimetry with dissipation (QCMD) to characterize multilayer assembly in situ, and find adsorbed Fn mass on PLL terminated films to exceed that on DS terminated films by 40%, correlating with the positive charge and lower degree of hydration of PLL terminated films. The extent and initial rate of Fn adsorption to both PLL and DS terminated films exceed those onto the bare substrate, indicating the important role of electrostatic complexation between negatively charged protein and positively charged PLL at or near the film surface. We use phase contrast optical microscopy to investigate the time dependent morphological changes of HUVEC as a function of layer number, charge of terminal layer, and the presence of Fn. We observe HUVEC to attach, spread, and lose circularity on all surfaces. (Positively charged) PLL terminated films exhibit a greater extent of cell spreading than do (negatively charged) DS terminated films, and spreading is enhanced while circularity loss is suppressed by the presence of adsorbed Fn. The number of layers plays a significant role only for DS terminated films with Fn, where spreading on a bilayer greatly exceeds that on a multilayer, and PLL terminated films without Fn, where initial spreading is significantly higher on a monolayer. We observe initial cell spreading to be followed by retraction (i.e. decreased cell

  17. Hydrogen adsorption on palladium: a comparative theoretical study of different surfaces

    NASA Astrophysics Data System (ADS)

    Dong, W.; Ledentu, V.; Sautet, Ph.; Eichler, A.; Hafner, J.

    1998-08-01

    The interaction of atomic hydrogen with the Pd(111), Pd(100) and Pd(110) surfaces is studied by ab-initio density functional calculations within the generalized gradient approximation (GGA). For the three surfaces, we have determined the preferred adsorption sites, the adsorption structures, the work function changes and the surface diffusion barrier, including relaxation effects. This comparative study allows some common features to be seen, in particular in the adsorption energies and geometries for both surface and subsurface H-atoms, and some significant differences such as the surface diffusion and the dispersion of the H-induced surface state. The origin of these differences is explained by a detailed analysis of the electronic structures of both clean and hydrogen-covered surfaces. Our study leads to an interesting correlation between the hydrogen diffusion barrier and the surface roughness since it plays an important part in the catalytic activity of the respective surfaces.

  18. Fabrication of interpenetrating polymer network chitosan/gelatin porous materials and study on dye adsorption properties.

    PubMed

    Cui, Li; Xiong, Zihao; Guo, Yi; Liu, Yun; Zhao, Jinchao; Zhang, Chuanjie; Zhu, Ping

    2015-11-01

    One kind of adsorbent based on chitosan and gelatin with interpenetrating polymer networks (IPN) and porous dual structures was prepared using genipin as the cross-linker. These dual structures were demonstrated by means of Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Adsorptions of acid orange II dye from aqueous solution were carried out at different genipin contents, adsorption times and pH values. The results showed that this material was put up the largest adsorption capacity when the genipin content is 0.25 mmol/L, meanwhile, the lower the solution pH value the greater the adsorption capacity. The chitosan/gelatin interpenetrating polymer networks porous material displayed pH-sensitive and rapidly response in adsorption and desorption to pH altered. It is indicated that the cross-linked chitosan/gelatin interpenetrating polymer networks porous material could be used as a recyclable adsorbent in removal or separation of anionic dyes as environmental pH condition changed. PMID:26256356

  19. Adsorption of CO2 on amine-functionalised MCM-41: experimental and theoretical studies.

    PubMed

    dos Santos, Thiago Custódio; Bourrelly, Sandrine; Llewellyn, Philip L; Carneiro, José Walkimar de M; Ronconi, Célia Machado

    2015-04-28

    Adsorption of CO2 on MCM-41 functionalised with [3-(2-aminoethylamino)propyl]trimethoxysilane (MCM-41-N2), N(1)-(3-trimethoxysilylpropyl)diethylenetriamine (MCM-41-N3), 4-aminopyridine (MCM-41-aminopyridine), 4-(methylamino)pyridine (MCM-41-methylaminopyridine) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (MCM-41-guanidine) was investigated. The amine-functionalised materials were characterised by (29)Si and (13)C solid-state nuclear magnetic resonance, N2 adsorption/desorption isotherms, X-ray diffraction and transmission electron microscopy. CO2 adsorption at 1.0 bar and 30 °C showed that the amount of CO2 (nads/mmol g(-1)) adsorbed on MCM-41-N2 and MCM-41-N3 is approximately twice the amount adsorbed on MCM-41. For MCM-41-aminopyridine, MCM-41-methylaminopyridine and MCM-41-guanidine, the CO2 adsorption capacity was smaller than that of MCM-41 at the same conditions. The proton affinity (computed with wB97x-D/6-311++G(d,p)) of the secondary amino groups is higher than that of the primary amino groups; however, the relative stabilities of the primary and secondary carbamates are similar. The differential heat of adsorption decreases as the number of secondary amino groups increases. PMID:25826235

  20. 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...

  1. Adsorption of branched and dendritic polymers onto flat surfaces: A Monte Carlo study

    SciTech Connect

    Sommer, J.-U.; Kłos, J. S.; Mironova, O. N.

    2013-12-28

    Using Monte Carlo simulations based on the bond fluctuation model we study the adsorption of starburst dendrimers with flexible spacers onto a flat surface. The calculations are performed for various generation number G and spacer length S in a wide range of the reduced temperature τ as the measure of the interaction strength between the monomers and the surface. Our simulations indicate a two-step adsorption scenario. Below the critical point of adsorption, τ{sub c}, a weakly adsorbed state of the dendrimer is found. Here, the dendrimer retains its shape but sticks to the surface by adsorbed spacers. By lowering the temperature below a spacer-length dependent value, τ*(S) < τ{sub c}, a step-like transition into a strongly adsorbed state takes place. In the flatly adsorbed state the shape of the dendrimer is well described by a mean field model of a dendrimer in two dimensions. We also performed simulations of star-polymers which display a simple crossover-behavior in full analogy to linear chains. By analyzing the order parameter of the adsorption transition, we determine the critical point of adsorption of the dendrimers which is located close to the critical point of adsorption for star-polymers. While the order parameter for the adsorbed spacers displays a critical crossover scaling, the overall order parameter, which combines both critical and discontinuous transition effects, does not display simple scaling. The step-like transition from the weak into the strong adsorbed regime is confirmed by analyzing the shape-anisotropy of the dendrimers. We present a mean-field model based on the concept of spacer adsorption which predicts a discontinuous transition of dendrimers due to an excluded volume barrier. The latter results from an increased density of the dendrimer in the flatly adsorbed state which has to be overcome before this state is thermodynamically stable.

  2. Adsorption kinetics of phosphate and arsenate on goethite. A comparative study.

    PubMed

    Luengo, Carina; Brigante, Maximiliano; Avena, Marcelo

    2007-07-15

    The adsorption kinetics of phosphate and arsenate on goethite is studied and compared. Batch adsorption experiments were performed at different adsorbate concentrations, pH, temperatures and stirring rates. For both oxoanions the adsorption rate increases by increasing adsorbate concentration, decreasing pH and increasing temperature. It does not change by changing stirring rate. The adsorption takes place in two processes: a fast one that takes place in less than 5 min and a slow one that takes place in several hours or more. The rate of the slow process does not depend directly on the concentration of phosphate or arsenate in solution, but depends linearly on the amount of phosphate or arsenate that was adsorbed during the fast process. Apparent activation energies and absence of stirring rate effects suggest that the slow process is controlled by diffusion into pores, although the evidence is not conclusive. The similarities in the adsorption kinetics of phosphate and arsenate are quantitatively shown by using a three-parameters equation that takes into account both the fast and the slow processes. These similarities are in line with the similar reactivity that phosphate and arsenate have in general and may be important for theoretical and experimental studies of the fate of these oxoanions in the environment. PMID:17448491

  3. Evaluation of Fuller's earth for the adsorption of mercury from aqueous solutions: a comparative study with activated carbon.

    PubMed

    Oubagaranadin, John U Kennedy; Sathyamurthy, N; Murthy, Z V P

    2007-04-01

    Fuller's earth (FE) has been used as an adsorbent in this work to remove mercury from aqueous solutions. For the purpose of comparison, simultaneous experiments using activated carbon (AC) have also been done. The aim of the work is to test how best FE can be used as an adsorbent for mercury. Equilibrium isotherms, such as Freundlich, Langmuir, Dubinin-Redushkevich, Temkin, Harkins-Jura, Halsey and Henderson have been tested. Kinetic studies based on Lagergren first-order, pseudo-second-order rate expressions and intra-particle diffusion studies have been done. The batch experiments were conducted at room temperature (30 degrees C) and at the normal pH (6.7+/-0.2) of the solution. It has been observed that Hg(II) removal rate is better for FE than AC, due to large dosage requirement, whereas the adsorption capacity of AC is found to be much better than FE. Hence, although FE can be used as an adsorbent, a high dosage is required, when compared to AC. Hybrid fractional error function analysis shows that the best-fit for the adsorption equilibrium data is represented by Freundlich isotherm. Kinetic and film diffusion studies show that the adsorption of mercury on FE and AC is both intra-particle diffusion and film diffusion controlled. PMID:16987602

  4. 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.

  5. 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.

  6. 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

  7. Study the adsorption of sulfates by high cross-linked polystyrene divinylbenzene anion-exchange resin

    NASA Astrophysics Data System (ADS)

    Fathy, Mahmoud; Moghny, Th. Abdel; Awadallah, Ahmed E.; El-Bellihi, Abdel-Hameed A.-A.

    2014-11-01

    In response to rising concerns about the effect of sulfate on water quality, human health, and agriculture, many jurisdictions around the world are imposing tighter regulations for sulfate discharge. This is driving the need for environmental compliance in industries like mining, metal processing, pulp and paper, sewage treatment, and chemical manufacturing. The sulfate removal from synthetic water by high cross-linked polystyrene divinylbenzene resin was studied at batch experiments in this study. The effect of pH, contact time, sulfates concentration, and adsorbent dose on the sulfate sequestration was investigated. The optimum conditions were studied on Saline water as a case study. The results showed that with increasing of the absorbent amount; contact time, and pH improve the efficiency of sulfate removal. The maximum sulfates uptake was obtained in pH and contact time 3.0 and 120 min, respectively. Also, with increasing initial concentration of sulfates in water, the efficiency of sulfate removal decreased. The obtained results in this study were matched with Freundlich isotherm and pseudo-second-order kinetic. The maximum adsorption capacity (Qm) and constant rate were found 0.318 (mg/g) and 0.21 (mg/g.min), respectively. This study also showed that in the optimum conditions, the sulfate removal efficiency from Saline water by 0.1 mg/L sulfates was 65.64 %. Eventually, high cross-linked polystyrene divinylbenzene resin is recommended as a suitable and low cost absorbent to sulfate removal from aqueous solutions.

  8. 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.

  9. Adsorption mechanisms for fatty acids on DLC and steel studied by AFM and tribological experiments

    NASA Astrophysics Data System (ADS)

    Simič, R.; Kalin, M.

    2013-10-01

    Fatty acids are known to affect the friction and wear of steel contacts via adsorption onto the surface, which is one of the fundamental boundary-lubrication mechanisms. The understanding of the lubrication mechanisms of polar molecules on diamond-like carbon (DLC) is, however, still insufficient. In this work we aimed to find out whether such molecules have a similar effect on DLC coatings as they do on steel. The adsorption of hexadecanoic acid in various concentrations (2-20 mmol/l) on DLC was studied under static conditions using an atomic force microscope (AFM). The amount of surface coverage of the adsorbed fatty-acid molecules was analysed. In addition, tribological tests were performed to correlate the wear and friction behaviours in tribological contacts with the adsorption of molecules on the surface under static conditions. A good correlation between the AFM results and the tribological behaviour was observed. We confirmed that fatty acids can adsorb onto the DLC surfaces and are, therefore, potential boundary-lubrication agents for DLC coatings. The adsorption of the fatty acid onto the DLC surfaces reduces the wear of the coatings, but it is less effective in reducing the friction. Tentative adsorption mechanisms that include an environmental species effect, a temperature effect and a tribochemical effect are proposed for DLC and steel surfaces based on our results and few potential mechanisms found in literature.

  10. 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. PMID:26292774

  11. 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

    2015-07-01

    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). PMID:26055623

  12. Adsorption of phthalic acid esters (PAEs) by amphiphilic polypropylene nonwoven from aqueous solution: the study of hydrophilic and hydrophobic microdomain.

    PubMed

    Zhou, Xiangyu; Wei, Junfu; Zhang, Huan; Liu, Kai; Wang, Han

    2014-05-30

    A kind of amphiphilic polypropylene nonwoven with hydrophilic and hydrophobic microdomain was prepared through electron beam induced graft polymerization and subsequent ring opening reaction and then utilized in the adsorption of phthalic acid esters (PAEs). To elucidate the superiority of such amphiphilic microdomain, a unique structure without hydrophilic part was constructed as comparison. In addition, the adsorption behaviors including adsorption kinetics, isotherms and pH effect were systematically investigated. The result indicated that the amphiphilic structure and the synergy between hydrophilic and hydrophobic microdomain could considerably improve the adsorption capacities, rate and affinity. Particularly the existence of hydrophilic microdomain could reduce the diffusion resistance and energy barrier in the adsorption process. These adsorption results showed that the amphiphilic PP nonwoven have the potential to be used in environmental application. PMID:24721695

  13. Theoretical studies of the adsorption of hydroxymethylidyne (COH) on Pt-alloy surfaces using density functional theory

    NASA Astrophysics Data System (ADS)

    Cahyanto, Wahyu Tri; Widanarto, Wahyu; Shukri, Ganes; Kasai, Hideaki

    2016-02-01

    We present density functional calculations for the adsorption of hydroxymethylidyne (COH) on Pt, PtRu, and PtRuMo (111) surfaces. Here we clarify the adsorption mechanism by using a charge transfer analysis related to the adsorption energy. We observe that the preferred binding sites for COH are the hcp hollow Pt-Pt-Pt, hcp hollow Pt-Ru-Pt, and hcp hollow Pt-Ru-Pt adsorption sites for Pt, PtRu, and PtRuMo, respectively. Addition of Ru to form a PtRu surface increases the adsorption energy, while addition of Mo to form a PtRuMo surface decreases it. Our analyses show that the adsorption energy is determined by electron transfer between the molecular COH and the metal surfaces associated with bonding.

  14. Polyelectrolyte adsorption layers studied by streaming potential and particle deposition.

    PubMed

    Adamczyk, Z; Zembala, M; Michna, A

    2006-11-15

    Adsorption of a cationic polyelectrolyte, polyallylamine hydrochloride (PAH), having a molecular weight of 70,000 on mica was characterized by the streaming potential method and by deposition of negative polystyrene latex particles. Formation of PAH layers was followed by determining the apparent zeta potential of surface zeta as function of bulk PAH concentration. The zeta potential was calculated from the streaming potential measured in the parallel-plate channel formed by two mica plates precovered by the polyelectrolyte. The experimental data were expressed as the dependence of the reduced zeta potential zeta/zeta0 on the PAH coverage Theta(PAH), calculated using the convective diffusion theory. It was found that for the ionic strength of 10(-2) M, the dependence of zeta/zeta0 on Theta(PAH) can be reflected by the theoretical model formulated previously for surfaces covered by colloid particles. The electrokinetic measurements were complemented by particle deposition experiments on PAH-covered mica surfaces. A direct correlation between the polymer coverage and the initial deposition rate of particles, as well as the jamming coverage, was found. For ThetaPAH > 0.3 the initial deposition rate attained the value predicted from the convective diffusion theory for homogeneous surfaces. The initial deposition rates for surfaces modified by PAH were compared with previous experimental and theoretical results obtained for heterogeneous surfaces formed by preadsorption of colloid particles. It was revealed that negative latex deposition occurred at surfaces exhibiting negative apparent zeta potential, which explained the anomalous deposition of particles observed in previous works. It was suggested that the combined electrokinetic and particle deposition methods can be used for detecting adsorbed polyelectrolytes at surfaces for coverage range of a percent. This enables one to measure bulk polyelectrolyte concentrations at the level of 0.05 ppm. PMID:16949085

  15. Study of polystyrene-poly(ethylene oxide) diblock copolymer monolayers as barriers to protein adsorption

    NASA Astrophysics Data System (ADS)

    Jogikalmath, Gangadhar

    Protein adsorption resistant surfaces find use in many biomedical applications, such as catheters, dialysis devices and biosensors that involve blood contacting surfaces. To ensure long-term functioning of a device in an environment containing protein, there is a need to produce homogeneous surfaces that are resistant to protein adsorption. A polymer brush covered surface, produced by either physical adsorption or chemical grafting of hydrophilic polymers to surfaces, is one of the approaches used in creating such surfaces. High grafting densities needed to make an effective barrier are usually not realized in chemical grafting/adsorption from solution, due to self-exclusion of surface grafted molecules. In this dissertation polymer brush surfaces formed by chemically grafted PEO molecules and transferred monolayers of PS-b-PEO diblock copolymers are investigated using atomic force microscopy (AFM), surface plasmon resonance (SPR) and surface pressure measurement techniques. An AFM adhesion mapping technique was used to evaluate the surface heterogeneity of chemically modified PEO and transferred diblock copolymer monolayer surfaces. The behavior of PS-b-PEO molecules at the air-water interface was studied using Langmuir trough. The stability of transferred diblock copolymer monolayers was investigated using AFM. Using SPR, protein adsorption to the diblock copolymer layers was investigated as a function of protein size (using HSA and ferritin) as a function of grafting density of PEO in the monolayer. It was seen that a lower density of the PS-b-PEO monolayer was sufficient to prevent ferritin adsorption (larger protein) while a higher density brush layer was required to achieve complete prevention of HSA adsorption to the surface. The effect of mobility of the polymer brush layer on protein adsorption prevention was analyzed using SPR and surface pressure measurements. It was seen that the copolymer monolayer (at the air-buffer interface) rearranged itself to

  16. Adsorption of Trametes versicolor laccase to soil iron and aluminum minerals: enzyme activity, kinetics and stability studies.

    PubMed

    Wu, Yue; Jiang, Ying; Jiao, Jiaguo; Liu, Manqiang; Hu, Feng; Griffiths, Bryan S; Li, Huixin

    2014-02-01

    Laccases play an important role in the degradation of soil phenol or phenol-like substance and can be potentially used in soil remediation through immobilization. Iron and aluminum minerals can adsorb extracellular enzymes in soil environment. In the present study, we investigated the adsorptive interaction of laccase, from the white-rot fungus Trametes versicolor, with soil iron and aluminum minerals and characterized the properties of the enzyme after adsorption to minerals. Results showed that both soil iron and aluminum minerals adsorbed great amount of laccase, independent of the mineral specific surface areas. Adsorbed laccases retained 26-64% of the activity of the free enzyme. Compared to the free laccase, all adsorbed laccases showed higher Km values and lower Vmax values, indicating a reduced enzyme-substrate affinity and a lower rate of substrate conversion in reactions catalyzed by the adsorbed laccase. Adsorbed laccases exhibited increased catalytic activities compared to the free laccase at low pH, implying the suitable application of iron and aluminum mineral-adsorbed T. versicolor laccase in soil bioremediation, especially in acid soils. In terms of the thermal profiles, adsorbed laccases showed decreased thermal stability and higher temperature sensitivity relative to the free laccase. Moreover, adsorption improved the resistance of laccase to proteolysis and extended the lifespan of laccase. Our results implied that adsorbed T. versicolor laccase on soil iron and aluminum minerals had promising potential in soil remediation. PMID:24225344

  17. Adsorption of CO2 on Cu2O (1 1 1) oxygen-vacancy surface: First-principles study

    NASA Astrophysics Data System (ADS)

    Wu, Huanwen; Zhang, Ning; Wang, Hongming; Hong, Sanguo

    2013-05-01

    The adsorption of CO2 on Cu2O (1 1 1) oxygen-vacancy surface has been investigated by using the first-principles calculations based on the density functional theory (DFT). The geometry, adsorption energy, charge population and projected density of states (PDOS) were calculated. The results show dissociative adsorption of CO2 on the surface is thermodynamically unfeasible. The oxygen vacancy has the negative effects on the adsorption of CO2 at the coordinately unsaturated surface copper and oxygen (CuCUS and OCUS) sites. Oxygen vacancies are the active sites. CO2 can be directly adsorbed and converted into CO2δ- radical anion species at these sites.

  18. Van der Waals corrected DFT study of adsorption of groups VA and VIA hydrides on graphene monoxide

    NASA Astrophysics Data System (ADS)

    Notash, M. Yaghoobi; Ebrahimzadeh, A. Rastkar

    2016-06-01

    Adsorption properties of H2O, H2S, NH3 and PH3 on graphene monoxide (GMO) nano flack are investigated using density functional theory (DFT). Calculations were carried out by van der Waals correction and general gradient approximation. The adsorption energies and charge transfer between species are obtained and discussed for the considered positions of adsorbate molecules. Charge transfer analysis show that the gas molecules act as an electron acceptor in all cases. The analysis of the adsorption energies suggest GMO can be a good candidate for the adsorption of these molecules.

  19. Adsorption of halide ions from aqueous solutions at a Cd(0 0 0 1) electrode surface: quantum chemical modelling and experimental study

    NASA Astrophysics Data System (ADS)

    Nazmutdinov, Renat R.; Zinkicheva, Tamara T.; Probst, Michael; Lust, Karmen; Lust, Enn

    2005-03-01

    Adsorption of the halide ions X (X = Cl -, Br -, I -) at a cadmium monocrystalline face (0 0 0 1) from aqueous solutions has been studied by the impedance spectroscopy. Analysis of the impedance data does not predict specific adsorption for Cl - and shows that the Gibbs adsorption energy increases from Br - to I - in accordance with the decrease of the hydration energy of anions. The adsorption of halide ions and their atomic forms on a Cd(0 0 0 1) electrode at the potential of zero charge (pzc) has been studied with the use of the cluster model. The quantum chemical calculations were performed at the DFT and the SCF levels involving the hydrated species X -(H 2O) 3 and X -(H 2O) 6 besides the bare anions. The effective distance-dependent solvation energy of halide ions constructed on the basis of molecular dynamics simulations was used to build the adsorption terms. For all three halides contact adsorption was found to be the most favourable state. The partial charge transfer (PCT) from the adsorbed species to the metal was analysed in terms of the Anderson-Newns model. A combined consideration of the solvation and PCT effects enables prediction of the experimentally observed metal-ion interaction order (Cl - < Br - < I -).

  20. Comparative studies on adsorptive removal of heavy metal ions by biosorbent, bio-char and activated carbon obtained from low cost agro-residue.

    PubMed

    Kırbıyık, Çisem; Pütün, Ayşe Eren; Pütün, Ersan

    2016-01-01

    In this study, Fe(III) and Cr(III) metal ion adsorption processes were carried out with three adsorbents in batch experiments and their adsorption performance was compared. These adsorbents were sesame stalk without pretreatment, bio-char derived from thermal decomposition of biomass, and activated carbon which was obtained from chemical activation of biomass. Scanning electron microscopy and Fourier transform-infrared techniques were used for characterization of adsorbents. The optimum conditions for the adsorption process were obtained by observing the influences of solution pH, adsorbent dosage, initial solution concentration, contact time and temperature. The optimum adsorption efficiencies were determined at pH 2.8 and pH 4.0 for Fe(III) and Cr(III) metal ion solutions, respectively. The experimental data were modelled by different isotherm models and the equilibriums were well described by the Langmuir adsorption isotherm model. The pseudo-first-order, pseudo-second-order kinetic, intra-particle diffusion and Elovich models were applied to analyze the kinetic data and to evaluate rate constants. The pseudo-second-order kinetic model gave a better fit than the others. The thermodynamic parameters, such as Gibbs free energy change ΔG°, standard enthalpy change ΔH° and standard entropy change ΔS° were evaluated. The thermodynamic study showed the adsorption was a spontaneous endothermic process. PMID:26819399

  1. 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. PMID:23646573

  2. Scanning electrochemical microscopy of genomic DNA microarrays--study of adsorption and subsequent interactions.

    PubMed

    Roberts, William S; Davis, Frank; Higson, Séamus P J

    2009-07-01

    The adsorption of genomic DNA and subsequent interactions between adsorbed and solvated DNA have been studied using scanning electrochemical microscopy (SECM). Microarrays of polyethylenimine (PEI) films could be deposited on screen-printed carbon substrates using the SECM. Single stranded herring DNA was electrostatically adsorbed at the surface of the polyethylenimine. The further adsorption of complementary single stranded DNA on the surface was observed to give rise to substantial decreases in interfacial impedance at the surface as measured by increases of tip current of the order of 1-2 nA (6%). Conversely adsorption of DNA from alternate species, i.e. salmon ssDNA on herring ssDNA, yielded much smaller changes in tip current of 0.2 nA. The significance of this work is that the approach opens up the possibility for direct label-free electrochemical interrogation of DNA microarrays as an alternative to other existing optical techniques. PMID:19562194

  3. Adsorption studies on fruits of Gular (Ficus glomerata): removal of Cr(VI) from synthetic wastewater.

    PubMed

    Rao, Rifaqat A K; Rehman, Fouzia

    2010-09-15

    The adsorption of Cr(VI) was studied in batch system using fruits of Ficus glomerata as adsorbent. The effect of temperature, pH, initial Cr(VI) concentration and time was investigated. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) was used to investigate surface morphology and active functional groups present on the adsorbent surface. Thermodynamic parameters like free energy change (DeltaG(0)), enthalpy (DeltaH(0)) and entropy (DeltaS(0)) indicate the spontaneous, endothermic and increased randomness nature of Cr(VI) adsorption. Equilibrium data were fitted well with Langmuir isotherm at 50 degrees C. The magnitude of mean free energy indicates chemical nature of adsorption. The breakthrough and exhaustive capacities were found to be 5 and 23.1 mg g(-1) respectively. The applicability of the adsorbent has been demonstrated by removing Cr(VI) from electroplating wastewater. PMID:20605325

  4. Theoretical studies of urea adsorption on single wall boron-nitride nanotubes

    NASA Astrophysics Data System (ADS)

    Chermahini, Alireza Najafi; Teimouri, Abbas; Farrokhpour, Hossein

    2014-11-01

    Surface modification of a boron nitride nanotube (BNNT) with urea molecule was investigated in terms of its energetic, geometric, and electronic properties using B3LYP and PW91 density functionals. In this investigation, various armchair (n,n) nanotubes, where n = 5, 6, 7 have been used. Two different interaction modes, including interaction with outer layer and inner layer of tube were studied. The results indicated that the adsorption of single urea molecule in all of its configurations is observed to be exothermic and physical in nature. Interestingly, the adsorption energy for the most stable configuration of urea was observed when the molecule located inside of the nanotube. Besides, the adsorption of urea on BNNTs changes the conductivity of nanotube.

  5. 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.

  6. Monomolecular adsorption on nanoparticles with repulsive interactions: a Monte Carlo study.

    PubMed

    Pinto, O A; López de Mishima, B A; Leiva, E P M; Oviedo, O A

    2016-06-01

    In the present work, we study the adsorption of different monomolecular species on nanoparticles with different sizes and geometries using a grand canonical Monte Carlo method. These species are characterized by repulsive lateral interactions between themselves, as takes place in the case of the adsorption of partially charged atoms or molecules. Nanosize effects are analyzed in terms of adsorption on edge and facet sites. The energy minimization in these systems comes out as a complex conjugation of the repulsive lateral interactions between the adsorbates and the attractive interactions of the adsorbates with the nanoparticle. The phenomenon is analyzed as a function of the occurrence of different ordered structures being formed on the surface of the nanoparticle. We find that layers with different structures may coexist on different facets of the nanoparticle. Finally, a discussion of deposition on flat surfaces and in finite systems is given. PMID:27181601

  7. A new chitosan biopolymer derivative as metal-complexing agent: synthesis, characterization, and metal(II) ion adsorption studies.

    PubMed

    Krishnapriya, K R; Kandaswamy, M

    2010-09-23

    In this study, a new chitosan biopolymer derivative (CTSL) has been synthesized by anchoring a new vanillin-based complexing agent or ligand, namely 4-hydroxy-3-methoxy-5-[(4-methylpiperazin-1-yl)methyl] benzaldehyde, (L) with chitosan (CTS) by means of condensation. The new material was characterized by elemental (CHN), spectral (FTIR and solid state (13)C NMR), thermal (TG-DTA and DSC), structural (powder XRD), and morphological (SEM) analyses. The CTSL was employed to study the equilibrium adsorption of various metal ions, namely, Mn(II), Fe(II), Co(II), Cu(II), Ni(II), Cd(II), and Pb(II), as functions of pH of the solutions. Its kinetics of adsorption was evaluated utilizing the pseudo first order and pseudo second order equation models and the equilibrium data were analyzed by Langmuir isotherm model. The CTSL shows good adsorption capacity for metal ions studied in the order Cu(II)>Ni(II)>Cd(II)> or =Co> or =Mn(II)>Fe(II)>Pb(II) in all studied pH ranges due to the presence of many coordinating moieties present in it. PMID:20708730

  8. The effects of the specific adsorption of anion on the reactivity of the Ru(0001) surface towards CO adsorption and oxidation: in situ FTIRS studies.

    PubMed

    Jin, J M; Lin, W F; Christensen, P A

    2008-07-01

    The dynamics of adsorption and oxidation of CO on Ru(0001) electrode in sulfuric acid solution have been studied using in situ FTIR spectroscopy under potential control and at open circuit, the latter at 20 and 55 degrees C. The in situ IR data show clearly that the bisulfate anion adsorbs on the Ru(0001) surface over the potential range from -200 mV to 350 mV (vs. Ag/AgCl) at 20 degrees C in the absence and presence of adsorbed CO; however, increasing the temperature to 55 degrees C and/or increasing the concentration of dissolved O(2) reduces the bisulfate adsorption. The formation of surface (hydro-) oxide at higher potentials replaces the bisulfate adsorbates. Both linear (CO(L)) and three-fold hollow bonded CO (CO(H)) adsorbates were produced following CO adsorption at Ru(0001) in H(2)SO(4), as was observed in our previous studies in HClO(4). However, the amount of adsorbed CO observed in H(2)SO(4) was ca. 10% less than that in HClO(4); in addition, the CO(L) and CO(H) frequencies were higher in H(2)SO(4), and the onset potential for CO(ads) oxidation 25 mV lower. These new results are interpreted in terms of a model in which the adsorbed bisulfate weakens the CO adlayer, allowing the active Ru oxide layer to form at lower potentials. Significantly different results were observed at open circuit in H(2)SO(4) compared both to the data under potential control and to our earlier data in HClO(4), and these observations were rationalized in terms of the adsorbed HSO(4)(-) anions (pre-adsorbed at -200 mV) inhibiting the oxidation of the surface at open circuit (after stepping from the initial potential of -200 mV), as the latter was no longer driven by the imposed electrochemical potential but via chemical oxidation by trace dissolved O(2). Results from experiments at open circuit at 55 degrees C and using oxygen-saturated H(2)SO(4) supported this model. The difference in Ru surface chemistry between imposed electrochemical control and chemical control has potential

  9. Mechanism of Arsenic Adsorption Using Wheat Biomass -- a spectroscopic study

    NASA Astrophysics Data System (ADS)

    Calvo, Oscar; Manciu, Felicia; Maldonado, Josefina; Gardea-Torresdey, Jorge

    2006-10-01

    Arsenic is a trace element that is toxic to animals, humans included. Since the current Environmental Protection Agency guidelines regarding water quality standards indicate that arsenic concentrations in excess of 50 ppb are hazardous to welfare of humans, the search for new water remediation methods or improvements of previous methods have been a focus in environmental technology. Investigations of arsenic uptake have used wide range of sorbents including iron oxides and oxyhydroxides, for which it have been proved that arsenic shows high affinity. In this study, we used far-infrared spectroscopy to examine the arsenic reduction using biomaterials. pH dependence analysis by FTIR demonstrates the sorption of iron oxides and oxyhydroxides by the wheat biomass. The splitting of 350 cm-1 amorphous iron oxide vibrations is a direct proof of the arsenic uptake. In addition, there is evidence of sorption of arsenic at sulfhydryl group of cysteine existent in wheat.

  10. Unrestricted density functional study on the adsorption of hydrogen molecule on nickel surface

    NASA Astrophysics Data System (ADS)

    Ishiwatari, Ryo; Tachikawa, Masanori

    2005-02-01

    The adsorption of hydrogen molecule on Ni(100) and (111) surfaces is studied by unrestricted hybrid density functional calculation. Ni6 and Ni8 clusters are used as small single layer models, while Ni13 cluster as a model containing the second layer. The total energy of triplet state is most stable for both Ni6 (100) fourfold and Ni8 (111) threefold sites. We have found that the optimized geometrical parameters become closer to the experimental values, as the multiplicity increases from singlet to quintet states. Our adsorption energy on Ni13 (100) bridge site gives in reasonable agreement with the experimental value.

  11. Hydrogen adsorption in ZIF-7: A DFT and ab-initio molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Dixit, Mudit; Major, Dan Thomas; Pal, Sourav

    2016-05-01

    Primary H2 adsorption sites in a zeolitic imidazolate framework, ZIF-7, are identified using ab-initio density functional theory (DFT) based molecular dynamics annealing simulations. The simulations suggest several low energy adsorption sites. The effect of light transition metal decoration on hydrogen storage properties was studied. Our ab-intio DFT calculations illustrate that decorating the ZIF with Sc increases both the number of H2 molecules, as well as the H2 binding energy. The binding energy (∼25 kJ/mol per H2) at 8H2 loading in the pore, suggests that Sc-ZIFs can be potential candidates for hydrogen storage.

  12. 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.

  13. 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.

  14. From porphyrins to pyrphyrins: adsorption study and metalation of a molecular catalyst on Au(111)

    NASA Astrophysics Data System (ADS)

    Mette, Gerson; Sutter, Denys; Gurdal, Yeliz; Schnidrig, Stephan; Probst, Benjamin; Iannuzzi, Marcella; Hutter, Jürg; Alberto, Roger; Osterwalder, Jürg

    2016-04-01

    The molecular ligand pyrphyrin, a tetradentate bipyridine based macrocycle, represents an interesting but widely unexplored class of molecules. It resembles the well-known porphyrin, but consists of pyridyl subunits instead of pyrroles. Metal complexes based on pyrphyrin ligands have recently shown promise as water reduction catalysts in homogeneous photochemical water splitting reactions. In this study, the adsorption and metalation of pyrphyrin on a single crystalline Au(111) surface is investigated in an ultrahigh vacuum by means of scanning tunneling microscopy, low-energy electron diffraction, X-ray photoelectron spectroscopy and density functional theory. Pyrphyrin coverages of approximately one monolayer and less are obtained by sublimation of the molecules on the substrate kept at room temperature. The molecules self-assemble in two distinct phases of long-range molecular ordering depending on the surface coverage. The deposition of cobalt metal and subsequent annealing lead to the formation of Co-ligated pyrphyrin molecules accompanied by a pronounced change of the molecular self-assembly. Electronic structure calculations taking the herringbone reconstruction of Au(111) into account show that the molecules are physisorbed, but preferred adsorption sites are identified where Co and the N atoms of the two terminal cyano groups are optimally coordinated to the surface Au atoms. An intermediate state of the metalation reaction is observed and the reaction steps for the Co metalation of pyrphyrin molecules on Au(111) are established in a joint experimental and computational effort.The molecular ligand pyrphyrin, a tetradentate bipyridine based macrocycle, represents an interesting but widely unexplored class of molecules. It resembles the well-known porphyrin, but consists of pyridyl subunits instead of pyrroles. Metal complexes based on pyrphyrin ligands have recently shown promise as water reduction catalysts in homogeneous photochemical water splitting

  15. Adsorption states of amphipatic solutes at the surface of naturally hydrophobic minerals: a molecular dynamics simulation study.

    PubMed

    Du, Hao; Miller, J D

    2007-11-01

    An initial molecular dynamics simulation study regarding interfacial phenomena at selected naturally hydrophobic surfaces is reported. Simulation results show that, due to the natural hydrophobicity of graphite and talc basal planes, the cationic surfactant dodecyltrimethylammonium bromide preferentially adsorbs at these surfaces through hydrophobic interactions. When a model dextrin molecule is considered, the simulation results suggest that the hydrophobic interaction between the naturally hydrophobic surfaces of graphite, talc basal plane, and sulfur and the hydrophobic moieties (C-H and methylene groups) in the dextrin molecule plays a significant role in dextrin adsorption at these surfaces. The hydroxyl group in the dextrin molecule also contributes to its adsorption at the talc basal plane surface. In contrast, dextrin was not found to adsorb at talc edge surfaces. PMID:17929842

  16. A batch adsorption study on bentonite clay Pertinence to transport modeling?

    NASA Astrophysics Data System (ADS)

    BOURG, I.; BOURG, A. C.; SPOSITO, G.

    2001-12-01

    Bentonite clay is often used as a component of engineered barriers for the isolation of high-level toxic wastes. This swelling clay is used for its physical (impermeability, self-healing) but also for its chemical properties, mostly a high cation exchange capacity (CEC). The adsorbed cations being temporarily immobilized, this should slow down the release of cations from the waste to the surrounding environment. In order to assess the performance of the engineered barrier, the partitioning of solutes between the liquid and solid phases needs to be quantified for use in transport models. The usual method for characterizing the adsorption is through batch adsorption experiments on dispersed suspensions of the solid, yielding an adsorption isotherm (adsorbed concentration vs. dissolved concentration). This isotherm however should be a function of various environmental variables (e.g., pH, ionic strength, concentrations of various ligands and competing adsorbents), so that extrapolation of lab data to performance assessment in the field is problematic. We present results from a study of the adsorption of cesium, strontium, cadmium and lead on dispersed suspensions of the standard BX-80 bentonite. Through a wide range of experimental parameters (pH, ionic strength, reaction time, reactor open or closed to the atmosphere, study of a range of cations of differing properties), we seek a mechanistic interpretation of the results instead of an empirical determination of adsorption parameters. Depending on the mechanisms that control the adsorption in different experimental ranges, we discuss the degree to which the partitioning coefficient (Kd) obtained in the lab can be extrapolated to a transport model through compacted bentonite in a natural environment.

  17. Adsorption of lipase on polypropylene powder.

    PubMed

    Gitlesen, T; Bauer, M; Adlercreutz, P

    1997-04-01

    Adsorption of different lipases by EP-100 polypropylene powder from crude and pure lipase preparations was studied. Langmuir isotherms described the adsorption equilibria well both for protein and lipase activity adsorption. Adsorption isotherms for five different proteins all gave a similar saturation level of 220 mg protein per g carrier. Twelve commercial lipase preparations were tested for selectivity in the adsorption of lipase. For all preparations the selectivity factor was larger than one. In a crude lipase preparation from Pseudomonas fluorescence, the specific activity in solution decreased by two orders of magnitude after adsorption. The adsorption was not significantly influenced by pH changes in the adsorption buffer, indicating that hydrophobic and not electrostatic interactions are the dominating adsorption forces. Adsorption of a crude lipase from Candida rugosa (Sigma) was fast and equilibrium was reached in 30 and 100 min for protein and lipase activity adsorption respectively. Desorption in aqueous solution was negligible. Investigations with seven different lipases showed no correlation between the specific lipolytic activity of dissolved enzyme in aqueous solution and the specific activity of adsorbed enzyme in an esterification reaction in organic solvent. PMID:9106498

  18. 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. PMID:26871732

  19. Comparative study of carbon nanotubes and granular activated carbon: Physicochemical properties and adsorption capacities.

    PubMed

    Gangupomu, Roja Haritha; Sattler, Melanie L; Ramirez, David

    2016-01-25

    The overall goal was to determine an optimum pre-treatment condition for carbon nanotubes (CNTs) to facilitate air pollutant adsorption. Various combinations of heat and chemical pre-treatment were explored, and toluene was tested as an example hazardous air pollutant adsorbate. Specific objectives were (1) to characterize raw and pre-treated single-wall (SW) and multi-wall (MW) CNTs and compare their physical/chemical properties to commercially available granular activated carbon (GAC), (2) to determine the adsorption capacities for toluene onto pre-treated CNTs vs. GAC. CNTs were purified via heat-treatment at 400 °C in steam, followed by nitric acid treatment (3N, 5N, 11N, 16N) for 3-12 h to create openings to facilitate adsorption onto interior CNT sites. For SWNT, Raman spectroscopy showed that acid treatment removed impurities up to a point, but amorphous carbon reformed with 10h-6N acid treatment. Surface area of SWNTs with 3 h-3N acid treatment (1347 m(2)/g) was higher than the raw sample (1136 m(2)/g), and their toluene maximum adsorption capacity was comparable to GAC. When bed effluent reached 10% of inlet concentration (breakthrough indicating time for bed cleaning), SWNTs had adsorbed 240 mg/g of toluene, compared to 150 mg/g for GAC. Physical/chemical analyses showed no substantial difference for pre-treated vs. raw MWNTs. PMID:26476807

  20. Experimental and first-principles study of guanine adsorption on ZnO clusters.

    PubMed

    Chandraboss, V L; Karthikeyan, B; Senthilvelan, S

    2014-11-14

    Theoretical investigation of guanine, DNA base adsorption on the ZnO model clusters, viz., Zn2O2, Zn3O3, Zn4O4 ring (R) and Zn4O4 wurtzite (W) in terms of geometry, binding site, binding energy (EB), energy gap (Eg), electronic and spectral properties were studied by a density functional theory (DFT) method. The guanine adsorption on the ZnO (G-ZnO) clusters is modeled by the B3LYP/LanL2DZ method. The calculated binding energy (EB) and energy gap (Eg) of the guanine molecule are highly dependent on the nature of the cluster size and vary with the size of the clusters. Physisorption proceeded via formation of the NZn bond between guanine and the active Zn(2+) site on ZnO. The HOMO-LUMO energies show that charge transfer occurs in the G-ZnO clusters, from ZnO to guanine to better understand the interaction. The Mulliken charges are computed. The electronic properties of ZnO and G-ZnO clusters were compared with different basis sets (B3LYP/6-31G, B3LYP/6-311G, MP2/6-31G and MP2/LanL2DZ). Experimental information like microscopic and spectroscopic evidence is also included for understanding the guanine-ZnO interactions. The G-ZnO composite was prepared by a precipitation method and characterized by SEM with EDX, FT-IR and FT-RAMAN analysis. The interaction of guanine with ZnO nanoparticles was observed by UV-vis spectroscopy. The experimental results are compared with the DFT results in the light of these new insights. PMID:25266048

  1. A study of molecular adsorption of a cationic surfactant on complex surfaces with atomic force microscopy.

    PubMed

    Sokolov, I; Zorn, G; Nichols, J M

    2016-02-01

    The study of molecular adsorption on solid surfaces is of broad interest. However, so far the study has been restricted to idealized flat smooth rigid surfaces which are rarely the case in real world applications. Here we describe a study of molecular adsorption on a complex surface of the submicron fibers of a fibrous membrane of regenerated cellulose in aqueous media. We use a cationic surfactant, cetyltrimethylammonium chloride (CTAC), as the adsorbing molecule. We study the equilibrium adsorption of CTAC molecules on the same area of the fibers by sequentially immersing the membrane in pure water, 1 mM and then a 20 mM solution of CTAC. Atomic force microscopy (AFM) is applied to study the adsorption. The force-volume mode is used to record the force-deformation curves of the adsorbed molecules on the fiber surface. We suggest a model to separate the forces due to the adsorbed molecules from the elastic deformation of the fiber. Interestingly, knowledge of the surface geometry is not required in this model provided the surface is made of elastically homogeneous material. Different models are investigated to estimate the amount of the adsorbed molecules based on the obtained force curves. The exponential steric repulsion model fits the force data the best. The amount of the adsorbed surfactant molecules and its dependence on the concentration are found to be reasonable compared to the data previously measured by means of Raman scattering done on a flat surface of silica. PMID:26730682

  2. 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. PMID:20346574

  3. 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. PMID:19395160

  4. A pulse chromatographic study of the adsorption properties of the amino-MIL-53 (Al) metal-organic framework.

    PubMed

    Couck, Sarah; Rémy, Tom; Baron, Gino V; Gascon, Jorge; Kapteijn, Freek; Denayer, Joeri F M

    2010-08-28

    Low-coverage adsorption properties of the metal-organic framework amino-MIL-53 (Al) were determined using the pulse chromatographic technique. By using n-alkanes, iso-alkanes, 1-alkenes, cyclohexane and benzene as probe molecules, the nature of the adsorptive interactions in amino-MIL-53 (Al) was studied. Henry adsorption constants and adsorption enthalpies of iso-alkanes are significantly lower than those of the linear alkanes, demonstrating the shape selective properties of amino-MIL-53. The presence of amino-groups in the pores of the material increases the electrostatic contributions with molecules containing double bonds. A simple model relates adsorption enthalpies to the number of hydrogen atoms and double bonds in the molecule. The effective pore size of the material was estimated based on the relationship between adsorption enthalpy and entropy. PMID:20532387

  5. Investigation of the adsorption of amino acids on Pd(1 1 1): A density functional theory study

    NASA Astrophysics Data System (ADS)

    James, Joanna N.; Han, Jeong Woo; Sholl, David S.

    2014-05-01

    Density functional theory calculations have been used to study the adsorption of glycine, alanine, norvaline, valine, proline, cysteine, and serine on Pd(1 1 1). Most amino acids except cysteine adsorb onto the surface in a tridentate fashion through a nitrogen atom and both oxygen atoms. For cysteine, an additional bond is formed with the surface due to the strong affinity of the sulfur atom, resulting in a significantly larger adsorption energy. The adsorption patterns of amino acids we examined are supported by the shifts in vibrational frequencies associated with NHH and COO. The adsorption strength of amino acids depends on how much the molecules deform during the adsorption process. Understanding the adsorption of amino acids on Pd(1 1 1) provides fundamental information for future consideration of the interactions between their derivatives or more complicated biomolecules and metal surfaces.

  6. Adsorption Behavior of Cellulose and Its Derivatives toward Ag(I) in Aqueous Medium: An AFM, Spectroscopic, and DFT Study.

    PubMed

    Zhu, Chuantao; Dobryden, Illia; Rydén, Jens; Öberg, Sven; Holmgren, Allan; Mathew, Aji P

    2015-11-17

    The aim of this study was to develop a fundamental understanding of the adsorption behavior of metal ions on cellulose surfaces using experimental techniques supported by computational modeling, taking Ag(I) as an example. Force interactions among three types of cellulose microspheres (native cellulose and its derivatives with sulfate and phosphate groups) and the silica surface in AgNO3 solution were studied with atomic force microscopy (AFM) using the colloidal probe technique. The adhesion force between phosphate cellulose microspheres (PCM) and the silica surface in the aqueous AgNO3 medium increased significantly with increasing pH while the adhesion force slightly decreased for sulfate cellulose microspheres (SCM), and no clear adhesion force was observed for native cellulose microspheres (CM). The stronger adhesion enhancement for the PCM system is mainly attributed to the electrostatic attraction between Ag(I) and the negative silica surface. The observed force trends were in good agreement with the measured zeta potentials. The scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) analyses confirmed the presence of silver on the surface of cellulose microspheres after adsorption. This study showed that PCM with a high content of phosphate groups exhibited a larger amount of adsorbed Ag(I) than CM and SCM and possible clustering of Ag(I) to nanoparticles. The presence of the phosphate group and a wavenumber shift of the P-OH vibration caused by the adsorption of silver ions on the phosphate groups were further confirmed with computational studies using density functional theory (DFT), which gives support to the above findings regarding the adsorption and clustering of Ag(I) on the cellulose surface decorated with phosphate groups as well as IR spectra. PMID:26501836

  7. A study of the thermodynamic properties of surfactant mixtures: Mixed micelle formation and mixed surfactant adsorption

    SciTech Connect

    Lopata, J.J.

    1992-12-31

    The volumetric mixing in anionic/nonionic, cationic/nonionic, and anionic/cationic mixed micelles was determined by examining the total surfactant apparent molar volumes at total surfactant concentrations much greater than the mixture critical micelle concentration. The mixed surfactant systems investigated were: sodium dodecyl sulfate and a polyethoxylated nonylphenol, at 0.15 M NaCl and with no added NaCl; cetyl pyridinium chloride and polyethoxylated nonylphenol, at 0.03 M NaCl; and sodium dodecyl sulfate and dodecyl pyridinium chloride, at 0.15 M NaCl. The results of this study suggest that the electrostatic interactions in the mixed micelles do no significantly effect the molar volume of the mixed micelle. Therefore, the micelle hydrophobic core dominates the volumetric mixing in mixed micelles. The adsorption of sodium dodecyl sulfate and a polyethoxylated nonylphenol and well defined mixtures thereof was measured on gamma alumina. A pseudo-phase separation model to describe mixed anionic/nonionic admicelle (adsorbed surfactant aggregate) formation was developed. In this model, regular solution theory was used to describe the anionic/nonionic surfactant interactions in the mixed admicelle and a patch-wise adsorption model was used to describe surfactant adsorption on a heterogeneous surface. Regular solution theory was tested on specific homogeneous surface patches by examining constant total surfactant adsorption levels. For the adsorption of binary surfactant mixtures adsorbing at total equilibrium concentrations above the mixture critical micelle concentration, simultaneous solution of the pseudo-phase separation models for mixed admicelle and mixed micelle formation predicts that the surfactant compositions in the monomer, micelle, and admicelle pseudo-phases are constant at a constant total adsorption level.

  8. High-resolution photoemission study of acetylene adsorption and reaction with the Si(100)-2x1 surface

    SciTech Connect

    Xu, S.H.; Yang, Y.; Keeffe, M.; Lapeyre, G.J.; Rotenberg, E.

    1999-02-09

    The adsorption and reaction of acetylene with the Si{approximately}100-231 surface has been studied using high-resolution photoemission by monitoring the Si 2p,C 1s, and valence-band (VB) spectra as a function of both acetylene coverage and post-adsorption annealing temperature. After the clean Si(100) surface is exposed to 0.5 monolayer (ML) acetylene, the surface state in the VB is absent. Meanwhile, the curve-fitting results show that there is only one interface component in the Si 2p core level. These results indicate that the asymmetric Si dimers may become symmetric dimers after acetylene adsorption, which can be explained well by the tetra-sigma model determined from our previous photoelectron holographic results. Significant changes in the electronic structure (Si 2p,C 1s, and VB) are found after subsequent annealing of the saturation overlayer. Annealing at lower temperature can induce some acetylene molecule desorption while most of the molecules decompose into C2Hx (x=1,0) and H species. After annealing above 660C, both of the reacted components of the Si 2p and C 1s lines show that the SiC species form clusterlike features. At the same time, the VB and Si 2p spectra indicate a restoration of a Si(100)-2x1 structure, and the asymmetric Si dimers reappear on the surface.

  9. 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.

  10. 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.

  11. Efficient removal of crystal violet using Fe3O4-coated biochar: the role of the Fe3O4 nanoparticles and modeling study their adsorption behavior

    NASA Astrophysics Data System (ADS)

    Sun, Pengfei; Hui, Cai; Azim Khan, Rashid; Du, Jingting; Zhang, Qichun; Zhao, Yu-Hua

    2015-07-01

    Biochar shows great promise for use in adsorbing pollutants. However, a process for enhancing its adsorption capacity and re-collection efficiency is yet to be further developed. Hence, in this study, we developed a type of biochar coated with magnetic Fe3O4 nanoparticles (i.e., magnetic biochar (MBC)) and assessed its use for crystal violet (CV) adsorption as well as its recycling potential. The coating of Fe3O4 nanoparticles, which was not only on the surface, but also in the interior of biochar, performed two functions. Firstly, it produced a saturation magnetization of 61.48 emu/g, which enabled the biochar being efficiently re-collected using a magnet. Secondly, it significantly enhanced the adsorption capacity of the biochar (from 80.36 to 99.19 mg/g). The adsorption capacity of the MBC was determined to be the largest by so far (349.40 mg/g) for an initial CV concentration of 400 mg/L, pH of 6.0, and temperature of 40 °C, and the adsorption capacity of re-collected MBC was 73.31 mg/g. The adsorption of CV by the MBC was found to be a spontaneous and endothermic physical process in which the intraparticle diffusion was the limiting step. These findings inspire us to use other similar materials to tackle the menace of pollutions.

  12. Efficient removal of crystal violet using Fe3O4-coated biochar: the role of the Fe3O4 nanoparticles and modeling study their adsorption behavior

    PubMed Central

    Sun, Pengfei; Hui, Cai; Azim Khan, Rashid; Du, Jingting; Zhang, Qichun; Zhao, Yu-Hua

    2015-01-01

    Biochar shows great promise for use in adsorbing pollutants. However, a process for enhancing its adsorption capacity and re-collection efficiency is yet to be further developed. Hence, in this study, we developed a type of biochar coated with magnetic Fe3O4 nanoparticles (i.e., magnetic biochar (MBC)) and assessed its use for crystal violet (CV) adsorption as well as its recycling potential. The coating of Fe3O4 nanoparticles, which was not only on the surface, but also in the interior of biochar, performed two functions. Firstly, it produced a saturation magnetization of 61.48 emu/g, which enabled the biochar being efficiently re-collected using a magnet. Secondly, it significantly enhanced the adsorption capacity of the biochar (from 80.36 to 99.19 mg/g). The adsorption capacity of the MBC was determined to be the largest by so far (349.40 mg/g) for an initial CV concentration of 400 mg/L, pH of 6.0, and temperature of 40 °C, and the adsorption capacity of re-collected MBC was 73.31 mg/g. The adsorption of CV by the MBC was found to be a spontaneous and endothermic physical process in which the intraparticle diffusion was the limiting step. These findings inspire us to use other similar materials to tackle the menace of pollutions. PMID:26220603

  13. A novel polar-modified post-cross-linked resin and its enhanced adsorption to salicylic acid: Equilibrium, kinetics and breakthrough studies.

    PubMed

    Wang, Xiaomei; Li, Guoqiang; Guo, Deping; Zhang, Yaling; Huang, Jianhan

    2016-05-15

    Improving the surface polarity is of significance for the post-cross-linked resins to enhance their adsorption to polar aromatic compounds. In the present study, we prepared a novel polar-modified post-cross-linked PDEpc_D by the Friedel-Crafts alkylation reaction and the amination reaction, the Brunauer-Emmett-Teller (BET) surface area and pore volume increased significantly after the Friedel-Crafts alkylation reaction and the surface polarity improved greatly after the amination reaction. Batch adsorption showed that PDEpc_D possessed a much enhanced adsorption to salicylic acid as compared the precursors PDE and PDEpc as well as the non-polar post-cross-linked PDVBpc. The equilibrium data was characterized by the Freundlich model, π-π stacking, hydrogen bonding and static interaction were the possible driving forces. The adsorption was a fast process and the kinetic data obeyed the micropore diffusion model. Column adsorption-desorption experiments suggested that PDEpc_D was a potential candidate for adsorptive removal of salicylic acid from aqueous solution. PMID:26928058

  14. Insights into the effect of coverage on CO adsorption and dissociation over Rh(1 0 0) surface: A theoretical study

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaojun; Zhang, Riguang; Ling, Lixia; Wang, Baojun

    2014-11-01

    The adsorption, dissociation and desorption of CO at different coverage over Rh(1 0 0) surface have been systematically investigated using density functional theory method together with the periodic slab model. Our results show that at the coverage less than or equal to 4/12 ML, CO favored the most stable bridge site adsorption, and the adsorption energies of CO have little difference; while at the coverage greater than or equal to 5/12 ML, the lateral repulsive interaction begins to affect the adsorption structures and the corresponding adsorption energies of adsorbed CO molecules, and the interaction will be stronger with the increasing of CO coverage, which leads to CO migration over Rh(1 0 0) surface when CO coverage is greater than or equal to 10/12 ML. The adsorption energies of these CO molecules will decrease successively until the saturated adsorption with the CO coverage of 12/12 ML. Further calculations on CO dissociation indicate that when CO coverage is greater than or equal to 3/12 ML, the dissociation of adsorbed CO molecules will be unfavorable both kinetically and thermodynamically, suggesting that only molecule CO adsorption are favored. Considering the catalytic activity of Rh(1 0 0) surface toward CO dissociation and the higher CO coverage under the continuous supply of CO in syngas conversion, it is to be expected that only molecule CO adsorption exist on Rh catalyst.

  15. Pulse gas chromatographic study of adsorption of substituted aromatics and heterocyclic molecules on MIL-47 at zero coverage.

    PubMed

    Duerinck, Tim; Couck, Sarah; Vermoortele, Frederik; De Vos, Dirk E; Baron, Gino V; Denayer, Joeri F M

    2012-10-01

    The low coverage adsorptive properties of the MIL-47 metal organic framework toward aromatic and heterocyclic molecules are reported in this paper. The effect of molecular functionality and size on Henry adsorption constants and adsorption enthalpies of alkyl and heteroatom functionalized benzene derivates and heterocyclic molecules was studied using pulse gas chromatography. By means of statistical analysis, experimental data was analyzed and modeled using principal component analysis and partial least-squares regression. Structure-property relationships were established, revealing and confirming several trends. Among the molecular properties governing the adsorption process, vapor pressure, mean polarizability, and dipole moment play a determining role. PMID:22958218

  16. Equilibrium and kinetics studies of arsenate adsorption by FePO(4).

    PubMed

    Hamayun, M; Mahmood, T; Naeem, A; Muska, M; Din, S U; Waseem, M

    2014-03-01

    The present work is focusing on removal of arsenate from aqueous solution using FePO4. The equilibrium study regarding the removal of arsenic by FePO4 was carried out at 298, 308, 318 and 328K. Langmuir parameters were found to increase with the increase in temperature indicating that the adsorption is favorable at high temperature. Kinetic study of arsenate adsorption on FePO4 was also carried out at different temperatures and at pH 6 and 8. Different kinetic models were used to the kinetic data amongst which pseudo second order model was best fitted. The mechanism of the adsorption kinetics was investigated by employing intraparticle diffusion and Richenberg models. The energy of activation (Ea) was found to be 30 and 35.52kJmol(-1) at pH 6 and pH 8, respectively, suggesting chemisorption nature of the adsorption process. The negative entropic values of activation signified the existence of entropy barrier while the positive ΔG(#) values indicated the existence of energy barrier to be crossed over for the occurrence of a chemical reaction. Both the spectroscopic studies and increase in equilibrium pH reveal the anion exchange removal of arsenate from aqueous solution to the solid surface. PMID:24280053

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

    DOE PAGESBeta

    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

  18. 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.

  19. 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.

  20. 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.

  1. Random sequential adsorption on fractals

    NASA Astrophysics Data System (ADS)

    Ciesla, Michal; Barbasz, Jakub

    2012-07-01

    Irreversible adsorption of spheres on flat collectors having dimension d < 2 is studied. Molecules are adsorbed on Sierpinski's triangle and carpet-like fractals (1 < d < 2), and on general Cantor set (d < 1). Adsorption process is modeled numerically using random sequential adsorption (RSA) algorithm. The paper concentrates on measurement of fundamental properties of coverages, i.e., maximal random coverage ratio and density autocorrelation function, as well as RSA kinetics. Obtained results allow to improve phenomenological relation between maximal random coverage ratio and collector dimension. Moreover, simulations show that, in general, most of known dimensional properties of adsorbed monolayers are valid for non-integer dimensions.

  2. Random sequential adsorption on fractals.

    PubMed

    Ciesla, Michal; Barbasz, Jakub

    2012-07-28

    Irreversible adsorption of spheres on flat collectors having dimension d < 2 is studied. Molecules are adsorbed on Sierpinski's triangle and carpet-like fractals (1 < d < 2), and on general Cantor set (d < 1). Adsorption process is modeled numerically using random sequential adsorption (RSA) algorithm. The paper concentrates on measurement of fundamental properties of coverages, i.e., maximal random coverage ratio and density autocorrelation function, as well as RSA kinetics. Obtained results allow to improve phenomenological relation between maximal random coverage ratio and collector dimension. Moreover, simulations show that, in general, most of known dimensional properties of adsorbed monolayers are valid for non-integer dimensions. PMID:22852643

  3. 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. PMID:26921544

  4. Markedly different adsorption behaviors of gas molecules on defective monolayer MoS2: a first-principles study.

    PubMed

    Li, Hongxing; Huang, Min; Cao, Gengyu

    2016-06-01

    Sulfur vacancy (SV) is one of the most typical defects in two-dimensional monolayer MoS2, leading to reactive sites. We presented a systematic study of the adsorption behaviors of gas molecules, CO2, N2, H2O, CO, NH3, NO, O2, H2 and NO2, on monolayer MoS2 with single SV by first-principles calculations. It was found that CO2, N2 and H2O molecules physisorbed at the proximity of single SV. Our adsorption energy calculations and charge transfer analysis showed that the interactions between CO2, N2 and H2O molecules and defective MoS2 are stronger than the cases of CO2, N2 and H2O molecules adsorbed on pristine MoS2, respectively. The defective MoS2 based gas sensors may be more sensitive to CO2, N2 and H2O molecules than pristine MoS2 based ones. CO, NO, O2 and NH3 molecules were found to chemisorb at the S vacancy site and thus modify the electronic properties of defective monolayer MoS2. Magnetism was induced upon adsorption of NO molecules and the defective states induced by S vacancy can be completely removed upon adsorption of O2 molecules, which may provide some helpful information for designing new MoS2 based nanoelectronic devices in future. The H2 and NO2 molecules were found to dissociate at S vacancy. The dissociation of NO2 molecules resulted in O atoms located at the S vacancy site and NO molecules physisorbed on O-doped MoS2. The calculated results showed that NO2 molecules can help heal the S vacancy of the MoS2 monolayer. PMID:27198064

  5. First principles study of nanoscale mechanism of oxygen adsorption on lanthanum zirconate surfaces

    NASA Astrophysics Data System (ADS)

    Guo, Xingye; Wu, Linmin; Zhang, Yi; Jung, Yeon-Gil; Li, Li; Knapp, James; Zhang, Jing

    2016-09-01

    Lanthanum zirconate (La2Zr2O7) is a rare-earth pyrochlore material, which has been proposed as a promising thermal barrier coating (TBC) material due to its low thermal conductivity and high temperature phase stability. At elevated temperatures, degradation of La2Zr2O7 may occur due to adsorption of oxygen (O2) on La2Zr2O7 surfaces. This paper investigates nanoscale mechanism of O2 adsorption on La2Zr2O7 coating surfaces using the density functional theory (DFT) calculations. La2Zr2O7 surface energies on (001), (011) and (111) planes are calculated. The surface free energy of (011) plane is lower than those of (001) and (111) planes. On (001), (011) and (111) planes of La2Zr2O7, the lowest adsorption energy occurs at 4-fold site, bridge site, and 3-fold-FCC site, respectively. Among all calculated cases, the lowest adsorption energy site is 3-fold-FCC on (111) plane, which is confirmed by the Bader charge transfer analyses. Charge density difference analyses show that the 3-fold-FCC site on (111) surface has the largest charge density, suggesting the strongest interaction between O2 and La2Zr2O7 surface.

  6. Glyphosate degradation by immobilized bacteria: laboratory studies showing feasibility for glyphosate removal from waste water.

    PubMed

    Heitkamp, M A; Adams, W J; Hallas, L E

    1992-09-01

    To evaluate immobilized bacteria technology for the removal of low levels of glyphosate (N-phosphonomethylglycine) from aqueous industrial effluents, microorganisms with glyphosate-degrading activity obtained from a fill and draw enrichment reactor inoculated with activated sludge were first exposed to glyphosate production wastes containing 500-2000 mg glyphosate/L. The microorganisms were then immobilized by adsorption onto a diatomaceous earth biocarrier contained in upflow Plexiglas columns. The columns were aerated, maintained at pH 7.0-8.0, incubated at 25 degrees C, supplemented with NH4NO3 (50 mg/L), and exposed to glyphosate process wastes pumped upflow through the biocarrier. Glyphosate degradation to aminomethylphosphonic acid was initially > 96% for 21 days of operation at flows yielding hydraulic residence times (HRTs) as short as 42 min. Higher flow rate studies showed > 98% removal of 50 mg glyphosate/L from the waste stream could be achieved at a HRT of 23 min. Glyphosate removal of > 99% at a 37-min HRT was achieved under similar conditions with a column inoculated with a pure culture of Pseudomonas sp. strain LBr, a bacterium known to have high glyphosate-degrading activity. After acid shocking (pH 2.8 for 18 h) of a column of immobilized bacteria, glyphosate-degrading activity was regained within 4 days without reinoculation. Although microbial growth and glyphosate degradation were not maintained under low organic nutrient conditions in the laboratory, the low levels of degradable carbon (45-94 mg/L) in the industrial effluent were sufficient to support prolonged glyphosate-degrading activity. The results demonstrated that immobilized bacteria technology is effective in removing low levels of glyphosate in high-volume liquid waste streams. PMID:1464067

  7. 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.

  8. 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 .

  9. CO adsorption on the Ni2Pb/Ni(1 1 1) surface alloy: A DFT study

    NASA Astrophysics Data System (ADS)

    Kośmider, K.; Kucharczyk, R.; Jurczyszyn, L.

    2013-02-01

    Structural and electronic properties of the Pb/Ni(1 1 1) overlayer and the Ni2Pb/Ni(1 1 1) surface alloy have been investigated within a DFT-PBE approach in order to determine its reactivity towards adsorption of CO molecules. This work has been motivated by a photoemission study of CO adsorption on Pb/Ni(1 1 1) surface phases [V. Matolín et al., Phys. Rev. B 74 (2006) 075416] indicating that Pb adatoms inhibit CO adsorption in a purely geometrical way by site blocking at Ni(1 1 1), whereas surface alloying has a poisoning effect of the Ni-CO bond weakening. In general, our DFT computations confirm experimental findings for the Pb/Ni(1 1 1) overlayer, as the very high activation barrier of about 2 eV due to the presence of Pb adatoms makes the CO chemisorption virtually impossible. For the Ni2Pb/Ni(1 1 1) surface alloy, we show that CO can bind to Ni atoms in the on-top position, and this process occurs to be exothermic with the energy gain of 0.35 eV per CO molecule. Dramatic reduction of the computed adsorption energy with respect to the pure Ni(1 1 1) substrate is in apparent agreement with experiment. However, it follows from our simulations that the CO adsorption process is accompanied by a substantial rearrangement of Ni atoms within the Ni2Pb surface alloy layer. Taking into account the associated deformation energy in the overall energetic balance yields nearly the same interaction energy between the CO molecules and the Ni atoms for the alloyed and the pure Ni(1 1 1) substrate, so the Ni-CO bond appears not to be weakened. The experimentally observed suppression of CO adsorption upon the alloy formation can be explained by a notable increase of the activation barrier for CO chemisorption from about 0.1 eV for the pure Ni(1 1 1) to roughly 0.5 eV for the Ni2Pb/Ni(1 1 1) surface alloy, affecting the corresponding reaction rate.

  10. 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.

  11. Hydrogen adsorption capacities of multi-walled boron nitride nanotubes and nanotube arrays: a grand canonical Monte Carlo study.

    PubMed

    Ahadi, Zohreh; Shadman, Muhammad; Yeganegi, Saeed; Asgari, Farid

    2012-07-01

    Hydrogen adsorption in multi-walled boron nitride nanotubes and their arrays was studied using grand canonical Monte Carlo simulation. The results show that hydrogen storage increases with tube diameter and the distance between the tubes in multi-walled boron nitride nanotube arrays. Also, triple-walled boron nitride nanotubes present the lowest level of hydrogen physisorption, double-walled boron nitride nanotubes adsorb hydrogen better when the diameter of the inner tube diameter is sufficiently large, and single-walled boron nitride nanotubes adsorb hydrogen well when the tube diameter is small enough. Boron nitride nanotube arrays adsorb hydrogen, but the percentage of adsorbed hydrogen (by weight) in boron nitride nanotube arrays is rather similar to that found in multi-walled boron nitride nanotubes. Also, when the Langmuir and Langmuir-Freundlich equations were fitted to the simulated data, it was found that multi-layer adsorptivity occurs more prominently as the number of walls and the tube diameter increase. However, in single-walled boron nitride nanotubes with a small diameter, the dominant mechanism is monolayer adsorptivity. PMID:22160758

  12. Ni adsorption and Ni-Al LDH precipitation in a sandy aquifer: an experimental and mechanistic modeling study.

    PubMed

    Regelink, Inge C; Temminghoff, Erwin J M

    2011-03-01

    Mining activities and industries have created nickel (Ni) contaminations in many parts of the world. The objective of this study is to increase our understanding of Ni adsorption and Nickel-Aluminium Layered Double Hydroxide (Ni-Al LDH) precipitation to reduce Ni mobility in a sandy soil aquifer. At pH ≥ 7.2 both adsorption and Ni-Al LDH precipitation occurred. In batch experiments with the sandy soil up to 70% of oxalate-extractable Al was taken up in LDH formation during 56 days. In a long term column experiment 99% of influent Ni was retained at pH 7.5 due to Ni adsorption (≈ 34%) and Ni-Al LDH precipitation (≈ 66%) based on mechanistic reactive transport modeling. The subsequent leaching at pH 6.5 could be largely attributed to desorption. Our results show that even in sandy aquifers with relatively low Al content, Ni-Al LDH precipitation is a promising mechanism to immobilize Ni. PMID:21186070

  13. Experimental and Quantum Studies on Adsorption and Corrosion Inhibition Effect of Imidazole Derivatives on N80 Steel in Hydrochloric Acid

    NASA Astrophysics Data System (ADS)

    Yadav, M.; Kumar, Sumit; Sharma, Dipti; Yadav, P. N.

    2013-12-01

    The inhibition effect of synthesized N‧-(phenylmethylidene)-2-(2-methyl-1H-benzimidazol-1-yl)acetohydrazides, N‧-(4-methylphenylmethylidene)-2-(2-methyl-1H-benzimidazol-1-yl)acetohydrazides, and N‧-(4-methoxyphenylmethylidene)-2-(2-methyl-1H-benzimidazol-1-yl)acetohydrazides on the corrosion behaviour of N80 steel in 15% hydrochloric acid solution was investigated using weight loss, potentiostatic polarization and electrochemical impedance spectroscopy methods. The inhibition efficiency increased as the concentration of the inhibitors was increased. The effect of temperature on corrosion inhibition was investigated by weight loss method and thermodynamic parameters were calculated. Potentiodynamic polarization measurements show that all the three studied inhibitors act as mixed inhibitor. The adsorption of inhibitors on N80 steel surface obeys Langmuir adsorption isotherm. The structure of inhibitors was optimized using semiemperical AM1 method. Theoretical parameters such as the highest occupied molecular orbital (EHOMO), lowest unoccupied molecular orbital (ELUMO) energy levels, energy gap (ΔE = ELUMO - EHOMO), dipole moment (μ), global hardness (γ), softness (σ), binding energy, molecular surface area and the fraction of electrons transferred (ΔN) were calculated and the adsorption mechanism was discussed. Scanning electron microscopy was used to characterize the surface marphology of the N80 steel.

  14. The adsorption of nitrogen oxides and water on rare-earth ion-exchanged ZSM-5: a density functional study

    NASA Astrophysics Data System (ADS)

    Luo, Yi; Wan, Xiaohong; Ito, Yuki; Takami, Seiichi; Kubo, Momoji; Miyamoto, Akira

    2002-12-01

    In this study, we present the adsorption behavior of NO, NO 2 and H 2O on trivalent rare-earth ion-exchanged ZSM-5 (RE-ZSM-5; RE=La, Ce, Nd, Sm, Gd and Dy) using density functional theory. The results show that Ce-ZSM-5 is more effective for the activation of NO x than La-ZSM-5 and Nd-ZSM-5, which is in good agreement with experimental results. The present investigation also suggests that Dy-ZSM-5 has a considerable ability for the activation of NO 2 as compared to Sm-ZSM-5 and Gd-ZSM-5. Furthermore, the Ce-, Nd- and Dy-analogues posses a quite stronger affinity for NO x and that the low affinity of H 2O indicate the poisoning resistance ability of these catalysts. In addition, the relationship between the adsorption energy of NO and the contribution of NO-2π g1 molecular orbital was also investigated in the NO/RE-ZSM-5 adsorption complex.

  15. 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

  16. Adsorption kinetics of surfactant mixtures from micellar solutions as studied by maximum bubble pressure technique.

    PubMed

    Frese, Ch; Ruppert, S; Sugár, M; Schmidt-Lewerkühne, H; Wittern, K P; Fainerman, V B; Eggers, R; Miller, R

    2003-11-15

    The adsorption kinetics of micellar solutions of anionic/cationic SDS/DATB mixtures with mixing ratios of 10/1 and 10/2, respectively, are studied experimentally by means of the maximum bubble pressure method. For long adsorption times the adsorption of the highly surface-active anionic/cationic complex leads to a decrease of dynamic surface tension in comparison to the single SDS system. However, the situation is the reverse for short adsorption times where the dynamic surface tension is increased by addition of the cationic surfactant, although the overall concentration is increased. This unexpected behavior is explained by partial solubilization of free SDS molecules into micelles formed by SDS/DTAB complexes. With increasing overall concentration, when eventually the CMC of SDS is reached, the anionic/cationic complex itself is solubilized by SDS micelles. Finally, no complex micelles, which for their part can solubilize an excess of SDS molecules, are present. Hence, the dynamic properties of the solution are no longer influenced by the depletion of SDS molecules and the mixture tends to behave like a pure SDS solution. PMID:14583225

  17. DFT study of the chlorine promotion effect on the ethylene adsorption over iron clusters.

    PubMed

    Pahlavan, Farideh; Pakiari, Ali H

    2016-05-01

    This work explores how electronic perturbations induced by chlorine atoms can enhance the activity of iron toward ethylene. The metal clusters include Fen (n=2-4), in which each adatom (Cl) has an inclination to be adsorbed at the bridge site with electrostatic interaction. Ethylene adsorption over pure and chlorine-doped FenClm (n,m≤4) clusters is analyzed using density functional theory (DFT) calculations, in π and di-σ adsorption modes. One of the interesting features is that the adsorption mode of ethylene changes by going from trimers to tetramers. Ethylene never orients toward di-σ mode for FeFe bond in Fe2 and Fe3 series, while this orientation is preferred in tetramers. Our results demonstrate that the progressive change in the ethylene adsorption could not be sustained with increasing portion of chlorine in metal cluster. In this study, we attempt to provide a sensible justification for this phenomenon by the natural bond orbital (NBO) and quantum theory of atoms-in-molecules (QTAIM) analyses. PMID:27041445

  18. Infrared spectroscopic studies of galvanic effect influence on surface modification of sulfide minerals by surfactant adsorption.

    PubMed

    Mielczarski, Ela; Mielczarski, Jerzy A

    2005-08-15

    The influence of interaction between mineral components in natural mixtures on the adsorption of organic and inorganic species on the mineral surfaces is recognized. However, the surface phenomena have been meagerly investigated. In this study the formation of different surface species of surfactant (amyl xanthate, C5H11OC(S)S-) adsorbed on FeS2, PbS, and CuFeS2 has been spectroscopically investigated in single-mineral and complex systems. The type and amount of adsorbed species were determined directly on each mineral surface by infrared external reflection spectroscopy. Galvanic interaction between grains of different minerals could have tremendous consequence on the adsorption of surfactants on each mineral component and their future reactivity. The detected changes are dramatic, from no adsorption to the formation of several layers of hydrophobic or hydrophilic surface products depending on which minerals are in contact. It has been documented that even very short contact time between different mineral grains by collision is sufficient to produce dramatic modification of the surface composition and structure. The results obtained indicate clearly that the observations and conclusions aboutthe surfactant adsorption made in a single mineral system cannot be simply extrapolated to describe the real situation in natural multicomponent mineral systems. The obtained information on sulfide mineral interaction in complex systems is indispensable to understand processes taking place in nature at mineral-water interfaces (dissolution of heavy metals). An additional benefit is the improved ability to design efficient separation processes of these minerals. PMID:16173571

  19. 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.

  20. 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.

  1. Formaldehyde molecule adsorption on the doped monolayer MoS2: A first-principles study

    NASA Astrophysics Data System (ADS)

    Ma, Dongwei; Ju, Weiwei; Li, Tingxian; Yang, Gui; He, Chaozheng; Ma, Benyuan; Tang, Yanan; Lu, Zhansheng; Yang, Zongxian

    2016-05-01

    Based on first-principles calculations, formaldehyde (H2CO) adsorption on the pristine monolayer MoS2 and that doped with Cl, P, or Si was theoretically studied to explore the potential of the MoS2 sheets as H2CO gas sensors. It is found that under Mo-rich conditions it is viable for Cl to be filled into the S vacancies acting as n-type dopant and for P and Si acting as p-type dopants. The results on the H2CO adsorption on the pristine and the Cl-doped monolayer MoS2 indicate that both are insensitive to H2CO. In contrast, H2CO exhibits strong adsorption on the P or Si-doped monolayer MoS2. And there are large electron transfer from the P or Si-doped monolayer MoS2 to the H2CO and obvious change in the electronic densities of states of both systems induced by the H2CO adsorption. These suggest that P and Si can be appropriate dopants filled into MoS2 sheets for detecting H2CO molecule.

  2. 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. PMID:24603029

  3. 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. PMID:25031081

  4. Adsorption of methyl orange and salicylic acid on a nano-transition metal composite: Kinetics, thermodynamic and electrochemical studies.

    PubMed

    Arshadi, M; Mousavinia, F; Amiri, M J; Faraji, A R

    2016-12-01

    In this work synthesis of Mn-nanoparticles (MnNPs) supported on the Schiff base modified nano-sized SiO2Al2O3 mixed-oxides (Si/Al) and its implementation as an adsorbent for the removal of organic pollutions such as methyl orange (MO) and salicylic acid (SA) was investigated. Si/Al were functionalized by grafting Schiff base ligand and in the next step, MnNPs were prepared over the modified nano sol-gel Si/Al. Structures and adsorption characteristics of the obtained organometallic-modified SiO2/Al2O3 mixed oxide were studied by several methods such as elemental analysis, diffuse reflectance UV-vis spectroscopy, FT-IR spectroscopy, nitrogen adsorption/desorption, scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray (EDX), inductively coupled plasma (ICP-AES), Electron Paramagnetic Resonance (EPR), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). EPR data of the immobilized manganese ions resulted that the transition state of active sites in the nano-adsorbent are in the form of Mn(II) ions at the surface. The adsorption properties of heterogeneous Mn(II) ions showed that this nano-adsorbent has very good potential to remove MO and SA ions from aqueous solution. The removal efficiency of the SAPAS@MnNPs towards MO reached out to 89.3 and 29.1% and for SA approached to 54.6 and 18.9% at 150 and 500mg/dm(3) initial organic pollution concentrations, respectively. To investigate the adsorption kinetic of Mn(II) ions onto the nano-sized support, pseudo first and pseudo second order kinetics, and the Freundlich, Langmuir and Langmuir-Freundlich isotherm models have also been applied to the equilibrium adsorption data. The contact time to obtain equilibrium for maximum adsorption capacity was 45min. The adsorption process was spontaneous and endothermic in nature and it was well explained with pseudo-second-order kinetic model. No remarkable loss of removal capacity even after 8th times regeneration

  5. [Synthesis and Study on Adsorption Property of Congo Red Molecularly Imprinted Polymer Nanospheres].

    PubMed

    Chang, Zi-qiang; Chen, Fu-bin; Zhang, Yu; Shi, Zuo-long; Yang, Chun-yan; Zhang, Zhu-jun

    2015-07-01

    Molecularly imprinted polymer nanospheres (MIP) were prepared with Congo red as the template, methacrylic acid (MAA) as a functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross linker, azodiisobutyronitrile (AIBN) as an initiator, and acetonitrile as the porogen by precipitation polymerization. The morphology of MIP was characterized by SEM and TEM which showed that the diameter of MIP was nanometer grade (90 nm) and the shape was homogeneous. The specific surface area and pore volumes of MIP and NIP were examined through Brunauer-Emett-Teller method of nitrogen adsorption experiments. Then, the adsorption and selective recognition ability of MIPs were evaluated using the equilibrium rebinding experiments. The results indicated that the prepared MIP showed a good selectivity recognition ability to its template. It concluded that MIP could be employed as an effective material for removing Congo red from waste water. PMID:26489326

  6. First-principles study of Sb adsorption on Ag (110)(2×2)

    SciTech Connect

    Nie, JL; Xiao, H Y.; Zu, Xiaotao; Gao, Fei

    2006-08-01

    The adsorption of antimony atom on the Ag(110) surface has been studied within the density functional theory framework. It was turned out that Sb-Ag surface alloy was formed in which Sb atoms substitute Ag atom in the outermost layer and subsurface site absorption was not preferred, suggesting that Sb is well segregated to the surface. Geometric analysis showed that rumpling between substitutional Sb and Ag in the alloy surface is negligible. These results are found to agree well with the experimental finding of Nascimento et al. [Surf. Sci. 572 (2004) 337]. In addition, investigation of the diffusion of Ag atom on bare and Sb-covered Ag(110) surface showed that Ag adatoms will jump along the so call in-channel direction and Sb substitution has little effect on the diffusion of Ag adatoms on Ag(110) surface. Such diffusion behavior was found to be different from that of Ag adatoms on Ag(111) surface, where the diffusion energy barrier was reported to be significantly increased upon Sb substitution [Phys. Rev. Lett. 73 (1993) 2437].

  7. Surface Characterization and in situ Protein Adsorption Studies on Carbene-Modified Polymers.

    PubMed

    Nelson, Geoffrey W; Parker, Emily M; Singh, Kulveer; Blanford, Christopher F; Moloney, Mark G; Foord, John S

    2015-10-13

    Polystyrene thin films were functionalized using a facile two-step chemical protocol involving carbene insertion followed by azo-coupling, permitting the introduction of a range of chemical functional groups, including aniline, hexyl, amine, carboxyl, phenyl, phosphonate diester, and ethylene glycol. X-ray photoelectron spectroscopy (XPS) confirmed the success of the two-step chemical modification with a grafting density of at least 1/10th of the typical loading density (10(14)-10(15)) of a self-assembled monolayer (SAM). In situ, real-time quartz crystal microbalance with dissipation (QCM-D) studies show that the dynamics of binding of bovine serum albumin (BSA) are different at each modified surface. Mass, viscoelastic, and kinetic data were analyzed, and compared to cheminformatic descriptors (i.e., c log P, polar surface area) typically used for drug discovery. Results show that functionalities may either resist or adsorb BSA, and uniquely influence its adsorption dynamics. It is concluded that carbene-based surface modification can usefully influence BSA binding dynamics in a manner consistent with, and more robust than, traditional systems based on SAM chemistry. PMID:26391812

  8. An EXAFS study on the effects of natural organic matter and the expandability of clay minerals on cesium adsorption and mobility

    NASA Astrophysics Data System (ADS)

    Fan, Q. H.; Tanaka, M.; Tanaka, K.; Sakaguchi, A.; Takahashi, Y.

    2014-06-01

    The relationship between cesium (Cs) adsorption on clay minerals with various expandabilities and Cs mobility in environment was investigated using sequential extraction, batch adsorption, X-ray diffraction (XRD), generalized adsorption model (GAM), and Cs LIII-edge extended X-ray absorption fine structure (EXAFS) analyses with molecular simulations using the density functional theory (DFT). In particular, the difference between the affinities of illite (non-expansion) and vermiculite (intermediate expansion) for Cs and the effect of humic acid (HA) addition on the Cs/clay mineral system were highlighted in this study. These two factors affect Cs mobility and bioavailability in surface soil and sediments. The batch adsorption results showed that Cs adsorption was inhibited to some extent in the ternary clay + HA + Cs system because of (i) the blocked access of Cs to the frayed edge site (FES) and type II site [inner-sphere (IS) complex in GAM] by HA, and (ii) the reduced availability of the interlayer site in vermiculite. EXAFS analysis further confirmed that the adsorbed Cs in clay minerals was drastically changed by the sequential addition of HA. In addition, the dominant IS complex in the illite + Cs and illite + Cs + HA systems (in which HA was added after Cs adsorption on illite) can be converted to the outer-sphere (OS) complex largely in the illite + HA + Cs system (in which HA was added prior to Cs adsorption). These results are consistent with the sequential extraction and GAM results. The IS complex of dehydrated Cs+ mainly formed at the FES and interlayer site on illite (non-expansion) without resulting in any illite structural changes. However, on vermiculite (intermediate expansion), the dehydrated Cs+ can be adsorbed as an IS complex associated with the siloxane group of the di-trigonal cavity in the tetrahedral SiO4 sheet. This adsorption is accompanied by collapse of the layer, which can be easily coated by HA molecules to prevent Cs fixation

  9. Theoretical study of heavy metal Cd, Cu, Hg, and Ni(II) adsorption on the kaolinite(0 0 1) surface

    NASA Astrophysics Data System (ADS)

    Zhao, Jian; He, Man-Chao

    2014-10-01

    Heavy metal pollution is currently of great concern because it has been recognized as a potential threat to air, water, and soil. Adsorption was one of the most popular methods for the removal of heavy metal. The adsorption of heavy metal Cd, Cu, Hg, and Ni(II) atoms on the hydroxylated (0 0 1) surface of kaolinite was investigated using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics were systematically studied for a wide range of coverage Θ [from 0.11 to 1.0 monolayers (ML)] and adsorption sites. The most stable among all possible adsorption sites for Cd(II) atom was the two-fold bridge site followed by the one-fold top site, and the top site was the most favorite adsorption site for Cu and Ni(II) atoms, while the three-fold hollow site was the most stable adsorption site for Hg(II) atom followed by the two-fold bridge site. The adsorption energy increases with the coverage for Cd, Cu, and Hg(II) atoms, thus indicating the higher stability of surface adsorption and a tendency to the formation of adsorbate islands (clusters) with increasing the coverage. However, the adsorption energy of Ni(II) atoms decreases when increasing the coverage. The adsorption capabilities of the kaolinite clay for the heavy metal atoms were in the order of Ni > Cu > Cd > Hg(II). The other properties of the Cd, Cu, Hg, and Ni(II)/kaolinite(0 0 1) system including the different charge distribution, the lattice relaxation, and the electronic density of states were also studied and discussed in detail.

  10. A mechanistic study of H2S adsorption and dissociation on Cu2O(1 1 1) surfaces: Thermochemistry, reaction barrier

    NASA Astrophysics Data System (ADS)

    Zhang, Riguang; Liu, Hongyan; Li, Jingrui; Ling, Lixia; Wang, Baojun

    2012-10-01

    The interaction mechanism of H2S with different Cu2O(1 1 1) surfaces, including perfect, oxygen-vacancy and sulfur-containing surfaces, have been systematically studied using periodic density functional calculations. Different kinds of possible modes of H2S, as well as the resultant SH and S species adsorbed on these surfaces are identified. Two types of pathways via molecular and dissociative adsorption processes are mapped out. Our results show that sulfur species (H2S, SH and S) interact with surface Cu centers; H2S exists in the form of molecular adsorption on perfect and sulfur-containing surfaces; the dissociative adsorption of H2S occurs predominantly on oxygen-vacancy surface, suggesting that oxygen-vacancy exhibits a strong catalytic activity toward the dissociation of H2S. On the other hand, the dissociation processes of the molecular and dissociative adsorption H2S, leading to final product S species on these Cu2O(1 1 1) surfaces, show that the overall dissociation process is exothermic. Meanwhile, with respect to molecular adsorption H2S, the activation barrier and reaction energy of the overall dissociation process on perfect and oxygen-vacancy surfaces indicate that H2S can easily dissociate into S species. Importantly, in the case of dissociative adsorption of H2S, the dissociation of H2S into S species is a spontaneous process with respect to molecular adsorption H2S. However, on sulfur-containing surface, the presence of surface S atom goes against the Hsbnd S bond-breaking process both thermodynamically and kinetically. Finally, the vibrational frequencies for the adsorbed H2S, SH and S species on these surfaces have been obtained, which can be applied to guide surface vibrational spectroscopy in experiment.

  11. Removal of phenol from aqueous solutions by adsorption.

    PubMed

    Roostaei, Nadia; Tezel, F Handan

    2004-02-01

    Experiments have been conducted to examine the liquid-phase adsorption of phenol from water by silica gel, HiSiv 3000, activated alumina, activated carbon, Filtrasorb-400, and HiSiv 1000. Experiments were carried out for the analysis of adsorption equilibrium capacities and kinetics. The adsorption isotherm model of the Langmuir-Freundlich type was the best to describe adsorption equilibrium data for phenol for the adsorbents studied. Results of kinetic experiments indicated that HiSiv 1000 had the highest rate of adsorption among the adsorbents studied and therefore more detailed studies were carried out with this adsorbent. The influence of particle size, temperature, and thermal regeneration on adsorption of phenol by HiSiv 1000 was evaluated. From particle size experiments it appeared that adsorption capacity of HiSiv 1000 did not change by changing the particle size, but the rate of adsorption decreased considerably by increasing the particle size. The effect of temperature on adsorption was studied by determining equilibrium isotherms for HiSiv 1000 at 25, 40, and 55 degrees C. The results showed that adsorption capacity decreased with increasing temperature. Thermal regeneration of HiSiv 1000 was performed at 360 degrees C. It was observed that adsorption capacity of HiSiv 1000 did not change after 14 regeneration cycles. Equilibrium experiments showed that the adsorption capacities of activated carbon and Filtrasorb-400 were several times higher than that of HiSiv 1000. PMID:15160741

  12. 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

    , H. Nakamura, and M. Machida, Mechanism of Strong Affinity of Clay Minerals to Radioactive Cesium : First-Principles Calculation Study for Adsorption of Cesium at Frayed Edge Sites in Muscovite, Journal of the Physical Society of Japan 82, 033802 (2013).

  13. Adsorption Studies with AFM of Human Plasma Fibrinogen on Silicon Surfaces

    NASA Astrophysics Data System (ADS)

    Gause, Sheena; Kong, Wendy; Rowe

    2007-11-01

    Fibrinogen (FGN) plays an important role in the clotting of blood. Human plasma fibrinogen (HPF) is a protein that readily adsorbs on biomaterial surfaces. The purpose of this experiment was to use the Atomic Force Microscope to study the adsorption of HPF molecules or FGN onto several silicon surfaces with different orientations and resistivities. The size of the FGN molecules found to be somewhat different of Si(111), (100) and (110) were compared to the size of the FGN molecules in solution (45 nm in length, the end dynodes measures to be 6.5 nm in diameter, and the middle dynode measures to be 5 nm in diameter. For this study, the CPR (Thermo-microscope) Atomic Force Microscope (AFM) was used to observe the amount of fibrinogen molecules adsorbed by Si (111) with a resistance of .0281-.0261 φ cm, Si (111) with a resistance of 1 φ cm, Si (100), and Si (110) surfaces. In finding any single fibrinogen molecules, the appropriate image scans and measurements were taken. After collection and analysis of the data, it was found from AFM that the fibrinogen molecules found on Si (110) mostly resembled fibrinogen molecules found in solution. The other images showed that the fibrinogen molecules adsorbed on Silicon substrates is significantly greater (˜10-20 %) than those in solution.

  14. A simple statistical mechanical approach for studying multilayer adsorption of interacting rigid polyatomics

    NASA Astrophysics Data System (ADS)

    García, G. D.; Sánchez-Varretti, F. O.; Romá, F.; Ramirez-Pastor, A. J.

    2009-04-01

    A simple statistical mechanical approach for studying multilayer adsorption of interacting rigid molecular chains of length k ( k-mers) has been presented. The new theoretical framework has been developed on a generalization in the spirit of the lattice-gas model and the classical Bragg-Williams (BWA) and quasi-chemical (QCA) approximations. The derivation of the equilibrium equations allows the extension of the well-known Brunauer-Emmet-Teller (BET) isotherm to more complex systems. The formalism reproduces the classical theory for monomers, leads to the exact statistical thermodynamics of interacting k-mers adsorbed in one dimension, and provides a close approximation for two-dimensional systems accounting multisite occupancy and lateral interactions in the first layer. Comparisons between analytical data and Monte Carlo simulations were performed in order to test the validity of the theoretical model. The study showed that: (i) the resulting thermodynamic description obtained from QCA is significantly better than that obtained from BWA and still mathematically handable; (ii) for non-interacting k-mers, the BET equation leads to an underestimate of the true monolayer volume; (iii) attractive lateral interactions compensate the effect of the multisite occupancy and the monolayer volume predicted by BET equation agrees very well with the corresponding true value; and (iv) repulsive couplings between the ad-molecules hamper the formation of the monolayer and the BET results are not good (even worse than those obtained in the non-interacting case).

  15. Methanol adsorption on magnesium oxide surface with defects: a DFT study

    NASA Astrophysics Data System (ADS)

    Branda, M. M.; Ferullo, R. M.; Belelli, P. G.; Castellani, N. J.

    2003-03-01

    The methanol adsorption on several defects of the magnesium oxide surface were studied. Structural and electronic study with geometrical optimization and natural bond orbital (NBO) analysis were performed using a density functional theory (DFT) method. Oxygen and magnesium with different coordination numbers have very different reactivity in this surface producing dissociated and non-dissociated species. These results are in agreement with infrared spectroscopy observations where CH 3OH, OCH 3 and OH species were found in defective MgO surfaces.

  16. Charge effect in S enhanced CO adsorption: A theoretical study of CO on Au, Ag, Cu, and Pd (111) surfaces coadsorbed with S, O, Cl, and Na

    NASA Astrophysics Data System (ADS)

    Gan, Li-Yong; Zhao, Yu-Jun

    2010-09-01

    The extraordinary sulfur enhanced CO adsorption on Au surface creates curiosity to many scientists in the field, and is expected to have potential applications in catalyst design. In this work, we have investigated the interactions of the coadsorption of CO and various adatoms X (X=Na, S, O, and Cl) on Au and Pd(111) surfaces and made further comparison with CO adsorption on charged Au and Pd surfaces by a first-principles study. We find out that the enhancement of CO adsorption by S on Au originates from S-induced positive polarization of Au surface. The d band of metal atoms in the positively polarized Au surface shifts up toward the Fermi level (EF) without remarkable changes of its shape and occupation. In contrast, in the negatively polarized Au(111) surface, achieved by electropositive adatom such as Na adsorption or artificially adding additional electrons to the substrate, d bands shift down relative to EF, and thus CO adsorption is weakened. Further study of CO coadsorption with X on two other noble metal (Ag and Cu) surfaces manifests that Ag shows the same behavior as Au does, while the situation of Cu is just between that on Au and Pd. It suggests that the extraordinary S-induced enhancement of CO adsorption on Au/Ag, different from other transition metals (TMs), ultimately results from the inertness of d bands buried below EF. The S-induced charge can introduce a significant d band shift on Au/Ag with respect to EF due to their narrow density of states at EF and thus strengthens CO adsorption subsequently.

  17. 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). PMID:23399273

  18. Studies on adsorption of carnosine on silver nanoparticles by SERS

    NASA Astrophysics Data System (ADS)

    Thomas, S.; Biswas, N.; Malkar, V. V.; Mukherjee, T.; Kapoor, S.

    2010-05-01

    The surface-enhanced Raman scattering (SERS) studies of L-carnosine was carried out in aqueous silver sol at pH ˜ 9 and compared with the normal Raman spectrum of the molecule. The experimentally observed Raman bands were assigned based on the results of DFT calculations. Significant changes in the relative intensity are seen in the SERS spectrum when compared to the normal Raman spectrum. The studies suggest that the interaction of carnosine is primarily through the carboxylate group with the imidazole ring in an upright position with respect to the silver surface and the alanine moiety assuming a parallel orientation with the surface where NH 2 group is close to the silver surface.

  19. In situ photoelectron spectroscopy study of water adsorption on model biomaterial surfaces

    SciTech Connect

    Salmeron, Miquel; Ketteler, Guido; Ashby, Paul; Mun, B.S.; Ratera, I.; Bluhm, Hendrik; Kasemo, B.; Salmeron, Miquel

    2007-07-10

    Using in situ photoelectron spectroscopy at near ambient conditions, we compare the interaction of water with four different model biomaterial surfaces: self-assembled thiol monolayers on Au(111) that are functionalized with methyl, hydroxyl, and carboxyl groups, and phosphatidylcholine (POPC) lipid films on Silicon. We show that the interaction of water with biomaterial surfaces is mediated by polar functional groups that interact strongly with water molecules through hydrogen bonding, resulting in adsorption of 0.2-0.3 ML water on the polar thiol films in 700 mTorr water pressure and resulting in characteristic N1s and P2p shifts for the POPC films. Provided that beam damage is carefully controlled, in situ electron spectroscopy can give valuable information about water adsorption which is not accessible under ultra-high vacuum conditions.

  20. Modified SBA-15 as the carrier for metoprolol and papaverine: Adsorption and release study

    SciTech Connect

    Moritz, MichaL; Laniecki, Marek

    2011-07-15

    A series of modified SBA-15 materials were applied in drug delivery systems. The internal surface of siliceous hexagonal structure of SBA-15 was modified with different amount of (3-mercaptopropyl)trimethoxysilane (MPTMS) and oxidized in the presence of hydrogen peroxide. The sulfonated material was loaded with metoprolol tartrate or papaverine hydrochloride. Both drugs indicated strong chemical interaction with modified mesoporous surface. The characteristic of the obtained materials was performed with XRD and DRUV-vis spectrometry, themogravimetry and nitrogen adsorption (BET) measurements. The obtained results show that modification of the mesoporous materials leads towards significant decrease of the drug delivery rate. - Graphical abstract: XRD and DSC of the -SO{sub 3}H modified SBA-15 loaded with metoprolol. Highlights: > Modification of SBA-15 internal channels with SO{sub 3}H groups. > Adsorption of metoprolol and papaverine on modified SBA-15. > Uniform and homogeneous distribution of the drugs inside the mesoporous structure of SBA-15. > Release of the supported drugs.

  1. Adsorption of diazinon and hinosan molecules on the iron-doped boron nitride nanotubes surface in gas phase and aqueous solution: A computational study

    NASA Astrophysics Data System (ADS)

    Farmanzadeh, Davood; Rezainejad, Hamid

    2016-02-01

    In this study, the geometric structures and electronic properties of two widely used organophosphorus pesticides, diazinon and hinosan, boron nitride nanotubes (BNNTs) and Fe doped boron nitride nanotubes (FeBNNTs) as adsorbents of these pesticides are studied by density functional theory calculation as well as dispersion correction by Grimme method. The results show that Fe doping in boron nitride nanotubes structures increases the potency of nanotubes to adsorb mentioned pesticides, especially when Fe atom located instead of N atom. Comparing the adsorption energies of diazinon on FeBNNTs with ones for hinosan demonstrate that the adsorption of hinosan is energetically more favorable by FeBNNTs. Assessment of adsorption energies in aqueous solution confirmed significant decrease in their values compared to ones in gaseous phase. However, the adsorption of diazinon and hinosan on both BNNTs and FeBNNTs are exothermic. So, BNNTs and FeBNNTs may be promising candidates as appropriate adsorbents for adsorbing diazinon and hinosan. Also, the results of calculations have revealed that van der Waals interaction energies are remarkably large in adsorption of diazinon and hinosan on all boron nitride nanotubes.

  2. The behavior of the adsorption of cytochrome C on lipid monolayers: A study by the Langmuir-Blodgett technique and theoretical analysis.

    PubMed

    Li, Junhua; Sun, Runguang; Hao, Changchun; He, Guangxiao; Zhang, Lei; Wang, Juan

    2015-10-01

    Cytochrome c (Cyt c) is an essential component of the inner mitochondrial respiratory chain because of its function of transferring electrons. The feature is closely related to the interaction between Cyt c and membrane lipids. We used Langmuir-Blodgett monolayer technique combined with AFM to study the interaction of Cyt c with lipid monolayers at air-buffer interface. In our work, by comparing the mixed Cyt c-anionic (DPPS) and Cyt c-zwitterionic (DPPC/DPPE) monolayers, the adsorption capacity of Cyt c on lipid monolayers is DPPS>DPPE>DPPC, which is attributed to their different headgroup structures. π-A isothermal data show that Cyt c (v=2.5 μL) molecules are at maximum adsorption quantity on lipid monolayer. Moreover, Cyt c molecules would form aggregations and drag some lipids with them into subphase if the protein exceeds the maximum adsorption quantity. π-T curve indicates that it takes more time for Cyt c molecular conformation to rearrange on DPPE monolayer than on DPPC. The compressibility study reveals that the adsorption or intermolecular aggregation of Cyt c molecules on lipid monolayer will change the membrane fluidization. In order to quantitatively estimate Cyt c molecular adsorption properties on lipid monolayers, we fit the experimental isotherm with a simple surface state equation. A theoretical model is also introduced to analyze the liquid expanded (LE) to liquid condensed (LC) phase transition of DPPC monolayer. The results of theoretical analysis are in good agreement with the experiment. PMID:26071844

  3. 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. PMID:26017810

  4. Theoretical study of the adsorption of CHO radicals on hexagonal boron nitride sheet: Structural and electronic changes

    NASA Astrophysics Data System (ADS)

    Tian, Yu; Pan, Xiao-fan; Liu, Yue-jie; Zhao, Jing-xiang

    2014-03-01

    It is well known that pristine hexagonal boron nitride sheet (h-BN sheet) exhibits large insulating band gap, thus hindering its application to some extent. In this regard, surface chemisorption of certain groups on h-BN sheet is shown to be the most popular method to tune its band gap and thus modify its electronic properties. In the present work, we performed density functional theory (DFT) calculations to study the adsorption of CHO radicals with different coverages on h-BN sheet. Particular attention is paid to explore the effects of CHO adsorption on the geometrical structures and electronic properties of h-BN sheet. The results indicate that the adsorption of a single CHO radical on pristine h-BN sheet is very weak with a negligible adsorption energy (-0.09 eV). In contrast, upon adsorption of more CHO radicals on h-BN sheet, these adsorbates prefer to adsorb in pairs on the B and the nearest N atoms from both sides of h-BN sheet. An energy diagram of the average adsorption energy of CHO radicals on h-BN sheet as a function of its coverage indicates that up to 20 CHO radicals (40%) can be attached to h-BN sheet with the adsorption energy of -0.29 eV. More importantly, the adsorption of CHO radicals can induce certain impurity states within the band gap of h-BN sheet, thus reducing the band gap and enhancing its electrical conductivity.

  5. 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). PMID:27612776

  6. Experimental and Theoretical Studies of Wetting and Multilayer Adsorption

    NASA Technical Reports Server (NTRS)

    Moldover, M. R.; Schmidt, J. W.; Cahn, J. W.; Kayser, R. F.

    1985-01-01

    The recent work with partially miscible binary liquid mixtures has established that the structure of the liquid-vapor interface can undergo a first-order phase transition from incomplete to complete wetting of the vapor as the temperature is raised. A discontinuity in the change of interfacial tension as a function of temperature at the phase transition has been predicted to occur in many systems and to play an important role in the growth of uniform composites from alloy melts at monotectic points. These measurements are the first to establish the order of the transition. Studies of capillary rise in SF6 in a unique interferometer have led to the first measurements of the thickness of wetting layers (or equivalently, multilayer adsorbed films) on a solid surface near a liquid-vapor critical point. Instabilities in wetting layers were observed. A theory for the instabilities is being developed and will be checked by both static and dynamic optical experiments. The effect of gravity on the apparent thickness of interfaces (as measured by ellipsometry) is under study.

  7. Adsorption studies of C6H6 on Cu (111), Ag (111), and Au (111) within dispersion corrected density functional theory

    NASA Astrophysics Data System (ADS)

    Chwee, T. S.; Sullivan, M. B.

    2012-10-01

    The adsorption energies and changes in surface work functions for benzene on unreconstructed Cu(111), Ag (111), and Au (111) at low coverages have been studied within the framework of dispersion corrected Kohn-Sham density functional theory. Corrections to account for long range dispersive effects between the adsorbate and metal substrate were incorporated via the exchange-hole dipole moment method of Becke and Johnson [J. Chem. Phys. 123, 154101 (2005), 10.1063/1.2065267]. We show that the dispersion corrected calculations yield significantly improved adsorption energies and work function shifts that are in good agreement with experimental values.

  8. 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.

  9. A quantitative study of aromatic amine permeation through protective gloves using amine adsorptive pads.

    PubMed

    Vo, E; Berardinelli, S P; Hall, R C; El Ayouby, N

    2000-01-01

    A quantitative study of aromatic amine permeation through a glove material using Permea-Tec aromatic amine pads, used for the detection of chemical breakthrough of protective clothing, was performed for aniline following the microwave extraction process and gas chromatographic analysis. Aniline exhibited >99% adsorption on the pads at a spiking level of 1.94 mg (1.9 microL). Aniline showed recoveries from 65 to 89% (RSD < or =5.6%) over the range 1.1-1.9 microL (1.12-1.94 mg) of aniline applied to pads. The modified ASTM F739 and direct permeability testing procedures were used to determine breakthrough times for five protective glove materials using aniline as a challenge chemical. Breakthrough times for six protective gloves were determined, ranging from 182 sec to 82 min. The quantitative concentration of aniline on the pads following permeation through the gloves also was determined, ranging from 0.53 to 0.55 mg/cm2 (1.79-1.88 mg/pad). PMID:11192217

  10. Adsorption of Acetylene on a Pd-Pb Bimetallic Surface — a Theoretical Study

    NASA Astrophysics Data System (ADS)

    Ferullo, R. M.; Touroude, R.; Castellani, N. J.

    A semiempirical molecular orbital study of acetylene adsorption over Pd(111) and Pd3Pb(111) has been performed. A strong negative effect of Pb atoms on Pd chemisorptive strength was observed in the alloy. This behavior is related to a lower hybridization between acetylene π* and Pd orbitals when this mental interacts with Pb. Moreover this negative effect of Pb is of a strong local character.

  11. 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. PMID:23108613

  12. Studies of liquid adsorption, condensation and surface conductivity in porous media

    NASA Astrophysics Data System (ADS)

    Qi, Hao

    In the petroleum industry, accurate estimates of hydrocarbon reserve and its producibility are without a doubt among the most important issues. Quantitative estimates require the knowledge of three basic parameters of the rock formation: the porosity φ, the water saturation S w and the permeability k. Electrical conductivity is one of the most commonly made measurements used to deduce these quantities. Some empirical relationships used to make such estimates are quite well established and understood, however, many still lack a sound scientific foundation. Systematic laboratory investigation and theoretical understanding of the underlying petrophysics are much needed. This dissertation consists of three projects aimed at understanding both the surface conductivity observed in shaly sandstone, and the related phenomena of molecular adsorption on heterogeneous surfaces. In the first project, we carried out nitrogen adsorption experiments on three shale samples whose fractal dimensions had been previously characterized by small angle scattering (SANS). We found that analyzing the adsorption isotherm data according to the available theoretical predictions always resulted in D values that are lower than those obtained by SANS. The second project, a numerical simulation of adsorption on fractal surfaces, was designed to understand the origin of discrepancies revealed in the first project. We found that the interplay between van der Waals adsorption and capillary condensation always leads to a crossover between the two theoretical limits. The simulated isotherms exhibit the same general features we observed in our experimental data. The third project was aimed at understanding the surface conduction in porous media. We isolated the surface conductivity by growing water layers on the surface with water adsorption isotherm technique. Some of our results indicate that AC impedance measurement could let us determine the surface conductivity and separate it from that of the

  13. 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.

  14. In situ ATR-FTIR spectroscopic study of adsorption of perchlorate, sulfate, and thiosulfate ions onto chromium(III) oxide hydroxide thin films

    SciTech Connect

    Degenhardt, J.; McQuillan, A.J.

    1999-06-22

    A thin chromium oxide hydroxide colloid film has been used as a model of the passive stainless steel surface for studies of anion adsorption from aqueous solutions. The adsorption of perchlorate, sulfate, and thiosulfate ions has been investigated by in situ attenuated total reflection infrared (ATR-IR) spectroscopy. Surface charge was monitored from the surface excess concentrations of tetramethylammonium ions and of perchlorate ions using the infrared spectroscopic STIRS technique. The colloid film showed a high positive charge at low pH and a low negative charge at high pH. The adsorption of sulfate was only observed for a positive surface charge. The infrared spectrum of adsorbed sulfate coordination to surface Cr(III) ions. Thiosulfate gave adsorption behavior analogous to sulfate. Adsorption isotherms for sulfate and for thiosulfate were determined from infrared spectral data, and Langmuir binding constants of (2.3 {plus{underscore}minus} 0.4) x 10{sup 5} and (1.4 {plus{underscore}minus} 0.4) x 10{sup 5} M{sup {minus}1} were obtained for the respective adsorbates. The lack of chemical binding of sulfate and of thiosulfate to the chromium oxide hydroxide surface may be part of the basis for the corrosion-promoting properties of these ions at stainless steel surfaces.

  15. A study of interaction potentials for H2 adsorption in Single Walled Nano Tubes: a possible way to more realistic predictions.

    PubMed

    Lerario, Marco; Magalhães, Alexandre L

    2014-06-01

    A comparative analysis of interaction potentials, classified according to the parametrization method, namely Lorentz-Berthelot rules, semi-empirical or ab initio calculations, found their energy depths to scale, respectively, to ca 30K, ca 40K, and ca 60K. We draw the Potential Energy Surfaces (PESs) for a hydrogen probe molecule inside a Carbon Nano-Tube (CNT): it is shown that the adsorption energy increases with the hard radius of the interaction potential and decreases as the CNT pore enlarges. This is valid just for low-medium pressures, when hydrogen repulsions are negligible. If not, adsorption is driven by H2-H2 hard radius despite all other parameters. Monte Carlo (MC) simulations, following the Gibbs Ensemble (GE) in high density conditions, confirm that the thermodynamic equilibrium of an order-disorder phase transition show no changes throughout any of the studied potentials. We also analyse, in the Grand Canonical (GC) ensemble, the geometric and structural characteristics of square lattice bundles of Single Walled Nano Tubes (SWNTs) with regard to their influence on adsorption storage. To do so, we develop a method for independently simulate inner or outer adsorption in infinitely long nanotube lattice systems. Our results suggest a pressure range for convenient H2 storage and enlighten the influence of CNT size on adsorption performance. In addition, larger CNTs are capable to host further hydrogen layers, but only at very high pressures. PMID:24893959

  16. 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. PMID:20365027

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

    DOE PAGESBeta

    Kroning, Annika; Furchner, Andreas; Aulich, Dennis; Bittrich, Eva; Rauch, Sebastian; Uhlmann, Petra; Eichhorn, Klaus-Jochen; Seeber, Michael; Luzinov, Igor; Kilbey, S. Michael; et al

    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

  18. Dopamine adsorption on anatase TiO2(101): a photoemission and NEXAFS spectroscopy study.

    PubMed

    Syres, K; Thomas, A; Bondino, F; Malvestuto, M; Grätzel, M

    2010-09-21

    The adsorption of dopamine onto an anatase TiO(2)(101) single crystal has been studied using photoemission and NEXAFS techniques. Photoemission results suggest that the dopamine molecule adsorbs on the surface in a bidentate geometry, resulting in the removal of band gap states in the TiO(2) valence band. Using the searchlight effect, carbon K-edge NEXAFS spectra indicate that the phenyl rings in the dopamine molecules are orientated normal to the surface. A combination of experimental and computational results indicates the appearance of new unoccupied states arising following adsorption. The possible role of these states in the charge-transfer mechanism of the dopamine-TiO(2) system is discussed. PMID:20735026

  19. 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. PMID:27399852

  20. 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.

  1. 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. PMID:26010751

  2. 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.

  3. Shear rheology of mixed protein adsorption layers vs their structure studied by surface force measurements.

    PubMed

    Danov, Krassimir D; Kralchevsky, Peter A; Radulova, Gergana M; Basheva, Elka S; Stoyanov, Simeon D; Pelan, Eddie G

    2015-08-01

    The hydrophobins are proteins that form the most rigid adsorption layers at liquid interfaces in comparison with all other investigated proteins. The mixing of hydrophobin HFBII with other conventional proteins is expected to reduce the surface shear elasticity and viscosity, E(sh) and η(sh), proportional to the fraction of the conventional protein. However, the experiments show that the effect of mixing can be rather different depending on the nature of the additive. If the additive is a globular protein, like β-lactoglobulin and ovalbumin, the surface rigidity is preserved, and even enhanced. The experiments with separate foam films indicate that this is due to the formation of a bilayer structure at the air/water interface. The more hydrophobic HFBII forms the upper layer adjacent to the air phase, whereas the conventional globular protein forms the lower layer that faces the water phase. Thus, the elastic network formed by the adsorbed hydrophobin remains intact, and even reinforced by the adjacent layer of globular protein. In contrast, the addition of the disordered protein β-casein leads to softening of the HFBII adsorption layer. Similar (an even stronger) effect is produced by the nonionic surfactant Tween 20. This can be explained with the penetration of the hydrophobic tails of β-casein and Tween 20 between the HFBII molecules at the interface, which breaks the integrity of the hydrophobin interfacial elastic network. The analyzed experimental data for the surface shear rheology of various protein adsorption layers comply with a viscoelastic thixotropic model, which allows one to determine E(sh) and η(sh) from the measured storage and loss moduli, G' and G″. The results could contribute for quantitative characterization and deeper understanding of the factors that control the surface rigidity of protein adsorption layers with potential application for the creation of stable foams and emulsions with fine bubbles or droplets. PMID:24828304

  4. 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

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

    PubMed

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

    2016-03-01

    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. PMID:26551224

  6. Adsorptive separation of ethylene/ethane mixtures using carbon nanotubes: a molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Tian, Xingling; Wang, Zhigang; Yang, Zaixing; Xiu, Peng; Zhou, Bo

    2013-10-01

    Ethylene/ethane separation is a very important process in the chemical industry. Traditionally, this process is achieved by cryodistillation, which is extremely energy-intensive. The adsorptive separation is an energy-saving and environmentally benign alternative. In this study, we employ molecular dynamics simulations to study the competitive adsorption of an equimolar mixture of gaseous ethane and ethylene inside single-walled carbon nanotubes (SWNTs) of different diameters at room temperature. We find that for narrow SWNTs, i.e. the (6, 6) and (7, 7) SWNTs, the selectivities towards ethane, fselec, can reach values of 3.1 and 3.7, respectively. Such high selectivities are contrary to the opinion of many researchers that the adsorptive separation of an ethylene/ethane mixture by means of dispersion interaction is difficult due to the same carbon number of ethane and ethylene. The key for our observation is that the role of dispersion interaction of ethane's additional two hydrogen atoms with the SWNT becomes significant under extreme confinement. Interestingly, the (8, 8) SWNT prefers ethylene to ethane with fselec = 0.6. For wider SWNTs, fselec converges to ∼1. The mechanisms behind these observations, as well as the kinetics of single-file nanopore filling and kinetics of confined gas molecules are discussed. Our findings suggest that efficient ethane/ethylene separation can be achieved by using bundles/membranes of SWNTs with appropriate diameters.

  7. A density functional study on adsorption and dissociation of O 2 on Ir(1 0 0) surface

    NASA Astrophysics Data System (ADS)

    Erikat, I. A.; Hamad, B. A.; Khalifeh, J. M.

    2011-06-01

    The adsorption and the reaction barrier for the dissociation of O 2 on Ir(1 0 0) surface are studied using periodic self-consistent density functional theory (DFT) calculations. Dissociative adsorption is found to be energetically more favorable compared to molecular adsorption. Parallel approaches Prl1 and Prl2 on a hollow site with the same adsorption energy of -3.93 eV for both of them are found to have the most energetically preferred sites of adsorptions among all the studied cases. Hybridization between p-O 2 and d-metal orbitals is responsible for the dissociative adsorption. The minimum energy path is determined by using the nudge elastic band method (NEB). We found that the dissociation occurs immediately and very early in the dissociation path with a small activation barrier (0.26 eV), which means that molecular adsorption of O 2 on Ir(1 0 0) surface occurs at very low temperatures; this is consistent with previous experimental and theoretical studies on Ir surfaces.

  8. First-principles study of Mn adsorption on Al4C3(0 0 0 1) surface

    NASA Astrophysics Data System (ADS)

    Yao, L. F.; Li, K.; Zhou, N. G.

    2016-02-01

    First-principle calculation based on the density functional theory was adopted to investigate the adsorption energy, stability, electronic structure and bonding of Mn atom adsorption on Al-terminated and C-terminated Al4C3(0 0 0 1) surface under 0.25 ML and 0.5 ML. Results show that the structure of Mn adsorption on C-terminated Al4C3(0 0 0 1) surface is more stable than that on Al-terminated surface according to the formation energy calculation. For Mn adsorption on Al-terminated surface, Mn is more favorable to reside at the site H1 comparing with other sites. As well, for Mn adsorption on C-terminated surface, the structure of Mn adsorption at site H‧1 is the most stable one. By analyzing the electronic structure and bonding, it is found that the mixed metallic/covalent bonds are formed between Mn atoms and Al-terminated surface, while the covalent bonds are formed between Mn atoms and C-terminated surface. According to the interlayer spacing calculation, Al4C3(0 0 0 1) surfaces are reconstructed after Mn adsorption, which in turn affect the following stacking of Mg atoms on Al4C3(0 0 0 1) surface. The above analysis provided effective theoretical support to the experimental phenomenon that high Mn content has negative influence on the heterogeneous nucleation of Al4C3 particles for α-Mg grains.

  9. Selectivity of Ni-based surface alloys toward hydrazine adsorption: A DFT study with van der Waals interactions

    NASA Astrophysics Data System (ADS)

    He, Yan-Bin; Jia, Jian-Feng; Wu, Hai-Shun

    2015-06-01

    We use dispersion corrected DFT calculations (DFT + D3) to investigate the selectivity of Ni-based surface alloys toward hydrazine adsorption. A series of Ni-M (M = Fe, Pt, Ir, Pd and Rh) alloy films were investigated, namely Ni15/M1/Ni(1 1 1), Ni14/M2/Ni(1 1 1), Ni12/M4/Ni(1 1 1) and Ni8/M8/Ni(1 1 1). Our results show that the doped atoms of Ir, Rh and Fe provide stronger adsorption sites than the Ni atom on the Ni(1 1 1) surface, while the doped atoms of Pt and Pd provide weaker adsorption sites. By analyzing the most favorable adsorption of hydrazine on Ni-M alloy surfaces we found that Ni8Fe8/Ni(1 1 1), Ni8Rh8/Ni(1 1 1), Ni15Ir1/Ni(1 1 1) and Ni14Ir2/Ni(1 1 1) present enhanced adsorption properties if compared to the pure Ni(1 1 1) surface, and seem to be better candidates for hydrazine catalysis, which are in agreement with that found by experiments. The correlation between d-band center position and adsorption energies of top modes in the Ni or doped atom has been calculated at DFT + D3 level to provide further insight into the Ni-based surface alloy properties for hydrazine adsorption.

  10. Alkali extraction of beta-d-glucans from Saccharomyces cerevisiae cell wall and study of their adsorptive properties toward zearalenone.

    PubMed

    Yiannikouris, Alexandros; François, Jean; Poughon, Laurent; Dussap, Claude-Gilles; Bertin, Gérard; Jeminet, Georges; Jouany, Jean-Pierre

    2004-06-01

    The isolated cell wall of Saccharomyces cerevisiae has some capacity to adsorb zearalenone (affinity near 30%) and reduce the bioavailability of toxins in the digestive tract. The adsorption process was quantified in vitro, and the data obtained when plotted with Hill's equation indicated a cooperative process. The model showed that the adsorption capacity was related to the yeast cell wall composition. This work focused on the role of various beta-d-glucan types in the efficacy of zearalenone adsorption by yeast cell wall and sought to elucidate some of the adsorption mechanisms. Zearalenone was mixed at 37 degrees C with a constant quantity of alkali-soluble or alkali-insoluble beta-d-glucans isolated from yeast cell walls, and the amount of adsorbed zearalenone was measured. Given that the alkali solubility of beta-d-glucans is a determining factor for their three-dimensional conformation and that the alkali-insoluble fraction had a greater affinity (up to 50%) than the alkali-soluble fraction ( approximately 16%), it was concluded that the three-dimensional structure strongly influences the adsorption process. The alkali insolubility of beta-d-glucans led to the formation of single and/or triple helices, which have been identified as the most favorable structures for zearalenone adsorption efficacy. The beta(1,3)-d-glucan and beta(1,6)-d-glucan compositions of the two alkali-extracted fractions and their involvement in the adsorption process are discussed. PMID:15161247

  11. Ligand Functionalization in Metal-Organic Frameworks for Enhanced Carbon Dioxide Adsorption.

    PubMed

    Wang, Hao; Peng, Junjie; Li, Jing

    2016-06-01

    Ligand functionalization in metal-organic frameworks (MOFs) has been studied extensively and has been demonstrated to enhance gas adsorption and induce interesting gas adsorption phenomena. This account summarizes our recent study of three series of MOFs by ligand functionalization, as well as their carbon dioxide adsorption properties. While ligand functionalization does not change the overall structure of the frameworks, it can influence their gas adsorption behavior. In the first two series, we show how ligand functionalization influences the CO2 affinity and adsorption capacity of MOFs. We also show a special case in which subtle changes in ligand functionality alter the CO2 adsorption profile. PMID:27071491

  12. 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. PMID:25679491

  13. CO2 adsorption using TiO2 composite polymeric membranes: A kinetic study.

    PubMed

    Hafeez, Sarah; Fan, X; Hussain, Arshad; Martín, C F

    2015-09-01

    CO2 is the main greenhouse gas which causes global climatic changes on larger scale. Many techniques have been utilised to capture CO2. Membrane gas separation is a fast growing CO2 capture technique, particularly gas separation by composite membranes. The separation of CO2 by a membrane is not just a process to physically sieve out of CO2 through the controlled membrane pore size. It mainly depends upon diffusion and solubility of gases, particularly for composite dense membranes. The blended components in composite membranes have a high capability to adsorb CO2. The adsorption kinetics of the gases may directly affect diffusion and solubility. In this study, we have investigated the adsorption behaviour of CO2 in pure and composite membranes to explore the complete understanding of diffusion and solubility of CO2 through membranes. Pure cellulose acetate (CA) and cellulose acetate-titania nanoparticle (CA-TiO2) composite membranes were fabricated and characterised using SEM and FTIR analysis. The results indicated that the blended CA-TiO2 membrane adsorbed more quantity of CO2 gas as compared to pure CA membrane. The high CO2 adsorption capacity may enhance the diffusion and solubility of CO2 in the CA-TiO2 composite membrane, which results in a better CO2 separation. The experimental data was modelled by Pseudo first-order, pseudo second order and intra particle diffusion models. According to correlation factor R(2), the Pseudo second order model was fitted well with experimental data. The intra particle diffusion model revealed that adsorption in dense membranes was not solely consisting of intra particle diffusion. PMID:26354705

  14. 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. PMID:25668395

  15. 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.

  16. Facile approach to synthesize chitosan based composite--Characterization and cadmium(II) ion adsorption studies.

    PubMed

    Pandey, Sadanand; Tiwari, Stuti

    2015-12-10

    In this present study, the physicochemical properties, nature and morphology of prepared composite materials involving Activated Eskom fly ash (A-FA) and biopolymer-chitosan (Ch) for two components composite materials were investigated. The nature, morphology, elemental characterizations of these materials were carried out by means of modern analytical methods such as scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), UV-vis spectroscopy (UV-vis), and Fourier transform infrared spectroscopy (FTIR. Other physicochemical characterizations undertaken were carbon, nitrogen and hydrogen (CNH) analysis, and ash content. The precursors and composite materials were then applied to the sorption of cadmium (Cd(2+)) from aqueous water. Maximum Cd(2+) adsorption capacity (Qmax) was recorded to be 87.72 mg/g at pH 8. The adsorption kinetics of the composite materials fitted well with the pseudo second-order kinetic model while the adsorption isotherm data could be well described by the Langmuir isotherm model. PMID:26428168

  17. Arsenic Adsorption Equilibrium Concentration and Adsorption Rate of Activated Carbon Coated with Ferric-Aluminum Hydroxides

    NASA Astrophysics Data System (ADS)

    Zhang, M.; Sugita, H.; Oguma, T.; Hara, J.; Takahashi, S.

    2015-12-01

    In some areas of developing countries, ground or well water contaminated with arsenic has been reluctantly used as drinking water. It is highly desirable that effective and inexpensive arsenic removal agents should be developed and provided to reduce the potential health risk. Previous studies demonstrated that activated carbon coated with ferric-aluminum hydroxides (Fe-Al-C) has high adsorptive potential for removal of arsenic. In this study, a series of experiments using Fe-Al-C were carried to discuss adsorption equilibrium time, adsorption equilibrium concentration and adsorption rate of arsenic for Fe-Al-C. Fe-Al-C used in this study was provided by Astec Co., Ltd. Powder reagent of disodium hydrogen arsenate heptahydrate was dissolved into ion-exchanged water. The solution was then further diluted with ion-exchanged water to be 1 and 10 mg/L as arsenic concentration. The pH of the solution was adjusted to be around 7 by adding HCl and/or NaOH. The solution was used as artificial arsenic contaminated water in two types of experiments (arsenic adsorption equilibrium and arsenic adsorption rate tests). The results of the arsenic equilibrium tests were showed that a time period of about 3 days to reach apparent adsorption equilibrium for arsenic. The apparent adsorption equilibrium concentration and adsorbed amount of arsenic on Fe-Al-C adsorbent could be estimated by application of various adsorption isotherms, but the distribution coefficient of arsenic between solid and liquid varies with experimental conditions such as initial concentration of arsenic and addition concentration of adsorbent. An adsorption rate equation that takes into account the reduction in the number of effective adsorption sites on the adsorbent caused by the arsenic adsorption reaction was derived based on the data obtained from the arsenic adsorption rate tests.

  18. A density functional theory study of the adsorption behaviour of CO2 on Cu2O surfaces

    NASA Astrophysics Data System (ADS)

    Mishra, Abhishek Kumar; Roldan, Alberto; de Leeuw, Nora H.

    2016-07-01

    Copper has many applications, particularly in electro-catalysis, where the oxidation state of the copper electrode plays a significant role in the selectivity towards products. Although copper-based materials have clear potential as catalysts in the reduction of CO2 and conversion to products, fundamental understanding of CO2 adsorption and activation on different copper oxide surfaces is still limited. We have used DFT+U methodology to study the surface reconstruction of the three most exposed (111), (110), and (001) surfaces of Cu2O with different possible terminations. Considering several adsorbate geometries, we have investigated CO2 adsorption on five different possible terminations and proposed eight different configurations in which CO2 binds with the surface. Similar to earlier findings, CO2 binds weakly with the most stable Cu2O(111):O surface showing no molecular activation, whereas a number of other surfaces, which can appear in the Cu2O particles morphology, show stronger binding as well as activation of the CO2 molecule. Different CO2 coverages were studied and a detailed structural and electronic charge analysis is presented. The activation of the CO2 molecule is characterized by structural transformations and charge transfer between the surface and the CO2 molecule, which is further confirmed by considerable red shifts in the vibrational frequencies.

  19. Adsorption of bacteria and polycations on model surfaces of cellulose, hemicellulose and wood extractives studied by QCM-D.

    PubMed

    Leino, Taina; Raulio, Mari; Salkinoja-Salonen, Mirja; Stenius, Per; Laine, Janne

    2011-08-01

    Quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) were used as the tools to study the adsorption of bacteria onto surfaces of silica and polystyrene coated with materials related to papermaking. Cationic polyelectrolytes used as fixatives and retention aids in paper industry were found to promote irreversible adsorption of the ubiquitous white water bacterium, Pseudoxanthomonas taiwanensis, onto model surfaces of cellulose (pH 8). The high charged low molecular weight polyelectrolyte, poly(diallyldimethyl) ammonium chloride (pDADMAC) adsorbed to silica surface as a flat and rigid layer, whereas the low charged cationic polyacryl amide (C-PAM) of high molecular weight adsorbed as a thick and loose layer. AFM images showed that the polyelectrolytes accumulated as layers around each bacterial cell. In the presence of wood hemicellulose (O-acetyl-galactoglucomannan) the bacteria adsorbed massively, as large, tightly packed rafts (up to 0.05mm in size) onto the polystyrene crystal surface coated with wood extractives (pH 4.7). AFM and FESEM micrographs also showed large naked areas (with no bacteria) in between the bacterial rafts on the crystal surface. In this case, QCM-D only incompletely responded to the massiveness of the bacterial adsorption. The results indicate that cationic polymers can be used to increase the retention of bacteria from the process water onto the fibre web and that, depending on the balance between hemicelluloses and wood extractives and pH of the process waters, bacteria can be drawn from process waters onto surfaces. PMID:21507615

  20. High-resolution photoemission study of acetylene adsorption and reaction with the Si(100)-2{times}1 surface

    SciTech Connect

    Xu, S.H.; Yang, Y.; Keeffe, M.; Lapeyre, G.J.; Rotenberg, E.

    1999-10-01

    The adsorption and reaction of acetylene with the Si(100)-2{times}1 surface has been studied using high-resolution photoemission by monitoring the Si&hthinsp;2p, C&hthinsp;1s, and valence-band (VB) spectra as a function of both acetylene coverage and post-adsorption annealing temperature. After the clean Si(100) surface is exposed to 0.5 monolayer (ML) acetylene, the surface state in the VB is absent. Meanwhile, the curve-fitting results show that there is only one interface component in the Si&hthinsp;2p core level. These results indicate that the asymmetric Si dimers may become symmetric dimers after acetylene adsorption, which can be explained well by the tetra-{sigma} model determined from our previous photoelectron holographic results. Significant changes in the electronic structure (Si&hthinsp;2p, C&hthinsp;1s, and VB) are found after subsequent annealing of the saturation overlayer. Annealing at lower temperature can induce some acetylene molecule desorption while most of the molecules decompose into C{sub 2}H{sub x} (x=1,0) and H species. After annealing above 660&hthinsp;{degree}C, both of the reacted components of the Si&hthinsp;2p and C&hthinsp;1s lines show that the SiC species form clusterlike features. At the same time, the VB and Si&hthinsp;2p spectra indicate a restoration of a Si(100)-2{times}1 structure, and the asymmetric Si dimers reappear on the surface. {copyright} {ital 1999} {ital The American Physical Society}

  1. Density functional study of the adsorption of aspirin on the hydroxylated (0 0 1) α-quartz surface

    NASA Astrophysics Data System (ADS)

    Abbasi, A.; Nadimi, E.; Plänitz, P.; Radehaus, C.

    2009-08-01

    In this study the adsorption geometry of aspirin molecule on a hydroxylated (0 0 1) α-quartz surface has been investigated using DFT calculations. The optimized adsorption geometry indicates that both, adsorbed molecule and substrate are strongly deformed. Strong hydrogen bonding between aspirin and surface hydroxyls, leads to the breaking of the original hydroxyl-hydroxyl hydrogen bonds (Hydrogenbridges) on the surface. In this case new hydrogen bonds on the hydroxylated (0 0 1) α-quartz surface appear which significantly differ from those at the clean surface. The 1.11 eV adsorption energy reveals that the interaction of aspirin with α-quartz is an exothermic chemical interaction.

  2. Adsorption Study on Moringa Oleifera Seeds and Musa Cavendish as Natural Water Purification Agents for Removal of Lead, Nickel and Cadmium from Drinking Water

    NASA Astrophysics Data System (ADS)

    Aziz, N. A. A.; Jayasuriya, N.; Fan, L.

    2016-07-01

    The effectiveness of plant based materials Moringa oleifera (Moringa) seeds and Musa cavendish (banana peel) for removing heavy metals namely lead (Pb), nickel (Ni) and cadmium (Cd) from contaminated groundwater was studied. Tests were carried out with individual and combined biomass at neutral pH condition on synthetic groundwater samples. The optimum biomass doses were determined as 200 mg/L for single biomass and 400 mg/L (in the ratio of 200 mg/L: 200 mg/L) for combined biomasses and used for adsorption isotherm studies with contact time of 30 minutes. Results showed that combined biomasses was able to met the Pb, Ni and Cd WHO standards from higher Pb, Ni and Cd initial concentrations which were up to 40 µg/L, 50 µg/L 9 µg/L, respectively compared to individual biomass of Moringa seed and banana peel. Moringa seeds exhibited the highest removal of Pb (81%) while the combined biomasses was most effective in removing Ni (74%) and Cd (97%) over wider their initial concentration ranges. The experimental data were linearized with Langmuir and Freundlich adsorption isotherm models. Freundlich model described the Pb adsorption better than the Langmuir model for all the tested biomasses. However, the Langmuir model fit better with the experimental data of Ni adsorption by Moringa seeds. Both models showed negligible differences in the coefficient of determination (R2) when applied for Ni and Cd adsorption on banana peel and combined biomasses, suggesting that there were multiple layers on the biomass interacting with the metals. Chemisorption is suggested to be involved in Pb adsorption for all tested biomasses as the value of nF calculated was lower than one. This type of adsorption could explain the phenomenon of different behavior of Pb removal and the higher Pb adsorption capacity (represented by KF values) compared to Ni and Cd. The study demonstrates that Moringa seeds, banana peel and their combination have the potential to be used as a natural alternative

  3. Adsorption-desorption and leaching behavior of kresoxim-methyl in different soils of India: kinetics and thermodynamic studies.

    PubMed

    Sabale, Rupali P; Shabeer T P, Ahammed; Dasgupta, Soma; Utture, Sagar C; Banerjee, Kaushik; Oulkar, Dasharath P; Adsule, Pandurang G; Deshmukh, Madhukar B

    2015-07-01

    The sorption and leaching behavior of kresoxim-methyl was explored in four different soils, viz., clay, sandy loam, loamy sand, and sandy loam (saline), representing vegetables and fruits growing regions of India. Adsorption of kresoxim-methyl in all the soils reached equilibrium within 48 h. The rate constants for adsorption and desorption at two different temperatures were obtained from the Lindstrom model, which simultaneously evaluated adsorption and desorption kinetics. The data for rate constants, activation energies, enthalpy of activation, entropy of activation, and free energy indicated physical adsorption of kresoxim-methyl on soil. The relative adsorptivity of the test soils could be attributed to different organic matter and clay contents of the soils. A good fit to the linear and Freundlich isotherms was observed for both adsorption as well as desorption. The groundwater ubiquity score (GUS) for different soils varied between 0 and 2.26. The GUS and leaching study indicated moderately low leaching potential of kresoxim-methyl. The adsorption on four soil types largely depended on the soil physicochemical properties such as organic carbon content, cation-exchange capacity, and texture of the soil. PMID:26082423

  4. 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. PMID:18022316

  5. An extensive computational study of the adsorption of thiophene on transition metal surfaces: role of van der Waals

    NASA Astrophysics Data System (ADS)

    Rojas, Tomas; Kara, Abdelkader

    2014-03-01

    Van der Waals (vdWs) interactions play a significant role in the determination of the adsorption characteristics at the interface between a molecule and a substrate. In this study, self-consistent inclusion of vdW interactions in density functional theory provides a good perspective to understand the interaction between organic adsorbates and inorganic interfaces. We present the results of adsorption of thiophene (C4H4S) on various transition metal surfaces with the goal of comparing the performance of five different vdW functionals (optB86, optB88, optPBE, revPBE, rPW86). Seven metallic substrates (100) are used for our study; three coinage metals (Au, Ag, Cu) and four reactive metals (Pt, Pd, Rh, Ni). The results show that vdWs inclusion enhances the interaction for Ag (0.08 to 0.73 eV), Au (0.14 to 0.86 eV), Cu (0.12 eV to 0.77 eV), Ni(1.56 to 2.34 eV), Pt (1.6 to 2.51 eV), Pd (1.67 to 2.54), Rh (1.74 to 2.96 eV). In addition, we performed calculations for adsorption heights along with analysis of the electronic changes (charge transfer, changes in the d-band of the substrate, and change in the work function) to complement our understanding of these systems. This work is funded by the U.S. Department of Energy Basic Energy Science under Contract No DE-FG02-11ER16243.

  6. Modified SBA-15 as the carrier for metoprolol and papaverine: Adsorption and release study

    NASA Astrophysics Data System (ADS)

    Moritz, MichaŁ; łaniecki, Marek

    2011-07-01

    A series of modified SBA-15 materials were applied in drug delivery systems. The internal surface of siliceous hexagonal structure of SBA-15 was modified with different amount of (3-mercaptopropyl)trimethoxysilane (MPTMS) and oxidized in the presence of hydrogen peroxide. The sulfonated material was loaded with metoprolol tartrate or papaverine hydrochloride. Both drugs indicated strong chemical interaction with modified mesoporous surface. The characteristic of the obtained materials was performed with XRD and DRUV-vis spectrometry, themogravimetry and nitrogen adsorption (BET) measurements. The obtained results show that modification of the mesoporous materials leads towards significant decrease of the drug delivery rate.

  7. Comprehensive study of carbon dioxide adsorption in the metal–organic frameworks M₂(dobdc) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn)

    SciTech Connect

    Queen, Wendy L.; Hudson, Matthew R.; Bloch, Eric D.; Mason, Jarad A.; Gonzalez, Miguel I.; Lee, Jason S.; Gygi, David; Howe, Joshua D.; Lee, Kyuho; Darwish, Tamim A.; James, Michael; Peterson, Vanessa K.; Teat, Simon J.; Smit, Berend; Neaton, Jeffrey B.; Long, Jeffrey R.; Brown, Craig M.

    2014-01-01

    Analysis of the CO₂ adsorption properties of a well-known series of metal–organic frameworks M₂(dobdc) (dobdc⁴⁻ = 2,5-dioxido-1,4-benzenedicarboxylate; M = Mg, Mn, Fe, Co, Ni, Cu, and Zn) is carried out in tandem with in situ structural studies to identify the host–guest interactions that lead to significant differences in isosteric heats of CO₂ adsorption. Neutron and X-ray powder diffraction and single crystal X-ray diffraction experiments are used to unveil the site-specific binding properties of CO₂ within many of these materials while systematically varying both the amount of CO₂ and the temperature. Unlike previous studies, we show that CO₂ adsorbed at the metal cations exhibits intramolecular angles with minimal deviations from 180°, a finding that indicates a strongly electrostatic and physisorptive interaction with the framework surface and sheds more light on the ongoing discussion regarding whether CO₂ adsorbs in a linear or nonlinear geometry. This has important implications for proposals that have been made to utilize these materials for the activation and chemical conversion of CO₂. For the weaker CO₂ adsorbents, significant elongation of the metal–O(CO₂) distances are observed and diffraction experiments additionally reveal that secondary CO₂ adsorption sites, while likely stabilized by the population of the primary adsorption sites, significantly contribute to adsorption behavior at ambient temperature. Density functional theory calculations including van der Waals dispersion quantitatively corroborate and rationalize observations regarding intramolecular CO₂ angles and trends in relative geometric properties and heats of adsorption in the M₂(dobdc)–CO₂ adducts.

  8. Molecular dynamics study of calcite, hydrate and the temperature effect on CO2 transport and adsorption stability in geological formations

    NASA Astrophysics Data System (ADS)

    Van Cuong, Phan; Kvamme, Bjørn; Kuznetsova, Tatiana; Jensen, Bjørnar

    2012-06-01

    Molecular dynamics (MD) simulations at several different temperatures were run to investigate the transport, adsorption, and stability of carbon dioxide (CO2) and water phases in contact with a ? calcite surface. All simulated systems showed evidence of CO2 transport and interface stability heavily affected by the presence of calcite and the simulation temperature. The number of CO2 molecules that successfully traversed the water layer and adsorbed on the calcite surface increased with temperature, while the adsorption stability (indicated by the adsorption energy) decreased. It was found that the short-range potential has a significant impact on the preferred CO2 orientation and adsorption selectivity. Carbon dioxide tended to fill partial hydrate cavities at the water-hydrate interface, potentially promoting the formation of new hydrate. These findings indicate the need to consider the implications that CO2 injection will have for reservoirs with pre-existing clathrate hydrates.

  9. {010}-Oriented micro-flower-like hierarchical Bi2WO6 with high adsorptivity and visible-light-driven photoactivity: experimental studies and first-principles modeling

    NASA Astrophysics Data System (ADS)

    Wang, Jiawei; Li, Jiajun; Zhao, Naiqin; Sha, Junwei; Hao, Shuang; Liu, Enzuo; Shi, Chunsheng; He, Chunnian; Wang, Defa

    2015-01-01

    {010}-Oriented flower-like Bi2WO6 with high adsorptivity and photoactivity was prepared via a hydrothermal method without any additives under neutral environment. The anisotropic flower-like Bi2WO6 shows greatly enhanced adsorptivity and photoactivity compared with isotropic particle Bi2WO6 as well as most of other forms of Bi2WO6. The superior adsorptivity shows potential in suitability for majority of dyes. Detailed study on microstructure and morphology indicates that mesoporous structure and large surface area mainly contribute to the superior properties. Especially, {010} crystal planes of flower-like Bi2WO6 terminated with [Bi2O2]2+ layers provide more adsorption sites for dyes than other facets. In combination with first-principles calculations, it is initially revealed that {010}-oriented facets preference benefits hole distribution at surface and provides the most reactive sites, thus enhances the photoactivity of the flower-like Bi2WO6. Moreover, the anisotropic flower-like Bi2WO6 shows excellent recyclability and cycling stability with great potential in environmental applications.

  10. Studies on Adsorption and Corrosion Inhibitive Properties of Indoline Compounds on N80 Steel in Hydrochloric Acid

    NASA Astrophysics Data System (ADS)

    Yadav, M.; Sarkar, T. K.; Purkait, Taniya

    2015-12-01

    Corrosion inhibition performance of synthesized indoline compounds, namely, 3'-(4-(1-acetyl-5-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazol-3-yl)phenyl)spiro[indoline-3,2'-thiazolidine]-2,4'-dione (MPIT ) and 1-(4-(1-acetyl-5-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazol-3-yl)phenyl)spiro[imidazolidine-2,3'-indoline]-2',5-dione (MPII) on N80 steel in 15% HCl solution was studied using weight loss measurement, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. Polarization studies showed that both studied inhibitors were of mixed type in nature. The adsorption of inhibitors on the N80 steel surface obeys Langmuir adsorption isotherm. The potential of zero charge ( E PZC) for the N80 steel was determined by EIS method. Scanning electron microscopy, energy-dispersive x-ray spectroscopy, and atomic force microscopy were used to characterize the surface morphology of uninhibited and inhibited N80 steel specimens. The density functional theory was employed for theoretical calculations.

  11. Adsorption/desorption of Cd(II), Cu(II) and Pb(II) using chemically modified orange peel: Equilibrium and kinetic studies

    NASA Astrophysics Data System (ADS)

    Lasheen, Mohamed R.; Ammar, Nabila S.; Ibrahim, Hanan S.

    2012-02-01

    Waste materials from industries such as food processing may act as cost effective and efficient biosorbents to remove toxic contaminants from wastewater. This study aimed to establish an optimized condition and closed loop application of processed orange peel for metals removal. A comparative study of the adsorption capacity of the chemically modified orange peel was performed against environmentally problematic metal ions, namely, Cd 2+, Cu 2+ and Pb 2+, from aqueous solutions. Chemically modified orange peel (MOP) showed a significantly higher metal uptake capacity compared to original orange peel (OP). Fourier Transform Infrared (FTIR) Spectra of peel showed that the carboxylic group peak shifted from 1637 to 1644 cm -1 after Pb (II) ions binding, indicated the involvement of carboxyl groups in Pb(II) ions binding. The metals uptake by MOP was rapid and the equilibrium time was 30 min at constant temperature and pH. Sorption kinetics followed a second-order model. The mechanism of metal sorption by MOP gave good fits for Freundlich and Langmuir models. Desorption of metals and regeneration of the biosorbent was attained simultaneously by acid elution. Even after four cycles of adsorption-elution, the adsorption capacity was regained completely and adsorption efficiency of metal was maintained at around 90%.

  12. [Adsorption and Desorption Characteristics of Endosulfan in Purple Soil].

    PubMed

    Zhao, Yan; Zheng, Guo-can; Zhu, Heng; Zhang, Jin-zhong; Zhu, Xiu-ying; Hu, Shu-chun; Wu, Ya-lin

    2015-09-01

    In order to reveal the residual process of endosulfan in purple soil and protect soil ecological environment, the adsorption and desorption characteristics of endosulfan in purple soil were investigated, and effects of temperature, adsorbent amount, and initial pH of adsorption solution on the adsorption capacity were also examined by static adsorption and desorption experiments. The results showed that the adsorption kinetic process could be well described by the second-order kinetic equation with the initial rate constants of α-, β-endosulfan as 0. 157 and 0. 115 mg.(g.min)-1, respectively. The adsorption thermodynamic process could be well described by the Langmuir isotherm with the maximum adsorption capacities of α-, β-endosulfan as 0. 257 mg . g -1 and 0. 155 mg . g -1, respectively. The adsorption process of endosulfan in purple soil may be an exothermic physicochemical process, and is dominated by physical adsorption. Under the experimental conditions examined in this study, the initial pH of adsorption solution had a relative great influence on the adsorption capacity, whereas the temperature and adsorbent amount had no significant influence. The desorption experiments found that the maximum desorption capacities of α-, β-endosulfan adsorbed in purple soil were 0. 029 mg . g -1 and 0. 017 mg . g -1 at 6 and 4 h, and accounted for 10. 5% and 16. 1% in the maximum adsorption capacities, respectively. PMID:26717711

  13. Studies on the adsorption of americium on alumina from aqueous nitric acid-oxalic acid solutions

    SciTech Connect

    Subba Rao, M.; Gaikwad, A.M.; Rao, V.K.; Natarajan, P.R.

    1985-01-01

    This paper reports a study on the adsorption of Am(III) on alumina from oxalic acid-nitric acid solutions. Distribution coefficients for Am(III) on alumina at different oxalic acid-nitric acid concentrations have been determined and optimum conditions for loading and elution of Am from alumina columns have been established. Separation of Am from Pu and the effects of other ions, such as U(VI) and Fe(III), have also been studied. Am and Pu recoveries better than 99.5% were obtained. 3 references, 2 figures, 5 tables.

  14. Study on Super-Hydrophobic and Oleophobic Surfaces Prepared by Chemical Adsorption Technique

    NASA Astrophysics Data System (ADS)

    Tsuji, Issei; Ohkubo, Yuji; Ogawa, Kazufumi

    2009-04-01

    Preparation techniques for super-hydrophobic and oleophobic surfaces were studied by forming a fractally roughened surface and preparing a hydrophobic monolayer. In this study, the fractal structure on the surface of an aluminum substrate was formed by combining sand-blasting with electrolytical etching. Then, a hydrophobic monolayer was prepared on the roughened surface, without decreasing roughness. The surface of the treated substrate can be evaluated by contact angle measurement and field emission scanning electron microscopy (FE-SEM). The surface treated by a technique combining chemical adsorption, sandblasting, and electrolytical etching was super-hydrophobic and highly oleophobic.

  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. Extracorporeal adsorption of endotoxin.

    PubMed

    Staubach, K H; Rosenfeldt, J A; Veit, O; Bruch, H P

    1997-02-01

    In a porcine endotoxin shock model using a continuous intravenous endotoxin infusion of 250 ng/kg body weight per hour, the cardiorespiratory and hematologic parameters were studied while applying a new on-line polymyxin B immobilized adsorption system. This preliminary report shows that the new adsorbent can remove endotoxin selectively from the circulation and confers a good amount of protection from endotoxin-induced cardiopulmonary decompensation as well as hematologic alterations. Survival time could be extended from 216 min to 313 min. Whereas cardiac output and mean arterial pressure declined critically after 3 h in the controls, the treated group remained stable for another 3 h. These data show that endotoxin adsorption by polymyxin B coupled covalently to acrylic spheres as an adjunctive on-line measure in the septic syndrome seems feasible. PMID:10225785

  17. 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)

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

    PubMed

    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). PMID:24329084

  19. 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. PMID:25189843

  20. Scanning tunneling microscopy study of formate species synthesized from CO{sub 2} hydrogenation and prepared by adsorption of formic acid over Cu(111)

    SciTech Connect

    Fujitani, T.; Choi, Y.; Sano, M.; Kushida, Y.; Nakamura, J.

    2000-02-17

    The adsorption structure of formate species on Cu(111), prepared by two different methods, was studied using ultrahigh vacuum scanning tunneling microscopy (UHV-STM), that is, the synthesis by the hydrogenation of CO{sub 2} at atmospheric pressure and the adsorption of formic acid on an oxygen-precovered Cu(111). Linear chains of formate molecules were imaged by the hydrogenation of CO{sub 2} by STM at low formate coverage with the distance to the nearest neighbor of the formate species estimated to be 5.0 {+-} 0.2{angstrom}, twice that of the nearest Cu--Cu neighbor. The adsorption phase of formate thus grows linearly at the initial stage by an anisotropic attractive interaction between the formate species. The ordered structure of the formate species changed in the order of p(2 x 4), c(2 x 8), (7 x 7), p(2 x 3), (5 x 5), and c(2 x 4) with increasing formate coverage, indicating that various ordered structures appeared corresponding to the small change in the formate coverage. All the formate structures, except for (7 x 7) and (5 x 5), consisted of the same chain as observed at low coverage, with the distance between the formate chains, resulting in a lowering of the adsorption energy of the formate species as reported in the literature. On the other hand, (4 x 4) and (3 x 7/2) structures were observed upon exposing the Cu(111) surface to formic acid at 2 and 15 L, respectively, showing no chain structure of the formate species. At low formate coverage, no molecular image was observed, indicating that the formate species diffuses more rapidly than the scanning of the STM tip. Thus, the adsorption structure of formate on Cu(111) was found to be different depending on the preparation method. It is suggested that the difference in the adsorption structure strongly influences the rate constant of the previously reported formate decomposition.

  1. First-principles study of molecular hydrogen adsorption and dissociation on Al(n)Cr (n = 1-13) clusters.

    PubMed

    Guo, Ling

    2013-04-25

    Hydrogen adsorption dissociation on clusters is a widely studied subject that provides the opportunity to gain a basic understanding of the complicated nature of many interesting problems, such as hydrogen embrittlement of metals, catalytic processes, hydrogen storage, etc. In this study, I present density functional calculations of H2 adsorption and dissociation on small-sized Al(n)Cr clusters for n = 1-13. My results show that H2 is easily physically absorbed on the top Cr atom of AlnCr clusters with a side-on orientation rather than an end-on orientation. In addition, I investigate a possible dissociation mechanism and dissociation pathway of H2 on selected Al2Cr and Al7Cr. My findings suggest that the hydrogen dissociation behavior on Al(n)Cr clusters characterized by the activation barrier and reaction energy can be tuned by controllable doping. Thus, Al2Cr and Al7Cr clusters might serve as highly efficient and low-cost catalysts for hydrogen dissociation. PMID:23581518

  2. 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. PMID:23653315

  3. Adsorption of Cu(II) to Bacillus subtilis: A pH-dependent EXAFS and thermodynamic modelling study

    NASA Astrophysics Data System (ADS)

    Moon, Ellen M.; Peacock, Caroline L.

    2011-11-01

    Bacteria are very efficient sorbents of trace metals, and their abundance in a wide variety of natural aqueous systems means biosorption plays an important role in the biogeochemical cycling of many elements. We measured the adsorption of Cu(II) to Bacillus subtilis as a function of pH and surface loading. Adsorption edge and XAS experiments were performed at high bacteria-to-metal ratio, analogous to Cu uptake in natural geologic and aqueous environments. We report significant Cu adsorption to B. subtilis across the entire pH range studied (pH ˜2-7), with adsorption increasing with pH to a maximum at pH ˜6. We determine directly for the first time that Cu adsorbs to B. subtilis as a (CuO 5H n) n-8 monodentate, inner-sphere surface complex involving carboxyl surface functional groups. This Cu-carboxyl complex is able to account for the observed Cu adsorption across the entire pH range studied. Having determined the molecular adsorption mechanism of Cu to B. subtilis, we have developed a new thermodynamic surface complexation model for Cu adsorption that is informed by and consistent with EXAFS results. We model the surface electrostatics using the 1p K basic Stern approximation. We fit our adsorption data to the formation of a monodentate, inner-sphere tbnd RCOOCu + surface complex. In agreement with previous studies, this work indicates that in order to accurately predict the fate and mobility of Cu in complex biogeochemical systems, we must incorporate the formation of Cu-bacteria surface complexes in reactive transport models. To this end, this work recommends log K tbnd RCOOCu + = 7.13 for geologic and aqueous systems with generally high B. subtilis-to-metal ratio.

  4. Adsorption of SO2 molecule on doped (8, 0) boron nitride nanotube: A first-principles study

    NASA Astrophysics Data System (ADS)

    Deng, Zun-Yi; Zhang, Jian-Min; Xu, Ke-Wei

    2016-02-01

    Adsorptions of SO2 on Al-, Ca-, Co-, Cu-, Ge-, Ni-, and Si-doped (8, 0) boron nitride nanotube (BNNT) have been studied using first-principles approach based on density functional theory in order to exploit their potential applications as SO2 gas sensors. The electronic properties of the BNNT-molecule adsorption adducts are strongly dependent on the dopants. The most stable adsorption geometries, adsorption energies, charge transfers, and density of states of these systems are thoroughly discussed. This work reveals that the sensitivity of (8, 0) BNNT based chemical gas sensors for SO2 can be drastically improved by introducing appropriate dopant. Si is found to be the best choice among all the dopants.

  5. Density functional study of manganese atom adsorption on hydrogen-terminated armchair boron nitride nanoribbons

    NASA Astrophysics Data System (ADS)

    Abdullahi, Yusuf Zuntu; Rahman, Md. Mahmudur; Shuaibu, Alhassan; Abubakar, Shamsu; Zainuddin, Hishamuddin; Muhida, Rifki; Setiyanto, Henry

    2014-08-01

    In this paper, we have investigated stable structural, electric and magnetic properties of manganese (Mn) atom adsorption on armchair hydrogen edge-terminated boron nitride nanoribbon (A-BNNRs) using first principles method based on density-functional theory with the generalized gradient approximation. Calculation shows that Mn atom situated on the ribbons of A-BNNRs is the most stable configuration, where the bonding is more pronounced. The projected density of states (PDOS) of the favored configuration has also been computed. It has been found that the covalent bonding of boron (B), nitrogen (N) and Mn is mainly contributed by s, d like-orbitals of Mn and partially occupied by the 2p like-orbital of N. The difference in energy between the inner and the edge adsorption sites of A-BNNRs shows that Mn atoms prefer to concentrate at the edge sites. The electronic structures of the various configurations are wide, narrow-gap semiconducting and half-metallic, and the magnetic moment of Mn atoms are well preserved in all considered configurations. This has shown that the boron nitride (BN) sheet covered with Mn atoms demonstrates additional information on its usefulness in future spintronics, molecular magnet and nanoelectronics devices.

  6. Adsorption of poly acrylic acid onto the surface of calcite: an experimental and simulation study.

    PubMed

    Sparks, David J; Romero-González, Maria E; El-Taboni, Elfateh; Freeman, Colin L; Hall, Shaun A; Kakonyi, Gabriella; Swanson, Linda; Banwart, Steven A; Harding, John H

    2015-11-01

    Macromolecular binding to minerals is of great importance in the formation of biofilms, and carboxylate functional groups have been found to play a pivotal role in the functioning of these macromolecules. Here we present both fluorescence time-resolved anisotropy measurements and simulation data on the conformational behaviour and binding of a poly acrylic acid polymer. In solution the polymer exhibits a pH dependent behaviour, with a coiled conformation at a low pH and extended conformation at higher pH values. The polymer is readily adsorbed on the surface of calcite, preferring to bind in an extended conformation, with the strength of the adsorption dependent on the pH and presence of counter ions. We discuss the reasons why the calculated adsorption free energy differs from that obtained from a Langmuir isotherm analysis, showing that they refer to different quantities. The enhanced binding of the extended conformations shows the importance of flexibility in the binding of macromolecules. PMID:26418100

  7. Arsenic Adsorption on Lanthanum-Impregnated Activated Alumina: Spectroscopic and DFT Study.

    PubMed

    Shi, Qiantao; Yan, Li; Chan, Tingshan; Jing, Chuanyong

    2015-12-01

    Rare earth-modified adsorbents (REMAs) have been widely used to remove oxyanion pollutants from water, including arsenic (As). However, the molecular-level structural information and reactions at the liquid/solid interface are still murky, which limits the design of applicable REMAs. Herein, a lanthanum-impregnated activated alumina (LAA) was synthesized as a representative REMA, and its As uptake mechanisms were explored using multiple complementary characterization techniques. Our adsorption experiments showed that LAA exhibited 2-3 times higher As adsorption capacity than AA. In contrast to the bidentate configuration formed on most metal oxide surfaces, our EXAFS and DFT results suggest that As(III) and As(V) form monodentate surface complexes on LAA through As-O-La coordinative bonding. In situ flow cell ATR-FTIR observed a strong dependence of As-O peak positions on pH, which could be interpreted as the change in the fractions of As(V) surface complexes with zero- to double-protonation on LAA, AA, and LaOOH. As(V) on LAA existed as singly and doubly protonated surface species, and the pKa of transition from double to single protonation (∼5.8) was lower than that for its soluble counterpart (6.97). The surface reaction and structural configuration were incorporated in a CD-MUSIC model to satisfactorily predict macroscopic As adsorption behaviors. The insights gained from the molecular-level reactions shed light on the design and application of REMAs in environmental remediation for As and its structural analogues. PMID:26565426

  8. 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.

  9. 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. PMID:25201086

  10. Design of a new integrated chitosan-PAMAM dendrimer biosorbent for heavy metals removing and study of its adsorption kinetics and thermodynamics.

    PubMed

    Zarghami, Zabihullah; Akbari, Ahmad; Latifi, Ali Mohammad; Amani, Mohammad Ali

    2016-04-01

    In this research, different generations of PAMAM-grafted chitosan as integrated biosorbents were successfully synthesized via step by step divergent growth approach of dendrimer. The synthesized products were utilized as adsorbents for heavy metals (Pb(2+) in this study) removing from aqueous solution and their reactive Pb(2+) removal potential was evaluated. The results showed that as-synthesized products with higher generations of dendrimer, have more adsorption capacity compared to products with lower generations of dendrimer and sole chitosan. Adsorption capacity of as-prepared product with generation 3 of dendrimer is 18times more than sole chitosan. Thermodynamic and kinetic studies were performed for understanding equilibrium data of the uptake capacity and kinetic rate uptake, respectively. Thermodynamic and kinetic studies showed that Langmuir isotherm model and pseudo second order kinetic model are more compatible for describing equilibrium data of the uptake capacity and kinetic rate of the Pb(2+) uptake, respectively. PMID:26836608

  11. Theoretical study of the NO, NO2, CO, SO2, and NH3 adsorptions on multi-diameter single-wall MoS2 nanotube

    NASA Astrophysics Data System (ADS)

    Cao, Rongfang; Zhou, Bo; Jia, Cuifang; Zhang, Xiaodong; Jiang, Zhenyi

    2016-02-01

    On the basis of first-principles calculations, the ability of a single-wall MoS2 nanotube to detect NO, NO2, CO, SO2, and NH3 gas molecules is studied. The most stable adsorption configurations, adsorption energies, and charge transfers are calculated. Among these gas molecules, the NO molecule has the biggest interaction with the MoS2 nanotube. The adsorption energy of NO on the nanotube is 129.3 meV, which is almost double compared to that for the monolayer (74.4 meV). The charge density difference calculation shows that all the molecules on the MoS2 nanotube act as electron acceptors except NH3. The charge transfer between NO and the nanotube is still one order of magnitude higher than that for the monolayer. Compared with the results for these molecules adsorbed on the MoS2 monolayer, the nanotube is more sensitive, especially for the NO molecule. Moreover, a comparative study of MoS2 nanotubes with different diameters (curvatures) indicates that the NO adsorption capability of the outer surface decreases on the increasing radius. It is predicted that the MoS2 nanotube with a smaller diameter should increase the stability and sensitivity of MoS2-based field-effect-transistor (FET) sensors.

  12. Adsorption of chromium(VI) and Rhodamine B by surface modified tannery waste: kinetic, mechanistic and thermodynamic studies.

    PubMed

    Anandkumar, J; Mandal, B

    2011-02-28

    In this study, various activation methods have been employed to examine the potential reuse of tannery residual biomass (TRB) obtained from vegetable tanning process for the removal of Cr(VI) and Rhodamine B (RB) from aqueous solution. The maximum BET surface area (10.42 m(2)/g), honey comb pore distribution and uptake of both Cr(VI) and RB were achieved when only 3-fold volume of HCl was used to activate the biomass. The pH and temperature experiment showed that they have considerable impact on the adsorption capacity of the used adsorbent. The presence of other ions (Na(+), Ca(2+) and NH(4)(+)) significantly reduces the metal uptake but marginal enhancement in the dye removal was observed when Na(+) and NH(4)(+) ions were present in the solution. The equilibrium data fitted satisfactorily with the Langmuir model and monolayer sorption capacity obtained as 177-217 and 213-250 mg/g for Cr(VI) and RB at 30-50°C, respectively. The sorption kinetics was found to follow the pseudo-second-order kinetic model. The increase in adsorption capacity for both metal and dye with increase in temperature indicates that the uptake was endothermic in nature. The results indicate that the HCl modified TRB (A-TRB) could be employed as a low cost adsorbent for the removal of both Cr(VI) and RB from the aqueous solution including industrial wastewater. PMID:21168268

  13. Studies of Bilayers and Vesicle Adsorption to Solid Substrates: Development of A Miniature Streaming Potential Apparatus (SPA)

    PubMed Central

    Min, Younjin; Pesika, Noshir; Zasadzinski, Joe; Israelachvili, Jacob

    2010-01-01

    A new miniature streaming potential apparatus (SPA) was developed to determine the streaming potentials (Ψstr) and zeta potentials (ζ) of substrates under different ionic conditions while simultaneously visualizing the state of the surfaces, such as the adsorption of surfactants or polymers, using fluorescence microscopy and/or fluorescence recovery after photobleaching (FRAP). Experimental results with different surfaces show that the new SPA provides streaming potential values (hence zeta potentials) that agree with results obtained using traditional electrokinetic analyzers. Using the new SPA, the formation of supported lipid bilayers (SLBs) on glass from fluorescently labeled, unilamellar (~100 nm diameter), charge neutral dimyristoyl-sn-glycero-3-phosphocholine (DMPC) vesicles was studied in aqueous electrolyte solutions at different lipid concentrations. Simultaneous zeta potential measurements and fluorescence imaging for measuring diffusion coefficients by confocal microscopy enabled us to precisely monitor the changes in the surface charge as well as in the surface morphology during SLB formation from vesicles. For a fixed incubation time of 5 minutes, both results revealed that the adsorption of intact vesicles and/or discrete bilayer patches were observed below a threshold concentration, above which the formation of continuous SLBs occurred leading to an estimate for the ζ-potential and for the diffusion coefficient of −9.1±1.6 mV and (1.1±0.02)×10−12 m2/s, respectively. PMID:20180570

  14. Study of the kinetics and the adsorption isotherm of cadmium(II) from aqueous solution using green algae (Ulva lactuca) biomass.

    PubMed

    Asnaoui, H; Laaziri, A; Khalis, M

    2015-01-01

    Batch experiments were conducted to study the adsorption of hazardous cadmium onto low-cost algae biomass in aqueous solution with respect to concentration of adsorbate, adsorbent dosage, contact time, solution pH and temperature. Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were determined. The activation energy of adsorption was also evaluated for the adsorption of cadmium onto Ulva lactuca biomass. Experimental data were tested in terms of biosorption kinetics using pseudo-first-order and pseudo-second-order kinetic models. The results showed that the biosorption processes of Cd(II) followed well pseudo-second-order kinetics. Langmuir and Freundlich models were applied to describe the biosorption isotherm of the metal ions by Ulva lactuca biomass. Langmuir model fitted the equilibrium data better than the Freundlich isotherm. The biosorption capacity of Ulva lactuca biomass for cadmium was found to be 3.02 mg/g at pH 5.60 min equilibrium time and 20 °C. The mean free energy which was calculated was 6.24 kJ/mol for Cd(II) biosorption, which shows that the adsorption is physical. The calculated thermodynamic parameters (ΔG0, ΔH0 and ΔS0) showed that the biosorption of Cd(II) onto Ulva lactuca biomass was feasible, spontaneous and exothermic under examined conditions. The results indicate that algae Ulva lactuca could be employed as a low-cost material for the removal of metal ions from aqueous solution. PMID:26524441

  15. 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. PMID:27084802

  16. Calcium adsorption at the rutile-water interface: A potentiometric study in NaCl media to 250 C

    SciTech Connect

    Ridley, M.K.; Machesky, M.L.; Wesolowski, D.J.; Palmer, D.A.

    1999-10-01

    Calcium adsorption by rutile was studied potentiometrically from 25 to 250 C, at ionic strengths of 0.03 and 0.30 m in NaCl media, using two complementary experimental methodologies. In the first, net proton adsorption in the presence and absence of Ca{sup 2+} was monitored, and in the second, samples were periodically withdrawn during the course of a titration to determine Ca{sup 2+} adsorption directly. These experiments revealed that Ca{sup 2+} adsorption systematically increased with temperature relative to the pH of zero net proton charge in NaCl media alone (pH{sub znpc(NaCl)} - pH). That is, as temperature increased, Ca{sup 2+} adsorption commenced at progressively more positive pH{sub znpc(NaCl)} - pH values. Increasing ionic strength from 0.03 to 0.30 m NaCl suppressed Ca{sup 2+} adsorption at all temperatures as a result of either increased competition from Na{sup +} or greater complexation of Ca{sup 2+} by Cl{sup {minus}}. Finally, there was no apparent trend in the proton stoichiometric ratios (moles H{sup +} released/moles Ca{sup 2+} adsorbed) with increasing temperature. This suggests that the electrostatic and/or chemical processes involved in Ca{sup 2+} adsorption do not change greatly with increasing temperature. Favorable entropic effects, related to the increasing ease of releasing Ca{sup 2+} waters of hydration, are believed to be primarily responsible for the increase in adsorption with temperature.

  17. 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. PMID:25723785

  18. Adsorption of aerosol-OT to sapphire: lamellar structures studied with neutrons.

    PubMed

    Hellsing, Maja S; Rennie, Adrian R; Hughes, Arwel V

    2011-04-19

    The adsorption of sodium bis 2-ethylhexyl sulfosuccinate, NaAOT, to a sapphire surface from aqueous solution has been studied by neutron reflection at concentrations above the critical micelle concentration (cmc). Complementary measurements of the bulk structure were made with small-angle neutron scattering and grazing incidence small-angle neutron scattering. At a concentration of about 1% wt (10 × cmc), lamellar phase NaAOT was observed both at the surface and in the bulk. The structure seen at the interface for a solution of 2% wt NaAOT is a 35 ± 2 Å thick bilayer adsorbed to the sapphire surface at maximum packing density, followed by an aligned stack of fluctuating bilayers of thickness 51 ± 2 Å and with an area per molecule of 40 ± 2 Å(2). Each bilayer is separated by a water: at 25 °C, this layer is 148 ± 2 Å. A simple model for the reflectivity from fluctuating layers is presented, and for 2.0% wt NaAOT the fluctuations were found to have an amplitude of 25 ± 5 Å. The temperature sensitivity of the structure at the surface was investigated in the range 15-30 °C. The effect of temperature was pronounced, with the solvent layer becoming thinner and the volume occupied by the NaAOT molecules in a bilayer increasing with temperature. The amplitude of the fluctuations, however, is approximately temperature independent in this range. The adsorption of NaAOT at the sapphire surface resembles that previously found at hydrophilic and hydrophobic silica surfaces. The coexisting bulk lamellar phase has a spacing of layers similar to that observed at the surface. These observations are an indication that the major driving force for adsorption is self-assembly, independent of the chemical nature of the interface. PMID:21443213

  19. A computational study on choline benzoate and choline salicylate ionic liquids in the pure state and after CO2 adsorption.

    PubMed

    Aparicio, Santiago; Atilhan, Mert

    2012-08-01

    Choline-based ionic liquids show very adequate environmental, toxicological, and economical profiles for their application in many different technological areas. We report in this work a computational study on the properties of choline benzoate and choline salicylate ionic liquids, as representatives of this family of compounds, in the pure state and after CO(2) adsorption. Quantum chemistry calculations using the density functional theory approach for ionic pairs and ions, CO(2) pairs, were carried out, and the results analyzed using natural bond orbital and atoms in a molecule approaches. Classical molecular dynamics simulations of ionic liquids were done as a function of pressure, temperature, and CO(2) concentration. Microscopic structuring and intermolecular forces are analyzed together with the dynamic behavior of the studied fluids. PMID:22738425

  20. A sum-frequency generation spectroscopic study of the Gibbs analysis paradox: monolayer or sub-monolayer adsorption?

    PubMed

    Shahir, Afshin Asadzadeh; Nguyen, Khoi Tan; Nguyen, Anh V

    2016-03-23

    The Gibbs adsorption isotherm (GAI) has been considered as the foundation of surfactant adsorption studies for over a century; however, its application in determining the limiting surface excess has recently been intensively discussed, with contradictory experimental evidence either supporting or refuting the theory. The available arguments are based on monolayer adsorption models. In this paper, we experimentally and intellectually propose and validate the contribution of sub-monolayer adsorption to the GAI paradox. We utilize a powerful intrinsically surface-sensitive technique, vibrational sum-frequency generation spectroscopy (SFG), complementing with conventional tensiometric measurements to address these controversies both quantitatively and qualitatively. Our SFG results revealed that the precipitous decrease in surface tension directly corresponds to surface occupancy by adsorbates. In addition, the Gibbs analysis was successfully applied to the soluble monolayer of a surface-active alcohol to full saturation. However, the full saturation of the topmost monolayer does not necessarily mean that the surface adsorption was completed because the adsorption was observed to continuously occur in the sub-monolayer region soon after the topmost monolayer became saturated. Nonetheless, the Gibbs isotherm failed to account for the excess of alcohol adsorbed in this sub-monolayer region. This new concept of surface excess must therefore be treated thermodynamically. PMID:26661072

  1. 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. PMID:19773115

  2. Study of intradrystalline diffusion in zeolites communication 3. Kinetics of adsorption of trans-2-butene by NaA and NaMgA zeolites

    SciTech Connect

    Broddak, R.; Dubinin, M.M.; Falko, L.A.; Gorlov, V.A.; Kuhlmann, B.; Scholner, E.; Voloshchuk, A.M.

    1985-09-10

    This article studies the kinetics of adsorption of trans-2-butene by NaA zeolite with a varying crystal size, microcrystalline granulated NaA zeolite using granules of different sizes, and microcrystalline powdered Na/sub 8/Mg/sub 2/A zeolite. It is shown that the rate of adsorption is determined by the intracrystalline diffusion and that the effect of transfer in the transport pores and the final rate of dissipation of the heat of adsorption can be neglected. In adsorption of trans-2-butene by Na/sub 8/Mg/sub 2/A zeolite with a stepwise change in the pressure of the adsorbate, the kinetic curves are satisfactorily described by an internal diffusion equation for the kinetics of isothermal adsorption. The kinetics of adsorption were studied at 303 degrees K from the one-component vapor phase on a vacuum adsorption setup using quartz spring balance.

  3. An ab-initio study of adsorption of gaseous molecules on doped graphene structures

    NASA Astrophysics Data System (ADS)

    Balangi, H. R.; Shokri, A. A.

    2015-11-01

    In this work, electronic properties of bare and doped graphene layers in the presence of N, B and a type of defective impurities are investigated under adsorption of CO, NO, NH3 and NO2 molecules on it's external surface. We use a fully self-consistent density function theory (DFT) based calculations as implemented in SIESTA package. The local-density approximation (LDA) is considered for the exchange-correlation function. Total density of state (TDOS), partial density of state (PDOS) and charge density calculations are also considered to elucidate the difference in the CO, NO, NH3 and NO2 gases detection mechanism of pristine and doped graphene structures. With regard to that the charge transfer is occurring between the graphene sheet and gaseous molecules, the NO2 and NH3 molecules are considered as the recipient and donor of electrons, respectively. We show that the states contributed by the adsorbed CO and NO molecules are quite localized near the center of original band gap and they suggest that the charge transport in such systems cannot be enhanced considerably, while NO2 and NH3 molecules adsorption acts as the acceptor and donor, respectively. Our results can serve as a base for developments in designing nano-electronic devices.

  4. Enhanced Li adsorption and diffusion in single-walled silicon nanotubes: an ab initio study.

    PubMed

    Kulish, Vadym V; Ng, Man-Fai; Malyi, Oleksandr I; Wu, Ping; Chen, Zhong

    2013-04-15

    We report a first-principles investigation of Li adsorption and diffusion in single-walled Si nanotubes (SWSiNTs) of interest to Li-ion battery anodes. We calculate Li insertion characteristics in SWSiNTs and compare them with the respective ones in carbon nanotubes (CNTs) and other silicon nanostructures. From our calculations, SWSiNTs show higher reactivity toward the adsorption of Li adatoms than CNTs and Si nanoclusters. Considering the importance of Li kinetics, we demonstrate that the interior of SWSiNTs may serve as a fast Li diffusion channel. The important advantage of SWSiNTs over their carbon analogues is a sevenfold reduction in the energy barrier for the penetration of the Li atoms into the nanotube interior through the sidewalls. This prepossesses easier Li diffusion inside the tube and subsequent utilization of the interior sites, which enhances Li storage capacity of the system. The improvements in both Li uptake and Li mobility over their analogues support the great potential of SWSiNTs as Li-ion battery anodes. PMID:23564742

  5. Study on two stage activated carbon/HFC-134a based adsorption chiller

    NASA Astrophysics Data System (ADS)

    >K Habib, M. Amin B. A.; Sulaiman, Shaharin Anwar B.

    2013-06-01

    In this paper, a theoretical analysis on the performance of a thermally driven two-stage four-bed adsorption chiller utilizing low-grade waste heat of temperatures between 50°C and 70°C in combination with a heat sink (cooling water) of 30°C for air-conditioning applications has been described. Activated carbon (AC) of type Maxsorb III/HFC-134a pair has been examined as an adsorbent/refrigerant pair. FORTRAN simulation program is developed to analyze the influence of operating conditions (hot and cooling water temperatures and adsorption/desorption cycle times) on the cycle performance in terms of cooling capacity and COP. The main advantage of this two-stage chiller is that it can be operational with smaller regenerating temperature lifts than other heat-driven single-stage chillers. Simulation results shows that the two-stage chiller can be operated effectively with heat sources of 50°C and 70°C in combination with a coolant at 30°C.

  6. Ab initio study of silane and disilane adsorption on Si(100)-(2x1) surface

    NASA Astrophysics Data System (ADS)

    Huang, Min; Randall, John; Chabal, Yves J.; Wallace, Robert M.; Cho, Kyeongjae

    2010-03-01

    Silane (SiH4) and disilane (Si2H6) are common precursors for the growth of Si and SiO2 thin films for microelectronic and photovoltaic devices. The adsorption of silane and disilane on Si(100)-(2x1) surface, which are important steps in the growth of Si films in atomic layer epitaxy (ALE), were investigated using density functional theory calculations. The silane molecule dissociates on the Si surface at the intra-dimer site with barrier energy of 0.22 eV. We investigate both Si-Si bond cleavage and Si-H bond cleavage mechanisms for adsorption of Si2H6 on Si (100) surface. A Si-H bond cleavage mechanism was found to be more favored than Si-Si bond cleavage mechanism due to the lower barrier energy of 0.04 eV. The lower barrier energy for Si2H6 dissociation than that of SiH4 agrees well with the experimental results showing that Si2H6 has higher sticking coefficient than SiH4 on Si surface at 300K. The vibration frequencies of Si2H5, SiH3, SiH2, SiH resulting from dissociation of silane and disilane were calculated and compared with experimental results available. The simulation results will facilitate the controlled ALE for atomically precise manufacturing applications.

  7. CO2 adsorption-assisted CH4 desorption on carbon models of coal surface: A DFT study

    NASA Astrophysics Data System (ADS)

    Xu, He; Chu, Wei; Huang, Xia; Sun, Wenjing; Jiang, Chengfa; Liu, Zhongqing

    2016-07-01

    Injection of CO2 into coal is known to improve the yields of coal-bed methane gas. However, the technology of CO2 injection-enhanced coal-bed methane (CO2-ECBM) recovery is still in its infancy with an unclear mechanism. Density functional theory (DFT) calculations were performed to elucidate the mechanism of CO2 adsorption-assisted CH4 desorption (AAD). To simulate coal surfaces, different six-ring aromatic clusters (2 × 2, 3 × 3, 4 × 4, 5 × 5, 6 × 6, and 7 × 7) were used as simplified graphene (Gr) carbon models. The adsorption and desorption of CH4 and/or CO2 on these carbon models were assessed. The results showed that a six-ring aromatic cluster model (4 × 4) can simulate the coal surface with limited approximation. The adsorption of CO2 onto these carbon models was more stable than that in the case of CH4. Further, the adsorption energies of single CH4 and CO2 in the more stable site were -15.58 and -18.16 kJ/mol, respectively. When two molecules (CO2 and CH4) interact with the surface, CO2 compels CH4 to adsorb onto the less stable site, with a resulting significant decrease in the adsorption energy of CH4 onto the surface of the carbon model with pre-adsorbed CO2. The Mulliken charges and electrostatic potentials of CH4 and CO2 adsorbed onto the surface of the carbon model were compared to determine their respective adsorption activities and changes. At the molecular level, our results showed that the adsorption of the injected CO2 promoted the desorption of CH4, the underlying mechanism of CO2-ECBM.

  8. [Characteristic of ammonia nitrogen adsorption on karst underground river sediments].

    PubMed

    Guo, Fang; Chen, Kun-Kun; Jiang, Guang-Hui

    2011-02-01

    Karst aquifers are one of the most important aquifers in Southwestern China. One of the characteristics of karst aquifers is the enhanced permeability permits high flow velocities are capable of transporting suspended and bedload sediments. Mobile sediment in karst may act as a vector for the transport of contaminates. 14 sediment samples were collected from two underground rivers in two typical karst areas in Liuzhou city, Guangxi Autonomous Region, China. According to simulated experiment methods, characteristic of adsorption of ammonia nitrogen on sediment was studied. The results of ammonia nitrogen adsorption dynamics on sediments showed that the maximum adsorption velocity was less than 2 h. The adsorption balance quantity in 5 h accounted for 71% - 98% of the maximum adsorption quantity. The maximum adsorption quantity of ammonia nitrogen was 385.5 mg/kg, which was sediment from a cave in the middle areas of Guancun underground river system. The study of isotherm adsorption indicated adsorption quantity of NH4+ increase followed by incremental balance concentration of NH4+ in the aquatic phase. Adsorption quantity of ammonia nitrogen in sediments has a relative linear relationship with adsorption balance concentrations. Adsorption-desorption balance concentrations were all low, indicating sediments from underground rivers have great adsorption potential. Under the condition of low and high concentrations of ammonia nitrogen in overlying water, Langmuir and Tempkin couldn't simulate or simulate results couldn't reach remarkable level, whilst Linear and Freundlich models could simulate well. Research on different type sediments, sampling times and depths from two underground rivers shows characteristic of ammonia nitrogen adsorption on karst underground river sediments doesn't have good correspondence with the type of sediments. One of the reasons is there is no big difference between sediments in the development of climate, geology, hydrological conditions

  9. Dynamic, equilibrium and human studies of adsorption of 201Tl by Prussian blue.

    PubMed

    Bhardwaj, Nidhi; Bhatnagar, Aseem; Pathak, D P; Singh, A K

    2006-03-01

    Prussian blue is the recommended but infrequently required antidote for radiocesium and thallium chemical poisoning. Conceivably, its most frequent application will be the decontamination of radiothallium (thallous chloride) from human body following myocardial scintigraphy. Dosage schedule and physicochemical parameters of interaction with radiothallium, however, need to be defined, as the known data is inadequate on this account. The objective of the present study is to create physiologically relevant and mathematically rigorous data on interaction of Prussian blue with Tl, to estimate dosage schedule of Prussian blue suitable for myocardial scintigraphy, and to perform preliminary human studies to evaluate the efficacy of the antidote in reducing the considerable radiation burden imparted by this radiotracer. Adsorption efficacy of Prussian blue for radiothallium was found to be more than 95% at basic (intestinal) pH even at low concentrations and in presence of the physiological cations, potassium and sodium. Isotherm analysis and derivations using Langmuir, Bajpai, Lagergreen, and Freundlich equations suggest a favorable adsorption of Tl on Prussian blue with qmax being 5,000 MBq g. Based on these findings and clinical considerations, particularly preferential gall bladder excretion and enterohepatic recycling of radioactive thallous chloride, a dose of 100 mg Prussian blue with every major meal for 3 days was considered adequate for the purpose. Our experience with the first two patients (serving as their own self-controls) suggests that Prussian blue therapy is a safe and effective method to significantly reduce radiation burden imparted by thallium myocardial scintigraphy. PMID:16505622

  10. Adsorption studies of recalcitrant compounds of molasses spentwash on activated carbons.

    PubMed

    Figaro, S; Louisy-Louis, S; Lambert, J; Ehrhardt, J-J; Ouensanga, A; Gaspard, S

    2006-10-01

    Due to high levels of residual chemical oxygen demand (COD) in the effluent of molasses spentwash (MSW) after anaerobic treatment, acceptable COD levels for discharge cannot be achieved without some form of post-treatment. In this study, the particulate composition of molasses spentwash after anaerobic digestion (MSWD), is characterised as to its particle size distribution, using micro- and ultrafiltration and three activated carbons are characterised as to their ability to reduce significantly the COD of MSWD effluent. The activated carbons tested as adsorbent, were characterised by XPS spectroscopy, elemental analysis, surface area, pore size distribution, and acid-base titration using the Boehm's method. Adsorption of phenol, used here as a reference compound, and of some organic compounds contained in MSWD (gallic acid, tannic acid, and melanoidin, respectively), was studied. It was clearly demonstrated that an activated carbon with a significant distribution of both micropores and mesopores and a significant amount of macropores that are assumed to act as conduits providing access to micro- and mesopores, have a good adsorption efficiency for compounds such as tannic acid and melanoidins. It is a good adsorbent for melanoidin and coloured compounds of MSWD, which represents a large source of the aqueous pollution in sugar cane industries. PMID:16987542

  11. 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.

  12. 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.

  13. Adsorptive removal of 2-chlorophenol by low-cost coir pith carbon.

    PubMed

    Namasivayam, C; Kavitha, D

    2003-03-17

    Adsorption of 2-chlorophenol (2-CP) by coir pith carbon was carried out by varying the parameters such as agitation time, 2-CP concentration, adsorbent dose, pH and temperature. Adsorption equilibrium reached at 40, 60, 80 and 100 min for 2-CP concentration of 10, 20, 30 and 40 mg/l, respectively. Adsorption followed second-order kinetics. The adsorption equilibrium data obeyed Freundlich isotherm. Acidic pH was favorable for the adsorption of 2-CP. Desorption studies showed that chemisorption plays a major role in the adsorption process. PMID:12628792

  14. Efficient adsorption of phenanthrene by simply synthesized hydrophobic MCM-41 molecular sieves

    NASA Astrophysics Data System (ADS)

    Hu, Yun; He, Yinyun; Wang, Xiaowen; Wei, Chaohai

    2014-08-01

    Hydrophobic molecular sieve MCM-41 including surfactant template was synthesized by a simple method. The adsorption properties of this material toward phenanthrene were studied. The effects of adsorbent dose and pH value on the adsorption process as well as the adsorption mechanism and reuse performance were investigated. The template-containing MCM-41 showed a significant adsorption for phenanthrene, due to its hydrophobicity created by the surfactant template in MCM-41. The solution pH had little effect on the adsorption capacity. The adsorption kinetic could be fitted well with pseudo-second-order kinetic model. The adsorption equilibrium was fitted well by the linear model, and the adsorption process followed the liquid/solid phase distribution mechanism. The thermodynamic results indicated that the adsorption was a spontaneous and exothermic process.

  15. Growth of epitaxial Pt1-xPbx alloys by surface limited redox replacement and study of their adsorption properties.

    PubMed

    Mercer, M P; Plana, D; Fermίn, D J; Morgan, D; Vasiljevic, N

    2015-10-01

    The surface limited redox replacement (SLRR) method has been used to design two-dimensional Pt-Pb nanoalloys with controlled thickness, composition, and structure. The electrochemical behavior of these alloys has been systematically studied as a function of alloy composition. A single-cell, two-step SLRR protocol based on the galvanic replacement of underpotentially deposited monolayers of Pb with Pt was used to grow epitaxial Pt1-xPbx (x < 0.1) alloys of up to 10 ML thickness on Au substrates. It is shown that by varying the terminating potential of the galvanic replacement step, the Pb atomic content can be controlled in the films. Electrochemical analysis of the alloys showed that the adsorption of both H and CO exhibits similar, and systematic, decreases with small increases in the Pb content. These measurements, commonly used in electrocatalysis for the determination of active surface areas of Pt, suggested area values much lower than those expected based on the net Pt composition in the alloy as measured by XPS. These results show that Pb has a strong screening effect on the adsorption of both H and CO. Moreover, changes in alloy composition result in a negative shift in the potential of the peaks of CO oxidation that scales with the increase of Pb content. The results suggest electronic and bifunctional effects of incorporated Pb on the electrochemical behavior of Pt. The study illustrates the potential of the SLRR methodology, which could be employed in the design of 2-dimensional bimetallic Pt nanoalloys for fundamental studies of electrocatalytic behavior in fuel cell reactions dependent on the nature of alloying metal and its composition. PMID:26372676

  16. A study of Au adsorption on yttrium disilicide nanowires on Si (001) substrate from first principles

    NASA Astrophysics Data System (ADS)

    Ouyang, Wenjie; Shinde, Aniketa; Cao, Juexian; Wu, Ruqian

    2010-03-01

    Core-shell nanoclusters with Au coating layer on uniformly dispersed rear-earth disilicide nanowires are very promising for various applications such as nanocatalysis. Using the first principles approach, we studied the structure and electronic properties of a single Au atatom on yttrium disilicide nanowires on the Si(100) substrate. A series of possible adsorption sites were explored and we found that the ``hollow'' site on the YSi2 nanowire is the most preferential one, where the Au adatom binds to two Si atoms and an Y atom underneath. The most stable site for Au on Si(001) is the ``cave'' site, but the binding energy is 0.11 eV higher than that on the wire. This indicates that the Au atoms tend to aggregate toward nanowires, which leads to growth of core-shell metallic structures. Electrons deplete from Au adatom and accumulated in regions between Au and Si. The chemical activity of Au/YSi2 will be discussed in light of charge density, density of states and adsorption energy of CO molecules.

  17. Adsorption and conformational modification of fibronectin and fibrinogen adsorbed on hydroxyapatite. A QCM-D study.

    PubMed

    Fernández-Montes Moraleda, Belén; San Román, Julio; Rodríguez-Lorenzo, Luís M

    2016-10-01

    Hydroxyapatite is a bioactive ceramic frequently used for bone engineering/replacement. One of the parameters that influence the biological response to implanted materials is the conformation of the first adsorbed protein layer. In this work, the adsorption and conformational changes of two fibroid serum proteins; fibronectin and fibrinogen adsorbed onto four different hydroxyapatite powders are studied with a Quartz Crystal Microbalance with Dissipation (QCM-D). Each of the calcined apatites adsorbs less protein than their corresponding synthesized samples. Adsorption on synthesized samples yields always an extended conformation whereas a reorganization of the layer is observed for the calcined samples. Fg acquires a "Side on" conformation in all the samples at the beginning of the experiment except for one of the synthesized samples where an "End-on" conformation is obtained during the whole experiment. The Extended conformation is the active conformation for Fn. This conformation is favored by apatites with large specific surface area (SSA) and on highly concentrated media. Apatite surface features should be considered in the selection or design of materials for bone regeneration, since it is possible to control the conformation mode of attachment of Fn and Fg by an appropriate selection of them. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2585-2594, 2016. PMID:27254464

  18. Behavior of aluminum adsorption and incorporation at GaN(0001) surface: First-principles study

    SciTech Connect

    Qin, Zhenzhen; Xiong, Zhihua Wan, Qixin; Qin, Guangzhao

    2013-11-21

    First-principles calculations are performed to study the energetics and atomic structures of aluminum adsorption and incorporation at clean and Ga-bilayer GaN(0001) surfaces. We find the favorable adsorption site changes from T4 to T1 as Al coverage increased to 1 monolayer on the clean GaN(0001) surface, and a two-dimensional hexagonal structure of Al overlayer appears. It is interesting the Al atoms both prefer to concentrate in one deeper Ga layer of clean and Ga-bilayer GaN(0001) surface, respectively, while different structures could be achieved in above surfaces. For the case of clean GaN(0001) surface, corresponding to N-rich and moderately Ga-rich conditions, a highly regular superlattice structure composed of wurtzite GaN and AlN becomes favorable. For the case of Ga-bilayer GaN(0001) surface, corresponding to extremely Ga-rich conditions, the Ga bilayer is found to be sustained stable in Al incorporating process, leading to an incommensurate structure directly. Furthermore, our calculations provide an explanation for the spontaneous formation of ordered structure and incommensurate structure observed in growing AlGaN films. The calculated results are attractive for further development of growth techniques and excellent AlGaN/GaN heterostructure electronic devices.

  19. Substrate-induced structures of bismuth adsorption on graphene: a first principles study.

    PubMed

    Lin, Shih-Yang; Chang, Shen-Lin; Chen, Hsin-Hsien; Su, Shu-Hsuan; Huang, Jung-Chun; Lin, Ming-Fa

    2016-07-28

    The geometric and electronic properties of Bi-adsorbed monolayer graphene, enriched by the strong effect of a substrate, are investigated by first-principles calculations. The six-layered substrate, corrugated buffer layer, and slightly deformed monolayer graphene are all simulated. Adatom arrangements are thoroughly studied by analyzing the ground-state energies, bismuth adsorption energies, and Bi-Bi interaction energies of different adatom heights, inter-adatom distance, adsorption sites, and hexagonal positions. A hexagonal array of Bi atoms is dominated by the interactions between the buffer layer and the monolayer graphene. An increase in temperature can overcome a ∼50 meV energy barrier and induce triangular and rectangular nanoclusters. The most stable and metastable structures agree with the scanning tunneling microscopy measurements. The density of states exhibits a finite value at the Fermi level, a dip at ∼-0.2 eV, and a peak at ∼-0.6 eV, as observed in the experimental measurements of the tunneling conductance. PMID:27354143

  20. Photoemission study of the adsorption of nitric oxide on gallium arsenide (110) at low temperature

    SciTech Connect

    Bermudez, V.M. ); Williams, R.T. Physics Department, Wake Forest University, Winston-Salem, NC ); Williams, G.P. Jr.; Rowe, M.W.; Liu, H.; Wu, A. ); Sadeghi, H.R.; Rife, J.C. )

    1990-05-01

    Photoelectron spectroscopy with synchrotron radiation has been used to study changes in the region of the valence band and Ga and As 3{ital d} core levels of GaAs (110) resulting from exposure to nitric oxide (NO) at substrate temperatures of 40--140 K. Up to about 60 K, NO physisorbs. Thermal and photochemical effects have been observed during annealing of the adsorbed layer or irradiation by the monochromatized synchrotron radiation beam. At about 70 K, a distinct molecular species forms along with adsorbed O. This species, which desorbs and/or dissociates above about 90 K, is identified as nitrous oxide (N{sub 2}O ) on the basis of comparison with similar data for N{sub 2}O condensed on GaAs. Pre-adsorbed O inhibits N{sub 2}O formation, suggesting that the GaAs surface participates actively in the process. Above about 100 K, only O adsorption is observed, occurring by a mechanism different from that leading to O adsorption at lower temperature.

  1. ATR-FTIR spectroscopic studies of boric acid adsorption on hydrous ferric oxide

    NASA Astrophysics Data System (ADS)

    Peak, Derek; Luther, George W.; Sparks, Donald L.

    2003-07-01

    Boron is an important micronutrient for plants, but high B levels in soils are often responsible for toxicity effects in plants. It is therefore important to understand reactions that may affect B availability in soils. In this study, Attenuated Total Reflectance Fourier transform Infrared (ATR-FTIR) spectroscopy was employed to investigate mechanisms of boric acid (B(OH) 3) and borate (B(OH) 4-) adsorption on hydrous ferric oxide (HFO). On the HFO surface, boric acid adsorbs via both physical adsorption (outer-sphere) and ligand exchange (inner-sphere) reactions. Both trigonal (boric acid) and tetrahedral (borate) boron are complexed on the HFO surface, and a mechanism where trigonal boric acid in solution reacts to form either trigonal or tetrahedral surface complexes is proposed based upon the spectroscopic results. The presence of outer-sphere boric acid complexes can be explained based on the Lewis acidity of the B metal center, and this complex has important implications for boron transport and availability. Outer-sphere boric acid is more likely to leach downward in soils in response to water flow. Outer-sphere boron would also be expected to be more available for plant uptake than more strongly bound boron complexes, and may more readily return to the soil solution when solution concentrations decrease.

  2. Adsorption studies of cationic, anionic and azo-dyes via monodispersed Fe3O4 nanoparticles.

    PubMed

    Chaudhary, Ganga Ram; Saharan, Priya; Kumar, Arun; Mehta, S K; Mor, Suman; Umar, Ahmad

    2013-05-01

    The present paper reports the applicability of magnetite (Fe3O4) nanoparticles as an adsorbent for the removal of three dyes viz. Acridine orange (cationic dye), Comassie Brilliant Blue R-250 (anionic dye) and Congo red (azo dye) from their aqueous solution. The Fe3O4 nanoparticles were synthesized via simple chemical precipitation method using CTAB, as surfactant. The as-prepared nanoparticles were characterized in terms of their morphological, structural and optical properties by using transmission electron microscopy X-ray diffraction and UV-visible spectroscopic measurements. The dye removal efficiency of Fe3O4 NPs have been determined by investigating several factors such as effect of pH, amount of adsorbent dose and effect of contact time on different dye concentrations. Langmuir and Freundlich adsorption isotherms have also been studied to explain the interaction of dyes. The experimental data indicate that the adsorption rate follows pseudo- second-order kinetics for the removal of all the three dyes. Moreover, the nanoparticles and the adsorbed dyes were desorbed. The identities of recovered nanoparticles as well as the three dyes have been found, as same and were reused. PMID:23858837

  3. Comparative study of metal adsorption on the metal and the oxide surfaces

    NASA Astrophysics Data System (ADS)

    Magkoev, T. T.; Vladimirov, G. G.; Remar, D.; Moutinho, A. M. C.

    2002-05-01

    Adsorption of Ti, Cr, Fe, Ni and Cu atoms at coverage not exceeding two monolayers on the surface of ultrathin (10-15 Å) alumina and magnesia films (γ-Al 2O 3(111) or α-Al 2O 3(1000) and MgO(111) grown on Mo(110) were studied in ultrahigh vacuum by means of electron spectroscopy techniques (Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), high resolution electron energy loss spectroscopy (HREELS), low energy electron diffraction (LEED), work function measurements and reflection absorption infrared spectroscopy (RAIRS)). At very low metal coverage and low substrate temperature (85 K) when the film can be viewed as consisting of separate adatoms and/or very small clusters the electronic properties of adatoms on the oxide films, on one hand, and on Mo(110) surface, on the other hand, are quite different. With increasing metal coverage, the properties on both the oxide and the metallic substrates change becoming similar at the coverage close to monolayer. On the Mo(110) surface the electronic properties change gradually with the metal coverage, whereas on the oxide there is a critical coverage of about 0.15 ML separating ionic and metallic adsorption of the metal species. It is shown that the lateral interaction of adatoms on the oxide surface plays a dominant role in the formation of the band-like structure of the adsorbed 2D film.

  4. Equilibrium study of single-solute adsorption of anionic surfactants with polymeric XAD resins

    SciTech Connect

    Garcia-Delgado, R.A.; Cotoruelo-Minguez, L.M.; Rodriguez, J.J. )

    1992-06-01

    Equilibrium data for the adsorption of sodium lauryl sulfate (SLS) and sodium dodecylbenzene sulfonate (SDBS) from aqueous solutions by Amberlite XAD-4 and XAD-7 polymeric resins at temperatures in the 10-40C range have been obtained. The specific surface area of the resins plays a major role in adsorption, and thus the best results have been obtained with XAD-4 resin. A higher adsorption of SDBS over SLS was also observed. Several adsorption isotherm models have been used to fit the experimental data. The best results have been obtained with the Redlich-Peterson and Langmuir-Freundlich equations. Estimations of the isosteric heat of adsorption, free energy, and entropy of adsorption are also reported.

  5. DFT model cluster studies of O₂ adsorption on hydrogenated titania sub-nanoparticles.

    PubMed

    Andreev, Alexey S; Kuznetsov, Vyacheslav N; Chizhov, Yuri V

    2013-11-01

    In the present paper, we examine the general applicability of different TiO2 model clusters to study of local chemical events on TiO2 sub-nanoparticles. Our previous DFT study of TiO2 activation through H adsorption and following deactivation by O2 adsorption using small amorphous Ti8O16 cluster were complemented by examination of rutile-type and spherical Ti15O30 nanoclusters. The obtained results were thoroughly compared with experimental data and results of related computational studies using other TiO2 models including periodic structures. It turned out that all considered model TiO2 model systems provide qualitatively similar results. It was shown that atomic hydrogen is adsorbed with negligible activation energy on surface O atoms, which is accompanied by the appearance of reduced Ti(3+) species and corresponding localized band gap 3d-Ti states. Oxygen molecule is adsorbed on Ti(3+) sites spontaneously forming molecular O2 (-) species by capturing an extra electron of Ti(3+) ion, which results in disappearance of Ti(3+) species and corresponding band gap states. Calculated g-tensor values of Ti(3+) and O2 (-) species agree well with the results of EPR studies and do not depend on the used TiO2 model cluster. Additionally, it was shown that the various cluster calculations provide results comparable with the calculations of periodic structures with respect to the modeling of chemical processes under study. As a whole, the present study approves the validity of molecular cluster approach to study of local chemical events on TiO2 sub-nanoparticles. PMID:24085538

  6. Effect of grain size on uranium(VI) surface complexation kinetics and adsorption additivity.

    PubMed

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

    2011-07-15

    The contribution of variable grain sizes to uranium adsorption/desorption was studied using a sediment from the US DOE Hanford site. The sediment was wet sieved into four size fractions: coarse sand (1-2 mm), medium sand (0.2-1 mm), fine sand (0.053-0.2 mm), and clay/silt fraction (<0.053 mm). For each size fraction and their composite (sediment), batch and flow-cell experiments were performed to determine uranium adsorption isotherms and kinetic uranium adsorption and subsequent desorption. The results showed that uranium adsorption isotherms and adsorption/desorption kinetics were size specific, reflecting the effects of size-specific adsorption site concentration and kinetic rate constants. The larger-size fraction had a larger mass percentage in the sediment but with a smaller adsorption site concentration and generally a slower uranium adsorption/desorption rate. The same equilibrium surface complexation reaction and reaction constant could describe uranium adsorption isotherms for all size fractions and the composite after accounting for the effect of adsorption site concentration. Mass-weighted, linear additivity was observed for both uranium adsorption isotherms and adsorption/desorption kinetics in the composite. One important implication of this study is that grain-size distribution may be used to estimate uranium adsorption site and adsorption/desorption kinetic rates in heterogeneous sediments from a common location. PMID:21648458

  7. Studies of adsorption equilibria and kinetics in the systems: Aqueous solution of dyes-mesoporous carbons

    NASA Astrophysics Data System (ADS)

    Derylo-Marczewska, A.; Marczewski, A. W.; Winter, Sz.; Sternik, D.

    2010-06-01

    Two carbonaceous materials were synthesized by using the method of impregnation of mesoporous silicas obtained by applying the Pluronic copolymers as pore-creating agents. The isotherms of adsorption of methylene blue and methyl orange from aqueous solutions were measured by the static method. The profiles of adsorbate concentration change in time were obtained from the UV-vis spectra. The adsorption isotherms and kinetic dependence were discussed in the terms of theory of adsorption on heterogeneous surfaces.

  8. Application of activated carbon derived from scrap tires for adsorption of Rhodamine B.

    PubMed

    Li, Li; Liu, Shuangxi; Zhu, Tan

    2010-01-01

    Activated carbon derived from solid hazardous waste scrap tires was evaluated as a potential adsorbent for cationic dye removal. The adsorption process with respect to operating parameters was investigated to evaluate the adsorption characteristics of the activated pyrolytic tire char (APTC) for Rhodamine B (RhB). Systematic research including equilibrium, kinetics and thermodynamic studies was performed. The results showed that APTC was a potential adsorbent for RhB with a higher adsorption capacity than most adsorbents. Solution pH and temperature exert significant influence while ionic strength showed little effect on the adsorption process. The adsorption equilibrium data obey Langmuir isotherm and the kinetic data were well described by the pseudo second-order kinetic model. The adsorption process followed intra-particle diffusion model with more than one process affecting the adsorption process. Thermodynamic study confirmed that the adsorption was a physisorption process with spontaneous, endothermic and random characteristics. PMID:21179969

  9. Kinetic and calorimetric study of the adsorption of dyes on mesoporous activated carbon prepared from coconut coir dust.

    PubMed

    Macedo, Jeremias de Souza; da Costa Júnior, Nivan Bezerra; Almeida, Luis Eduardo; Vieira, Eunice Fragoso da Silva; Cestari, Antonio Reinaldo; Gimenez, Iara de Fátima; Villarreal Carreño, Neftali Lênin; Barreto, Ledjane Silva

    2006-06-15

    Mesoporous activated carbon has been prepared from coconut coir dust as support for adsorption of some model dye molecules from aqueous solutions. The methylene blue (MB) and remazol yellow (RY) molecules were chosen for study of the adsorption capacity of cationic and anionic dyes onto prepared activated carbon. The adsorption kinetics was studied with the Lagergren first- and pseudo-second-order kinetic models as well as the intraparticle diffusion model. The results for both dyes suggested a multimechanism sorption process. The adsorption mechanisms in the systems dyes/AC follow pseudo-second-order kinetics with a significant contribution of intraparticle diffusion. The samples simultaneously present acidic and basic sites able to act as anchoring sites for basic and acidic dyes, respectively. Calorimetric studies reveal that dyes/AC interaction forces are correlated with the pH of the solution, which can be related to the charge distribution on the AC surface. These AC samples also exhibited very short equilibrium times for the adsorption of both dyes, which is an economically favorable requisite for the activated carbon described in this work, in addition to the local abundance of the raw material. PMID:16497318

  10. A photoelectric technique for the study of adsorption: the aluminum-oxygen and aluminum-water systems.

    PubMed

    Batt, R J; Mee, C H

    1970-01-01

    Gas adsorption on clean metal surfaces may be studied by observing the change in work function of the surface as adsorption proceeds. A photoelectric technique for following these changes by measuring the photocurrent excited by two spectral lines is developed, and a graphical method of analysis of the results is given. This method has the advantage of being much quicker than other photoelectric techniques such as the determination of the retarding-potential characteristic, and may thus be applied to the study of more rapid adsorption processes. As examples of its use, the method has been applied to a study of the adsorption of oxygen and water vapor on films of aluminum evaporated under conditions of ultrahigh vacuum. The work function of the clean aluminum films was 4.27 eV. For small oxygen exposures (up to about 10(18) molecules cm(-2)) the work function of the contaminated aluminum decreased by about 0.05 eV; for larger exposures (up to about 10(20) molecules cm(-2)) the work function increased by about 0.05 eV. Water vapor adsorption causes a reduction in the work function by more than 1 eV for an exposure of about 10(19) molecules cm(-2). PMID:20076140

  11. Adsorption and dissociation of O2 on Ni-doped (5, 5) SWCNT: A DFT study

    NASA Astrophysics Data System (ADS)

    Li, Xiaodong; Liu, Liangliang; Wang, Mingguang; Wang, Zhu

    2016-05-01

    The effect of nickel doping on the adsorption and dissociation of the O2 molecule on a (5, 5) single-walled carbon nanotube (SWCNT) is investigated using first-principles density functional theory calculations in company with the nudged elastic band (NEB). Our calculated results show that nickel doping can make it much easier for oxygen adsorbed on the SWCNT, and the chemisorption energy is high enough to alter the O-O bond. What's more, the activation barrier for oxygen dissociation is lowered to 0.399 eV through nickel doping, which is much lower than Pt doped CNT. Our work have done here would be of help to develop platinum-free oxygen reduction reaction catalysts based on SWCNTs.

  12. Theoretical study of SO2 adsorption on goethite (1 1 0) surface

    NASA Astrophysics Data System (ADS)

    Zubieta, Carolina E.; Fortunato, Leandro F.; Belelli, Patricia G.; Ferullo, Ricardo M.

    2014-09-01

    Adsorption of SO2 on fully hydrated and partially dehydrated (1 1 0) surface of goethite (α-FeOOH) has been investigated using density functional theory (DFT) and periodic conditions. Different degrees of dehydration were modeled by eliminating one or two water molecules from the fully hydrated surface. Calculations indicate that SO2 shows preference to adsorb on dehydrated surface and the transformation to surface sulfite, bisulfite and sulfate was observed. In particular, surface sulfite can be formed over a variety of different dehydrated surfaces as monodentate and bidentate complexes. Theoretical vibrational frequencies of all the species have also been computed. Taking into account all the structures, we found frequency values within the 650-1030 cm-1 region due to Ssbnd OFe stretching, and between 1010 and 1190 cm-1 due to Ssbnd O stretching. Furthermore, monodentate mononuclear and bidentate binuclear sulfite complexes present distinctive features at low frequencies (600-700 cm-1).

  13. Direct observation of oriented molecular adsorption at step edges: a cryogenic scanning tunneling microscopy study

    NASA Astrophysics Data System (ADS)

    Frank, E. R.; Chen, X. X.; Hamers, R. J.

    1995-07-01

    A cryogenic scanning tunneling microscope has been used to investigate the adsorption of thiophene, 2,5-dimethylthiophene, and 2,2'-bithiophene on the Ag(111) surface at 120 K. STM images reveal that all three molecules preferentially bond at step edges. Images of 2,2'-bithiophene and 2,5-dimethylthiophene at the step edge show them to be elongated, while thiophene molecules appear nearly circular. The observed elongation for 2,2'-bithiophene and 2,5-dimethylthiophene is attributed to geometric contrast reflecting the intrinsic shape of these molecules. All molecules of a given chemical identity appear to be oriented in the same direction with respect to the step edge, demonstrating that the interactions between the molecules and the step edge are sufficiently strong and sufficiently local to hold the molecules in specific rotational configurations at the step edge.

  14. Adsorption of CO2 in hydrated MCM-41 Studied by SANS

    NASA Astrophysics Data System (ADS)

    Wang, Bo; Warren, Garfield T.; Bryan, Matthew; Sokol, Paul E.; Indiana University Team

    Adsorption of CO2 in hydrated MCM-41 was studied as a function of CO2 pressure by Small-Angle Neutron Scattering (SANS). Measurements were carried out on hydrophobic Si-MCM-41 and hydrophilic Al-MCM-41 with pore sizes of 4nm with no aqueous layer as well as monolayers and bilayers of water pre-adsorbed on the surface. SANS was measured as CO2 was introduced into the pores, which has the ability to probe the microscopic arrangement of water and CO2 confined within the pores. We will present the results of analysis indicating whether water or CO2 is more strongly attracted to the surface in these different samples. This study was prepared by Indiana University under Award 70NANB10H255 from the National Institute of Standards and Technology, U.S. Department of Commerce.

  15. Ab initio molecular orbital study of adsorption of oxygen, nitrogen, and ethylene on silver-zeolite and silver halides

    SciTech Connect

    Chen, N.; Yang, R.T.

    1996-11-01

    An ab initio molecular orbital study is undertaken on the adsorption of N{sub 2}, O{sub 2}, and C{sub 2}H{sub 4} (adsorbate) on Ag-zeolite and Ag halides (adsorbent). Geometry optimization is performed at the HF/3-21G level, while MP2/3-21G with natural bond orbital calculations are performed to obtain energies, atomic charges, orbital energies, and orbital populations (occupancies). The bonding of adsorbate to adsorbent is discussed in the context of {sigma}-donation (i.e., overlap of the 2p orbitals of the adsorbate molecule with the 5s orbital of Ag) and d-{pi}* back donation (i.e., overlap of the 4d{sub yz} orbitals of Ag with the 2p* antibonding orbitals of the adsorbate). For all adsorbate-adsorbent pairs, the ratio of {sigma}-donation to d-{pi}* back donation is approximately 3:1. Results on occupancy analysis indicate that a considerable electron redistribution from the 4d{sub zy} orbitals to the 4d{sub yz} orbitals occurs in Ag during adsorption and that this redistribution has possibly enhanced the d-{pi}* back donation. Net charge and energy gap ({Delta}{epsilon}) analyses indicate that it is slightly easier for N{sub 2} than O{sub 2} to adsorb, whereas a comparison of N{sub 2} and O{sub 2} adsorption from calculations of the energies of adsorption is inconclusive. However, a fair agreement is obtained in comparison of theory and experiment for energy of adsorption of N{sub 2} and C{sub 2}J{sub 4} on Ag-zeolite. The dispersion energies of adsorption, based on the MP2 correlation energies, are nearly the same for all adsorption pairs, i.e,, approximately 4--5 kcal/mol.

  16. Formation of sandwich structure through ion adsorption at the mineral and humic interfaces: A combined experimental computational study

    NASA Astrophysics Data System (ADS)

    Gao, Xiaodan; Yang, Gang; Tian, Rui; Ding, Wuquan; Hu, Feinan; Liu, Xinmin; Li, Hang

    2015-08-01

    Although ion adsorption at interfaces governs a variety of chemical processes, the underlying mechanisms remain controversial. We present a combination of dynamic light scattering, FT-IR spectroscopy and DFT calculations to probe the ion adsorption behaviors on montmorillonite and its mixture with humic acid (HA) as well as to unravel the composite structure and formation mechanism. Interaction structures of Ca2+ with HA, montmorillonite and their mixture are calculated, and computational frequencies show fine agreement with FT-IR results. The low ion affinities for HA explain that the aggregation kinetics of montmorillonite is significantly inhibited by forming composite with HA. Adsorption of Ca2+ on the mixture of HA and montmorillonite facilely obtains sandwich-structured composite, where Ca2+ is situated at the midst and exhibits an essential stabilization effect. Furthermore, conformational transitions occur frequently for HA carboxylic groups during composite formation.

  17. Solvothermal synthesis of different phase N-TiO2 and their kinetics, isotherm and thermodynamic studies on the adsorption of methyl orange.

    PubMed

    Fan, Jimin; Zhao, Zhihuan; Liu, Wenhui; Xue, Yongqiang; Yin, Shu

    2016-05-15

    The different crystal forms of nitrogen doped-titanium oxide (N-TiO2) with different particle sizes were produced by precipitation-solvothermal method and their adsorption mechanism were also investigated. The adsorption kinetics showed that rutile N-TiO2 displayed higher adsorption capacity than anatase for methyl orange (MO) and its adsorption behavior followed the pseudo-second-order kinetics. The equilibrium adsorption rate of N-TiO2 for MO was well fitted by the Langmuir isotherm model and the adsorption process was monolayer adsorption. The adsorption capacity decreased with increasing temperature. The average correlation coefficient was beyond 97%. The thermodynamic parameters (ΔaGm(ө), ΔaHm(ө), and ΔaSm(ө)) were calculated. It was found that anatase and rutile N-TiO2 had different adsorption enthalpy and entropy. The smaller the particle size, the greater the surface area and surface energy was, then ΔaGm(ө) decreased and the standard equilibrium constant increased at the same time. The adsorption process onto different crystalline phase N-TiO2 was exothermic and non-spontaneous. PMID:26945716

  18. Impact of carbon nanotube morphology on phenanthrene adsorption.

    PubMed

    Apul, Onur Guven; Shao, Ting; Zhang, Shujuan; Karanfil, Tanju

    2012-01-01

    The present study examined the roles of the specific surface area (SSA), diameter, and length of carbon nanotubes (CNT) on the adsorption of phenanthrene (PNT) by analyzing the adsorption isotherms obtained with several single-walled carbon nanotubes (SWNT) and multiwalled carbon nanotubes (MWNT). At low equilibrium concentrations (e.g., 1 ppb), MWNTs with larger outer diameters exhibited higher PNT adsorption capacity on an SSA basis than those with smaller diameters. With increasing equilibrium concentration, adsorption on an SSA basis became independent of MWNT diameter, and the total surface area controlled maximum adsorption capacity. A similar analysis for the adsorption of naphthalene, a planar molecule with one less benzene ring but 20 times higher solubility than PNT, showed no correlation with respect to MWNT outer diameter. The results indicated that the surface curvature of MWNT was more important on the adsorption of PNT than on the adsorption of naphthalene. Specific surface area normalized isotherms did not show a correlation between PNT adsorption and lengths of SWNTs and MWNTs. Characterization results indicated that the morphology of CNTs plays an important role on the SSA and pore volume. Data from the manufacturer may not always represent the characteristics of CNTs in a particular batch. Therefore, accurate characterization of CNTs is critical to systematically examine the behavior of CNTs, such as adsorption and transport, in environmental systems. PMID:22002628

  19. 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). PMID:18406058

  20. 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

    2016-01-01

    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. PMID:26602974

  1. 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

  2. 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. PMID:23666826

  3. 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)

  4. Oleate adsorption at an apatite surface studied by ex-situ FTIR internal reflection spectroscopy

    SciTech Connect

    Lu, Y.; Drelich, J.; Miller, J.D.

    1998-06-15

    Oleate adsorption at an apatite surface was investigated by ex-situ Fourier transform infrared internal reflection spectroscopy (FTIR/IRS). Adsorption isotherms have been determined using an apatite internal reflection element (IRE) and it has been found that pH has a significant influence on oleate adsorption by apatite. At pH 8.0 and 20 C, oleate adsorption density increases monotonically as equilibrium oleate concentration increases from 5 {times} 10{sup {minus}6} to 1 {times} 10{sup {minus}3} M. These results are in contrast to the results at pH 9.5 and 20 C in which case the adsorption density is limited to that corresponding to approximately monolayer coverage. Oleate adsorption by apatite was compared to oleate adsorption by fluorite and calcite and the different adsorption behavior at these three mineral surfaces is attributed to the differences in the densities of surface calcium sites and to the differences in the solubilities of these minerals. Contact angles have been measured at the apatite IRE surface and it has been demonstrated that both the amount and the nature of the adsorbed species influence the hydrophobic state of the surface.

  5. 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…

  6. 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

  7. A comparative study of water adsorption and desorption of swellable and non-swellable 2:1 layer silicates

    NASA Astrophysics Data System (ADS)

    Schnetzer, Florian; Thissen, Peter; Emmerich, Katja

    2015-04-01

    Our society aims for sustainable use of natural resources and conscientious land use. By far the most abundant natural resources are phyllosilicate-containing geomaterials (clays and soils) that are utilized as they occur in nature in various applications. One of the most important type of clays are bentonites. Bentonites act as binders of mineral particles and as hydraulic sealing by swelling under hydration. Bentonites consist of swellable clay minerals (smectites) and other phases (minerals, liquids, organic matter and air). Smectites hydrate and swell. Saturation depends on available moisture and compaction of the bentonites, which determine the ratio between strongly bound water in hydration shells of interlayer cations and surface bound water together with pore water. Thus, understanding of hydration of smectites is mandatory for understanding and controlling related processes and for monitoring of the hydration state in different applications. The hydration properties and the resulting interlayer organization of water (0W, 1W, 2W) were thoroughly studied for interlayer cations in particular by Ferrage et al., 2005; 2007 (and references herein). However, correlation with structure properties (layer charge, aspect ratio) was restricted to few samples. The influence of the ratio of interlayer to edge exchangeable cations is even more pronounced for small particles with an increased contribution from edge sites to CEC [Emmerich et al., 2011]. For a better understanding of hydration behavior of clay minerals, swellable and non-swellable 2:1 clay minerals are compared with respect to layer charge, exchangeable cations and particle size properties. The aim of the present work is to study the adsorption and desorption of water on homoionic smectites and vermiculite compare to a non-swellable illite. First results from water vapor adsorption isotherms show different kinetics of smectite hydration at low and high relative humidity (r. h.) with respect to equilibration

  8. Gun shows and gun violence: fatally flawed study yields misleading results.

    PubMed

    Wintemute, Garen J; Hemenway, David; Webster, Daniel; Pierce, Glenn; Braga, Anthony A

    2010-10-01

    A widely publicized but unpublished study of the relationship between gun shows and gun violence is being cited in debates about the regulation of gun shows and gun commerce. We believe the study is fatally flawed. A working paper entitled "The Effect of Gun Shows on Gun-Related Deaths: Evidence from California and Texas" outlined this study, which found no association between gun shows and gun-related deaths. We believe the study reflects a limited understanding of gun shows and gun markets and is not statistically powered to detect even an implausibly large effect of gun shows on gun violence. In addition, the research contains serious ascertainment and classification errors, produces results that are sensitive to minor specification changes in key variables and in some cases have no face validity, and is contradicted by 1 of its own authors' prior research. The study should not be used as evidence in formulating gun policy. PMID:20724672

  9. Gun Shows and Gun Violence: Fatally Flawed Study Yields Misleading Results

    PubMed Central

    Hemenway, David; Webster, Daniel; Pierce, Glenn; Braga, Anthony A.

    2010-01-01

    A widely publicized but unpublished study of the relationship between gun shows and gun violence is being cited in debates about the regulation of gun shows and gun commerce. We believe the study is fatally flawed. A working paper entitled “The Effect of Gun Shows on Gun-Related Deaths: Evidence from California and Texas” outlined this study, which found no association between gun shows and gun-related deaths. We believe the study reflects a limited understanding of gun shows and gun markets and is not statistically powered to detect even an implausibly large effect of gun shows on gun violence. In addition, the research contains serious ascertainment and classification errors, produces results that are sensitive to minor specification changes in key variables and in some cases have no face validity, and is contradicted by 1 of its own authors’ prior research. The study should not be used as evidence in formulating gun policy. PMID:20724672

  10. Neutron-reflectometry study of alcohol adsorption on various DLC coatings

    NASA Astrophysics Data System (ADS)

    Kalin, M.; Simič, R.; Hirayama, T.; Geue, T.; Korelis, P.

    2014-01-01

    Diamond-like carbon (DLC) coatings are notable for their excellent tribological properties. Our understanding of the lubrication of DLC coatings has improved drastically over the past decade. However, only a few details are known about the properties of the adsorbed layers on DLC, which crucially affect their tribological properties under lubricated conditions. In this work we used neutron reflectometry to determine the thickness and the density of adsorbed layers of alcohol molecules on several different types of DLC coatings, i.e., non-hydrogenated (a-C) and hydrogenated, of which both non-doped (a-C:H) and doped (a-C:H:F and a-C:H:Si) coatings were used. The results showed that a 0.9-nm-thick and relatively dense (≈45%) layer of alcohol adsorbed on the a-C coating. In contrast, no adsorption layer was found on the a-C:H, confirming the important role of hydrogen, which predominantly acts as a dangling-bond passivation source and affects the reactivity and tribochemistry of DLC coatings. The incorporation of F into a DLC coating also did not cause an increase in the adsorption ability with respect to alcohol molecules. On the contrary, the incorporation of Si increased the reactivity of the DLC coating so that a 1.3-nm-thick alcohol layer with a 35% bulk density was detected on the surface. We also discuss the very good agreement of the current results with the surface energy of selected coatings found in these experiments.

  11. Coordination polymers from a highly flexible alkyldiamine-derived ligand: structure, magnetism and gas adsorption studies.

    PubMed

    Hawes, Chris S; Chilton, Nicholas F; Moubaraki, Boujemaa; Knowles, Gregory P; Chaffee, Alan L; Murray, Keith S; Batten, Stuart R; Turner, David R

    2015-10-28

    The synthesis and structural, magnetic and gas adsorption properties of a series of coordination polymer materials prepared from a new, highly flexible and internally functional tetrakis-carboxybenzyl ligand H4L derived from 1,2-diaminoethane have been examined. The compound poly-[Ni3(HL)2(OH2)4]·2DMF·2H2O 1, a two-dimensional coordination polymer, contains aqua- and carboxylato-bridged trinuclear Ni(II) clusters, the magnetic behaviour of which can be well described through experimental fitting and ab initio modelling to a ferromagnetically coupled trimer with a positive axial zero-field splitting parameter D. Compound poly-[Zn2L]·2DMF·3H2O 2, a three-dimensional coordination polymer displaying frl topology, contains large and well-defined solvent channels, which are shown to collapse on solvent exchange or drying. Compound poly-[Zn2(L)(DMSO)4]·3DMSO·3H2O 3, a highly solvated two-dimensional coordination polymer, displayed poor stability characteristics, however a structurally related material poly-[Zn2(L)(bpe)(DMSO)2]·DMSO·3H2O 4 was prepared under similar synthetic conditions by including the 1,2-bis(4-pyridyl)ethylene bpe co-ligand. Compound 4, containing small one-dimensional solvent channels, shows excellent structural resilience to solvent exchange and evacuation, and the evacuated material displays selective adsorption of CO2 over N2 at 273 K in the pressure range 0-1 atm. Each of the coordination polymers displays subtle differences in the conformation and binding mode of the ligand species, with switching between two distinct conformers (X-shaped and H-shaped), as well as a variable protonation state of the central core, with significant effects on the resulting network structures and physical properties of the materials. PMID:26223788

  12. 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…

  13. Claus catalysis. 2. An FTIR study of the adsorption of H/sub 2/S on the alumina catalyst

    SciTech Connect

    Datta, A. Cavell, R.G.

    1985-01-31

    The adsorption of H/sub 2/S on alumina activated at 400 and 700/sup 0/C has been studied by Fourier transform infrared (FTIR) spectroscopy. Contrary to earlier reports, it appears that H/sub 2/S is adsorbed on alumina in not one but two different forms. Both these forms involve adsorption on an aluminum ion site. In one case, the adsorption is dissociative through interaction with an adjacent hydroxyl and oxide ion and leads to the formation of Al-S species. In the other case, the H/sub 2/S is adsorbed in an undissociated form. The latter form is found to desorb on heating to 100/sup 0/C whereas the Al-S species are inferred to be still present at temperatures above 300/sup 0/C. Dissociative adsorption takes place to a much lesser extent on the 700/sup 0/C activated sample, but the extent of undissociative adsorption is similar in the samples activated at 400 and 700/sup 0/C. 13 refs., 8 figs.

  14. Magnetic hydrogel beads based on PVA/sodium alginate/laponite RD and studying their BSA adsorption.

    PubMed

    Mahdavinia, Gholam Reza; Mousanezhad, Sedigheh; Hosseinzadeh, Hamed; Darvishi, Farshad; Sabzi, Mohammad

    2016-08-20

    In this study double physically crosslinked magnetic hydrogel beads were developed by a simple method including solution mixing of sodium alginate and poly(vinyl alcohol) (PVA) containing magnetic laponite RD (Rapid Dispersion). Sodium alginate and PVA were physically crosslinked by Ca(2+) and freezing-thawing cycles, respectively. Magnetic laponite RD nanoparticles were incorporated into the system to create magnetic response and strengthen the hydrogels. All hybrids double physically crosslinked hydrogel beads were stable under different pH values without any disintegration. Furthermore, adsorption of bovine serum albumin (BSA) on the hydrogel beads was investigated on the subject of pH, ion strength, initial BSA concentration, and temperature. Nanocomposite beads exhibited maximum adsorption capacity for BSA at pH=4.5. The experimental adsorption isotherm data were well followed Langmuir model and based on this model the maximum adsorption capacity was obtained 127.3mgg(-1) at 308K. Thermodynamic parameters revealed spontaneous and monolayer adsorption of BSA on magnetic nanocomposites beads. PMID:27178944

  15. 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.

  16. 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.

  17. Adsorptive removal of heavy metals by magnetic nanoadsorbent: an equilibrium and thermodynamic study

    NASA Astrophysics Data System (ADS)

    Shirsath, D. S.; Shirivastava, V. S.

    2015-11-01

    An efficient and new magnetic nanoadsorbent photocatalyst was fabricated by co-precipitation technique. This research focuses on understanding metal removal process and developing a cost-effective technology for treatment of heavy metal-contaminated industrial wastewater. In this investigation, magnetic nanoadsorbent has been employed for the removal of Zn(II) ions from aqueous solutions by a batch adsorption technique. The adsorption equilibrium data fitted very well to Langmuir and Freundlich adsorption isotherm models. The thermodynamics of Zn(II) ions adsorption onto the magnetic nanoadsorbents indicated that the adsorption was spontaneous, endothermic and physical in nature. Surface morphology of magnetic nanoadsorbent by scanning electron microscopy (SEM) and elemental analysis by EDX technique. The structural and photocatalytic properties of magnetic nanoadsorbent were characterized using X-ray diffraction (XRD) and FTIR techniques. Also, the magnetic properties of synthesized magnetic nanoadsorbent were determined by vibrating spinning magnetometer (VSM).

  18. Studies on the adsorption of sulfo-group-containing aromatics by chitosan-β-cyclodextrin.

    PubMed

    Shi, Wenjian; Chen, Shuwei; Chang, Fei; Han, Yue; Zhang, Yuanzhang

    2012-01-01

    Chitosan-β-cyclodextrin (CTS-CD) prepared through a crosslinking reaction between chitosan and β-cyclodextrin was employed to adsorb the three following sulfo-group-containing aromatics: disodium 2-naphthol-3,6-disulfonate (R salt), 2-naphthalene sulfonic acid (NSA), and sodium dodecylbenzene sulfonate (SDBS). At 318 K, the saturated adsorption capacity of CTS-CD for R salt, NSA, and SDBS was 431, 416, and 376 mg/g, respectively. The experimental data fitted the second-order model well and the rate constant of the adsorption increased with the temperature increment. The values of apparent activation energy for R salt, NSA, and SDBS were calculated as 33.2, 34.2, and 16.8 kJ/mol respectively. The isothermal adsorption was found following the Langmuir adsorption equation. The negative values of ΔG and the positive values of ΔH indicated that the adsorption process was spontaneous and exothermic. PMID:22339013

  19. Adsorption of adenine, cytosine, thymine, and uracil on sulfide-modified montmorillonite: FT-IR, Mössbauer and EPR spectroscopy and X-ray diffractometry studies.

    PubMed

    Carneiro, Cristine E A; Berndt, Graciele; de Souza Junior, Ivan G; de Souza, Cláudio M D; Paesano, Andrea; da Costa, Antonio C S; di Mauro, Eduardo; de Santana, Henrique; Zaia, Cássia T B V; Zaia, Dimas A M

    2011-10-01

    In the present work the interactions of nucleic acid bases with and adsorption on clays were studied at two pHs (2.00, 7.00) using different techniques. As shown by Mössbauer and EPR spectroscopies and X-ray diffractometry, the most important finding of this work is that nucleic acid bases penetrate into the interlayer of the clays and oxidize Fe(2+) to Fe(3+), thus, this interaction cannot be regarded as a simple physical adsorption. For the two pHs the order of the adsorption of nucleic acid bases on the clays was: adenine ≈ cytosine > thymine > uracil. The adsorption of adenine and cytosine on clays increased with decreasing of the pH. For unaltered montmorillonite this result could be explained by electrostatic forces between adenine/cytosine positively charged and clay negatively charged. However for montmorillonite modified with Na(2)S, probably van der Waals forces also play an important role since both adenine/cytosine and clay were positively charged. FT-IR spectra showed that the interaction between nucleic acid bases and clays was through NH(+) or NH (2) (+) groups. X-ray diffractograms showed that nucleic acid bases adsorbed on clays were distributed into the interlayer surface, edge sites and external surface functional groups (aluminol, silanol) EPR spectra showed that the intensity of the line g ≈ 2 increased probably because the oxidation of Fe(2+) to Fe(3+) by nucleic acid bases and intensity of the line g = 4.1 increased due to the interaction of Fe(3+) with nucleic acid bases. Mössbauer spectra showed a large decreased on the Fe(2+) doublet area of the clays due to the reaction of nucleic acid bases with Fe(2+). PMID:21717172

  20. ER Docs Only Ask Half of Suicidal Patients about Guns, Study Shows

    MedlinePlus

    ... Docs Only Ask Half of Suicidal Patients About Guns, Study Shows Finding points to missed chances to ... EDs) are asked if they have access to guns, a new study finds. National guidelines say doctors ...

  1. 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

  2. Synthesis and characterization of various zeolites and study of dynamic adsorption of dimethyl methyl phosphate over them

    SciTech Connect

    Khanday, Waheed Ahmad; Majid, Sheikh Abdul; Chandra Shekar, S.; Tomar, Radha

    2013-11-15

    Graphical abstract: Thermal desorption pattern of DMMP over various zeolites (a) 1st desorption and (b) 2nd desorption. - Highlights: • Synthesis of Zeolite-A, MCM-22, Zeolite-X and Erionite by hydrothermal method. • Zeolites were characterized by using XRD, FTIR, BET, NH{sub 3}-TPD, SEM and EDS techniques. • Dynamic adsorption of DMMP on zeolites was carried out using TPD plus chemisorption system. • Thermal desorption of DMMP on zeolites was carried using the same system. - Abstract: Zeolite-A, MCM-22, Zeolite-X and Erionite were synthesized successfully under hydrothermal conditions and were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Brunauer–Emmett–Teller (BET) surface area analysis and thermal programmed desorption (TPD). Dynamic adsorption of dimethyl methyl phosphate (DMMP) was carried out on these zeolites. Zeolite-X having high surface area among all four zeolites shows highest adsorption capacity followed by Erionite and MCM-22 where as Zeolite-A shows the least. For all zeolites adsorption was found to be high initially and it then decreases with increase in injected volume. Then desorption pattern was analyzed which shows two types of peaks, sharp peak representing desorption of physisorbed DMMP and a broad peak representing desorption of strongly chemisorbed DMMP.

  3. Adsorption of 2,4,6-trinitrotoluene on carboxylated porous polystyrene microspheres

    NASA Astrophysics Data System (ADS)

    Ye, Zhengfang; Meng, Qingqiang; Lu, Shengtao

    2012-02-01

    Large-pore-size (150 nm) polystyrene (PSt) microspheres were carboxylated with phthalic anhydride (PA) through Friedel-Crafts acetylation to study the adsorption of 2,4,6-trinitrotoluene (TNT) on this material from aqueous solution. The scanning electron microscope (SEM) images and mercury porosimetry measurements (MPM) of the microspheres showed that the pore structure was unchanged during the reaction. High adsorption capacity (11.2 mg g-1 of suction-dried adsorbent) and adsorption rate (33.9 mg g-1 h-1) for TNT were observed during the study. As shown by the adsorption isotherm, the adsorption of TNT on PA-PSt can be described by the Freundlich adsorption equation, indicating heterogeneous adsorption process. On-column adsorption of TNT on PA-PSt and elution indicated that TNT can be completely removed from aqueous solution and condensed into acetone.

  4. Ab initio studies on the adsorption and implantation of Al and Fe to nitride materials

    NASA Astrophysics Data System (ADS)

    Riedl, H.; Zálešák, J.; Arndt, M.; Polcik, P.; Holec, D.; Mayrhofer, P. H.

    2015-09-01

    The formation of transfer material products on coated cutting and forming tools is a major failure mechanism leading to various sorts of wear. To describe the atomistic processes behind the formation of transfer materials, we use ab initio to study the adsorption energy as well as the implantation barrier of Al and Fe atoms for (001)-oriented surfaces of TiN, Ti0.50Al0.50N, Ti0.90Si0.10N, CrN, and Cr0.90Si0.10N. The interactions between additional atoms and nitride-surfaces are described for pure adhesion, considering no additional stresses, and for the implantation barrier. The latter, we simplified to the stress required to implant Al and Fe into sub-surface regions of the nitride material. The adsorption energies exhibit pronounced extrema at high-symmetry positions and are generally highest at nitrogen sites. Here, the binary nitrides are comparable to their ternary counterparts and the average adhesive energy is higher (more negative) on CrN than TiN based systems. Contrary, the implantation barrier for Al and Fe atoms is higher for the ternary systems Ti0.50Al0.50N, Ti0.90Si0.10N, and Cr0.90Si0.10N than for their binary counterparts TiN and CrN. Based on our results, we can conclude that TiN based systems outperform CrN based systems with respect to pure adhesion, while the Si-containing ternaries exhibit higher implantation barriers for Al and Fe atoms. The data obtained are important to understand the atomistic interaction of metal atoms with nitride-based materials, which is valid not just for machining operations but also for any combination such as interfaces between coatings and substrates or multilayer and phase arrangements themselves.

  5. The adsorption of glyphosate and phosphate to goethite: a molecular-scale atomic force microscopy study

    NASA Astrophysics Data System (ADS)

    Dideriksen, K.; Stipp, S. L. S.

    2003-09-01

    The adsorption of glyphosate and phosphate to the goethite {010} surface (Pbnm notation) was studied using an atomic force microscope (AFM). The microscope was capable of producing molecular scale images of surfaces exposed to glyphosate, phosphate and nitric acid. In 0.08 mol/L HNO 3 solution with pH of 1, the goethite {010} surface displayed the periodicities of the surface unit cell. The presence of a secondary periodicity in the 2D-Fourier transform suggests that the surface relaxes or reconstructs slightly, either after cleavage or as a result of exposure to air or acid solution. Images obtained in 0.01 mol/L glyphosate solution with pH of 2.5 displayed a well-defined √2 × √2 superstructure and a somewhat diffuse √2 × 2√2 superstructure that alternated in orientation within single imaging areas. The √2 × √2 superstructure indicates that glyphosate functional groups adsorb in a 1:2 ratio with the singly coordinated hydroxyl groups and suggests that all functional groups coordinate similarly. The √2 × 2√2 superstructure is interpreted to originate from different behaviour of the tip during imaging of the adsorbed phosphonic and carboxylic groups, indicating that both groups coordinate to the surface and that the glyphosate molecule bridges the rows of singly coordinated hydroxyl groups. In 0.01 mol/L phosphate solution with pH of 2.6, the imaged pattern was identical to that obtained in HNO 3. The similarity suggests that phosphate adsorbs in 1:1 ratio with the singly coordinated hydroxyl groups and that phosphate thus coordinates monodentately. The relative maximum adsorption density of phosphate and glyphosate on the {010} surface expected from the AFM data was in agreement with that determined with X-ray photoelectron spectroscopy (XPS).

  6. Atomic force microscopy and tribology study of the adsorption of alcohols on diamond-like carbon coatings and steel

    NASA Astrophysics Data System (ADS)

    Kalin, M.; Simič, R.

    2013-04-01

    Polar molecules are known to affect the friction and wear of steel contacts via adsorption onto the surface, which represents one of the fundamental boundary-lubrication mechanisms. Since the basic chemical and physical effects of polar molecules on diamond-like carbon (DLC) coatings have been investigated only very rarely, it is important to find out whether such molecules have a similar effect on DLC coatings as they do on steel. In our study the adsorption of hexadecanol in various concentrations (2-20 mmol/l) on DLC was studied under static conditions using an atomic force microscope (AFM). The amount of surface coverage, the size and the density of the adsorbed islands of alcohol molecules were analyzed. Tribological tests were also performed to correlate the wear and friction behaviours with the adsorption of molecules on the surface. In this case, steel surfaces served as a reference. The AFM was successfully used to analyze the adsorption ability of polar molecules onto the DLC surfaces and a good correlation between the AFM results and the tribological behaviour of the DLC and the steel was found. We confirmed that alcohols can adsorb physically and chemically onto the DLC surfaces and are, therefore, potential boundary-lubrication agents for the DLC coatings. The adsorption of alcohol onto the DLC surfaces reduces the wear of the coatings, but it is less effective in reducing the friction because of the already inherently low-friction properties of DLC. Tentative adsorption mechanisms that include the environmental species effect, the temperature effect and the tribological rubbing effect are proposed for DLC and steel surfaces.

  7. Effects of reactor decontamination complexing agents on soil adsorption-column studies

    SciTech Connect

    Serne, R. Jeffrey; Lindenmeier, Clark W.; Cantrell, Kirk J.; Owen, Antionette T.

    1999-12-01

    The effects of picolinate, an organic ligand used to decontaminate nuclear reactor cooling systems, in leachates generated from shallow-land burial (SLB) of low-level nuclear wastes (LLW) on soil adsorption was determined. Using batch adsorption tests and varying the concentration of picolinate, the adsorption tendencies of two metals [Ni(II) and U(VI)] and the ligand were measured as a function of solution pH. We found that when total metal concentrations were fixed at 10^-5 M, picolinate at ligand-to-metal [L:M] ratios $10 did significantly reduce adsorption of Ni but even at a L:M ratio of 100 there was no effect on U(VI) adsorption. These results are compared with data on other metals in the presence of picolinate and for metal adsorption in the presence of EDTA. We conclude that picolinic acid is less of a threat than EDTA in waste leachates to reduce metal adsorption (increase mobility) and that picolinate concentrations must reach or exceed 10^-4 M for the most impacted metals (i.e., those that form the very strongest complexes with picolinate). There are no leachate data on these decontamination agents for the common burial technique (disposal of de-watered resins in high integrity containers) that can be used to evaluate potential hazards of these organo-radionuclide complexes.

  8. Adsorption of nonmetallic elements on defect-free MgO(001) surface - DFT study

    NASA Astrophysics Data System (ADS)

    Pašti, Igor A.; Baljozović, Miloš; Skorodumova, Natalia V.

    2015-02-01

    Adsorption of 11 non-metals (H, B, C, N, O, F, Si, P, S, Cl and Br) on defect-free MgO(001) surface was investigate using DFT approach. Adsorption energies were found to be between - 0.56 eV (hydrogen adsorption) and - 2.63 eV (carbon adsorption). Charge transfer from substrate to adsorbate was observed to follow the periodicity in the Periodic Table of Elements, as increases from left to right and decreases from top to bottom. All investigated adsorbates prefer oxygen sites on MgO surface. The analysis of adsorbate-MgO(001) electronic structure suggested that the electronic structure of the O adsorption center and adsorbate atom is molecule-like and there is no strong interaction with MgO electronic bands. Based on the obtained dataset for adsorption energies of selected non-metallic adsorbates (X) the reactivity of MgO towards the bond cleavage in the cases of X-X, H-X and HO-X bonds was discussed. Obtained results point to weak reactivity of MgO(001) towards atomic adsorption and low activity for bond cleavage. However, these results can be used as a starting point for the functionalization of MgO, particularly in the cases where bond cleavage activity and surface-mediated stabilization of dissociation products are desired.

  9. Calcium lignosulfonate adsorption and desorption on Berea sandstone.

    PubMed

    Grigg, Reid B; Bai, Baojun

    2004-11-01

    This paper describes adsorption and desorption studies carried out with calcium lignosulfonate (CLS) on Berea sandstone. Circulation experiments were performed to determine CLS adsorption isotherms and the effects of CLS concentration, temperature, salinity, brine hardness, and injection rate on adsorption density. Flow-through experiments were performed to assess the reversibility of CLS adsorption and the influence of postflush rate, brine concentration, brine hardness, brine pH, and temperature on the desorption process. Results indicate that CLS adsorption isotherms on Berea sandstone follow the Freundlich isotherm law. The results presented in this paper on the effects of CLS adsorption and desorption on Berea sandstone show that: (1) increasing CLS concentration and salinity increases CLS adsorption density; (2) increasing temperature will decrease adsorption density; (3) increasing injection rate of CLS solution will slightly decrease CLS adsorption density; (4) postflush rate and salinity of brine have a large impact on the CLS desorption process; (5) the adsorption and desorption process are not completely reversible; and (5) temperature and pH of the postflush brine have little effect on desorption. PMID:15380409

  10. A novel zinc(ii) metal-organic framework with a diamond-like structure: synthesis, study of thermal robustness and gas adsorption properties.

    PubMed

    Almáši, Miroslav; Zeleňák, Vladimír; Zukal, Arnošt; Kuchár, Juraj; Čejka, Jiří

    2016-01-21

    A solvothermal reaction of Zn(ii) salt with methanetetrabenzoic acid (H4MTB) and 1,4,8,11-tetraazacyclotetradecane (cyclam, CYC) created a new microporous metal-organic framework {[Zn2(μ4-MTB)(κ(4)-CYC)2]·2DMF·7H2O}n (DMF = N,N'-dimethylformamide). Single crystal X-ray diffraction showed that the complex exhibits a four-fold interpenetrated diamond-like structure topology with 1D jar-like channels with sizes about 14.1 × 14.1 and 2.4 × 2.4 Å(2). The stability of the framework and activation conditions of the compound have been studied by high-energy powder X-ray diffraction during in situ heating, thermogravimetric analysis coupled with mass spectrometry and infrared spectroscopy performed at different temperatures. The gas adsorption behaviour of {[Zn2(μ4-MTB)(κ(4)-CYC)2]·2DMF·7H2O}n was studied by adsorption of Ar, N2, CO2 and H2. Nitrogen and argon adsorption showed that the activated sample exhibits Brunauer-Emmet-Teller (BET) specific surface areas of 644 m(2) g(-1) (N2) and 562 m(2) g(-1) (Ar). The complex adsorbs carbon dioxide with a maximum storage capacity of 10.5 wt% at 273 K and 101 kPa. The observed hydrogen uptake was 1.27 wt% at 77 K and 800 Torr, which is the highest value reported for the compounds containing a MTB(4-) linker. The adsorption heats of carbon dioxide and hydrogen, calculated according to the Clausius-Clapeyron equation, were in the range 22.8-22.4 kJ mol(-1) for CO2 and 8.9-3.2 kJ mol(-1) for H2, indicating weak interactions of the gases with the framework. PMID:26671614

  11. Effect of substitutional carbon-doping in BNNTs on HF adsorption: DFT study

    NASA Astrophysics Data System (ADS)

    Kaur, Jasleen; Singhal, Sonal; Goel, Neetu

    2014-11-01

    We employed density functional calculations to investigate the adsorption behavior of HF gas on the side walls of pure and carbon-doped boron nitride nanotubes (BNNTs). The HF adsorption over the pure BNNT opens a door for its functionalization without causing significant changes in its electronic properties. The substitutional doping of carbon atom on the BNNT considerably enhances its affinity towards HF where the effect of the dopant concentration plays a vital role. The change in electronic properties of the doped BNNT on HF adsorption is significant enough to consider it a potential sensor for HF detection.

  12. A first-principles study of Pt thin films on SrTiO{sub 3}(100): Support effects on CO adsorption

    SciTech Connect

    Yuk, Simuck F.; Asthagiri, Aravind

    2015-03-28

    Density functional theory was used to study CO adsorption on thin Pt metal films supported on SrO- and TiO{sub 2}-terminated SrTiO{sub 3}(100) surfaces. Regardless of substrate-termination, significant enhancement in CO binding occurred on the Pt monolayer compared to the bulk Pt(100) surface. We also observed CO-coverage dependent shifting of Pt atoms, influenced by the nature of underlying oxide atoms. These oxide-induced effects become negligible after depositing more than 2 monolayers of Pt. Evaluating the electronic structures of oxide-supported Pt showed that the interaction of filled Pt d{sub xz+yz} and empty Pt d{sub z{sup 2}} states with CO molecular orbitals can be directly related to CO adsorption on the Pt/SrTiO{sub 3}(100) surface. A hybrid d-band model is able to capture the CO adsorption trends for systems that do not show large lateral distortion except for the case of Pt adsorbed above the Sr atom on the SrO-termination. For this case, charge transfer from adjacent Pt atoms leads to a large filled d{sub z{sup 2}} peak below the Fermi level that weakens the Pt–CO σ bonding due to Pauli repulsion.

  13. MRI and PGSE NMR Studies of Long-range, Pore-pore Interaction Effects in Gas Adsorption

    NASA Astrophysics Data System (ADS)

    Hitchcock, Iain; Rigby, Sean; Chudek, John; Holt, Liz; Lowe, John

    2011-03-01

    In this work MRI and PGSE NMR have been used to directly study the advanced condensation effect during water adsorption in a macroscopically heterogeneous sol-gel silica pellet. It has been found that capillary condensation will occur at unexpectedly lower pressures in regions of much larger pores that lie in close proximity to smaller pores.

  14. Adsorption and Separation of Light Gases on an Amino-Functionalized Metal–Organic Framework: An Adsorption and In Situ XRD Study

    SciTech Connect

    Couck S.; Stavitski E.; Gobehiya, E.; Kirschhock, C.E.A.; Serra-Crespo, P.; Juan-Alcaniz, J.; Martinez Joaristi, A.; Gascon, J.; Kapteijn, F.; Baron, G. V.; Denayer J.F.M.

    2012-02-29

    The NH{sub 2}-MIL-53(Al) metal-organic framework was studied for its use in the separation of CO{sub 2} from CH{sub 4}, H{sub 2}, N{sub 2} C{sub 2}H{sub 6} and C{sub 3}H{sub 8} mixtures. Isotherms of methane, ethane, propane, hydrogen, nitrogen, and CO{sub 2} were measured. The atypical shape of these isotherms is attributed to the breathing properties of the material, in which a transition from a very narrow pore form to a narrow pore form and from a narrow pore form to a large pore form occurs, depending on the total pressure and the nature of the adsorbate, as demonstrated by in-situ XRD patterns measured during adsorption. Apart from CO{sub 2}, all tested gases interacted weakly with the adsorbent. As a result, they are excluded from adsorption in the narrow pore form of the material at low pressure. CO{sub 2} interacted much more strongly and was adsorbed in significant amounts at low pressure. This gives the material excellent properties to separate CO{sub 2} from other gases. The separation of CO{sub 2} from methane, nitrogen, hydrogen, or a combination of these gases has been demonstrated by breakthrough experiments using pellets of NH{sub 2}-MIL-53(Al). The effect of total pressure (1-30 bar), gas composition, temperature (303-403 K) and contact time has been examined. In all cases, CO{sub 2} was selectively adsorbed, whereas methane, nitrogen, and hydrogen nearly did not adsorb at all. Regeneration of the adsorbent by thermal treatment, inert purge gas stripping, and pressure swing has been demonstrated. The NH{sub 2}-MIL-53(Al) pellets retained their selectivity and capacity for more than two years.

  15. Kinetic and isotherm studies of adsorption and biosorption processes in the removal of phenolic compounds from aqueous solutions: comparative study

    PubMed Central

    2013-01-01

    The phenolic compounds are known by their carcinogenicity and high toxicity as well as creating unpleasant taste and odor in water resources. The present study develops a cost-effective technology for the treatment of water contaminated with phenol